Expression and distribution of cortical type aromatase mRNA variant in the adult rat brain.

Our previous study showed that a relatively high level of the aromatase mRNA existed in the cerebral cortex (CC) of the rat, where the aromatase activity was reported to be little or absent. To elucidate the identity of the aromatase mRNA in the CC of the rat, we investigated the 5'-region of the aromatase mRNA in the rat CC. When the sequence of the 5'-region of the cortical message was analysed by the 5'-rapid amplification of cDNA ends (5'-RACE) with the antisense primer for exon II using the RNA extracted from the CC, no clone could be isolated. However, the upstream sequence from the 5'-end of exon IV of the aromatase clones, isolated from the CC by RACE with the antisense primers for exon V, was different from that on the aromatase mRNA encoding the full translated region. The new sequence of the cortical type message, called the cortical type aromatase mRNA variant, was located on the intron upstream of exon IV in the genomic cDNA. Distribution of the brain aromatase message with exons III-V and the cortical type aromatase mRNA variant were analysed by the reverse transcription-polymerase chain reaction (RT-PCR) using total RNAs extracted from the hypothalamus-preoptic area (HPOA), amygdala (AMY) and CC. The PCR products with primers for exons III-V were generated from the HPOA and AMY, but not from the CC. On the other hand, the PCR products with primers for exon IIIv (cortical type aromatase mRNA variant specific)-V were detected in significant amounts in the CC as well as the HPOA and AMY. These results indicate the existence of the aromatase mRNA variant lacking exons I-III in the adult rat brain. This cortical type mRNA variant seemed to be widely distributed in the tissues.