Developing Schwann cells survive thanks to neuregulin, a survival and proliferation factor that is produced by neurons and detected by the ErbB2 and ErbB3 receptor tyrosine kinases. Later on, the Schwann cells rely on autocrine factors for survival, even as they start to wrap neurons (the source of the original survival signal) in myelin.
But neuregulin production continues, and on page 1035 Garratt et al. show that ErbB2 is necessary for continued myelination. Schwann cell precursors develop normally in mice with a conditional knockout of ErbB2, but myelin sheaths around neurons are thinner and wraps are less numerous than normal. This defect, and some motoneuron loss, lead to problems with gait, wasting, and even death. This is a clear example of the function of a growth factor changing as the cell achieves different stages of maturation, although the problem...
