Assessment using hydra of endocrine disruptors contaminated in freshwater environment

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The effects of bisphenol A (BPA), an estrogenic compound, on asexual and sexual reproduction were examined in an evolutionarily primitive invertebrate, Hydra oligactis, living in freshwater environment. When hydra was fed and cultured at 20℃, it continuously produced buds (asexual reproduction). When hydra exposed to low temperature (10℃) was starved, it started to produce gonads (sexual reproduction) in stead of buds. BPA at 0.5-4 ppm given to male or female hydra under the condition for sexual reproduction had the adverse effects not selectively on testis formation (differential effects were expected because of estrogenic nature of the compound) but both on testis and egg formation. On the other hand, BPA at 0.5-1 ppm had stimulatory whereas that at 2-3 ppm had suppressive effects on the budding under the condition for asexual reproduction. When male hydra placed at 10℃ was continued to feed, it produced buds as well as testes. Interestingly, doses of BPA required for stimulatory and adverse effects on budding were lower at 10℃ than at 20℃. The fact suggested more accumulation of BPA in hydra at lower temperature, which is proven correct with radio-labeled BPA, It is known that processes involved in testis differentiation are sensitive to high temperature. We showed here that the condition under which budding was stimulated by BPA at 0.5-1 ppm, caused suppression of testis formation even at low temperature. Balance between proliferation of stem cells and differentiation into gonad cells seems to be decisive of budding or testis formation. All these facts suggest that BPA at relatively high doses affect sexual and asexual reproduction of hydra maybe via effects on proliferation of stem cells and differentiation of committed stem cells into germ cells.