Allelic diversity at the Mhc-DQA locus of woodmouse populations (Apodemus sylvaticus) present in the islands and mainland of the northern Mediterranean

Aim Polymorphism at neutral markers and at MHC loci in rodent populations living on islands is generally low. The main genetic factors that may contribute to a reduced level of genetic variability are genetic drift, reduced gene flow and founder events. We investigated the pattern of polymorphism at the second exon of the Mhc‐DQA gene in island populations of Apodemus sylvaticus and in their mainland counterparts to investigate the pattern of MHC polymorphism in a phylogeographical context and to assess the impact of insularity on diversity at this locus. Location Eight north Mediterranean populations of Apodemus sylvaticus were studied, including five island populations (Majorca, Minorca, Porquerolles, Port‐Cros and Sicily) and three mainland populations. Methods cDNA sequencing and nucleotide sequences analyses. Synonymous and non‐synonymous substitutions were examined at the PBR and non‐PBR sites. The DQA allelic distribution in populations was compared with the woodmouse phylogeography. Results This study presents novel DQA alleles. High polymorphism of the DQA locus is recorded in natural populations of A. sylvaticus with 13 alleles being widely distributed irrespective of the geographical origin and palaeoclimatic history of populations. The DQA locus does not show the expected pattern for non‐synonymous substitutions at the PBR sites. However, island populations show a weak loss of polymorphism in comparison with their mainland counterparts. Main conclusions The DQA locus in the woodmouse seems to be subject to weak selection and does not allow resolution of phylogeographical relationships among European woodmouse populations. The presence of at least three alleles in island populations and the maintenance of five alleles between the two European lineages over 1.5 Myr suggest that balancing selection may act within populations, and more precisely within island populations, to maintain genetic variability. This study shows that phylogeographical studies are a prerequisite for any genetic investigation of selected genes in natural populations.     

Genetic distinction between contiguous urban and rural multimammate mice in Tanzania despite gene flow

Special conditions are required for genetic differentiation to arise at a local geographical scale in the face of gene flow. The Natal multimammate mouse, Mastomys natalensis, is the most widely distributed and abundant rodent in sub‐Saharan Africa. A notorious agricultural pest and a natural host for many zoonotic diseases, it can live in close proximity to humans and appears to compete with other rodents for the synanthropic niche. We surveyed its population genetic structure across a 180‐km transect in central Tanzania along which the landscape varied between agricultural land in a rural setting and natural woody vegetation, rivers, roads and a city (Morogoro). We sampled M. natalensis across 10 localities and genotyped 15 microsatellite loci from 515 individuals. Hierarchical STRUCTURE analyses show a K‐invariant pattern distinguishing Morogoro suburbs (located in the centre of the transect) from nine surrounding rural localities. Landscape connectivity analyses in Circuitscape and comparison of rainfall patterns suggest that neither geographical isolation nor natural breeding asynchrony could explain the genetic differentiation of the urban population. Using the isolation‐with‐migration model implemented in IMa2, we inferred that a split between suburban and rural populations would have occurred recently (<150 years ago) with higher urban effective population density consistent with an urban source to rural sink of effective migration. The observed genetic differentiation of urban multimammate mice is striking given the uninterrupted distribution of the animal throughout the landscape and the high estimates of effective migration (2N_eM = 3.0 and 29.7), suggesting a strong selection gradient across the urban boundary.     

Endothelial cell junctions

In the course of a freeze-cleave study on intercellular junctions in the regenerating rat liver, we observed an unusual array of intramembranous particles located in regions of contact between endothelial cells lining the hepatic sinusoids. These arrays were characterized by an accumulation of particles which resembled a zonula occludens in their linear deployment but differed in that the contact regions were composed of individual particles which remained separated from each other by regular particle-free intervals.     

Metabolic characterization of primary human colorectal cancers using high resolution magic angle spinning 1H magnetic resonance spectroscopy

Colorectal cancer is one of the most frequent and most lethal forms of cancer in the western world. The aim of this study is to characterize by ¹H high resolution magic angle spinning NMR spectroscopy (HRMAS) the metabolic fingerprint of both tumoral and healthy tissue samples obtained from a cohort of patients affected by primary colorectal adenocarcinoma. By analyzing HRMAS data using multivariate statistical analysis (PLS-DA), the two types of tissues could be discriminated with a high level of confidence. The identification of the metabolites at the origin of this discrimination revealed that adenocarcinomas are richer in taurine, glutamate, aspartate, and lactate whereas healthy tissues contain a higher amount of myo-inositol and β-glucose. The statistical model resulting from the PLS-DA analysis was subsequently used to perform a blind test on tumoral and healthy colon biopsies. The results of the classification showed that the HRMAS analysis has very high sensitivity and specificity.     

WHERE ARE THE WORMY MICE? A REEXAMINATION OF HYBRID PARASITISM IN THE EUROPEAN HOUSE MOUSE HYBRID ZONE

Wormy mice in a hybrid zone have been interpreted as evidence of low hybrid fitness, such that parasites contribute to species separation. However, because of its natural heterogeneity, observations of parasite load must be numerous with good field area coverage. We sampled 689 mice from 107 localities across the Bavaria-Bohemia region of the European house mouse hybrid zone and calculated their hybrid indices using 1401 diagnostic single nucleotide polymorphisms (SNPs). We tested whether hybrids have greater or lesser diversity and load of parasite helminths than additive expectations, performing load analyses on the four most common taxa. We found hybrids have significantly reduced diversity and load of each of the commonest helminths; rarer helminths further support reduced load. Although within-locality comparisons have little power, randomization tests show the repeated pattern is unlikely to be due to local parasite heterogeneity, and simulations show a patch of low parasite diversity is unlikely to fall by chance just so in the field area, such that it produces the observed effects. Our data therefore contradict the idea that helminths reduce hybrid fitness through increased load. We discuss a vicariant Red Queen model that implies immune genes tracking parasites will escape Dobzhansky-Muller incompatibilities, generating hybrid variants untargeted by parasites.