Sequences in the myosin A rod interact with UNC-89/obscurin and the zinc-finger protein UNC-98 during thick filament assembly and M-line formation in C. elegans striated muscle

Cytoskeleton (Hoboken). 2024 Dec;81(12):775-788. doi: 10.1002/cm.21846. Epub 2024 Feb 24.

Abstract

The M-line of striated muscle is a complex structure that anchors myosin-containing thick filaments and also participates in signaling and proteostasis. While the physical associations among many M-line components have been defined, the mechanism of thick filament attachment is not completely understood. In Caenorhabditis elegans, myosin A is essential for viability and forms the site of M-line attachment at the center of the filament, whereas myosin B forms the filament arms. Using a mutant myosin A that forms ectopic filaments, we examined interactions between myosin A and M-line proteins in intact muscle cells. Ectopic myosin A recruits the giant kinase UNC-89/obscurin, a presumed scaffolding protein, in an interaction that requires the zinc-finger protein UNC-98, but not UNC-82/NUAK, UNC-97/PINCH, or UNC-96. In myosin A mutants, UNC-89/obscurin patterning is highly defective in embryos and adults. A chimeric myosin containing 169 residues of the myosin A C-terminal rod, coincident with the UNC-98/ZnF binding site, is sufficient for colocalization of UNC-89/obscurin and UNC-98/ZnF in M-line structures whereas a myosin chimera lacking these residues colocalizes with UNC-89/obscurin in M-lines that lack UNC-98. Thus, at least two myosin A rod regions contribute independently to M-line organization. We hypothesize that these M-line-organizing functions correspond to the essential "filament initiation function" performed by this isoform.

Keywords: M‐line; muscle development; myosin assembly; striated muscle; thick filament.

MeSH terms

  • Animals
  • Caenorhabditis elegans Proteins* / genetics
  • Caenorhabditis elegans Proteins* / metabolism
  • Caenorhabditis elegans* / metabolism
  • Muscle Proteins
  • Muscle, Striated* / metabolism
  • Nonmuscle Myosin Type IIA / metabolism
  • Zinc Fingers

Substances

  • Caenorhabditis elegans Proteins
  • Unc-89 protein, C elegans
  • Nonmuscle Myosin Type IIA
  • Muscle Proteins