Arrested proliferation of radial glial cells during midgestation in rhesus monkey

Abstract

AUTORADIOGRAPHIC analysis using ³H-thymidine labelled DNA demonstrates that some radial glial cells in the fetal monkey cerebrum stop dividing during hiidgestation. After two months they re-enter the mitotic cycle and become transformed into astrocytes. In their amitotic period, radial glial cells remain stretched across the width of the rapidly expanding telencephalic wall. This is significant because elongated glial fibres may have a role in guidance of neuronal migration^1–3. The pause in proliferation of radial glial cells could ensure a faithful mapping of the proliferative ventricular surface upon the expanding and convoluted cerebral cortex of primates, including man³. Elongated radial glial cells span the distance between the ventricular and pial surface of the developing telencephalon (Fig. 1). Studies using Golgi silver impregnations^4–7, electron microscopy^1,8,9 and immunohistochemistry^10–12substantiate the glial nature of this transient cell class (for review see refs 12, 13). In the monkey occipital lobe, radial glial cells are present throughout the last two-thirds of gestation^12,14. The process of transformation of radial glial cells into astrocytes and ependymal cells begins during the first half of gestation and is completed by the second postnatal month^12,14. However, during midgestation, when neuronal migration is at a peak¹⁵, many radial glial cells remain attached to the ventricular and pial surfaces (Fig. 1); they increase in length, and curve with the expansion and convolution of the cerebral wall^3,12,14. The present study was undertaken to determine whether such glial cells undergo cell division after attaining their radial configuration.