Exploring demographic, physical, and historical explanations for the genetic structure of two lineages of Greater Antillean bats

Observed patterns of genetic structure result from the interactions of demographic, physical, and historical influences on gene flow. The particular strength of various factors in governing gene flow, however, may differ between species in biologically relevant ways. We investigated the role of demographic factors (population size and sex-biased dispersal) and physical features (geographic distance, island size and climatological winds) on patterns of genetic structure and gene flow for two lineages of Greater Antillean bats. We used microsatellite genetic data to estimate demographic characteristics, infer population genetic structure, and estimate gene flow among island populations of Erophylla sezekorni/E. bombifrons and Macrotus waterhousii (Chiroptera: Phyllostomidae). Using a landscape genetics approach, we asked if geographic distance, island size, or climatological winds mediate historical gene flow in this system. Samples from 13 islands spanning Erophylla's range clustered into five genetically distinct populations. Samples of M. waterhousii from eight islands represented eight genetically distinct populations. While we found evidence that a majority of historical gene flow between genetic populations was asymmetric for both lineages, we were not able to entirely rule out incomplete lineage sorting in generating this pattern. We found no evidence of contemporary gene flow except between two genetic populations of Erophylla. Both lineages exhibited significant isolation by geographic distance. Patterns of genetic structure and gene flow, however, were not explained by differences in relative effective population sizes, island area, sex-biased dispersal (tested only for Erophylla), or surface-level climatological winds. Gene flow among islands appears to be highly restricted, particularly for M. waterhousii, and we suggest that this species deserves increased taxonomic attention and conservation concern.     

Evolutionary instability of symbiotic function in Bradyrhizobium japonicum

Bacterial mutualists are often acquired from the environment by eukaryotic hosts. However, both theory and empirical work suggest that this bacterial lifestyle is evolutionarily unstable. Bacterial evolution outside of the host is predicted to favor traits that promote an independent lifestyle in the environment at a cost to symbiotic function. Consistent with these predictions, environmentally-acquired bacterial mutualists often lose symbiotic function over evolutionary time. Here, we investigate the evolutionary erosion of symbiotic traits in Bradyrhizobium japonicum, a nodulating root symbiont of legumes. Building on a previous published phylogeny we infer loss events of nodulation capability in a natural population of Bradyrhizobium, potentially driven by mutation or deletion of symbiosis loci. Subsequently, we experimentally evolved representative strains from the symbiont population under host-free in vitro conditions to examine potential drivers of these loss events. Among Bradyrhizobium genotypes that evolved significant increases in fitness in vitro, two exhibited reduced symbiotic quality, but no experimentally evolved strain lost nodulation capability or evolved any fixed changes at six sequenced loci. Our results are consistent with trade-offs between symbiotic quality and fitness in a host free environment. However, the drivers of loss-of-nodulation events in natural Bradyrhizobium populations remain unknown.     

Accuracy of the Interpretation of Chest Radiographs for the Diagnosis of Paediatric Pneumonia

Introduction

World Health Organization (WHO) radiological classification remains an important entry criterion in epidemiological studies of pneumonia in children. We report inter-observer variability in the interpretation of 169 chest radiographs in children suspected of having pneumonia.

Methods

An 18-month prospective aetiological study of pneumonia was undertaken in Northern England. Chest radiographs were performed on eligible children aged ≤16 years with clinical features of pneumonia. The initial radiology report was compared with a subsequent assessment by a consultant cardiothoracic radiologist. Chest radiographic changes were categorised according to the WHO classification.

Results

There was significant disagreement (22%) between the first and second reports (kappa = 0.70, P<0.001), notably in those aged <5 years (26%, kappa = 0.66, P<0.001). The most frequent sources of disagreement were the reporting of patchy and perihilar changes.

Conclusion

This substantial inter-observer variability highlights the need for experts from different countries to create a consensus to review the radiological definition of pneumonia in children.     

Thiolutin inhibits endothelial cell adhesion by perturbing Hsp27 interactions with components of the actin and intermediate filament cytoskeleton

Thiolutin is a dithiole synthesized by Streptomyces sp. that inhibits endothelial cell adhesion and tumor growth. We show here that thiolutin potently inhibits developmental angiogenesis in zebrafish and vascular outgrowth from tissue explants in 3D cultures. Thiolutin is a potent and selective inhibitor of endothelial cell adhesion accompanied by rapid induction of HSPB1 (Hsp27) phosphorylation. The inhibitory effects of thiolutin on endothelial cell adhesion are transient, potentially due to a compensatory increase in Hsp27 protein levels. Accordingly, heat shock induction of Hsp27 limits the anti-adhesive activity of thiolutin. Thiolutin treatment results in loss of actin stress fibers, increased cortical actin as cells retract, and decreased cellular F-actin. Mass spectrometric analysis of Hsp27 binding partners following immunoaffinity purification identified several regulatory components of the actin cytoskeleton that associate with Hsp27 in a thiolutin-sensitive manner including several components of the Arp2/3 complex. Among these, ArpC1a is a direct binding partner of Hsp27. Thiolutin treatment induces peripheral localization of phosphorylated Hsp27 and Arp2/3. Hsp27 also associates with the intermediate filament components vimentin and nestin. Thiolutin treatment specifically ablates Hsp27 interaction with nestin and collapses nestin filaments. These results provide new mechanistic insights into regulation of cell adhesion and cytoskeletal dynamics by Hsp27.     

Sequences downstream of the 5' splice donor site are required for both packaging and dimerization of human immunodeficiency virus type 1 RNA

Two copies of human immunodeficiency virus type 1 RNA are incorporated into each virus particle and are further converted to a stable dimer as the virus particle matures. Several RNA segments that flank the 5' splice donor site at nucleotide (nt) 289 have been shown to act as packaging signals. Among these, RNA stem-loop 1 (SL1) (nt 243 to 277) can trigger RNA dimerization through a "kissing-loop" mechanism and thus is termed the dimerization initiation site. However, it is unknown whether other packaging signals are also needed for dimerization. To pursue this subject, we mutated stem-loop 3 (SL3) (nt 312 to 325), a GA-rich region (nt 325 to 336), and two G-rich repeats (nt 363 to 367 and nt 405 to 409) in proviral DNA and assessed the effects on RNA dimerization by performing native Northern blot analyses. Our results show that the structure but not the specific RNA sequence of SL3 is needed not only for efficient viral RNA packaging but also for dimerization. Mutations of the GA-rich sequence severely diminished viral RNA dimerization as well as packaging; the combination of mutations in both SL3 and the GA-rich region led to further decreases, implying independent roles for each of these two RNA motifs. Compensation studies further demonstrated that the RNA-packaging and dimerization activity of the GA-rich sequence may not depend on a putative interaction between this region and a CU repeat sequence at nt 227 to 233. In contrast, substitutions in the two G-rich sequences did not cause any diminution of viral RNA packaging or dimerization. We conclude that both the SL3 motif and GA-rich RNA sequences, located downstream of the 5' splice donor site, are required for efficient RNA packaging and dimerization.     

Identification of instars and species in some larval Polypedilum (Polypedilum) (Diptera: Chironomidae)

Instars II and III of Polypedilum aviceps Townes, Polypedilum convictum (Walker), and Polypedilum illinoense (Malloch) can be identified to species by associating them with instar IV because key taxonomic characters remain relatively unchanged from instar to instar. Instars I cannot be identified to species or genus unless they are associated with older, identifiable larvae reared from the same egg masses. No single character evaluated on slide material can be used to clearly separate instars in all three species. Larvae of P. aviceps can be separated into instars based on any four of seven characters; P. convictum by either of two characters; and, P. illinoense by a combination of two characters. Changes in structures of instars II, III, and IV are described for all three species. Growth ratios for some structures are compared and discussed with regard to Dyar's Rule.