RB and RB2/P130 genes cooperate with extrinsic signals to promote differentiation of rat neural stem cells.

Mechanisms governing commitment and differentiation of the cells of the nervous system begin to be elucidated: how extrinsic and intrinsic components are related remains poorly understood. To investigate this issue, we overexpressed genes of the retinoblastoma (Rb) family RB and RB2/p130, which play an important role during nerve cell maturation, in rat neural stem cells (NSCs). Immunostaining of neurons, astrocytes and oligodendrocytes in cultures overexpressing pRb or pRb2/p130 revealed that these genes affect lineage specification of differentiating NSCs. We observed modifications in percentage of differentiated cells indicating a shift towards the phenotype induced by culture conditions. Results were confirmed by detection of the expression levels of differentiation markers by RT-PCR. Analysis of BrdU incorporation and detection of an early marker of apoptosis suggest that the effect of pRb and pRb2/p130 overexpression is not dependent on the inhibition of cell proliferation, nor does it rely on the regulation of cell survival. Our findings suggest that Rb family genes are involved in fate determination of the cells of the nervous system. However, their role seems subsidiary to that of the extrinsic signals that promote lineage specification and appear to be mediated by a direct effect on the acquisition of a specific phenotype.