科技 延长寿命 谢啦，老妈！

　　An obscure group of animals may reveal the secret of elongating life

　　一群不为人知的动物可能会揭开长寿之谜

　　THE one sure way to prolong an animal's life is, paradoxically, to starve it. "Caloric restriction", as it is known in the trade, works for everything from threadworms to mammals (people included, as far as can be ascertained without the luxury of controlled experiments). So it is no surprise that it also works for a group of small creatures known as rotifers. If that were the only result of Shugo Watabe's experiments on the critters, at the University of Tokyo, it would scarcely be worth reporting. What makes this news is that the offspring of the rotifers in question also lived longer than normal. And that—the inheritance of an acquired characteristic—is quite startling.

　　矛盾的是，延长动物寿命的方法，竟然是使其挨饿。科学界的同行都知道，有名的"热量限制"法则对小至线虫，大至哺乳动物的动物界都适用（包括人类，就还未有大量的对照实验验证而言）。所以当该条法则运用到一群名叫轮虫的生物上也就不足为奇了。如果东京大学的修吾渡部的轮虫实验仅是如此的话，也就没有报道的价值了。具有新闻价值的是，上述轮虫后代的生命也比普通轮虫要长。那后天的从父辈继承下的特质实在很令人吃惊。

　　Rotifers are unusual in that they often reproduce by parthenogenesis (some species, indeed, can reproduce only in this way). A parthenogenetic population is, by definition, all female and the result, give or take the odd mutation, is that a rotifer's daughters are genetically identical to her. That makes rotifers convenient subjects for studies of the controversial idea that characteristics acquired during an individual's life can be passed down the generations in ways that are independent of mutations in the DNA.

　　轮虫并不普通，因为他们的繁殖方式是孤雌生殖（确实，一些物种甚至只有这一种繁殖方式）。顾名思义，孤雌生殖群体全是雌性；如果没有接受和传递罕见基因突变，那么轮虫的雌性后代与母体是完全相同的。这使得轮虫成为十分方便的研究对象：人们对在个体生命期中，后天习得的特征与繁殖后代中的DNA突变并不相关这个观点存在争议。

　　Dr Watabe and his colleagues first looked at whether caloric restriction does, indeed, work its magic on rotifers. It does. Without it, as they report in Functional Ecology, their animals lived for an average of 8.8 days. With it they lived for 13.5 days. The intriguing result came when they did the same thing with the rotifers' offspring. The daughters of those rotifers which had been fed as much as they could eat lived for 9.5 days if treated likewise (not significantly different from their mothers) and 14.4 if put on short commons. Those born of calorie-restricted mothers lived for 12.7 and 16.8 days respectively. Something, then, is being passed on that is having an effect down the generations.

　　渡边博士和他的同事第一次研究热量限制的机制是否对轮虫同样有效。确实有效。他们在《机能生态学》杂志上报道说，没有了热量限制，轮虫的平均生命期为13.5天。当它们对轮虫的后代采取了同样的热量限制后，得到了有趣的结果。轮虫的母系如果得到了饱和的食物量，它们那些也同样饱食的后代可以存活了9.5天（与其母系的上一代并无明显区别），如果后代食物量减少，则可以活14.4天。那些诞生于热量限制的母系后代则在饱食和不饱食的情况下分别存活了12.7 和16.8天。那么，一定有某种物质通过上下代传递，对个体生命产生了影响。

　　That something seems to be related to an enzyme called catalase. This enzyme degrades hydrogen peroxide, a highly reactive chemical that creates cellular damage of the sort associated with ageing. Dr Watabe found that the offspring of calorie-restricted mothers have more catalase than those of mothers who were fed without restriction.

　　这种物质似乎与一种名叫过氧化氢酶的酶有关。这种酶分解过氧化氢这种反映活性很高、可以在细胞老化过程中损害细胞的物质。渡边博士发现这种经过热量限制的母体的后代，其过氧化氢酶含量比没有食量限制的母体后代更多。

　　The researchers also detected higher levels of the enzyme in the eggs of calorie-restricted mothers, so it could be that their offspring are simply endowed with the stuff. A more intriguing possibility, though, is that the relevant genes are affected by epigenesis, a process in which chemicals attached to the DNA control its activity. Epigenetic modifications are often retained when cells divide, and can sometimes be passed on to offspring.

　　研究人员同时检测了得到热量控制的母体产下的卵，它的过氧化氢酶浓度较高，所以这可能是这些后代与生俱来的。然而，一个更有意思的可能性是后生作用影响了这些基因。后生作用是指与DNA相接的化学物质来控制其活动。细胞分裂期往往阻碍表观遗传修饰，并且会把这种机制传递给下一代。

　　If inherited epigenetic changes were causing daughter rotifers to produce more catalase, it would raise the question of whether a similar thing happens in other species and, if so, whether it might be induced artificially, without all the tedious business of a lifetime's starvation. That would certainly be worth looking at. The search for an elixir of life has taken people to some strange places. Few, though, are stranger than rotifers.

　　如果母系轮虫后代从母体继承了后生变化，产生了更多的过氧化氢酶，人们同样也会考虑相似的事情会不会也发生在其他物种上；而且，如果同样发生，可否通过人工诱导的方法，而不是通过冗长到一辈子都饿着肚子。长生不老的研究已经将人类指向了一些奇怪的领域。而没有几个比轮虫更奇怪的了。