Stallion spermatozoa: putative target of estrogens; presence of the estrogen receptors ESR1, ESR2 and identification of the estrogen-membrane receptor GPER.

The research investigates the presence of estrogen receptors in horse spermatozoa and suggests that these can be targets for estrogens, which could potentially influence the sperm during its journey through the epididymis or within the female genital tract.

Understanding Horse Testicular Physiology

• The study hinges on understanding how the body of a stallion, a male horse, produces and uses estrogens, a type of steroid hormone. Among mammals, stallions produce the largest amount of these hormones. They’re created mainly in Leydig and Sertoli cells located in the testis and in the epididymis, a tube where sperm cells are stored and mature.
• Until now, the role of estrogens in horse testicular physiology has been unclear, as is their potential capacity to act on spermatozoa. The researchers set out to find out if the sperm cells are targets for estrogens by investigating the presence of estrogen receptors on mature, ejaculated spermatozoa.

Presence of Estrogen Receptors

• The researchers found the existence of a single isoform of two estrogen receptors, ESR1 (66kDa) and ESR2 (61kDa), by applying a technique known as Western-blot analysis on samples gathered from seven stallions.
• Using a different technique called confocal analysis, they discovered that these receptors are primarily located in the flagellar region of the sperm cells, which is the part that enables the movement of the cell.
• Immuno-TEM experiments, another kind of analysis, further revealed that the receptors were found mostly near the membranes, locations typically associated with rapid, non-genomic effects.

Discovery of GPER in Colt Testis

• Besides discovering ESR1 and ESR2, the researchers also found the expression of the seven transmembrane estradiol binding receptor GPER in the testis of a young horse, or colt.
• Like the other receptors, this protein too was localized at the connecting piece in mature spermatozoa.

Conclusion

• The findings of this research propose that stallion spermatozoa could be a target for estrogens. The observation that the receptors are located at the membrane and connecting piece of the spermatozoa suggests that the estrogens could potentially act on these receptors during the sperm’s transit through the epididymis or within the female reproductive system.