Neural bHLH genes control the neuronal versus glial fate decision in cortical progenitors

We have addressed the role of the proneural bHLH genes Neurogenin2 (Ngn2) a nd Mash1 in the selection of neuronal and glial fates by neural stem cells. We show that mice mutant for both genes present severe defects in developm ent of the cerebral cortex, including a reduction of neurogenesis and a pre mature and excessive generation of astrocytic precursors. An analysis of wi ld-type and mutant cortical progenitors in culture showed that a large frac tion of Ngn2; Mash1 double-mutant progenitors failed to adopt a neuronal fa te, instead remaining pluripotent or entering an astrocytic differentiation pathway. Together, these results demonstrate that proneural genes are invo lved in lineage restriction of cortical progenitors, promoting the acquisit ion of the neuronal fate and inhibiting the astrocytic fate.