Identification of a Novel First Exon of Prolactin Receptor Gene Expressed in the Rat Brain

Abstract

A novel first exon, E1(4), whose sequence was distinct from those of the three known first exons, E1(1), E1(2), and E1(3), of the rat PRL receptor (PRL-R) gene was identified by cDNA cloning for the 5'-end region of PRL-R mRNA expressed in the rat brain. Sequence analysis revealed the presence of two different length E1(4) cDNAs. The longer cDNA contained the 243-bp E1(4) sequence, and the shorter cDNA lacked the 139-bp sequence at the 5'-end of the longer one. Neither E1(4) cDNA has a second exon sequence, indicating that the E1(4) first exon is extensively spliced to the third exon. E1(4)-containing PRL-R mRNAs were detected only in the brain by RT-PCR and ribonuclease protection assay. The longer E1(4) mRNA was expressed as the major PRL-R mRNA species in the brain and was greatly increased in pregnant (d 18) and lactating (d 5) rats. A genomic clone containing the E1(4) first exon together with its 5'- and 3'-flanking regions was isolated from a rat kidney genomic library. Ribonuclease protection assay revealed that the position corresponding to the 5'-end of the shorter E1(4) cDNA is the major transcription start point for the E1(4) exon. The 5'-flanking region of E1(4) contained a TATA box-like element 23 bp upstream of the major transcription start point. Other putative transcription factor-binding sites, such as CCAAT, Sp1, and glucocorticoid-responsive elements, were observed at further upstream regions. These results suggest that PRL-R gene expression in rat brain is controlled by the promoter for the E1(4) first exon.

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

“…We have previously demonstrated that the higher levels of PRL-R mRNA in the rat brain in late pregnancy and the following lactating period are dependent on the expression of E1 4 , Tanaka et al 2002. It has also been shown that the expression levels of PRL-R mRNA in the different brain regions are regulated by oestrogen, which increases the utilization of E1 2 and E1 3 first exons (Pi et al 2003).…”

“…The 5 -end of the PRL-R cDNA was synthesized by the oligocapping method (Maruyama & Sugano 1994) as previously described (Tanaka et al 2002), cloned into pGEM-T Easy vector (Promega, Palo Alto, CA, USA) and sequenced.…”

“…The activation of the E1 3 promoter by the transcription factors C/EBP and SP1 accounts for the generic expression of E1 3 (Hu et al 1998b). We have recently found another first exon, E1 4 , which is preferentially expressed in the brain, though its location in the rat PRL-R gene is not known (Tanaka et al 2002). In the human PRL-R gene, six alternative first exons, hE1 3 , hE1 N1 hE1 N2 , hE1 N3 , hE1 N4 and hE N5 , have been identified (Hu et al 1999(Hu et al , 2002.…”

Regulation of Prolactin Receptor Gene Expression in the Rat Choroid Plexus via Transcriptional Activation of Multiple First Exons during Postnatal Development and Lactation

“…in mammals, PRLR gene expression is regulated via the transcriptional activation of multiple alternative first exons that encode 5'-untranslated regions. Five first exons have been identified in the rat PRLR gene, i.e., E1 1 , E1 2 , E1 3 , E1 4 , and E1 5 [16,22,34,35]. the E1 1 variant of PRLR mRNA is expressed specifically in gonadal tissues [17], whereas the E1 2 variant is transcribed in the liver and kidney [22,35].…”

“…the E1 1 variant of PRLR mRNA is expressed specifically in gonadal tissues [17], whereas the E1 2 variant is transcribed in the liver and kidney [22,35]. the E1 3 variant is expressed generically in a wide range of tissues [18], whereas the E1 4 variant is expressed preferentially in the cerebrum, including the choroid plexus [27,34]. the E1 5 variant is transcribed in the brain, liver, and kidney [35].…”