Developmental changes in the expression levels of alternative first exons of prolactin receptor gene in rat brain

One of the alternative first exons, E1(4), of the rat prolactin receptor (PRLR) gene was identified 5.4 kb downstream of exon 2 by sequence analysis of a rat genomic clone. In female and male rat brains, expression levels of E1(4)-containing PRLR mRNA increased remarkably between 2 and 4 weeks of age during postnatal development, whereas the levels of PRLR mRNAs containing other first exons, E1(3) and E1(5), did not change throughout the development. The levels of E1(4)-containing PRLR mRNA in the female rats at 8 weeks of age decreased by ovariectomy, and recovered by the administration of 17beta-estradiol, whereas castration and following testosterone treatment showed no effect on the levels of E1(4)-containing PRLR mRNA in the male rats. The levels of E1(3)- and E1(5)-containing PRLR mRNAs were not affected by gonadectomy and following sex steroid hormone treatments in both sexes. These results indicate that expression of PRLR gene in the female and male rat brains increases during postnatal development due to the transcriptional activation of the E1(4) first exon.