Characterization of the transcriptional coactivator Ncoa7 and its role during the onset of puberty in European sea bass (Dicentrarchus labrax)

Abstract

Puberty comprises the developmental period that leads to the first successful reproduction. In European sea bass (Dicentrarchus labrax) intensive rearing results in a high percentage of precocious maturation one year before the physiological onset. Recent studies in European sea bass using an hemigonadectomy approach and transcriptomic analyses have revealed several genes potentially involved in the onset of puberty in female gonads. In these studies histological observation of the developmental stage achieved by the non-extracted gonad and plasma profiles of different reproductive hormones were used to classify the fish into precocious or non-precocious. RNA samples from precocious and non-precocious extracted ovaries were subsequently hybridized on a sea bass specific microarray for the identification of differentially expressed genes. One of these genes is ncoa7 that encodes a nuclear receptor co-activator that, in mammals, increases the transcriptional activity of the estrogen receptor. This study is aimed at the molecular and functional characterization of the ncoa7 gene. We have cloned the complete cDNA of sea bass ncoa7 and studied its expression in different tissues showing high expression in brain and gonads. Functional analyses using HEK293 cells co-transfected with Ncoa7 together with the estrogen, androgen and progesterone receptors, and exposed to E2, Testosterone or 17,20ß-P, show that Ncoa7 is able to increase the transcriptional activity of all the different receptors, suggesting that can control different processes in early gametogenesis. Finally, quantification of the expression of ncoa7 in the ovary and testis of adult sea bass during a whole reproductive cycle showed different expression patterns among stages, reinforcing the hypothesis that Ncoa7 could be involved in the onset of puberty in sea bass.