Evolutionary impact of human Alu repetitive elements

Early studies of human Alu retrotransposons focused on their origin, evolution and biological properties, but current focus is shifting toward the effect of Alu elements on evolution of the human genome. Recent analyses indicate that numerous factors have affected the chromosomal distribution of Alu elements over time, including male-driven insertions, deletions and rapid CpG mutations after their retrotransposition. Unequal crossing over between Alu elements can lead to local mutations or to large segmental duplications responsible for genetic diseases and long-term evolutionary changes. Alu elements can also affect human (primate) evolution by introducing alternative splice sites in existing genes. Studying the Alu family in a human genomic context is likely to have general significance for our understanding of the evolutionary impact of other repetitive elements in diverse eukaryotic genomes.     

Orthologs, paralogs and genome comparisons

During the past decade, ancient gene duplications were recognized as one of the main forces in the generation of diverse gene families and the creation of new functional capabilities. New tools developed to search data banks for homologous sequences, and an increased availability of reliable three-dimensional structural information led to the recognition that proteins with diverse functions can belong to the same superfamily. Analyses of the evolution of these superfamilies promises to provide insights into early evolution but are complicated by several important evolutionary processes. Horizontal transfer of genes can lead to a vertical spread of innovations among organisms, therefore finding a certain property in some descendants of an ancestor does not guarantee that it was present in that ancestor. Complete or partial gene conversion between duplicated genes can yield phylogenetic trees with several, apparently independent gene duplications, suggesting an often surprising parallelism in the evolution of independent lineages. Additionally, the breakup of domains within a protein and the fusion of domains into multifunctional proteins makes the delineation of superfamilies a task that remains difficult to automate.     

Neurobiology: Paper alert

A selection of interesting papers that were published in the two months before our press date in major journals most likely to report significant results in neurobiology.     

Motor systems: Neurobiology of behaviour: Web alert

A selection of World Wide Web sites relevant to the reviews published in this issue of Current Opinion in Neurobiology.     

Genomic changes following host restriction in bacteria

Many genomic sequences have been recently published for bacteria that can replicate only within eukaryotic hosts. Comparisons of genomic features with those of closely related bacteria retaining free-living stages indicate that rapid evolutionary change often occurs immediately after host restriction. Typical changes include a large increase in the frequency of mobile elements in the genome, chromosomal rearrangements mediated by recombination among these elements, pseudogene formation, and deletions of varying size. In anciently host-restricted lineages, the frequency of insertion sequence elements decreases as genomes become extremely small and strictly clonal. These changes represent a general syndrome of genome evolution, which is observed repeatedly in host-restricted lineages from numerous phylogenetic groups. Considerable variation also exists, however, in part reflecting unstudied aspects of the population structure and ecology of host-restricted bacterial lineages.     

Neurobiology

A selection of interesting papers that were published in the two months before our press date in major journals most likely to report significant results in neurobiology.     

The devil in the details of life-history evolution: Instability and reversal of genetic correlations during selection on<Emphasis Type="Italic">Drosophila</Emphasis> development

The evolutionary relationships between three major components of Darwinian fitness, development rate, growth rate and preadult survival, were estimated using a comparison of 55 distinct populations ofDrosophila melanogaster variously selected for age-specific fertility, environmental-stress tolerance and accelerated development. Development rate displayed a strong net negative evolutionary correlation with weight at eclosion across all selection treatments, consistent with the existence of a size-versus-time tradeoff between these characters. However, within the data set, the magnitude of the evolutionary correlation depended upon the particular selection treatments contrasted. A previously proposed tradeoff between preadult viability and growth rate was apparent only under weak selection for juvenile fitness components. Direct selection for rapid development led to sharp reductions in both growth rates and viability. These data add to the mounting results from experimental evolution that illustrate the sensitivity of evolutionary correlations to (i) genotype-by-environment (G X E) interaction, (ii) complex functional-trait interactions, and (iii) character definition. Instability, disappearance and reversal of patterns of genetic covariation often occur over short evolutionary time frames and as the direct product of selection, rather than some stochastic process. We suggest that the functional architecture of fitness is a rapidly evolving matrix with reticulate properties, a matrix that we understand only poorly.     

Chemical biology: Paper alert

A selection of interesting papers that were published in the two months before our press date in major journals most likely to report significant results in chemical biology.     

Pharmaceutical biotechnology, Chemical biotechnology: Web alert

A selection of World Wide Web sites relevant to papers published in this issue of Current Opinion in Biotechnology.     

Growth and development

A selection of World Wide Web sites relevant to papers published in this issue of Current Opinion in Microbiology.     

Human altruism: economic, neural, and evolutionary perspectives

Human cooperation represents a spectacular outlier in the animal world. Unlike other creatures, humans frequently cooperate with genetically unrelated strangers, often in large groups, with people they will never meet again, and when reputation gains are small or absent. Experimental evidence and evolutionary models suggest that strong reciprocity, the behavioral propensity for altruistic punishment and altruistic rewarding, is of key importance for human cooperation. Here, we review both evidence documenting altruistic punishment and altruistic cooperation and recent brain imaging studies that combine the powerful tools of behavioral game theory with neuroimaging techniques. These studies show that mutual cooperation and the punishment of defectors activate reward related neural circuits, suggesting that evolution has endowed humans with proximate mechanisms that render altruistic behavior psychologically rewarding.     

Microbiology: Paper alert

A selection of interesting papers that were published in the two months before our press date in major journals most likely to report significant results in microbiology.     

Growth and development. Web alert

A selection of World Wide Web sites relevant to the reviews published in this issue of Current Opinion in Microbiology.     

Pharmaceutical biotechnology: Chemical biotechnology: Web alert

A selection of World Wide Web sites relevant to papers published in this issue of Current Opinion in Biotechnology.     

Motor systems: Neurobiology of behaviour

A selection of World Wide Web sites relevant to papers published in this issue of Current Opinion in Neurobiology.     

Proteins

Proteins continue to surprise and amaze us in the myriad of ways in which they achieve biological function. The Proteins section in this issue of Current Opinion in Structural Biology highlights several proteins in which large conformational changes and evolutionary divergence in structure and function, play essential roles in their adaptation to a variety of biological functions. In addition, fundamental advances have been made in research, spurred on by industrial interest in the use of proteins as drug targets or as catalysts. All of the reviews in this section document the fact that multiple crystal structures of a protein in different functional states, and of different members of protein families, are necessary for the composition of a complete structural picture.     

Web alert. Biopolymers model systems

A selection of World Wide Web sites relevant to papers published in this issue of Current Opinion in Chemical Biology.     

Reward representations and reward-related learning in the human brain: insights from neuroimaging

This review outlines recent findings from human neuroimaging concerning the role of a highly interconnected network of brain areas including orbital and medial prefrontal cortex, amygdala, striatum and dopaminergic mid-brain in reward processing. Distinct reward-related functions can be attributed to different components of this network. Orbitofrontal cortex is involved in coding stimulus reward value and in concert with the amygdala and ventral striatum is implicated in representing predicted future reward. Such representations can be used to guide action selection for reward, a process that depends, at least in part, on orbital and medial prefrontal cortex as well as dorsal striatum.     

Cell biology. Web alert

A selection of World Wide Web sites relevant to papers published in this issue of Current Opinion in Plant Biology.     

Chemical biology

A selection of interesting papers that were published in the two months before our press date in major journals most likely to report significant results in chemical biology.