The estrogen receptor in seabream Sparus aurata reproduction: diversity, expression, mechanisms and physiological actions

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Diversity, expression and mechanism of action of estrogen receptors in sea bream, Sparus auratus

Publication . Pinto, Patricia IS; Canario, Adelino V. M.; Sweeney, G. E.

Two estrogen receptor subtypes (ERα and ERβ) mediate most estrogen actions in vertebrates, including fishes. Furthermore in teleost fishes two ERβ genes are differentially expressed. In this thesis, an ERβ (sbERβb) was cloned from the hermaphrodite teleost fish sea bream (Sparus auratus) which added to the previously cloned sbERα and sbERβa. sbERβb specifically binds estrogen agonists and antagonists with high affinity. The three sbER genes (α, βa, βb) have a partially overlapping but differential distribution in male and female sea bream tissues and produce multiple transcripts. Two exon2 deleted sbERα variants were also identified with different tissue distribution and hormonal regulation. Estradiol-17β up-regulated the expression of sbERα and down-regulated both sbERβs in liver, suggesting a major role for ERα in vitellogenesis. Agonistic effects were identified for the “pure antiestrogen” ICI 182,780 in several estrogenic responses, probably mediated by sbERα up regulation in liver. The immunolocalization of sbER proteins in sea bream scales suggested that the calcium mobilising actions of E2 in scales are via a direct action on osteoclasts. Subtractive hybridization followed by RT-PCR demonstrated for the first time in fish testis the E2 up regulation of some typical liver E2-induced genes (e.g. vitellogenins and choriogenins).

2005Doctoral thesis

Open Access

ICI 182,780 has agonistic effects and synergizes with estradiol-17 beta in fish liver, but not in testis

Publication . Pinto, Patricia IS; Singh, Pratap B.; Condeça, João B.; Teodósio, H. R.; Power, Deborah; Canario, Adelino V. M.

ICI 182,780 (ICI) belongs to a new class of antiestrogens developed to be pure estrogen antagonists and, in additi on to its therapeutic use, it has been used to knock-out estrogen and estrogen receptor (ER) actions in several mammalian species. In the present study, the effects and mechanism of action of ICI were investigated in the teleost fish, sea bream (Sparus auratus). Three independent in vivo experiments were performed in which mature male tilapia (Oreochromis mossambicus) or sea bream received intra-peritoneal implants containing estradiol-17 beta (E2), ICI or a combination of both compounds. The effects of E2 and ICI on plasma calcium levels were measured and hepatic and testicular gene expression of the three ER subtypes, ER alpha, ER beta a and ER beta b, and the estrogen-responsive genes, vitellogenin II and choriogenin L, were analyzed by semi-quantitative RT-PCR in sea bream. E2 treatment caused an increase in calcium levels in tilapia, while ICI alone had no noticeable effect, as expected. However, pretreatment with ICI synergistically potentiated the effect of E2 on plasma calcium in both species. ICI mimicked some E2 actions in gene expression in sea bream liver upregulating ER alpha, vitellogenin II and choriogenin L, although, unlike E2, it did not downregulate ER beta a and ER beta b. In contrast, no effects of E2 or ICI alone were detected in the expression of ERs in testis, while vitellogenin II and choriogenin L were upregulated by E2 but not ICI. Finally, pretreatment with ICI had a synergistic effect on the hepatic E2 down- regulation of ER beta b, but apparently blocked the ER alpha up-regulation by E2. These results demonstrate that ICI has agonistic effects on several typical estrogenic responses in fish, but its actions are tissue-specific. The mechanisms for the ICI agonistic activity are still unknown; although the ICI induced up-regulation of ER alpha mRNA could be one of the factors contributing to the cellular response.

2006-12-27Journal article

Open Access

Distribution and cellular localization of sea bream estrogen receptors in calcified tissues

Publication . Pinto, Patricia IS; Estêvão, Dulce; Redruello, Begoña; Power, Deborah; Canario, Adelino

In teleost fish, estradiol has been shown to induce calcium mobilization from internal stores, in particular the scales. In the present study, we have localized the estrogen receptor proteins (α, βa and βb) in the scales of juvenile and adult sea bream, using immunohistochemistry with ER isoform-specific antibodies. The ERs co-localized in cells of the scale posterior region that also expressed TRACP, the putative osteoclasts. These results suggest that the calcium mobilising action of estradiol on fish scales is via its direct action on osteoclasts.

2005Conference object

Open Access