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(Circulation Research. 2009;105:61.)
© 2009 American Heart Association, Inc.

Cellular Biology

Gene Expression Profiling of the Forming Atrioventricular Node Using a Novel Tbx3-Based Node-Specific Transgenic Reporter

Thomas Horsthuis^*, Henk P.J. Buermans^*, Janynke F. Brons^*, Arie O. Verkerk, Martijn L. Bakker, Vincent Wakker, Danielle E.W. Clout, Antoon F.M. Moorman, Peter A.C. 't Hoen, Vincent M. Christoffels

From the Heart Failure Research Center (T.H., J.F.B., A.O.V., M.L.B., V.W., D.E.W.C., A.F.M.M., V.M.C.), Academic Medical Center, University of Amsterdam; and Center for Human and Clinical Genetics (H.P.J.B., P.A.C.H.), Leiden University Medical Center, The Netherlands.

Correspondence to Vincent M. Christoffels, Heart Failure Research Center, AMC, University of Amsterdam, Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands. E-mail v.m.christoffels{at}amc.uva.nl

The atrioventricular (AV) node is a recurrent source of potentially life-threatening arrhythmias. Nevertheless, limited data are available on its developmental control or molecular phenotype. We used a novel AV nodal myocardium–specific reporter mouse to gain insight into the gene programs determining the formation and phenotype of the developing AV node. In this reporter, green fluorescent protein (GFP) expression was driven by a 160-kbp bacterial artificial chromosome with Tbx3 and flanking sequences. GFP was selectively active in the AV canal of embryos and AV node of adults, whereas the Tbx3-positive AV bundle and sinus node were devoid of GFP, demonstrating that distinct regulatory sequences and pathways control expression in the components of the conduction system. Fluorescent AV nodal and complementary Nppa-positive chamber myocardial cell populations of embryonic day 10.5 embryos and of embryonic day 17.5 fetuses were purified using fluorescence-activated cell sorting, and their expression profiles were assessed by genome-wide microarray analysis, providing valuable information concerning their molecular identities. We constructed a comprehensive list of sodium, calcium, and potassium channel genes specific for developing nodal or chamber myocardium. Furthermore, the data revealed that the AV node and the chamber (working) myocardium phenotypes diverge during development but that the functional gene classes characterizing both subtypes are maintained. One of the repertoires identified in the AV node–specific gene profiles consists of multiple neurotrophic factors and semaphorins, not yet appreciated to play a role in nodal development, revealing shared characteristics between nodal and nervous system development.

Key Words: cardiac development • gene expression • gene regulation • ion channels • transgenic mice