title: Leiomodin 3 and tropomodulin 4 have overlapping functions during skeletal myofibrillogenesis.
abstract: Precise regulation of thin filament length is essential for optimal force generation during muscle contraction. The thin filament capping protein tropomodulin (Tmod) contributes to thin filament length uniformity by regulating elongation and depolymerization at thin filament ends. The leiomodins (Lmod1-3) are structurally related to Tmod1-4 and also localize to actin filament pointed ends, but in vitro biochemical studies indicate that Lmods act instead as robust nucleators. Here, we examined the roles of Tmod4 and Lmod3 during Xenopus skeletal myofibrillogenesis. Loss of Tmod4 or Lmod3 resulted in severe disruption of sarcomere assembly and impaired embryonic movement. Remarkably, when Tmod4-deficient embryos were supplemented with additional Lmod3, and Lmod3-deficient embryos were supplemented with additional Tmod4, sarcomere assembly was rescued and embryonic locomotion improved. These results demonstrate for the first time that appropriate levels of both Tmod4 and Lmod3 are required for embryonic myofibrillogenesis and, unexpectedly, both proteins can function redundantly during in vivo skeletal muscle thin filament assembly. Furthermore, these studies demonstrate the value of Xenopus for the analysis of contractile protein function during de novo myofibril assembly.
authors.affiliation: Department of Cellular and Molecular Medicine, Sarver Molecular Cardiovascular Research Program, University of Arizona, 1656 E. Mabel St, Tucson, AZ 85724, USA.
authors.forename: Chinedu U
authors.initials: CU
authors.lastname: Nworu
authors.affiliation: Department of Cellular and Molecular Medicine, Sarver Molecular Cardiovascular Research Program, University of Arizona, 1656 E. Mabel St, Tucson, AZ 85724, USA.
authors.forename: Robert
authors.initials: R
authors.lastname: Kraft
authors.affiliation: Department of Cellular and Molecular Medicine, Sarver Molecular Cardiovascular Research Program, University of Arizona, 1656 E. Mabel St, Tucson, AZ 85724, USA.
authors.forename: Daniel C
authors.initials: DC
authors.lastname: Schnurr
authors.affiliation: Department of Cellular and Molecular Medicine, Sarver Molecular Cardiovascular Research Program, University of Arizona, 1656 E. Mabel St, Tucson, AZ 85724, USA gregorio@email.arizona.edu.
authors.forename: Carol C
authors.initials: CC
authors.lastname: Gregorio
authors.affiliation: Department of Cellular and Molecular Medicine, Sarver Molecular Cardiovascular Research Program, University of Arizona, 1656 E. Mabel St, Tucson, AZ 85724, USA.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Krieg
mesh_terms: D008841:Actin Cytoskeleton / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D000818:Animals; D004625:Embryo, Nonmammalian; D018507:Gene Expression Regulation, Developmental; D008840:Microfilament Proteins; D009119:Muscle Contraction / Q000235:genetics; D024510:Muscle Development / Q000235:genetics*; D009124:Muscle Proteins / Q000096:biosynthesis* / Q000378:metabolism; D018482:Muscle, Skeletal / Q000196:embryology / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism / Q000648:ultrastructure; D012518:Sarcomeres / Q000235:genetics / Q000648:ultrastructure; D051348:Tropomodulin / Q000096:biosynthesis* / Q000235:genetics; D014982:Xenopus laevis / Q000196:embryology / Q000235:genetics
chemical_list: C000595329:LMOD3 protein, human; D008840:Microfilament Proteins; D009124:Muscle Proteins; D051348:Tropomodulin
keywords: Actin thin filament; Leiomodin; Sarcomere; Skeletal muscle; Tropomodulin