Morpho-functional characteristics of sex reversal in Synbranchidae (Teleostei: Synbranchiformes) / Perfil morfo-funcional da inversão de sexo em Synbranchidae (Teleostei: Synbranchiformes)

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

Teleost fishes exhibit several sexual patterns during their ontogeny, in which the gonads change into functional ovaries or testes. In distinct Orders, both gonochoristic and hermaphrodite species, simultaneous as well as sequential or consecutive, can be found. In sequential hermaphroditism (protandrous or protogynous), sex change in adult individuais involves the degeneration of the primary sex gonadal tissue and the growth and maturation of the opposite sex, passing through an intersex phase. In protogynous hermaphrodite species, most frequently observed in teleosts, individuais first develop into females and later, at adulthood, their functional ovaries are gradually replaced by testes, becoming them into active reproductively males. Internal and external (environmenta) factors seem to control the sex change in sequential hermaphrodite species. In vertebrates, the dynamic of reproductive system involves the nervous system and complex hormonal biosynthetic pathways, all of them integrated in the called brain-pituitary-gonad axis. In teleost fish, sex steroids, as well as brain and pituitary hormones, are considered to be the main factors controlling gonadal sex development, and may be involved in sex reversal in hermaphrodite species. Synbranchus marmoratus is a protogynous diandric fish. Depending on the degree of female gametogenesis decrease and male tissue activity increase, the sex reversal process was divided into three phases: early, intermediate, and final. S. marmoratus transitional gonad was characterized by the: a) disorganization of the typical ovarian structure; b) massive degeneration of the female germ cells; c) appearance of initial male germ cells . at the border of ovigerous lamellae in association with putative Sertoli cells; d) intense proliferation and migration of myoid cells; e) intense macrophage activity with the presence of melanomacrophages and melanomacrophage centers; and f) appearance of clusters of Leydig cells in the interstitial compartment. Leydig cells constitute the pioneer male structures to arise in the ovary, considered the early transitional gonad at this point. Thus, these cells were considered morphological and functional markers of the sex reversal process in this species. Leydig cells presented the typical fine structures associated to steroidogenesis, such as high steroidogenic activity (3 beta -HSD), probably, producing androgens necessary to development of gonadal male tissue, and spermatogenesis. In the intermediate phase, the male gonadal architecture begins to be defined, with the proliferation of numerous spermatocysts containing germ cells at different developmental stages. In final transitional gonads, only few degenerating oocytes and melanomacrophage centers remain. The morphology of transitional gonad at this phase is characterized by the complete formation of the testicular lamellae and the seminiferous lobules, which can be classified as unrestricted lobular type. At hormonal level, the beginning of the sexual transition is associated with the decrease of plasma estradiol-17 beta levels and the increase of circulating testosterone, suggesting the implication of such circumstances to trigger the natural sex change in S. marmoratus. Plasma 11-ketotestosterone levels onlysuffered weak variations during the initiation and progress of such process, which may indicate the secondary role of this androgen in S. marmoratus sex reversal. The identification of the adenohypophyseal cells of Synbranchus marmoratus during sex reversal does not show any alteration in the immunomarcation pattern of secretory cells of different hormones during the process, except for gonadotropin-producing oolls, which synthesis activity was very high in the initial intersexes. Probably, these cells offer hormonal support for sex reversal in this species. Therefore, sex reversal in S. marmoratus seems to occur under hypothalamic-hypophyseal-gonadal axis control. Morphological alterations necessary to sex reversal process accomplishment - disorganization of female gonadal tissue and development of the tissue of opposite sex - are gradually promoted by the estrogens privation, and/or by the androgens levels increase. Therefore, S. marmoratus constitutes an excellent model for the studying of morpho-functional eventsof sex change

ASSUNTO(S)

sex steroids transexualism hermaphroditism esteroides sexuais adenohypophysis hermafroditismo protoginia transexualismo protogyny adenohipofise

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