Retinoic acid signaling pathway: gene regulation during the onset of puberty in the european sea bass
- Autores: Paula Javiera Medina Henríquez
- Directores de la Tesis: Mercedes Blazquez Peinado (dir. tes.), Vicente Gracia García (tut. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2019
- Idioma: español
- Tribunal Calificador de la Tesis: Jordi Viñas de Puig (presid.), Laia Navarro Martín (secret.), Neil Duncan (voc.)
- Programa de doctorado: Programa de Doctorado en Ciencias del Mar por la Universidad de Barcelona y la Universidad Politécnica de Catalunya
- Materias:
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- Resumen
European sea bass (Dicentrarchus labrax) aquaculture is a thriving industry in Spain where it reached about 23,500 t and a market value of approximately 133 million euros. However, most of the sea bass farms produce a high percentage of males (70-90%) since the rearing temperature is increased during the initial stages of development to speed up development and growth. This is a problem because in this species, generally, females exhibit higher growth rates than males. This situation is aggravated as nearly 30% of these males reach puberty precociously during the first year of life, before attaining commercial size. Puberty is accompanied by a decrease in growth rates as energy diverts towards gonadal growth instead of somatic growth. In addition, it comes along with muscle waste and losses in the organoleptic properties of the meat. Because of these biological responses to captive breeding, there is a great need to understand the reproductive process and its control under intensive production conditions. The main objective of this thesis is to increase the knowledge of European sea bass reproduction. It is focussed on the role of the retinoic acid (RA) signalling pathway during early development and puberty.
Using a costume-made sea bass oligomicroarray we found several groups of genes that were differentially expressed in testis during the onset of male puberty. One of these groups included genes that belong to the RA signalling pathway. RA is the active form of vitamin A and is known to be essential for the onset of meiosis in tetrapods, although its role in fish is yet to be confirmed. These results prompted us to deepen on the possible role of the RA signalling pathway in gonad development and gametogenesis. An in silico analysis allowed us to describe for the first time the structure, phylogeny and evolutionary history of several genes and proteins involved in the synthesis and degradation of RA in the European sea bass. After an exhaustive histological study of gonad development, we could accurately identify specific stages of ovarian and testicular differentiation in this species. The expression of the main genes of the RA signalling pathway in specific stages of gonad development confirmed its role in the onset of puberty. Finally, an in vitro culture system of testicular explants from juvenile prepubertal fish and of testicular preparations from adult fish were set up to study the role of this pathway in the onset of puberty in sea bass males. The functional responses of genes related to RA transport, synthesis, degradation and receptor signaling were evaluated in the presence of stimulators and an inhibitors of the pathway and in different meiosis scenarios.
The results show that in the sea bass: a) the onset of meiosis coincides with an increase of 11KT levels and involves several pathways, including RA signalling; b) the enzymes related to RA synthesis and degradation have all the structural features to fulfil their specific functions; c) there is a well conserved evolutionary history of the enzymes involved in RA synthesis and degradation; d) the absence of stra8, a meiosis gatekeeper present in vertebrates and also in some fish, suggests that RA signaling in this species does not occur through the transduction of this particular gene; e) the genes involved in the RA signaling pathway are evolutionarily well conserved and play an important role in gonad development and gametogenesis; f) the expression dynamics of cyp26a1 during gonad development makes it an excellent molecular marker for the onset of meiosis.
This thesis increases the understanding of the early molecular and endocrine events leading to puberty in the European sea bass by characterizing the RA signaling pathway. Moreover, it provides new questions and opens a novel research line to study the role of RA in puberty.
