Multilocus genetic analyses differentiate between widespread and spatially restricted cryptic species in a model ascidian

Elucidating the factors that shape species distributions has long been a fundamental goal in ecology and evolutionary biology. In spite of significant theoretical advancements, empirical studies of range limits have lagged behind. Specifically, little is known about how the attributes that allow species to expand their ranges and become widespread vary across phylogenies. Here, we studied the ascidian Botryllus schlosseri, a worldwide invasive species that is also characterized by marked genetic subdivision. Our study includes phylogenetic and population genetic data based on mitochondrial and nuclear genes, as well as polymorphic microsatellites for B. schlosseri colonies sampled from the southern and northern coasts of Europe and the eastern and western coasts of North America. We demonstrate that this well-known model organism comprises three highly divergent and probably reproductively isolated cryptic species (A, D and E), with two more (B and C) being suggested by data retrieved from GenBank. Among these, species A, recovered in all of the surveyed regions, is by far the most common and widespread. By contrast, species B-E, occurring mostly in sites from northern Europe, are considerably more geographically restricted. These findings, along with inferences made on transport opportunity, suggest that divergent evolutionary histories promoted differences in invasive potential between B. schlosseri sibling species, indicating that attributes that facilitate dramatic shifts in range limits can evolve more easily and frequently than previously thought. We propose environmental disturbance as a selective force that could have shaped the evolution of invasiveness in the B. schlosseri complex.     

Scale‐dependent post‐establishment spread and genetic diversity in an invading mollusc in South America

Aims Our study aimed to characterize the dispersal dynamics and population genetic structure of the introduced golden mussel Limnoperna fortunei throughout its invaded range in South America and to determine how different dispersal methods, that is, human‐mediated dispersal and downstream natural dispersal, contribute to genetic variation among populations. Location Paraná–Uruguay–Río de la Plata watershed in Argentina, Brazil, Paraguay and Uruguay. Methods We performed genetic analyses based on a comprehensive sampling strategy encompassing 22 populations (N = 712) throughout the invaded range in South America, using the mitochondrial cytochrome c oxidase subunit I (COI) gene and eight polymorphic nuclear microsatellites. We employed both population genetics and phylogenetic analyses to clarify the dispersal dynamics and population genetic structure. Results We detected relatively high genetic differentiation between populations (F_ST = ?0.041 to 0.111 for COI, ?0.060 to 0.108 for microsatellites) at both fine and large geographical scales. Bayesian clustering and three‐dimensional factorial correspondence analyses consistently revealed two genetically distinct clusters, highlighting genetic discontinuities in the invaded range. Results of all genetic analyses suggest ship‐mediated ‘jump’ dispersal as the dominant mode of spread of golden mussels in South America, while downstream natural dispersal has had limited effects on contemporary genetic patterns. Main conclusions Our study provides new evidence that post‐establishment dispersal dynamics and genetic patterns vary across geographical scales. While ship‐mediated ‘jump’ dispersal dominates post‐establishment spread of golden mussels in South America, once colonies become established in upstream locations, larvae produced may be advected downstream to infill patchy distributions. Moreover, genetic structuring at fine geographical scales, especially within the same drainages, suggests a further detailed understanding of dynamics of larval dispersal and settlement in different water systems. Knowledge of the mechanisms by which post‐establishment spread occurs can, in some cases, be used to limit dispersal of golden mussels and other introduced species.     

IL-21 stimulates human myeloma cell growth through an autocrine IGF-1 loop

IL-21 is a member of the type I cytokine family related most closely to IL-2 and IL-15. IL-21 is a pleiotropic cytokine, produced by T, NKT, and dendritic cells, which modulates lymphoid and myeloid cell functions. Besides its activities on normal lymphoid cells, it has been shown that IL-21 is a growth factor for myeloma cells. In the present study, we demonstrate that IL-21 generated myeloma colonies from 9 of 24 human myeloma cell lines (HMCL) in a collagen-based assay. Of major interest, the capacity of IL-21 to stimulate clonogenicity was restricted to CD45(-) HMCL. We found that IL-21 induced tyrosine phosphorylation of STAT-3, STAT-1, and Erk1/2. Interestingly, an Akt activation was observed lately after 30 min to 1 h of IL-21 stimulation, indicating that this Akt phosphorylation could be due to an IGF-1 autocrine loop. This hypothesis was sustained both by the fact that IL-21 treatment induced an IGF-1 mRNA synthesis and that an antagonistic anti-IGF-1 receptor mAb (AVE1642) strongly inhibits the IL-21-induced clonogenicity. Thus, we demonstrated by quantitative PCR that IL-21 induced clonogenicity through an autocrine IGF-1 secretion in HMCL and primary myeloma cells. Because we have previously demonstrated that CD45 phosphatase inhibits the IGF-1 signaling, this inhibitory effect of CD45 explains why the IL-21-induced clonogenicity was restricted to CD45(-) HMCL. These results support that therapy against IGF-1R, which are presently under investigation in multiple myeloma, could be beneficial, not only to suppress IGF-1-mediated myeloma cell growth, but also IL-21-mediated myeloma cell growth.     

Vaccination against GIP for the treatment of obesity

Background

According to the WHO, more than 1 billion people worldwide are overweight and at risk of developing chronic illnesses, including cardiovascular disease, type 2 diabetes, hypertension and stroke. Current therapies show limited efficacy and are often associated with unpleasant side-effect profiles, hence there is a medical need for new therapeutic interventions in the field of obesity. Gastric inhibitory peptide (GIP, also known as glucose-dependent insulinotropic polypeptide) has recently been postulated to link over-nutrition with obesity. In fact GIP receptor-deficient mice (GIPR^−/−) were shown to be completely protected from diet-induced obesity. Thus, disrupting GIP signaling represents a promising novel therapeutic strategy for the treatment of obesity.

Methodology/Principal Findings

In order to block GIP signaling we chose an active vaccination approach using GIP peptides covalently attached to virus-like particles (VLP-GIP). Vaccination of mice with VLP-GIP induced high titers of specific antibodies and efficiently reduced body weight gain in animals fed a high fat diet. The reduction in body weight gain could be attributed to reduced accumulation of fat. Moreover, increased weight loss was observed in obese mice vaccinated with VLP-GIP. Importantly, despite the incretin action of GIP, VLP-GIP-treated mice did not show signs of glucose intolerance.

Conclusions/Significance

This study shows that vaccination against GIP was safe and effective. Thus active vaccination may represent a novel, long-lasting treatment for obesity. However further preclinical safety/toxicology studies will be required before the therapeutic concept can be addressed in humans.     

Coarse-grained molecular simulation of diffusion and reaction kinetics in a crowded virtual cytoplasm

We present a general-purpose model for biomolecular simulations at the molecular level that incorporates stochasticity, spatial dependence, and volume exclusion, using diffusing and reacting particles with physical dimensions. To validate the model, we first established the formal relationship between the microscopic model parameters (timestep, move length, and reaction probabilities) and the macroscopic coefficients for diffusion and reaction rate. We then compared simulation results with Smoluchowski theory for diffusion-limited irreversible reactions and the best available approximation for diffusion-influenced reversible reactions. To simulate the volumetric effects of a crowded intracellular environment, we created a virtual cytoplasm composed of a heterogeneous population of particles diffusing at rates appropriate to their size. The particle-size distribution was estimated from the relative abundance, mass, and stoichiometries of protein complexes using an experimentally derived proteome catalog from Escherichia coli K12. Simulated diffusion constants exhibited anomalous behavior as a function of time and crowding. Although significant, the volumetric impact of crowding on diffusion cannot fully account for retarded protein mobility in vivo, suggesting that other biophysical factors are at play. The simulated effect of crowding on barnase-barstar dimerization, an experimentally characterized example of a bimolecular association reaction, reveals a biphasic time course, indicating that crowding exerts different effects over different timescales. These observations illustrate that quantitative realism in biosimulation will depend to some extent on mesoscale phenomena that are not currently well understood.     

Residues at the active site of the esterase 2 from Alicyclobacillus acidocaldarius involved in substrate specificity and catalytic activity at high temperature.

The recently solved three-dimensional structure of the thermophilic esterase 2 from Alicyclobacillus acidocaldarius allowed us to have a snapshot of an enzyme-sulfonate complex, which mimics the second stage of the catalytic reaction, namely the covalent acyl-enzyme intermediate. The aim of this work was to design, by structure-aided analysis and to generate by site-directed and saturation mutagenesis, EST2 variants with changed substrate specificity in the direction of preference for monoacylesters whose acyl-chain length is greater than eight carbon atoms. Positions 211 and 215 of the polypeptide chain were chosen to introduce mutations. Among five variants with single and double amino acid substitutions, three were obtained, M211S, R215L, and M211S/R215L, that changed the catalytic efficiency profile in the desired direction. Kinetic characterization of mutants and wild type showed that this change was achieved by an increase in k(cat) and a decrease in K(m) values with respect to the parental enzyme. The M211S/R215L specificity constant for p-nitrophenyl decanoate substrate was 6-fold higher than the wild type. However, variants M211T, M211S, and M211V showed strikingly increased activity as well as maximal activity with monoacylesters with four carbon atoms in the acyl chain, compared with the wild type. In the case of mutant M211T, the k(cat) for p-nitrophenyl butanoate was 2.4-fold higher. Overall, depending on the variant and on the substrate, we observed improved catalytic activity at 70 degrees C with respect to the wild type, which was a somewhat unexpected result for an enzyme with already high k(cat) values at high temperature. In addition, variants with altered specificity toward the acyl-chain length were obtained. The results were interpreted in the context of the EST2 three-dimensional structure and a proposed catalytic mechanism in which k(cat), e.g. the limiting step of the reaction, was dependent on the acyl chain length of the ester substrate.