Development/Plasticity/Repair Functional Properties of Neurons Derived from In Vitro

With the exception of astroglia-like cells in the neurogenic niches of the telencephalic subependymal or hippocampal subgranular zone, astroglia in all other regionsof the adultmousebraindonotnormally generateneurons. Previous studies have shown, however, that early postnatal cortical astroglia in culture canbe reprogrammed toadopt aneuronal fate after forcedexpressionofPax6, a transcription factor (TF) required for proper neuronal specification during embryonic corticogenesis. Here we show that also the proneural genes neurogenin-2 and Mash1 (mammalian achaete schute homolog 1) possess the ability to reprogram astroglial cells from early postnatal cerebral cortex. By means of time-lapse imaging of green fluorescent astroglia, we provide direct evidence that it is indeed cells with astroglial characteristics that give rise to neurons. Using patch-clamp recordings in culture, we show that astroglia-derived neurons acquire active conductances andare capable of firing actionpotentials, thusdisplayinghallmarks of trueneurons.However, independent of theTFused for reprogramming, astroglia-derivedneuronsappear tomaturemore slowly comparedwith embryonic-bornneuronsand fail to generate a functional presynaptic output within the culturing period. However, when coculturedwith embryonic cortical neurons, astroglia-derived neurons receive synaptic input, demonstrating that they are competent of establishing a functional postsynaptic compartment. Our data demonstrate that single TFs are capable of inducing a remarkable functional reprogramming of astroglia toward a truly neuronal identity. Key words: stem cells; neurogenesis; astrocyte (astroglia); transcription factor; gene transfer; regeneratio