Absence of heartbeat in the Xenopus tropicalis mutation muzak is caused by a nonsense mutation in cardiac myosin myh6.
Mechanisms coupling heart function and cardiac morphogenesis can be accessed in lower vertebrate embryos that can survive to swimming tadpole stages on diffused oxygen. Forward genetic screens in Xenopus tropicalis have identified more than 80 mutations affecting diverse developmental processes, including cardiac morphogenesis and function. In the first positional cloning of a mutation in X. tropicalis, we show that non-contractile hearts in muzak (muz) embryos are caused by a premature stop codon in the cardiac myosin heavy chain gene myh6. The mutation deletes the coiled-coil domain responsible for polymerization into thick filaments, severely disrupting the cardiomyocyte cytoskeleton. Despite the lack of contractile activity and absence of a major structural protein, early stages of cardiac morphogenesis including looping and chamber formation are grossly normal. Muz hearts subsequently develop dilated chambers with compressed endocardium and fail to form identifiable cardiac valves and trabeculae.
Abu-Daya
Anita
A
MRC National Institute for Medical Research, The Ridgeway, Mill Hill, London, NW7 1AA, UK.
Sater
Amy K
AK
Wells
Dan E
DE
Mohun
Timothy J
TJ
Zimmerman
Lyle B
LB
D000818:Animals; D024722:Cardiac Myosins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D018389:Codon, Nonsense; D004625:Embryo, Nonmammalian / Q000196:embryology / Q000378:metabolism; D005260:Female; D018507:Gene Expression Regulation, Developmental; D006321:Heart / Q000196:embryology / Q000502:physiology; D015151:Immunoblotting; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D008297:Male; D009200:Myocardial Contraction / Q000235:genetics* / Q000502:physiology; D009206:Myocardium / Q000378:metabolism; D018995:Myosin Heavy Chains / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014981:Xenopus / Q000196:embryology / Q000235:genetics* / Q000254:growth & development; D029867:Xenopus Proteins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology
D018389:Codon, Nonsense; D029867:Xenopus Proteins; D024722:Cardiac Myosins; D018995:Myosin Heavy Chains