work demonstrated already that absolute levels and the dynamic expression of reprogramming factors are of critical importance. With Ngn2 and Dlx2 in the new retroviral construct, the authors could demonstrate that forced expression of those two transcription factors individually in postnatal cortical astroglial cells give rise to synaptically competent glutamatergic and GABAergic neurons respectively. The same group also later proved that cultured Ng2+ and GFAP+ glia cells from postnatal rat cortex can be converted to glutamatergic neurons by mere Ngn2 transduction [15]. More recently, de-novo in vivo generation of cells expressing neuronal markers were demonstrated by a number of groups, however due to the limitations of transgenic reporter systems the exact cell of origin remains elusive in these cases and functionality of newly induced cells has not been shown [16–20].
