INVESTIGATING SPERM MATURATION DURING EPIDIDYMAL TRANSIT IN THE DOMESTIC CAT FOR THE DEVELOPMENT OF ASSISTED REPRODUCTIVE TECHNIQUES

Abstract

Understanding the physiological processes involved in the sperm maturation process is critical to elucidating mechanisms underlying male infertility. Maturation of the spermatozoa during epididymal transit is associated with the integration of specific proteins and acquisition of functionality. Many underlying processes are unclear thereby making it challenging to develop applications for assisted reproductive technologies. The goal of this research was to understand key phases in the sperm maturation process associated with functional effects of protein incorporation via epididymosome secretion on sperm cell motility and fertilization. Specific objectives were to (1) identify essential proteins that contribute to sperm centrosome maturation throughout epididymal transit, (2) characterize the transfer of key factors via epididymosomes between the epididymis and maturing sperm cells and (3) demonstrate the impact of such mechanisms on the acquisition of motility and fertilizing ability by the spermatozoa. Using the domestic cat model (Felis catus), we demonstrated that the secreted epididymal vesicles termed epididymosomes supply critical proteins to the developing spermatozoa and examined the effects of exposure of these vesicles on motility and ability to successfully fertilize an oocyte. Exposure of immature sperm cells to epididymosomes in vitro resulted in the significant incorporation of cenexin, critical for the maturation of the sperm centrosome, which then enables proper pronuclear syngamy and formation of the first mitotic spindle following oocyte penetration. Furthermore, this research focused on assessing the impact of malformed spermatozoa at the centrosome on fertilization success in the domestic cat. Findings revealed that improper maturation of the centrosome may be a source of infertility in this species as well as in wild felids. In summary, this research has provided insights into the sperm cell maturation process which will enhance the use of assisted reproductive techniques and reproductive success of many species including the human and wild felids.