The transcription factor HAND2 plays a key role in heart development. Conditional endocardial deletion of Hand2 results in embryonic lethality due to multiple heart defects, but the transcriptional changes underlying these defects had not been well described. Now, Anthony Firulli and colleagues use single-cell RNA sequencing to interrogate the gene regulatory networks downstream of HAND2 in mice. They identify several pathways that are dysregulated within the Hand2-depleted endothelial/endocardial cells, including wound healing, pulmonary fibrosis and healing, and shear-stress response. They find that the shear-stress response master regulator gene Klf2 is regulated by HAND2 specifically in the ventricular endocardium. Using HAND2 occupancy data and chromatin immunoprecipitation, the authors discover two putative HAND2-dependent enhancers within the Klf2 locus. They confirm that the conserved non-coding element 50kb upstream of Klf2 functions as a transcriptional enhancer within the developing heart but is only dependent on HAND2 in the ventricular endocardium. Together, these data identify gene regulatory networks downstream of HAND2 in the endocardium and uncover new endocardial enhancers.
