Extracellular Signal-Regulated Kinases 1 and 2 Regulate Neuromuscular Junction and Myofiber Maintenance In Vivo
Extracellular signal-regulated kinases 1 and 2 (ERK1/2) regulate multiple cellular processes, but their role in skeletal muscle fibers in vivo has remained untested genetically. Seaberg et al. (p. 1238–1253) abrogated ERK1/2 selectively in mouse skeletal myofibers. Mice displayed stunted postnatal growth, muscle weakness, and shorter life span. Muscles showed a mix of fiber loss and mild atrophy, with minimal changes in fiber type composition, fragmented neuromuscular junctions, and reduced acetylcholine receptor expression. Evidence of partial denervation was also found. Thus ERK1/2 are required in the adult for maintaining muscle mass, synaptic acetylcholine receptor expression, and overall structural integrity at neuromuscular junctions.
The Actvity of PRC1 Is Regulated by USP7 with the Help of SCML2
The ubiquitination of histone H2A by Polycomb repressive complex 1 (PRC1) is key to its gene-repressive activity. Lecona et al. (p. 1157–1168) show that the ubiquitin-specific protease USP7 associates with PRC1 on target genes and that its activity is necessary to maintain the levels of ubiquitinated histone H2A. USP7 forms a complex with SCML2, a Polycomb protein that binds to PRC1 containing BMI1. In the absence of SCML2, USP7 cannot act on PRC1 and the levels of BMI1 are reduced. The regulation of PRC1 is a multilayered process involving the action of different associated proteins including the USP7-SCML2 complex.
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