Immunocytochemical identification of GtH1 and GtH2 cells during the temperature-sensitive period for sex determination in pejerrey, Odontesthes bonariensis

The ontogeny of gonadotropin 1 (GtH1) and 2 (GtH2) cells and its possible l ink to gonadal sex differentiation were studied in pejerrey, Odontesthes bo nariensis, by immunocytochemistry using anti-chum salmon beta -GtH1 and bet a -GtH2 antisera. In adults, GtH1 cells were found in the proximalis pars d istalls (PPD) close to the neurohypophysis, whereas GtH2 cells were identif ied surrounding GtH1 cells, at the external layer of the PPD and in the par s intermedia. Essentially the same distribution was observed in larvae. In pejerrey, the phenotypic sex is governed by the temperature during the crit ical period of sex determination (temperature-dependent sex determination, TSD). Female proportions vary gradually from 100% at 13-19 degrees to 0% at 29 degrees, and the critical time of TSD has been estimated to be 3-5, 2-4 , and 1-4 weeks after hatching at 17, 19, and 27 degrees, respectively. Thu s, the expression of both GtHs was examined weekly in larvae reared from ha tching to week 11, at 17, 24, and 29 degrees. The proportion of females at 17, 24, and 29 degrees was, 100%, 78% and 0%, respectively. Histological ov arian differentiation was noticed at 7 and 4 weeks at 17 and 24 degrees, wh ereas testicular differentiation occurred at 7 and 4 weeks at 24 and 29 deg rees. GtH1 cells were first observed at week 3 at 29 degrees and at week 4 at 17 and 24 degrees. These cells increased in number until week 4 and then decreased, disappearing after week 6 at all temperature regimes. GtH2 cell s appeared at week 2 at 24 and 29 degrees and at week 3 at 17 degrees. GtH2 cell number increased until week 3 at 29 degrees and until week 4 at 17 an d 24 degrees and then temporarily decreased, thereafter increasing again. T hese results strongly suggest that GtH1 and GtH2 are expressed by different cells. The fact that GtH1 and GtH2 cells appear just before histological g onadal differentiation at all temperatures, together with the peak of GtH1 and GtH2 cell number during the temperature-sensitive period, suggests that GtHs are related to sex differentiation or TSD in O. bonariensis. (C) 2001 Academic Press.