Endothelins control the timing of Schwann cell generation in vitro and in vivo

Schwann cell precursors, derivatives of the neural crest, generate Schwann cells in a process that is tightly timed, well characterized, and directly controlled by axonal signals, in particular beta-neuregulins. Here we provide evidence that endothelins (ETs) are also important for survival and lineage progression in this system. We show that ETs promote rat Schwann cell precursor survival in vitro without stimulation of DNA synthesis. Using ET receptor agonists and antagonists, we demonstrate that this action of ET is mediated by the ET(B) receptor. RT-PCR reveals the presence of ET and ET receptor mRNA in the developing rat PNS. We showed previously that in vitro beta-neuregulins promote the generation of Schwann cells from precursors on schedule and that this process can be accelerated by fibroblast growth factor 2. Here we show that although ETs promote long-term precursor survival the transition of precursors to Schwann cells is delayed. Moreover, ETs block the maturation effects of beta-neuregulins. In spotting lethal rats, in which functional ET(B) receptors are absent, we find accelerated expression of the Schwann cell marker S100 in developing nerves. These observations indicate that complex growth factor interactions control the timing of Schwann cell development in embryonic nerves and that ETs act as negative regulators of Schwann cell generation.