The wrong mice

时间:2019-03-07 10:15:00166网络整理admin

By Philip Cohen GENDER-BENDING research may be barking up the wrong tree in choosing ultra-male mice to study the environmental effects of chemicals that mimic hormones. A team at the University of California at Davis found that a strain of lab mice commonly used to test these chemicals is unusually insensitive to the effects of the hormone oestrogen. Chemicals dubbed endocrine disrupters, can mimic the effects of oestrogen, and have been linked to feminisation of male sex organs in wild animals. This has raised concerns that similar chemicals polluting the environment might cause changes in human reproductive development. Scientists hunting for such “gender bender” substances prefer the mouse strain CD-1 because they breed quickly and have large litters. But this choice worried Jimmy Spearow, a reproductive geneticist at UC Davis. Spearow and his colleagues knew that animals bred for their fecundity could have unusual responses to reproductive hormones. To see if this was the case for CD-1, Spearow’s team gave different strains of young male mice oestrogen-releasing implants and then compared their reproductive development. The results were dramatic. At the lowest dose, the strain most susceptible to the effects of oestrogen showed a 60 per cent loss in testicular weight. But even at the top dose—sixteenfold higher—the testes of CD-1 males lost barely a third of their weight (Science, vol 285, p 1259). Similarly, the lowest dose of oestrogen all but obliterated sperm production in the most susceptible strains. But even at the highest dose, the hormone merely knocked back maturing sperm by 20 per cent for the CD-1 males. “I never dreamt we would see such a large difference,” says Spearow. “This work opens whole new areas of consideration,” says Kenneth Korach, who heads the laboratory for reproductive toxicology at the National Institute of Environmental Health Sciences in Research Triangle Park, North Carolina. The next question, he says, is which strain of mice is most like a human. “CD-1 may still be the best model for people,