| Congenital heart defects are the most common form of birth defects. Despite the high frequency of occurrence, the molecular mechanisms underlying congenital heart defects remain poorly understood. Jarid2/Jumonji is a transcriptional repressor that is required for proper cardiac development. Whole body deletion of Jarid2 results in lethality at birth due to congenital heart defects including ventricular septal defects, double outlet right ventricle, hypertrabeculation accompanied by noncompaction of the ventricular wall, and edema. Here, we show the generation of a mouse harboring loxP sites flanking exon 3 of Jarid2. This provides a tool for the conditional deletion of Jarid2 in specific cell lineages. We also report that Jarid2 interacts with Zinc Finger Protein 496 (Zfp496) that contains a Scan Domain, a KRAB domain, and a zinc finger region. Zfp496 has been shown to be important for genetic regulation through histone modifications. We also generated a myocardial, endocardial, epicardial, and neural crest specific deletion of Jarid2 using Cre-loxP technology. Here we report that only an endocardial specific deletion of Jarid2 results in a deviation from expected Mendelian ratio and recapitulation of cardiac defects observed in the whole body Jarid2 mutant. We further demonstrate that the whole body or endocardial deletion of Jarid2 results in the dysregulation of Notch1 in the developing heart, which likely leads to the myocardial defects observed. Further, Jarid2 directly regulates Notch1 by occupying a previously unidentified site on the Notch1 locus through recruitment of the histone methylase Setdb1, which results in the trimethylation of histone H3, lysine 9 and repression of Notch1 in later stages of cardiac development. The epigenetic regulation of genes by transcription factors in normal cardiac development remains largely unknown. The identification of Notch1 as a direct downstream target of Jarid2 has provides the exciting opportunity to investigate how Jarid2 regulates target genes during cardiac development. |
