cells, and the testicular localization of the intermediate filament protein nestin, known to be expressed in neural stem cells, by our group was the first step to define mural cells (pericytes and vascular smooth muscle cells) of the testis microvascu- ture as the stem/progenitor cells of the adult Leydig cells. In summary, we were able to demonstrate specific proliferation of vascular progenitors and their subsequent transdifferentiation into steroidogenic Leydig cells, which - in addition - rapidly acquire neuronal and glial properties. Since both newly developed fetal and adult Leydig cell...