title: The evolutionary origin of bilaterian smooth and striated myocytes.
abstract: The dichotomy between smooth and striated myocytes is fundamental for bilaterian musculature, but its evolutionary origin is unsolved. In particular, interrelationships of visceral smooth muscles remain unclear. Absent in fly and nematode, they have not yet been characterized molecularly outside vertebrates. Here, we characterize expression profile, ultrastructure, contractility and innervation of the musculature in the marine annelidPlatynereis dumeriliiand identify smooth muscles around the midgut, hindgut and heart that resemble their vertebrate counterparts in molecular fingerprint, contraction speed and nervous control. Our data suggest that both visceral smooth and somatic striated myocytes were present in the protostome-deuterostome ancestor and that smooth myocytes later co-opted the striated contractile module repeatedly - for example, in vertebrate heart evolution. During these smooth-to-striated myocyte conversions, the core regulatory complex of transcription factors conveying myocyte identity remained unchanged, reflecting a general principle in cell type evolution.
authors.affiliation: Developmental Biology Unit, European Molecular Biology Laboratory, Heidelberg, Germany.
authors.forename: Thibaut
authors.identifier: 0000-0002-1843-1613
authors.initials: T
authors.lastname: Brunet
authors.affiliation: Developmental Biology Unit, European Molecular Biology Laboratory, Heidelberg, Germany.
authors.forename: Antje Hl
authors.initials: AH
authors.lastname: Fischer
authors.affiliation: Developmental Biology Unit, European Molecular Biology Laboratory, Heidelberg, Germany.
authors.forename: Patrick Rh
authors.initials: PR
authors.lastname: Steinmetz
authors.affiliation: Developmental Biology Unit, European Molecular Biology Laboratory, Heidelberg, Germany.
authors.forename: Antonella
authors.initials: A
authors.lastname: Lauri
authors.affiliation: Developmental Biology Unit, European Molecular Biology Laboratory, Heidelberg, Germany.
authors.forename: Paola
authors.initials: P
authors.lastname: Bertucci
authors.affiliation: Developmental Biology Unit, European Molecular Biology Laboratory, Heidelberg, Germany.
authors.forename: Detlev
authors.identifier: 0000-0001-7833-050X
authors.initials: D
authors.lastname: Arendt
mesh_terms: D000818:Animals; D005075:Biological Evolution; D020869:Gene Expression Profiling; D032342:Muscle Cells / Q000502:physiology* / Q000648:ultrastructure*; D009119:Muscle Contraction; D009132:Muscles / Q000166:cytology* / Q000502:physiology*; D011077:Polychaeta / Q000502:physiology*
keywords: <i>p. dumerilii</i>; Platynereis; Urbilateria; cell type evolution; developmental biology; evo-devo; evolutionary biology; genomics; musculature; smooth muscle; stem cells