Thiostrepton inhibits stable 70S ribosome binding and ribosome-dependent GTPase activation of elongation factor G and elongation factor 4

Thiostrepton, a macrocyclic thiopeptide antibiotic, inhibits prokaryotic translation by interfering with the function of elongation factor G (EF-G). Here, we have used 70S ribosome binding and GTP hydrolysis assays to study the effects of thiostrepton on EF-G and a newly described translation factor, elongation factor 4 (EF4). In the presence of thiostrepton, ribosome-dependent GTP hydrolysis is inhibited for both EF-G and EF4, with IC(50) values equivalent to the 70S ribosome concentration (0.15 μM). Further studies indicate the mode of thiostrepton inhibition is to abrogate the stable binding of EF-G and EF4 to the 70S ribosome. In support of this model, an EF-G truncation variant that does not possess domains IV and V was shown to possess ribosome-dependent GTP hydrolysis activity that was not affected by the presence of thiostrepton (>100 μM). Lastly, chemical footprinting was employed to examine the nature of ribosome interaction and tRNA movements associated with EF4. In the presence of non-hydrolyzable GTP, EF4 showed chemical protections similar to EF-G and stabilized a ratcheted state of the 70S ribosome. These data support the model that thiostrepton inhibits stable GTPase binding to 70S ribosomal complexes, and a model for the first step of EF4-catalyzed reverse-translocation is presented.     

Geographical variation in male genitalia in Brachyrhaphis episcopi (Poeciliidae): is it sexually or naturally selected?

Male poeciliid fishes inseminate females using an intromittent organ called the gonopodium. Here we report on natural variation in gonopodium size both within and between 12 populations of the freshwater fish Brachyrhaphis episcopi (Poeciliidae) in Panama. We show that males from sites with more predatory fish species have, on average, a relatively longer gonopodium than males inhabiting sites with fewer predatory fish. Gonopodium length was not correlated with the site-specific adult sex ratio and the average sex ratio was more strongly female biased at sites with more predatory fish. The gonopodium exhibited lower phenotypic variance than the average for sexually selected traits and it generally showed negative allometry. Our results are similar to those reported for the guppy Poecilia reticulata . Two alternative hypotheses for these findings are discussed. First, that population differences are sexually selected. Second, that they are an incidental consequence of environmental differences between sites. Specifically, that higher water flow rates select for enlarged fin size and stockier bodies in downstream sites where predatory fish are more common.     

Mate guarding, competition and variation in size in male orb-web spiders, Metellina segmentata: a field experiment

In the common orb-web spider Metellina segmentata, males are more powerfully built with longer legs, although females are heavier because of their egg load. Males guard females before attempting to mate, and there is considerable male-male competition because of the male-biased operational sex ratio. We used a field removal experiment to examine (1) seasonal changes in the average morphology of guarding males and (2) whether there is a pool of small males that is excluded from the webs of females. Morphological measures were subjected to a principal components analysis and changes in PC scores were examined for seasonal effects and the effects of previous removal of males. The size of guarding males (PC1) increased over the season, suggesting that smaller males were increasingly excluded from webs, but the condition of guarding males (PC2) decreased, indicating that energy reserves are depleted because the males gain little access to food during the reproductive season. When guarding males were removed, smaller males were able to take up residence. Our results show that large males have a clear advantage in monopolizing females. We discuss the manner in which selection acts to maintain large male size in this spider.Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.      

Urbanization disrupts latitude‐size rule in 17‐year cicadas

Many ectotherms show a decrease in body size with increasing latitude due to changes in climate, a pattern termed converse Bergmann's rule. Urban conditions—particularly warmer temperatures and fragmented landscapes—may impose stresses on development that could disrupt these body size patterns. To test the impact of urbanization on development and latitudinal trends in body size, we launched a citizen science project to collect periodical cicadas (Magicicada septendecim) from across their latitudinal range during the 2013 emergence of Brood II. Periodical cicadas are long‐lived insects whose distribution spans a broad latitudinal range covering both urban and rural habitats. We used a geometric morphometric approach to assess body size and developmental stress based on fluctuating asymmetry in wing shape. Body size of rural cicadas followed converse Bergmann's rule, but this pattern was disrupted in urban habitats. In the north, urban cicadas were larger than their rural counterparts, while southern populations showed little variation in body size between habitats. We detected no evidence of differences in developmental stress due to urbanization. To our knowledge, this is the first evidence that urbanization disrupts biogeographical trends in body size, and this pattern highlights how the effects of urbanization may differ over a species’ range.     

Side chain orientation of residues lining the selectivity filter of epithelial Na+ channels

Epithelial Na(+) channels (ENaCs) selectively conduct Na(+) and Li(+) but exclude K(+). A three-residue tract ((G/S)XS) present within all three subunits has been identified as a key structure forming a putative selectivity filter. We investigated the side chain orientation of residues within this tract by analyzing accessibility of the introduced sulfhydryl groups to thiophilic Cd(2+). Xenopus oocytes were used to express wild-type or mutant mouse alphabetagammaENaCs. The blocking effect of external Cd(2+) was examined by comparing amiloride-sensitive Na(+) currents measured by two-electrode voltage clamp in the absence and presence of Cd(2+) in the bath solution. The currents in mutant channels containing a single Cys substitution at the first or third position within the (G/S)XS tract (alphaG587C, alphaS589C, betaG529C, betaS531C, gammaS546C, and gammaS548C) were blocked by Cd(2+) with varying inhibitory constants (0.06-13 mm), whereas the currents in control channels were largely insensitive to Cd(2+) at concentrations up to 10 mm. The Cd(2+) blocking effects were fast, with time constants in the range of seconds, and were only partially reversible. The blocked currents were restored by 10 mm dithiothreitol. Mutant channels containing alanine or serine substitutions at these sites within the alpha subunit were only poorly and reversibly blocked by 10 mm Cd(2+). These results indicate that the introduced sulfhydryl groups face the conduction pore and suggest that serine hydroxyl groups within the selectivity filter in wild-type ENaCs face the conduction pore and may contribute to cation selectivity by participating in coordination of permeating cations.     

Pre-Weaning Growth Hormone Treatment Reverses Hypertension and Endothelial Dysfunction in Adult Male Offspring of Mothers Undernourished during Pregnancy

Maternal undernutrition results in elevated blood pressure (BP) and endothelial dysfunction in adult offspring. However, few studies have investigated interventions during early life to ameliorate the programming of hypertension and vascular disorders. We have utilised a model of maternal undernutrition to examine the effects of pre-weaning growth hormone (GH) treatment on BP and vascular function in adulthood. Female Sprague-Dawley rats were fed either a standard control diet (CON) or 50% of CON intake throughout pregnancy (UN). From neonatal day 3 until weaning (day 21), CON and UN pups received either saline (CON-S, UN-S) or GH (2.5 ug/g/day)(CON-GH, UN-GH). All dams were fed ad libitum throughout lactation. Male offspring were fed a standard diet until the end of the study. Systolic blood pressure (SBP) was measured at day 150 by tail cuff plethysmography. At day 160, intact mesenteric vessels mounted on a pressure myograph. Responses to pressure, agonist-induced constriction and endothelium-dependent vasodilators were investigated to determine vascular function. SBP was increased in UN-S groups and normalised in UN-GH groups (CON-S 121±2 mmHg, CON-GH 115±3, UN-S 146±3, UN-GH 127±2). Pressure mediated dilation was reduced in UN-S offspring and normalised in UN-GH groups. Vessels from UN-S offspring demonstrated a reduced constrictor response to phenylephrine and reduced vasodilator response to acetylcholine (ACh). Furthermore, UN-S offspring vessels displayed a reduced vasodilator response in the presence of L-NG-Nitroarginine Methyl Ester (L-NAME), carbenoxolone (CBX), L-NAME and CBX, Tram-34 and Apamin. UN-GH vessels showed little difference in responses when compared to CON and significantly increased vasodilator responses when compared to UN-S offspring. Pre-weaning GH treatment reverses the negative effects of maternal UN on SBP and vasomotor function in adult offspring. These data suggest that developmental cardiovascular programming is potentially reversible by early life GH treatment and that GH can reverse the vascular adaptations resulting from maternal undernutrition.     

Extended gene map reveals tripartite motif, C-type lectin, and Ig superfamily type genes within a subregion of the chicken MHC-B affecting infectious disease

MHC haplotypes have a remarkable influence on whether tumors form following infection of chickens with oncogenic Marek's disease herpesvirus. Although resistance to tumor formation has been mapped to a subregion of the chicken MHC-B region, the gene or genes responsible have not been identified. A full gene map of the subregion has been lacking. We have expanded the MHC-B region gene map beyond the 92-kb core previously reported for another haplotype revealing the presence of 46 genes within 242 kb in the Red Jungle Fowl haplotype. Even though MHC-B is structured differently, many of the newly revealed genes are related to loci typical of the MHC in other species. Other MHC-B loci are homologs of genes found within MHC paralogous regions (regions thought to be derived from ancient duplications of a primordial immune defense complex where genes have undergone differential silencing over evolutionary time) on other chromosomes. Still others are similar to genes that define the NK complex in mammals. Many of the newly mapped genes display allelic variability and fall within the MHC-B subregion previously shown to affect the formation of Marek's disease tumors and hence are candidates for genes conferring resistance.     

Do alternative reproductive strategies in the Wellington tree weta represent different behavioural types?

In many animal species, variation in reproductive success among individuals has led to the evolution of alternative mating strategies, which in the case of insects can often be correlated with developmental trajectories. In the Wellington tree weta, Hemideina crassidens, males can mature at the 8th, 9th or 10th instar, while females mature at the 10th instar only. A number of morphological attributes including male head and mandible size correlate with final instar number, and as these attributes represent a form of weaponry, they are often used in mate/site guarding and male–male competition. Tenth instar males have larger head/mandible/body sizes and show a conventional (guarder) reproductive strategy, whereas smaller 8th instar males typically show an unconventional (sneaker) strategy. In contrast, 9th instar males are predicted to adopt a “jack‐of‐all‐trades” strategy whereby they can fight or sneak depending context. Here, we tested whether alternative reproductive morphs exhibit strategy‐specific differences in risk‐taking associated with refuge emergence, activity and antipredator behaviour and further, whether these traits correlate to form a behavioural syndrome. We found that tree weta show consistent and repeatable differences in activity and refuge use at the individual level; however, behavioural covariances suggest that only 8th instar males exhibit a behavioural syndrome. That 9th instar males show high plasticity and variance in their gallery‐related behaviours supports the hypothesis that these males are a “jack‐of‐all‐trades.” Contrary to our predictions, antipredator behaviour was not correlated with other traits, and differences in behaviour overall were consistently more pronounced between individuals rather than between male morphs or sexes.