Generation of neurons by transient expression of neural bHLH proteins in mammalian cells

Basic helix-loop-helix (bHLH) transcription factors are known to function d uring mammalian neurogenesis, Here we show that transient transfection of v ectors expressing neuroD2, MASH1, ngn1 or related neural bHLH proteins, wit h their putative dimerization partner E12, can convert mouse P19 embryonal carcinoma cells into differentiated neurons. Transfected cells express nume rous neuron-specific proteins, adopt a neuronal morphology and are electric ally excitable. Thus, the expression of neural bHLH proteins is sufficient to confer a neuronal fate on uncommitted mammalian cells. Neuronal differen tiation of transfected cells is preceded by elevated expression of the cycl in-dependent kinase inhibitor p27(Kip1) and cell cycle withdrawal, This dem onstrates that the bHLH proteins can link neuronal differentiation to withd rawal from the cell cycle, possibly by activating the expression of p27(Kip 1), The ability to generate mammalian neurons by transient expression of ne ural bHLH proteins should create new opportunities for studying neurogenesi s and devising neural repair strategies.