ARS | Publication request: Estrogen Receptor Alpha-2: a Novel Isoform from the Rainbow Trout

Submitted to: Society for the Study of Reproduction Annual Meeting
Publication Type: Abstract
Publication Acceptance Date: July 24, 2005
Publication Date: July 24, 2005
Citation: Nagler, J., Cavileer, T., Cyr, D., Rexroad III, C.E. 2005. Estrogen receptor alpha-2: a novel isoform from the rainbow trout. Society for the Study of Reproduction Annual Meeting. 38:M184.

Technical Abstract: Estrogens have multi-faceted and wide-ranging effects in vertebrate animals. To understand the complexity of estrogen activity in a given animal the full suite of estrogen receptors (ERs) must be known. In many fishes, the nuclear ER beta subtype is duplicated with two isoforms. This has not been shown in any fish species for the ER alpha subtype. Herein we present evidence for a novel ER alpha isoform in the rainbow trout, which is termed ER alpha-2 in contrast to the previously described ER alpha-1 for this species. The ER alpha-2 mRNA has 1677 nucleotides and codes for a 558 amino acid protein. DNA sequence characterization of ER alpha-2 and comparison with ER alpha-1 show high similarity in the conserved DNA-binding (91%) and ligand-binding domains (89%). All the intron-exon boundaries are nearly identical, although variable intron size was noted in some cases. Ligand binding studies demonstrate an estradiol-17 beta saturable receptor with a Km of 0.16. An investigation on tissue distribution showed that ER alpha-2 is present in both ovaries and testes of rainbow trout, similar to ER alpha-1. However, unlike ER alpha-1, ER alpha-2 is not present in the liver. A comprehensive phylogenetic analysis utilizing all currently known fish nuclear ER sequences confirm that two distinct ER clades representing the two subtypes, ER alpha and ER beta, are apparent. The rainbow trout ER alpha-2 falls clearly in the ER alpha clade and is most closely related to rainbow trout ER alpha-1. These results provide strong support for ER alpha-2 being the other ER alpha isoform in the rainbow trout.