Epigenetic modification of histone 3 at lysine 9 in sheep zygotes and its relationship with DNA methylation.
BACKGROUND
Previous studies indicated that, unlike mouse zygotes, sheep zygotes lacked the paternal DNA demethylation event. Another epigenetic mark, histone modification, especially at lysine 9 of histone 3 (H3K9), has been suggested to be mechanically linked to DNA methylation. In mouse zygotes, the absence of methylated H3K9 from the paternal pronucleus has been thought to attribute to the paternal DNA demethylation.


RESULTS
By using the immunofluorescence staining approach, we show that, despite the difference in DNA methylation, modification of H3K9 is similar between the sheep and mouse zygotes. In both species, H3K9 is hyperacetylated or hypomethylated in paternal pronucleus relative to maternal pronucleus. In fact, sheep zygotes can also undergo paternal DNA demethylation, although to a less extent than the mouse. Further examinations of individual zygotes by double immunostaining revealed that, the paternal levels of DNA methylation were not closely associated with that of H3K9 acetylation or tri-methylation. Treatment of either 5-azacytidine or Trichostatin A did not induce a significant decrease of paternal DNA methylation levels.


CONCLUSIONS
Our results suggest that in sheep lower DNA demethylation of paternal genomes is not due to the H3K9 modification and the methylated DNA sustaining in paternal pronucleus does not come from DNA de novo methylation.
State Key Laboratory for Agrobiotechnology, College of Biological Science, China Agricultural University, Beijing 100094, PR China. houjian@cau.edu.cn
Jian
J
Hou
Lei
L
Liu
Jing
J
Zhang
Xiu-Hong
XH
Cui
Feng-Xiang
FX
Yan
Hong
H
Guan
Yong-Fu
YF
Chen
Xiao-Rong
XR
An
D000818:Animals; D001374:Azacitidine / Q000494:pharmacology; D019175:DNA Methylation / Q000187:drug effects; D004622:Embryo, Mammalian / Q000378:metabolism*; D044127:Epigenesis, Genetic; D005260:Female; D005455:Fluorescent Antibody Technique; D006657:Histones / Q000235:genetics* / Q000378:metabolism; D006877:Hydroxamic Acids / Q000494:pharmacology; D008239:Lysine / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D009865:Oocytes / Q000378:metabolism; D012756:Sheep / Q000235:genetics* / Q000378:metabolism; D015053:Zygote / Q000378:metabolism
D006657:Histones; D006877:Hydroxamic Acids; C012589:trichostatin A; D008239:Lysine; D001374:Azacitidine