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SCIENCE, VOL. 255

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Anything Goes at the Cell Biology Meeting

dence that RNA is contained within specific compartments in the nucleus. They see recently synthesized RNA only within small, discrete islands they call "transcription domains." The domains also appear to contain the machinery for snipping noncoding seThese days, cell biology is pretty much an umbrella term describing anything that quences out of the RNAs and performing can happen inside or outside a cell. And perhaps nothing illustrates that point better the other modifications necessary before than the annual meeting of the American Society for Cell Biology, which drew more they are exported out of the nucleus. In than 7000 biologists to Boston last month to hear talks on topics ranging from contrast, the group finds that DNA synthecellular architecture and embryonic development to neurobiology and immunology. sis, particularly of DNA that replicates later in the cell cycle, is sequestered in very differThe following summarizes some highlights of the meeting. ent regions of the nucleus, which means that something is physically separating the DNA But the treatments used were so harsh, say and RNA compartments. New Evidence Found for a disbelievers, that they might have artificially In further support of a nuclear matrix, the caused nuclear proteins to bind together in Lawrence lab traced the fate of newly synNuclear Matrix what appears to be a meshwork, even though thesized RNA molecules, reasoning that a Is it real, or is it artifact? That's a question no such thing actually exists in nature. nuclear architecture should include a conmany cell biologists have been asking since What's more, because the putative matrix duit system for exporting these molecules to the mid- 1980s about "the nuclear matrix," proteins are extremely insoluble, no one has the cytoplasm, where they ultimately direct a network of interlaced protein filaments been able to isolate and characterize them. protein synthesis. And in fact, that's exactly thought to provide a sort of internal skel- In addition, every cell type seems to have a what they saw. Tagging newly transcribed eton for the nuclei of the cells of higher distinct set of proteins making up its matrix. RNA molecules gives tracks radiating to the The trick then has been to demonstrate a nuclear membrane. That work, says Ken organisms. Recently, however, evidence in favor of a nuclear support system has started regular nuclear architecture, without know- Carter, a postdoc in the Lawrence lab, had to come in from several researchers, includ- ing exactly what proteins are involved and nuclear matrix proponents, "jumping out of ing Jean Lawrence and her colleagues at the under conditions that do not disturb what- their skin." All in all, the experimental University of Massachusetts Medical School ever structures may be there. To perform foundation for a nuclear matrix is becomin Worcester, who presented their new data that feat, the Lawrence group made use of ing much more solid. in a talk and several posters in Boston. a technique they developed for quite a If they're right, it would mean that the different purpose. In 1987 the researchers conventional wisdom about how the genetic worked out a scheme to locate the exact Fruit Fly Learning Research materials DNA and RNA are synthesized position of a gene on a specific chromo- Mushrooms would have to be revised. The current view is some. They found they could pinpoint the that these synthesis reactions occur anywhere gene's position more precisely if they When researchers started to investigate learnwithin the aqueous medium that fills the tagged it with a fluorescent probe during ing and memory in the fruit fly Drosophila nucleus. But if there is a matrix, the nucleus interphase, the part of the cell cycle when melanogaster a few years ago, it seemed like would be more highly organized and the the chromosomes are least tightly wound. a match made in heaven, the perfect marriage Lawrence and her colleagues subse- between genetics and physiology. Initially, reactions would likely take place at discrete sites within the cell's nucleus, possibly while quently showed that the technique, which is however, the matchmaking didn't go so well. the synthetic machinery is attached to the relatively gentle, could also be used to lo- The genetics were there, but like a shy bride, the brain's locus for learning was not showmatrix itself. Such a J ing itself. And without knowing where in the situation would alter , brain learning takes place, it would be imposthe current percep- of sible to correlate physical changes with altertion of the geometry W ations in the genes associated with Drosand hence of the very t ophila learning. But all that has begun to mechanism and regu- M change as a result of recent work by Ron lation of nucleic acid Davis and his colleagues at Cold Spring Harsynthesis. bor Laboratory. They've found that a brain The doubts about the existence of a Located together. The same cell stained for RNA (left) and structure known as the mushroom body because of its shape is the primary site for nuclear matrix stem snRNPs, which are part of the RNA splicing machinery (right). learning and memory in Drosophila, and from the way the early experiments purporting to show its cate sites of active gene expression, where have begun to trace out the candidate existence were done. In those experiments, DNA is being copied into RNA. During memory genes that are active there. And at done independently in several labs, research- that work, they noticed that the active genes the meeting, Davis outlined some of the ers treated the nucleus with degradative are limited to the inner 50% of the nuclear work leading up to this conclusion as well as enzymes called nucleases that remove all of volume, which suggested that there was a some new work that strengthens it. The first clue to the mushroom body's the nucleic acids and also with detergents defined place within the nucleus for tranand salts that remove almost all of the pro- scription and hence a defined nuclear archi- importance came early this year, when Davis found that dunce, a mutant gene associated teins. When all those cellular elements were tecture to support it. In their most recent work, members of with learning defects in the fruit fly, is excleared away, a meshwork of protein filaments-the nuclear matrix-still remained. the Lawrence lab have found further evi- tremely active in that brain region (see

New evidence found for a nuclear matrix.

34 SCIENCE, VOL. 255 Downloaded from on March 28, 2016 Anything Goes at the Cell Biology Meeting dence that RNA is contained within specific compa...
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