Molecular Reclassification of Crohn’s Disease: A Cautionary Note on Population Stratification

Complex human diseases commonly differ in their phenotypic characteristics, e.g., Crohn’s disease (CD) patients are heterogeneous with regard to disease location and disease extent. The genetic susceptibility to Crohn’s disease is widely acknowledged and has been demonstrated by identification of over 100 CD associated genetic loci. However, relating CD subphenotypes to disease susceptible loci has proven to be a difficult task. In this paper we discuss the use of cluster analysis on genetic markers to identify genetic-based subgroups while taking into account possible confounding by population stratification. We show that it is highly relevant to consider the confounding nature of population stratification in order to avoid that detected clusters are strongly related to population groups instead of disease-specific groups. Therefore, we explain the use of principal components to correct for population stratification while clustering affected individuals into genetic-based subgroups. The principal components are obtained using 30 ancestry informative markers (AIM), and the first two PCs are determined to discriminate between continental origins of the affected individuals. Genotypes on 51 CD associated single nucleotide polymorphisms (SNPs) are used to perform latent class analysis, hierarchical and Partitioning Around Medoids (PAM) cluster analysis within a sample of affected individuals with and without the use of principal components to adjust for population stratification. It is seen that without correction for population stratification clusters seem to be influenced by population stratification while with correction clusters are unrelated to continental origin of individuals.     

Body condition helps to explain metabolic rate variation in wolf spiders

1. Metabolism is the fundamental process that powers life. Understanding what drives metabolism is therefore critical to our understanding of the ecology and behaviour of organisms in nature. 2. Metabolic rate generally scales with body size according to a power law. However, considerable unexplained variation in metabolic rate remains after accounting for body mass with scaling functions. 3. We measured resting metabolic rates (oxygen consumption) of 227 field‐caught wolf spiders. Then, we tested for effects of body mass, species, and body condition on metabolic rate. 4. Metabolic rate scales with body mass to the 0.85 power in these wolf spiders, and there are metabolic rate differences between species. After accounting for these factors, residual variation in metabolic rate is related to spider body condition (abdomen:cephalothorax ratio). Spiders with better body condition consume more oxygen. 5. These results indicate that recent foraging history is an important determinant of metabolic rate, suggesting that although body mass and taxonomic identity are important, other factors can provide helpful insights into metabolic rate variation in ecological communities.     

Pinocytic uptake and intracellular degradation of N-(2-hydroxypropyl)methacrylamide copolymers a potential drug delivery system

Synthetic ¹²⁵I-labelled N-(2-hydroxypropyl)methacrylamide copolymers containing four different, potentially degradable peptidyl side chains were incubated with rat visceral yolk sacs cultured in vitro. All copolymers were captured by fluid-phase pinocytosis and three of the side chains were susceptible to lysosomal hydrolysis, resulting in release of [¹²⁵I]iodotyrosine back into the culture medium. Uptake and degradation was completely inhibited by 2,4-dinitrophenol. The thiol-proteinase inhibitor leupeptin did not affect the rate of pinocytosis, but caused different degrees of inhibition of hydrolysis depending on side chain composition.     

Hyperosmosis enhances radiation and hydroxyurea resistance of Schizosaccharomyces pombe checkpoint mutants through the spindle checkpoint and delayed cytokinesis

The DNA damage and stress response pathways interact to regulate cellular responses to genotoxins and environmental stresses. How these pathways interact in Schizosaccharomyces pombe is not well understood. We demonstrate that osmotic stress suppresses the DNA damage sensitivity of checkpoint mutants, and that this occurs through three distinct cell cycle delays. A delay in G2/M is dependent on Srk1. Progression through mitosis is halted by the Mad2‐dependent spindle checkpoint. Finally, cytokinesis is impaired by modulating Cdc25 expression. These three delays, imposed by osmotic stress, together compensate for the loss of checkpoint signalling.