This definition appears rarely
Just as with neuronal cell specification, canonical signaling factors like Sonic hedgehog (SHH), Fibroblast growth factor (FGFs), WNTs and bone morphogenetic proteins (BMPs), provide positional information to developing macroglial cells through morphogen gradients along the dorsal–ventral, anterior–posterior and medial–lateral axes. The resultant patterning along the neuraxis leads to segmentation of the neuroepithelium into progenitor domains (p0, p1 p2, p3 and pMN) for distinct neuron types in the developing spinal cord. On the basis of several studies it is now believed that that this model also applies to macroglial cell specification. Studies carried out by Hochstim and colleagues have demonstrated that three distinct populations of astrocytes arise from the p1, p2 and p3 domains.  These subtypes of astrocytes.