Putative transcription factor binding sites and polymorphisms in the proximal promoter of the PRL-A gene in percomorphs and European sea bass (Dicentrarchus labrax)

There is an increasing interest in exploring how the mechanisms that regulate gene expression might generate diversity in phenotypes as a function of habitat Utilisation (at both inter- and intra-specific levels). Prolactin (PRL) is the main hormone involved in adaptation to low salinity in teleosts. Several mechanisms regulating PRL-A gene expression have been described. The main mechanisms involve Pit-1 binding sites and length polymorphism of a short sequence repeat (SSR) located in the proximal promoter (PP) of the gene. Together, these processes may generate phenotypes with potentially distinct physiological responses to salinity. To gain insight into their relative roles and importance, we sequenced the PP of the PRL-A gene in the euryhaline European sea bass (Dicentrarchus labrax) and in the stenohalnie sister species, Dicentrarchus punctatus. Then, we assessed the presence of both SSR and binding elements in PP among several teleost lineages, by checking available data from the literature and GenBank. The sequence of PRL-A PP was completely distinct between the percomorphs and other lineages Such as salmoniform, siluriform and cypriniform, except for short stretches of nucleotides that were highly conserved across all species, also including mammals. Most of them were identified as Putative cis-regulatory elements, including Pit-1, but also delta EF1, c-ETS, CEBP, and GATA binding factor 2, previously unreported as regulating PRL-A transcription in teleosts, but involved in gene regulation in mammals. This result Suggests that there is greater conservation of PRL-A regulatory mechanisms across vertebrate lineages than previously thought, and offers new perspectives for future Studies. The presence and homology of all SSR in the PP of PRL-A gene of percomorphs was demonstrated, but no SSR polymorphisms were found amongst the two Dicentrarchus species, or within natural D. labrax populations covering the known range of natural genetic variation, including marine, brackish water and freshwater populations.