Rat Sertoli cell-specific regulation of the transferrin gene

F. Guillou, E. Schaeffer, D. Part, S. Suire, I. Fontaine, M. Zakin
1993 Reproduction nutrition development (Print)  
In the testis, Sertoli cells are responsible for creating a unique environment in which germinal cells divide and differentiate into spermatozoa. A number of Sertoli cell secretory products have been identified and their function deter-' mined; among them is the iron transport protein transferrin. It is an important marker of testis function since its synthesis and secretion are involved in the control of spermatogenesis. Our purpose is to elucidate the mechanisms controlling the transferrin
more » ... the transferrin gene expression in the Sertoli cells. We have previously shown that the proximal promoter region (PR) of the human transferrin gene is sufficient to activate transcription in primary cultured Sertoli cells of rat testis (F Guillou et al (1991) J Biol Chem 266, 9876-9884). The relative importance of the PRI and PRII sequences has been tested by mutation of specific nucleotides within each sequence, followed by transient expression experiments in Sertoli cells, compared to hepatoma cells. The mutation of the PRI and PRII site inhibits transcription by 20% and 50% respectively in Sertoli cells, versus 85% and 70% in Hep 3B cells. This suggests that different DNA binding proteins interact with each site in testis compared to liver. This conclusion is further supported by methylation interference assays which show that testis and liver proteins interact in a different manner with the DNA sequence. The transcription factors present in testis or liver nuclear extracts have been further characterized by fractionation on a heparin-Sepharose column. The purified active fractions were tested in gel retardation assays with antibodies directed against various transcription factors. In liver, the PRI sequence is the binding site of the 2 proteins, HNF4 and COUP-TF; PRII is the binding site of the C/EBP transcription factors family. In testis, only COUP-TF interacts with PRI, since HNF4 is absent; the 2 proteins interacting with the PRII site do not belong to the C/ EBP family and remain to be further characterized. Transferrin secretion and transferrin mRNA increase when Sertoli cells are stimulated by follicle-stimulating hormone (FSH). By transfection experiments, we have identified a FSH response element via cAMP pathway in the -82, -52 pb region. The CRE element is absent in this region. During post-natal testicular differentiation, there is a correlation between the increase in transferrin secretion and the initiation of spermatogenetic function. In Sertoli cell of 10-d-old rats, transferrin is secreted at a very low level; in 17d-old rats, the level of secreted transferrin increases dramatically (30 times). However, in Sertoli cells of either 10-d-old or 17-d-old rats, the level of transferrin mRNA is identical. The post-transcriptional mechanism which regulates transferrin expression during testicular differentiation remains to be further characterized. Salmon GH (sGH) binds specifically to trout testis membranes. In vitro, sGH modulates testicular steroidogenesis, while in vivo, GH and 17a20!-OH-P vary concomitantly (Le Gac et a/, 1992 Biol Reprod 46, 949-957). Pickford et al (1972, Biol Reprod 7, 370-386) observed that in vivo treatment with b-GH stimulated spermatogonial proliferation in hypophysectomized killifish. It is not known whether GH acts directly or through IGF in steroidogenic cells and germ cells and until recently, no study dealt with possible secretion and function of IGF in the fish testis. We investigated these 2 points. We found that trout testis RNAs hybridized with a coho salmon IGF-I DNA probe (fig 1 The size and/or relative intensity of the 2 main IGF-I transcripts observed on Northem blots of testicular RNA differed from those obtained with trout liver RNA. In vivo treatment with recombinant trout GH (Eurogentec) significantly increased IGF-I mRNA concentration in both the liver and the testis (fig 1 ) .
doi:10.1051/rnd:19930109 fatcat:ksxaezviebgghbk2evobxaj5oi