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Myosin VI insert responsible for reverse motion

876 Competition, not cooperation, drives biofilm production979 Intestinal microbiota can alter energy balance1039 Critical neural pathway connecting nose to brain1087 North China’s earliest crops

BIOPHYSICS

Myosin VI insert responsible forreverse motionMyosin motor proteins ‘‘walk’’ along actin filaments, generatingbiological motion such as skeletal muscle contraction. Most myo-sins move toward the rapidly growing, or plus, end of the fila-

ments. However, myosin VI,despite its extensive sequenceand structural homology withplus end myosins, walks in theopposite direction. In two sepa-rate studies, Hyokeun Park etal. and Zev Bryant et al. foundthat a class-specific stretch ofamino acids located betweenthe myosin VI converter regionand its lever arm is critical forthis reverse motion toward theminus end of actin. Withoutthis insert or with a truncatedversion, myosin VI walked to-

ward the plus end of the actin filaments; it changed course whenthe insert was reattached. An unusual rotation of the converterdomain underlies the myosin VI power stroke, contributing to itslarge and variable step size. This unconventional movement mayhelp myosin VI play diverse roles in cells, including endocytosis,cell migration, and the maintenance of stereociliar membrane ten-sion in the inner ear. — F.A.

‘‘The power stroke of myosin VI and the basis of reverse directionality’’by Zev Bryant, David Altman, and James A. Spudich (see pages772–777)

and

‘‘The unique insert at the end of the myosin VI motor is the soledeterminant of directionality’’ by Hyokeun Park, Anna Li, Li-QiongChen, Anne Houdusse, Paul R. Selvin, and H. Lee Sweeney (seepages 778–783)

EVOLUTION

Competition, not cooperation, drivesbiofilm productionA central aspect of microbial life, biofilms consist of a com-munal ‘‘slime’’ of enzymes and polymers secreted by micro-bial cells. Biofilm communities often consist of multiplestrains and species. Little isknown about how these dis-parate groups cooperate andavoid ‘‘cheater’’ strains thatbenefit from the biofilmwithout expending energy toproduce and secrete com-ponents. Joao Xavier andKevin Foster carried out sim-ulations, using individualsfrom different microbialstrains, that considered carbon f luxes, involved from the up-take of a substrate (glucose), between growth and secretion.The authors observed that evolutionary forces favored poly-mer secretion. Within bacterial lineages, rapid secretion al-lowed cells to push future generations into more favorable,nutrient-accessible positions within the biofilm. At the sametime, the expansion of these productive cells suffocated less-active polymer producers. Xavier and Foster likened thisstrategy to vertical growth in plants, with the cells of a treetrunk dividing to allow descendents to rise up to the bestgrowth conditions while blocking out sunlight from competi-tors. Multilineage biofilm communities do not need to de-velop a global cooperation system, the authors say, becausethe selfish drive of each strain ensures that all members willcontribute to the production of the entire biofilm. — N.Z.

‘‘Cooperation and conflict in microbial biofilms’’ by Joao B. Xavierand Kevin R. Foster (see pages 876–881)

Model of myosin VI power stroke.

Pseudomonas aeruginosa biofilm.

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MEDICAL SCIENCES

Intestinal microbiota can alterenergy balanceThe intestinal tract is host to a vast microbial community thatcan be viewed as an integral part of human metabolism. Intesti-nal microbiota thus should be factored in formulating energybalance equations. Fredrik Backhed et al. highlight two com-plementary pathways by which gut microbes can affect the de-velopment of obesity. The authors find that germ-free mice,engineered to lack an intestinal biota, were protected from obe-sity when fed a Western-style diet. The leanness of the micewas associated with increased liver and skeletal-muscle levels ofphosphorylated AMP-activated kinase (AMPK), a molecular‘‘fuel gauge’’ that monitors cellular energy metabolism. Thisobesity protection in germ-free mice was abolished if the ani-mals lacked fasting-induced adipose factor (Fiaf), a lipoproteinlipase inhibitor that is normally suppressed by gut microbes.Although Fiaf-knockout mice had high levels of AMPK, theyhad reduced expression of other genes involved in fatty acidmetabolism. Backhed et al. suggest that targeting componentsof the microbiota and/or microbe-regulated gene products suchas AMPK and Fiaf may provide strategies for preventing diet-induced obesity. — N.Z.

‘‘Mechanisms underlying the resistance to diet-induced obesity ingerm-free mice’’ by Fredrik Backhed, Jill K. Manchester, Clay F.Semenkovich, and Jeffrey I. Gordon (see pages 979–984)

NEUROSCIENCE

Critical neural pathway connecting noseto brainThe neurons dedicated to the sense of smell have �1,000different odorant receptors to detect the �3,000 volatile chemi-cals responsible for different scents. In mammals, these olfac-

tory sensory neurons of thenose send out axons to theolfactory bulb in the brain,where they coalesce into glo-meruli and make synapses.Each glomerulus is populatedby axons expressing the sameodorant receptor, but howthese axons sort themselvesinto odorant receptor-specificstructures has remained un-

clear. To determine the factors that govern glomeruli forma-tion, Alexander Chesler et al. expressed various proteins in

embryonic mouse olfactory epithelium using a retrovirus tocarry the genes. The authors found that, although functionalodorant receptors induced axon coalescence as expected, activa-tion of a specific G protein (G�s) signaling pathway was suffi-cient to cause axon sorting. In addition, the generation ofcAMP, a downstream product of the G protein pathway, waskey to establishing axonal identity. Contrary to the previoustheory that axon sorting was independent of olfactory receptoractivation, these results suggest that the G�s pathway is the crit-ical link that helps guide olfactory neurons to their properplace in the brain. — M.M.

‘‘A G protein/cAMP signal cascade is required for axonal convergenceinto olfactory glomeruli’’ by Alexander T. Chesler, Dong-Jing Zou,Claire E. Le Pichon, Zita A. Peterlin, Glennis A. Matthews, Xin Pei,Michael C. Miller, and Stuart Firestein (see pages 1039–1044)

ANTHROPOLOGY

North China’s earliest cropsWith one of the world’s longest-lasting agriculture systems,northern China is one of the major regions where agriculturefirst began. Gyoung-Ah Lee etal. report that millet, not rice,was the most important cropin ancient times for feed andtrade in this region. Lee et al.carbon-dated charred plantremains from sediment sam-ples obtained throughout theYiluo valley of northernChina. The samples of crops,plants, and weeds dated from6000 to 1300 B.C. The authors found that foxtail millet wasgrown during the early Neolithic era and was the principal cropfor at least four millennia. Growth of broomcorn millet was farless significant. Rice appeared in the area by 3000 B.C. butnever became a predominant crop in this region, which is rela-tively drier than other parts of China. After rice, wheat becamea significant crop between 1600 and 1300 B.C. Few signs ex-isted of any nuts or fleshy fruits. Local weeds were mostlygrasses that diversified over time and were probably fodder fordomesticated animals. Lee et al. say that northern China’s farm-ing tradition of mostly dry crops, such as millets, wheat, le-gumes, and a little rice, appears to have been established at thelatest by 1300 B.C. These findings provide insight into how agri-culture and civilization first developed in China. — P.D.

‘‘Plants and people from the Early Neolithic to Shang periods in NorthChina’’ by Gyoung-Ah Lee, Gary W. Crawford, Li Liu, and XingcanChen (see pages 1087–1092)

Olfactory axonal sorting.

Ancient lambsquarter (Chenopo-

dium), a common annual, weedy

plant, from northern China site.

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