Towards the development of clonal lines in the European sea bass (Dicentrarchus labrax L.): application of uniparental reproduction techniques with an insight into sea bass eggs

Clonal lines are a powerful scientific tool for improved genetic characterization of organisms used in research. Inbred fish lines can be produced in only two generations using uniparental reproduction techniques. Androgenesis, achieved with variable success in several freshwater species, has been attempted in the European sea bass (Dicentrarchus labrax L), a marine fish of commercial and scientific interest. The low yields of progenies inheriting only the paternal genome after UV-irradiation of eggs led to considerations on the occurrence of UV screening compounds in pelagic eggs. Mycosporine-like amino acids and gadusol were found in many marine and freshwater organisms, but their occurrence in fish eggs was not clearly related to a behavioral pattern and while gadusol appeared in higher proportions in pelagic marine eggs compared to benthic species, this statement did not apply in freshwater, and moreover the kind of compounds was related to phylogeny. Further studies on DNA photorepair could enlighten hypotheses to understand the mechanisms underlying the disparate results obtained in inducing androgenesis in different fish species. Gynogenesis was reported successful to produce clonal founders in the sea bass, but high numbers of meiotic individuals contaminating fully homozygous progenies highlighted the need for efficient DNA markers to distinguish mitotic gynogenetic individuals. Furthermore, gonad development was highly delayed in gynogenetic progenies enhancing the difficulties to produce clonal lines. A high variability between individuals in the success of uniparental reproduction brought out gamete characterization and quality as a prerequisite.Les lignees clonales sont un outil puissant pour une meilleure caracterisation genetique des organismes utilises en recherche. En utilisant les techniques de reproduction uniparentale, de telles lignees peuvent etre developpees chez les poissons en seulement deux generations. L.androgenese avait deja ete realisee chez plusieurs especes d.eau douce et a ete tentee chez le loup, une espece d.interet economique et scientifique. Le faible nombre d.individus contenant effectivement uniquement le patrimoine genetique du pere, apres irradiation des oeufs aux UV, a souleve des questions quant a la presence de composes photoprotecteurs dans les oeufs pelagiques. Les acides amines de type mycosporines et le gadusol ont ete recenses dans de nombreux organismes marins et d.eau douce, mais leur presence n.a pu etre reliee au comportement flottant ou coulant des oeufs. Tandis que le gadusol apparaissait en plus grande quantite dans les oeufs marins flottants, ce resultat etait beaucoup moins clair en eau douce et le type de compose photoprotecteur semble lie a la phylogenie. D.autres etudes sur les mecanismes de photoreparation de l.ADN pourraient eclairer les resultats obtenus dans les experiences d.androgenese. La gynogenese avait deja ete reportee chez le loup mais le grand nombre d.individus meiotiques contaminant les descendances homozygotes produites a conduit a valider des marqueurs de l.ADN efficaces a distinguer les individus mitotiques. De plus, un retard de developpement des gonades a ete observe, augmentant les difficultes a obtenir les lignees clonales. La grande variabilite observee entre les individus quant au succes des reproductions uniparentales a montre que la caracterisation et la qualite des gametes sont un prealable indispensable