Similarity between three glia progenitors
During development, first generate common ancestors, then firstly astrocyte progenirots, following with OPC. That explains why their cellmorphology and migratory behaviors are strikingly similar. In fact, both populations are attracted to blood vessels through
Cxcr4 (cxcr4-cxcl12) signaling (and also the microglia migration, which is interesting because microglia has a total different origin), suggesting common molecular mechanisms for blood vessel-guided migration.
Summary of astrocyte progenitor charateristics
They showed that astrocyte progenitors derived from prenatal cortical VZ ((E15–E17 in mice) cells were remarkably (1)motile and followed an erratic migration pattern through irregular movements within the IZ and CP or (2) a blood vessel-guided migration process (transition between these two pattern still unknown), which was frequently observed in the superficial CP. They eventually differentiated into protoplasmic astrocytes extending highly branched fine processes from the cell body. On the other hand, the astrocytes derived from postnatal VZ cells remained in the white matter or in deep positions in the cortical gray matter and differentiated into GFAP-strongly positive fibrous astrocytes.(whereas the previous one, protoplasmic astrocytes, are GFAP weekly expressing) We also showed that Cxcr4 and Cxcr7 were involved in blood vessel-guided migration probably by activating integrin β1.
Meaning of erratic (random) movement of astrocyte progenitors
People can base on movement to distinguish astrocyte progenitor with neurogeneic progenitors. The former moves erraticly (randomly without specifc direction), whereas the latter moves radially and directionally.
They assume that this random dispersion facilitates the even distribution of astrocytes throughout the CP. Protoplasmic astrocytes form mutually exclusive territories by extending highly branched processes. To achieve this, astrocytes need to be
spread apart from each other.
Interneuron migration
Interneurons migrate into the cortical marginal zone (MZ) from the medial ganglionic eminence, and then move in various directions tangentially within the MZ before diving into the CP. This process of multidirectional interneuronmigration is believed to contribute to their even dispersion throughout the cortex. The erratic migration of astrocyte progenitors might have a similar role of dispersing astrocytes evenly in the cortex.
Outside-Inside pattern of astrocyte formation
We observed that astrocyte progenitors derived from the E15 VZ were localized more superficially than those deriving from the E17 VZ. Moreover, fibrous astrocytes in the white matterwere generated postnatally, indicating that astrocytes tend to be aligned in an outside-in manner during cortical development, although this trend was not as clear as the birthdate-dependent positioning of cortical neurons.
Astrocyte progenitors may promote angiogenesis and blood branch formation, which is strikingly similar with macrophages/microglia in the hind brain and retina. Another similarity among glia cells.
