Role of apoptosis in temperature-dependent sex determination of pejerrey Odontesthes bonariensis
This report outlines the findings of a preliminary study on the possibility that apoptosis (programmed cell death) plays a role in gonadal sex differentiation of pejerrey Odontesthes bonariensis (Pisces, Atherinopsidae), a “differentiated” gonochorist fish with a striking degree of temperature-dependent sex determination (TSD). Two experiments were conducted in which larvae were reared at feminizing (17°C), masculinizing (29°C), and intermediate (24 or 25°C) temperatures between hatching and 10 weeks. Samples were taken weekly for examination of gonadal sex by light histology and the detection of apoptosis in gonadal cells by the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) method. TUNEL staining revealed only occasional, isolated apoptotic cells in the gonads of individuals reared at the feminizing temperature throughout the observation period. In contrast to 17°C, virtually all individuals sampled from the masculinizing temperature between 4 and 8 weeks post-hatch (the estimated time of histological differentiation of the gonads) had moderate to intense TUNEL labeling in the gonads. Staining patterns at the intermediate temperatures were bimodal and individuals showed either negligible or moderate/intense apoptosis during the time frame for gonadal differentiation. In all cases, TUNEL labeling appeared to be primarily concentrated in the somatic cells of the anterior region of the right gonad of each individual. Only individuals histologically classified as males showed apoptosis in the weeks following gonadal sex differentiation. These results provide strong evidence that apoptosis is crucial for the formation of the testis during gonadal sex differentiation of pejerrey and that it may be implicated also in TSD of this species.