Prolactin receptor expression in the testis of the ram: localisation, functional activation and the influence of gonadotrophins

The present study investigated the pattern and site of expression of the pr olactin receptor gene in the testis of the seasonally breeding Soay sheep. In experiment 1, Northern blot analysis confirmed expression of the prolact in receptor gene in the testis which was encoded by RNA transcripts of appr oximate to 3.6, 11.2, 12.6, and 14.1 kb. In situ hybridisation localised ex pression of the receptor within the interstitial and seminiferous tubule co mpartments of the testis and immunohistochemistry localised expression of t he receptor to Leydig cells and to pachytene spermatocytes, round and elong ating spermatids. In experiment 2, phosphorylation of Jak2, Stat1 and Stat5 proteins in response to prolactin was investigated by Western blotting fol lowing incubation of testicular samples with 100 ng/ml ovine prolactin. Jak 2 and Stat1 phosphorylation were induced by prolactin within 10 min and Sta t5 within 30 min. In experiment 3, intact and hypothalamo-pituitary disconn ected (HPD) rams were transferred from a short to a long day photoperiod re gimen for a period of 8 weeks. By week 8, testicular diameter had declined in intact rams (52.71 +/- 1.06 cm vs. 48.00 +/- 0.49 cm for weeks 1 and 8 a fter transfer respectively, P < 0.01, n = 3) and increased in HPD rams (27. 00 +/- 0.45 cm and 29.66 +/- 0.99 cm for weeks 1 and 8 after transfer respe ctively, P < 0.05, n = 3). RT-PCR using RNA extracted from intact and HPD r ams confirmed expression of the prolactin receptor in the testis of both gr oups. Immunohistochemistry localised prolactin receptor expression in Leydi g cells and in pachytene spermatocytes, round and elongating spermatids of intact sheep testis. In HPD rams, prolactin receptor expression was localis ed in Leydig cells and germ cells which were arrested predominantly at the pachytene spermatocyte stage. These data demonstrate expression of function al prolactin receptors in the testis of Soay rams. The site and pattern of expression of the receptor gene suggest a role for prolactin in the regulat ion of steroidogenesis and spermatogenesis. (C) 1999 Elsevier Science Irela nd Ltd. All rights reserved.