The role of histone methyltransferase SMYD4 in cardioprogenitor cell specification and differentiation

Abstract

SMYD4 belongs to a SET and MYND domain-containing lysine methyltransferase. In zebrafish, smyd4 is maternally and ubiquitously expressed in early embryos, and becomes more restricted in the developing cardiovascular system at 48 hours post-fertilization (hpf). We have generated a smyd4 knockout zebrafish line. The maternal and zygotic knockout mutants (zmsmyd4-/-) demonstrate that majority of mutant embryos (62%) halt the development at late gastrula (8 hpf) and about 20% mutant embryos can survive to later stage, showing a series of cardiac developmental defects, including left/right patterning and heart looping defect, and hypoplastic ventricle. To determine the underlying molecular events, we performed transcriptomic analysis of zmsmyd4-/- embryos at blastula and gastrula stages. Our data demonstrate that the genes involved in the mesendodermal and cardioprogenitor cell specification and differentiation are significantly altered; brachyury, gata5, mespbb, mespaa, mespab, and nkx2.5 are downregulatedin zmsmyd4-/- embryos. Consistent with this finding, the key signaling pathways that regulate early embryonic pattern, such as TGFβ/NODAL/BMP signaling and Wnt signaling, are also significantly altered, suggesting that smyd4 is an important epigenetic regulator in mesendodermal and cardioprogenitor cells specification and differentiation. Additionally, our biochemical analyses suggest that SMYD4 is a positive epigenetic regulator for transcription by promoting trimethylation of H3K4 and inhibiting HDAC1. Importantly, two rare genetic variants of SMYD4 are found in CHDs. Both biochemical and functional analyses indicated that SMYD4(G345D) was highly pathogenic. Taken together, our data suggest that smyd4 is a key epigenetic regulator of cardiogenesis, likely via its regulation of early cardiogenic lineage specification and differentiation.