The gene for the beta subunit of porcine FSH: absence of consensus oestrogen-responsive element and presence of retroposons

Abstract

To elucidate the structure and control of expression of the porcine FSH-beta subunit gene, two genomic clones were isolated and the entire gene structure was determined to the extent of 10 kb, consisting of 6 kb of the 5'-flanking region and 4 kb of the transcriptional unit. The porcine FSH-beta gene consisted of three exons the same as the human and bovine genes, but the positions of both splicing sites of porcine intron-1 were unique. It is known that the synthesis of FSH is regulated by gonadal steroids, gonadotrophin-releasing hormone (GnRH) and inhibin. However, the consensus steroid-responsive element was unexpectedly absent in the 5'-flanking region of 6 kb. On the other hand, the potential binding sites for activator protein-1 (AP1) and AP2, which might be stimulated by the GnRH-protein kinase C cascade, were present at seven and five positions respectively. An imperfect cyclic AMP-responsive element was also present. Southern blot analyses, using the cDNA and genomic fragments as probes, gave smear patterns suggesting the presence of repetitive sequences in the porcine FSH-beta gene. A survey of homology with the repetitive sequences revealed that short interspersed repeated sequences (SINES)-type non-viral retroposons were present with about 250 bp length repeats twice in the 5'-flanking region and once each in intron-1 and the 3'-flanking region. Other SINES-like sequences were also found in intron-1, exon-2 and exon-3. In comparison with the 5'-flanking sequences of the porcine alpha and LH-beta genes, there were no significantly conserved regions, implying a lack of common modulation of the three subunit genes.