Effects of 17ß-estradiol on early gonadal development and expression of genes implicated in sexual differentiation of a South American teleost, Astyanax altiparanae.

Gonadal sex differentiation in teleost fish shows greater plasticity as compared to other vertebrates, as it can be influenced by a variety of factors such as exogenous sex steroids. Exogenous estrogens, such as 17ß-estradiol (E2), can induce feminization when administered during early embryonic development. However, the mechanisms underlying the E2-induced feminization are not fully understood, especially in Neotropical species. Therefore, the aim of this study was to evaluate the effects of E2 administration on the phenotypic sex characteristics, histological assessment of the gonads, and the expression of selected genes in Astyanax altiparanae exposed to dietary E2 prior to gonadal differentiation. At 4 days post-hatch (dph), groups of 30-40 undifferentiated larvae were fed with a diet containing varying amounts of E2 for 28 days, and fish were sampled at 90 dph. Previous studies revealed that ovary formation in A. altiparanae occurred at 58 dph, whereas the first sign of testis formation was found at 73 dph. In relation to the control, E2 exposure increased the proportion of phenotypic females in 120% and 148.4% for 4 and 6 mg E2/Kg, respectively. However, histological analysis revealed that treatments did not affect gonadal sex ratio between males and females, but induced intersex (testis-ova) in the group treated with 6 mg E2/Kg food. Treatment with E2 also altered gonadal transcript levels of a selected number of genes implicated in sexual differentiation. Males overexpressed dmrt1, sox9 and amh following E2 treatment as compared to control. Females showed increased mRNA levels of dmrt1 and sox9, which might be related to the down-regulation of cyp19a1a after E2 exposure. In summary, E2 exposure during early gonadal development affected male secondary characteristics without changing the gonadal sex ratio, and altered expression of genes implicated in sexual differentiation.

Duration of spermatogenesis and identification of spermatogonial stem cell markers in a Neotropical catfish, Jundiá (Rhamdia quelen).

Spermatogenesis is a process driven by stem cell, where germ cell cycle is under the control of a specific genotype species. Considering that Jundiá (Rhamdia quelen) is a Neotropical catfish with great economical importance and useful experimental model, little information is available on basic aspects of its reproductive biology, especially on spermatogenesis. As a result, this study aimed to characterize the male germ cells, estimate the duration of spermatogenesis and evaluate the expression of selected stem cell genes in Jundiá testis. Similar to other fish species, our results showed a remarkable decrease of germ cell nuclear volume during Jundiá spermatogenesis, particularly from type A undifferentiated to late type B spermatogonia and from diplotene to late spermatids. Using a S-phase marker, bromodeoxyuridine (BrdU), the combined duration of meiotic and spermiogenic phases in this species was estimated in approximately 7 days. This is considered very short when compared to mammals, where spermatogenesis last from 30 to 74 days. Selected stem cell genes were partially sequenced and characterized in Jundiá testis. Expression analysis showed higher plzf and pou5f3 mRNA levels in the cell fractions enriched by type A undifferentiated spermatogonia. These results were further confirmed by in situ hybridization that showed strong signal of plzf and pou5f3 mRNA in type A undifferentiated spermatogonia. Altogether, these information will expand our knowledge of the reproductive biology of this species, contributing to improve its production and management, and also for biotechnological applications, such as germ cell transplantation.