Search results for "Negative selection"

Regulatory T-Cells in Antitumor Therapy: Isolation and Functional Testing of CD4<SUP>+</SUP>CD25<SUP>+</SUP> Regulatory T-Cel…

2004

Naturally occurring CD4+CD25+ T regulatory cells originate from the thymus and play a central role regarding the maintenance of peripheral tolerance by suppression of autoreactive T-cell populations. However, T regulatory cells can have beneficial as well as harmful effects. On the one hand, they prevent a variety of autoimmune and inflammatory diseases; but on the other hand, they concomitantly inhibit antitumor immune reactions by suppressing tumor-specific T-cell responses. Therefore, these ambivalent properties of T regulatory cells require detailed investigation especially with respect to a potential therapeutic exploitation of these cells. A prerequisite for such analyses is the isola…

Genomic determinants of speciation and spread of the Mycobacterium tuberculosis complex

2019

14 páginas, 6 figuras

2006

Understanding evolutionary processes that drive genome reduction requires determining the tempo (rate) and the mode (size and types of deletions) of gene losses. In this study, we analysed five endosymbiotic genome sequences of the gamma-proteobacteria (three different Buchnera aphidicola strains, Wigglesworthia glossinidia, Blochmannia floridanus) to test if gene loss could be driven by the selective importance of genes. We used a parsimony method to reconstruct a minimal ancestral genome of insect endosymbionts and quantified gene loss along the branches of the phylogenetic tree. To evaluate the selective or functional importance of genes, we used a parameter that measures the level of ad…

EFFECT OF DELETERIOUS MUTATION-ACCUMULATION ON THE FITNESS OF RNA BACTERIOPHAGE MS2

2000

RNA viruses show the highest mutation rate in nature. It has been extensively demonstrated that, in the absence of purifying selection, RNA viruses accumulate deleterious mutations at a high rate. However, the parameters describing this accumulation are, in general, poorly understood. The present study reports evidences for fitness declines by the accumulation of deleterious mutations in the bacteriophage MS2. We estimated the rate of fitness decline to be as high as 16% per bottleneck transfer. In addition, our results agree with an additive model of fitness effects.

Gene connectivity and enzyme evolution in the human metabolic network

2019

[Background] Determining the factors involved in the likelihood of a gene being under adaptive selection is still a challenging goal in Evolutionary Biology. Here, we perform an evolutionary analysis of the human metabolic genes to explore the associations between network structure and the presence and strength of natural selection in the genes whose products are involved in metabolism. Purifying and positive selection are estimated at interspecific (among mammals) and intraspecific (among human populations) levels, and the connections between enzymatic reactions are differentiated between incoming (in-degree) and outgoing (out-degree) links.

Evolutionary Dissection of the Dot/Icm System Based on Comparative Genomics of 58 Legionella Species

2019

14 páginas, 2 figuras, 2 tablas

The molecular evolution of sperm zonadhesin.

2008

Based on pioneering work of Hardy and Garbers, zonadhesin has become one of the best studied sperm ligands in boreoeutherian mammals, both from a biochemical and evolutionary perspective. Zonadhesin is a mosaic-type protein that localizes to the apical head of spermatozoa. In pig, cattle, rabbit and primates, zonadhesin precursor essentially consists of two or three MAM (meprin/A5 antigen/mu receptor tyrosine phosphatase) domains, one mucin-like domain, one incomplete and four complete D domains (homologous to vWFD). Mouse zonadhesin is distinguished from this general pattern by 20 extra partial D3 domains. While concerted evolution drives the divergence of the mucin-like domain in the orth…

INTERSPECIFIC AGGRESSION CAUSES NEGATIVE SELECTION ON SEXUAL CHARACTERS

2005

Interspecific aggression originating from mistaken species recognition may cause selection on secondary sexual characters, but this hypothesis has remained untested. Here we report a field experiment designed to test directly whether interspecific aggression causes selection on secondary sexual characters, wing spots, in wild damselfly populations. Males of Calopteryx virgo are more aggressive toward males of C. splendens with large than with small wing spots. This differential interspecific aggression may cause negative selection on wing spot size. Indeed, our results show that directional survival selection on wing spot size of C. splendens males was changed by experimental removal of C. …

Evolution of Snake Venom Disintegrins by Positive Darwinian Selection

2008

PII-disintegrins, cysteine-rich polypeptides broadly distributed in the venoms of geographically diverse species of vipers and rattlesnakes, antagonize the adhesive functions of beta(1) and beta(3) integrin receptors. PII-disintegrins evolved in Viperidae by neofunctionalization of disintegrin-like domains of duplicated PIII-snake venom hemorrhagic metalloproteinase (SVMP) genes recruited into the venom proteome before the radiation of the advanced snakes. Minimization of the gene (loss of introns and coding regions) and the protein structures (successive loss of disulfide bonds) underpins the postduplication divergence of disintegrins. However, little is known about the underlying genetic …

Genomic determinants of protein folding thermodynamics in prokaryotic organisms.

2004

Here we investigate how thermodynamic properties of orthologous proteins are influenced by the genomic environment in which they evolve. We performed a comparative computational study of 21 protein families in 73 prokaryotic species and obtained the following main results. (i) Protein stability with respect to the unfolded state and with respect to misfolding are anticorrelated. There appears to be a trade-off between these two properties, which cannot be optimized simultaneously. (ii) Folding thermodynamic parameters are strongly correlated with two genomic features, genome size and G+C composition. In particular, the normalized energy gap, an indicator of folding efficiency in statistical…