Differential expression of largemouth bass ( Micropterus salmoides) estrogen receptor isotypes alpha, beta, and gamma by estradiol

Abstract

The expression levels of three estrogen receptor (ER) isotypes alpha, beta, and gamma were quantified in female largemouth bass ( Micropterus salmoides) (LMB) liver, ovary, brain, and pituitary tissues. ER alpha and beta expression predominated in the liver, while ERs beta and gamma predominated in the other tissues. Temporally in females, ER alpha was highly up-regulated, ER gamma was slightly up-regulated, and ER beta levels remained unchanged in the liver when plasma 17-β estradiol (E 2) and vitellogenin (Vtg) levels were elevated in the spring. In ovarian tissue from these same fish, all three ERs were maximally expressed in the fall, during early oocyte development and prior to peak plasma E 2 levels. When males were injected with E 2, ER alpha was highly inducible, ER gamma was moderately up-regulated, and ER beta levels were not affected. None of the ER isotypes were induced by E 2 in gonadal tissues. These results combined suggest that the ERs themselves are not regulated in the same manner by E 2, and furthermore, do not contribute equally to the transcriptional regulation of genes involved in fish reproduction such as Vtg.