Cloning is the transliteration of the English word "clone", which is generally translated as reproduction or transfer in Taiwan, Hong Kong and MacaoAsexual reproductionThe production is identical to the original individualgeneThe process of organizing future generations.Scientists call the process of artificial genetic manipulation of animal reproduction cloning. This biotechnology is called cloning technology, which meansAsexual reproduction。Cloning technology is called“BioamplificationTechnology ".
Cloning technology is a pure cell line formed by the division and reproduction of the same ancestor cell. The genes of each cell in this cell line are the same.The cloned English "clone" originates from the Greek "kl ō n" (twig).1963J.B.S.HaldaneThe term "Clone" was used in the speech entitled "Biological possibility of human race in the next 20000 years".
In horticulture, the word "clone" was used until the 20th century.Later, sometimes "e" is added at the end of the word to become "clone" to indicate that "o" is pronounced as a long vowel.As this concept and word are widely used in public life, the spelling has been limited to "clone".The Chinese translation of the word is transliterated as "clone" in mainland China, while in Hong Kong and Taiwan, it is mostly translated as "transfer" or "copy".The former "clone" is like the transliteration "copy" of copy, which has the disadvantage of not being literal;The latter "copy" can roughly express the meaning of clone, but it is not accurate and easy to misunderstand.
Clone is the transliteration of "clone" or "cloning" in English, while the English "clone" originates from the Greek "Klone", which originally means cutting seedlings or twigs toAsexual reproductionorVegetative reproductionThe way to cultivate plants, such as cutting and grafting.In mainland China, it is translated as "asexual reproduction" in Taiwan, Hong Kong and Macao.
Clone sheep Dolly
The Chinese language also has more precise words to express cloning, "asexual reproduction", "asexualization" and "pure lineage".Cloning refers to the asexual reproduction of organisms through somatic cells and the formation of asexual reproductiongenotypeA population of identical offspring.Usually, biotechnology is used toAsexual reproductionThe process of producing offspring with identical genetic tissue as the original individual.
Asexual cloning
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Asexual reproduction refers to the reproduction mode without the combination of bisexual germ cells or the natural asexual reproduction mode (such as plants).A clone is a multicellular organism genetically identical to another organism.Clones can beNatural cloningFor example, two genetically identical individuals (likeIdentical twinsThe same, but the genes of identical twins sometimes have subtle differences).However, what we usually refer to as cloning is the exact replication (such asArtificial cloning）。There are subtle differences between the two.
Encyclopedia x confusion: graphical cloning
development
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Cloning technology has gone through three stages of development: the first stage is microbial cloning, that is, using one bacterium to quickly replicate thousands of bacteria identical to it, and become a bacterial colony;The second period is biotechnology cloning, such as using genetic genes - DNA cloning;The third period isAnimal cloningThat is, from a cell to an animal.Dolly, a cloned sheep, was cloned from the somatic cell of a ewe using animal cloning technology.
Re cloning technology
In 2013, the scientists of the Japanese Institute of Physics and Chemistry successfully bred a total of 598 laboratory mice of 26 generations with one laboratory mouse by virtue of the "re cloning" technology of breeding cloned animals with cloned animals. Moreover, the cloned laboratory mice were very healthy, and their reproductive capacity and life span were not different from ordinary laboratory mice.Researchers believe that this shows that re cloning can continue indefinitely.This research was published as a cover story in Cell on March 7-stem cells》(Cell Stem Cell) magazine online.One of the major issues facing cloning technology is the low fertility of cloned animals. The more generations of reproduction, the lower the fertility.So far, the breeding of experimental mice for six generations and cattle for two generations has reached the limit.Once the animal that provided the cells for cloning died, the genetic information would be cut off.
The research team led by Ruoyama Zhaoyan, a researcher of the Institute of Physics and Chemistry, once found in 2005 that when cloning experimental mice were cultivated, the egg cells with transplanted nuclei were immersed in a kind of "trichostatin A"“Histone deacetylase inhibitor”The fertility rate will increase.The research team continued to improve the technology and successfully bred 26 generations of experimental mice, with a maximum fertility rate of about 15%.[1]
A research group of Oregon University of Health and Science published an article on the online edition of the American scientific journal Cell on the 15th, announcing that it has used“Somatic cell cloning technology”, implanted the nucleus of other skin cells into the egg cell, and successfully produced embryonic stem cells that can differentiate into various tissues for the first time.
Biological application
In biology, cloning is usually used in two aspects: cloning a gene or cloning a species.Clone ageneIt refers to obtaining a gene from an individual (for example, by PCR) and then inserting it.In addition, in the animal kingdomAsexual reproductionHowever, it is mostly found in invertebrates, such as protozoan fission reproduction, caudateBudding reproductionEtc.But for advanced animals, under natural conditions, onlysexual propagationTherefore, scientists must go through a series of complex operating procedures to make it reproduce asexually.In the 1950s, scientists successfully cloned an amphibian -Xenopus Laevis , opened a new chapter in cell biology.
In the late 1980s, Britain and China successively used embryonic cells as donors to "clone" mammals.By the mid-1990s, China had used this method to "clone" five mammals: mice, rabbits, goats, cattle and pigs.
Clone Dolly sheep
On July 5, 1996, a lamb with the same gene structure as the donor was cloned“Dolly”(Dolly), the world public opinion is in an uproar."Dolly" is special in that its life was born without the participation of sperm.The researchers first took a sheepEgg cellIngenetic materialSuck it out to make it become an empty shell, then take out a breast cell from a 6-year-old ewe, and inject the genetic material into the empty shell of the egg cell.In this way, an egg cell with new genetic material but no sperm is obtained.This transformed egg cell divides and proliferates to form an embryo, which is then implanted into another ewe's uterus. With the successful delivery of the ewe, "Dolly" came to the world.
But why didn't other cloned animals have such a big impact in the world?This is because the genetic genes of other cloned animals come from embryos and are all nuclear transplants carried out with embryonic cells, which cannot be strictly said to be“Asexual reproduction”。Another reason is that embryonic cells themselves reproduce sexually, and half of the genome in their nuclei comes from the male parent and half from the female parent.
The genome of "Dolly" comes from a single parent, which is true asexual reproduction.Therefore, in a strict sense, Dolly is the first mammal in the world to be truly cloned.Its characteristics lie in its supply of genetic material. On February 23, 1997, scientists from Roslin Research Institute in Scotland, England announced that their research team had successfully cloned goats using goat somatic cells. Cloning technology is the result of scientific development, and it has extremely broad application prospects.
In horticulture and animal husbandry, cloning technology is an ideal means of breeding varieties with stable genetic properties, through which high-quality fruit trees and improved livestock can be bred.In the medical field, the United States, Switzerland and other countries have been able to use "cloning" technology to cultivate human skin forSkin grafting。This new achievement avoided the possible rejection reaction of allograft and brought good news to patients.
According to the report of China's Xinhua News Agency on April 4, 1997, Cao Yilin, an expert in plastic surgery at Shanghai Ninth People's Hospital, successfully reproduced human ears on rats by using the method of in vitro cell reproduction for the first time in the world, bringing hope for the repair and reconstruction of missing organs in the human body.Cloning technology can also be used to multiply many valuable genes, such as those for treating diabetesinsulin. It is hoped that dwarfism patients will grow taller againgrowth hormoneAnd resistant to multiple diseasesinterferonwait.
Cloning technology
Cloning is a major technological breakthrough in the field of biological science, which reflects the nuclear differentiation technologycell cultureAnd control technology.It is a transliteration of English clone, which means that organisms are formed through asexual reproduction of cellsgenotypeA population composed of identical offspring, referred to as“Asexual reproduction”。 The major breakthrough in animal cloning technology has also brought widespread controversy.
dogIn 2005, the experimental team of Seoul University, South Korea,Snoopy
Pig: the first pig in China on August 8, 2005Donor cellCloned pig
Sources and results
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Source of technology
The word "clone" was introduced into horticulture in 1903, and later gradually applied to botany, zoology, medicine, etc.In fact, "cloning" in a broad sense is often encountered in our daily life, but it is not called "cloning".In nature, there are many plants with innate cloning instinct, such as sweet potato, potato, rose and other plants.Animal cloning technology has experienced the development process from embryonic cells to somatic cells.
Cloning technology
Dolly and the 6-year-old ewe have identical genes, which can be described as a copy of her mother.It is worth noting that cloning technology will not only bring great benefits to mankind, but also bring disasters and problems to mankind. However, we cannot stop the development of this technology because it may bring serious consequences. In the final analysis, its advantages outweigh its disadvantages, and it will be widely used in areas beneficial to mankind.An individual (usually through a carrier), and then research or use it.Cloning sometimes refers to the successful identification of certain - {A | zh cn:phenotype;zh-tw:dominance}-The gene of.So when a biologist says that the gene of a certain disease has been successfully cloned, it means that the position and DNA sequence of the gene have been determined.Obtaining a copy of the gene can be considered as a by-product of identifying the gene.
Cloning an organism means creating a new organism with the same genetic information as the original organism.In the context of modern biology, this usually includesSomatic cell nuclear translocationPlanting.staynuclear transfer of somatic cellMedium,oocyteThe nucleus is removed and replaced by the nucleus taken from the cell of the cloned organism. Generally, both the oocyte and the nucleus it has transferred into should come from the same species.Because the nucleus contains almost all the genetic information of life, the host oocyte will develop into an organism genetically identical to the nuclear donor.Mitochondrial DNAAlthough it has not been transplanted here, there is relatively little mitochondrial DNA, and its impact on organisms can usually be ignored.
In horticulture, cloning meansVegetative reproductionThe offspring of a single plant produced.Many plants are clonedAsexual reproductionMethods A large number of progeny individuals were obtained from a single plant.
The use of cloning technology can play a role in rescuing rare and endangered animals, expanding the population of improved species of animals, providing sufficient experimental animals, promoting the research of transgenic animals, tackling genetic diseases, developing high-level new drugs, producing visceral organs for human transplantation and other research. However, if it is applied to human reproduction, there will be a huge ethical crisis.
Cloning is a transliteration of English clone, which is simply an artificial inductionAsexual reproductionMode.But cloning and asexual reproduction are different.Asexual reproduction refers to the process of not having sexgerm cellThe reproductive mode of producing offspring by only one organism, including spore reproductionBudding reproductionandMitogenesis。The generation of new individuals from roots, stems and leaves of plants by layering, cutting or grafting is also called asexual reproduction.Animals such as sheep, monkeys and cattle cannot reproduce asexually without manual operation.Scientists put artificialGenetic manipulationThe reproductive process of animals and plants is called cloning, and this biotechnology is called cloning technology.
The idea of cloning technology was first put forward by German embryologists in 1938. In 1952, scientists first carried out cloning experiments with frogs, and then people continued to use various animals for cloning technology research.Since almost no progress has been made in this technology, research work once entered a low ebb in the early 1980s.Later, some people succeeded in cloning with mammalian embryonic cells.July 5, 1996, British scientistIan WIImut Adult sheep for doctorSomatic cloningA live born sheep has brought a major breakthrough to the research of cloning technology. It has broken through the technical difficulty of animal cloning only using embryonic cells in the past, and has realized the first time to usesomatic cellThe goal of animal cloning has realized animal replication in a higher sense.The goal of research on cloning technology is to find a better way to change the genetic composition of livestock, and to breed a group of animals that can provide consumers with better food or any chemical substances they may need.
The basic process of cloning is to first transplant the nucleus of donor cell containing genetic material into the egg cell with the nucleus removed, use micro current stimulation to fuse the two into one, and then promote the new cell to divide and reproduce to develop into an embryoembryonic developmentTo a certain extent（RoslinThe time used for cloning sheep by the research institute is about 6 days) and then it is implanted into the animal uterus to make the animal pregnant so that it can give birth to animals with the same gene as the cell provider.In this process, if the donor cellsGenetic modification, thenAsexual reproductionThe same changes will occur in the genes of 30% of the offspring of animals.The main difference between the "Honolulu technology" of successfully breeding three generations of cloned mice and the technology of cloning Dolly sheep is that the genetic material in the cloning process is not cultured in the culture medium, but directly injected into the egg cells by physical methods.In this process, chemical stimulation method is used instead of electrical stimulation method to restore theEgg cellControl.On July 5, 1998, scientists from Ishikawa Prefecture Animal Production Comprehensive Center and the Animal Production Research Department of Kinki University announced that they had cloned two calves using adult animal somatic cells.These two endsCloned cattleThe birth of shows that the technology of cloning adult animals is repeatable.
In ancient mythology, the Monkey King used his own hair to turn into countless strange stories of the Monkey King, expressing the illusion of human beings to copy themselves.In 1938, German scientists first put forward the idea of mammalian cloning. In 1996, after the birth of somatic cloned sheep "Dolly", cloning quickly became the focus of attention of the world. People can't help asking: will we follow sheep?This kind of question makes everyone uneasy.However, the clamor against cloning has not withstood the persistent pursuit of scientists. With the successful cloning of cattle, mice, pigs and even monkeys, primates with the closest biological characteristics to human beings, it has been believed that one day, scientists will use a human cell to replicate the same person as the cell provider,Human cloningIt is no longer a dream in science fiction, but a reality that is ready to emerge.At present, three foreign organizations have officially announced that they will carry out human cloning experiments. Professor Zavos of the University of Kentucky is working with a man named AndyNorleyAn Italian expert from the United States of America is planning to clone a person within two years.
Due to the complex consequences of human cloning, some countries with advanced biotechnology have adopted an attitude of explicitly prohibiting or severely restricting it.ClintonHe said, "It is dangerous to copy human beings through this technology and should be stopped!"National Gene Research Center, Chinese Academy of SciencesHong Guofan, the director, also clearly expressed his opposition to the research of human cloning, and advocated to distinguish cloning technology from human cloning.
Moral barriers
Human cloning, really likePandora boxIs it as scary as the devil in?
In fact, the main reason why people can't accept the experiment of human cloning is the obstruction of traditional ethics.For thousands of years, human beings have followed the way of sexual reproductionHuman cloningIt is a product in the laboratory, a life created under human manipulation.Especially in the West, the cloning of "abandoning God and separating Adam and Eve" was opposed by many religious organizations.Moreover, the relationship between the cloned person and the cloned person is also contrary to the traditional ethical way of determining kinship by blood.All these have made it impossible for human clones to find a suitable place to live in the traditional human ethics of Daodelhi.However, as He Zuoxiu, an academician of the Chinese Academy of Sciences, said, "The ethical problems arising from human cloning should be faced squarely, but there is no reason to oppose scientific and technological progress".The development of human society itself tells us that it is a historical progress that science and technology drives people's concept updating, while it is rigid to restrict the development of science and technology with outdated concepts.Historically, blood transfusion technologyorgan transplantAll of them have brought about great ethical disputes. When the first IVF baby was born in 1978, it caused a great stir. But in the 21st century, people can already treat all of this correctly.This shows that the constantly updated ideas in the face of scientific and technological development have not brought disasters to mankind, on the contrary, it has benefited mankind.As far as cloning technology is concerned, "therapeutic cloning" will make breakthroughs in producing transplanted organs and tackling diseases, bringing revolutionary changes to biotechnology and medical technology.For example, when your daughter needs a bone marrow transplant and no one can provide it for her;When you unfortunately lose your 5-year-old child and can't get rid of the pain;When you want to raise your own children but cannot have children... maybe you can realize the great scientific value and practical significance of cloning.Research and integrity of therapeutic cloningHuman cloningThe experiments of,Therapeutic cloningThe end point is the emergence of complete human cloning. If properly used, they can and should bring good news to human society.
Science has always been a double-edged sword.However, whether a scientific and technological progress is really beneficial to mankind depends on how humans treat and apply it, rather than giving up food because it is temporarily unreasonable.Cloning technology is indeed possibleatomic energyLike technology, it can not only benefit mankind, but also cause endless disasters.But the essence of "technology fear" is the fear of misusing technology, not the fear of technology itself.At present, the attitude of countries around the world towards human cloning is mostly "ambiguous". In 2012, Britain passed the bill allowing the cloning of human early embryos with more than two-thirds of the votes. In the United States, Germany and Australia, people gradually heard the voice of relaxing the restrictions on therapeutic cloning.It can be said that which country first masteredHuman cloningIt means that this country has advantages and initiative, and countries that start late may suffer from unpredictable losses.As the United States first masteredAtomic energy technologyAlthough this technology showed its evil side from the beginning, later countries had to step up research and experiments in this area.From this point of view alone, it is also worth discussing the simple negative attitude towards human cloning experiments.
As for the fear that once the cloning technology is mature, there will be thousands of "Hitlers" cloned by ill intentioned people, or another celebrity cloned to confuse the public, it is a misunderstanding of cloning.What is cloned is only genetic characteristics, but the social attributes such as thinking and personality affected by many factors in the acquired environment cannot be exactly the same, that is, no matter how the cloning technology develops, it can only clone human body, not human soul, and there is an age gap between cloned people and cloned people.Therefore, the so-calledHuman cloningIt is not a complete copy of human beings. Historical figures will not be reborn, and real figures need not worry about adding a "self".
Although great progress has been made in cloning research, the success rate of cloning is still quite low at present: researchers experienced 276 failed attempts before Dolly was born;70 calves were born successfully after 9000 attempts, and one third of them died at an early age;Prometea also took 328 attempts to be born successfully.For some species, such as cats and orangutans, there was no report of successful cloning by 2013.The dog cloning experiment is also the result of hundreds of repeated experiments.
Dolly's age test after birth showed that he was old at birth.When she was 6 years old, she got arthritis that usually comes from old age.Such aging is considered astelomereCaused by abrasion.Telomere is the end of chromosome.along withcell divisionTelomeres are constantly worn in the process of replication, which is generally considered as a reason for aging.However, researchers found that cows were actually younger after cloning them successfully.Analysis of their telomeres showed that they not only returned to the length of birth, but also were longer than the normal telomeres at birth.This means that they can live longer than ordinary cattle, but many of them died prematurely due to overgrowth.Researchers believe that relevant research can eventually be used to change human lifespan.
Research achievements of various countries
The birth of cloned sheep "Dolly" set off an upsurge of cloning research all over the world. Subsequently, reports about cloned animals continued.In March 1997, nearly one month after the birth of Dolly, scientists from the United States, Taiwan, China and Australia respectively published the news that they had successfully cloned monkeys, pigs and cattle.However, they all use embryonic cells for cloning, which cannot be compared with "Dolly".In July of the same year,Roslin Institute And PPLGenetic modificationPast fetusFibroblastThe world's first transgenic sheep "Polly" with human genes was cloned.This achievement shows that cloning technology is developingTransgenic animalIt has great application value.
In July 1998,University of Hawaii Wakayama et al. reported that 27 live mice were cloned from mouse cumulus cells, of which 7 were the offspring of cloned mice, which was the second batch of mammals after Dollynuclear transfer of somatic cellDescendants.In addition, Wakayama et al
For simple cloning technology with high success rate, this technology is named "Honolulu Technology" after the location of the university.
Since then, scientists from the United States, France, the Netherlands and South Korea have also reported the success of somatic cloning of cattle;Japanese scientists are particularly enthusiastic about research. From July 1998 to April 1999,Tokyo Agricultural UniversityKinki University, Livestock Improvement Group, local (Ishikawa County, Dafen County, Kagoshima County, etc.) livestock experimental farms and private enterprises (such as Japan's largest dairy commodity company, Xueyin Dairy, etc.) have reported their achievements in cloning cattle using cow ears, buttock muscles, cumulus cells and mammary gland cells extracted from colostrum.By the end of 1999, there were six types of cells in the world - fetusFibroblast, breast cellsCumulus ovaleSomatic clone offspring of cells, oviduct/uterine epithelial cells, muscle cells and ear skin cells were born successfully.
In June 2000, China Northwest University of Agriculture and Forestry Science and Technology cloned two "cloned sheep" from adult goat somatic cells, but one of them died prematurely due to respiratory dysplasia.It is reported that the cloning technology used is the research team's own research, which is completely different from the technology of cloning "Dolly", which shows that Chinese scientists have also masteredSomatic cloningAdvanced technology.
Between speciesNuclear transferThe experiment also achieved some gratifying results. In January 1998, scientists from Wisconsin Madison University in the United States successfully cloned the embryos of five mammals, pig, cow, sheep, mouse and macaque, using cow eggs as receptors. This research result shows that the unfertilized eggs of a species can be combined with mature nuclei from a variety of animals.Although these embryos were aborted, it made a useful attempt to the possibility of xenocloning.In 1999, American scientists cloned the embryos of argali, a rare animal, from cow eggs;Chinese scientists have also cloned the early embryos of giant pandas from rabbit eggs, which shows that cloning technology may become a new way to protect and save endangered animals.
Advantages and disadvantages of cloning
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Text selected from Wen Wei Po on November 8, 2000
The advantages and disadvantages of biotechnology mainly refer to cloning, and the advantages and disadvantages are
Advantages: 1) Cloning technology can relieve the pain of women who cannot become mothers.
2) The implementation of cloning experiment has promoted the development of genetics and opened up a prospect for "manufacturing" animal organs that can be transplanted into human body.
3) Cloning technology can also be used to detect fetalGenetic defect。The cloned fertilized eggs are used to detect various genetic diseases, and the cloned embryos have identical genetic characteristics with the fetuses developed in the uterus.
4) Cloning technology can be used to treat the damage of nervous system.Adult nerve tissue has no regenerative capacity, butstem cellsIt can repair nervous system damage.
5) OnIn vitro fertilizationDuring surgery, doctors often need to implant multiple fertilized eggs into the uterus to screen one of them for pregnancy.But many women can only provide one egg for fertilization.Cloning can solve this problem well.This egg cell can be cloned into multiple ones for fertilization, thus greatly improving the success rate of pregnancy.
Disadvantages: 1) Cloning will reduce genetic variation. Individuals generated by cloning have the same genetic genes and the same disease sensitivity. One disease can destroy the whole population generated by cloning.It can be imagined that if the cattle in a country are the same clone product, a virus that is not serious may destroy the animal husbandry in the country.
2) The use of cloning technology will make people tend to multiply the most valuable individuals in the existing population, rather than promote the survival of the fittest in the whole population according to the natural law.In this sense, cloning technology interferes with the natural evolution process
3) Cloning technology is an expensive technology, which requires a lot of money and the participation of biological professionals. The failure rate is very high.Dolly is the only result of 277 experiments.Although more advanced technologies have been developed, the success rate can only reach 2-3%.
4)Transgenic animalIncreased risk of disease transmission.For example, if a cow producing medicated milk is infected with a virus, the virus may infect patients through milk
5) The application of cloning technology to human body will lead to the artificial control of genetic traits of offspring.The core of the controversy over cloning technology is whether it is allowed to conductGenetic manipulation。This is unacceptable to many ethicists.
6) Cloning technology can also be used to create "supermen", or people with strong physique but low intelligence.Moreover, if cloning technology can be effectively used in humans, men will lose their genetic significance.
7) The impact of cloning technology on family relations will also be enormous.A child born from the father's DNA clone can be regarded as the father's twin brother, but the birth is delayed for decades.It is hard to imagine how a person will feel when he or she finds that he or she is just a complete replica of another person?
application prospect
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Wonderful cloningTechnology has shown broad application prospects, which can be summarized in the following four aspects:
(1) Breeding fine breeds and producing experimental animals;
(4) Reproduction of endangered animal species, conservation and dissemination of animal species resources.
The following is about the production of transgenic animals andembryonic stem cellGive a brief description.
The research of transgenic animals is one of the most attractive and promising topics in the field of animal bioengineering, and transgenic animals can be used for medical purposesorgan transplantIt can be used as a donor, as a bioreactor, and for genetic improvement of livestock, and to create disease experimental models.But nowTransgenic animalThere are not many practical applications ofgene modificationOftransgenic miceIn addition to the earlier application of medical models, transgenicAnimal mammary gland bioreactorThe research on the production of drug protein has been carried out for more than 10 years, but at present, there are only 2 cases of drugs in phase 3 clinical trials worldwide, and 5 to 6 drugs in phase 2 clinical trials;However, the transgenic livestock strains whose agronomic traits have been improved and can be used in animal husbandry have not been born yet.The low production efficiency of transgenic animals, the high cost and regulation failure caused by the difficulty of fixed-point integration, and the separation of genetic traits from the offspring of sexual reproduction of transgenic animals, which is difficult to maintain the good traits of the ancestor, are the main reasons that restrict the practical process of transgenic animals today.
The success of somatic cell cloning isTransgenic animalProduction sets off a new revolution, animalSomatic cell cloning technologyIt provides a technical possibility for rapidly amplifying the germplasm innovation effect of transgenic animals.Using simple somatic cell transfection technology to transfer target genes can avoid the difficulty and low efficiency of livestock germ cell source.At the same time, transgenic somatic cell lines can be used for transgenic integration pre testing and gender pre selection under laboratory conditions.staynuclear transferBefore, the target foreign gene andMarker gene(such as LacZ gene and neomycin resistance gene)fusion geneTransgenic positive cells and their clones were screened through the expression of marker genes, and then the positive cells were transplanted toDenuclearizationoocyteIn theory, the final produced animals should be 100% positive transgenic animals.With this method, Schnieke et al. (Bio Report, 1997) have successfully obtained 6 transgenic sheep, of which 3 have human coagulation factor IX gene and marker gene (neomycin resistance gene), and 3 have marker gene. The integration rate of target foreign gene is as high as 50%.Cibelli (Science, 1997) also obtained 3 heads by nuclear transplantationTransgenic cattle, which proves the effectiveness of the law.It can be seen that one of the most important application directions of animal cloning technology today is to transformGene cloningAnimal research and development.
embryonic stem cell(ES) has the potential to form all adult cell typesTotipotent stem cell。Scientists have been trying to induce variousstem cellsDifferentiate into specific tissue types to replace damaged tissues in the body, such as implanting insulin producing cells into diabetic patients.Scientists have been able to turn pig ES cells into beating onesCardiac myocyte, enable human ES cells to generate nerve cells andMesenchymal cellsAnd mouse EScell differentiationbyEndodermCells.These results open the way for cell and tissue replacement therapy.In 1998, scientists successfully isolated human ES cells (Thomson et al., 1998, Science)Somatic cell cloning technologyIt is possible to produce patients' own ES cells.Transplant patient's somatic cells toDenuclearizationoocyteTo form recombinant embryosin vitro culturereachblastulaThen, ES cells were isolated from the blastocyst, and the obtained ES cells were directed to differentiate into specific cell types (such as nerve cells, muscle cells and blood cells) needed for substitution therapy.The ultimate purpose of this nuclear transplantation method is to be used for stem cell therapy, rather than obtaining cloned individuals, which scientists call "therapeutic cloning".
The application of cloning technology in basic research is also very meaningfulEmbryogenesis, cell and tissue differentiation, gene expression regulation, nucleocytoplasmic interaction and other mechanisms provide tools.
As a new research team, in practice, the success rate of cloning animals is still very low. In the experiment of cultivating "Dolly", Wilmut's research team fused 277 oocytes with transplanted nuclei, and only obtained "Dolly", a live lamb, with a success rate of only 0.36%FibroblastThe success rate of cloning experiments with embryonic cells is only 1.7% and 1.1%, respectively, even when using"Honolulu" technologyWith cumulus cells with lower differentiation as nuclear donors, the success rate was only a few percent.
In addition, some individuals born showed physiological or immune deficiency.withCloned cattleFor example, many cloned cattle bred in Japan, France and other countries died within two months after birth;By February 2000, 121 somatic cloned cattle had been born in Japan, but only 64 survived.The results showed that the placental function of some calves was not perfect, and the oxygen content in blood and the concentration of growth factors were lower than normal;The thymus, spleen and lymph glands of some calves did not develop normally;Cloned animal fetuses generally have a tendency to develop faster than ordinary animals, which may be the cause of death.
Even the normally developed "Dolly" has been found to have signs of premature aging.The ends of chromosomes are calledtelomereIt determines the number of times a cell can divide: each time it divides, the telomere will be shortened, and when the telomere is exhausted, the cell will lose its ability to divide.In 1998, scientists found that the telomeres of Dolly's cells were shorter than normal, that is, their cells were in a more senescent state.At that time, it was thought that this might be done with adult sheepCell cloning"Dolly", which makes its cells have the mark of adult cells, but this explanation has been challenged at present. Robert Lanza, a doctor in Massachusetts, United States, and others use cultured aging cellsCloned cattleSix calves were obtained. After 5-10 months of birth, it was found that the telomeres of these cloned calves were longer than those of ordinary calves of the same age, and some were even longer than those of ordinary newborn calves.The reason for this phenomenon is not clear, nor is it clear why it is so different from "Dolly". But this experiment shows that in some cases, the cloning process can change theMolecular clockThe impact of this change on the life span of cloned animals remains to be further observed.
In addition to the above theoretical and technical barriers, the impact of cloning technology (especially its application in human embryos) on ethics and the strong response of the public also limit the application of cloning technology.However, the development of cloning technology in recent years shows that the world's major scientific and technological countries are unwilling to lag behind, and no one has given up the research of cloning technology.In this regard, the British government's attitude is very representative. Less than one month after the announcement of the suspension of investment in Dolly's research group at the end of February 1997, the British Science and Technology Council issued a special report on cloning technology, indicating that the British government will reconsider this decision and that it is not wise to ban research in this field blindly,The key is to establish certain norms and use them for the benefit of mankind.
A bacterium can be divided into two after about 20 minutes;A grape branch cut into ten sections may become ten grapes;The cactus is cut into several pieces and takes root when each piece falls to the ground;A strawberry can grow hundreds of strawberry seedlings within a year by relying on its "creeping" stolon... All these are the offspring of organisms by splitting themselves in two or expanding a small part of themselves, which isAsexual reproductionThe English name of asexual reproduction is "Clone", which is translated as "clone".
Many animals in nature, under normal circumstances, rely on the male cell (sperm) produced by the father and the female cell (egg) produced by the mother to fuse (fertilize) into a fertilized egg (zygote), and then from the fertilized egg through a series of cell divisions to grow into an embryo, finally forming a new individual, which relies on both parents to provide sex cellsThe reproduction method that produces offspring through the fusion of bisexual cells is called sexual reproduction. However, if we use surgery to divide an embryo into two, four, eight... Finally, through a special method, an embryo grows into two, four, eight... organisms, which are called cloned individuals, and these two, four, eight... individuals are calledAsexual line(Also called cloning).
In the spring of 1979, scientists from the Wuhan Institute of Hydrobiology, Chinese Academy of Sciences, artificially cultured crucian carp blastocyst cells. After 385 days and 59 generations of continuous culture, they used glass tubes with a diameter of about 10 microns to suck out the nucleus from the cultured cells under a microscope. At the same time, they removed the nucleus from the crucian carp egg cell, leaving room for the egg cell to prepare for receiving the nucleus of the blastocyst,When everything was ready, the nuclei sucked out of the glass tube were transferred to the free position of the crucian carp egg cells, and most of the oocytes with blastocyst nuclei died in artificial culture. Of 189 such nucleated eggs, only two hatched fry, and finally only one young fish survived the difficulty, and after more than 80 days of culture, the carp grew into 8 cm long crucian carp.This kind of crucian carp has not beenMale cellThe combination ofClone fish。
Before the advent of cloned crucian carp,Oxford UniversityIn 1960 and 1962, scientists of（Xenopus Laevis ）The cloning test was conducted.The test method is to irradiate Xenopus with ultraviolet ray firstEgg cell, destroy the nucleus, and then rely on superb surgery from the intestines of Xenopus tadpolesepithelial cells, hepatocytesRenal cellThe nuclei of these cells were precisely put into the egg cells whose nuclei had been destroyed by ultraviolet light. After careful care, some of these nuclear exchange eggs finally grew up lively Xenopus. This kind of Xenopus was not born through the combination of sperm cells and egg cells, so it was also a clone of Xenopus.
Mr. Tong Dizhou, a famous biologist in China, successfully carried out the cloning experiment of Rana nigromaculata in 1978. He transferred the red cell nucleus of Rana nigromaculata to the eggs of Rana nigromaculata whose nuclei were removed first, and the transformed eggs eventually grew into tadpoles that could swim freely in water.
The maturity of fish nuclear exchange technology and the success of amphibian nuclear exchange have excited a group of scientists engaged in the breeding of improved varietiesBlastocyst nucleusThe cloned fish can be obtained by replacing the nucleus of crucian carp egg, so can the new hybrid fish be obtained by replacing the nucleus of hetero fish?Chinese scientists first raised and solved this problem, that is, the research institute that successfully cultivated and cloned crucian carp managed to replace the nucleus of carp embryo cells with that of crucian carp egg cells.Carp Nucleus and Crucian CarpEgg cellThe quality was able to live in peace, and started a process similar to the division and development of the fertilized egg, and finally grew a "beard"“Carp and crucian carp”This kind of fish has a "beard" and grows fast. It is completely like a carp, but its number of lateral scales and vertebrae is the same as that of crucian carp, and its taste is as delicious as that of crucian carp.suchArtificial cloningThe emergence of new fish species has opened up a new way for fish breeding.
The pursuit of science is endless. The success of cloning fish and amphibians naturally led scientists to focus on mammals.Scientists in the United States and Switzerland took the lead in removing the nucleus from the embryo cells of gray mice, and replacing the nucleus of black mouse fertilized eggs with this nucleus.In fact, the fertilized egg of this black mouse removes the sperm nucleus along with the nucleus of the egg cell just after the sperm nucleus enters the egg cell.The nuclei of the embryonic cells of chinchilla were transplanted into the black miceDenuclearizationAfter fertilization, the eggs were artificially cultured in test tubes for four days, and then implanted into the uterus of white mice. After hundreds of operations such as gray, black and white, the white mice finally gave birth to three little gray mice.
The British journal "Nature" published on February 27, 1996 published the research results of Wilmot and others from Edinburgh Roslin Research Institute: after 247 failures, they got a cloned female sheep named "Dolly" in July of the previous year.
How did Dolly sheep "create" it?Wilmot and other scholars first injected "Scottish black faced sheep"Gonadotropin, urge it to ovulate, immediately take out the nucleus from the egg cell with a very thin straw after getting the egg, at the same time, take out the nucleus from the mammary gland cell of the sixth age ewe of "Fendoshite" who is three months pregnant, and immediately send it to the egg cell of the "Scottish Black faced Sheep" who took the nucleus. After the operation is completed, use the same frequency electric pulse to stimulate the change of the nucleus egg, so that the "Scottish Black faced Sheep"The cytoplasm of the "Fendoshite" ewe's egg is coordinated with the nucleus of the "Fendoshite" ewe's mammary gland cell, so that this "assembled" cell undergoes the process of cleavage and development like a fertilized egg in a test tube to form an embryo, and then the embryo is skillfully implanted into the uterus of another ewe.By July 2012, this ewe that "nursed" embryos in vitro finally gave birth to the baby sheep "Dolly".Dolly is not made by ewesEgg cellThe product of fertilization with ram's sperm cell is the result of the step by step development of "replacement eggs", so it is "cloned sheep".
The birth of "cloned sheep" has caused shock all over the world. It is valuable that the nucleus of somatic cell is replaced instead of embryonic nucleus.This result proves that the so-called highly differentiated cells that perform special functions and have specific forms in animals have the same potential ability to develop into complete individuals as fertilized eggs.in other words,Animal cellAndplant cellIt is also omnipotent.
Cloning technology will bring great benefits to human beings. For example, British PPL company has cultivated sheep milk containing a-1 for the treatment of emphysemaAntitrypsinThe ewe of.The price of this kind of goat milk is 6000 dollars a liter.A ewe is like a pharmaceutical factory. What is the most effective and convenient way to expand the breeding of this kind of sheep?The best way is to "clone".Similarly, the Dutch PHP company has cultivated people who can secretelactoferrinThe Israeli LAS company has bred cattle that can produceserum albuminHow can these high value-added livestock breed effectively?The answer is, of course, cloning.
If a mare matches a male donkey, she can get an animal with strong heterosis -- a mule. Mules can't breed offspring. So, how can a good mule breed more?The best way is also to "clone". China's giant panda is a national treasure, but the success rate of natural mating is low, so it is on the verge of extinction.How to save these rare animals?"Cloning" provides a practical way for human beings.
Cloning animals is also important for researchCancer biologyThe research on immunology and life span of people can not be underestimated.
It cannot be denied that the advent of "cloned sheep" has also aroused many people's interest in "cloning human beings". For example, some people are considering whether they can use their own cells to clone an embryo and freeze it before it takes shape.One day in the future, when one of its own organs has a problem, it can take this organ from the embryo for culture, and then replace its diseased organ, which is to provide "accessories" for human beings by cloning.
The discussion on "human cloning" reminds people that scientific and technological progress is a mixed march.The more development of science and technology, the more extensive and deep penetration of society, the more likely it will cause many related ethical, moral and legal issues.I want to use the Nobel Prize winner, the famous molecular biologist JD. Watson concluded this article with his words: "It can be expected that many biologists, especially those engaged in asexual reproduction research, will seriously consider its implications and launch scientific discussions to educate people around the world."
As a cutting-edge science in the new century, cloning technology has attracted the attention of many people from the moment it was born.As the largest developing country in the world, China has been committed to cutting-edge scientific research.According to the current situation, cloning, as an emerging technology, has received unprecedented attention in China and has achieved fruitful results:
1. On June 16, 2000, Northwest A&F University of Science and TechnologyAnimal Embryo EngineeringexpertZhang YongThe world's first adult somatic cloned goat "Yuanyuan" bred by professor was successfully born in the school's sheep breeding farm."Yuanyuan" only survived for 36 hours due to lung development defects.On June 22 of the same year, the second somatic goat "Yang Yang" was born againNorthwest Agriculture and Forestry Universitybirth.On August 8, 2001, "Yangyang" gave birth to a pair of "twins" in Northwest A&F University of Science and Technology, indicating that the first generationcloned sheepIt has normal breeding ability.
It was reported that on February 26, 2003, the daughter of cloned sheep "Yangyang", "Qingqing", gave birth to her daughter "Tiantian", and on February 6, 2004, "Tiantian" gave birth to her daughter "Xiaoxiao"."Yangyang" family realizes four generations in the same hall.This not only shows that the first generation of cloned sheep has fertility, but their offspring still have normal fertility.At present, "Yangyang" lives happily with her daughter "Qingqing", granddaughter "Tiantian" and great granddaughter "Xiaoxiao".It is reported that by the end of May 2004, more than 1 million people had come to visit
2. Not long ago, onHebei Agricultural UniversityUnder the joint research with the Biotechnology Research Center of Shandong Academy of Agricultural Sciences, Chinese scientists and technicians successfully cloned two white rabbits, "Lu Xing" and "Lu Yue", through an experimental project entitled "Research on the Isolation and Cloning of Animal Primordial Germ Cells Embryonic Stem Cells".This experiment shows that China has successfully masteredEmbryonic cloningAlthough it has not reached the level of somatic cell cloned sheep "Dolly" in technology, it has laid a foundation for China's progress in cloning technology.
After that, ChinaGuangxi UniversityThe Institute of Animal Reproduction has successfully bred cloned rabbits larger than ordinary rabbits.Because the physiology of rabbits is closer to that of humans, the successful birth of cloned rabbits will contribute to human medical research.
3. On 27 May 2002,China Agricultural UniversityAndBeijing Genda Technology Co., LtdAnd HebeiLutai FarmCooperation throughSomatic cell cloning technology, successfully cloned the first high-quality yellow cattle in China - red line Jinan cattle.This one named "Bova"Somatic cloningSome cloning technical indicators of yellow cattle have reached the international level after being identified by the authoritative department.Jinan cattle is an excellent local cattle breed unique to China, which is distributed in Hebei Province of China. Its main characteristics are cold resistance, fat rich meat and less fat.But at present, the number has decreased sharply and is on the verge of extinction.The successful cloning has a far-reaching impact on the protection of endangered species in China.
4. At noon on October 16, 2002, China's first somatic cloned cattle bred by vitrification technology was born in Liangshan County, Shandong Province.
The nuclear donor of this cloned cow comes from a high-quality cow with an annual output of more than 10 tons of fresh milkBlack and white cowSkin of earFibroblast。The cloned embryo passes throughvitrificationFrozen and transplanted to one endLuxi cattleIn vivo, after 281 days, a healthy black and white cow was born at 11:52 on October 16, 2002.this endCloned cattleAt birth, she weighed 40 kg, was 80 cm tall, 72 cm long, 80 cm chest circumference, and 11.5 cm tube circumference.14:20 that daycolostrumAt 14:30, he started to stand, and he could bark, lie and jump that night, which was no different from the physical signs of normal born cows.This is the first cloned bovine somatic cell produced by vitrification technology in China.Prior to this, China has always used the fresh embryo transfer technology, and there is no precedent for successful cloning by freezing technology.
