title: Differentiation of tropomyosin-containing myofibrils in cleavage-arrested ascidian zygotes expressing acetylcholinesterase.
abstract: Two muscle differentiation programs, acetylcholinesterase and tropomyosin-containing filaments and fibrils, occur together in the same cleavage-arrested zygotes (1-celled) of the ascidian Ciona intestinalis. Coexpression in such undivided but developing 'embryos' is consistent with the idea that separate elements of muscle differentiation are related at some regulatory level, perhaps through a single multi-gene regulatory factor. Fertilized Ciona eggs were exposed to cytochalasin B for 20 h and then briefly reacted histochemically for acetylcholinesterase activity. Strongly reacting specimens were selected and processed for transmission electron microscopy to reveal regions of muscle ultrastructure. Every acetylcholinesterase-reactive zygote tested contained muscle contractile elements; no example lacking acetylcholinesterase was found with myofilaments and myofibrils. As demonstrated by immunogold labelling, a polyclonal antibody to tropomyosin from Ciona adult body wall reacted differentially with the presumed ultrastructural muscle elements in cleavage-arrested zygotes. Site-specific reactions were also observed in larval tail muscle and the siphon muscles of postmetamorphic zooids.
authors.affiliation: Laboratory of Developmental Genetics, Marine Biological Laboratory, Woods Hole, MA 02543.
authors.forename: R J
authors.initials: RJ
authors.lastname: Crowther
authors.forename: T H
authors.initials: TH
authors.lastname: Meedel
authors.forename: J R
authors.initials: JR
authors.lastname: Whittaker
mesh_terms: D000110:Acetylcholinesterase / Q000502:physiology*; D000818:Animals; D002455:Cell Division; D002938:Ciona intestinalis / Q000196:embryology*; D003571:Cytochalasin B / Q000494:pharmacology; D008854:Microscopy, Electron; D009132:Muscles / Q000187:drug effects / Q000196:embryology* / Q000648:ultrastructure; D014335:Tropomyosin / Q000502:physiology*; D015053:Zygote / Q000166:cytology / Q000187:drug effects
chemical_list: D014335:Tropomyosin; D003571:Cytochalasin B; D000110:Acetylcholinesterase