Prolactin Induces Protamine 2 mRNA Expression in Rat Testis

Abstract

The effect of prolactin on transcription during spermatogenesis was examined by subtractive DNA hybridization and differential screening. A protamine 2 cDNA fragment was isolated from one of the genes up-regulated in testes of rat 6 h after prolactin injection. In situ hybridization to detect protamine 2 mRNA was also performed using digoxigenin-labeled cRNA probes. Weak signals were detected from preleptotene to early pachytene spermatocytes, elongated spermatids and spermatozoa; strong ones were recognized from mid- to late-pachytene, diplotene, and secondary spermatocytes, and early round spermatids. Localization of protamine 2 mRNA coincided with that of prolactin receptor mRNA described in our previous report. We then compared the time-dependent expression of protamine 2 mRNA with that of luteinizing hormone receptor mRNA after prolactin administration, using Northern blot analysis. Protamine 2 mRNA was up-regulated 1 h after the prolactin treatment, and stable levels were maintained for another 13 h. In contrast, luteinizing hormone receptor mRNA levels increased much later, at 13 h after prolactin injection. Therefore, protamine 2 gene responds rapidly to prolactin administration and up-regulation of expression appears to be independent of the luteinizing hormone pathway.