Is There Selection on RFLP Differences in Mitochondrial Dna?

Experimental populations of Drosophila simulans were established for the purpose of detecting the presence or absence of selection on a restriction fragment length polymorphism in mitochondrial DNA (mtDNA). It was then discovered that the founding strains differed with respect to the Rickettsia-mediated incompatibility system in this species, which is maternally transmitted together with the mtDNA differences. A population model was constructed using the known fitness effects of the incompatibility system, with the result that the population trajectories can be completely explained by the effects of the microorganism with no need to invoke selection on mtDNA. The strong conclusion is that in this case we can rule out the strong selection proposed by MacRae and Anderson to explain the "dramatic mtDNA changes" in their Drosophila pseudoobscura populations. The population theory used for the experiments is discussed in the context of natural populations. Estimated parameters include the possibility that with two populations, one with the organism and one without it, there may be no bias as to which will invade the other, which in turn suggests no global tendency for the infection to spread or decline.     

Maintenance of function without selection:Alu sequences as “Cheap Genes”

Summary Continued insertion into the genome of functionalAlu sequences is expected to compensate for the functional eclipse of older sequences attributable to structural adulteration and can be presumed to establish a renewable store of functional sequences at a relatively elevated numerical level. This store of functional sequences could be maintained at almost no selective cost. A strategy of maintaining function in multiple sequence copies with selection limited to a very few master (source) sequences may be resorted to also by other types of DNA sequences that are generated repeatedly during evolution and that are spread over many sectors of the genome.     

Plasmodium falciparum signal sequences: simply sequences or special signals?

The malaria parasite, Plasmodium falciparum, synthesises and exports several proteins inducing morphological and biochemical modifications of erythrocytes during the erythrocytic cycle. The protein trafficking machinery of the parasite is similar to that of other eukaryotic cells in several ways. However, some unusual features are also observed. The secretion of various polypeptides was inhibited when P. falciparum-infected erythrocytes were incubated with Brefeldin A. Immunoelectron microscopy studies revealed substantial morphological changes in the endoplasmic reticulum following exposure of parasitised erythrocytes to the drug. Immunofluorescence studies of Brefeldin A-treated parasites suggest that polypeptide sorting to different intracellular destinations begins at the endoplasmic reticulum. The parasite also secretes polypeptides by a Brefeldin A-insensitive route that bypasses the classical endoplasmic reticulum-Golgi complex pathway.     

Do Kin Selection and Intra-Sexual Selection Operate in Spider Mites?

Between the two subsocial spider mites, Schizotetranychus longus Saito and S. miscanthi Saito, a big difference exists in male reproductive behavior. The males of the former species have an extraordinarily mild relationship with conspecific males, whereas those of the latter species show mortal aggression against conspecific males. Field and experimental observations on the structure of mating populations showed that S. longus is under inbreeding conditions because of a lack of males in early spring, whereas S. miscanthi is under outbreeding conditions. Therefore, I hypothesized that the difference in male antagonism between the two species may reflect the difference in relatedness of males, that is, it has evolved by kin selection. The recent discovery of two clinal trends in male–male aggression in S. miscanthi provided evidence in favour of this hypothesis. Furthermore, a correlation analyses between experimentally evaluated male aggression and distribution patterns of males in the field indicated that the variation in male antagonism is actually reflected in field populations. Based on these studies, I discuss the solidity of the kin-selection hypothesis. Lastly I address how spider mites are fruitful model animals for conducting behavioral, ecological and genetic studies to understand the evolution of haplo-diploidy.     

Hinge sequences as signaling agents?

We report an unexpected finding of common structural principles in two unrelated signaling systems: the FAS death domain transformation that initializes the extrinsic apoptotic pathway and signaling by calmodulin bending. The location and design of the hinge is postulated to be a general principle for creating potential signaling event. We suggest that already existing tool can predict the existence of such a hinge and formulate the hypothesis that the internal instabilities designed into the hinge sequences are necessary devices in effective signaling events.     

Retrotransposition of Alu elements: how many sources?

It is generally thought that only a few Alu elements are capable of retrotransposition and that these 'master' sources produce inactive copies. Here, we use a network phylogenetic approach to demonstrate that recently integrated human-specific Alu subfamilies typically contain 10-20% of secondary source elements that contributed 20-40% of all subfamily members. This multiplicity of source elements provides new insight into the remarkably successful amplification strategy of the Alu family.     

Are introns in-series error-detecting sequences?

The probability of the accurate transmission of a message sequence can be increased by the addition of non-message sequences which permit errors in the message sequence to be detected and corrected. It is proposed that sequences in introns (or in other non-message genomic regions) serve this function with respect to the transmission of genetic information.     

The Pivotal Roles of TIA Proteins in 5′ Splice-Site Selection of Alu Exons and Across Evolution

More than 5% of alternatively spliced internal exons in the human genome are derived from Alu elements in a process termed exonization. Alus are comprised of two homologous arms separated by an internal polypyrimidine tract (PPT). In most exonizations, splice sites are selected from within the same arm. We hypothesized that the internal PPT may prevent selection of a splice site further downstream. Here, we demonstrate that this PPT enhanced the selection of an upstream 5′ splice site (5′ss), even in the presence of a stronger 5′ss downstream. Deletion of this PPT shifted selection to the stronger downstream 5′ss. This enhancing effect depended on the strength of the downstream 5′ss, on the efficiency of base-pairing to U1 snRNA, and on the length of the PPT. This effect of the PPT was mediated by the binding of TIA proteins and was dependent on the distance between the PPT and the upstream 5′ss. A wide-scale evolutionary analysis of introns across 22 eukaryotes revealed an enrichment in PPTs within ∼20 nt downstream of the 5′ss. For most metazoans, the strength of the 5′ss inversely correlated with the presence of a downstream PPT, indicative of the functional role of the PPT. Finally, we found that the proteins that mediate this effect, TIA and U1C, and in particular their functional domains, are highly conserved across evolution. Overall, these findings expand our understanding of the role of TIA1/TIAR proteins in enhancing recognition of exons, in general, and Alu exons, in particular.     

Alu元件研究进展

Alu序列是灵长类动物特有的且最重要的短散在元件,在基因组中约有100万份拷贝,占基因组11%以上。这一基因家族曾被认为是垃圾序列,但随着对Alu序列研究的深入,Alu在基因调控表达网络中的功能逐渐被发现,Alu与人类的疾病密切相关,并且可能影响人类衰老,在人类多样性中也发挥重要作用。     

Canine Evolution in Sabretoothed Carnivores: Natural Selection or Sexual Selection?

The remarkable elongated upper canines of extinct sabretoothed carnivorous mammals have been the subject of considerable speculation on their adaptive function, but the absence of living analogues prevents any direct inference about their evolution. We analysed scaling relationships of the upper canines of 20 sabretoothed feliform carnivores (Nimravidae, Barbourofelidae, Machairodontinae), representing both dirk-toothed and scimitar-toothed sabretooth ecomorphs, and 33 non-sabretoothed felids in relation to body size in order to characterize and identify the evolutionary processes driving their development, using the scaling relationships of carnassial teeth in both groups as a control. Carnassials display isometric allometry in both sabretooths and non-sabretooths, supporting their close relationship with meat-slicing, whereas the upper canines of both groups display positive allometry with body size. Whereas there is no statistical difference in allometry of upper canine height between dirk-toothed and scimitar-toothed sabretooth ecomorphs, the significantly stronger positive allometry of upper canine height shown by sabretooths as a whole compared to non-sabretooths reveals that different processes drove canine evolution in these groups. Although sabretoothed canines must still have been effective for prey capture and processing by hypercarnivorous predators, canine morphology in these extinct carnivores was likely to have been driven to a greater extent by sexual selection than in non-sabretooths. Scaling relationships therefore indicate the probable importance of sexual selection in the evolution of the hypertrophied sabretooth anterior dentition.     

Product patents on human DNA sequences: where do we stand in Europe?

In July 1998, the Directive 98/44/EC was adopted by the competent European Community bodies. It should have been implemented into national laws of the member states by the end of July 2000. So far, however, most member states missed that deadline. One reason for resistance and hesitations are concerns about potential negative effects of product patents based on gene sequences. Reasons for this situation are analysed and solutions sought for minimising the prospects of increasing dependencies on dominant patents on genes.     

Alu transcription: A rheostat for stem cell aging?

Comment on: Wang J, et al. Cell Cycle 2011; 10:3016-30.     

Insect Choice and Floral Size Dimorphism: Sexual Selection or Natural Selection?

In considerations of sexual floral size dimorphism, there is a conflict between sexual selection theory, which predicts that larger floral displays attract more pollinators, and optimality theory—particularly the ideal free distribution—which predict that pollinators' visits should match nutritional rewards. As an alternate explanation of this dimorphism, Müller reported that pollinators tend to visit larger male flowers before visiting smaller female flowers, thereby promoting effective pollination. To investigate optimality predictions, I offered pollinators a choice between smaller, less numerous, but more rewarding flowers; and larger, more numerous, but less rewarding flowers. Foragers initially favored the larger and more numerous flowers, but rapidly shifted preferences to conform with the predictions of the ideal free distribution. To test Müller's hypothesis, I offered pollinators choices between larger and smaller corollas of equal caloric reward. Results showed that although pollinators tended to visit larger corollas first, they did not visit them more often. These experiments highlight the need for further investigation into the tradeoff between natural and sexual selection, and their respective influences in pollination ecology.