RESUMEN
Cellular infiltrations forming lymphoid-like aggregates were previously observed in gonads of two turtle species exhibiting temperature-dependent sex determination (TSD): at hatching in Chelydra serpentina; at and after hatching in Emys orbicularis. We show here that such aggregates are also present in gonads of Testudo graeca by the end of embryonic development, suggesting that their occurrence is general in turtles. Since in C. serpentina, infiltrations were observed mainly in testes exhibiting remnants of the germinal epithelium, it was assumed that their occurrence was an expression of maleness leading to rejection of this epithelium. The generality of this hypothesis was tested in E. orbicularis by looking for lymphoid-like aggregates in three types of gonads (testes, ovotestes, and ovaries) and for the stages at which they occur. Gonads were from embryos, hatchlings, and young incubated at various temperatures. Ovotestes obtained by treatment with an aromatase inhibitor of eggs incubated at female-producing temperature were also examined. In these gonads, the differentiation of Sertoli cells in testicular cords/tubes was ascertained by expression of SOX9. Moreover, the cell composition of aggregates was determined on electron micrographs. Aggregates appear in ovaries and ovotestes by the end of embryonic development and are present in the majority of these gonads at hatching, and at least up to one year after hatching. They are composed mainly of lymphocytes and fibroblasts. Aggregates are not present in typical testes. Since they occur in most ovaries, they cannot be seen as an expression of maleness. Rather, lymphocytic infiltration and formation of lymphoid aggregates in turtle gonads can be seen as components of the immune system, and can be under the control of gonadal endogenous sex steroids.
Asunto(s)
Gónadas/citología , Linfocitos/fisiología , Temperatura , Tortugas/fisiología , Animales , Técnicas Histológicas , Linfocitos/ultraestructura , Microscopía Electrónica , Diferenciación Sexual/fisiología , Tortugas/anatomía & histología , Tortugas/embriologíaRESUMEN
In order to determine the temperature sensitive stages for sexual differentiation of the gonads in Emys orbicularis, eggs of this turtle were shifted at different stages of embryonic development from the male-producing temperature of 25°C to the female-producing temperature of 30°C and reciprocally. Based on the series of developmental stages described by Yntema ('68) for Chelydra serpentina, temperature begins to influence sexual differentiation of Emys orbicularis at stage 16, a stage in which the gonads are still histologically undifferentiated. Its action lasts over the first steps of histological differentiation of the gonads. The minimal exposure at 25°C required for male differentiation of all individuals extends from stage 16 to somewhat before stage 21. For 100% female differentiation, incubation at 30°C must be longer, from stage 16 to somewhat before stage 22. Shorter exposures at 25°C or 30°C during these periods result in different percentages of males, females, and intersexes. Our results show that there is a critical stage (stage 16) which is the same for both male and female differentiation of the gonads. The thermosensensitive periods are rather long, corresponding to 11-12 days at 25°C and 30°C.