新普京娱乐网址

Minuscule but perfectly formed

作者:洪蹦    发布时间:2019-03-07 07:17:10    

By Philip Cohen BIG flies, small flies—their cells are all the same size, right? Not necessarily. Miniflies made of tiny cells have got biologists puzzling over how animals control their size. They have also suggested a new battle plan in the fight against cancer. Some neurons and muscle cells in a Great Dane, for instance, are significantly larger than those in a cocker spaniel. But most of the cells in the two breeds are the standard size—the larger dog simply has more of them. What isn’t clear is how each cell “knows” that there has been enough growth and replication to make an animal of normal size. “No one has any idea yet of how cells sense that,” says George Thomas, a developmental biologist at the Friedrich Miescher Institute in Basel, Switzerland. Even when biologists have used genetic trickery to shrink cells in fruit flies or make them larger in salamanders, the resulting animals were the usual size, but simply had more or fewer cells than normal. But another kind of genetic engineering has thrown up a different result. Thomas and his team were breeding flies with a mutation in a gene that produces S6 kinase, an enzyme the fly needs to respond to a particular growth factor. They found that the mutant flies had cells that were just two-thirds the normal size. The researchers thought the insects would simply compensate by producing more cells to reach the same bulk. But instead, the mutant flies had exactly the same number of cells, so they were tiny and weighed about half as much as a normal fly (Science, vol 285, p 2126). “Everything in the fly is perfectly in proportion, just smaller,” says Thomas. Martin Raff, an expert on animal development at University College London, suspects S6 kinase is involved in helping cells sense the total cell mass in flies. Without it, they can only control size by counting the number of cells. “What it really emphasises is how little we still know,” he says. “This experiment should catalyse a lot of interest in the field.” Thomas also found that the S6 kinase mutation not only shrinks cells and reduces overall bulk,

 

Copyright © 网站地图