title: G9a co-localized with histone H3 lysine 9 monomethylation but not dimethylation in a nuclear membrane-dependent manner during mouse preimplantation embryo development.
abstract: OBJECTIVE
  Histone H3 lysine 9 (H3K9) methylation plays an important role in the regulation of preimplantation embryo development. G9a has been reported to be a major H3K9mono (m1)/dimethylation(m2) methyltransferase and to contain nuclear localization signals. This study was performed to investigate the correlation between H3K9 methylation level and G9a localization when the nuclear membrane undergoes periodic reconstruction in the cell cycle during preimplantation embryo development.
  
  
  METHODS
  The fluorescence intensity was examined via immunofluorescence. The mRNA expression of G9awas determined using real-time reverse transcriptase (RT)-PCR. Eight-cell embryos were cultured in KSOM supplemented with nocodazole (0.5 μM) for 12 h.
  
  
  RESULTS
  In this study, it was observed that the fluorescence intensity of H3K9m2 and G9a began to increase significantly from the 4-cell stage and reached the peak at the morula stage (p < 0.001), but the fluorescence intensity declined to 4-cell-stage levels when it reached the blastula stage. We observed a similar pattern when we examined G9a mRNA expression. Once the nuclear membrane disintegrated, G9a and H3K9m1 were not detectable by immunofluorescence; when it was reconstructed, G9a and H3K9m1 had relocated to the cell nucleus. However, no significant change was observed in the H3K9m2 localization or in the G9a mRNA level (p > 0.05) during the whole process. JHDM2A was consistently localized in the cytoplasm irrespective of the presence or absence of a nuclear membrane.
  
  
  CONCLUSIONS
  These results indicate dynamic changes in the expression level of H3K9m2 and G9a as preimplantation embryogenesis progresses. G9a co-localized with H3K9 m1 in a nuclear membrane-dependent manner during mouse preimplantation embryo development.
authors.affiliation: Department of Obstetrics and Gynecology, Tang-du Hospital, the Fourth Military Medical University, Xi'an, People's Republic of China.
authors.forename: Bo
authors.initials: B
authors.lastname: Li
authors.forename: Na
authors.initials: N
authors.lastname: Tang
authors.forename: Shuqiang
authors.initials: S
authors.lastname: Chen
authors.forename: Xue
authors.initials: X
authors.lastname: Li
authors.forename: Xiuying
authors.initials: X
authors.lastname: Huang
authors.forename: Xiaohong
authors.initials: X
authors.lastname: Wang
authors.forename: Fangzhen
authors.initials: F
authors.lastname: Sun
mesh_terms: D000818:Animals; D001755:Blastocyst / Q000166:cytology; D047108:Embryonic Development / Q000235:genetics*; D005260:Female; D018507:Gene Expression Regulation, Developmental; D011495:Histone-Lysine N-Methyltransferase; D006657:Histones / Q000235:genetics*; D008239:Lysine / Q000235:genetics; D008745:Methylation; D051379:Mice; D009685:Nuclear Envelope / Q000235:genetics*; D019913:Nuclear Localization Signals; D011247:Pregnancy
chemical_list: D006657:Histones; D019913:Nuclear Localization Signals; C533711:G9a protein, mouse; D011495:Histone-Lysine N-Methyltransferase; D008239:Lysine