Detection and localization of an estrogen receptor beta splice variant protein (ERβ2) in the adult female rat Forebrain and midbrain regions

Estrogens regulate neural processes such as neuronal development, reproductive behavior, and hormone secretion, and signal through estrogen receptor (ER) a and ERP (here called ERP 1). Recent studies have found variations in ER alpha and ERP 1 mRNA splicing in rodents and humans. Functional reporter gene assays suggest that these splicing variations alter ER-mediated transcriptional regulation. Estrogen receptor beta 2 (ER beta 2), an ER beta 1 splice variant containing an 18 amino acid (AA) insert in the ligand binding domain, binds estradiol with approximate to 10-fold lower affinity than ER beta 1, suggesting that it may serve as a low-affinity ER. Moreover, ER beta 2 reportedly acts in a dominant-negative fashion when heterodimerized with ER beta 1 or ER alpha. To explore the function of ER beta 2 in brain, an antiserum (Two beta ER.1) targeting the 18 AA insert was developed and characterized. Western blot analysis and transient expression of ER beta 2 in cell lines demonstrated that Two beta ER.1 recognizes ER beta 2. In the adult female rat brain, ER beta 2 immunoreactivity is localized in the cell nucleus and is expressed with a distribution similar to that of ER beta 1 mRNA. ER beta 2 immunoreactive cell numbers were high in, for example, piriforin cortex, paraventricular nucleus, supraoptic nucleus, arcuate nucleus, and hippocampal CA regions, whereas it was low in the dentate gyrus. Moreover, ER beta 2 is coexpressed in gonadotropin-releasing hormone and oxytocin neurons. These studies demonstrate ER beta splice variant proteins in brain and support the hypothesis that ER signaling diversity depends not only on ligand or coregulatory proteins, but also on regional and phenotypic selectivity of ER splice variant proteins.