All ZZ male Xenopus laevis provides a clear sex-reversal test for feminizing endocrine disruptors

Determining the optimal developmental stages of Xenopus laevis for initiating exposures to chemicals for sensitively detecting their feminizing effects on gonadal differentiation

“…Therefore, we propose that high concentrations of estrogens with strong estrogenic activities have potential to result in gonadal feminization even if when the gonads have lower sensitivity to estrogens, whereas it will not effectively induce sex-reversal of genetic males with lower sensitivity when the concentrations of estrogens decrease. In consistence with our results, Oka et al (2006) reported that when exposure was initiated at stages 49/50 (at which gonadal differentiation is low sensitive to estrogens according to our propose), 10 nM estradiol resulted in gonadal feminization of all genetic male X. laevis, whereas 0.1 nM estradiol only induced 16.7% hermaphroditism (Table 1). In Kloas' studies, 1.5 g/L (5.5 nM) estradiol resulted in similar female percentages (92.3-95.8%) whether exposure began at stages 45/46 or stages 47/48; however, when the concentration of estradiol decreased to 0.2 g/L (0.73 nM), exposure beginning at stages 45/46 produced 88.4% phenotypic female, with 5% males, whereas phenotypic females decreased to 70.5% and phenotypic males increased to 25% when exposure began at stages 47/48 (Lutz et al, 2008;Wolf et al, 2010).…”

“…Thus, estrogenic EDCs have become one of suspicious contributors to global amphibian declines in recent years (Collins, 2010;Hayes et al, 2010a). Although many amphibian species have been demonstrated to be sensitive to estrogenic EDCs (Hogan et al, 2008;Ohtani et al, 2001), Xenopus laevis is the most used model species for detecting feminizing effects of EDCs on amphibians (Kloas, 2002;Oka et al, 2006). For example, some EDCs with weak estrogenic activities, such as BPA and PCBs, were reported to cause significant intersexes in X. laevis (Kloas et al, 1999;Levy et al, 2004;Qin et al, 2003).…”

Sex reversal assessments reveal different vulnerability to endocrine disruption between deeply diverged anuran lineages

“…Different estrogenic compounds with concentrations reaching from the low nanogram- to the high microgram-per-liter range have been shown to provoke phenotypic male-to-female sex reversals in X. laevis 46 47 48 models. To our knowledge, only one previous study 26 has examined sex reversals after EE2-exposure using molecular sexing in X. laevis , examining a similar range of concentrations (90, 840, 8,810 ng/L).…”

Developmental disorders and altered gene expression in the tropical clawed frog (Silurana tropicalis) exposed to 17α‐ethinylestradiol

“…laevis and S . tropicalis , resulting in female‐biased sex ratios and the induction of testis‐ova (Oka et al ., : Pettersson et al, ). A high incidence of testis‐ova was found in wild populations of R .…”

“…Amphibians are good models for studying metamorphosis and sex reversal triggered by thyroid hormones and estrogenic chemicals, respectively (Kloas, ; Kloas et al ., ; Villalpando and Merchant‐Larios ; Mitsui et al ., ; Oka et al ., , ; Opitz e t al ., ). During their different developmental phases (tadpole and frog, respectively), amphibians occupy distinctive habitats, and change in habitat is accompanied by dietary changes, indicating high adaptation for various environments.…”