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Proc Natl Acad Sci U S A August 18, 2015; 112 (33): 10509-14.
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Astrocytes phagocytose focal dystrophies from shortening myelin segments in the optic nerve of Xenopus laevis at metamorphosis.

Mills EA , Davis CH , Bushong EA , Boassa D , Kim KY , Ellisman MH , Marsh-Armstrong N .

Oligodendrocytes can adapt to increases in axon diameter through the addition of membrane wraps to myelin segments. Here, we report that myelin segments can also decrease their length in response to optic nerve (ON) shortening during Xenopus laevis metamorphic remodeling. EM-based analyses revealed that myelin segment shortening is accomplished by focal myelin-axon detachments and protrusions from otherwise intact myelin segments. Astrocyte processes remove these focal myelin dystrophies using known phagocytic machinery, including the opsonin milk fat globule-EGF factor 8 (Mfge8) and the downstream effector ras-related C3 botulinum toxin substrate 1 (Rac1). By the end of metamorphic nerve shortening, one-quarter of all myelin in the ON is enwrapped or internalized by astrocytes. As opposed to the removal of degenerating myelin by macrophages, which is usually associated with axonal pathologies, astrocytes selectively remove large amounts of myelin without damaging axons during this developmental remodeling event.

PubMed ID: 26240339
PMC ID: PMC4547286
Article link: Proc Natl Acad Sci U S A
Grant support: [+]

Species referenced: Xenopus laevis
Genes referenced: abca1 casp3.2 cd63 crk dock1 egf elmo1 elmo2 fabp7 gap43 gulp1 isl2 itgb3 itgb5 lrp1 mbp megf10 megf11 mfge8 nfasc plp1 rac1 tuba4b
Antibodies: Casp3 Ab1 Fabp7 Ab1 Lama1 Ab3 Mbp Ab2 Neuronal Ab4 Nfasc Ab1 Tuba4b Ab16

Article Images: [+] show captions
References [+] :
Amaya, A method for generating transgenic frog embryos. 1999, Pubmed, Xenbase