PT  - JOURNAL ARTICLE
AU  - Minou Djannatian
AU  - Ulrich Weikert
AU  - Shima Safaiyan
AU  - Christoph Wrede
AU  - Cassandra Deichsel
AU  - Georg Kislinger
AU  - Torben Ruhwedel
AU  - Douglas S. Campbell
AU  - Tjakko van Ham
AU  - Bettina Schmid
AU  - Jan Hegermann
AU  - Wiebke Möbius
AU  - Martina Schifferer
AU  - Mikael Simons
TI  - Myelin biogenesis is associated with pathological ultrastructure that is resolved by microglia during development
AID  - 10.1101/2021.02.02.429485
DP  - 2021 Jan 01
TA  - bioRxiv
PG  - 2021.02.02.429485
4099  - http://biorxiv.org/content/early/2021/02/04/2021.02.02.429485.short
4100  - http://biorxiv.org/content/early/2021/02/04/2021.02.02.429485.full
AB  - To enable rapid propagation of action potentials, axons are ensheathed by myelin, a multilayered insulating membrane formed by oligodendrocytes. Most of the myelin is generated early in development, in a process thought to be error-free, resulting in the generation of long-lasting stable membrane structures. Here, we explored structural and dynamic changes in CNS myelin during development by combining ultrastructural analysis of mouse optic nerves by serial block face scanning electron microscopy and confocal time-lapse imaging in the zebrafish spinal cord. We found that myelin undergoes extensive ultrastructural changes during early postnatal development. Myelin degeneration profiles were engulfed and phagocytosed by microglia in a phosphatidylserine-dependent manner. In contrast, retractions of entire myelin sheaths occurred independently of microglia and involved uptake of myelin by the oligodendrocyte itself. Our findings show that the generation of myelin early in development is an inaccurate process associated with aberrant ultrastructural features that requires substantial refinement.