Intrafollicular sulfated steroids might affect the developmental capacity of oocytes in cattle (subproject 10, DFG research group 1369 “Sulfated Steroids in Reproduction”)

Present in vitro maturation (IVM) systems do not completely mimic the in vivo situation resulting in oocytes of reduced quality. Steroid hormones are regulators in the fine-tuned mechanism of follicular development. Therefore, the release and metabolism of sulfated steroids during follicular and oocyte development will be investigated in cattle. Furthermore, an IVM system will be established to improve the quality and developmental competence of the resulting matured oocytes. In pooled follicular fluid obtained from abattoir-derived ovaries estrone-3-sulfate (E1S), β-estradiol-sulfate (E2S), pregnenolone-sulfate were detected. Transcripts of the steroid metabolizing and transporting enzymes (SULT1E1, STS, SLC10A6) were determined in cumulus cells from immature bovine cumulus-oocyte-complex via RT-qPCR. Further steps will be to characterize the impact of sulfated steroids during in vivo and in vitro maturation. Follicular fluid and IVM medium will be analyzed by LC-MS/MS. Relative transcript abundance of specific markers of developmental competence will be determined in cumulus/granulosa cells and oocytes/blastocysts using RT-qPCR (i.e. SULTs, STS, SLC10A6, SLCO2B1). Protein expression (SULTs, STS, SLC10A6, SLCO2B1) will be investigated in cumulus cells and granulosa cells via immunohistochemistry. Finally, the level of apoptosis in cumulus/granulosa cells and embryos via TUNEL staining, the total cell number, the number of inner cell mass and trophectodermal cells via differential staining and the live-dead ratio in blastocysts using live-dead staining will be examined. A better understanding of the fragile follicle environment will also have an important relevance for human assisted reproductive technologies.

We gratefully acknowledge the financial support of the German Research Foundation (DFG; FOR 1369).