Click here to close
Hello! We notice that you are using Internet Explorer, which is not supported by Xenbase and may cause the site to display incorrectly.
We suggest using a current version of Chrome,
FireFox, or Safari.
???displayArticle.abstract???
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.
Fig. 2. muzak is encoded by myh6. WISH shows myh6 expression in wild type heart (A, black arrow) and jaw muscle (white arrow) is diminished in muz (B). (C, D) myh6.2 is expressed in jaw muscle (white arrow) but not heart (black arrow), and is unaffected by the mutation. (E) Schematic showing domain structure of wild type X. tropicalis myh6 and the truncated protein lacking the myosin coiled-coil tail encoded by the muz allele. (F) Western blot analysis does not detect sarcomeric MHC protein in extracts of muzheart; silver stained loading control below. (Movie S2 and G) myh6 morphant hearts do not beat and show strong depletion of sarcomeric MHC protein relative to control morpholino-injected tadpoles; silver stained loading control below.
Figure 2. muzak is encoded by myh6 WISH shows myh6 expression in wild type heart (A, black arrow) and jaw muscle (white arrow) is diminished in muz (B). (C, D) myh6.2 is expressed in jaw muscle (white arrow) but not heart (black arrow), and is unaffected by the mutation. (E)
Schematic showing domain structure of wild type X. tropicalis myh6 and the truncated protein lacking the myosin coiled-coil tail encoded by the muz allele. (F) Western blot analysis does not detect sarcomeric MHC protein in extracts of muzheart; silver stained loading control below. (Movie S2 and G) myh6 morphant hearts do not beat and show strong
depletion of sarcomeric MHC protein relative to control morpholino-injected tadpoles; silver stained loading control below.
Figure 3. MHC genes expressed in stage 40 wild type and muz
heartsRT-PCR from isolated stage 40 hearts shows lower levels of
myh6 in muz; myh7B
and myh8 are unaffected. (A) myh6.2 mRNA
is not detected in wild type or mutant tadpole hearts or wild type adult
heart, although it is amplified from whole-embryo mRNA;
myh15 is expressed in adult but not stage 40tadpoleheart(B).
Figure 4. Muz hearts lack myofibrils3D confocal projections of wild type (A) and muz (B) hearts immunostained with the pan-sarcomeric MHC A4.1025 antibody (green) and counterstained with phalloidin (red). In wild type hearts, MHC and actin colocalize to myofibrils, while muz hearts show very little A4.1025 immunostaining and no fibrillar structures.
Figure 5. Altered chamber morphology in muz heartsCoronal plastic sections of stage 40 wild type and muz
hearts (top rows) numbered from ventral side of cardiac cavity, and
indicated by white lines in 3D models (bottom rows). m= myocardium, e= inner
endocardial tube, v= ventricle, ot= outflow tract , a= atrium. No blood
cells are seen in the muz sections due to lack of
circulation, and myocardial layer appears thinner throughout the
muz heart compared to wild type. The
muz ventricle is wider than in wild type (sections 7
and 11), while outflow tract and atrium are dilated (sections 14, 23 and
41). Abnormal muz chamber morphology is highlighted in 3D
projections of outlines of myocardium (A, C, E, G, red=ventricle,
blue=outflow tract, green=atrium) and endocardium (B, D, F, H, orange),
including elongated ventricle, dilated outflow tract (black arrowhead in E)
and narrow cardiac tube at AVC level (black arrow in G).
muz endocardium is very compressed with drastically
reduced lumen (white arrows in 23, F and H)
Figure 6. Muz hearts become dilated and lack valves and
trabeculaeCoronal plastic sections of stage 42 wt and muz hearts (top
rows) numbered from ventral side of cardiac cavity, and indicated by white
lines in 3D models (middle rows). v= ventricle, ot= outflow tract , a=
atrium. Wild type hearts show a spiral valve in the outflow tract (sections
14, 23, black arrows), and thickening of endocardium preceding
atrioventricular valve formation (section 23, black asterisk). Valve
formation is not detected in muz hearts, and endocardial
lumen is drastically reduced in outflow tract and AVC regions (white
arrowheads sections 54, 58, also compare models B and F). Endocardial
cushion formation in AVC can also be seen in transverse sections of stage 42
wild type (I, white arrowhead) hearts but not in muz (J).
Trabeculation has initiated in the wild type ventricle (I, black arrowheads)
but is absent in muz (J). At this stage the ventricular
myocardium has a vacuolated appearance in both wt and mutant embryos (I, J
black arrows). Middle two rows: 3D projections of outlines of myocardium (A,
C, E, G) and endocardium (B, D, F, H) highlight abnormal
muz chamber morphology; red = ventricle, green =
atrium, blue = outflow tract, orange = endocardium. Muz
ventricles are elongated relative to wild type (E, G white arrows). A narrow
tube connects muzventricle and atrium (section 54 and G,
black arrowheads; compare to 23, C).
Armstrong,
Heart valve development: endothelial cell signaling and differentiation.
2004,
Pubmed
Auman,
Functional modulation of cardiac form through regionally confined cell shape changes.
2007,
Pubmed
Bartman,
Early myocardial function affects endocardial cushion development in zebrafish.
2004,
Pubmed
Beis,
Genetic and cellular analyses of zebrafish atrioventricular cushion and valve development.
2005,
Pubmed
Branford,
Regulation of gut and heart left-right asymmetry by context-dependent interactions between xenopus lefty and BMP4 signaling.
2000,
Pubmed
,
Xenbase
Burggren,
Interruption of cardiac output does not affect short-term growth and metabolic rate in day 3 and 4 chick embryos.
2000,
Pubmed
Carruthers,
Genetic and genomic prospects for Xenopus tropicalis research.
2006,
Pubmed
,
Xenbase
Ching,
Mutation in myosin heavy chain 6 causes atrial septal defect.
2005,
Pubmed
Dan-Goor,
Localization of epitopes and functional effects of two novel monoclonal antibodies against skeletal muscle myosin.
1990,
Pubmed
,
Xenbase
Ehler,
Myofibrillogenesis in the developing chicken heart: assembly of Z-disk, M-line and the thick filaments.
1999,
Pubmed
Eisenberg,
Molecular regulation of atrioventricular valvuloseptal morphogenesis.
1995,
Pubmed
Evans,
tinman, a Drosophila homeobox gene required for heart and visceral mesoderm specification, may be represented by a family of genes in vertebrates: XNkx-2.3, a second vertebrate homologue of tinman.
1995,
Pubmed
,
Xenbase
Force,
Preservation of duplicate genes by complementary, degenerative mutations.
1999,
Pubmed
Fu,
Vertebrate tinman homologues XNkx2-3 and XNkx2-5 are required for heart formation in a functionally redundant manner.
1998,
Pubmed
,
Xenbase
Gallego,
Anatomy and development of the sinoatrial valves in the dogfish (Scyliorhinus canicula).
1997,
Pubmed
Garriock,
Developmental expression and comparative genomic analysis of Xenopus cardiac myosin heavy chain genes.
2005,
Pubmed
,
Xenbase
Gassmann,
Aberrant neural and cardiac development in mice lacking the ErbB4 neuregulin receptor.
1995,
Pubmed
Geisterfer-Lowrance,
A molecular basis for familial hypertrophic cardiomyopathy: a beta cardiac myosin heavy chain gene missense mutation.
1990,
Pubmed
Goda,
Genetic screens for mutations affecting development of Xenopus tropicalis.
2006,
Pubmed
,
Xenbase
Grammer,
Identification of mutants in inbred Xenopus tropicalis.
2005,
Pubmed
,
Xenbase
Grego-Bessa,
Notch signaling is essential for ventricular chamber development.
2007,
Pubmed
Groenendijk,
Changes in shear stress-related gene expression after experimentally altered venous return in the chicken embryo.
2005,
Pubmed
Grow,
Tinman function is essential for vertebrate heart development: elimination of cardiac differentiation by dominant inhibitory mutants of the tinman-related genes, XNkx2-3 and XNkx2-5.
1998,
Pubmed
,
Xenbase
Hove,
Intracardiac fluid forces are an essential epigenetic factor for embryonic cardiogenesis.
2003,
Pubmed
Huang,
Embryonic atrial function is essential for mouse embryogenesis, cardiac morphogenesis and angiogenesis.
2003,
Pubmed
Hyatt,
The left-right coordinator: the role of Vg1 in organizing left-right axis formation.
1998,
Pubmed
,
Xenbase
Icardo,
The development of the sturgeon heart.
2004,
Pubmed
Jones,
Ablation of the murine alpha myosin heavy chain gene leads to dosage effects and functional deficits in the heart.
1996,
Pubmed
Khokha,
Rapid gynogenetic mapping of Xenopus tropicalis mutations to chromosomes.
2009,
Pubmed
,
Xenbase
Klein,
Resources for genetic and genomic studies of Xenopus.
2006,
Pubmed
,
Xenbase
Klein,
Genetic and genomic tools for Xenopus research: The NIH Xenopus initiative.
2002,
Pubmed
,
Xenbase
Kolker,
Confocal imaging of early heart development in Xenopus laevis.
2000,
Pubmed
,
Xenbase
Latinkić,
Induction of cardiomyocytes by GATA4 in Xenopus ectodermal explants.
2003,
Pubmed
,
Xenbase
Mahdavi,
Cardiac alpha- and beta-myosin heavy chain genes are organized in tandem.
1984,
Pubmed
Mahdavi,
Molecular characterization of two myosin heavy chain genes expressed in the adult heart.
1982,
Pubmed
Manasek,
Cytodifferentiation: a causal antecedent of looping?
1978,
Pubmed
Meyer,
Multiple essential functions of neuregulin in development.
1995,
Pubmed
Mohun,
The morphology of heart development in Xenopus laevis.
2000,
Pubmed
,
Xenbase
Nicol,
From the sarcomere to the nucleus: role of genetics and signaling in structural heart disease.
2000,
Pubmed
Nishii,
Targeted disruption of the cardiac troponin T gene causes sarcomere disassembly and defects in heartbeat within the early mouse embryo.
2008,
Pubmed
Noramly,
A gynogenetic screen to isolate naturally occurring recessive mutations in Xenopus tropicalis.
2005,
Pubmed
,
Xenbase
Oana,
The complete sequence and expression patterns of the atrial myosin heavy chain in the developing chick.
1998,
Pubmed
Pelster,
Disruption of hemoglobin oxygen transport does not impact oxygen-dependent physiological processes in developing embryos of zebra fish (Danio rerio).
1996,
Pubmed
Peltz,
mRNA destabilization triggered by premature translational termination depends on at least three cis-acting sequence elements and one trans-acting factor.
1993,
Pubmed
Peterkin,
Redundancy and evolution of GATA factor requirements in development of the myocardium.
2007,
Pubmed
,
Xenbase
Postlethwait,
Zebrafish comparative genomics and the origins of vertebrate chromosomes.
2000,
Pubmed
Ramsdell,
Cardiac looping and the vertebrate left-right axis: antagonism of left-sided Vg1 activity by a right-sided ALK2-dependent BMP pathway.
1999,
Pubmed
,
Xenbase
Sater,
The specification of heart mesoderm occurs during gastrulation in Xenopus laevis.
1989,
Pubmed
,
Xenbase
Scherz,
High-speed imaging of developing heart valves reveals interplay of morphogenesis and function.
2008,
Pubmed
Sedmera,
Form follows function: developmental and physiological view on ventricular myocardial architecture.
2005,
Pubmed
Sehnert,
Cardiac troponin T is essential in sarcomere assembly and cardiac contractility.
2002,
Pubmed
Sehnert,
A window to the heart: can zebrafish mutants help us understand heart disease in humans?
2002,
Pubmed
Shi,
BMP signaling is required for heart formation in vertebrates.
2000,
Pubmed
,
Xenbase
Small,
Myocardin is sufficient and necessary for cardiac gene expression in Xenopus.
2005,
Pubmed
,
Xenbase
Smith,
Expression cloning of noggin, a new dorsalizing factor localized to the Spemann organizer in Xenopus embryos.
1992,
Pubmed
,
Xenbase
Stainier,
Zebrafish genetics and vertebrate heart formation.
2001,
Pubmed
Taber,
Mechanics of cardiac looping.
1995,
Pubmed
Taber,
Biophysical mechanisms of cardiac looping.
2006,
Pubmed
Territo,
Cardio-respiratory ontogeny during chronic carbon monoxide exposure in the clawed frog Xenopus laevis.
1998,
Pubmed
,
Xenbase
Vos,
AFLP: a new technique for DNA fingerprinting.
1995,
Pubmed
Warkman,
Xenopus as a model system for vertebrate heart development.
2007,
Pubmed
,
Xenbase
Whitfield,
Nonsense-mediated mRNA decay in Xenopus oocytes and embryos.
1994,
Pubmed
,
Xenbase