Department for Molecular Evolution and Development, Centre for Organismal Systems Biology, University of Vienna, A-1090 Vienna, Austria.
Nature. 2012 Jul 12;487(7406):231-4. doi: 10.1038/nature11180.
Striated muscles are present in bilaterian animals (for example, vertebrates, insects and annelids) and some non-bilaterian eumetazoans (that is, cnidarians and ctenophores). The considerable ultrastructural similarity of striated muscles between these animal groups is thought to reflect a common evolutionary origin. Here we show that a muscle protein core set, including a type II myosin heavy chain (MyHC) motor protein characteristic of striated muscles in vertebrates, was already present in unicellular organisms before the origin of multicellular animals. Furthermore, 'striated muscle' and 'non-muscle' myhc orthologues are expressed differentially in two sponges, compatible with a functional diversification before the origin of true muscles and the subsequent use of striated muscle MyHC in fast-contracting smooth and striated muscle. Cnidarians and ctenophores possess striated muscle myhc orthologues but lack crucial components of bilaterian striated muscles, such as genes that code for titin and the troponin complex, suggesting the convergent evolution of striated muscles. Consistently, jellyfish orthologues of a shared set of bilaterian Z-disc proteins are not associated with striated muscles, but are instead expressed elsewhere or ubiquitously. The independent evolution of eumetazoan striated muscles through the addition of new proteins to a pre-existing, ancestral contractile apparatus may serve as a model for the evolution of complex animal cell types.
横纹肌存在于两侧对称动物（例如，脊椎动物、昆虫和环节动物）和一些非两侧对称后生动物（即刺胞动物和栉水母动物）中。这些动物群体之间横纹肌的显著超微结构相似性被认为反映了共同的进化起源。在这里，我们表明，一种肌肉蛋白核心集，包括一种 II 型肌球蛋白重链（MyHC）运动蛋白，是脊椎动物横纹肌特有的，在多细胞动物起源之前就已经存在于单细胞生物中。此外，在两种海绵中，“横纹肌”和“非肌肉”myhc 同源物表现出不同的表达模式，这与真正肌肉起源之前的功能多样化以及随后在快速收缩的平滑肌和横纹肌中使用横纹肌 MyHC 是一致的。刺胞动物和栉水母动物拥有横纹肌 myhc 同源物，但缺乏两侧对称横纹肌的关键成分，如编码肌联蛋白和肌钙蛋白复合物的基因，这表明横纹肌的趋同进化。一致的是，水母同源物共享的一套两侧对称 Z 盘蛋白不与横纹肌相关，而是在其他地方或普遍表达。通过向原有的收缩装置添加新的蛋白质，后生动物横纹肌的独立进化可能成为复杂动物细胞类型进化的模型。
