Differential developmental requirements for individual histone H3K9 methyltransferases in cleavage-stage porcine embryos.

Dimethylated H3K9 is a heritable epigenetic mark that is closely linked with transcriptional silencing and known to undergo global remodelling during cleavage development. Five mammalian histone methyltransferases (HMTases), namely Suv39H1, Suv39H2, SetDB1, EHMT1 and EHMT2, have been shown to mediate the methylation of H3K9. The aim of the present study was to determine the developmental requirements of these HMTases during cleavage development in porcine embryos. We hypothesised that knockdown of the abovementioned HMTases would differentially affect porcine cleavage development. To test this hypothesis, IVM and IVF porcine oocytes were divided into one of three treatment groups, including non-injected controls, oocytes injected with a double-stranded interfering RNA molecule specific for one of the HMTases and oocytes injected with a corresponding mutated (control) double-stranded RNA molecule. Nuclei were counted in all embryos 6 days after fertilisation. Although no significant difference in total cell number was detected in embryos injected with EHMT1 and EHMT2 interfering RNAs (compared with their respective control groups), embryos injected with interfering RNAs that targeted Suv39H1, Suv39H2 and SetDB1had significantly lower cell numbers than their respective control groups (P<0.05). This suggests that individual HMTases differentially affect in vitro developmental potential.