The sperm reservoir occurs as sperm adhere specifically to the densely ciliated oviduct epithelial cells (OECs) that line the isthmic portion of the oviduct of the female reproductive tract. This phenomenon stores sperm in a quiescent state until the onset of ovulation. From this point, sperm spontaneously dissociate from their epithelial containment and continue their ascent towards the awaiting oocyte. Unfortunately this phenomenon still remains rather enigmatic in mammalian species. This research project aims to dissect the molecular mechanisms of the sperm reservoir, focusing in the horse (Equus caballus).
Uncovering the proteins of the oviduct lumen in the mare was of priority in order to shed light upon potential binding proteins involved in the sperm reservoir. Isolated OECs from mares (n=9) were subjected to trypsin digestion, cleaving peptides from the apical surface of oviduct epithelial cell explants. LC-MS analysis of this lysate was able to collate a proteomics list of oviduct luminal surface proteins in the horse for the first time. Proteins that have been previously identified as potentially playing a role in the sperm reservoir in other species were identified within the list. Furthering this, through western blotting the presence of selected proteins of interest were positively identified in OECs. Using immunohistochemistry a portion of these proteins were localised to the apical epithelia of the isthmus. These findings are important as the isthmus is the region of the oviduct in which the sperm reservoir is formed. Our current OEC proteins of interest within the mare from this work now include ANXA2, GRP94, HSP70 and E-CADHERIN.
Future development should assist in providing information to improve and prolong the viability and fertilising ability of stored stallion sperm use in assisted reproductive techniques, a technique of ever increasing importance in the horse breeding industry.