Effect On Of H3K27me3 On The Onset Of Puberty In C57BL/6J Mice

The puberty period of female mammals refers to the period when female mammals first exhibit estrus symptoms and ovulation,which is a sign of sexual maturity.The early and late age of the puberty period is directly related to the level of reproductive performance of female mammals.The earlier age of the puberty,the animal can enter production cycle earlier.The trimethylation(H3K27me3)modification of lysine No.27 on histone H3 is an important inhibitory post-translational modification in epigenetics,which participates in many reproductive physiological processes.Previous studies have found that H3K27me3 may affect the initiation of female mammals by affecting follicular development.In this study,C57 BL /6J mice were used as animal models to investigate the effects of H3K27me3 on mouse reproductive traits.In the experiment,C57BL/6J mice were examined for door of vaginal sex and vaginal exfoliated cells were collected to observe the changes in cells to determine the age at the first puberty.Then,mice were injected with agonists and inhibitors of 2,6,12,18,24 and 30m M for 3 consecutive days.After 48 h after injection,the ovarian tissue was dissected to detect the expression of ovarian H3K27me3.In the second experiment,the drug was injected continuously at a concentration of 6m M for 3 days.After24,48 and 96 h after injection,the ovarian tissue was dissected to detect the expression of ovarian H3K27me3.Determine the injection concentration and time according to the protein expression effect.In the experiment,72 21-day-old female mice were randomly divided into 4 groups.The first group was injected with 20 μL of normal saline(Saline group)daily,and the second group was injected with 20 μL of 6 m M solvent DMSO(DMSO group)daily.Three groups were injected with 20 μL of 6 m M H3K27me3 inhibitor EPZ005687(EPZ005687 group)daily,and the fourth group was injected with 20 μL of 6 m M H3K27me3 agonist GSK-J4(GSK-J4 group)daily.Each agent was continuously injected for 21 days:(1)daily observation and recording of vaginal swelling and age of puberty in mice;(2)each group was slaughtered and blood was collected on day 7,14 and 21 to detect blood changes in hormone concentrations of FSH,LH,Gn RH and E2 in vivo;(3)After 21 days,the remaining 6 mice in each group naturally mate with adult male rats,and record production data of 1-7 fetuses of each female,including litter size,the number of live both,and birth weight.The results show that:(1)Experiments were conducted to confirm that the puberty age of C5BL/6J mice was5 weeks.Estrus cycle 4 ～ 5 days.(2)It was confirmed through experiments that the average age of puberty of mice in the Saline group,DMSO group,EPZ005687 group,and GSK-J4 group was 36.44,35.9,36.64 and 38.4 respectively days.Among them,EPZ005687 group’s age of puberty is earlier than DMSO group;agonist GSK-J4 group’s puberty first started,but the average age of puberty was significantly later than other groups(P <0.05).It is shown that inhibition of H3K27me3 can promote the age of puberty in mice.Conversely,promotion of H3K27me3 can inhibit the age of puberty in mice.(3)Effects of H3K27me3 on steroid hormones in mice: Up-regulation of H3K27me3 can promote the secretion of E2,but inhibit the secretion of FSH,LH and Gn RH.Downregulation of H3K27me3 can inhibit the secretion of E2,FSH and LH,but promote the secretion of Gn RH.(4)Up-regulation or inhibition of endogenous H3K27me3 had no significant differences in the effects of parity,fetal spacing,total litter size,live litter size and stillbirth number in mice(P> 0.05).Taken together,this experiment determined that the use of 6 m M GSK-J4 and EPZ005687 could significantly up-regulate and down-regulate the expression of H3K27me3 within 48 hours.Inhibition of H3K27me3 could significantly promote the initiation of puberty in mice.Conversely,up-regulation of H3K27me3 could inhibit the initiation of puberty in mice.The mechanism may be that down-regulating H3K27me3 can promote the content of serum Gn RH and E2,thereby promoting the initiation of puberty in mice.The results of this study provide a theoretical basis for further revealing the mechanism of action of H3K27me3 in the initiation of puberty,but the molecular mechanism therein needs further research.