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The GAL4-UAS system is a biochemical method used to study gene expression and function in organisms such as the fruit fly. It was developed by Andrea Brand and Norbert Perrimon in 1993 and is considered a powerful technique for studying the expression of genes. The system has two parts: the GAL4 gene, encoding the yeast transcription activator protein GAL4, and the UAS (Upstream Activation Sequence), an enhancer to which GAL4 specifically binds to activate gene transcription. == Overview == The GAL4 system allows separation of the problems of defining which cells express a gene or protein and what the experimenter wants to do with this knowledge. Geneticists have created genetic varieties of model organisms (typically fruit flies), called ''GAL4 lines'', each of which expresses GAL4 in some subset of the animal's tissues. For example, some lines might express GAL4 only in muscle cells, or only in nerves, or only in the antennae, and so on. For fruit flies in particular, there are tens of thousands of such lines, with the most useful expressing GAL4 in only a very specific subset of the animal—perhaps, for example, only those neurons that connect two specific compartments of the fly's brain. The presence of GAL4, by itself, in these cells has little or no effect, since GAL4's main effect is to bind to a UAS region, and most cells have no (or innocuous) UAS regions. Since GAL4 by itself is not visible, and has little effect on cells, the other necessary part of this system are the "reporter lines". These are strains of flies with the special UAS region next to a desired gene. These genetic instructions occur in every cell of the animal, but in most cells nothing happens since that cell is not producing GAL4. In the cells that ''are'' producing GAL4, however, the UAS is activated, the gene next to it is turned on, and it starts producing its resulting protein. This may report to the investigator which cells are expressing GAL4, hence the term "reporter line", but genes intended to manipulate the cell behavior are often used as well. Typical reporter genes include: * Fluorescent proteins like green (GFP) or red fluorescent proteins (RFP), which allow scientists to see which cells express GAL4 * Channelrhodopsin, which allows light-sensitive triggering of nerve cells * Halorhodopsin, which conversely allows light to suppress the firing of neurons * Shibire, which shuts neurons off, but only at higher temperatures (30 °C and above). Flies with this gene can be raised and tested at lower temperatures where their neurons will behave normally. Then the body temperature of the flies can be raised (since they are cold-blooded), and these neurons turn off. If the fly's behavior changes, this gives a strong clue to what those neurons do. * GECI (Genetically Encoded Calcium Indicator), often a member of the GCaMP family of proteins. These proteins glow when exposed to calcium, which, in most cells, happens when the neuron fires. This allows scientists to take pictures, or movies, that show the nervous system in operation. For example, scientists can first visualize a class of neurons by choosing a fly from a GAL4 line that expresses GAL4 in the desired set of neurons, and crossing it with a reporter line that express GFP. In the offspring, the desired subset of cells will make GAL4, and in these cells the GAL4 will bind to the UAS, and enable the production of GFP. So the desired subset of cells will now fluoresce green and can be followed with a microscope. Next, to figure out what these cells might do, the experimenter might express channelrhodopsin in each of these cells, by crossing the same GAL4 line with a channelrhodopsin reporter line. In the offspring the selected cells, and only those cells, will contain channelrhodopsin and can be triggered by a bright light. Now the scientist can trigger these particular cells at will, and examine the resulting behavior to see what these cells might do. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「GAL4/UAS system」の詳細全文を読む スポンサード リンク
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