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).
