The Role Of SIRT7 During Mouse Oocyte Maturation

SIRT7 is a protein deacetylase involved in multiple biological functions.However,its role in meiotic oocytes remains to be explored.We first examined its distribution at different stages of the mouse oocyte.SIRT7 is predominantly distributed in the nucleus of GV oocytes.Accompany with the meiotic resumption,SIRT7 resides in the entire oocytes,and many of them appear to be colocalized with the chromosomes from Pre-Metaphase Ⅰ to MⅡ stages.To investigate the role of SIRT7,fully grown GV oocytes were microinjected with specifically designed siRNAs.We found that the average rates of GVBD and Pbl extrusion in SIRT7-KD oocytes were significantly decreased compared to controls.Confocal microscopy showed that SIRT7-KD oocytes present disorganized spindle/chromosomes and loss of cortical actin cap.We analyzed the karyotype of matured oocytes by chromosome spreading.We found that loss of SIRT7 resulted in about 3-fold increase in incidence of aneuploidy eggs compared to control cells.Altogether,these findings suggest that SIRT7-KD oocytes,in many cases,are unable to properly execute the cytoskeletal organization,and thus prone to generate aneuploid eggs.SIRT7 knockdown resulted in a～40%reduction in ATP content compared to control oocytes,indicating the impairment of mitochondrial function.Meantime,in order to examine the redox homeostasis,live oocytes were stained with CM-H2DCFDA,a mitochondrial specific dye that fluoresces when oxidized by ROS.SIRT7-KD oocytes showed significantly more mitochondrial ROS than controls,as determined by mean fluorescence.These results suggest that SIRT7 functions in the control of metabolic activity during oocyte maturation.We then examined the developmental of embryos.We observed high levels of H2A.X phosphorylation at the 2-cell embryos and significant positive signals at the blastocyst stage in the SIRT7 depletion group.To assess the blastocyst quality,cell apoptosis was evaluated by TUNEL assay.Significant positive signals were observed in the SIRT7-KD group compared to controls.Taken together,our data indicate that SIRT7 downregulation in oocytes affect the developmental competence of early embryos.Of note,we found the SIRT7 downregulation in oocytes from obese mice,and the maternal obesity-associated deficient phenotypes in mouse oocyte can be partly rescued through overexpression of SIRT7.Collectively,our data reveal the essential role for SIRT7 in oocyte quality,and may mediate the effects of obesity on female reproduction.