Characterization of the Rac guanine nucleotide exchange factor P-Rex1 in platelets

Background

Blood platelets undergo a carefully regulated change in shape to serve as the primary mediators of hemostasis and thrombosis. These processes manifest through platelet spreading and aggregation and are dependent on platelet actin cytoskeletal changes orchestrated by the Rho GTPase family member Rac1. To elucidate how Rac1 is regulated in platelets, we captured Rac1-interacting proteins from platelets and identified Rac1-associated proteins by mass spectrometry.

Findings

Here, we demonstrate that Rac1 captures the Rac guanine nucleotide exchange factor P-Rex1 from platelet lysates. Western blotting experiments confirmed that P-Rex1 is expressed in platelets and associated with Rac1. To investigate the functional role of platelet P-Rex1, platelets from P-Rex1 ^-/- -deficient mice were treated with platelet agonists or exposed to platelet activating surfaces of fibrinogen, collagen and thrombin. Platelets from P-Rex1 ^-/- mice responded to platelet agonists and activating surfaces similarly to wild type platelets.

Conclusions

These findings suggest that P-Rex1 is not required for Rac1-mediated platelet activation and that the GEF activities of P-Rex1 may be more specific to GPCR chemokine receptor mediated processes in immune cells and tumor cells.     

Hybrid metabolic flux analysis: combining stoichiometric and statistical constraints to model the formation of complex recombinant products

Background  

Stoichiometric models constitute the basic framework for fluxome quantification in the realm of metabolic engineering. A recurrent bottleneck, however, is the establishment of consistent stoichiometric models for the synthesis of recombinant proteins or viruses. Although optimization algorithms for in silico metabolic redesign have been developed in the context of genome-scale stoichiometric models for small molecule production, still rudimentary knowledge of how different cellular levels are regulated and phenotypically expressed prevents their full applicability for complex product optimization.     

Loss of genetic diversity in an outbreeding species: small population effects in the African wild dog <Emphasis Type="Italic">(Lycaon pictus</Emphasis>)

Genetic studies on the endangered African wild dog (Lycaon pictus) have primarily focused on the few remaining large and viable populations. However, investigations on the many isolated small African wild dog populations might also be informative for species management because the majority of extant populations are small and may contain genetic variability that is important for population persistence and for species conservation. Small populations are at higher risk of extinction from stochastic and deterministic demographic processes than larger populations and this is often of more immediate conservation concern than loss of genetic diversity, particularly for species that exhibit out-breeding behaviour such as long distance dispersal which may maintain gene flow. However, the genetic advantages of out-breeding behaviour may be reduced if dispersal is compromised beyond reserve borders (edge effects), further weakening the integrity of small populations. Mitochondrial DNA and 11 microsatellite genetic markers were used to investigate population genetic structure in a small population of out-breeding African wild dogs in Zambia, which occupies an historical dispersal corridor for the species. Results indicated the Zambian population suffered from low allelic richness, and there was significant evidence of a recent population bottleneck. Concurrent ecological data suggests these results were due to habitat fragmentation and restricted dispersal which compromised natural out-breeding mechanisms. This study recommends conservation priorities and management units for the African wild dog that focus on conserving remaining levels of genetic diversity, which may also be applicable for a range of out-breeding species.     

Populations genetically rifting within a complex geological system: The case of strong structure and low genetic diversity in the migratory freshwater catfish,Bagrus docmak,in East Africa

The complex geological history of East Africa has been a driving factor in the rapid evolution of teleost biodiversity. While there is some understanding of how macroevolutionary drivers have shaped teleost speciation in East Africa, there is a paucity of research into how the same biogeographical factors have affected microevolutionary processes within lakes and rivers. To address this deficiency, population genetic diversity, demography, and structure were investigated in a widely distributed and migratory (potamodromous) African teleost species, Ssemutundu (Bagrus docmak ). Samples were acquired from five geographical locations in East Africa within two major drainage basins; the Albertine Rift and Lake Victoria Basin. Individuals (N  = 175) were genotyped at 12 microsatellite loci and 93 individuals sequenced at the mitochondrial DNA control region. Results suggested populations from Lakes Edward and Victoria had undergone a severe historic bottleneck resulting in very low nucleotide diversity (π = 0.004 and 0.006, respectively) and negatively significant Fu values (?3.769 and ?5.049; p  < .05). Heterozygosity deficiencies and restricted effective population size (N _eLD) suggested contemporary exposure of these populations to stress, consistent with reports of the species decline in the East African Region. High genetic structuring between drainages was detected at both historical (?_ST = 0.62 for mtDNA; p  < .001) and contemporary (microsatellite F _ST = 0.460; p  < .001) levels. Patterns of low genetic diversity and strong population structure revealed are consistent with speciation patterns that have been linked to the complex biogeography of East Africa, suggesting that these biogeographical features have operated as both macro‐ and micro‐evolutionary forces in the formation of the East African teleost fauna.     

The first comprehensive genetic linkage map of a marsupial: the tammar wallaby (Macropus eugenii)

The production of a marsupial genetic linkage map is perhaps one of the most important objectives in marsupial research. This study used a total of 353 informative meioses and 64 genetic markers to construct a framework genetic linkage map for the tammar wallaby (Macropus eugenii). Nearly all markers (93.8%) formed a significant linkage (LOD > 3.0) with at least one other marker, indicating that the majority of the genome had been mapped. In fact, when compared with chiasmata data, >70% (828 cM) of the genome has been covered. Nine linkage groups were identified, with all but one (LG7; X-linked) allocated to the autosomes. These groups ranged in size from 15.7 to 176.5 cM and have an average distance of 16.2 cM between adjacent markers. Of the autosomal linkage groups (LGs), LG2 and LG3 were assigned to chromosome 1 and LG4 localized to chromosome 3 on the basis of physical localization of genes. Significant sex-specific distortions toward reduced female recombination rates were revealed in 22% of comparisons. When comparing the X chromosome data to closely related species it is apparent that they are conserved in both synteny and gene order.     

Low levels of genetic variation within introduced Javan rusa deer (<Emphasis Type="Italic">Cervus timorensis russa</Emphasis>) in Australia

Javan rusa deer (Cervus timorensis russa) is one of six introduced wild deer species in Australia. The largest population is located in the Royal National Park (RNP), New South Wales, Australia. Although the deer are considered a pest in certain areas, they are also commercially valuable. Using molecular markers we aimed to characterise the level of genetic diversity within the RNP population and identify a possible genetic bottleneck associated with the introduction of seven founding individuals. We also aimed to identify appropriate polymorphic microsatellite loci that could assist in commercial breeding programmes and wild population management in Australia. The results indicate that Javan rusa deer from the RNP (n=37) had an average (±SE) of only 2.29±0.095 alleles/locus, which is substantially lower than that reported in source populations from New Caledonia (7.60±0.933 alleles/locus). These data combined with the presence of genetic reduction signatures (P<0.001) indicate that this population has experienced a population bottleneck possibly at the time of establishment in Australia. Despite low allelic diversity, the large suite of identified polymorphic loci (n=24) shows promise for applications in population genetics, including parentage analysis (total parentage exclusion 0.944) within Australia. These data will contribute significantly to improving commercial breeding programmes and possibly to wild population management plans.     

The Role of Self-Compassion in Buffering Symptoms of Depression in the General Population

Self-compassion, typically operationalized as the total score of the Self-Compassion Scale (SCS; Neff, 2003b), has been shown to be related to increased psychological well-being and lower depression in students of the social sciences, users of psychology websites and psychotherapy patients. The current study builds on the existing literature by examining the link between self-compassion and depressive symptomatology in a sample representative of the German general population (n = 2,404). The SCS subscales of self-judgment, isolation, and over-identification, and the “self-coldness”, composite score, which encompass these three negative subscales, consistently differed between subsamples of individuals without any depressive symptoms, with any depressive syndromes, and with major depressive disorder. The contribution of the positive SCS subscales of self-kindness, common humanity, and mindfulness to the variance in depressive symptomatology was almost negligible. However, when combined to a “self-compassion composite”, the positive SCS subscales significantly moderated the relationship between “self-coldness” and depressive symptoms in the general population. This speaks for self-compassion having the potential to buffer self-coldness related to depression—providing an argument for interventions that foster self-caring, kind, and forgiving attitudes towards oneself.     

Reconstruction of cell population dynamics using CFSE

Background  

Quantifying cell division and death is central to many studies in the biological sciences. The fluorescent dye CFSE allows the tracking of cell division in vitro and in vivo and provides a rich source of information with which to test models of cell kinetics. Cell division and death have a stochastic component at the single-cell level, and the probabilities of these occurring in any given time interval may also undergo systematic variation at a population level. This gives rise to heterogeneity in proliferating cell populations. Branching processes provide a natural means of describing this behaviour.     

CXCR7 expression disrupts endothelial cell homeostasis and causes ligand-dependent invasion

The homeostatic function of endothelial cells (EC) is critical for a number of physiological processes including vascular integrity, immunity, and wound healing. Indeed, vascular abnormalities resulting from EC dysfunction contribute to the development and spread of malignancies. The alternative SDF-1/CXCL12 receptor CXCR7 is frequently and specifically highly expressed in tumor-associated vessels. In this study, we investigate whether CXCR7 contributes to vascular dysfunction by specifically examining the effect of CXCR7 expression on EC barrier function and motility. We demonstrate that CXCR7 expression in EC results in redistribution of CD31/PECAM-1 and loss of contact inhibition. Moreover, CXCR7+ EC are deficient in barrier formation. We show that CXCR7-mediated motility has no influence on angiogenesis but contributes to another motile process, the invasion of CXCR7+ EC into ligand-rich niches. These results identify CXCR7 as a novel manipulator of EC barrier function via alteration of PECAM-1 homophilic junctions. As such, aberrant expression of CXCR7 in the vasculature has the potential to disrupt vascular homeostasis and could contribute to vascular dysfunction in cancer systems.