Tbx2 and Tbx3 induce atrioventricular myocardial development and endocardial cushion formation

Abstract

A key step in heart development is the coordinated development of the atrioventricular canal (AVC), the constriction between the atria and ventricles that electrically and physically separates the chambers, and the development of the atrioventricular valves that ensure unidirectional blood flow. Using knock-out and inducible overexpression mouse models, we provide evidence that the developmentally important T-box factors Tbx2 and Tbx3, in a functionally redundant manner, maintain the AVC myocardium phenotype during the process of chamber differentiation. Expression profiling and ChIP-sequencing analysis of Tbx3 revealed that it directly interacts with and represses chamber myocardial genes, and induces the atrioventricular pacemaker-like phenotype by activating relevant genes. Moreover, mutant mice lacking 3 or 4 functional alleles of Tbx2 and Tbx3 failed to form atrioventricular cushions, precursors of the valves and septa. Tbx2 and Tbx3 trigger development of the cushions through a regulatory feed-forward loop with Bmp2, thus providing a mechanism for the co-localization and coordination of these important processes in heart development.Electronic supplementary materialThe online version of this article (doi:10.1007/s00018-011-0884-2) contains supplementary material, which is available to authorized users.

Genetic Networks Governing Heart Development

“…ChIP using antibodies specific for native or tagged TFs, or specific histone modifications, followed by microarray analysis (ChIP-chip) or deep sequencing (ChIP-seq), is now commonly used. Mammalian cardiac TFs recently surveyed for target genes or effects on the transcriptome include MESP1, GATA4, MEF2A, NKX2-5, SRF, TBX3, TBX5, and TBX20 (Prall et al 2007;Holler et al 2010;Bondue et al 2011;He et al 2011;Schlesinger et al 2011;Shen et al 2011;Singh et al 2012). Furthermore, genome-wide binding profiles of the ubiquitously expressed histone acetyltransferases, p300 and CBP, cofactors of many transcriptional activators, have allowed the mapping of active and tissue-specific developmental enhancers without reference to specific TF binding (Blow et al 2010;May et al 2012).…”

Tbx2 Controls Lung Growth by Direct Repression of the Cell Cycle Inhibitor Genes Cdkn1a and Cdkn1b

“…This notion is supported by the finding that mice homozygous for a null allele of Tbx3 exhibit lungs morphologically and histologically indistinguishable from the wildtype at E14.5, shortly before these mice die ( [8] and data not shown). Since mice with more than two mutant alleles of Tbx2 and Tbx3 die around E9.5 due to cardiac defects [10], analysis of the functional redundancy of the two genes in early lung development was not possible with the mouse lines available to us. ) lungs at E14.5, E16.5 and E18.5 as indicated.…”

“…For this, we crossed the Tbx2 cre line and an Hprt TBX2 -allele, that was generated by integration of a bicistronic transgenecassette containing the human TBX2 ORF followed by IRES-GFP in the ubiquitously expressed X-chromosomal Hypoxanthine guanine phosphoribosyl transferase (Hprt) locus [10,42] to maintain TBX2 expression in its endogenous domains including the lung mesenchyme. Male (Tbx2 cre/+ ;Hprt TBX2/y ) embryos were not recovered after E12.5 most likely due to cardiac defects.…”

“…[10] were maintained on an outbred (NMRI) background. For timed pregnancies, vaginal plugs were checked in the morning after mating; noon was taken as embryonic day (E) 0.5.…”

“…Tbx2 and Tbx3 are two closely related members of the Tbx2-subfamily that are required in the development of numerous organs during mammalian embryogenesis including the heart, the palate, the limbs, and the liver [5][6][7][8][9][10]. In these contexts, these two transcriptional repressors mainly seem to regulate cell fate decisions and differentiation.…”