The Ink4a/Arf locus is a barrier to direct neuronal transdifferentiation

Non-neurogenic cell types, such as cortical astroglia and fibroblasts, can be directly converted into neurons by the overexpression of defined transcription factors. Normally, the cellular phenotype of such differentiated cells is remarkably stable and resists direct cell transdifferentiation. Here we show that theInk4a/Arf(also known asCdkn2a) locus is a developmental barrier to direct neuronal transdifferentiation induced by transcription factor overexpression. With serial passagein vitro, wild-type postnatal cortical astroglia become progressively resistant toDlx2-induced neuronal transdifferentiation. In contrast, the neurogenic competence ofInk4a/Arf-deficient astroglia is both greatly increased and does not diminish through serial cell culture passage. Electrophysiological analysis further demonstrates the neuronal identity of cells induced fromInk4a/Arf-null astroglia, and short hairpin RNA-mediated acute knockdown of p16Ink4a and p19Arf p16Ink4aand p19Arfindicates that these gene products function postnatally as a barrier to cellular transdifferentiation. Finally, we found that mouse fibroblasts deficient forInk4a/Arfalso exhibit greatly enhanced transcription factor-induced neuronal induction. These data indicate thatInk4a/Arfis a potent barrier to direct neuronal transdifferentiation and further suggest that this locus functions normally in the progressive developmental restriction of postnatal astrocytes.