Little is known about the innate defense mechanisms of the male reproductive tract. We cloned a 385-base pair complementary DNA and its genomic DNA named Bin1b that is exclusively expressed in the caput region of the rat epididymis and that is responsible for sperm maturation, storage, and protection. Bin1b exhibits structural characteristics and antimicrobial activity similar to that of cationic antimicrobial peptides, beta-defensins. Bin1b is maximally expressed when the rats are sexually mature and can be up-regulated by inflammation. Bin1b appears to be a natural epididymis-specific antimicrobial peptide that plays a role in reproductive tract host defense and male fertility.

Germ cell nuclear factor (GCNF/RTR), a novel orphan receptor in the nuclear receptor superfamily of ligand‐activated transcription factors, is expressed predominantly in developing germ cells. In several mammalian species two GCNF/RTR mRNAs are present in the testis, with the smaller 2.3‐kb transcript generally expressed at higher levels than the larger 7.4‐ or 8.0‐kb transcript. In both the mouse and rat, the 2.3‐ and 7.4‐kb GCNF/RTR transcripts were detected in isolated spermatogenic cells, but not in Sertoli cells. Expression of these transcripts is differentially regulated, with the larger 7.4‐kb mRNA appearing earlier during testicular development. The major 2.3‐kb transcript is expressed predominantly in round spermatids in the mouse and rat. In situ hybridization studies in the rat demonstrated that GCNF/RTR transcripts reach maximal steady‐state levels in round spermatids at stages VII and VIII of the spermatogenic cycle, and then decline abruptly as spermatids begin to elongate. RNase protection assays were used to predict the 3′ termination site of the 2.3‐kb transcript. An alternative polyadenylation signal (AGUAAA) was identified just upstream of this termination site. These studies suggest that GCNF/RTR may regulate transcription during spermatogenesis, particularly in round spermatids just prior to the initiation of nuclear elongation and condensation. Mol. Reprod. Dev. 50:93–102, 1998. © 1998 Wiley‐Liss, Inc.

Germ cell nuclear factor (GCNF), a nuclear orphan receptor, involved in spermatogenesis, neurogenesis, differentiation, and embryo development, was highly expressed with two transcripts (7.4 and 2.3 kb) in mouse testis and with only one transcript (7.4 kb) slightly expressed in brain, liver, and kidney. The 2.3-kb transcript was restricted to round spermatids at stages VII and VIII of the spermatogenic cycle. The present report demonstrated its expression in epididymis as well, but at a very low level. Northern blot analysis showed two transcripts: a common 7.4-kb transcript and a unique 3.1-kb transcript. The expression levels of both GCNF transcripts in epididymis were down-regulated by androgen, as observed in castrated animals and aged mice. Polyclonal antisera against GCNF protein were raised. Western blot analysis showed the presence of only one band in total protein extracts from either mouse testis or epididymis. It indicated that the two mRNAs (7.4 and 3.1 kb) encode for the same protein as in testis. Fluorescent immunohistochemical staining and in situ hybridization showed that its expression was in the principal cell abundant in the corpus region. It implies that some androgen-regulated gene expressions located at the corpus principal cells might be controlled by GCNF.

A full length cDNA named HongrES1 was isolated and cloned by screening rat epididymis cDNA library using a mouse EST as a probe and 5 RACE followed. It contained 1590bp nucleotides and its predicted protein had 415 amino acid residues including a serpin (serine protease inhibitor) conserved domain. Tissue distribution pattern showed it was specifically expressed in adult rat epididymis; moreover, in situ hybridyzation indicated this gene was expressed in a limited region of the cauda epididymis near vas deference. Such kind of expression pattern sugested that HongrES1 had potential function in male reproduction.