Browsing by Subject "Temperature-dependent sex determination"
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Item Elucidating the molecular network underlying temperature-dependent sex determination in the red-eared slider turtle, Trachemys scripta(2009-05) Shoemaker, Christina May; Crews, DavidComponents of the molecular pathway underlying gonadogenesis in organisms with temperature-dependent sex determination (TSD) have been retained from genetic sex determination. Furthermore, although much of this network has been conserved, new functions for these genes have evolved in this different mode of sex determination. We find that the transcription factors Sox9 and Dmrt1 and the hormone Mis are involved in the formation of a testis and/or the repression of an ovary at a male-producing temperature. While Mis expression may be maintained by Sox9, the initial upregulation of Mis in the developing testis is most likely modulated by some other upstream factor. Dmrt1 appears to play an upstream role in testis sex determination. We provide evidence that the transcription factor Dax1 and the signaling molecule Wnt4, cloned for the first time in an organism with TSD, play roles in gonadogenesis in both sexes. Finally, we show that the transcription factor FoxL2 and the signaling molecule Rspo1 are involved in the formation of an ovary and/or the repression of a testis at a female-producing temperature. In the first investigation of Rspo1 in any organism exhibiting TSD, we demonstrate it is involved upstream in ovarian sex determination. Complementary to descriptive studies, we optimize a whole organ culture system in which gonad explants develop in vitro for up to three weeks. We show that expression of the sex-determining network in isolated gonads mimics in ovo patterns, revealing an endogenous temperature-sensing mechanism that does not require other embryonic tissues. Ectopic expression of Sox9 reveals a possible positive feedback regulation of Dmrt1. The use of this culture system opens the door to functional manipulation of the gonad at the molecular level and is suitable for a myriad of future studies. This work makes strides in elucidating the molecular network underlying gonadogenesis in an organism exhibiting TSD, and invites investigation of the evolution of gene function. The data lend insight into the changing roles of molecules in sex determination across diverse taxa, and into the evolution of developmental pathways in general.Item Ontogenetic and mechanistic explanations of within-sex behavioral variation in a lizard with temperature- dependent sex determination(2013-12) Huang, Victoria; Crews, DavidThe leopard gecko (Eublepharis macularius) is a reptile species in which embryonic temperature contributes both to sex determination and within- sex polymorphisms. Its life history makes the leopard gecko a model system for seeking ontogenic and proximate explanations for within-sex variation in sexually dimorphic behavior and neurophysiology, necessary attributes for reproductive success. For my dissertation I have incorporated the role of androgens that potentially modulate incubation temperature effects on behavioral and brain variation, which I approached using embryo and adult leopard geckos. First, I found that that the bias of same-sex clutch siblings is primarily incubation temperature- dependent and any maternal or genetic effects on same-sex clutch siblings are secondary. Second, I found that testosterone concentrations in the yolk-albumen were higher in eggs of late development than early development at 26 °C, a female-producing incubation temperature, but did not differ from eggs incubated at another female-biased temperature. This increase in testosterone concentrations during the temperature sensitive period in putative females is a finding opposite of reported trends in most other reptiles studied to date. Further, I found that the embryonic environment influences male sociosexual investigation in the absence of gonadal hormones. Lastly, in adult males of 32.5 °C, a male-biased incubation temperature, I found that the phosphoprotein DARPP-32 that is activated by the D1 dopamine receptor in limbic brain regions is correlated to this sociosexual investigatory behavior. Neurons immunopositive for phosphorylated DARPP-32 were not only less dense in the nucleus accumbens of males who spent more time with other males, but also more dense in the preoptic area of males who spent more time with females. The use of phosphorylated DARPP-32 as marker for sociosexual exposure is novel in a lizard species. Taken together, in support of previous studies, these results show that differences in embryonic environment stem primarily from incubation temperature, can explain behavioral differences in adulthood in the absence of hormones, and, in concert with hormonal manipulation, can influence neuronal marker sensitivity to sociosexual exposure.