Structure, tissue distribution and estrogen regulation of splice variants of the sea bream estrogen receptor alpha gene

Estrogen actions are mainly mediated by specific nuclear estrogen receptors (ERs), for which different genes and a diversity of transcript variants have been identified, mainly in mammals. In this study, we investigated the presence of ER splice variants in the teleost fish gilthead sea bream (Sparus auratus), by comparison with the genomic organization of the related species Takifugu rubripes. Two exon2-deleted ERα transcript variants were isolated from liver cDNA of estradiol-treated fish. The ΔE2 variant lacks ERα exon 2, generating a premature termination codon and a putative C-terminal truncated receptor, while the ΔE2,3* variant contains an in-frame deletion of exon 2 and part of exon 3 and codes for a putative ERα protein variant lacking most of the DNA-binding domain. Both variants were expressed at very low levels in several female and male sea bream tissues, and their expression was highly inducible in liver by estradiol-17β treatment with a strong positive correlation with the typical wild-type (wt) ERα response in this tissue. These findings identify novel estrogen responsive splice variants of fish ERα, and provide the basis for future studies to investigate possible modulation of wt-ER actions by splice variants.

Combining multispecies home range and distribution models aids assessment of MPA effectiveness

Marine protected areas (MPAs) are today's most important tools for the spatial management and conservation of marine species. Yet, the true protection that they provide to individual fish is unknown, leading to uncertainty associated with MPA effectiveness. In this study, conducted in a recently established coastal MPA in Portugal, we combined the results of individual home range estimation and population distribution models for 3 species of commercial importance and contrasting life histories to infer (1) the size of suitable areas where they would be fully protected and (2) the vulnerability to fishing mortality of each species. Results show that the relationship between MPA size and effective protection is strongly modulated by both the species' home range and the distribution of suitable habitat inside and outside the MPA. This approach provides a better insight into the true potential of MPAs in effectively protecting marine species, since it can reveal the size and location of the areas where protection is most effective and a clear, quantitative estimation of the vulnerability to fishing throughout an entire MPA.