Abstract 231: A Hand1 Left Ventricular Enhancer that is Associated With Prolonged QRS Interval

Abstract

Throughout the process of cardiogenesis, dynamic changes in cardiomyocyte morphology are defined by gene regulatory networks that drive atrial, ventricular, septal, compact zone or trabecular cardiomyocyte cellular identity. The bHLH transcription factors Hand1 and Hand2 are both critical for heart development. We have isolated a 750 bp evolutionarily conserved non-coding sequence 5’ to the Hand1 transcription start site that is necessary and sufficient to drive left ventricle (LV)-specific Hand1 expression. Regulatory cis -elements include Gata and T-box binding sights. We show this enhancer as necessary and sufficient for LV expression using CrispR/Cas9 deletion. Mice homozygous for this enhancer deletion ( Hand1 αLV/ αLV ) are viable and fertile. Adult Hand1 αLV/ αLV mice exhibit a prolonged QRS interval. Interestingly, human HAND1 SNPs associated with prolonged QRS are located near the LV enhancer, but these SNP sequences are not conserved in mice. More refined examination of the human sequences revealed additional prolonged QRS-associated human nucleotide changes occurring directly within the conserved enhancer that alter cis -element DNA binding. Ventricular conduction system gene expression is altered in Hand1 enhancer deletion mice, validating in vivo a human GWAS association study that links Hand1 function to the development and perhaps maintenance of the LV purkinje fiber network. Additionally, using the Hand1 LV-enhancer, we have generated a novel Cre transgenic mouse line ( Hand1 LV -Cre ), in which LV-specific recombination is observed. We use this Cre to delete both cardiomyocytes and Hand genes from the developing LV, discovering that specification of subpopulations of ventricular cardiomyocytes regulates myocardial growth and, thereby, cardiac function.