Widespread polyphyly among Alopiinae snail genera: when phylogeny mirrors biogeography more closely than morphology

Consider a group of species that is evenly divided by an easily identifiable complex morphological character. Most biologists would assume that this character should provide better phylogenetic information than, say, the spatial distribution of these species over a fairly continuous 500-km radius area. Paradoxically, this is not the case among terrestrial snail genera in the clausiliid subfamily Alopiinae. Phylogenetic analysis using the nuclear markers ITS1/ITS2 and mitochondrial markers COI/12S reveals widespread homoplasy in the clausilial apparatus (a complex aperture-closing mechanism), and concomitant extensive polyphyly among Carinigera, Isabellaria, and Sericata. In contrast, phylogenetic relationships as revealed by molecular data are closely congruent with biogeography at a relatively small scale. A combination of extremely low vagility and extremely high morphological convergence has conspired to produce this unexpected result. Implications as to the function of the clausilial apparatus are discussed.     

M phase phosphoprotein 1 is a human plus-end-directed kinesin-related protein required for cytokinesis

The human M phase phosphoprotein 1 (MPP1), previously identified through a screening of a subset of proteins specifically phosphorylated at the G2/M transition (Matsumoto-Taniura, N., Pirollet, F., Monroe, R., Gerace, L., and Westendorf, J. M. (1996) Mol. Biol. Cell 7, 1455-1469), is characterized as a plus-end-directed kinesin-related protein. Recombinant MPP1 exhibits in vitro microtubule-binding and microtubule-bundling properties as well as microtubule-stimulated ATPase activity. In gliding experiments using polarity-marked microtubules, MPP1 is a slow molecular motor that moves toward the microtubule plus-end at a 0.07 microm/s speed. In cycling cells, MPP1 localizes mainly to the nuclei in interphase. During mitosis, MPP1 is diffuse throughout the cytoplasm in metaphase and subsequently localizes to the midzone to further concentrate on the midbody. MPP1 suppression by RNA interference induces failure of cell division late in cytokinesis. We conclude that MPP1 is a new mitotic molecular motor required for completion of cytokinesis.     

Microtubule release from the centrosome in migrating cells

In migrating cells, force production relies essentially on a polarized actomyosin system, whereas the spatial regulation of actomyosin contraction and substrate contact turnover involves a complex cooperation between the microtubule (MT) and the actin filament networks (Goode, B.L., D.G. Drubin, and G. Barnes. 2000. Curr. Opin. Cell Biol., 12:63-71). Targeting and capture of MT plus ends at the cell periphery has been described, but whether or not the minus ends of these MTs are anchored at the centrosome is not known. Here, we show that release of short MTs from the centrosome is frequent in migrating cells and that their transport toward the cell periphery is blocked when dynein activity is impaired. We further show that MT release, but not MT nucleation or polymerization dynamics, is abolished by overexpression of the centrosomal MT-anchoring protein ninein. In addition, a dramatic inhibition of cell migration was observed; but, contrary to cells treated by drugs inhibiting MT dynamics, polarized membrane ruffling activity was not affected in ninein overexpressing cells. We thus propose that the balance between MT minus-end capture and release from the centrosome is critical for efficient cell migration.     

Characterization of terminal NeuNAcalpha2-3Galbeta1-4GlcNAc sequence in lipooligosaccharides of Neisseria meningitidis

Group B and C Neisseria meningitidis are the major cause of meningococcal disease in the United States and in Europe. N . meningitidis lipooligosaccharide (LOS), a major surface antigen, can be divided into 12 immunotypes of which L1 through L8 were found among Group B and C organisms. Groups B and C but not Group A may sialylate their LOSs with N-acetylneuraminic acid (NeuNAc) at the nonreducing end because they synthesize CMP-NeuNAc. Using sialic acid-galactose binding lectins as probes in an ELISA format, six of the eight LOS immunotypes (L2, L3, L4, L5, L7, and L8) in Groups B and C bound specifically to Maackia amurensis leukoagglutinin (MAL), which recognizes NeuNAcalpha2- 3Galbeta1-4GlcNAc/Glc sequence, but not to Sambucus nigra agglutinin, which binds NeuNAcalpha2-6Gal sequence. The combination of SDS-PAGE and MAL-blot analyses revealed that these six LOSs contained only the NeuNAcalpha2-3Galbeta1-4GlcNAc trisaccharide sequence in their 4.1 kDa LOS components, which have a common terminal lacto-N-neotetraose (LNnT, Galbeta1-4GlcNAcbeta1-3Galbeta1-4Glc) structure when nonsialylated as shown by previous studies. The LOS-lectin binding was abolished when the LOSs were treated with Newcastle disease viral neuraminidase which cleaves alpha2-->3 linked sialic acid. Methylation analysis of a representative LOS (L2) confirmed that NeuNAc is 2-->3 linked to Gal. Thus, these LOSs structurally mimic certain glycolipids, i.e., paragloboside (LNnT-ceramide) and sialylparagloboside and some glycoproteins in having LNnT and N-acetyllactosamine sequences, respectively, with or without alpha2-->3 linked NeuNAc. The molecular mimicry of the LOSs may play a role in the pathogenesis of N.meningitidis by assisting the organism to evade host immune defenses in man.      

Comparative multilocus phylogeography of two Palaearctic spruce bark beetles: influence of contrasting ecological strategies on genetic variation

While phylogeographic patterns of organisms are often interpreted through past environmental disturbances, mediated by climate changes, and geographic barriers, they may also be strongly influenced by species‐specific traits. To investigate the impact of such traits, we focused on two Eurasian spruce bark beetles that share a similar geographic distribution, but differ in their ecology and reproduction. Ips typographus is an aggressive tree‐killing species characterized by strong dispersal, whereas Dendroctonus micans is a discrete inbreeding species (sib mating is the rule), parasite of living trees and a poor disperser. We compared genetic variation between the two species over both beetles’ entire range in Eurasia with five independent gene fragments, to evaluate whether their intrinsic differences could have an influence over their phylogeographic patterns. We highlighted widely divergent patterns of genetic variation for the two species and argue that the difference is indeed largely compatible with their contrasting dispersal strategies and modes of reproduction. In addition, genetic structure in I. typographus divides European populations in a northern and a southern group, as was previously observed for its host plant, and suggests past allopatric divergence. A long divergence time was estimated between East Asian and other populations of both species, indicating their long‐standing presence in Eurasia, prior to the last glacial maximum. Finally, the strong population structure observed in D. micans for the mitochondrial locus provides insights into the recent colonization history of this species, from its native European range to regions where it was recently introduced.     

Widespread occurrence and genomic context of unusually small polyketide synthase genes in microbial consortia associated with marine sponges

Numerous marine sponges harbor enormous amounts of as-yet-uncultivated bacteria in their tissues. There is increasing evidence that these symbionts play an important role in the synthesis of protective metabolites, many of which are of great pharmacological interest. In this study, genes for the biosynthesis of polyketides, one of the most important classes of bioactive natural products, were systematically investigated in 20 demosponge species from different oceans. Unexpectedly, the sponge metagenomes were dominated by a ubiquitously present, evolutionarily distinct, and highly sponge-specific group of polyketide synthases (PKSs). Open reading frames resembling animal fatty acid genes were found on three corresponding DNA regions isolated from the metagenomes of Theonella swinhoei and Aplysina aerophoba. Their architecture suggests that methyl-branched fatty acids are the metabolic product. According to a phylogenetic analysis of housekeeping genes, at least one of the PKSs belongs to a bacterium of the Deinococcus-Thermus phylum. The results provide new insights into the chemistry of sponge symbionts and allow inference of a detailed phylogeny of the diverse functional PKS types present in sponge metagenomes. Based on these qualitative and quantitative data, we propose a significantly simplified strategy for the targeted isolation of biomedically relevant PKS genes from complex sponge-symbiont associations.     

Expression of the lantibiotic mersacidin in Bacillus amyloliquefaciens FZB42

Lantibiotics are small peptide antibiotics that contain the characteristic thioether amino acids lanthionine and methyllanthionine. As ribosomally synthesized peptides, lantibiotics possess biosynthetic gene clusters which contain the structural gene (lanA) as well as the other genes which are involved in lantibiotic modification (lanM, lanB, lanC, lanP), regulation (lanR, lanK), export (lanT(P)) and immunity (lanEFG). The lantibiotic mersacidin is produced by Bacillus sp. HIL Y-85,54728, which is not naturally competent.

Methodology/Principal Findings

The aim of these studies was to test if the production of mersacidin could be transferred to a naturally competent Bacillus strain employing genomic DNA of the producer strain. Bacillus amyloliquefaciens FZB42 was chosen for these experiments because it already harbors the mersacidin immunity genes. After transfer of the biosynthetic part of the gene cluster by competence transformation, production of active mersacidin was obtained from a plasmid in trans. Furthermore, comparison of several DNA sequences and biochemical testing of B. amyloliquefaciens FZB42 and B. sp. HIL Y-85,54728 showed that the producer strain of mersacidin is a member of the species B. amyloliquefaciens.

Conclusions/Significance

The lantibiotic mersacidin can be produced in B. amyloliquefaciens FZB42, which is closely related to the wild type producer strain of mersacidin. The new mersacidin producer strain enables us to use the full potential of the biosynthetic gene cluster for genetic manipulation and downstream modification approaches.     

Spatial distribution of leaf water-use efficiency and carbon isotope discrimination within an isolated tree crown

The spatial variations in the stable carbon isotope composition (δ¹³C) of air and leaves (total matter and soluble sugars) were quantified within the crown of a well‐watered, 20‐year‐old walnut tree growing in a low‐density orchard. The observed leaf carbon isotope discrimination (Δ) was compared with that computed by a three‐dimensional model simulating the intracanopy distribution of irradiance, transpiration and photosynthesis (previously parameterized and tested for the same tree canopy) coupled to a biophysically based model of carbon isotope discrimination. The importance of discrimination associated with CO₂ gradients encountered from the substomatal sites to the carboxylation sites was evaluated. We also assessed by simulation the effect of current irradiance on leaf gas exchange and the effect of long‐term acclimation of photosynthetic capacity and stomatal and internal conductances to light regime on intracanopy gradients in Δ. The main conclusions of this study are: (i) leaf Δ can exhibit important variations (5 and 8‰ in total leaf material and soluble sugars, respectively) along light gradients within the foliage of an isolated tree; (ii) internal conductance must be taken into account to adequately predict leaf Δ, and (iii) the spatial variations in Δ and water‐use efficiency resulted from the short‐term response of leaf gas exchange to variations in local irradiance and, to a much lesser extent, from the long‐term acclimation of leaf characteristics to the local light regime.