Immunocontraceptive target repertoire defined by systematic identification of sperm membrane alloantigens in a single species.

Sperm competence in animal fertilization requires the collective activities of numerous sperm-specific proteins that are typically alloimmunogenic in females. Consequently, sperm membrane alloantigens are potential targets for contraceptives that act by blocking the proteins' functions in gamete interactions. Here we used a targeted proteomics approach to identify the major alloantigens in swine sperm membranes and lipid rafts, and thereby systematically defined the repertoire of these sperm-specific proteins in a single species. Gilts with high alloantibody reactivity to proteins in sperm membranes or lipid rafts produced fewer offspring (73% decrease) than adjuvant-only or nonimmune control animals. Alloantisera recognized more than 20 potentially unique sperm membrane proteins and five sperm lipid raft proteins resolved on two-dimensional immunoblots with or without prior enrichment by anion exchange chromatography. Dominant sperm membrane alloantigens identified by mass spectrometry included the ADAMs fertilin α, fertilin ß, and cyritestin. Less abundant alloantigens included ATP synthase F1 ß subunit, myo-inositol monophosphatase-1, and zymogen granule membrane glycoprotein-2. Immunodominant sperm lipid raft alloantigens included SAMP14, lymphocyte antigen 6K, and the epididymal sperm protein E12. Of the fifteen unique membrane alloantigens identified, eleven were known sperm-specific proteins with uncertain functions in fertilization, and four were not previously suspected to exist as sperm-specific isoforms. De novo sequences of tryptic peptides from sperm membrane alloantigen "M6" displayed no evident homology to known proteins, so is a newly discovered sperm-specific gene product in swine. We conclude that alloimmunizing gilts with sperm membranes or lipid rafts evokes formation of antibodies to a relatively small number of dominant alloantigens that include known and novel sperm-specific proteins with possible functions in fertilization and potential utility as targets for immunocontraception.

A differential mechanism is involved during heparin- and cryopreservation-induced capacitation of bovine spermatozoa.

After ejaculation, mammalian spermatozoa must undergo capacitation to fertilize. Capacitation of bovine spermatozoa occurs in vitro in medium supplemented with heparin. Semen cryopreservation is an important tool for assisted reproduction, although the fertility of frozen-thawed spermatozoa is reduced, possibly due to precocious capacitation-like changes that are known to occur. Our purpose was to clarify the mechanisms involved in bull sperm cryocapacitation induced by cryopreservation. Our general hypothesis is that the signaling pathways that lead to capacitation are triggered by the cryopreservation procedure. Ejaculated bovine semen was divided into two aliquots and diluted in extender; one was then kept fresh, whereas the second was cryopreserved. Western blots of extracted sperm proteins with anti-phosphotyrosine antibody showed that capacitation, induced by either heparin in fresh sperm or cryopreservation (cryocapacitation), is associated with a differential profile of phosphotyrosine-containing proteins. Immunolocalization of phosphotyrosine-containing proteins in the fresh and cryopreserved spermatozoa showed that, after thawing, cryocapacitated sperm displayed labeling over the acrosomal region, whereas for fresh sperm, this labeling appeared after 5-h incubation with heparin. The chlortetracycline assay and the ability of the sperm to undergo the lysophosphatidylcholine-induced acrosome reaction were used to confirm that a subpopulation of cryopreserved sperm is capacitated at thawing, irrespective of heparin inclusion. Since glucose is known to inhibit heparin-induced capacitation, the semen extender was modified to include glucose as a means of inhibiting cryocapacitation; however, cryocapacitation was not prevented according to the chlortetracycline assay and profile of phosphotyrosine-containing sperm proteins.

Implication of calmodulin-dependent phosphodiesterase type 1 during bovine sperm capacitation.

Phosphodiesterases (PDEs) are enzymes that degrade cyclic nucleotides. The calcium-calmodulin dependent PDE type 1 (PDE 1) and the cyclic adenosine monophosphate (cAMP)-specific PDE type 4 (PDE 4) have been implicated in sperm function. We tested the hypothesis that specific PDEs regulate capacitation of bovine sperm in a manner independent of those that mediate motility. Our objectives were to determine the effects of inhibiting PDE 1 and PDE 4 on capacitation and motility, and to compare these effects to those of heparin, which is necessary for capacitation of bull sperm in vitro. Fresh sperm were supplemented either with 15 microg/mL heparin (positive control) or the PDE inhibitors vinpocetine (specific for PDE 1) and rolipram (specific for PDE 4), and then incubated for 5 hours. At 0, 3, and 5 hours, samples were assayed for capacitation and motility parameters according to the chlortetracycline (CTC) fluorescent pattern B and computer-assisted sperm analysis, respectively. A higher percentage of CTC pattern B sperm relative to heparin controls was observed at 0 and 3 hours when sperm were incubated with vinpocetine. After 5 hours, the percentage of heparin- and vinpocetine-treated sperm showing pattern B did not differ (P >.05). Rolipram did not affect CTC patterns (P >.05; n = 4). Vinpocetine and heparin both reduced the percentage of progressively motile sperm after 3 and 5 hours, but vinpocetine reduced it more than heparin (P <.05; n = 4). Rolipram transiently increased linearity versus sperm with heparin (P <.05; n = 4). To further test the hypothesis that PDE 1 inhibition permits capacitation, we conducted in vitro fertilization. Vinpocetine did not support the ability of sperm to penetrate homologous oocytes (n = 5). Although cAMP regulation by PDE 1 may occur early during capacitation, downstream events appear to prevent full capacitation from occurring prematurely.