spindleSpindle Apparatus, shaped like a spindle, is produced fromcell divisionA special type from pre prophase to telophaseOrganelle。Its main components includemicrotubuleMicrotubules, dynamic molecules attached to microtubulesMolecular motor(Motor motors), and a series of complexSupramolecular structure。Generally speaking, inAnimal cellMedium,CentrosomeIt is part of the spindle.higherplant cellThe spindle does not contain a centrosome.andFungal cellThe spindle body of contains a spindle pole body, which is generally regarded as a homologous organelle of the centrosome.
In cells containing centrosomes, spindle formation begins at the early stage before cell division - that is, before nuclear envelope breakdown (NEB).The initial structure consists of two independentCentrosomeThe stars are nuclei.When the nuclear membrane of the cell decomposes, the chromosome andStellate bodyA series of complex interactions occur.The final result is that all chromosomes are in the center of the spindle（Equatorial plate,) neatly arranged, with one for every two chromosomesCentromereEach centromere is surrounded by a bundle of microtubules with the same polarity (commonly referred to asSpindle yarn）Attach.At this time, the cell is inMetaphase of fission, Spindle generation is completed.Experiments have proved that the role of centrosome in this process is not necessary.Animal cellAfter the centrosome is destroyed by the laser, the spindle can still be constructed, but its position is usually not in the approximate position of the cellGeometric center, subsequentCytokinesisIt will also be seriously affected.
Spindle[1]
WithoutCentrosomeThe formation of the spindle is dominated by the chromosome itself.This process consists of a small molecular weightGTPConnexin(Ran GTPase) control.After the nucleus decomposes, the spindle filament is formed around the chromosome.Then these spindles willmicrotubuleUnder the influence of dynamic cooperation, they are automatically arranged into two groups with opposite polarity and approximately the same number.The polarity of each group is relative to a group of centromere.At the same timeDyneinDynein will focus these microtubule bundles to one point to form a spindle polar zone.At the same time, the dyeing experience automatically arranges neatly on the equatorial plate.Spindle generation completed.
Functional decomposition
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In cell division, its main role has two parts.One is arrangement and division of chromosomes.The integrity of the spindle determines the correctness of chromosome division.The normal formation of spindle isChromosome arrangementOfnecessary condition。After the completion of spindle formation, there will be a delay of 5-20 minutes for cells to adjust the polarity of microtubule bundles on the centromere and determine whether allCentromereAll are attached correctly.Then the cells enterAnaphaseChromosomes divide into two equal groups of sister chromatids.Similarly, the integrity of the spindle determines the temporal and spatialaccuracy。
spindleAnother function of soma is to determine cytokinesisSplit surface。At the same time as chromosome division, part of the spindlemicrotubuleInstead of splitting to the poles with chromosomes, they stop at the center of the spindle to form a spindleCentral body(central spindle)。At spindleMesosomaThe center of the spindle is the area where two groups of microtubules with opposite polarity overlap, called the spindle midzone, which is the next cytokinesis plane.Cytokinesis starts fromAnaphaseThe later stage of.Cytokinesis usually ends atAnaphaseIn the last 1-2 hours, during this period, two daughter cells from the centerGranular body(midbody) connection.It is generally believed that spindle breakdown occurs at the end of cell division.
staymitosisThe spindle usually has two poles.But inPolyspermyOfEgg cell、tumor cell, cultured HeLa cellsHybrid cellSpindles with 3, 4 or more poles can be formed with different conditions.When existsMultipolar spindleThe later distribution of chromosomes is irregular, and severalSmall nucleus。Use low concentrationColchicineAnd other drug treatments can induce the same changes.Equisetum and other special plants orEndosperm cell, often forms multipolar spindle at the initial stage of divisionMetaphase of fissionMost can be restored to two poles.
For a long time, scientists believed thatmammalThe first time of embryocell divisionIn the process, only one spindle is responsible for distributing embryonic chromosomes into two cells.But European researchers use mice to carry out the latestexperimental observation It is found that there are actually two spindles responsible for chromosomes from father and mother[2]。
Possibility of formation of double spindlesPartial explanationWhy mammals in the earlyDevelopmental stageThere is a very high error rate.If the poles of the spindle are not aligned and fused, then,ZygoteOfgenetic materialIt may be pulled in 3 or 4 directions instead of 2.This error can lead to multiplenucleusThe cells ofembryonic development。The double spindle theory provides a previously unknown mechanism.What needs to be discussed next is whether the dual spindle also plays the same role in humans.Because it will provide very valuable information for research on how to improve human infertility treatment[3]。
chromosome
When cells enter from interphasemitosisInterphase cellmicrotubuleNetwork depolymerization into free α - β - microtubulesProtein dimer, and then reconstitute the spindle to mediate the movement of chromosomes;AnaphaseSpindle microtubuleDisaggregation and recombinationcytoplasmMicrotube network.
The movement of chromosomes depends on the assembly and disassembly of spindle microtubules.In this processkinetochore microtubuleThe sliding with moving particles mainly depends on theKinesinandDyneinAlong the microtubule.MicrotubuleInterlaced in the middle of the spindle, some are distributed between the special bipolar microtubulesMotor protein, two motor proteins move along one microtubule, and the other two motorsDomainMove along another microtubule.Since two microtubules are fromBipolarTherefore, the polarity is opposite.When the bipolar kinesin tetramer moves along the microtubule to the positive electrode, the distance between the two poles of the spindle increases.On the contrary, the spindle distance is shortened.
stayAnimal cellAt the end of cell division,mother cellsIn a“Cytokinesis”The process of dividing into two daughter cells and segregating chromosomes.mitosisSpindles control "cytokinesis" events on the plasma membrane, but connect the twoMacrostructureThe mechanism of has been unclear.Mark Petronczki and his colleagues provide a structure and functionAnalysis results, they found thatSpindle protein(A protein complex in the middle region of the spindle and the intermediate) is the missing link between the mitotic spindle and the plasma membrane, which ensures the final result of the "cytokinesis" process.The authors also found that a region in the MgcRacGAP subunit of the central spindle protein is a "tether", which connects to thePhosphoinositollipidOn.[4]
