Krox-20 conducts the Schwann song

When Schwann cells begin to myelinate large-diameter axons, they stop dividing, become resistant to apoptosis, and start producing myelin proteins. How are all of these changes coordinated? On page 385, Parkinson et al. identify several new signaling interactions in Schwann cells, and show that the transcription factor Krox-20 is a master regulator of myelination.

The authors found that Krox-20 expression makes Schwann cells resistant to the mitogen NRG-1 and the apoptosis-inducing action of TGF-β. Rather than specifically targeting these signaling molecules, Krox-20 appears to act through a general mechanism, suppressing the activity of the JNK/c-Jun pathway. The data show that JNK/c-Jun signaling is required for both proliferative and apoptotic responses in Schwann cells. Krox-20 expression increases the expression of the scaffold protein JIP-1, a known inhibitor of JNK activity, and also decreases the level of c-Jun protein...