Department of Biological Sciences, CW405, Biological Sciences Building, University of Alberta, Edmonton, AB, Canada T6G 2E9.
Department of Biological Sciences, CW405, Biological Sciences Building, University of Alberta, Edmonton, AB, Canada T6G 2E9.
Dev Biol. 2014 Jun 1;390(1):26-40. doi: 10.1016/j.ydbio.2014.02.022. Epub 2014 Mar 5.
Despite the prevalence of developmental myopathies resulting from muscle fiber defects, the earliest stages of myogenesis remain poorly understood. Unc45b is a molecular chaperone that mediates the folding of thick-filament myosin during sarcomere formation; however, Unc45b may also mediate specific functions of non-muscle myosins (NMMs). unc45b Mutants have specific defects in striated muscle development, which include myocyte detachment indicative of dysfunctional adhesion complex formation. Given the necessity for non-muscle myosin function in the formation of adhesion complexes and premyofibril templates, we tested the hypothesis that the unc45b mutant phenotype is not mediated solely by interaction with muscle myosin heavy chain (mMHC). We used the advantages of a transparent zebrafish embryo to determine the temporal and spatial patterns of expression for unc45b, non-muscle myosins and mMHC in developing somites. We also examined the formation of myocyte attachment complexes (costameres) in wild-type and unc45b mutant embryos. Our results demonstrate co-expression and co-regulation of Unc45b and NMM in myogenic tissue several hours before any muscle myosin heavy chain is expressed. We also note deficiencies in the localization of costamere components and NMM in unc45b mutants that is consistent with an NMM-mediated role for Unc45b during early myogenesis. This represents a novel role for Unc45b in the earliest stages of muscle development that is independent of muscle mMHC folding.
尽管肌肉纤维缺陷导致的发育性肌病普遍存在，但肌发生的最早阶段仍知之甚少。Unc45b 是一种分子伴侣，可在肌节形成过程中介导粗丝肌球蛋白的折叠；然而，Unc45b 也可能介导非肌肉肌球蛋白（NMM）的特定功能。unc45b 突变体在横纹肌发育中存在特定缺陷，包括肌细胞脱离，表明粘连复合物形成功能障碍。鉴于非肌肉肌球蛋白在粘连复合物和预制肌原纤维模板形成中的必要性，我们检验了以下假设：unc45b 突变体表型不是仅通过与肌肉肌球蛋白重链（mMHC）相互作用来介导的。我们利用透明斑马鱼胚胎的优势，确定了 unc45b、非肌肉肌球蛋白和 mMHC 在发育中的体节中的时空表达模式。我们还检查了野生型和 unc45b 突变体胚胎中肌细胞附着复合物（costameres）的形成。我们的结果表明，Unc45b 和 NMM 在肌生成组织中的共表达和共调控发生在任何肌肉肌球蛋白重链表达之前几个小时。我们还注意到，在 unc45b 突变体中，costamere 成分和 NMM 的定位存在缺陷，这与 Unc45b 在早期肌发生过程中发挥 NMM 介导的作用一致。这代表了 Unc45b 在肌肉发育的最早阶段的一个新作用，与肌肉 mMHC 折叠无关。
