Sex reversal and aromatase in the European pond turtle: Treatment with letrozole after the thermosensitive period for sex determination (original) (raw)
Related papers
Cloning and expression of aromatase in a turtle with temperature-dependent sex determination
General and Comparative Endocrinology, 2003
It has been hypothesized that estrogen production may play a pivotal role in the sex determination of reptiles with temperaturedependent sex determination (TSD). This hypothesis has been furthered by studies that have shown higher aromatase activity in the developing ovaries in some reptiles. However, other studies have not consistently supported this hypothesis. In the current study we addressed this issue by cloning P450 aromatase cDNA in the turtle, Trachemys scripta, and developing a quantitative competitive RT-PCR for aromatase. This assay was then used to quantify aromatase mRNA levels in adrenal-kidney-gonad complexes (AKG) during TSD. Aromatase mRNA was detected in the AKGs at both male-and female-producing temperatures from the earliest stage of development sampled (stage 15), through hatching (stage 26). However, levels remained relatively constant during the thermosensitive period of TSD. Further, no significant difference was detected between male-and female-producing temperatures during the thermosensitive period. After the thermosensitive period, aromatase mRNA levels increased in females (this coincides with the period during which the ovaries are differentiating). These results are consistent with those of several previous studies of certain reptiles with TSD. The current results suggest that the expression of aromatase may not be a pivotal regulatory step in the sex determination cascade of this turtle.
General and Comparative Endocrinology, 1996
triol treatment also resulted in cranially hypertrophied In many turtles the temperature during the middle of oviducts at all incubation temperatures in a dose-depenincubation determines the gonadal sex of the hatchling. dent manner, whereas animals treated with estradiol-Sex steroid hormones have been implicated in tempera-17b and estrone had normal oviducts. These results supture-dependent sex determination in the red-eared slider port the hypothesis that estrogens are involved in the turtle, Trachemys scripta; nonaromatizable androgens final common pathway of female sex determination in are involved in male sex determination and estrogens this species. ᭧ 1996 Academic Press, Inc. and aromatizable androgens in female sex determination. Administration of exogenous estradiol-17b to eggs incubating at a temperature that normally produces only In many reptiles gonadal sex is determined by the males can overcome the effect of temperature and result temperature of the incubating egg, a process known as in all offspring being female. Further, estradiol-17b and temperature-dependent sex determination (TSD). In the incubation temperature synergize to produce a greater red-eared slider turtle (Trachemys scripta), incubation of feminizing effect at intermediate incubation temperaeggs at relatively low temperatures (e.g., 20-28.6Њ) retures that produce mixed sex ratios. This study demonsults in only male hatchlings, whereas relatively high strates that, in the red-eared slider, there is a complex temperatures (e.g., 29.6-35Њ) results in only female interaction between incubation temperature, different hatchlings; when eggs are incubated at temperatures estrogens, and the dosage effect of each hormone. There intermediate to these, varying sex ratios are produced are changes in potency of different estrogens with incu-(Crews et al., 1994). Sex steroid hormones appear to be bation temperature such that estriol is more potent than the physiological equivalent of incubation temperature estrone and estradiol-17b at 26Њ (an all-male producing and both male-and female-producing incubation temincubation temperature), estrone and estriol are equipoperatures and exogenous steroids exert their effects tent to each other and more potent than estradiol-17b at during the mid-trimester of development (Crews et al., 28.8Њ (an incubation temperature that produced a male-1996; Wibbels et al., 1991a). Estrogens and aromatizable biased sex ratio), and estradiol-17b is more potent than androgens induce female sex determination, whereas estrone and estriol at 29Њ (an incubation temperature nonaromatizable androgens induce male sex determithat produced equal numbers of males and females).
General and Comparative Endocrinology, 1997
Reptile embryos with temperature sex determination have a thermosensitive period (TSP). The finding that exogenous estradiol (E2) overcomes the effect of malepromoting 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 ridley Lepidochelys 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 mg 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 femalepromoting 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 thermo-sensitive 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. r 1997 Academic Press Sexual differentiation of the gonads is dependent on incubation temperature in five sea turtle species: Eretmochelys imbricata , Lepidochelys olivacea Caretta caretta Mrosovsky, 1980, 1982), Chelonia mydas Limpus, 1980, Morreale et al., 1982), and Dermochelys coriacea . Pivotal temperatures (temperature during incubation at constant temperature which gives 50% individuals of each sexual
Synergism between temperature and estradiol: A common pathway in turtle sex determination?
Journal of Experimental Zoology, 1991
In many reptiles, the temperature at which the eggs are incubated determines the sex of the hatchlings. Administration of estradiol will counteract the masculinizing effects of a male-producing temperature, resulting in female hatchlings. To address whether temperature and estrogen are biologically equivalent, two experiments were conducted with the red-eared slider turtle, Trachemys scripta. In the first experiment, varying dosages of estrogen were administered at Stage 17 (the middle of the temperature-sensitive window) to eggs maintained at two temperatures, 26°C (which normally produces all males) and 28.2"C (which produces mostly males but lies at the threshold of the transition from male-to female-producing temperatures). Results indicate that estrogen and temperature exert a synergistic effect on sex determination. In the second experiment, estrogen was administered at different stages of embryonic development. The results indicate an estrogen-sensitive period ranging from Stage 14 through Stage 21, a period similar to the temperature-sensitive period for this species. The results of these experiments are consistent with the hypothesis that temperature and estradiol act in a common pathway in temperature-dependent sex determination.
General and comparative …, 1996
triol treatment also resulted in cranially hypertrophied In many turtles the temperature during the middle of oviducts at all incubation temperatures in a dose-depenincubation determines the gonadal sex of the hatchling. dent manner, whereas animals treated with estradiol-Sex steroid hormones have been implicated in tempera-17b and estrone had normal oviducts. These results supture-dependent sex determination in the red-eared slider port the hypothesis that estrogens are involved in the turtle, Trachemys scripta; nonaromatizable androgens final common pathway of female sex determination in are involved in male sex determination and estrogens this species. ᭧ 1996 Academic Press, Inc. and aromatizable androgens in female sex determination. Administration of exogenous estradiol-17b to eggs incubating at a temperature that normally produces only In many reptiles gonadal sex is determined by the males can overcome the effect of temperature and result temperature of the incubating egg, a process known as in all offspring being female. Further, estradiol-17b and temperature-dependent sex determination (TSD). In the incubation temperature synergize to produce a greater red-eared slider turtle (Trachemys scripta), incubation of feminizing effect at intermediate incubation temperaeggs at relatively low temperatures (e.g., 20 -28.6Њ) retures that produce mixed sex ratios. This study demonsults in only male hatchlings, whereas relatively high strates that, in the red-eared slider, there is a complex temperatures (e.g., 29.6 -35Њ) results in only female interaction between incubation temperature, different hatchlings; when eggs are incubated at temperatures estrogens, and the dosage effect of each hormone. There intermediate to these, varying sex ratios are produced are changes in potency of different estrogens with incu- . Sex steroid hormones appear to be bation temperature such that estriol is more potent than the physiological equivalent of incubation temperature estrone and estradiol-17b at 26Њ (an all-male producing and both male-and female-producing incubation temincubation temperature), estrone and estriol are equipoperatures and exogenous steroids exert their effects tent to each other and more potent than estradiol-17b at during the mid-trimester of development (Crews et al., . Estrogens and aromatizable biased sex ratio), and estradiol-17b is more potent than androgens induce female sex determination, whereas estrone and estriol at 29Њ (an incubation temperature nonaromatizable androgens induce male sex determithat produced equal numbers of males and females).
Differentiation, 2007
Many egg-laying reptiles have temperaturedependent sex determination (TSD), where the offspring sex is determined by incubation temperature during a temperature-sensitive period (TSP) in the middle third of development. The underlying mechanism transducing a temperature cue into an ovary or testis is unknown, but it is known that steroid hormones play an important role. During the TSP, exogenous application of estrogen can override a temperature cue and produce females, while blocking the activity of aromatase (Cyp19a1), the enzyme that converts testosterone to estradiol, produces males from a female-biased temperature. The production of estrogen is a key step in ovarian differentiation for many vertebrates, including TSD reptiles, and temperature-based differences in aromatase expression during the TSP may be a critical step in ovarian determination. Steroidogenic factor-1 (Sf1) is a key gene in vertebrate sex determination and regulates many steroidogenic enzymes, including aromatase. We find that Sf1 and aromatase are differentially expressed during sex determination in the red-eared slider turtle, Trachemys scripta elegans. Sf1 is expressed at higher levels during testis development while aromatase expression increases during ovary determination. We also assayed Sf1 and aromatase response to sex-reversing treatments via temperature or the modulation of estrogen availability. Sf1 expression was redirected to low-level female-specific patterns with feminizing temperature shift or exogenous estradiol application and redirected to more intense male-specific patterns with male-producing temperature shift or inhibition of aromatase activity. Conversely, aromatase expression was redirected to more intense female-specific patterns with female-producing treatment and redirected toward diffuse low-level male-specific patterns with masculinizing sex reversal. Our data do not lend support to a role for Sf1 in the regulation of aromatase expression during slider turtle sex determination, but do support a critical role for estrogen in ovarian development.
Seminars in Cell & Developmental Biology, 2009
The developmental processes underlying gonadal differentiation are conserved across vertebrates, but the triggers initiating these trajectories are extremely variable. The red-eared slider turtle (Trachemys scripta elegans) exhibits temperature-dependent sex determination (TSD), a system where incubation temperature during a temperature-sensitive period of development determines offspring sex. However, gonadal sex is sensitive to both temperature and hormones during this period -particularly estrogen. We present a model for temperature-based differences in aromatase expression as a critical step in ovarian determination. Localized estrogen production facilitates ovarian development while inhibiting male-specific gene expression. At male-producing temperatures aromatase is not upregulated, thereby allowing testis development.
Developmental Biology, 2015
Temperature sex determining species offer a model for investigating how environmental cues become integrated to the regulation of patterning genes and growth, among bipotential gonads. Manipulation of steroid hormones has revealed the important role of aromatase in the regulation of the estrogen levels involved in temperature-dependent sex determination. Estradiol treatment counteracts the effect of male-promoting temperature, but the resulting ovarian developmental pattern differs from that manifested with the female-promoting temperature. Hypoplastic gonads have been reported among estradiol-treated turtles; however the estradiol effect on gonadal size has not been examined. Here we focused on the sea turtle Lepidochelys olivacea, which develops hypoplastic gonads with estradiol treatment. We studied the effect of estradiol on cell proliferation and on candidate genes involved in ovarian pattern. We found this effect is organ specific, causing a dramatic reduction in gonadal cell proliferation during the temperature-sensitive period. Although the incipient gonads resembled tiny ovaries, remodeling of the medullary cords and down-regulation of testicular factor Sox9 were considerably delayed. Contrastingly, with ovarian promoting temperature as a cue, exogenous estradiol induced the upregulation of the ovary factor FoxL2, prior to the expression of aromatase. The strong expression of estrogen receptor alpha at the time of treatment suggests that it mediates estradiol effects. Overall results indicate that estradiol levels required for gonadal growth and to establish the female genetic network are delicately regulated by temperature.
Differentiation, 1993
Gonadal differentiation associated with estrogen-induced female sex determination was examined in a turtle with temperature-dependent sex determination, and was compared to ovarian differentiation at a female-producing temperature. Freshly ladi eggs of the red-eared slider, Trachemys scripta, were incubated at a male-producing temperature (26 degrees C) and were experimentally manipulated at one of three embryonic stages: stage 15, 17, or 20 (i.e. early, midway, or late in the temperature-sensitive and estrogen-sensitive periods). At those developmental stages, groups of eggs were either: (1) treated with a control solution (95% ethanol) and placed back at the male-producing temperature, (2) treated with 10 micrograms of estradiol-17 beta and placed back at the male-producing temperature, or (3) shifted to a female-producing temperature (31 degrees C). Additionally, a control group of freshly laid eggs was continually incubated at 31 degrees C throughout embryonic development. To examine morphological events occurring after the treatments, a subset of embryos from each group was examined at the time of the treatment and at 1-2 stage intervals following the treatments. The results indicate that estradiol-17 beta as well as female-producing temperature may ensure female sex determination by facilitating medullary cord regression. Further, the results reveal a chronology of differentiation in which medullary cord regression temporally precedes cortical proliferation.
Embryonic sex steroid hormones accumulate in the eggshell of loggerhead sea turtle (Caretta caretta
Steroids hormones such as estradiol-17b (E2) and testosterone (T) are involved in gonadal differentiation of oviparous animals with temperature-dependent sex determination (TSD), and are greatly distributed. This hypothesizes that these embryonic steroid hormones probably accumulate in the eggshell throughout blood or/and chorioallantoic fluid in sea turtle species with TSD, producing females at higher temperature. To demonstrate this hypothesis, concentrations of E2 and T in the blood plasma from the hatchling loggerhead sea turtle (Caretta caretta) and in their eggshells were measured by radioimmunoassay. In the present study we propose that both concentrations of E2 and T in the blood plasma are correlated with amounts of these sex steroids in the eggshell. Moreover, contents of E2 in the eggshell showed a significant positive correlation with mean incubation temperatures during a thermosensitive period in the experimental nests, whereas T contents in the eggshell did not. Taken together, these findings indicated that embryonic E2 and T that accumulated in the eggshell can be extracted and measured. Furthermore, the present study suggested that contents of E2 in the eggshell may differ between male and female, and monitoring of these steroids is a useful method to identify the sex of loggerhead sea turtle hatchling.