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1449392 
Journal Article 
Independent evolution of striated muscles in cnidarians and bilaterians 
Steinmetz, PRH; Kraus, JEM; Larroux, C; Hammel, JU; Amon-Hassenzahl, A; Houliston, E; Wörheide, G; Nickel, M; Degnan, BM; Technau, U 
2012 
Nature
ISSN: 0028-0836
EISSN: 1476-4687 
Nature Publishing Group 
487 
7406 (Jul 12 
231-236 
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 origin1,2. Here we show that a muscle protein core set, including a type IImyosin 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 'nonmuscle'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 fastcontracting 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 bilaterianZ-disc proteins arenot 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. [PUBLICATION ABSTRACT] 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. 
Phylogenetics; Signal transduction; Animals; Myosin Heavy Chains; Gene Duplication; Cell division; Light; Vertebrates; Cnidaria; Proteins; Genomes; Phosphorylation; Gene Expression Regulation; Phylogeny; Kinases; Muscle, Striated; Comparative analysis; Gene expression; 2012) 
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