Identification of novel chicken estrogen receptor-alpha messenger ribonucleic acid isoforms generated by alternative splicing and promoter usage.

Using the rapid amplification of complementary DNA ends (RACE) methodology we have identified three new chicken estrogen receptor-α (cERα) messenger RNA (mRNA) variants in addition to the previously described form (isoform A). Whereas one of the new variants (isoform B) presents a 5′-extremity contiguous to the 5′-end of isoform A, the two other forms (isoforms C and D) are generated by alternative splicing of upstream exons (C and D) to a common site situated 70 nucleotides upstream of the translation start site in the previously assigned exon 1 (A). The 3′-end of exon 1C has been located at position −1334 upstream of the transcription start site of the A isoform (+1). Whereas the genomic location of exon 1D is unknown, 700 bp 5′ to this exon were isolated by genomic walking, and their sequence was determined. The transcription start sites of the cERα mRNA isoforms were defined. In transfection experiments, the regions immediately upstream of the A–D cERα mRNA isoforms were shown to possess cell-specific...