title: Differential effects of sex steroid hormones on the expression of multiple first exons including a novel first exon of prolactin receptor gene in the rat liver.
abstract: In addition to the known four alternative first exons E1(1), E1(2), E1(3) and E1(4) of the rat prolactin receptor (PRL-R) gene, a novel first exon, E1(5), was identified by cDNA cloning of the 5'-end region of PRL-R mRNA in the rat liver. Genomic fragments containing E1(5) and its 5'- or 3'-flanking regions were also cloned from rat kidney genomic DNA. A sequence search for E1(5) revealed that E1(5) is located 49 kb upstream of exon 2 of the PRL-R gene in rat chromosome 2q16. RT-PCR analysis revealed that E1(5) was preferentially expressed in the liver, brain and kidney. Expression profiles of E1(2)-, E1(3)- and E1(5)-PRL-R mRNAs in the liver of male and female rats at 5 days of age and those at 8 weeks of age were examined by RT-PCR. The levels of E1(2)-PRL-R mRNA in the female rat increased remarkably in rats at 8 weeks of age compared with those at 5 days of age, and the levels of E1(5)-PRL-R mRNA in the male rat decreased markedly at 8 weeks of age compared with those at 5 days of age. In the female rat, the levels of E1(2)-PRL-R mRNA at 8 weeks of age decreased with ovariectomy performed at 4 weeks of age and recovered with the administration of beta-oestradiol. On the contrary, the levels of E1(5)-PRL-R mRNA increased with ovariectomy and decreased with the oestrogen treatment. In the male rat liver, the levels of E1(2)-PRL-R mRNA at 8 weeks of age increased strikingly with castration performed at 4 weeks of age and became undetectable with the administration of testosterone. The levels of E1(5)-PRL-R mRNA increased slightly with castration and were restored by testosterone treatment. Removal of gonadal tissues and sex steroid hormone treatment had no effect on the expression levels of E1(3)-PRL-R mRNA in both female and male rat livers. These results indicated that the expression of the PRL-R gene in the liver is regulated by the differential effects of sex steroid hormones on the transcription of the multiple first exons including the novel one.
authors.affiliation: Department of Animal Science, Faculty of Applied Life Science, Nippon Veterinary and Animal Science University, Musashino, Tokyo 180-8602, Japan. mitanaka@nvau.ac.jp
authors.forename: M
authors.initials: M
authors.lastname: Tanaka
authors.forename: M
authors.initials: M
authors.lastname: Suzuki
authors.forename: T
authors.initials: T
authors.lastname: Kawana
authors.forename: M
authors.initials: M
authors.lastname: Segawa
authors.forename: M
authors.initials: M
authors.lastname: Yoshikawa
authors.forename: M
authors.initials: M
authors.lastname: Mori
authors.forename: M
authors.initials: M
authors.lastname: Kobayashi
authors.forename: N
authors.initials: N
authors.lastname: Nakai
authors.forename: T R
authors.initials: TR
authors.lastname: Saito
mesh_terms: D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D018076:DNA, Complementary; D005091:Exons; D005260:Female; D012739:Gonadal Steroid Hormones / Q000502:physiology*; D008099:Liver / Q000378:metabolism*; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011981:Receptors, Prolactin / Q000235:genetics*
chemical_list: D018076:DNA, Complementary; D012739:Gonadal Steroid Hormones; D012333:RNA, Messenger; D011981:Receptors, Prolactin