JARID2 is a regulator of histone methyltransferase complexes that plays an essential role in embryonic development, including heart and liver development, neural tube fusion process and hematopoiesis. JARID2 acts by recruiting histone methyltransferase complexes (PRC2) to their target genes and modulating the histone methyltransferase activity. It does not have histone demethylase activity but regulates activity of various histone methyltransferase complexes. In embryonic stem cells, it associates with the PRC2 complex and inhibits trimethylation of H3K27me3 by the PRC2 complex, thereby playing a key role in differentiation of embryonic stem cells and normal development. In cardiac cells, it is required to repress expression of cyclin-D1 (CCND1) by activating H3K9 methylation by the GLP1/EHMT1 and G9a/EHMT2 histone methyltransferases.