Adaptation or preadaptation: why are keelback snakes (<Emphasis Type="Italic">Tropidonophis mairii</Emphasis>) less vulnerable to invasive cane toads (<Emphasis Type="Italic">Bufo marinus</Emphasis>) than are other Australian snakes?

Biological invasions can expose native predators to novel prey which may be less nutritious or detrimental to predators. The introduction and subsequent spread of cane toads (Bufo marinus) through Australia has killed many anuran-eating snakes unable to survive the toad’s toxins. However, one native species, the keelback snake (Tropidonophis mairii), is relatively resistant to toad toxins and remains common in toad-infested areas. Is the keelback’s ability to coexist with toads a function of its ancestral Asian origins, or a consequence of rapid adaptation since cane toads arrived in Australia? And does the snake’s feeding preference for frogs rather than toads reflect an innate or learned behaviour? We compared keelback populations long sympatric with toads with a population that has encountered toads only recently. Unlike toad-vulnerable snake species, sympatry with toads has not affected keelback toxin tolerances or feeding responses: T. mairii from toad-sympatric and toad-naïve populations show a similar sensitivity to toad toxin, and a similar innate preference for frogs rather than toads. Feeding responses of neonatal keelbacks demonstrate that learning plays little or no role in the snake’s aversion to toads. Thus, behavioural aversion to B. marinus as prey, and physiological tolerance to toad toxins are pre-existing innate characteristics of Australian keelbacks rather than adaptations to the cane toad’s invasion of Australia. Such traits were most likely inherited from ancestral keelbacks that adapted to the presence of bufonids in Asia. Our results suggest that the impact of invasive species on native taxa may be strongly influenced by the biogeographic histories of the species involved.     

A family of zinc-finger proteins is required for chromosome-specific pairing and synapsis during meiosis in C. elegans

Homologous chromosome pairing and synapsis are prerequisite for accurate chromosome segregation during meiosis. Here, we show that a family of four related C2H2 zinc-finger proteins plays a central role in these events in C. elegans. These proteins are encoded within a tandem gene cluster. In addition to the X-specific HIM-8 protein, three additional paralogs collectively mediate the behavior of the five autosomes. Each chromosome relies on a specific member of the family to pair and synapse with its homolog. These "ZIM" proteins concentrate at special regions called meiotic pairing centers on the corresponding chromosomes. These sites are dispersed along the nuclear envelope during early meiotic prophase, suggesting a role analogous to the telomere-mediated meiotic bouquet in other organisms. To gain insight into the evolution of these components, we characterized homologs in C. briggsae and C. remanei, which revealed changes in copy number of this gene family within the nematode lineage.     

Crystal Structure of Human Protein N-Terminal Glutamine Amidohydrolase,an Initial Component of the N-End Rule Pathway

The N-end rule states that half-life of protein is determined by their N-terminal amino acid residue. N-terminal glutamine amidohydrolase (Ntaq) converts N-terminal glutamine to glutamate by eliminating the amine group and plays an essential role in the N-end rule pathway for protein degradation. Here, we report the crystal structure of human Ntaq1 bound with the N-terminus of a symmetry-related Ntaq1 molecule at 1.5 Å resolution. The structure reveals a monomeric globular protein with alpha-beta-alpha three-layer sandwich architecture. The catalytic triad located in the active site, Cys-His-Asp, is highly conserved among Ntaq family and transglutaminases from diverse organisms. The N-terminus of a symmetry-related Ntaq1 molecule bound in the substrate binding cleft and the active site suggest possible substrate binding mode of hNtaq1. Based on our crystal structure of hNtaq1 and docking study with all the tripeptides with N-terminal glutamine, we propose how the peptide backbone recognition patch of hNtaq1 forms nonspecific interactions with N-terminal peptides of substrate proteins. Upon binding of a substrate with N-terminal glutamine, active site catalytic triad mediates the deamination of the N-terminal residue to glutamate by a mechanism analogous to that of cysteine proteases.     

Inter- and intra-genomic heterogeneity of the intervening sequence in the 23S ribosomal RNA gene of Campylobacter jejuni and Campylobacter coli

An intervening sequence (IVS) can be present or absent in the 23S rRNA of Campylobacter jejuni and Campylobacter coli. As part of a survey, we used a polymerase chain reaction (PCR) assay to detect the presence of the IVS in 43 isolates of C. coli and 82 isolates of C. jejuni. An IVS was present in 40 (93.0%) of the C. coli and only 34 (41.5%) of the C. jejuni isolates. Twelve (27.9%) of the C. coli isolates and seven (8.5%) of the C. jejuni isolates resulted in two polymerase chain reaction products, indicating heterogeneity in the presence of the 23S rRNA IVS. Fourteen of the isolates with two products were evaluated by pulse-field gel electrophoresis; 13 different patterns were observed. The total band size of one isolate was substantially greater than the expected 1.7 Mb, possibly indicating a mixed culture. Southern blot analyses demonstrated the expected three rRNA operons in all tested isolates. Nested PCR reactions with operon-specific primers followed by primers for the IVS confirmed that the strains of interest contained either one or two operons carrying the IVS and the remaining operon(s) did not. Sequence analysis of the IVS and flanking regions of the 23S rRNA genes did not discriminate C. jejuni and C. coli as distinct populations. These results indicate horizontal transfer of 23S rRNA genes or portions of the genes between C. jejuni and C. coli. Also, data showing sequence polymorphisms between the three 23S rRNA loci outside of the IVS region suggest that the isolates with intra-genomic heterogeneity appear to be members of clones that have an ancient defect in gene conversion mechanisms needed for concerted evolution of the ribosomal operons.     

Variation in cuticular hydrocarbons among strains of the Anopheles gambiae sensu stricto by analysis of cuticular hydrocarbons using gas liquid chromatography of larvae

Cuticular hydrocarbons of larvae of individual strains of the Anopheles gambiae sensu stricto were investigated using gas liquid chromatography. Biomedical discriminant analysis involving multivariate statistics suggests that there was clear hydrocarbon difference between the Gambian(G3), the Nigerian (16CSS and, its malathion resistant substrain, REFMA) and the Tanzanian (KWA) strains. The high degree of segregation (95%) in hydrocarbons among the four strains investigated indicates that further analysis is needed to enable understanding of hydrocarbon variation in samples of An. gambiae especially from areas where these populations co-exist.     

Shiga toxin production and translocation during microaerobic human colonic infection with Shiga toxin‐producing E. coli O157:H7 and O104:H4

Haemolytic uraemic syndrome caused by Shiga toxin‐producing E. coli (STEC) is dependent on release of Shiga toxins (Stxs) during intestinal infection and subsequent absorption into the bloodstream. An understanding of Stx‐related events in the human gut is limited due to lack of suitable experimental models. In this study, we have used a vertical diffusion chamber system with polarized human colon carcinoma cells to simulate the microaerobic (MA) environment in the human intestine and investigate its influence on Stx release and translocation during STEC O157:H7 and O104:H4 infection. Stx2 was the major toxin type released during infection. Whereas microaerobiosis significantly reduced bacterial growth as well as Stx production and release into the medium, Stx translocation across the epithelial monolayer was enhanced under MA versus aerobic conditions. Increased Stx transport was dependent on STEC infection and occurred via a transcellular pathway other than macropinocytosis. While MA conditions had a similar general effect on Stx release and absorption during infection with STEC O157:H7 and O104:H4, both serotypes showed considerable differences in colonization, Stx production, and Stx translocation which suggest alternative virulence strategies. Taken together, our study suggests that the MA environment in the human colon may modulate Stx‐related events and enhance Stx absorption during STEC infection.     

Blastocystis hominis: pathogenic potential in human patients and in gnotobiotes.

Germfree guinea pigs were inoculated orally, in some experiments, and intracecally, in others, with Blastocystis hominis and the enteric flora from symptomatic patients. Other germfree guinea pigs received the parasite from axenic culture and still others from monoxenic culture with Proteus vulgaris. Fourteen of 43 animals inoculated orally with B. hominis and patient's enteric flora developed B. hominis infections and those with particularly heavy infections developed watery diarrhea of more than 1 week's duration immediately prior to sacrifice. Similar results were obtained from intracecal inoculations in that 13 of 28 animals developed infections and those with the greatest numbers of B. hominis had watery diarrhea for more than 1 week prior to sacrifice. Gross pathologic changes in these animals were mostly unremarkable, with only a slight hyperemia observed in several of the symptomatic animals. Microscopic examination, however, revealed frequent penetration of intestinal epithelium by B. hominis and the parasites in significant numbers were observed within the epithelium. There was a slight increase in cellularity in the lamina propria but parasites were not observed therein and their presence in the epithelium did not provoke an inflammatory response. Only one of eight animals inoculated from monoxenic cultures developed B. hominis infection (asymptomatic), and infections were not produced in animals inoculated from axenic culture. As a result of our observations of diarrhea in patients with particularly heavy infections with B. hominis together with the demonstration of similar symptoms in animals heavily infected with this parasite, we believe B. hominis may occasionally be related causally to the production of such symptoms by a mechanism not completely understandable.     

Synthesis and antibacterial activity of new N-linked 5-triazolylmethyl oxazolidinones

A new series of N-linked 5-triazolylmethyl oxazolidinones with varying substitution at the piperazine nitrogen 4-position were synthesized and tested against a panel of Gram-positive and Gram-negative bacteria including clinical isolates. Most of the compounds showed excellent antibacterial activity against susceptible and resistant Gram-positive organisms. One of the compounds showed enhanced antibacterial activity against Moraxella catarrhalis.     

Hyperthermia increases interleukin-6 in mouse skeletal muscle

Skeletal muscles produce and contribute to circulating levels of IL-6 during exercise. However, when core temperature is reduced, the response is attenuated. Therefore, we hypothesized that hyperthermia may be an important and independent stimulus for muscle IL-6. In cultured C2C12 myotubes, hyperthermia (42°C) increased IL-6 gene expression 14-fold after 1 h and 35-fold after 5 h of 37°C recovery; whereas exposure to 41°C resulted in a 2.6-fold elevation at 1 h. IL-6 protein was secreted and significantly elevated in the cell supernatant. Similar but reduced responses to heat were seen in C2C12 myoblasts. Isolated soleus muscles from mice, exposed ex vivo to 41°C for 1 h, yielded similar IL-6 gene responses (>3-fold) but without a significant effect on protein release. When whole animals were exposed to passive hyperthermia, such that core temperature increased to 42.4°C, IL-6 mRNA in soleus increased 5.4-fold compared with time matched controls. Interestingly, TNF-α gene expression was routinely suppressed at all levels of hyperthermia (40.5-42°C) in the isolated models, but TNF-α was elevated (4.2-fold) in the soleus taken from intact mice exposed, in vivo, to hyperthermia. Muscle HSP72 mRNA increased as a function of the level of hyperthermia, and IL-6 mRNA responses increased proportionally with HSP72. In cultured C2C12 myotubes, when heat shock factor was pharmacologically blocked with KNK437, both HSP72 and IL-6 mRNA elevations, induced by heat, were suppressed. These findings implicate skeletal muscle as a "heat stress sensor" at physiologically relevant hyperthermia, responding with a programmed cytokine expression pattern characterized by elevated IL-6.