Cell history determines the maintenance of transcriptional differences between left and right ventricular cardiomyocytes in the developing mouse heart

Abstract

IntroductionThe establishment and maintenance of transcriptional diversity during organogenesis is a key feature of embryonic development. Within the developing heart, myocardial cells in different cardiac chambers exhibit differences in gene expression, which reflect functional compartmentalisation (Christoffels et al., 2000). These transcriptional differences are established during early heart development and prefigure the formation of the specialised left and right atrial and ventricular chambers, which direct separate systemic and pulmonary blood flows.Molecular analysis of the regulatory circuits controlling cardiomyocyte diversity has identified a small number of cisacting motifs and trans-acting factors involved in atrial versus ventricular identity and in differential gene expression between cells of the ventricular and atrioventricular canal myocardium (Wang et al., 2001;Habets et al., 2002). In addition, several cisacting elements active in cardiomyocytes of either the left or right ventricle have been defined in transgenic mice (Schwartz and Olson, 1999;Kelly et al., 1999). Although the trans-acting factors that regulate such transgenes remain unknown, mutational analysis of transcription factors expressed throughout the heart has in some cases revealed compartmentrestricted roles during early development (Lyons et al., 1995;Lin et al., 1997). A small number of cardiac transcription factors, in particular the basic helix-loop-helix (bHLH) proteins Hand1 and Hand2, and the T-box-containing regulatory factor Tbx5, show left/right differences in expression pattern in the embryonic ventricles, and the generation of null alleles in the Hand1, Hand2 and Tbx5 genes has shown that these factors are important in chamber morphogenesis (Srivastava et al., 1997;Firulli et al., 1998;Riley et al., 1998;Bruneau et al., 2001). Despite these studies, the molecular mechanisms that initiate and maintain left versus right ventricular specific gene expression are poorly understood. In particular, little is known about the factors regulating transcriptional differences between left and right ventricular chambers at later developmental stages. How left/right ventricular transcriptional differences are maintained is of major interest, as the fundamentally different roles of the two ventricles become apparent only on the separation of pulmonary and systemic circulatory systems at birth. Furthermore, in the adult, cardiac hypertrophy elicits changes in gene expression that differ in the left versus right ventricular free walls (Vikstrom et al., 1998).

Characterization of a Cardiac-specific Enhancer, Which Directs α-Cardiac Actin Gene Transcription in the Mouse Adult Heart

“…38). In the case of a myosin light chain, MLC 3F , transgene expression in the left ventricle, but not the right, appears to reflect a phenomenon of in vivo chromatin silencing not seen in transitory transfection experiments (25).…”

“…The embryonic mouse fibroblast cell line C3H10T1/2 was grown in 10% fetal calf serum (24). Ventricular cardiocytes were prepared from hearts of 18 embryonic day Wistar rat fetuses according to the protocol of (25). Hearts were trimmed of the atria and outflow tract, and the ventricular cells were dissociated under gentle shaking in 1ϫ trypsin (T4674 Sigma) in ADS medium complemented with glucose.…”

Identification of Candidate Genes Potentially Relevant to Chamber-Specific Remodeling in Postnatal Ventricular Myocardium

“…Our study characterizes the transcription status of the LV and RV at birth rather than the establishment of LV/RV transcription differences in the course of development [28]. In embryonic and fetal heart, expression of a number of transcription factors, including Hand1, Hand2, and Tbx5, shows LV/RV differences [29, 30].…”

Myocardial Lineage Development

“…Epigenetic mechanisms are also likely to be involved in maintaining patterning of the mammalian myocardium 201. Maintenance of Mlc3f transgene expression is regulated by a cell-autonomous mechanism that is independent of DNA methylation, trichostatin A-sensitive histone deacetylation, or misexpression of transcription factors that are expressed in left or right ventricles of embryonic heart.…”