Project description:Tbx5 is expressed in the left ventricle of the developing mammalian heart. In order to test the transcriptional requirement of Tbx5 in the fetal left ventricle and bypass its early requirement in early cardiac formation, we used a combination of the ROSA26creERT2, a ubiquitously transcribed tamoxifen-dependent cre recombinase, and the Tbx5 floxed allele to remove both copies of Tbx5 at E11.5 followed by microdissection at E12.5. In addition to several well-known targets of Tbx5, we identified a novel signature of disrupted PDGF signaling.
Project description:The left atrium consists of three major parts: the peri-pulmonary vein portion, the appendage, and the vestibule. Previous transcriptional profiling of the adult left atrium and identification of the Tbx5-dependent transcriptome has focused on the atrial appendage (Nadadur et al 2016, Science Translational Medicine). In that study, Tbx5 was shown to regulate a gene regulatory network of atrial identity in the appendage and in its absence results in atrial fibrillation. In order to investigate the regional differences in the transcriptome of the left atrium, the left atrial appendage and the peri-pulmonary vein portion from adult mice were compared by RNA-sequencing. Additionally, as Tbx5 is major regulator of atrial identity, the peri-pulmonary vein portion of the atria was likewise examined following removal of Tbx5 using an adult specific conditional knockout of Tbx5.
Project description: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 increased 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 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. To confirm this hypothesis we analyzed chromatin looping of enhancers marked by H3K27Ac 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. Conversely, Tbx5 overexpression in the ventricular myocardium drove atrial gene expression. Together, these data demonstrate a role for TBX5 in maintaining the atrial gene expression program by binding to atrial enhancers to preserve tissue-specific chromatin architecture. We highlight this phenomenon at major atrial identity genes including Nppa, Bmp10 and Myl7.