Regulation of axonemal motility in demembranated equine sperm.

The study attempts to understand why horse sperm does not effectively capacitate in vitro, impacting the success of in vitro fertilization. Researchers developed a model using demembranated sperm and explained that factors like the presence of ATP and specific levels of pH and calcium, are critical for optimal motility. The results differed from other species and might be related to why horse sperm cannot penetrate eggs in lab conditions.

Plain Language Overview

The research investigates why equine sperm struggles to capacitate effectively in lab conditions, a process critical for successful in vitro fertilization. The study involves examining the motility of horse sperm under different conditions.

Demembranated Sperm Model

• Researchers created a model using demembranated equine sperm, which involves removing the cell membrane. It allowed clearer observation and analysis of factors that have direct impact on axonemal motility, the movement of the sperm’s tail.
• Computer-assisted sperm analysis was used to study the motility parameters under various conditions.
• Treatment of ejaculated equine sperm with 0.02% Triton X-100 for 30 seconds resulted in best permeabilization and highest total motility after reactivation.

Motility Influencing Factors

• The presence of Adenosine Triphosphate (ATP), a molecule involved in energy transfer, was necessary for the motility of the demembranated sperm after reactivation while cyclic Adenosine Monophosphate (cAMP), often involved in signal transduction processes in cells, was not.
• The optimal pH level for total motility was 7.14. Any increase or decrease in this pH level did not spur hyperactivated motility, an increased activity level in sperm that is typically necessary for successful capacitation.

Role of Calcium

• The motility of demembranated sperm with calcium levels as low as 27 pM was maintained.
• The sperm’s movement was arrested at significantly lower calcium concentrations than those seen in other species.
• However, calcium’s arrest of sperm motility was not accompanied by flagellar curvature, suggesting an absence or difference in calcium sensitivity of the proteins associated with this action and credited to support hyperactivated motility.

Conclusion

• The study points towards a different reaction to calcium of the equine sperm as compared to other species. This may be why horse sperm fails to penetrate oocytes (immature egg cells) under standard in vitro conditions.
• Additional research is required to identify the factors that trigger hyperactivated motility at the axonemal level in equine sperm.