A Bacterial Ras-Like Small GTP-Binding Protein and Its Cognate GAP Establish a Dynamic Spatial Polarity Axis to Control Directed Motility

Regulated cell polarity is central to many cellular processes. We investigated the mechanisms that govern the rapid switching of cell polarity (reversals) during motility of the bacterium Myxococcus xanthus. Cellular reversals are mediated by pole-to-pole oscillations of motility proteins and the frequency of the oscillations is under the control of the Frz chemosensory system. However, the molecular mechanism that creates dynamic polarity remained to be characterized. In this work, we establish that polarization is regulated by the GTP cycle of a Ras-like GTPase, MglA. We initially sought an MglA regulator and purified a protein, MglB, which was found to activate GTP hydrolysis by MglA. Using live fluorescence microscopy, we show that MglA and MglB localize at opposite poles and oscillate oppositely when cells reverse. In absence of MglB, MglA-YFP accumulates at the lagging cell end, leading to a strikingly aberrant reversal cycle. Spatial control of MglA is achieved through the GAP activity of MglB because an MglA mutant that cannot hydrolyze GTP accumulates at the lagging cell end, despite the presence of MglB. Genetic and cell biological studies show that the MglA-GTP cycle controls dynamic polarity and the reversal switch. The study supports a model wherein a chemosensory signal transduction system (Frz) activates reversals by relieving a spatial inhibition at the back pole of the cells: reversals are allowed by Frz-activated switching of MglB to the opposite pole, allowing MglA-GTP to accumulate at the back of the cells and create the polarity switch. In summary, our results provide insight into how bacteria regulate their polarity dynamically, revealing unsuspected conserved regulations with eukaryots.     

Data standards, sense and stability: Scratchpads, the ICZN and ZooBank

The International Commission of Zoological Nomenclature has used the Scratchpads platform (currently being developed and maintained by ViBRANT) as the foundation for its redesigned website and as a platform for engaging with its users. The existing Scratchpad tools, with extensions to provide additional functions, have allowed for a major transformation in presentation of linked nomenclatural tools. Continued development of the new website will act as a springboard for the ICZN to participate more fully in the wider community of biodiversity informatics.     

The rare Chrysopidae (Neuroptera) of southwestern Europe

Quantitative surveys of the chrysopid fauna from southwestern Europe, namely the Iberian and Italian peninsulas, France south of 46° N, and the west-Mediterranean Islands, were analysed. A total of 56 species of Chrysopidae were reported, of which three species were abundant. These, Chrysoperla carnea (Stephens, 1836) sensu lato, Dichochrysa prasina (Burmeister, 1839) and D. flavifrons (Brauer, 1850), comprised a large percentage of the specimens. For the rarer species, comments are made on their distributions, the enhanced geographic range of exotic ones, and on levels of endemism and stenotopy.     

An evolutionary analytical model of a complementary circular code

The subset X0=[AAC,AAT,ACC,ATC,ATT,CAG,CTC,CTG, GAA,GAC,GAG,GAT,GCC,GGC,GGT,GTA,GTC,GTT,TAC,TTC] of 20 trinucleotides has a preferential occurrence in the frame 0 (reading frame established by the ATG start trinucleotide) of protein (coding) genes of both prokaryotes and eukaryotes. This subset X0 is a complementary maximal circular code with two permutated maximal circular codes X1 and X2 in the frames 1 and 2 respectively (frame 0 shifted by one and two nucleotides respectively in the 5'-3' direction). X0 is called a C3 code (Arquès and Michel, 1997, J. Biosyst 44, 107-134). A quantitative study of these three subsets X0, X1 and X2 in the three frames 0, 1 and 2 of eukaryotic protein genes shows that their occurrence frequencies are constant functions of the trinucleotide positions in the sequences. The frequencies of X0, X1 and X2 in the frame 0 of eukaryotic protein genes are 48.5%, 29% and 22.5% respectively. These properties are not observed in the 5' and 3' regions of eukaryotes where X0, X1 and X2 occur with variable frequencies around the random value (1/3). Several frequency asymmetries unexpectedly observed, e.g. the frequency difference between X1 and X2 in the frame 0, are related to a new property of the C3 code X0 involving substitutions. An evolutionary analytical model at three parameters (p, q, t) based on an independent mixing of the 20 codons (trinucleotides in the frame 0) of X0 with equiprobability (1/20) followed by t approximately 4 substitutions per codon according to the proportions p approximately 0.1, q approximately 0.1 and r = 1 - p - q approximately 0.8 in the three codon sites respectively, retrieves the frequencies of X0, X1 and X2 observed in the three frames of protein genes and explains these asymmetries. The complex behaviour of these analytical curves is totally unexpected and a priori difficult to imagine. Finally, the evolutionary analytical method developed could be applied to the phylogenetic tree reconstruction and the DNA sequence alignment.     

Ultrastructural detection of an unusual intranuclear bacterium in Pentastiridius leporinus (Hemiptera: Cixiidae)

Pentastiridius leporinus is an important vector of sugar beet pathogens in eastern France. An electron microscope survey on the insect-associated microflora revealed the occurrence of intranuclear prokaryotic cells in every internal organ analysed. These bacteria, which could also be found in the cytoplasm surrounding the nucleus, had a homogeneous coccoid (ca. 0.45 microm) or rod (0.45-1 microm) shape. The presence of three membrane layers was observed, the outermost forming a kind of vacuole containing generally a single microorganism. No cytopathological abnormalities were detected in the infected cells. To our knowledge, this is the first report of a hemipteran species infected by intranuclear bacteria. The possible identity of this microorganism is discussed.     

Flagellin/TLR5 signalling activates renal collecting duct cells and facilitates invasion and cellular translocation of uropathogenic Escherichia coli

Uropathogenic Escherichia coli (UPEC) colonizing kidneys is the main cause of acute pyelonephritis. TLR5 that senses flagellin was shown to be highly expressed in the bladder and to participate in host defence against flagellated UPEC, although its role in kidneys still remains elusive. Here we show that TLR5 is expressed in renal medullary collecting duct (MCD) cells, which represent a preferential site of UPEC adhesion. Flagellin, like lipopolysaccharide, stimulated the production of the chemoattractant chemokines CXCL1 and CXCL2, and subsequent migration capacity of neutrophils in cultured wild‐type (WT) and Tlr4^?/? MCDs, but not in Tlr5^?/? MCDs. UPEC can translocate across intact MCD layers without altering tight junctions. Strikingly, the invasion capacity and transcellular translocation of the UPEC strain HT7 were significantly lower in Tlr5^?/? than in WT MCDs. The non‐motile HT7ΔfliC mutant lacking flagellin also exhibited much lower translocation capacities than the HT7 isolates. Finally, Tlr5^?/? kidneys exhibited less infiltrating neutrophils than WT kidneys one day after the transurethral inoculation of HT7, and greater delayed renal bacterial loads in the day 4 post‐infected Tlr5^?/? kidneys. Overall, these findings indicate that the epithelial TLR5 participates to renal antibacterial defence, but paradoxically favours the translocation of UPEC across intact MCD cell layers.     

Hypomorphic mutations in the gene encoding a key Fanconi anemia protein, FANCD2, sustain a significant group of FA-D2 patients with severe phenotype

FANCD2 is an evolutionarily conserved Fanconi anemia (FA) gene that plays a key role in DNA double-strand-type damage responses. Using complementation assays and immunoblotting, a consortium of American and European groups assigned 29 patients with FA from 23 families and 4 additional unrelated patients to complementation group FA-D2. This amounts to 3%-6% of FA-affected patients registered in various data sets. Malformations are frequent in FA-D2 patients, and hematological manifestations appear earlier and progress more rapidly when compared with all other patients combined (FA-non-D2) in the International Fanconi Anemia Registry. FANCD2 is flanked by two pseudogenes. Mutation analysis revealed the expected total of 66 mutated alleles, 34 of which result in aberrant splicing patterns. Many mutations are recurrent and have ethnic associations and shared allelic haplotypes. There were no biallelic null mutations; residual FANCD2 protein of both isotypes was observed in all available patient cell lines. These analyses suggest that, unlike the knockout mouse model, total absence of FANCD2 does not exist in FA-D2 patients, because of constraints on viable combinations of FANCD2 mutations. Although hypomorphic mutations arie involved, clinically, these patients have a relatively severe form of FA.