Correlation among Thermosensitive Period, Estradiol Response, and Gonad Differentiation in the Sea TurtleLepidochelys olivacea
Reptile embryos with temperature sex determination have a thermosensitive period (TSP). The finding that exogenous estradiol (E2) overcomes the effect of male-promoting temperature led to the idea that temperature may regulate estrogen concentration in the gonad during TSP. Since interspecific variations in TSP and in the effect of exogenous E2 exist, we undertook a study in the olive ridleyLepidochelys olivacea.Four parameters were correlated: the TSP (time dimension), the thermosensitive stages (rate of development), gonad development (histological aspect), and the estradiol response. Two kinds of experiments were performed: (1) Eggs were shifted once, at different stages of development, from a male-promoting temperature to a female-temperature (or vice versa) for the remainder of development. (2) Eggs at male-promoting temperature were treated once with 6 or 12 μg of estradiol (E2) at various times of incubation. Sex ratio was established around hatching in each experimental series. We found that the temporal dimension of the TSP was around 7 days (Days 20–27 of incubation) at a male-promoting or a female-promoting temperature. The rate of development of the whole embryo and gonadal growth was faster at female-promoting temperature than at male-promoting temperature. Formation of the genital ridge began at stage 21–22 and histological differentiation of the gonads occurred around stage 26–27. Although these stages coincided with the TSP, at male-promoting temperature the thermosensitive stages occurred earlier (from stages 20–21 to stages 23–24) than at female-promoting temperature (from stages 23–24 to stages 26–27). Thus, at male promoting-temperature, sex was determined in embryos with incipient or undifferentiated gonads. In contrast, E2 treatment continued to feminize the gonads of embryos at a male-promoting temperature beyond the TSP up to stage 25–26, but the E2-induced ovaries were significantly smaller than temperature-induced ovaries. It is suggested that the doses of E2 used were higher than the concentration of endogenous E2 required for normal sex determination. The lack of correlation between sex determination and gonad differentiation suggests that irreversible molecular processes underlying sex determination occur earlier at male- than at female-promoting temperature. Results suggest that the male sex may be the default state and that the female condition must be imposed upon it.
Available from: Xiaolong Tang
- "It is in close accord with the established taxonomic relationship and reflects the shift of sex determination modes successively from TSD to GSD (Figure 3). EmSox9 displays the highest similarity to those of turtles and crocodiles which prove to be TSD species (Ferguson and Joanen, 1982; Lang et al., 1989; Merchant-Larios et al., 1997; Morjan, 2003; Spotila et al., 1987; Wibbels et al., 1998), in accord with previous study that Sox9 plays conservative roles in male development of TSD species. Meanwhile, the EmSox9 closely clustered with the Sox9 of snake P. flavoviridis having ZZ/ZW sex determination system (Kawai et al., 2009) rather than E. macularius exhibiting TSD (Valleley et al., 2001). "
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ABSTRACT: Sox9 is an important member of Sox family which is involved in a variety of developmental processes including sex determination and gonadal differentiation. The cDNA of Sox9 from multiocellated racerunner E. multiocellata was cloned using reverse transcription-polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE). The sequence contains a 1497 bp open reading frame, which encodes a 498 amino acid protein with a predicted molecular weight of 55.45 kDa. EmSox9 displays high similarity to those of reptiles, and shows an overall amino acid identity of >82%. We also investigated the tissue-specifc expression of EmSox9 mRNA by realtime quantitative PCR. Sox9 mRNA is present in brain, heart, liver, kidney, gonads and muscle tissues of adult E. multiocellata, with the highest expression in brain and testis. The results indicate that Sox9 may play important roles in some tissues during E. multiocellata neural and gonadal development.
Available from: Jennifer M. Lynch
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ABSTRACT: Typescript. Thesis (Ph. D.)--Duke University, 2003. Vita. Includes bibliographical references (leaves 299-342).
Available from: Graeme C Hays
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