title: Transmembrane protein 2 (Tmem2) is required to regionally restrict atrioventricular canal boundary and endocardial cushion development.
abstract: The atrioventricular canal (AVC) physically separates the atrial and ventricular chambers of the heart and plays a crucial role in the development of the valves and septa. Defects in AVC development result in aberrant heart morphogenesis and are a significant cause of congenital heart malformations. We have used a forward genetic screen in zebrafish to identify novel regulators of cardiac morphogenesis. We isolated a mutant, named wickham (wkm), that was indistinguishable from siblings at the linear heart tube stage but exhibited a specific loss of cardiac looping at later developmental stages. Positional cloning revealed that the wkm locus encodes transmembrane protein 2 (Tmem2), a single-pass transmembrane protein of previously unknown function. Expression analysis demonstrated myocardial and endocardial expression of tmem2 in zebrafish and conserved expression in the endocardium of mouse embryos. Detailed phenotypic analysis of the wkm mutant identified an expansion of expression of known myocardial and endocardial AVC markers, including bmp4 and has2. By contrast, a reduction in the expression of spp1, a marker of the maturing valvular primordia, was observed, suggesting that an expansion of immature AVC is detrimental to later valve maturation. Finally, we show that immature AVC expansion in wkm mutants is rescued by depleting Bmp4, indicating that Tmem2 restricts bmp4 expression to delimit the AVC primordium during cardiac development.
authors: Hubrecht Institute, KNAW and University Medical Center Utrecht, 3584 CT Utrecht, The Netherlands. k.smith@imb.uq.edu.au
authors: Kelly A
authors: KA
authors: Smith
authors: Anne K
authors: AK
authors: Lagendijk
authors: Andrew D
authors: AD
authors: Courtney
authors: Huijun
authors: H
authors: Chen
authors: Scott
authors: S
authors: Paterson
authors: Benjamin M
authors: BM
authors: Hogan
authors: Carol
authors: C
authors: Wicking
authors: Jeroen
authors: J
authors: Bakkers
mesh_terms: D000483:Alleles; D000818:Animals; D055415:Bone Morphogenetic Protein 4 / Q000378:metabolism; D054089:Endocardial Cushions / Q000196:embryology* / Q000378:metabolism*; D005260:Female; D018507:Gene Expression Regulation, Developmental; D006330:Heart Defects, Congenital / Q000473:pathology; D008297:Male; D008540:Meiosis; D008565:Membrane Proteins / Q000378:metabolism* / Q000502:physiology; D051379:Mice; D008954:Models, Biological; D016296:Mutagenesis; D009154:Mutation; D020825:T-Box Domain Proteins / Q000235:genetics*; D015027:Zebrafish
chemical_list: C525810:Bmp4 protein, mouse; D055415:Bone Morphogenetic Protein 4; D008565:Membrane Proteins; D020825:T-Box Domain Proteins; C103172:T-box transcription factor 5; C485807:Tmem2 protein, mouse