title: Myocardium and BMP signaling are required for endocardial differentiation.
abstract: Endocardial and myocardial progenitors originate in distinct regions of the anterior lateral plate mesoderm and migrate to the midline where they coalesce to form the cardiac tube. Endocardial progenitors acquire a molecular identity distinct from other vascular endothelial cells and initiate expression of specific genes such as nfatc1. Yet the molecular pathways and tissue interactions involved in establishing endocardial identity are poorly understood. The endocardium develops in tight association with cardiomyocytes. To test for a potential role of the myocardium in endocardial morphogenesis, we used two different zebrafish models deficient in cardiomyocytes: the hand2 mutant and a myocardial-specific genetic ablation method. We show that in hand2 mutants endocardial progenitors migrate to the midline but fail to assemble into a cardiac cone and do not express markers of differentiated endocardium. Endocardial differentiation defects were rescued by myocardial but not endocardial-specific expression of hand2. In metronidazole-treated myl7:nitroreductase embryos, myocardial cells were targeted for apoptosis, which resulted in the loss of endocardial nfatc1 expression. However, endocardial cells were present and retained expression of general vascular endothelial markers. We further identified bone morphogenetic protein (BMP) as a candidate myocardium-derived signal required for endocardial differentiation. Chemical and genetic inhibition of BMP signaling at the tailbud stage resulted in severe inhibition of endocardial differentiation while there was little effect on myocardial development. Heat-shock-induced bmp2b expression rescued endocardial nfatc1 expression in hand2 mutants and in myocardium-depleted embryos. Our results indicate that the myocardium is crucial for endocardial morphogenesis and differentiation, and identify BMP as a signal involved in endocardial differentiation.
authors.affiliation: Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229, USA.
authors.forename: Sharina
authors.initials: S
authors.lastname: Palencia-Desai
authors.affiliation: Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229, USA.
authors.forename: Megan S
authors.initials: MS
authors.lastname: Rost
authors.affiliation: Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229, USA.
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Schumacher
authors.affiliation: Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229, USA.
authors.forename: Quynh V
authors.initials: QV
authors.lastname: Ton
authors.affiliation: Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229, USA.
authors.forename: Michael P
authors.initials: MP
authors.lastname: Craig
authors.affiliation: Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229, USA.
authors.forename: Kristina
authors.initials: K
authors.lastname: Baltrunaite
authors.affiliation: Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229, USA.
authors.forename: Andrew L
authors.initials: AL
authors.lastname: Koenig
authors.affiliation: Department of Cell Biology and Howard Hughes Medical Institute, Duke University Medical Center, Durham, NC 27710, USA.
authors.forename: Jinhu
authors.initials: J
authors.lastname: Wang
authors.affiliation: Department of Cell Biology and Howard Hughes Medical Institute, Duke University Medical Center, Durham, NC 27710, USA.
authors.forename: Kenneth D
authors.initials: KD
authors.lastname: Poss
authors.affiliation: Department of Biochemistry and Biophysics, UCSF, San Francisco, CA 94158, USA.
authors.forename: Neil C
authors.initials: NC
authors.lastname: Chi
authors.affiliation: Department of Biochemistry and Biophysics, UCSF, San Francisco, CA 94158, USA.
authors.forename: Didier Y R
authors.initials: DY
authors.lastname: Stainier
authors.affiliation: Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229, USA saulius.sumanas@cchmc.org.
authors.forename: Saulius
authors.initials: S
authors.lastname: Sumanas
mesh_terms: D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000378:metabolism; D002454:Cell Differentiation; D002470:Cell Survival; D004699:Endocardium / Q000166:cytology* / Q000378:metabolism*; D017353:Gene Deletion; D018869:Heat-Shock Response; D008954:Models, Biological; D009154:Mutation; D009206:Myocardium / Q000166:cytology* / Q000378:metabolism*; D050778:NFATC Transcription Factors / Q000378:metabolism; D015398:Signal Transduction; D015027:Zebrafish / Q000196:embryology* / Q000378:metabolism; D029961:Zebrafish Proteins / Q000378:metabolism
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D050778:NFATC Transcription Factors; D029961:Zebrafish Proteins; C410915:hand2 protein, zebrafish
keywords: Bone morphogenetic protein; Endocardium; Heart; Myocardium; Nfatc1; Zebrafish