MOLECULAR MECHANISM OF FERTILIZATION IN THE PIG

In-depth proteomic analysis of boar spermatozoa through shotgun and gel-based methods

Background

Mature spermatozoa contain numerous epididymal and seminal plasma proteins, which full identification through high-throughput technologies may allow for a better understanding of the sperm biology. Therefore, we conducted a global proteomic analysis of boar spermatozoa through shotgun and gel-based methodologies.

Results

The total proteins were extracted from mature spermatozoa and subjecsted to proteome analyses. Functional analyses of gene ontology representations and pathway enrichments were conducted on the shotgun dataset, followed by immunology and gene expression validations. Shotgun and gel-based approaches allowed the detection of 2728 proteins and 2123 spots, respectively. Approximately 38% and 59% of total proteins were respectively fully and partially annotated, and 3% were unknown. Gene ontology analysis indicated high proportions of proteins associated with intracellular and cytoplasm localizations, protein and nucleic acid binding, hydrolase and transferase activities, and cellular, metabolic, and regulation of biological processes. Proteins associated with phosphorylation processes and mitochondrial membranes, nucleic acid binding, and phosphate and phosphorous metabolics represented 77% of the dataset. Pathways associated with oxidative phosphorylation, citrate cycle, and extra-cellular matrix-receptor interaction were significantly enriched. Protein complex, intracellular organelle, cytoskeletal parts, fertilization and reproduction, and gap junction pathway were significantly enriched within the top 116 highly abundant proteins. Nine randomly selected protein candidates were confirmed with gel-based identification, immunofluorescence detection, and mRNA expression.

Conclusions

This study offers an in-depth proteomic mapping of mature boar spermatozoa that will enable comparative and discovery research for the improvement of male fertility.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4442-2) contains supplementary material, which is available to authorized users.

Effect of sperm survival and CTC staining pattern on in vitro fertilization of porcine oocytes

Polyspermy in pig oocytes fertilized in vitro remains unacceptably high. In this study, we evaluated the effects of gamete coincubation time, and determined if the proportion of capacitated spermatozoa would be predictive of the fertilizing ability of frozen-thawed semen in vitro. Cumulus-oocyte complexes were collected from slaughterhouse prepubertal gilt ovaries and matured in vitro for 44 h in TCM199, with EGF, FSH, cysteamine and follicular fluid. Fertilization was induced with 2 x 10(5) frozen-thawed spermatozoa/ml in TBM. Penetration of oocytes as well as polyspermic fertilization occurred 2 h after insemination. A strong correlation between penetration and polyspermic fertilization rates has been demonstrated, but there was no correlation between the proportion of capacitated spermatozoa, as assessed by chlortetracycline staining, at the time of insemination and fertilization rates. We also compared the results of IVF in three IVF media: TBM, m199 and TALP. Penetration and polyspermy were very different in these three media: 71 +/- 19% and 25 +/- 13% in TBM, 37 +/- 11% and 6 +/- 2% in m199, 10 +/- 2% and 0% in TALP, respectively. Nevertheless, survival of spermatozoa or modifications of the capacitation status were not different in these media after 6 h incubation. We concluded that survival and capacitation characteristics of the semen used for IVF could not be predictive of the IVF results. It seems necessary to act at the oocyte level to control both variability between replicates and the incidence of polyspermy. Improving the spermatozoa penetration blocking system of the oocytes and reducing the number of sperm-binding sites on the zona pellucida (ZP) are our further objectives.

Ram seminal plasma and fertility: results from an ongoing field study

The effects of partial replacement of ram semen diluent with ram seminal plasma on the fertility of ewes were studied. Crossbred Chios ewes (n = 152) were assigned to six groups. The oestrous cycles of the ewes were synchronised at the peak (Groups A, B, C and D) and at the end (Groups E and F) of the breeding season by means of intravaginal sponges impregnated with fluorogestone acetate (FGA) for 14 days. Four hundred IU of PMSG were injected intramuscularly at the time of sponge removal. Ewes of Groups A, C and E were artificially inseminated with ram semen diluted with skim milk extender, while those of Groups B, D and F with ram semen diluted with 50% skim milk and 50% ram seminal plasma. The addition of ram seminal plasma induced a significant increase (P < 0.05) in litter size in Groups B and D when compared with that of Groups A and C (1.85 and 1.88 vs. 1.39 and 1.52, respectively). This increase was not significant when insemination was performed at the end of the breeding season (2.0 vs. 1.4). These results indicate that the addition of seminal plasma can influence the fertility of ewes or the fertilising capacity of extended ram semen to some extent.

Equine CRISP-3: primary structure and expression in the male genital tract

Although originally described in the male rodent genital tract, cysteine-rich secretory proteins (CRISPs) are expressed in a variety of mammalian tissue and cell types. The proteins of the male genital tract have been observed associated to spermatozoa and are believed to play a role in mammalian fertilization. Here we describe the identification and primary structure of the first equine member of the CRISP family. Equine CRISP-3 is transcribed and expressed in the stallion salivary gland, in the ampulla and the seminal vesicle. It displays all 16 conserved cysteine residues and shows 82% homology to human and 78% to guinea pig CRISP-2 (AA1, TPX 1) and 77% to human CRISP-3. In contrast to other mammalia, in the horse CRISP-3 is synthesized in great amounts in the accessory sexual glands, ampulla and seminal vesicle, thus allowing the isolation of equine CRISP-3 in amounts suitable for biochemical, physiological and structural studies from stallion seminal plasma.

Molecules involved in mammalian sperm-egg interaction

To achieve fertilization, sperm and egg are equipped with specific molecules which mediate the steps of gamete interaction. In mammals, the first interaction between sperm and egg occurs at an egg-specific extracellular matrix, the zona pellucida (zp). The three glycoproteins, ZP1, ZP2, and ZP3, that comprise the zp have been characterized from many species and assigned different roles in gamete interaction. A large number of candidate-binding partners for the zp proteins have been described; a subset of these have been characterized structurally and functionally. Galactosyltransferase, sp56, zona receptor kinase, and spermadhesins are thought to participate in the primary binding between sperm and zp and may initiate the exocytotic release of hydrolytic enzymes in the sperm head, the acrosome reaction. Digestion of the zp by these enzymes enables sperm to traverse the zp, at which time the proteins PH20, proacrosin, sp38, and Sp17 are thought to participate in secondary binding between the acrosome-reacted sperm and zp. Once through the zp, sperm and egg plasma membranes meet and fuse in a process reported to involve the egg integrin alpha 6 beta 1 and the sperm proteins DE and fertilin. These molecules and the processes involved in gamete interaction are reviewed in this chapter within a physiological context.