Prevalence and polymorphism of a mussel transmissible cancer in Europe

Transmissible cancers are parasitic malignant cell lineages that acquired the ability to infect new hosts from the same species, or sometimes related species. First described in dogs and Tasmanian devils, transmissible cancers were later discovered in some marine bivalves affected by a leukemia-like disease. In Mytilus mussels, two lineages of Bivalve Transmissible Neoplasia (BTN), both emerged in a M. trossulus founder individual, have been described to date (MtrBTN1 and MtrBTN2). Here, we performed an extensive screening of genetic chimerism, a hallmark of transmissible cancer, by genotyping hundred SNPs of thousands of European Mytilus mussels. The genetic analysis allowed us to simultaneously obtain the genotype of hosts -M. edulis, M. galloprovincialis or hybrids- and the genotype of tumors of heavily infected individuals. In addition, a subset of individuals were systematically genotyped and analysed by histology in order to screen for possible non-transmissible cancers. We detected MtrBTN2 at low prevalence in M. edulis, and also in M. galloprovincialis and hybrids although at a much lower prevalence. No MtrBTN1 or new BTN were found but a few individuals with non-transmissible neoplasia were observed at a single polluted site on the same sampling date. We observed a diversity of MtrBTN2 genotypes that appeared more introgressed or more ancestral than MtrBTN1 and reference healthy M. trossulus individuals. The observed polymorphism is most likely due to somatic null alleles caused by structural variations or point mutations in primer-binding sites leading to enhanced detection of the host alleles. Despite low prevalence, two divergent sublineages, confirmed by mtCOI sequences, are co-spreading in the same geographic area, suggesting a complex diversification of MtrBTN2 since its emergence and host species shift.

Facultative social exploitation among Myxoccocus bacteria due to non-responsive local competition

Microbes cooperate in many ways, but it is unclear to what extent they also have adaptations to detect and exploit unrelated social partners. Experimental data often cannot discriminate between social exploitation caused by complex adaptive traits and exploitation caused by simple deleterious mutations. Here we demonstrate facultative social exploitation among Myxococcus bacteria due to simple non-responsive local competition. We show that the time dynamics of developmental exploitation by a tan phase variant are consistent with a model where cells do not respond to the presence of other genotypes but simply compete for some shared resource necessary to produce spores. The model also predicts the frequency-dependent responses of strains to genetic chimerism in multicellular fruiting bodies. Interactions between naturally occuring soil isolates, on the other hand, are consistent with strong interference competition where the winner almost completely prevents the loser from producing any spores. These results show how facultative social exploitation does not require elaborate mechanisms to detect and respond to foreign genotypes but can instead be caused by simple competition acting on a local scale. Myxococcus cells, like social insects, cooperate in some ways while simultaneously competing in others.

The Effect of Using DNA Obtained from Blood of Cattle with Genetic Chimerism on Illumina’s Beadchip Assay Performance

Blood cell chimerism is a common phenomenon occurring in cattle coming from double or multiple parturitions and can be observed as two DNA profiles present in blood of each of twin born animals. In the era of genomics, a large number of animals is being genotyped with high throughput genotyping methods, which are giving limited insight into the performance of single markers and rather only statistical description of the results is available for a common user. This hampers the detailed analysis of the results obtained and direct identification of the causes of poorer performance of some samples. In this study we describe the influence of analysis of DNA obtained from blood samples of cattle with genetic chimerism on basic parameters of Infinium technology-based Illumina’s genotyping arrays. The results obtained may help to identify such samples, especially when no precise information about the animals’ origin is available

The induced sector Arabidopsis apical embryonic fate map

Creation of an embryonic fate map may provide insight into the patterns of cell division and specification contributing to the apical region of the early Arabidopsis embryo. A fate map has been constructed by inducing genetic chimerism during the two-apical-cell stage of embryogenesis to determine if the orientation of the first anticlinal cell division correlates with later developmental axes. Chimeras were also used to map the relative locations of precursors of the cotyledon and leaf primordia. Genetic chimeras were induced in embryos doubly heterozygous for a heat shock regulated Cre recombinase and a constitutively expressed β-glucuronidase (GUS) gene flanked by the loxP binding sites for Cre. Individual cells in the two-apical-cell stage embryo responding to heat shock produce GUS-negative daughter cells. Mature plants grown from seed derived from treated embryos were scored for GUS-negative sector extent in the cotyledons and leaves. The GUS-negative daughters of apical cells had a strong tendency to contribute primarily to one cotyledon or the other and to physically adjacent true leaf margins. This result indicated that patterns of early cell division correlate with later axes of symmetry in the embryo and that these patterns partially limit the fates available for adoption by daughter cells. However, GUS-negative sectors were shared between all regions of the mature plant, suggesting that there is no strict fate restriction imposed on the daughters of the first apical cells.