Astroglial differentiation of cortical precursor cells triggered by activation of the cAMP-dependent signaling pathway

In the developing brain, differentiation of neural precursors into neurons or glial cells occurs in response to neurotrophic factors acting on the cel l surface. Intracellular signaling mechanisms that relay information to ini tiate differentiative responses of neural precursor cells are poorly unders tood. To investigate whether stimulation of the cAMP-dependent signaling pa thway participates in differentiative responses of cells in the developing CNS, we performed experiments using both conditionally immortalized neural precursor cells (RC2.E10 cells) and primary cultures of cells from developi ng rat cortex. Initially, we determined that RC2.E10 cells retain phenotypi c features of neural precursors after inactivation of the immortalizing onc ogene, a temperature-sensitive mutant of the simian virus 40 large-T antige n (SV40T). We found that, once SV40T is inactivated, RC2.E10 cells cease to divide and die. However, RC2.E10 cells can proliferate in the presence of basic fibroblast growth factor. In addition, they express nestin, a marker of neural precursor cells. Both RC2.E10 cells and primary cortical precurso r cells undergo astroglial differentiation in response to cAMP stimulation by treatment with 8-bromo-cAMP. In both cases, cAMP-induced astrocyte diffe rentiation is characterized by morphological changes, stimulation of glial fibrillary acidic protein expression, downregulation of nestin expression, and decreased proliferation. No increases in the expression of neuronal or oligodendrocytic markers were observed. Our results support the notion that the developing CNS contains neural precursor cells with the capacity of un dergoing astrocyte differentiation in response to increased intracellular c AMP concentrations.