Low host specificity of herbivorous insects in a tropical forest

Two decades of research have not established whether tropical insect herbivores are dominated by specialists or generalists. This impedes our understanding of species coexistence in diverse rainforest communities. Host specificity and species richness of tropical insects are also key parameters in mapping global patterns of biodiversity. Here we analyse data for over 900 herbivorous species feeding on 51 plant species in New Guinea and show that most herbivorous species feed on several closely related plant species. Because species-rich genera are dominant in tropical floras, monophagous herbivores are probably rare in tropical forests. Furthermore, even between phylogenetically distant hosts, herbivore communities typically shared a third of their species. These results do not support the classical view that the coexistence of herbivorous species in the tropics is a consequence of finely divided plant resources; non-equilibrium models of tropical diversity should instead be considered. Low host specificity of tropical herbivores reduces global estimates of arthropod diversity from 31 million (ref. 1) to 4 6 million species. This finding agrees with estimates based on taxonomic collections, reconciling an order of magnitude discrepancy between extrapolations of global diversity based on ecological samples of tropical communities with those based on sampling regional faunas.     

Structural determinants for GoLoco-induced inhibition of nucleotide release by Galpha subunits

Heterotrimeric G-proteins bind to cell-surface receptors and are integral in transmission of signals from outside the cell. Upon activation of the Galpha subunit by binding of GTP, the Galpha and Gbetagamma subunits dissociate and interact with effector proteins for signal transduction. Regulatory proteins with the 19-amino-acid GoLoco motif can bind to Galpha subunits and maintain G-protein subunit dissociation in the absence of Galpha activation. Here we describe the structural determinants of GoLoco activity as revealed by the crystal structure of Galpha(i1) GDP bound to the GoLoco region of the 'regulator of G-protein signalling' protein RGS14. Key contacts are described between the GoLoco motif and Galpha protein, including the extension of GoLoco's highly conserved Asp/Glu-Gln-Arg triad into the nucleotide-binding pocket of Galpha to make direct contact with the GDP alpha- and beta-phosphates. The structural organization of the GoLoco Galpha(i1) complex, when combined with supporting data from domain-swapping experiments, suggests that the Galpha all-helical domain and GoLoco-region carboxy-terminal residues control the specificity of GoLoco Galpha interactions.     

Formation and propagation of matter-wave soliton trains

Attraction between the atoms of a Bose-Einstein condensate renders it unstable to collapse, although a condensate with a limited number of atoms can be stabilized by confinement in an atom trap. However, beyond this number the condensate collapses. Condensates constrained to one-dimensional motion with attractive interactions are predicted to form stable solitons, in which the attractive forces exactly compensate for wave-packet dispersion. Here we report the formation of bright solitons of (7)Li atoms in a quasi-one-dimensional optical trap, by magnetically tuning the interactions in a stable Bose-Einstein condensate from repulsive to attractive. The solitons are set in motion by offsetting the optical potential, and are observed to propagate in the potential for many oscillatory cycles without spreading. We observe a soliton train, containing many solitons; repulsive interactions between neighbouring solitons are inferred from their motion.     

A mouse Mecp2-null mutation causes neurological symptoms that mimic Rett syndrome

Rett syndrome (RTT) is an inherited neurodevelopmental disorder of females that occurs once in 10,000-15,000 births. Affected females develop normally for 6-18 months, but then lose voluntary movements, including speech and hand skills. Most RTT patients are heterozygous for mutations in the X-linked gene MECP2 (refs. 3-12), encoding a protein that binds to methylated sites in genomic DNA and facilitates gene silencing. Previous work with Mecp2-null embryonic stem cells indicated that MeCP2 is essential for mouse embryogenesis. Here we generate mice lacking Mecp2 using Cre-loxP technology. Both Mecp2-null mice and mice in which Mecp2 was deleted in brain showed severe neurological symptoms at approximately six weeks of age. Compensation for absence of MeCP2 in other tissues by MeCP1 (refs. 19,20) was not apparent in genetic or biochemical tests. After several months, heterozygous female mice also showed behavioral symptoms. The overlapping delay before symptom onset in humans and mice, despite their profoundly different rates of development, raises the possibility that stability of brain function, not brain development per se, is compromised by the absence of MeCP2.     

Recombinational DNA double-strand breaks in mice precede synapsis

In Saccharomyces cerevisiae, meiotic recombination is initiated by Spo11-dependent double-strand breaks (DSBs), a process that precedes homologous synapsis. Here we use an antibody specific for a phosphorylated histone (gamma-H2AX, which marks the sites of DSBs) to investigate the timing, distribution and Spo11-dependence of meiotic DSBs in the mouse. We show that, as in yeast, recombination in the mouse is initiated by Spo11-dependent DSBs that form during leptotene. Loss of gamma-H2AX staining (which in irradiated somatic cells is temporally linked with DSB repair) is temporally and spatially correlated with synapsis, even when this synapsis is 'non-homologous'.     

Multigenic control of Listeria monocytogenes susceptibility in mice

We have used a novel quantitative trait locus model to study the genetics of survival of F2 progeny of susceptible BALB/cByJ and resistant C57BL/6ByJ mice that have been infected with Listeria monocytogenes. This allowed us to map modifiers of L. monocytogenes susceptibility to chromosomes 5 and 13.