title: Independent evolution of striated muscles in cnidarians and bilaterians.
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.
authors: Department for Molecular Evolution and Development, Centre for Organismal Systems Biology, University of Vienna, A-1090 Vienna, Austria.
authors: Patrick R H
authors: PR
authors: Steinmetz
authors: Johanna E M
authors: JE
authors: Kraus
authors: Claire
authors: C
authors: Larroux
authors: Jörg U
authors: JU
authors: Hammel
authors: Annette
authors: A
authors: Amon-Hassenzahl
authors: Evelyn
authors: E
authors: Houliston
authors: Gert
authors: G
authors: Wörheide
authors: Michael
authors: M
authors: Nickel
authors: Bernard M
authors: BM
authors: Degnan
authors: Ulrich
authors: U
authors: Technau
mesh_terms: D000818:Animals; D005075:Biological Evolution; D003063:Cnidaria / Q000033:anatomy & histology* / Q000235:genetics / Q000378:metabolism; D020440:Gene Duplication; D005786:Gene Expression Regulation; D054792:Muscle, Striated / Q000378:metabolism / Q000502:physiology*; D018995:Myosin Heavy Chains / Q000235:genetics / Q000378:metabolism; D010802:Phylogeny
chemical_list: D018995:Myosin Heavy Chains