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J Cell Sci 2015 Jan 15;1282:239-50. doi: 10.1242/jcs.152702.
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Leiomodin 3 and tropomodulin 4 have overlapping functions during skeletal myofibrillogenesis.

Nworu CU , Kraft R , Schnurr DC , Gregorio CC , Krieg PA .

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.

PubMed ID: 25431137
PMC ID: PMC4294772
Article link: J Cell Sci
Grant support: [+]

Species referenced: Xenopus laevis
Genes referenced: acta4 actc1 actl6a actn1 actn2 lmod1 lmod2 lmod3 myc tmod1 tmod2 tmod3 tmod4 ttn
Antibodies: Actn2 Ab3 Fluro-phalloidin Ab Lmod3 Ab1
Morpholinos: lmod3 MO1 lmod3 MO2 tmod4 MO1

Article Images: [+] show captions
References [+] :
Almenar-Queralt, Tropomodulin assembles early in myofibrillogenesis in chick skeletal muscle: evidence that thin filaments rearrange to form striated myofibrils. 1999, Pubmed