Emergence of Multiplex Communities in Collaboration Networks

Community structures in collaboration networks reflect the natural tendency of individuals to organize their work in groups in order to better achieve common goals. In most of the cases, individuals exploit their connections to introduce themselves to new areas of interests, giving rise to multifaceted collaborations which span different fields. In this paper, we analyse collaborations in science and among movie actors as multiplex networks, where the layers represent respectively research topics and movie genres, and we show that communities indeed coexist and overlap at the different layers of such systems. We then propose a model to grow multiplex networks based on two mechanisms of intra and inter-layer triadic closure which mimic the real processes by which collaborations evolve. We show that our model is able to explain the multiplex community structure observed empirically, and we infer the strength of the two underlying social mechanisms from real-world systems. Being also able to correctly reproduce the values of intra-layer and inter-layer assortativity correlations, the model contributes to a better understanding of the principles driving the evolution of social networks.     

Short-Term Effects of Traditional and Alternative Community Interventions to Address Food Insecurity

Background

Despite the effects of food insecurity on health are well documented, clear governmental policies to face food insecurity do not exist in western countries. In Canada, interventions to face food insecurity are developed at the community level and can be categorized into two basic strategies: those providing an immediate response to the need for food, defined “traditional” and those targeting the improvement of participants’ social cohesion, capabilities and management of their own nutrition, defined “alternative”.

Objective

The objective of this study was to evaluate the effects of food insecurity interventions on food security status and perceived health of participants.

Design

This was a longitudinal multilevel study implemented in Montreal, Quebec, Canada. Participants were recruited in a two-stage cluster sampling frame. Clustering units were community organizations working on food insecurity; units of analysis were participants in community food security interventions. A total of 450 participants were interviewed at the beginning and after 9 months of participation in traditional or alternative food security interventions. Food security and perceived health were investigated as dependent variables. Differences overtime were assessed through multilevel regression models.

Results

Participants in traditional interventions lowered their food insecurity at follow-up. Decreases among participants in alternative interventions were not statistically significant. Participants in traditional interventions also improved physical (B coefficient 3.00, CI 95% 0.42–5.59) and mental health (B coefficient 6.25, CI 95% 4.15–8.35).

Conclusions

Our results challenge the widely held view suggesting the ineffectiveness of traditional interventions in the short term. Although effects may be intervention-dependent, food banks decreased food insecurity and, in so doing, positively affected perceived health. Although study findings demonstrate that food banks offer short term reprise from the effects of food insecurity, the question as to whether food banks are the most appropriate solution to food insecurity still needs to be addressed.     

Transgenic mice recapitulate the phenotypic heterogeneity of genetic prion diseases without developing prion infectivity: Role of intracellular PrP retention in neurotoxicity

Genetic prion diseases are degenerative brain disorders caused by mutations in the gene encoding the prion protein (PrP). Different PrP mutations cause different diseases, including Creutzfeldt-Jakob disease (CJD), Gerstmann-Sträussler-Scheinker (GSS) syndrome and fatal familial insomnia (FFI). The reason for this variability is not known. It has been suggested that prion strains with unique self-replicating and neurotoxic properties emerge spontaneously in individuals carrying PrP mutations, dictating the phenotypic expression of disease. We generated transgenic mice expressing the FFI mutation, and found that they developed a fatal neurological illness highly reminiscent of FFI, and different from those of similarly generated mice modeling genetic CJD and GSS. Thus transgenic mice recapitulate the phenotypic differences seen in humans. The mutant PrPs expressed in these mice are misfolded but unable to self-replicate. They accumulate in different compartments of the neuronal secretory pathway, impairing the membrane delivery of ion channels essential for neuronal function. Our results indicate that conversion of mutant PrP into an infectious isoform is not required for pathogenesis, and suggest that the phenotypic variability may be due to different effects of mutant PrP on intracellular transport.     

Ontogenetic integration between force production and force reception: a case study in Ctenomys (Rodentia: Caviomorpha)

During ontogeny, complex adaptations undergo changes that sometimes entail different functional capabilities. This fact constrains the behaviour of organisms at each developmental stage. Rodents have ever‐growing incisors for gnawing, and a powerful jaw musculature. The incisors are long enough, relative to their diameter, to be affected by bending stresses. This is particularly true in the subterranean Ctenomys that uses its incisors for digging. We measured bite force (BF) in individuals of different ages using a force transducer. We estimated incisor section modulus Z, a geometrical parameter proportional to bending strength. A relative strength indicator was calculated as S = Z/BF incisor length. We found that ontogenetic BF scales to body mass with positive allometry. However, an anova showed non‐significant differences in S, neither between sexes nor among age classes. This result implies that during growth, incisors might have a rather similar ability to withstand bending stresses from increasing masticatory forces, what may be considered evidence of ontogenetic integration of force production (by muscles) and force reception (by the incisors). This fact well correlates with the observation that pups and juveniles of C. talarum incorporate solid foods shortly after birth, and they are able to dig burrows early in life.     

Exome sequencing discloses <Emphasis Type="Italic">KALRN</Emphasis> homozygous variant as likely cause of intellectual disability and short stature in a consanguineous pedigree

Background

The recent availability of whole-exome sequencing has opened new possibilities for the evaluation of individuals with genetically undiagnosed intellectual disability.

Results

We report two affected siblings, offspring of first-cousin parents, with intellectual disability, hypotonia, short stature, growth hormone deficiency, and delayed bone age. All members of the nuclear family were genotyped, and exome sequencing was performed in one of the affected individuals. We used an in-house algorithm (CATCH v1.1) that combines homozygosity mapping with exome sequencing results and provides a list of candidate variants. One identified novel homozygous missense variant in KALRN (NM_003947.4:c.3644C>A: p.(Thr1215Lys)) was predicted to be pathogenic by all pathogenicity prediction software used (SIFT, PolyPhen, Mutation Taster). KALRN encodes the protein kalirin, which is a GTP-exchange factor protein with a reported role in cytoskeletal remodeling and dendritic spine formation in neurons. It is known that mice with ablation of Kalrn exhibit age-dependent functional deficits and behavioral phenotypes.

Conclusion

Exome sequencing provided initial evidence linking KALRN to monogenic intellectual disability in man, and we propose that KALRN is the causative gene for the autosomal recessive phenotype in this family.

     

Structural and biochemical insights into 7β‐hydroxysteroid dehydrogenase stereoselectivity

Hydroxysteroid dehydrogenases are of great interest as biocatalysts for transformations involving steroid substrates. They feature a high degree of stereo‐ and regio‐selectivity, acting on a defined atom with a specific configuration of the steroid nucleus. The crystal structure of 7β‐hydroxysteroid dehydrogenase from Collinsella aerofaciens reveals a loop gating active‐site accessibility, the bases of the specificity for NADP⁺, and the general architecture of the steroid binding site. Comparison with 7α‐hydroxysteroid dehydrogenase provides a rationale for the opposite stereoselectivity. The presence of a C‐terminal extension reshapes the substrate site of the β‐selective enzyme, possibly leading to an inverted orientation of the bound substrate. Proteins 2016; 84:859–865. © 2016 Wiley Periodicals, Inc.