Differential impact of retrotransposon populations on the genome of allotetraploid tobacco (<Emphasis Type="Italic">Nicotiana tabacum</Emphasis>)

LTR-retrotransposons contribute substantially to the structural diversity of plant genomes. Recent models of genome evolution suggest that retrotransposon amplification is offset by removal of retrotransposon sequences, leading to a turnover of retrotransposon populations. While bursts of amplification have been documented, it is not known whether removal of retrotransposon sequences occurs continuously, or is triggered by specific stimuli over short evolutionary periods. In this work, we have characterized the evolutionary dynamics of four populations of copia-type retrotransposons in allotetraploid tobacco (Nicotiana tabacum) and its two diploid progenitors Nicotiana sylvestris and Nicotiana tomentosiformis. We have used SSAP (Sequence-Specific Amplification Polymorphism) to evaluate the contribution retrotransposons have made to the diversity of tobacco and its diploid progenitor species, to quantify the contribution each diploid progenitor has made to tobacco's retrotransposon populations, and to estimate losses or amplifications of retrotransposon sequences subsequent to tobacco's formation. Our results show that the tobacco genome derives from a turnover of retrotransposon sequences with removals concomitant with new insertions. We have detected unique behaviour specific to each retrotransposon population, with differences likely reflecting distinct evolutionary histories and activities of particular elements. Our results indicate that the retrotransposon content of a given plant species is strongly influenced by the host evolutionary history, with periods of rapid turnover of retrotransposon sequences stimulated by allopolyploidy.     

Carboxypeptidase cathepsin X mediates beta2-integrin-dependent adhesion of differentiated U-937 cells

Cathepsin X is a lysosomal carboxypeptidase with a potential role in processes of inflammation and immune response. The integrin-binding motifs RGD and ECD, present in the pro- and in mature forms of cathepsin X, respectively, suggest that this enzyme might have a function in cell signaling and adhesion. In this study, we report that cysteine protease inhibitors E-64 and CA-074 and 2F12 monoclonal antibody, all of which inhibit cathepsin X activity, significantly reduced adhesion of differentiated U-937 cells to polystyrene- and fibrinogen-coated surfaces via Mac-1 integrin receptor, whereas their binding to vitronectin, fibronectin or Matrigel was not affected. On the other hand, cathepsin X, added to differentiating U-937 cells, stimulated their adhesion. Using confocal microscopy, we demonstrated that the pro-form of cathepsin X was co-localized with beta(2) and beta(3) integrin subunits and its mature form solely with the beta(2) integrin subunit with the most intense signal in cell-cell junctions in differentiated U-937 cells and in co-cultures with endothelial cells. Our results indicate that active cathepsin X mediates the function of beta(2) integrin receptors during cell adhesion and that it could also be involved in other processes associated with beta(2) integrin receptors such as phagocytosis and T cell activation.     

Repeated reunions and splits feature the highly dynamic evolution of 5S and 35S ribosomal RNA genes (rDNA) in the Asteraceae family

Background  

In flowering plants and animals the most common ribosomal RNA genes (rDNA) organisation is that in which 35S (encoding 18S-5.8S-26S rRNA) and 5S genes are physically separated occupying different chromosomal loci. However, recent observations established that both genes have been unified to a single 35S-5S unit in the genus Artemisia (Asteraceae), a genomic arrangement typical of primitive eukaryotes such as yeast, among others. Here we aim to reveal the origin, distribution and mechanisms leading to the linked organisation of rDNA in the Asteraceae by analysing unit structure (PCR, Southern blot, sequencing), gene copy number (quantitative PCR) and chromosomal position (FISH) of 5S and 35S rRNA genes in ~200 species representing the family diversity and other closely related groups.     

Bardet–Biedl Syndrome ciliopathy is linked to altered hematopoiesis and dysregulated self‐tolerance

Bardet–Biedl Syndrome (BBS) is a pleiotropic genetic disease caused by the dysfunction of primary cilia. The immune system of patients with ciliopathies has not been investigated. However, there are multiple indications that the impairment of the processes typically associated with cilia may have influence on the hematopoietic compartment and immunity. In this study, we analyze clinical data of BBS patients and corresponding mouse models carrying mutations in Bbs4 or Bbs18. We find that BBS patients have a higher prevalence of certain autoimmune diseases. Both BBS patients and animal models have altered red blood cell and platelet compartments, as well as elevated white blood cell levels. Some of the hematopoietic system alterations are associated with BBS‐induced obesity. Moreover, we observe that the development and homeostasis of B cells in mice is regulated by the transport complex BBSome, whose dysfunction is a common cause of BBS. The BBSome limits canonical WNT signaling and increases CXCL12 levels in bone marrow stromal cells. Taken together, our study reveals a connection between a ciliopathy and dysregulated immune and hematopoietic systems.     

The Evolutionary Dynamics of Genetic Incompatibilities Introduced by Duplicated Genes in Arabidopsis thaliana

Although gene duplications provide genetic backup and allow genomic changes under relaxed selection, they may potentially limit gene flow. When different copies of a duplicated gene are pseudofunctionalized in different genotypes, genetic incompatibilities can arise in their hybrid offspring. Although such cases have been reported after manual crosses, it remains unclear whether they occur in nature and how they affect natural populations. Here, we identified four duplicated-gene based incompatibilities including one previously not reported within an artificial Arabidopsis intercross population. Unexpectedly, however, for each of the genetic incompatibilities we also identified the incompatible alleles in natural populations based on the genomes of 1,135 Arabidopsis accessions published by the 1001 Genomes Project. Using the presence of incompatible allele combinations as phenotypes for GWAS, we mapped genomic regions that included additional gene copies which likely rescue the genetic incompatibility. Reconstructing the geographic origins and evolutionary trajectories of the individual alleles suggested that incompatible alleles frequently coexist, even in geographically closed regions, and that their effects can be overcome by additional gene copies collectively shaping the evolutionary dynamics of duplicated genes during population history.     

Coupling between vesicle shape and the non-homogeneous lateral distribution of membrane constituents in Golgi bodies

In this work, a hypothesis is presented that could explain the non-homogeneous lateral distribution of membrane components in Golgi vesicles. It is shown that the non-homogeneous lateral distribution of membrane components and the specific flattened shape of Golgi vesicles are strongly coupled. In agreement with experimental evidence, it is indicated that some of the membrane components may be concentrated mainly on the curved bulbous rims of the Golgi vesicles, while the other components are distributed predominantly in their flat central part.     

Endovesicle formation and membrane perturbation induced by polyoxyethyleneglycolalkylethers in human erythrocytes

Polyoxyethyleneglycolalkylether (CmEn, m=12, n=8) can induce a large torocyte-like endovesicle in human erythrocytes. The present study aimed to examine how variations in the molecular structure of CmEn (m=10,12,14,16,18; n=1-10,23) affect the occurrence of torocyte endovesicles. Our results show that torocytes occur most frequently when m=12,14 and n=8,9. At this molecular configuration the detergents induce inward membrane bending (stomatocytic S1-S2 shapes) resulting in the formation of a large membrane invagination. These detergents have a strong membrane perturbing, i.e., haemolytic, effect. Theoretical calculations indicate that a torocyte-shaped inside-out membrane vesicle can be created from a large membrane invagination due to the impact of laterally mobile anisotropic membrane inclusions. Such inclusions may be detergent-membrane component complexes or unanchored integral membrane proteins. It is shown that a nonhomogeneous lateral distribution of anisotropic membrane inclusions may stabilise the torocyte endovesicle shape, characterised by having opposite membranes in the thin central region of the vesicles separated by a certain distance. Tubular, conical or inverted conical isotropic inclusions cannot do so.