Netrins and neogenin promote myotube formation.

Jong-Sun Kang,Jessica L Feinleib,Min-Jeong Yi,Robert S Krauss,Francesca Cole,Wei Zhang

doi:10.1083/jcb.200405039

Abstract

Differentiation of skeletal myoblasts into multinucleated myotubes is a multistep process orchestrated by several families of transcription factors, including myogenic bHLH and NFAT proteins. The activities of these factors and formation of myotubes are regulated by signal transduction pathways, but few extracellular factors that might initiate such signals have been identified. One exception is a cell surface complex containing promyogenic Ig superfamily members (CDO and BOC) and cadherins. Netrins and their receptors are established regulators of axon guidance, but little is known of their function outside the nervous system. We report here that myoblasts express the secreted factor netrin-3 and its receptor, neogenin. These proteins stimulate myotube formation and enhance myogenic bHLH- and NFAT-dependent transcription. Furthermore, neogenin binds to CDO in a cis fashion, and myoblasts lacking CDO are defective in responding to recombinant netrin. It is proposed that netrin-3 and neogenin may promote myogenic differentiation by an autocrine mechanism as components of a higher order complex of several promyogenic cell surface proteins.

Highlights

During skeletal muscle development mesodermal precursor cells give rise to committed myoblasts that, after proliferation and migration to appropriate sites in the embryo, exit the cell cycle, express muscle-specific genes, and fuse into multinucleated myofibers (Pownall et al, 2002)
Western blot analyses of C2C12 myoblasts revealed a uniform level of neogenin in cells cultured in growth medium (GM) and cells transferred into differentiation medium (DM) over a period of 4 d (Fig. 1 A)
F3, a myoblast line derived by treatment of 10T1/2 fibroblasts with 5-azacytidine, expressed neogenin under both GM and DM conditions (Fig. 1 B). 10T1/2 fibroblasts and 10T1/2 cells converted to myoblasts by stable expression of MyoD expressed indistinguishable levels of neogenin (Fig. 1 C); again, this contrasts with CDO expression, which was induced by MyoD (Fig. 1 C; Kang et al, 1998)

Summary

Introduction

During skeletal muscle development mesodermal precursor cells give rise to committed myoblasts that, after proliferation and migration to appropriate sites in the embryo, exit the cell cycle, express muscle-specific genes, and fuse into multinucleated myofibers (Pownall et al, 2002). This process is coordinated by a family of myogenic bHLH transcription factors that includes Myf, MyoD, myogenin, and MRF4 (Pownall et al, 2002). Several signaling pathways have been implicated in promoting myogenic differentiation (Puri and Sartorelli, 2000; Horsley and Pavlath, 2002; McKinsey et al, 2002); because the most commonly used stimulus for in vitro differentiation is removal of serum, the extracellular factors and receptors that initiate these pathways during myogenesis are largely unknown

Methods

Results

Conclusion