Ing. Petra Cupperová: Expression of CD9 molecule in bovine reproductive system and its participation in sperm-oocyte interaction Institute of Animal Biochemistry and Genetics, Slovak Academy of Sciences, Department of Immunogenetics, PhD thesis, Bratislava, 2015, 102 pages Fertilization is a complex process, where the interaction of multiple proteins found on the surface of gametes occurs. The proteins involved in this process are also some CD molecules. Previous studies performed in mice and other species have shown that CD9 molecule plays an important role in the process of fertilization, probably in the fusion of sperm and oocyte. The aim of our research was to perform analogous studies in cattle; analyse the presence, distribution and functional aspects of CD9 molecules in the reproductive organs of cattle. In all experiments, we used monoclonal antibody IVA-50, specific for the cells of cattle for detection of CD9. We analysed the distribution of CD9 using indirect immunofluorescence and indirect immunoperoxidase test. For biochemical studies, we used the method of electrophoretic separation of proteins, western blot analysis and fractionation of sperm membranes. From a functional point of view, we characterized the CD9 molecule during the processes of sperm capacitation, binding to oocytes and in vitro fertilization. The results of all our experiments clearly indicate the presence of CD9 molecules in male and female reproductive system of cattle. In immunoperoxidase test monoclonal antibody IVA-50 reacted strongly with nearly all kinds of tissue cells of the vagina, uterus and ovary. Positive reaction was observed on the sections of ovarian follicular oocytes. In bull genitals, we also detected the presence of CD9 molecule in collagen tissue and smooth muscle cells. CD9 molecule is highly expressed also in accessory bull glands (prostate, seminal vesicles). We have confirmed the presence of CD9 in the epididymal fluid of high intensity especially in the body of epididymis. We also observed a strong staining in epithelium stereocilia in the body and tail of epididymis. The presence of CD9 in the fluid and in the stereocilia points to secretion of CD9 molecules by epididymal epithelium. We found out the presence of CD9 on bull spermatozoa, which has not yet been detected. In contrast to mouse sperm, where the location of CD9 was described on the surface of equatorial segment of plasma membrane and on the inner acrosomal membrane of acrosome-reacted sperm, we detected CD9 molecule on plasma membrane of intact sperm. On immature and mature oocytes we have observed a positive reaction on plasma membrane and vesicles possibly extending into zona pellucida. To inspect the effect of CD9 molecule on the fertilization process, we first analysed intact oocytes in a binding assay where number of sperm bound to the zona pellucida was evaluated. After treatment of sperm, oocytes, or both gametes simultaneously by monoclonal antibody IVA-50, we noticed a statistically significant reduction in the number of sperm bound to the zona pellucida in comparison with a control group. Subsequently, we analysed the impact of CD9 molecule on reproduction using in vitro fertilization assay, where the gametes were independently or simultaneously pre-incubated with monoclonal antibody IVA-50, or IVA-50 was added directly to the fertilization drops. In the evaluation of fertilization; except for treated oocytes; a significant reduction in number of fertilized oocytes was found, compared to control group. The results suggest possible function of CD9 molecule in binding of sperm to the oocyte, but also in the fusion of gametes. Keywords: CD9 molecule, monoclonal antibody IVA-50, genital tract, gametes, reproduction