MLL1 combined with GSK3 and MAP2K inhibition improves the development of in vitro-fertilized embryos.

The MM-102 compound prevents the interaction between mixed lineage leukemia 1 (MLL1) and WD Trp-Asp repeat domain 5 (WDR5) and results in the inhibition of MLL1 H3K4 histone methyltransferase (HMT) activity. The inhibition of the FGFR signaling pathway and activation of the WNT pathway by small molecule inhibitors (known as 2i) improves blastocyst development. However, studies on the effects of MLL1 combined with GSK3 and MAP2K inhibition (3i) on the development of embryos have not been reported. Our results show that 3i improves bovine and mouse IVF development only when added at the appropriate time point and affects ICM-related gene (OCT4, SOX2 and NANOG) expression in a concentration-dependent manner. 3i increases the expression of blastocyst-related genes such as PRDM14, KLF4 and KLF17 and decreases the expression of the de novo DNA methyltransferase genes DNMT3L and DNMT1 in bovines, but increases Prdm14, Stella, Klf2 and Klf4 expression and significantly decreases Dnmt3l, Dnmt3b, and Dnmt1 expression in mice. The analysis of transcription data showed that the expression of DNMTs increases slightly later than that of PRDM14 during embryo development, which indicates that PRDM14 is the upstream regulator. 3i upregulates PRDM14 and then downregulates DNMTs to affect IVF embryo development. When 3i-treated mouse embryos were transplanted, the morphology and body weight of the offspring were not significantly different from those of the control group. These offspring were as fertile as normal mice. 3i improves the development of bovine and mouse IVF embryos but does not affect the quality of the embryos. The application of 3i provides a new method for improving IVF embryo production in domestic animals.