Oviductin or OVGP1, also known as oviduct-specific glycoprotein, has been shown to enhance sperm capacitation in addition to its other beneficial effects on fertilization and early embryo development. We hypothesized that estrus stage-specific hamster oviductin (eHamOVGP1) can potentiate the enhancement of tyrosine phosphorylation of sperm proteins during capacitation. Immunofluorescent staining and confocal microscopy as well as immunocytochemistry and surface replica technique localized tyrosine-phosphorylated proteins to the equatorial segment and midpiece after incubation of hamster sperm in capacitation medium in the presence or absence of eHamOVGP1. Increase of tyrosine phosphorylation level in the equatorial segment occurred as early as 5 min after incubation in the presence of eHamOVGP1. Immunostaining for eHamOVGP1 further increased upon prolonged incubation of sperm in medium containing the glycoprotein. Regardless of the presence or absence of eHamOVGP1, phosphotyrosine expression was observed along the tail, particularly at the midpiece. Western blotting of NP40-extracted sperm proteins (25, 37, and 44 kDa) and NP40-non-extractable sperm proteins (70, 83, 90 kDa) showed increased immunolabeling intensity after 5, 60, 120, and 180 min of capacitation in the presence of eHamOVGP1. Mass spectrometric analysis identified several proteins of functions known to be involved in metabolic pathways responsible for enhancement of tyrosine phosphorylation in its presence. The present investigation provides evidence that eHamOVGP1 regulates the expression of protein tyrosine phosphorylation in sperm capacitated in vitro, further supporting an important role of the presence of OVGP1 in the oviductal milieu during the process of fertilization.
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Vol. 89 • No. 2