Ca(2+) activity signatures of myelin sheath formation and growth in vivo

During myelination, individual oligodendrocytes initially over-produce short myelin sheaths that are either retracted or stabilised. By live imaging oligodendrocyte Ca(2+) activity in vivo, we find that high-amplitude long-duration Ca(2+) transients in sheaths prefigure retractions, mediated by calpain. Following stabilisation, myelin sheaths grow along axons, and we find that higher frequency Ca(2+) transient activity in sheaths precedes faster elongation. Our data implicate local Ca(2+) signalling in regulating distinct stages of myelination.