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Research Highlights

Copies on the fly

As if there were not already enough flies buzzing around, researchers in Canada have now succeeded in cloning the fruit fly Drosophila melanogaster. Lloyd and colleagues employed a standard cloning technique, nuclear transfer, but added their own twist to it: instead of transferring nuclei from adult cells, they removed nuclei from developing embryos to inject them into fertilized fly eggs. Out of approximately 800 transfers, only a small percentage of embryos developed into larvae and only 5 produced adult flies. Besides representing the first time any insect has been cloned, this work may also be relevant for better understanding the cloning process in higher animals, including humans. Most importantly, it may help elucidate why the seemingly straightforward process of cloning animals is often riddled with problems, such as low efficiency and high morbidity. Although the fruit fly has long been a model organism for studying reproductive biology, cloned flies could in the future serve as an alternative model for the study of therapeutic cloning in large mammals. (Genetics published online 16 October 2004, doi: 10.1534/genetics.104.035113) GTO

Male contraceptive

Although a greater number of contraceptives have traditionally been available for women, a recent report in Science suggests that men may soon also have greater choice. A group of scientists from the United States and India have shown that the fertility of male monkeys can be inhibited by immunization with Eppin, a protein specific to the testis and epididymis. The approach appears highly successful: all the male monkeys that produced high titers of Eppin antibodies in their serum and semen were infertile. What's more, the effect was reversible, with 71% of monkeys recovering fertility within 451 days after immunizations were halted. The authors speculate that anti-Eppin antibodies cause infertility by disrupting Eppin's interactions with the sperm surface or with semenogelin, a protein component of semen. Although hormone-based male contraceptives are currently being tested in clinical trials, this study suggests that men may one day have the option of a nonhormonal immunocontraceptive. (Science 306, 1189–1190, 2004) NC

Tethered arrays tell the story

Proteases, which number in the hundreds and figure in regulatory pathways of normal and disease processes, cannot be studied by high-throughput technologies, particularly those that look at expression levels. As most proteases are synthesized as zymogens (inactive precursors) and activated post-translationally, protease activities cannot be assessed by either message or protein levels. Now, Winssinger et al. have devised a platform that measures protease activity specifically and sensitively, and can also be used with complex mixtures. They created libraries of peptide nucleic acid (PNA) substrates conjugated with a fluorogenic probe, which, after being incubated with proteases, are sorted by hybridization to an oligonucleotide array, the sequences of which are linked to the PNA sequence. By creating libraries with hundreds of elements, they are able to determine the precise specificity of the proteases, in contrast to previous attempts to catalog proteases that determined only broad specificities. In the PNA system, the reaction is catalytic, thus the signal is amplified and able to detect picomoles of protease. In addition, the protease reaction is carried out in solution (rather than on a surface), which also favors the activity. A companion article uses mechanism-based probes that irreversibly bind to proteases to capture and later purify proteases from complex mixtures. (Chem. Biol. 11, 1351–1360, 2004) LD

Teasing apart a strong relationship

To tease apart a complex interrelationship, researchers have simultaneously studied the global transcription patterns of a plant and its associated, nodule-forming bacteria. The fixation of atmospheric nitrogen in a form that is available to legumes involves an intricate symbiotic relationship between the plant host and Rhizobium bacteria. The plant's roots secrete signals that induce the expression of nod (nodulation) genes in the free-living bacteria, which leads to synthesis of a bacterial factor that stimulates the growth of nitrogen-fixing nodules on the plant's root. Eventually, bacteria invade the plant and differentiate into bacteroids able to convert dinitrogen into bioavailable ammonium. To understand this complex process, Barnett et al. designed a microarray containing both the complete genome of the bacterium Sinorhizobium meliloti and about 10,000 probe sets from root libraries of the host legume, Medicago truncatula. The chip allows characterization of the gene expression profile and differentiation state of both organisms simultaneously, facilitating the study of the signal-and-response pattern underlying the symbiotic relationship. (Proc. Natl. Acad. Sci. USA 101, 16636–16641, 2004) MZ

RNAi takes on cholesterol

The therapeutic potential of small interfering RNA (siRNA) has recently been demonstrated in several animal models of disease and infection. But from a clinical perspective, the delivery methods adopted thus far are experimental (viral vectors), limited (local administration) or not relevant (high-pressure, high-volume intravenous injection). Writing in Nature, Soutschek et al. report a significant therapeutic benefit from synthetic siRNA delivered into the tail vein of mice at normal pressure and volume. To stabilize the siRNA and improve its pharmacokinetic properties, the authors used a partial phosphorothioate backbone, 2′-O-methyl substitutions and conjugation to cholesterol. The siRNA was designed to silence apolipoprotein B (apoB), a key player in the control of blood cholesterol levels. Systemic siRNA treatment of mice fed a normal diet led to sharp reductions of apoB mRNA in the liver and jejunum and of apoB protein in the blood. Serum cholesterol levels dropped substantially, with decreases of 40% in low-density lipoprotein, 25% in high-density lipoprotein and 37% in total cholesterol. It remains to be determined whether this approach has any negative side effects and whether it can be translated to human patients with hypercholesterolemia. (Nature, 432, 173–178, 2004) KA

Research Highlights written by Kathy Aschheim, Nadia Cervoni, Laura DeFrancesco, Gaspar Taroncher-Oldenburg and Mark Zipkin.

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Research Highlights. Nat Biotechnol 22, 1531 (2004).

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