title: An early requirement for nkx2.5 ensures the first and second heart field ventricular identity and cardiac function into adulthood.
abstract: Temporally controlled mechanisms that define the unique features of ventricular and atrial cardiomyocyte identities are essential for the construction of a coordinated, morphologically intact heart. We have previously demonstrated an important role for nkx genes in maintaining ventricular identity, however, the specific timing of nkx2.5 function in distinct cardiomyocyte populations has yet to be elucidated. Here, we show that heat-shock induction of a novel transgenic line, Tg(hsp70l:nkx2.5-EGFP), during the initial stages of cardiomyocyte differentiation leads to rescue of chamber shape and identity in nkx2.5(-/-) embryos as chambers emerge. Intriguingly, our findings link an early role of this essential cardiac transcription factor with a later function. Moreover, these data reveal that nkx2.5 is also required in the second heart field as the heart tube forms, reflecting the temporal delay in differentiation of this population. Thus, our results support a model in which nkx genes induce downstream targets that are necessary to maintain chamber-specific identity in both early- and late-differentiating cardiomyocytes at discrete stages in cardiac morphogenesis. Furthermore, we show that overexpression of nkx2.5 during the first and second heart field development not only rescues the mutant phenotype, but also is sufficient for proper function of the adult heart. Taken together, these results shed new light on the stage-dependent mechanisms that sculpt chamber-specific cardiomyocytes and, therefore, have the potential to improve in vitro generation of ventricular cells to treat myocardial infarction and congenital heart disease.
authors.affiliation: Division of Pediatric Cardiology, Department of Pediatrics, College of Physicians & Surgeons, Columbia University, 630 West 168th Street, New York, NY 10032 USA.
authors.forename: Vanessa
authors.initials: V
authors.lastname: George
authors.affiliation: Division of Pediatric Cardiology, Department of Pediatrics, College of Physicians & Surgeons, Columbia University, 630 West 168th Street, New York, NY 10032 USA.
authors.forename: Sophie
authors.initials: S
authors.lastname: Colombo
authors.affiliation: Division of Pediatric Cardiology, Department of Pediatrics, College of Physicians & Surgeons, Columbia University, 630 West 168th Street, New York, NY 10032 USA. Electronic address: kl284@columbia.edu.
authors.forename: Kimara L
authors.initials: KL
authors.lastname: Targoff
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002452:Cell Count; D002454:Cell Differentiation / Q000502:physiology; D017931:DNA Primers / Q000235:genetics; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D055786:Gene Knockout Techniques; D005838:Genotype; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006352:Heart Ventricles / Q000196:embryology*; D000072576:Homeobox Protein Nkx-2.5; D007091:Image Processing, Computer-Assisted; D017403:In Situ Hybridization; D008856:Microscopy, Fluorescence; D009024:Morphogenesis / Q000502:physiology*; D032383:Myocytes, Cardiac / Q000502:physiology*; D016133:Polymerase Chain Reaction; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*; D015027:Zebrafish / Q000196:embryology*; D029961:Zebrafish Proteins / Q000235:genetics / Q000502:physiology*
chemical_list: D017931:DNA Primers; D000072576:Homeobox Protein Nkx-2.5; C528182:Nkx2.5 protein, zebrafish; D014157:Transcription Factors; D029961:Zebrafish Proteins; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins
keywords: Atrium; Chamber identity; Ventricle; Zebrafish; nkx2.5; nkx2.7