FISH WITH THERMOLABILE SEX DETERMINATION (TSD) AS MODELS TO STUDY BRAIN SEX DIFFERENTIATION.

BLÁZQUEZ, MERCEDES; SOMOZA, GUSTAVO M.

Hong Kong, China

Congreso; 16th International Congress of Comparative Endocrinology; 2009

Fish are ectothermic animals and therefore water temperature can affect basic biological processes such as larval development, growth and reproduction. Similar to reptiles, the incubation temperature during early developmental stages is capable to modify final sex ratios in an increasing number of fish species. This phenomenon, known as thermolabile sex determination (TSD) was first reported in Menidia menidia, a species belonging to the family Atherinopsidae. Since then, an increasing number of fish have also been found to exhibit TSD. Traditionally, likewise in reptiles, several TSD patterns have been described in fish, however it has been recently postulated that only one pattern, i.e., females at low temperatures and males at high temperatures, may represent a “real” TSD. Many studies regarding the influence of temperature on the final sex ratios have been focused on the expression and activity of gonadal aromatase, the enzyme involved in the conversion of androgens into estrogens and encoded by the cyp19a1a gene. In this regard, teleost fish, may be due to a whole genome duplication event, produce another aromatase enzyme, commonly named brain aromatase, encoded by the cyp19a1b gene. Contrary to what has been described in other vertebrates, fish exhibit very high levels of aromatase activity in the brain and therefore synthesize high amounts of neuroestrogens. However, its biological significance is still not well understood. In addition, the mechanism whereby temperature can induce the development of a testis or an ovary still remains elusive. In this context the present review is aimed to discuss several theories about the possible role of brain aromatase using fish as models. The relevance of brain aromatase and therefore of neuroestrogens as the possible cue for gonadal differentiation is raised. In addition, the possible role of brain aromatase as the way to keep the high levels of neurogenesis in fish is also considered. Several key examples of how teleosts and aromatase regulation can offer more insight into basic mechanisms of TSD are also reviewed.