Fine‐scale geographic patterns of gene flow and reproductive character displacement in Drosophila subquinaria and Drosophila recens

When two species are incompletely isolated, strengthening premating isolation barriers in response to the production of low fitness hybrids may complete the speciation process. Here, we use the sister species Drosophila subquinaria and Drosophila recens to study the conditions under which this reinforcement of species boundaries occurs in natural populations. We first extend the region of known sympatry between these species, and then we conduct a fine‐scale geographic survey of mate discrimination coupled with estimates of gene flow within and admixture between species. Within D. subquinaria, reinforcement is extremely effective: we find variation in mate discrimination both against D. recens males and against conspecific allopatric males on the scale of a few kilometres and in the face of gene flow both from conspecific populations and introgression from D. recens. In D. recens, we do not find evidence for increased mate discrimination in sympatry, even where D. recens is rare, consistent with substantial gene flow throughout the species’ range. Finally, we find that introgression between species is asymmetric, with more from D. recens into D. subquinaria than vice versa. Within each species, admixture is highest in the geographic region where it is rare relative to the other species, suggesting that when hybrids are produced they are of low fitness. In sum, reinforcement within D. subquinaria is effective at maintaining species boundaries, but even when reinforcing selection is strong it may not always result in a pattern of strong reproductive character displacement due to variation in the frequency of hybridization and gene flow from neighbouring populations.     

Glutaraldehyde cross‐linking increases the stability of Lumbricus terrestris erythrocruorin

Since donated red blood cells must be constantly refrigerated, they are not available in remote areas and battlefields. We have previously shown that the hemoglobin of the earthworm Lumbricus terrestris (LtEc) is an effective and safe substitute for donated blood that is stable enough to be stored for long periods at the relatively high temperatures that may be encountered in remote areas. The goal of this study was to further increase the thermal stability of LtEc by covalently cross‐linking LtEc with glutaraldehyde (gLtEc). Our results show that the melting temperatures of the gLtEc samples steadily increase as the molar ratio of glutaraldehyde to heme increases (from T_m = 57°C for native LtEc up to T_m = 68°C at a ratio of 128:1). In addition, while native LtEc is susceptible to subunit dissociation at alkaline pH (8–10), cross‐linking with glutaraldehyde completely prevents dissociation of gLtEc at pH 10. Increasing the molar ratio of glutaraldehyde:heme also significantly increased the oxygen affinity of gLtEc, but this effect was decreased by cross‐linking gLtEc in the deoxygenated T state. Finally, while gLtEc samples cross‐linked at low G:H ratios (e.g., 2:1) exhibited slight increases in oxidation rate in Tris buffer, no significant difference in oxidation rate was observed between native LtEc and the gLtEc samples in Ringer's Solution, which contains antioxidants. Overall, cross‐linking LtEc with glutaraldehyde significantly increases its thermal and structural stability without any loss of function, making gLtEc an attractive blood substitute for deployment in remote areas and battlefields. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 34:521–528, 2018     

A Contiguous Clone Map over 3 Mb on the Long Arm of Chromosome 11 across a Balanced Translocation Associated with Schizophrenia

Forty-nine clones derived by microdissection of a schizophrenia-associated t(1;11)(q42.1;q14.3) breakpoint region have been assigned by somatic cell hybrid mapping to seven discrete intervals on the long arm of human chromosome 11. Eleven of the clones were shown to map to a small region immediately distal to the translocation breakpoint on 11q.A 3-Mb contiguous clone map of this region was established by isolation of corresponding YAC recombinants. The contig was oriented and shown to traverse the translocation breakpoint by FISH and microsatellite marker analysis. This contig will facilitate the isolation of candidate sequences whose expression may be affected by the translocation.     

A Transcultural Model of the Centrality of “Thinking a Lot” in Psychopathologies Across the Globe and the Process of Localization: A Cambodian Refugee Example

We present a general model of why “thinking a lot” is a key presentation of distress in many cultures and examine how “thinking a lot” plays out in the Cambodian cultural context. We argue that the complaint of “thinking a lot” indicates the presence of a certain causal network of psychopathology that is found across cultures, but that this causal network is localized in profound ways. We show, using a Cambodian example, that examining “thinking a lot” in a cultural context is a key way of investigating the local bio-cultural ontology of psychopathology. Among Cambodian refugees, a typical episode of “thinking a lot” begins with ruminative-type negative cognitions, in particular worry and depressive thoughts. Next these negative cognitions may induce mental symptoms (e.g., poor concentration, forgetfulness, and “zoning out”) and somatic symptoms (e.g., migraine headache, migraine-like blurry vision such as scintillating scotomas, dizziness, palpitations). Subsequently the very fact of “thinking a lot” and the induced symptoms may give rise to multiple catastrophic cognitions. Soon, as distress escalates, in a kind of looping, other negative cognitions such as trauma memories may be triggered. All these processes are highly shaped by the Cambodian socio-cultural context. The article shows that Cambodian trauma survivors have a locally specific illness reality that centers on dynamic episodes of “thinking a lot,” or on what might be called the “thinking a lot” causal network.     

The Anti-Diabetic Drug Metformin Reduces BACE1 Protein Level by Interfering with the MID1 Complex

Alzheimer’s disease (AD), the most common form of dementia in the elderly, is characterized by two neuropathological hallmarks: senile plaques, which are composed of Aβ peptides, and neurofibrillary tangles, which are composed of hyperphosphorylated TAU protein. Diabetic patients with dysregulated insulin signalling are at increased risk of developing AD. Further, several animal models of diabetes show increased Aβ expression and hyperphosphorylated tau. As we have shown recently, the anti-diabetic drug metformin is capable of dephosphorylating tau at AD-relevant phospho-sites. Here, we investigated the effect of metformin on the main amyloidogenic enzyme BACE1 and, thus, on the production of Aβ peptides, the second pathological hallmark of AD. We find similar results in cultures of primary neurons, a human cell line model of AD and in vivo in mice. We show that treatment with metformin decreases BACE1 protein expression by interfering with an mRNA-protein complex that contains the ubiquitin ligase MID1, thereby reducing BACE1 activity. Together with our previous findings these results indicate that metformin may target both pathological hallmarks of AD and may be of therapeutic value for treating and/or preventing AD.     

Using Flatbed Scanners to Collect High-resolution Time-lapsed Images of the Arabidopsis Root Gravitropic Response

Research efforts in biology increasingly require use of methodologies that enable high-volume collection of high-resolution data. A challenge laboratories can face is the development and attainment of these methods. Observation of phenotypes in a process of interest is a typical objective of research labs studying gene function and this is often achieved through image capture. A particular process that is amenable to observation using imaging approaches is the corrective growth of a seedling root that has been displaced from alignment with the gravity vector. Imaging platforms used to measure the root gravitropic response can be expensive, relatively low in throughput, and/or labor intensive. These issues have been addressed by developing a high-throughput image capture method using inexpensive, yet high-resolution, flatbed scanners. Using this method, images can be captured every few minutes at 4,800 dpi. The current setup enables collection of 216 individual responses per day. The image data collected is of ample quality for image analysis applications.     

Influence of venous emptying on the reactive hyperemic blood flow response

Background

Previous research indicates that venous emptying serves as a stimulus for vasodilation in the human forearm. This suggests the importance of recognizing the potential influence of venous volume on reactive hyperemic blood flow (RHBF) following occlusion. The purpose of this study was to examine the influence of venous emptying on forearm vascular function.

Methods

Forearm RHBF, venous capacitance and venous outflow were examined in 35 individuals (age = 22 ± 2 years), using mercury in-Silastic strain gauge plethysmography, at rest and following five minutes of upper arm occlusion using standard procedures (Control). In addition, the same measures were obtained following five minutes of upper arm occlusion preceded by two minutes of passive arm elevation (Pre-elevation).

Results

Average resting arterial inflow was 2.42 ± 1.11 ml·100 ml^-1·min^-1. RHBF and venous capacitance were significantly greater during Pre-elevation compared to Control (RHBF; Pre-elevation: 23.76 ± 5.95 ml·100 ml^-1 ·min^-1 vs. Control: 19.33 ± 4.50; p = 0.001), (venous capacitance; Pre-elevation: 2.74 ± 0.89 % vs. Control: 2.19 ± 0.97, p = 0.001). Venous outflow did not differ between the two conditions.

Conclusion

Venous emptying prior to upper arm occlusion results in a significant greater RHBF response and venous capacitance. Recognition of the influence of venous volume on RHBF is particularly important in studies focusing on arterial inflow, and also provides further evidence for the interplay between the venous and arterial system.

     

SpyA is a membrane-bound ADP-ribosyltransferase of Streptococcus pyogenes which modifies a streptococcal peptide, SpyB

All sequenced genomes of Streptococcus pyogenes (Group A Streptococcus, GAS) encode a protein, SpyA, with homology to C3-like ADP-ribosyltransferase toxins. SpyA is a novel virulence factor which plays a role in pathogenesis in a mouse model of soft-tissue infection. In this study we demonstrate that SpyA is a surface-exposed membrane protein which is anchored to the streptococcal membrane by an N-terminal transmembrane sequence. We identified a small gene upstream of spyA, designated spyB, which encodes a peptide of 35 amino acids, and is co-transcribed with spyA. Expression of spyBA is strongly influenced by translational coupling: mutational inactivation of spyB translation completely abolishes translation of spyA. spyB expression increases with increasing cell density and reaches its maximum at late exponential growth phase. The SpyB N-terminus is predicted to fold into an amphipathic α-helix, a structural motif that targets a protein to the cytoplasmic membrane. Consistent with the prediction, we found that a SpyB fusion with peptide affinity tags is located in the streptococcal membrane. An ADP-ribosylation assay with recombinant SpyA demonstrated that SpyA modifies SpyB. Thus, our study suggests that ADP-ribosylation of SpyB may be an important function of SpyA.     

Accumulation of diverse parasite genotypes within the bivalve second intermediate host of the digenean Gymnophallus sp

The complex life cycle of digenean trematodes with alternating stages of asexual multiplication and sexual reproduction can generate interesting within-host population genetic patterns. Metacercarial stages found in the second intermediate host are generally accumulated from the environment. Highly mobile second intermediate hosts can sample a broad range of cercarial genotypes and accumulate genetically diverse packets of metacercariae, but it is unclear whether the same would occur in systems where the second intermediate host is relatively immobile and cercarial dispersal is the sole mechanism that can maintain genetic homogeneity at the population level. Here, using polymorphic microsatellite markers, we addressed this issue by genotyping metacercariae of the trematode Gymnophallus sp. from the New Zealand cockle Austrovenus stutchburyi. Despite the relatively sessile nature of the second intermediate host of Gymnophallus, very high genotypic diversity of metacercariae was found within cockles, with only two cockles harbouring multiple copies of a single clonal lineage. There was no evidence of population structuring at the scale of our study, suggesting the existence of a well-mixed population. Our results indicate that (i) even relatively sessile second intermediate hosts can accumulate a high diversity of genotypes and (ii) the dispersal ability of cercariae, whether passive or not, is much greater than expected for such small and short-lived organisms. The results also support the role of the second intermediate host as an accumulator of genetic diversity in the trematode life cycle.