Tyrosine Phosphorylation of Sperm Proteins: What Does It Mean?
Bibliographic record
Abstract
Capacitation is defined as the ensemble of modifications that render ejaculated sperm competent to fertilise, either in the female tract or in vitro. Capacitation can occur spontaneously in vitro in defined media, suggesting it is intrinsically regulated and, once initiated, follows a pre-programmed pathway. Unlike other signalling cascades, capacitation is unique as it occurs without a specific ligand. Capacitated sperm can undergo the acrosome reaction, a calcium-dependent, exocytotic event upon interaction with the oocyte. The newly exposed inner acrosomal membrane reveals proteins that either anchor acrosome-reacted sperm to the oocyte zona pellucida (ZP) or fuse with the egg. How the sperm, a highly compartmentalised and non-transcriptional cell, undergoes the complexities of capacitation and the acrosome reaction remains unclear. Since sperm are non-transcriptional, however, protein modifications, including tyrosine phosphorylation are effective modulators of their cellular activities, including capacitation, the acrosome reaction and hyperactivated motility. Using the porcine model, our laboratory has demonstrated that capacitation is associated with the calcium-dependant appearance of a Mr 32 000 group of tyrosine phosphoproteins, collectively referred to as p32. The role and regulation of the p32 tyrosine phosphoprotein complex has remained elusive, although it has been suggested that it is involved in sperm-oocyte binding and/ or the acrosome reaction because sperm surface tyrosine phosphorylation appears during capacitation and high calcium dramatically enhances p32's presence. Moreover, ACRBP (Acrosin Binding Protein, also known as sp32), a proacrosin binding protein, is a principal component of the p32 complex, and is tyrosine phosphorylated during capacitation. ACRBP has been previously shown to catalyse prostacrosin to acrosin conversion in vitro, thereby enhancing the acrosome reaction. More recently, ACRBP was shown to have secondary ZP-binding affinity in overlay assays. In support of both reports, we have shown that ACRBP is located on the surface of capacitated sperm. However, there have been no biological studies assessing the role of ACRBP and the implication of its tyrosine phosphorylation is unknown. Therefore, to test the hypothesis that ACRBP and tyrosine phosphoproteins are necessary for sperm capacitation, the acrosome reaction and fertilization in the pig model, in vitro matured pig oocytes were inseminated with fresh boar sperm that were pre-capacitated in the presence of affinity purified mouse anti-phosphotyrosine and rabbit anti-ACRBP. Indeed, the presence of either anti-ACRBP or anti-phosphotyrosine decreased sperm-ZP binding and fertilization rate (P < 0.05). To assess the importance of surface ACRBP on the acrosome reaction, sperm were cultured in fertilization medium ±ACRBR antibody. The acrosome reaction was induced by A23187, thapsigargin or ZP. Interestingly, the presence of anti-ACRBP prevented the thapsigargin and ZP-induced acrosome reaction but not that induced by A23187. These results suggest that ACRBP influence calcium stores. Furthermore, inhibitors of SOCC (Store-Operated Calcium Channels) prevented spontaneous and thapsigargin-induced acrosome reactions, as well as p32 appearance. Taken together, these results suggest that ACRBP and the p32 tyrosine phosphoprotein complex are involved the stimulating the acrosome reaction, perhaps via SOCC. Funded by NSERC. (platform)
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.004 | 0.007 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.002 | 0.001 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 0.005 |
| Scholarly communication | 0.004 | 0.006 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.004 | 0.007 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".