Noncanonical roles for Tropomyosin during myogenesis

Abstract

For skeletal muscle to produce movement, individual myofibers must form stable contacts with tendon cells and then assemble sarcomeres. The myofiber precursor is the nascent myotube, and during myogenesis the myotube completes guided elongation to reach its target tendons. Unlike the well-studied events of myogenesis, such as myoblast specification and myoblast fusion, the molecules that regulate myotube elongation are largely unknown. In Drosophila, hoi polloi (hoip) encodes a highly conserved RNAbinding protein and hoip mutant embryos are largely paralytic due to defects in myotube elongation and sarcomeric protein expression. We used the hoip mutant background as a platform to identify novel regulators of myogenesis, and uncovered surprising developmental functions for the sarcomeric protein Tropomyosin 2 (Tm2). We have identified Hoip-responsive sequences in the coding region of the Tm2 mRNA that are essential for Tm2 protein expression in developing myotubes. Tm2 overexpression rescued the hoip myogenic phenotype by promoting F-actin assembly at the myotube leading edge, by restoring the expression of additional sarcomeric RNAs, and by promoting myoblast fusion. Embryos that lack Tm2 also showed reduced sarcomeric protein expression, and embryos that expressed a gain-of-function Tm2 allele showed both fusion and elongation defects. Tropomyosin therefore dictates fundamental steps of myogenesis prior to regulating contraction in the sarcomere.

FGF signaling directs myotube guidance by regulating Rac activity

“…We then performed in situ hybridization as previously described (Williams et al, 2015), except Dig-labeled probes were detected with HRP-conjugated α-Dig (Roche, 11207733910, 1:2000) in conjunction with the TSA system (Molecular Probes). Probe templates were generated by cloning PCR products from genomic DNA of P{UAS-htl}, P{UAS-pyr} and P{UAS-ths} flies into pBS.KS.…”

“…The intracellular pathways that reorganize the cytoskeleton during myotube guidance have been characterized in some detail. For example, the RNA-binding protein Hoi-polloi regulates the actin cytoskeleton by modulating Tropomyosin expression (Williams et al, 2015), and the Rho GTPase activating protein Tumbleweed, in combination with the kinesin Pavarotti, reorganizes the microtubule cytoskeleton (Guerin and Kramer, 2009). Although dynamic changes to both the actin and microtubule cytoskeletons are essential for myotube guidance, the extrinsic inputs that regulate cytoskeletal dynamics to guide myotube leading edges toward the correct muscle attachment sites remain incompletely understood.…”

Comparative Proteomic Profiling between Each of Two Consecutive Developmental Stages of the Solanum Fruit Fly, Bactrocera latifrons (Hendel)

“…SCO-spondin was upregulated by 4.37-fold at 1-day-old larvae. Both H. armigera A3a and A3b genes are expressed during pupal development and in the brain of newly enclosed adults based on polymerase chain reaction and northern blot analysis [ 11 ]. Muscle-specific Actin-2 was upregulated by 3.82-fold in the larvae in this study, which added a piece of information that is expressed in the larvae stage.…”

A genetic screen for regulators of muscle morphogenesis inDrosophila

“… Abstract The mechanisms that determine the final topology of skeletal muscles remain largely unknown. We have been developing Drosophila body wall musculature as a model to identify and characterize the pathways that control muscle size, shape, and orientation during embryogenesis (Johnson et al, 2013; Williams et al, 2015; Yang et al, 2020a; Yang et al, 2020b). Our working model argues muscle morphogenesis is regulated by (1) extracellular guidance cues that direct muscle cells toward muscle attachment sites, and (2) contact dependent interactions between muscles and tendons.…”