Proliferação e morte celular durante a foliculogenese de Prochilodus argenteus da bacia do Rio São Francisco

Abstract

Studies about of reproduction of teleosts provide informations about the understanding of the development of gametes and tenable better management of wild populations. The formation and growth of the ovarian follicles and the involution of postovulatory follicles are accompanied by changes in the extracellular matrix, proliferation and cell death. These changes may influence the follicular maturation and steroidogenesis. The major goal of this work was to analyze the extracellular matrix remodeling, proliferation and cell death during development and regression of ovarian follicles of Prochilodus argenteus. The present work was performed in two steps. Initially, we evaluated the folliculogenesis of fish kept in captivity and subjected to induced spawning. The drop in plasma 17 estradiol levels after spawning could be contributed to the intense apoptosis observed during postovulatory follicle involution. By immunohistochemical analysis, laminin 2 and collagen type IV were identified as the major constituents of the basement membrane. The loss of integrity of the basement membrane occurred due to lyses of the major constituents, and coincides with increased follicular apoptosis. The integrity of the basement membrane could be important for the survival of follicular cells. Furthermore, the matrix metalloproteinase 9 results suggest that this enzyme is involved in final oocyte maturation and regression of postovulatory follicles. In the second phase, folliculogenesis of P. argenteus was evaluated by quantification of ovarian structures, proliferation and cell death, and the vitellogenesis of fish caught in two sites of the São Francisco River, site 1 (S1) after the Três Marias dam, and site 2 (S2) at the confluence of the São Francisco River with the Abaeté River. Development of ovarian follicles, success in reproduction and frequency of follicular atresia are influenced by environmental factors that act in the hypothalamic-gonadal-hypophysal axis. In S1, low levels of dissolved oxygen were registered in the rainy period. The water temperature was higher in the São Francisco River immediately after the confluence with the Abaeté River (S2), regardless of the period. In S1, the ovaries showed smaller oocytes, high caspase-3 enzymatic activity and apoptosis, lower GSI and PCNA expression, as well as a lesser quantity of cathepsin-D when compared to females captured from S2. Regarding relative frequency of ovarian structures, in the dry period, only oogonia and perinucleolar oocytes were found in fish ovaries from both sites. On the other hand, in the rainy period, the relative frequency of oogonia and perinucleolar oocytes decreased and the vitellogenic oocytes increased in S2. Postovulatory follicles were observed only in S2, whereas atretic follicles occurred at a higher frequency in S1. In conclusion, our results suggest that the structure and composition of the extracellular matrix, and plasma levels of 17 estradiol related to apoptosis, play an important role during the follicular development and post-spawning involution in teleost fishes. Besides, our results showed that evaluation of apoptosis, cell proliferation and cathepsina-D can be used as biomarkers of environmental impact.