Expression and characterization of the intact N-terminal domain of streptokinase

Proteolytic studies have enabled two of the three putative domains of the fibrinolytic protein streptokinase to be isolated and characterized (Conejero-Lara F et al., 1996, Protein Sci 5:2583-2591). The N-terminal domain, however, could not be isolated in these experiments because of its susceptibility to proteolytic cleavage. To complete the biophysical characterization of the domain structure of streptokinase we have overexpressed, purified, and characterized the N-terminal region of the protein, residues 1-146. The results show this is cooperatively folded with secondary structure content and overall stability closely similar to those of the equivalent region in the intact protein.     

Transposable DNA elements and life history traits: II. Transposition of P DNA elements in somatic cells reduces fitness, mating activity, and locomotion of Drosophila melanogaster

Some transposable DNA elements in higher organisms are active in somatic cells, as well as in germinal cells. What effect does the movement of DNA elements in somatic cells have on life history traits? It has previously been reported that somatically active P and mariner elements in Drosophila induce genetic damage and significantly reduce lifespan. In this study, we report that the movement of P elements in somatic cells also significantly reduces fitness, mating activity, and locomotion of Drosophila melanogaster. If other elements cause similar changes in life history traits, it is doubtful if transposable DNA elements remain active for long in somatic cells in natural populations.     

Female reproductive strategies, paternity and community structure in wild West African chimpanzees

Although the variability and complexity of chimpanzee behaviour frustrates generalization, it is widely believed that social evolution in this species occurs in the context of the recognizable social group or community. We used a combination of field observations and noninvasive genotyping to study the genetic structure of a habituated community of 55 wild chimpanzees, Pan troglodytes verus, in the Ta? Forest, C?te d'Ivoire. Pedigree relationships in that community show that female mate choice strategies are more variable than previously supposed and that the observed social groups are not the exclusive reproductive units. Genetic evidence based on nuclear microsatellite markers and behavioural obser-vations reveal that females in the Ta? forest actively seek mating partners outside their social unit; noncommunity males accounted for half the paternities over 5 years. This female mating strategy increases male gene flow between communities despite male philopatry, and negates the predicted higher relatedness among community males. Kin selection seems unlikely to explain the frequent cooperation and sharing observed among group males in this population. Similarly, inbreeding avoidance is probably not the sole cause of permanent adolescent female dispersal as a combination of extragroup mating and avoidance of incest with home group males would allow females to avoid inbreeding without the hazards associated with immigration into a new community. Extragroup mating as part of chimpanzee females' reproductive strategy may allow them to choose from a wider variety and number of males, without losing the resources and support provided by their male social group partners. Copyright 1999 The Association for the Study of Animal Behaviour.     

Molecular Phylogeography of Oncomelania Lindoensis (Gastropoda: Pomatiopsidae), the Intermediate Host of Schistosoma Japonicum in Sulawesi

Oncomelania lindoensis from Lake Lindu, Sulawesi, was characterizedfor genetic variation at 21 allozyme loci and compared withO. hupensis (China) and O. quadrasi (Philippines). Geneticdistances and interpopulation patterns of allele-sharing pointto a closer relationship between Sulawesi and the Philippines(Nei's unbiased genetic distances (D) averaged 0.50) than betweenSulawesi and China (D= 0.79). These data, coupled with a considerationof the geographic distribution of the genus, support the hypothesisthat the Sulawesi Oncomelaniaoriginated by avian-facilitated colonizationfrom the Philippines about two million years ago. Oncomelania from Sulawesi were originally described as subspecificallydistinct: Oncomelania hupensis lindoensis. However, the allopatricdistribution, unique alleles at five loci, and significant geneticdistances from congeners in Mindanao and elsewhere in the Philippinessuggest that this taxon should be distinguished as a full specieswithin the Oncomelania hupensis species group, namely: O. lindoensisDavis & Carney 1973. Comparison with published data on variationwithin quadrasi and in three Chinese subspecies of hupensisshowed that D values increase with taxonomic level in this speciesgroup. D averaged 0.15 (0–0.26) within Chinese subspeciesand 0.04 (0–0.13) within the Philippines, but was 0.30(0.20–0.45) between Chinese subspecies, and 0.48–0.80between the three species (hupensis, quadrasi and lindoensis).The genotypic cluster species concept and these multilocus geneticdistances can be used to help define species and subspeciesin these medically important snails. (Received 14 May 1997; accepted 20 April 1998)     

Leaf photosynthetic traits scale with hydraulic conductivity and wood density in Panamanian forest canopy trees

We investigated how water transport capacity, wood density and wood anatomy were related to leaf photosynthetic traits in two lowland forests in Panama. Leaf-specific hydraulic conductivity (k_L) of upper branches was positively correlated with maximum rates of net CO₂ assimilation per unit leaf area (A_area) and stomatal conductance (g_s) across 20 species of canopy trees. Maximum k_L showed stronger correlation with A_area than initial k_L suggesting that allocation to photosynthetic potential is proportional to maximum water transport capacity. Terminal branch k_L was negatively correlated with A_area/g_s and positively correlated with photosynthesis per unit N, indicating a trade-off of efficient use of water against efficient use of N in photosynthesis as water transport efficiency varied. Specific hydraulic conductivity calculated from xylem anatomical characteristics (k_theoretical) was positively related to A_area and k_L, consistent with relationships among physiological measurements. Branch wood density was negatively correlated with wood water storage at saturation, k_L, A_area, net CO₂ assimilation per unit leaf mass (A_mass), and minimum leaf water potential measured on covered leaves, suggesting that wood density constrains physiological function to specific operating ranges. Kinetic and static indices of branch water transport capacity thus exhibit considerable co-ordination with allocation to potential carbon gain. Our results indicate that understanding tree hydraulic architecture provides added insights to comparisons of leaf level measurements among species, and links photosynthetic allocation patterns with branch hydraulic processes.     

Discrimination models using variance-stabilizing transformation of metabolomic NMR data

After the extensive work that is being done in the areas of genomics, proteomics, and metabolomics, the study of metabolites has come of interest in its own right. Metabolites in biological systems give an understanding of the state of the system and provide a powerful tool for the study of disease and other maladies. Several analytical techniques such as mass spectrometry and high-resolution NMR spectroscopy have been used to study metabolites. The data, however, from these techniques remains quite complex. Traditionally, multivariate analyses have been used for such data. These methods however have an underlying assumption that the data is multivariate normal with a constant variance. This is not necessarily the case. It has been shown that a generalized log transformation renders the variance of the data constant effectively making the data more suitable for multivariate analysis. We demonstrate the effectiveness of these transformations on NMR data taken on a set of 18 abalone that were categorized as either being healthy, stunted, or diseased. We show how the transformation makes multivariate classification of the abalone into the healthy, stunted and diseased categories much more effective and gives a tool for identifying potential metabolic biomarkers for disease.     

Genetic and morphological evolution following a founder event in the dark-eyed junco, Junco hyemalis thurberi

An isolated population of dark-eyed juncos, Junco hyemalis, became established on the campus of the University of California at San Diego (UCSD), probably in the early 1980s. It now numbers about 70 breeding pairs. Populations across the entire natural range of the subspecies J. h. thurberi are weakly differentiated from each other at five microsatellite loci (FST = 0.01). The UCSD population is significantly different from these populations, the closest of which is 70 km away. It has 88% of the genetic heterozygosity and 63% of the allelic richness of populations in the montane range of the subspecies, consistent with a harmonic mean effective population size of 32 (but with 95% confidence limits from four to > 70) over the eight generations since founding. Results suggest a moderate bottleneck in the early establishment phase but with more than seven effective founders. Individuals in the UCSD population have shorter wings and tails than those in the nearby mountains and a common garden experiment indicates that the morphological differences are genetically based. The moderate effective population size is not sufficient for the observed morphological differences to have evolved as a consequence of genetic drift, indicating a major role for selection subsequent to the founding of the UCSD population.     

Interactions between ant species increase arrival rates of an ant parasitoid

Behaviours or traits associated with aggression and communication may increase an animal's conspicuousness to predators or parasitoids. Most examples of this come from instances of aggression or communication within a species. We tested whether interspecific encounters between ants enhance the host location success of a parasitoid (Diptera: Phoridae) that attacks ants in the genus Linepithema. At food resources recruited to by Linepithema, parasitoid discovery rates were lower when Linepithema was alone than when other ant species were present. In experimentally controlled encounters, parasitoid discovery rates were elevated when Linepithema confronted an ant species that elicited use of chemicals, but not when it confronted an ant species that primarily elicited physical aggression. These results indicate that phorid parasitoids of Linepithema use the ant's chemicals as host location cues. Because Linepithema is known to abandon food resources in the presence of its phorid parasitoids, its use of chemicals during interspecific encounters may diminish its competitive success when phorids are nearby. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

For uptake of yolk precursors,epithelial cell-oocyte gap junctional communication is required by insects representing six different orders

For uptake of vitellogenin protein into nascent yolk spheres, communication through open gap junction channels between the follicle epithelium and oocyte is required by six different insects representing six different orders. It was recently shown in the hemipteran, Oncopeltus fasciatus, that endocytic uptake of yolk protein resulting in the formation of nascent yolk spheres depended upon an intact epithelium communicating with the oocyte through patent gap junctions. Following treatment with octanol, which down-regulated gap junctions below the level of dye coupling, vitellogenin uptake was terminated. Yet, for another hemipteran, Dysdercus intermedius, it has been shown that yolk spheres can form even when all epithelial cells have been stripped from the oocyte. To determine if the mechanism seen in Oncopeltus is present in other insects, we utilized the same techniques to study nascent yolk sphere production in a dipteran, Drosophila melanogaster, a lepidopteran, Actias luna, a hymenopteran, Xylocopa virginica, a coleopteran, Tenebrio molitor and an orthopteran, Acheta domesticus. In each of these, when gap junctions were down-regulated yolk uptake quickly stopped. That six different insects from six different orders all required a gap junctionally transmitted chemical signal of epithelial cell origin suggests that this mechanism is widespread throughout the insects.