Tbx5maintains atrial identity by regulating an atrial enhancer network

Abstract

Understanding how the atrial and ventricular chambers of the heart maintain their distinct identity is a prerequisite for treating chamber-specific diseases. Here, we selectively inactivated the transcription factor Tbx5 in the atrial working myocardium of the neonatal mouse heart to show that it is required to maintain atrial identity. Atrial Tbx5 inactivation downregulated highly chamber specific genes such as Myl7 and Nppa, and conversely, increased the expression of ventricular identity genes including Myl2. Using combined single nucleus transcriptome and open chromatin profiling, we assessed genomic accessibility changes underlying the altered atrial identity expression program, identifying 1846 genomic loci with greater accessibility in control atrial cardiomyocytes compared to KO aCMs. 69% of the control-enriched ATAC regions were bound by TBX5, demonstrating a role for TBX5 in maintaining atrial genomic accessibility. These regions were associated with genes that had higher expression in control aCMs compared to KO aCMs, suggesting they act as TBX5-dependent enhancers. We tested this hypothesis by analyzing enhancer chromatin looping using HiChIP and found 510 chromatin loops that were sensitive to TBX5 dosage. Of the loops enriched in control aCMs, 73.7% contained anchors in control-enriched ATAC regions. Together, these data demonstrate a genomic role for TBX5 in maintaining the atrial gene expression program by binding to atrial enhancers and preserving tissue specific chromatin architecture of atrial enhancers.

The MEK-ERK signaling pathway promotes maintenance of cardiac chamber identity

“…Perhaps there are atrium-specific repressive pathways that usually inhibit the effects of endogenous MEK-ERK signaling on chamber identity, such that only excessive levels of ERK signaling can override these repressive influences. Components of pathways that are known to regulate the maintenance of atrial identity, including the COUP-TFII, Nr2f1a, or TBX5 pathways (Martin et al, 2023;Sweat et al, 2023;Wu et al, 2013), might serve as such repressors. We note that the sparse expression of vmhc in the atrium of Tg(hsp:caMEK1) embryos contrasts with the broader expression of amhc in the ventricle of PD0325901-treated embryos.…”

“…For example, several transcription factors have been shown to be required for maintenance of chamber-specific gene expression patterns. In mouse, COUP-TFII and TBX5 are essential for atrial identity maintenance: both factors sustain the expression of atrial genes and repress the expression of ventricular genes in differentiated atrial cardiomyocytes (Sweat et al, 2023;Wu et al, 2013). Likewise, in zebrafish, Nr2f1a, a functional homolog of mammalian COUP-TFII, prevents atrial cardiomyocytes from developing ectopic ventricular and pacemaker cell identities (Martin et al, 2023).…”

Cardiac differentiation roadmap for analysis of plasticity and balanced lineage commitment

“…S7B). In the atrial EB culture condi�ons, an increase of TBX5 expression occurred directly a�er a transient increase of HOXA1 expression (Roux et al, 2016;Steimle & Moskowitz, 2017;Sweat et al, 2023) points (Supplementary Fig. S7B).…”

Role of Genetic Variation in Transcriptional Regulatory Elements in Heart Rhythm

“…TBX5 is crucial for correct cardiac and conduction system development and homeostasis and maintenance of atrial identity [ 23 , 94 , 96 , 97 , 98 , 99 ]. TBX5 is surrounded by a large non-coding region (gene desert) and shows a complex expression pattern, indicative of a complex regulatory landscape with many REs.…”