Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, TX 75390.
Hamon Center for Regenerative Science and Medicine, University of Texas Southwestern Medical Center, Dallas, TX 75390.
Proc Natl Acad Sci U S A. 2017 Nov 7;114(45):11950-11955. doi: 10.1073/pnas.1715229114. Epub 2017 Oct 23.
Skeletal muscle formation requires fusion of mononucleated myoblasts to form multinucleated myofibers. The muscle-specific membrane proteins myomaker and myomixer cooperate to drive mammalian myoblast fusion. Whereas myomaker is highly conserved across diverse vertebrate species, myomixer is a micropeptide that shows relatively weak cross-species conservation. To explore the functional conservation of myomixer, we investigated the expression and function of the zebrafish myomixer ortholog. Here we show that myomixer expression during zebrafish embryogenesis coincides with myoblast fusion, and genetic deletion of myomixer using CRISPR/Cas9 mutagenesis abolishes myoblast fusion in vivo. We also identify myomixer orthologs in other species of fish and reptiles, which can cooperate with myomaker and substitute for the fusogenic activity of mammalian myomixer. Sequence comparison of these diverse myomixer orthologs reveals key amino acid residues and a minimal fusogenic peptide motif that is necessary for promoting cell-cell fusion with myomaker. Our findings highlight the evolutionary conservation of the myomaker-myomixer partnership and provide insights into the molecular basis of myoblast fusion.
骨骼肌的形成需要单核成肌细胞融合形成多核肌纤维。肌肉特异性膜蛋白肌联蛋白和肌联蛋白混合器合作驱动哺乳动物成肌细胞融合。虽然肌联蛋白在不同的脊椎动物物种中高度保守，但肌联蛋白混合器是一种微肽，其跨物种保守性相对较弱。为了探索肌联蛋白混合器的功能保守性，我们研究了斑马鱼肌联蛋白同源物的表达和功能。在这里，我们表明斑马鱼胚胎发生过程中的肌联蛋白混合器表达与成肌细胞融合一致，并且使用 CRISPR/Cas9 诱变的遗传缺失会在体内消除成肌细胞融合。我们还在其他鱼类和爬行动物中鉴定出肌联蛋白混合器同源物，它们可以与肌联蛋白合作并替代哺乳动物肌联蛋白的融合活性。这些不同的肌联蛋白同源物的序列比较揭示了促进与肌联蛋白的细胞-细胞融合所必需的关键氨基酸残基和最小融合肽基序。我们的发现强调了肌联蛋白-肌联蛋白混合器伙伴关系的进化保守性，并为成肌细胞融合的分子基础提供了新的见解。
