Novel isoforms of the mRNA for human female sex steroid hormone receptors

Abstract In our recent reports, the novel isoform cDNAs of the ERα (ERα isoform S cDNA), ERβ (ERβ isoform M cDNA) and PR (PR isoform S and PR isoform T cDNAs) have been identified. These isoform cDNAs contained the previously unidentified 5′-sequences on exons 4–8 (ERα isoform S cDNA), exons 5–8 (ERβ isoform M cDNA) or exons 4–8 (PR isoform S and PR isoform T cDNAs). The genomic DNA analysis revealed that the 5′-sequences were derived from the novel independent exons, the ERα exon S, ERβ exon M, PR exon S and PR exon T, respectively. Furthermore, the existence of the novel variant mRNA, termed the i45 PR mRNA variant, with the insertion of the previously unidentified exons, termed the exons i45a and i45b, has been demonstrated by the reverse transcription-polymerase chain reaction on the RNA of the human uterine endometrium. From these results, we have concluded that the genes for the human female sex steroid hormone receptors contain the novel intronic exons, that the novel isoform mRNAs are transcribed using the intronic exon and exons 4–8 (or exons 5–8) of the gene, and that the novel variant mRNA is generated by the insertion of the intronic exons in the PR. In the present communication, our recent data along with others on the novel isoform/variant mRNAs for the human female sex steroid hormone receptors will be summarized.