Region-specific localization of retinoic acid receptor-alpha expression in the rat epididymis.

Vitamin A has been shown to be involved in spermatozoal maturation in the epididymis. The action of vitamin A in male reproduction is postulated to be mediated at least partly by retinoic acid receptor-alpha (RAR alpha). The objective of this study was to determine whether the RAR alpha gene exhibits regional specificity in its pattern of expression along the length of the epididymis. The results would indicate where in the epididymis vitamin A may be required during maturation of spermatozoa. Northern blot analyses of RNA from the epididymis revealed two major transcripts, 3.4 kb and 2.7 kb, similar to the two major transcripts found in testis. In situ hybridization analyses demonstrated the expression of transcripts in the luminal epithelia to be highest in the proximal caput, low in the corpus, and high again in the distal cauda. This regional specificity in expression of the RAR alpha transcripts along the epididymis was virtually identical to that for the proteins, as visualized by reactions with anti-RAR alpha antibody and immunohistochemical stains. These results suggest roles for RAR alpha in the regions of epididymal epithelium that are postulated to participate in spermatozoal maturation and storage.