Sex steroid receptors in livestock spermatozoa: localization, function, and physiological significance

Sex steroid hormones regulate fundamental aspects of male reproduction-behavior, secondary sexual traits, spermatogenesis, and sperm maturation-traditionally via indirect actions on somatic cells (Sertoli, Leydig, and epididymal epithelial cells). Emerging evidence, however, reveals that spermatozoon themselves express progesterone, androgen, and estrogen receptors, indicating direct signaling pathways. In this review, we evaluate current literature on receptor localization and function within the spermatozoa of livestock species. Progesterone receptors are consistently reported in the head region, where progesterone promotes hypermotility, capacitation, and chemotaxis. In contrast, androgen and estrogen receptor localization is more variable, although both likewise influence motility, capacitation, and the acrosome reaction. Methodological disparities and species-specific differences contribute to inconsistent findings, underscoring the need for standardized immunolocalization and quantitative assays. Elucidating the relative physiological importance of these direct pathways will inform the optimization of assisted reproductive technologies-such as tailored capacitation media and refined insemination protocols-to enhance fertility outcomes and semen preservation in production animals.