A critical Analysis of Equine Sperm Capacitation Media and its Components
Littell, Julia S.
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Sperm capacitation is the series of physiological changes that confer fertilization capabilities on newly ejaculated sperm. In vitro fertilization techniques in horses require in vitro capacitation of stallion sperm, through incubation in specialized capacitation media. Despite the vast research on sperm capacitation, we know surprisingly little about the specific effects of capacitation media components, with regard to the molecular pathways they act through. In this study we provide a critical analysis of three sperm capacitation media and their major components. The media we used were Tyrode's balanced salt medium, Biggers-Whitten Whittingham, and Modified Witten's. We compared the capacitation abilities of each media and looked closely at the individual and combined effects of BSA and HC03 in the media. We incubated fresh stallion sperm samples in various media treatments and then processed them for six hours at two-hour intervals. After processing samples, we analyzed them with Western blots to visualize tyrosine phosphorylation of protein residues. Results of the media comparison indicated equal levels of sperm capacitation in all three treatments, despite the chemical differences in media composition. The BSA/HC03 comparison yielded novel results indicating that BSA acts upstream of HC03 and promotes higher levels of sperm capacitation. These findings contribute to our understanding of the molecular sequence of events associated with stallion sperm capacitation and illuminate a molecular process that may be unique in horses.