Glial cellscolloidCells are another large type of cells in the nervous tissue except neurons. They also have processes, but no dendrites or axons. They are widely distributed in the central and peripheral nervous systems.In mammals, the proportion of glial cells to neurons is about 10:1.The glial cells in the central nervous system (CNS) mainly include astrocytes, oligodendrocytes (collectively referred to as macroglia with the former) and microglia.Traditionally, glia belong to connective tissue, and its role is only to connect and support various nerve components. In fact, glia also play a role in distributing nutrients, participating in repair and phagocytosis, and are different from ordinary connective tissue in morphology, chemical characteristics and embryonic origin.
Glial cells have complex and diverse structures and rich expression of secreted products. They contain most neurotransmitters, neuropeptides, hormones and neurotrophic factor receptors, ion channels, affinity carriers of neuroactive amino acids, cell recognition molecules, and can secrete a variety of neuroactive substances (growth factors, neurotrophic factors, cytokines, etc.).
Astrocyte
The molecular weight of glial fibrillary acidic protein (GFAP) is 50~52kD, which mainly exists in astrocytes of central nervous system.The GFAP gene is located at 17q21, and has high homology with other intermediate filament sequences, especially the base sequences of desmin and vimentin, of which 65% is homologous with desmin and 67% with vimentin.Astrocyte precursor cells mainly express Vimentin, and after maturation, they express Vimentin and GFAP, so GFAP is considered as a marker of astrocyte maturation.Some studies have found that GFAP positive cells in the central nerve cells of postpartum mice and adult rats are deeply stained and irregular "star" shaped, mainly located in the cell bodies and processes of astrocytes, densely distributed in the molecular layer, outer granular layer and pyramidal cell layer of the prefrontal cortex, hippocampus and substantia nigra, and only a few positive cells are expressed in the striatum;In the gray and white matter of the spinal cord, it is mainly expressed near the central canal of the spinal cord.In human brain, GFAP first appeared in the eighth week of embryonic development, and gradually expressed in glial cells, mainly in astrocytes, but also in ependymal cells, oligodendrocytes and other glial cells.In addition, GFAP can also be expressed in non central nervous system (CNS) cells such as Schwann cells, fibroblasts and hepatic stellate cells.As a component of mature astrocyte intermediate filament, GFAP protein has the functions of regulating cell metabolism, forming and maintaining blood brain barrier, producing and releasing neurotrophic factors, and plays an important role in maintaining the morphology and function of astrocytes, such as forming the connection between cell nucleus and cell membrane, participating in cytoskeleton reorganization, adhesion and stabilizing the structure of neuronsIt maintains the formation of myelin sheath in the brain and acts as a cell signal transduction pathway.
Oligodendrocyte
O1/O4Some studies have observed O1In mice cerebellum, brain, spinal cord, optic nerve and retinal cells labeled with O2, O3 and O4 antigens in the early postnatal period, no O antibody was detected on the surface of astrocytes, nerve cells and fibroblasts, but on the surface of oligodendrocytes, and O antigen was expressed in the central nervous system of mice, rats, chickens and humans.Both O4 and O1 antigens are oligodendrocyte markers, which are brain thioesters on the membrane surface. O4 can be expressed not only in late oligodendrocyte precursor cells, but also in immature oligodendrocytes. Q1 is mainly expressed in immature oligodendrocytes.O4 positive cells can become mature MBP positive oligodendrocytes, which are GC positive cells (oligodendrocyte precursor cells), so it can be speculated that O4 also specifically expresses oligodendrocyte precursor cells.Almost all O4 positive cells also express NG2 (glial precursor cells) in the mature cerebral cortex, while NG2 positive cells do not express OX-42 monoclonal antibodies, indicating that O4/NG2 positive cells are not microglial cells.In order to study whether O4 is only expressed in oligodendrocyte lineage, double immunoassay of O4, GFAP and NFP antibody was carried out. It was found that O4 was not expressed in NFP positive neurons and GFAP positive astrocytes in cortical gray matter.Therefore, it is considered that O4 antibody, like GC and NG2, can be used as a marker of oligodendrocyte precursor cells, but it can also label immature oligodendrocytes without labeling neurons, astrocytes and microglia;O1 is only a marker of immature oligodendrocytes.
Oligodendrocyte factor (OLIG)It is a family of transcription factors with basic helix loop helix structure. Analysis by Northern blot showed that OLIG1 (2.2 kb) and OLIG2 (2.4 kb) were specifically expressed in the brain.In adult rodent brain tissue, OLIG1/2 is specifically expressed in oligodendrocytes, but not in astrocytes and neurons.OLIG1 and OLIG2 are located on chromosome 16 in mice and chromosome 21 in humans.These two genes originate from the ventral region of the spinal cord in the embryonic stage, and are expressed in the neural tube, spinal cord, and thalamus in the embryonic stage. They can also be widely expressed in the corpus callosum, white matter of the brain, and hippocampus in adulthood, but rarely in the gray matter.The distribution of OLIG2 is wider than that of OLIG1. OLIG2 can be expressed in the ventricles (VZ), transverse SVZ (LGE), and E10.5 to E14.5 of the medial ganglia. OLIG1 is rarely expressed in these cells, which indicates that OLIG2 expression is not limited to oligodendrocyte lines, but can be expressed in multiple types of neural progenitor cells, including pluripotent neurons and glial progenitor cells.OLIG1 is located in the nucleus of oligodendrocyte and its precursor cells at embryonic stage, and migrated from the nucleus to the cytoplasm after birth, but it appears in the nucleus again after myelin sheath injury;However, OLIG2 always exists in the nucleus and does not migrate.Overexpression of OLIG1 and OLIG2 genes by gene transfection technology was found to increase the proliferation of oligodendrocyte precursor cells and the production of motor neuron precursor cells. OLIG1 played a role in the maturation of oligodendrocyte;OLIG2 plays a role in the development of somatic motor neurons in the spinal cord and the hindbrain, and also participates in the development of oligodendrocytes;OLIG1 can partially compensate for the function of OLIG2 in the developing brain.
Myelin basic protein (MBP)Markers of mature oligodendrocytes are widely found in oligodendrocytes and their myelin sheaths. They have four main types and can be divided into 21500kb, 18500kb, 17000kb and 14000kb according to their molecular weights.Both human and mouse MBP genes are located at the far end of chromosome 18, namely 18q22-23.There are two types of MBP: central MBP and peripheral MBP. Central MBP is synthesized and secreted by oligodendrocytes, and its content is the highest in white matter. It is mainly bound to the serous surface of myelin sheath by covalent bonds in oligodendrocytes, and also connected with cytoskeleton, microtubules, and microfilaments;Peripheral MBP is synthesized and secreted by Schwann cells and exists in the myelin sheath of peripheral nerve;In addition to nerve tissue, it also exists in heart, liver, kidney, adrenal gland, skeletal muscle and other organs and tissues, but the content is very low and difficult to detect.Immunofluorescence method and in situ hybridization method were used to study the expression of MBP gene in the development stage of myelin basic protein in the brain glial cell culture of newborn mice. A large number of MBP specific mRNA suddenly appeared in immature oligodendrocytes 5 to 6 days after delivery, and slowly increased in the maturation process. About 60% to 80% of cells can express MBP, but not in neurons.Some studies used double labeling method to find that MBP positive expression was in a small number of GC positive cells 8 to 9 days postnatal, and all GC positive cells were MBP positive in 10 to 13 days postnatal. The proportion of MBP labeled cells was the highest in cell culture 13 to 14 days postnatal, and GC was a marker of specific immature oligodendrocytes,The expression of MBP in GC positive cells strongly indicates that MBP expresses mature oligodendrocytes.Therefore, it is believed that MBP specifically marks oligodendrocytes rather than neurons.
Oligodendrocyte specific antibody (RIP)Some studies found that RIP positive cells were mainly distributed in mouse spinal cord and cerebellar oligodendrocyte myelin sheath axons by immunohistochemical method.In addition, RIP and MBP, GFAP double labeled cell labeling experiments showed that RIP was stained in MBP positive cells, but not in GFAP positive cells, indicating that RIP selectively stained oligodendrocytes and non astrocytes.
Microglia
CD11b monoclonal antibody (OX42)The microglia can be specifically labeled by OX42 antibody because it can recognize the CR3 receptor of mice, which is located in the branch of microglia.In normal adult brain tissue, microglia are in a resting state, with very small cell bodies and thin processes, and OX42 staining is negative or weakly positive, which is called "resting" microglia.When the body is stimulated (such as trauma, infection, physical and chemical or electrical stimulation), microglia are activated, and the early cell body becomes larger, the processes become thicker, the spines are clear, and the OX42 staining is deeper into the early reaction state, which is called "early reactive" microglia.With the presence of stimulation focus, the cell body of microglia becomes further hypertrophic, and the processes shrink short, becoming macrophage like "phagocytic" microglia.There were no OX42 positive microglia in the normal brain tissue sections of the young group and the old group, while in the cerebral hemorrhage group of rats, the number of activated OX42 positive microglia in the old group was significantly increased, and more than that in the young group.Therefore, it is believed that the OX42 monoclonal antibody is slightly or not stained in normal microglia, but more or more deeply stained in abnormal microglia.
Ionic calcium binding adaptor molecule 1 (IBA-1)It is an EF hand type protein that specifically expresses the monocyte lineage, such as microglia.IBA-1 is a conservative protein with actin attribute evolution. It has been found to co locate with F-actin and play an important role in membrane folding movement and phagocytosis of macrophage colony stimulating factor.IBA-1 was found in microglia of human, monkey, horse, rat and mouse tissues.In some studies, immunocytochemistry and laser confocal microscopy were used to detect the expression of IBA-1 protein only in microglia, macrophages in cerebrospinal membrane and ependyma, and macrophages in stromal cells on the surface of choroid plexus, and these cells all have phagocytic function. Microglia are one kind of macrophages,It was further confirmed that IBA-1 was specifically expressed in microglia in the central nervous system.Because IBA-1 is abundant and stable in microglia, it is considered as a reliable and specific marker of microglia.In addition, IBA-1 is also an inflammatory factor-1 (AIF1) in allogeneic transplantation and can be expressed in hematopoietic cells.
