Differential expression of estrogen receptor beta splice variants in rat brain: identification and characterization of a novel variant missing exon 4

Estrogen receptor beta (ER-beta) mRNA is found in abundance in rat brain. T he distribution of ER-beta mRNA in brain differs from that of ER-alpha sugg esting they subserve different functions. ER-beta mRNA has been reported to be variably spliced, in contrast to ER-alpha, resulting in numerous isofor ms that possess different functional properties. The present study was unde rtaken to determine whether the isoforms of ER-beta mRNA are differentially distributed in different brain regions. In order to assess the range of tr anscript forms expressed in various brain regions in the same assay, a micr opunch dissection technique was combined with semiquantitative RT-PCR, The relative abundance of each ER-beta isoform (beta 1>beta 2>beta 1 delta 3>be ta 2 delta 3) was similar in all ER-beta positive brain regions with the ex ception of the hippocampus, which contained low levels of most isoforms and a fifth ER-beta isoform, which we are calling ER-beta 1 delta 4, Based on its sequence, ER-beta 1 delta 4 encodes an ER-beta that is missing exon 4. Initial characterization studies of this showed that it did not bind estrog en, and that, unlike ER-beta 1, it localized to the cytoplasm when expresse d in cultured cells. The distribution of ER-beta 1 delta 4 was different fr om that of the other isoforms in that it was expressed at high levels in th e hippocampus, where the other isoforms were low, and that it was nearly un detectable in the brain regions that expressed the highest levels of the ot her ER-beta splice variants. These data suggest that a highly complex patte rn of estrogen signaling can occur in a region specific manner in the rat b rain. (C) 2000 Elsevier Science B.V. All rights reserved.