Abstract
In boar sperm, we have previously shown that capacitation is associated with the appearance of the p32 tyrosine phosphoprotein complex. The principal tyrosine phosphoprotein involved in this complex is the acrosin-binding protein (ACRBP), which regulates the autoconversion of proacrosin to intermediate forms of acrosin in both boar and mouse sperm. However, the complete biological role of ACRBP has not yet been elucidated. In this study, we tested the hypothesis that tyrosine phophorylation and the presence of the ACRBP in the sperm head are largely necessary to induce capacitation, the acrosome reaction (AR) and sperm-zona pellucida (ZP) binding, all of which are necessary steps for fertilization. In vitro fertilization (IVF) was performed using matured porcine oocytes and pre-capacitated boar sperm cultured with anti-phosphotyrosine antibodies or antibodies against ACRBP. Anti-ACRBP antibodies reduced capacitation and spontaneous AR (P<0.05). Sperm-ZP binding declined in the presence of anti-phosphotyrosine or anti-ACRBP antibodies. The localisation of anti-ACRBP antibodies on the sperm head, reduced the ability of the sperm to undergo the AR in response to solubilized ZP or by inhibiting the sarco/endoplasmic reticulum Ca2+-ATPase. These results support our hypothesis that tyrosine phosphorylated proteins and ACRBP are present upon the sperm surface in order to participate in sperm-ZP binding, and that ACRBP upon the surface of the sperm head facilitates capacitation and the AR in the porcine.
Highlights
In support of the hypothesis, protein tyrosine phosphoprotein and acrosin-binding protein (ACRBP) are important for capacitation, the acrosome reaction (AR), and fertilization in boar sperm
The presence of anti-ACRBP antibodies on the sperm surface prevented thapsigargin and solubilized zona pellucida (ZP)-induced AR
These results suggest that surface sperm tyrosine phosphorylation and ACRBP are important for gamete interactions and that ACRBP influences Ca2+ stores through the regulation of sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) pumps and, the regulation of calcium in the ZP induced-AR
Summary
Capacitation is regulated by signal transduction pathways occurring during sperm transit through the female reproductive tract that involves protein phosphorylation at tyrosine residues in order to prime sperm for the AR [5]. We tested the hypothesis that tyrosine phosphoproteins and ACRBP are necessary for sperm capacitation, the AR, and fertilization in the porcine model. To this end, in vitro matured pig oocytes were inseminated with pre-capacitated fresh boar sperm in the presence of affinity-purified mouse anti-phosphotyrosine or rabbit anti-ACRBP antibodies to conduct sperm function assays. We show that tyrosine phosphoproteins and ACRBP are involved in sperm-ZP binding
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