Neuroscientists now have an atlas of which genes are active in the brain
神经科学家们现在有了一张图谱，从中可以知道哪些基因在脑中表现活跃
MENTION the words “billionaire” and “Microsoft” in the same sentence, and the mind turns naturally to the name William Henry Gates III. But Bill Gates's original accomplice, Paul Allen, is not short of a dollar, either. Like Mr Gates, Mr Allen has devoted part of his fortune to charity. But whereas Mr Gates's billions are combating various diseases that plague poor countries, Mr Allen's cash has been focused on a single project. The full title of his organisation is the Allen Institute for Brain Science, and the project—just completed —is an atlas of the brain.
The brain is the most complex organ in the body. Indeed, it could be argued that it is the most complex object in the known universe, and it is only recently that tools sophisticated enough to examine it in detail have been developed. The Allen Institute has used one of these tools, known as in-situ hybridisation, to look at the activity in the brain of almost every gene in the genome. The result is available to all at www.brain-map.org.
When a gene is active it produces messenger molecules that tell cells what to do. In-situ hybridisation works by detecting these messengers using molecules that bind specifically to each. These, in turn, are tagged with dye molecules that show up purple under a microscope.
Since human brains are hard to come by in large numbers, and almost impossible to obtain fresh and whole, the institute's scientists, led by Allan Jones, used mouse brains instead. That is obviously a compromise, but at this early stage in research, it is not a huge one. The mouse and human genomes are similar, and although mouse brains are smaller than human ones and have a different shape, the basic anatomy is the same. Dr Jones and his team therefore bred an enormous number of mice, killed them, sliced up their brains into thin layers, and “developed” each layer with a solution containing molecular tags for the messenger from one particular gene. Cells in which the pertinent gene was active turned purple, and each slice was then photographed.
The atlas itself was constructed by reassembling the photographs into three-dimensional images of the activity pattern of each gene. And the result held some surprises. The first surprise was that about 80% of the 21,000 genes in the mouse genome are active in the brain. That was more than had been expected, although it is not yet clear how many of that 80% are brain-specific.
The second surprise was that any gene which is active in the brain at all tends to be active everywhere. The assumption had been thatbecause different bits of the brain do different things, they would show different activity patterns. That they do not will disappoint pharmaceutical companies who hoped that drugs might be tailored to hit particular parts of the brain by concentrating on genes that are active in those parts only.
On the other hand, the ability of the brain atlas to look at individual cells allows particular types of nerve cell to be recognised by their gene-activity patterns. The project has identified several hundred types of nerve cell this way, so it may be possible to tailor drugs to particular cell types, if not to particular brain regions.
Whether that will prove useful remains to be seen. But what the brain atlas seems to be showing is that different areas of the brain use the same parts list—just as different computers use the same sorts of electronic components. What matters is the way the parts are wired together. Discovering that circuit diagram is a job for the next brain atlas.
这有多大用处还不得而知。脑图谱所展示的是大脑的不同部位所用的“零件”是一样的，就像不同的电脑采用的是一样的电子元件。真正重要 的是这些零件怎样连接。下一个脑图谱的任务就是探索这些连接环路的构造了。翻译 by epicure