Zebrafish IRX1b in the embryonic cardiac ventricle


  • Elaine M. Joseph

    Corresponding author
    1. Department of Medicine, Harvard Medical School/Massachusetts General Hospital, Charlestown, Massachusetts
    • Department of Medicine, Harvard Medical School/Massachusetts General Hospital, 149 13th Street, 4th Floor, Charlestown, MA 02129
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  • The IRX1b gene presented here has been renamed IRX1a by Feijoo CG, Manzanares M, de la Calle-Mustienes E, Gomez-Skarmeta JL, Allende ML. 2004. The Irx gene family in zebrafish: genomic structure, evolution and initial characterization of irx5b. Dev Genes Evol 214:277–284.


The synchronous contraction of the vertebrate heart requires a conduction system. While coordinated contraction of the cardiac chambers is observed in zebrafish larvae, no histological evidence yet has been found for the existence of a cardiac conduction system in this tractable teleost. The homeodomain transcription factor gene IRX1 has been shown in the mouse embryo to be a marker of cells that give rise to the distinctive cardiac ventricular conduction system. Here, I demonstrate that zebrafish IRX1b is expressed in a restricted subset of ventricular myocytes within the embryonic zebrafish heart. IRX1b expression occurs as the electrical maturation of the heart is taking place, in a location analogous to the initial expression domain of mouse IRX1. The gene expression pattern of IRX1b is altered in silent heart genetic mutant embryos and in embryos treated with the endothelin receptor antagonist bosentan. Furthermore, injection of a morpholino oligonucleotide targeted to block IRX1b translation slows the heart rate. Developmental Dynamics 231:720–726, 2004. © 2004 Wiley-Liss, Inc.