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J Cell Biol. 2019 Jan 9. pii: jcb.201808176. doi: 10.1083/jcb.201808176. [Epub ahead of print]

The Drosophila Ninein homologue Bsg25D cooperates with Ensconsin in myonuclear positioning.

Author information

1
Program in Developmental Biology, Sloan Kettering Institute, Memorial Sloan Kettering Cancer Center, New York, NY.
2
Graduate Program in Areas of Basic and Applied Biology, Abel Salazar Biomedical Sciences Institute, University of Porto, Porto, Portugal.
3
Molecular Cytology Facility, Sloan Kettering Institute, Memorial Sloan Kettering Cancer Center, New York, NY.
4
Cell and Developmental Biology, Weill Cornell Graduate School of Medical Sciences, Cornell University, New York, NY.
5
Program in Developmental Biology, Sloan Kettering Institute, Memorial Sloan Kettering Cancer Center, New York, NY m-baylies@ski.mskcc.org.

Abstract

Skeletal muscle consists of multinucleated cells in which the myonuclei are evenly spaced throughout the cell. In Drosophila, this pattern is established in embryonic myotubes, where myonuclei move via microtubules (MTs) and the MT-associated protein Ensconsin (Ens)/MAP7, to achieve their distribution. Ens regulates multiple aspects of MT biology, but little is known about how Ens itself is regulated. We find that Ens physically interacts and colocalizes with Bsg25D, the Drosophila homologue of the centrosomal protein Ninein. Bsg25D loss enhances myonuclear positioning defects in embryos sensitized by partial Ens loss. Bsg25D overexpression causes severe positioning defects in immature myotubes and fully differentiated myofibers, where it forms ectopic MT organizing centers, disrupts perinuclear MT arrays, reduces muscle stiffness, and decreases larval crawling velocity. These studies define a novel relationship between Ens and Bsg25D. At endogenous levels, Bsg25D positively regulates Ens activity during myonuclear positioning, but excess Bsg25D disrupts Ens localization and MT organization, with disastrous consequences for myonuclear positioning and muscle function.

PMID:
30626718
DOI:
10.1083/jcb.201808176

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