Recent studies seem to indicate that apoptosis and autophagy can act cooperatively in fish ovaries in order to achieve more effective ovarian regression after spawning. Considering the importance of tissue remodeling in ovarian functioning, we sought to morphologically characterize the involution processes of follicular atresia and post-ovulatory complexes using Astyanax altiparanae as an experimental model, and to determine the location of proteins involved in apoptosis and autophagy throughout this process. Fifteen females were collected after reproductive management. Fragments of the left ovaries were removed, fixed, and prepared for light microscopy and immunofluorescence analyses. The main characteristics of the involution processes were found to be consistent with previous descriptions. However, there were certain morphological peculiarities that do not appear to have been described for any other species thus far. These peculiarities may be related to the focus of this study on a single species, which allows for a more detailed investigation into morphological changes than studies on multiple species. Autophagy was also found to precede apoptosis in both involution processes in A. altiparanae. This may be related to the energy recycling process required before the removal of degenerated follicular cells by apoptosis. Thus, these results support the idea that there is crosstalk between autophagy and apoptosis pathways in ovarian involution processes, as well as the idea that the cell death pathways of these processes are conserved between teleost species with external fertilization.

Undifferentiated type A spermatogonia are the foundation of fish spermatogenesis. This cell population includes the spermatogonial stem cell population, which is able to either self-renew or differentiate into cells that will generate the male gamete - the spermatozoa. Spermatogonia stem cells are located in a specific region of the testes known as the spermatogonial niche, which regulates spermatogonial stem cell function. This study characterizes undifferentiated type A spermatogonia and their S-phase label-retaining cell properties in Astyanax altiparanae testes. This is a fish species of substantial commercial, environmental, and academic importance. Two types of undifferentiated spermatogonia have been described in A. altiparanae testis: A and A. Among the main differences observed, A spermatogonia have an irregular nuclear envelope, decondensed chromatin, one or two nucleoli, and nuages in the cytoplasm; meanwhile, type A have a round nucleus. A is preferentially distributed in areas neighboring the interstitial compartment, whereas A is located in the intertubular area. Finally, this study found that undifferentiated type A spermatogonia were able to retain BrdU over a long chase period, suggesting that these cells have a long cell cycle and potential stem cell candidates among them. Based on these findings, undifferentiated type A spermatogonia may be characterized as putative stem cells in A. altiparanae testis. This work will contribute to further studies on thestem cell biology of this promising Neotropical experimental model.

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