The novel isoform of the estrogen receptor-α cDNA (ERα isoform S cDNA) in the human testis

In order to clone the novel isoform of the cDNA for the human estrogen receptor-alpha (ERalpha), the human testicular cDNA library was screened by the exons 4-8 corresponding sequence of the human ERalpha cDNA. As a result, a novel isoform of the ERalpha cDNA (termed the ERalpha isoform S cDNA), which consists of a previously unidentified 5'-sequence and the exons 4-8 of the ERalpha gene, has been cloned. The structure of the ERalpha isoform S cDNA is essentially similar to that of the progesterone receptor (PR) isoform S cDNA that was identified in our recent report. Analysis of the genomic DNA revealed that the 5'-sequence of the ERalpha isoform S mRNA originated from a novel exon (termed the exon S). Moreover, the reverse transcription-polymerase chain reaction (RT-PCR) was carried out using the primers specific to the ERalpha isoform S mRNA on the total RNA from the human spermatozoon (Sp), liver (Li), uterine endometrium (Em) and myometrium (Mm). The ERalpha isoform S mRNA was detected in the uterine Em and Sp. Moreover, the molecular size of the ERalpha isoform S encoded by the ERalpha isoform S mRNA, which was analyzed by the transfection of the expression vector with ERalpha isoform S cDNA into the 293T cell, was approximately 39kDa. It was indicated that the one of the ATGs in the exon S could be used as the translation initiation codon. This is the first report on the ERalpha mRNA isoform that is not caused by exon-skipping or alternative utilization of the untranslated 5'-exons.