The isolation of five new mouse estrogen receptor α mRNA variants (mERα A, B, F1, F2 and H) is described. All of these transcripts are generated by alternative splicing and all encode the 66 kDa ERα protein that the previously identified mRNA C variant generates. However, these transcripts differ in their 5′ untranslated regions. RT-PCR and S1 nuclease protection assays revealed a tissue- and sex-specific expression pattern of all variants. The C and F mRNA variants are the predominantly expressed mERα variants in mouse. The expression of mERα H mRNA is restricted to liver, although female mice produce around a five fold higher level of this transcript than males. Our results show that the mERα gene is a complex genomic unit in mice that exhibits alternative splicing which is regulated in a tissue-specific manner.
