P-70: Evidence for Differential Gene Expression of A Major EpigeneticModifier Enzyme, de novo DNA Methyltransferase 3b, through Vitrification of Mouse Ovary Tissue

Background: Ovarian tissue cryopreservation is a feasible method to preserve female reproductive potential, especially in young patients with cancer or in women at risk of premature ovarian failure. Vitrification has recently emerged as a new trend for biological specimen preservation. On the other hand, gene expression that changes during vitrification can influence oocyte maturation and need to be studied. Methylation of mammalian DNA is a major epigenetic regulatory mechanism that play a special role in gene expression regulation. DNA methyltransferase3b (Dnmt3b) is responsible for de novo methylation and essential for genome stability, imprinting and embryonic. development. The aim of the present study was to evaluate the effects of vitrification on mRNA expression level of Dnmt3b gene. Materials and Methods: Ovaries of 4- to 6-week old NMRI female mice were categorized in two control and needle immersed (NIV) vitrification groups. In vitrification group, ovaries were transferred into equilibration and vitrification medium, then immersed in liquid nitrogen after loading by acupuncture needle. Parallel to vitrification process, morphology of ovarian tissues in control and vitrification group were analyzed and compared by using hematoxylin and eosin staining. Then, the expression of Dnmt3b was investigated by real-time PCR. Results: In morphological analysis, ovarian tissue integrity was well preserved in vitrification group and was similar to the control group. However, the result of this study showed that the expression level of Dnmt3b in vitrification group was significantly higher in comparison with control group (p<0.05). Conclusion: In general we can conclude that despite normal morphology of ovarian tissue after vitrification, this process may induce changes at the genetic/epigenetic level of cryopreserved tissues.