The Novel Untranslated Exon “Exon 0T” Encoded between the Exon 0 and Exon 1 of the Rat Estrogen Receptor Alpha (ERα) Gene

抄録

We have recently isolated two untranslated first exons, exon ON and exon OS, of rat estrogen receptor alpha (ERα) gene from the liver by use of 5' -rapid amplification of the cDNA ends (5'-RACE) method. In this communication, we further analyzed the 5'-untranslated region (UTR) of the ERα mRNA in rat anterior hypophysis in order to investigate the existence of the other 5'-untranslated exon(s) of rat ERα gene. Total RNA from the anterior hypophysis of 8-week-old female Wistar strain male rats was subjected to 5' -RACE with antisense primers located in exon 1 of the rat ERα gene and one of the positive clones (clone 35) was sequenced. The nucleotide sequence of clone 35 revealed the insertion of a previously unidentified exon (which we termed “exon 0T”) between exon 0 (the first reported 5'-UTR form of rat ERa mRNA) and exon 1 of rat ERα mRNA. Analysis of rat genomic DNA indicated that exon 0T was located between exon 0 and exon 1 of rat ERα gene. We further investigated the distribution of ERα mRNA containing exon 0T in several brain regions and various peripheral tissues of 8-week-old male and female Wistar strain rats by use of reverse transcription-polymerase chain reaction (RT-PCR). The distribution of the ERα mRNA (0T-1) was essentially similar to that of ERα mRNA in which exon 0 was spliced onto exon 1 reported previously. These results indicate that (1) exon 0T is a novel untranslated exon of rat ERα gene which is located between exon 0 and exon 1 on rat genomic DNA, (2) exon 0T is inserted between exon 0 and exon 1 of ERα mRNA by alternative splicing, and (3) this alternative splicing may occur in tissues where the transcription of ERα gene is initiated from exon 0.