Immunocytochemical localization of lipocalin-type prostaglandin D synthasein the bull testis and epididymis and on ejaculated sperm

Previously, we identified a 26-kDa fertility-associated protein in bull sem inal plasma as lipocalin-type prostaglandin D synthase. The objective of th e present study was to immunohistochemically localize this enzyme to the va rious cell types within the bull testis and seven subsegments of the epidid ymis, and on ejaculated sperm in order to gain further insight into its pot ential function in male reproduction. In the testis, immunoperoxidase stain ing was localized within the elongating spermatids and Sertoli cells of the seminiferous tubules, varying with the stage of the spermatogenic cycle. T he highest level of staining occurred during stages III-VII. The cuboidal e pithelial cells of the rete testis and efferent ducts were also immunoreact ive. Expression of lipocalin-type prostaglandin D synthase was not uniform in the seven epididymal subsegments, suggesting a possible role in sperm ma turation. In all epididymal regions, expression was limited to the epitheli al principal cells; no immunoreactivity was apparent in other cell types. L ipocalin-type prostaglandin D synthase was strikingly localized in the capu t epididymidis, while moderate to weak staining was observed in the remaind er of the epididymis. Droplets of reaction product observed within the lume n increased progressively from the caput to cauda. Using fluorescence micro scopy, we also localized lipocalin-type prostaglandin D synthase to the api cal ridge of the acrosome on ejaculated sperm.