Analysis of a genetic hitchhiking model, and its application to DNA polymorphism data from Drosophila melanogaster

Begun and Aquadro have demonstrated that levels of nucleotide variation correlate with recombination rate among 20 gene regions from across the genome of Drosophila melanogaster. It has been suggested that this correlation results from genetic hitchhiking associated with the fixation of strongly selected mutants. The hitchhiking process can be described as a series of two-step events. The first step consists of a strongly selected substitution wiping out linked variation in a population; this is followed by a recovery period in which polymorphism can build up via neutral mutations and random genetic drift. Genetic hitchhiking has previously been modeled as a steady-state process driven by recurring selected substitutions. We show here that the characteristic parameter of this steady-state model is alpha v, the product of selection intensity (alpha = 2Ns) and the frequency of beneficial mutations v (where N is population size and s is the selective advantage of the favored allele). We also demonstrate that the steady-state model describes the hitchhiking process adequately, unless the recombination rate is very low. To estimate alpha v, we use the data of DNA sequence variation from 17 D. melanogaster loci from regions of intermediate to high recombination rates. We find that alpha v is likely to be > 1.3 x 10(-8). Additional data are needed to estimate this parameter more precisely. The estimation of alpha v is important, as this parameter determines the shape of the frequency distribution of strongly selected substitutions.      

Structure of a human carcinogen-converting enzyme,SULT1A1. Structural and kinetic implications of substrate inhibition

Sulfonation catalyzed by sulfotransferase enzymes plays an important role in chemical defense mechanisms against various xenobiotics but also bioactivates carcinogens. A major human sulfotransferase, SULT1A1, metabolizes and/or bioactivates many endogenous compounds and is implicated in a range of cancers because of its ability to modify diverse promutagen and procarcinogen xenobiotics. The crystal structure of human SULT1A1 reported here is the first sulfotransferase structure complexed with a xenobiotic substrate. An unexpected finding is that the enzyme accommodates not one but two molecules of the xenobiotic model substrate p-nitrophenol in the active site. This result is supported by kinetic data for SULT1A1 that show substrate inhibition for this small xenobiotic. The extended active site of SULT1A1 is consistent with binding of diiodothyronine but cannot easily accommodate beta-estradiol, although both are known substrates. This observation, together with evidence for a disorder-order transition in SULT1A1, suggests that the active site is flexible and can adapt its architecture to accept diverse hydrophobic substrates with varying sizes, shapes and flexibility. Thus the crystal structure of SULT1A1 provides the molecular basis for substrate inhibition and reveals the first clues as to how the enzyme sulfonates a wide variety of lipophilic compounds.     

12 Novel clonal groups of Leptospira infecting humans in multiple contrasting epidemiological contexts in Sri Lanka

Leptospirosis is a ubiquitous zoonotic disease and a major clinical challenge owing to the multitude of clinical presentations and manifestations that are possibly attributable to the diversity of Leptospira, the understanding of which is key to study the epidemiology of this emerging global disease threat. Sri Lanka is a hotspot for leptospirosis with high levels of endemicity as well as annual epidemics. We carried out a prospective study of Leptospira diversity in Sri Lanka, covering the full range of climatic zones, geography, and clinical severity. Samples were collected for leptospiral culture from 1,192 patients from 15 of 25 districts in Sri Lanka over two and half years. Twenty-five isolates belonging to four pathogenic Leptospira species were identified: L. interrogans, L. borgpetersenii, L. weilii, and L. kirschneri. At least six serogroups were identified among the isolates: Autumnalis (6), Pyrogenes (4), Icterohaemorrhagiae (2), Celledoni (1), Grippotyphosa (2) and Bataviae (1). Seven isolates did not agglutinate using available antisera panels, suggesting new serogroups. Isolates were sequenced using an Illumina platform. These data add 25 new core genome sequence types and were clustered in 15 clonal groups, including 12 new clonal groups. L. borgpetersenii was found only in the dry zone and L. weilii only in the wet zone. Acute kidney injury and cardiovascular involvement were seen only with L. interrogans infections. Thrombocytopenia and liver impairment were seen in both L. interrogans and L. borgpetersenii infections. The inadequate sensitivity of culture isolation to identify infecting Leptospira species underscores the need for culture-independent typing methods for Leptospira.     

Post-zygotic breakage of a dicentric chromosome results in mosaicism for a telocentric 9p marker chromosome in a boy with developmental delay

Chromosomal rearrangements resulting in an inverted duplication and a terminal deletion (inv dup del) can occur due to three known mechanisms, two of them resulting in a normal copy region between the duplicated regions. These mechanisms involve the formation of a dicentric chromosome, which undergo breakage during cell division resulting in cells with either an inverted duplication and deletion or a terminal deletion. We describe a mosaic 3 year old patient with two cell lines carrying a chromosome 9p deletion where one of the cell lines contains an additional telocentric marker chromosome. Our patient is mosaic for the product of a double breakage of a dicentric chromosome including a centric fission. Mosaicism involving different rearrangements of the same chromosome is rare and suggests an early mitotic breakage event.     

Synthesis and biological evaluation of solubilized sulfonamide analogues of the phosphatidylinositol 3-kinase inhibitor ZSTK474

Replacing one of the morpholine groups of the phosphatidylinositol 3-kinase (PI3K) inhibitor ZSTK474 with a variety of sulfonamide-linked solubilizing substituents produced a new class of active and potent PI3Kα inhibitors, with several derivatives demonstrating high PI3Kα enzyme potency and good cellular potency in two human derived cell lines. The overall results suggest a preference for linear and somewhat flexible solubilizing functions. From this series, compound 16, also known as SN32976, was selected for advanced preclinical evaluation.     

Cultivation and Differentiation of Dissociated Cells of Chick Embryo Encephalon

Dissociated cells from cerebral hemispheres of chick embryo at stages 17–18, 12–13 and 9–10, were cultivated for seven days. The cells were cultivated either completely covered with the nutrient medium in an atmosphere containing 5 percent CO₂ or they were covered by only a thin film of nutrient medium in contact with air.
For the embryos at stages 17–18 or 12–13, under both culture conditions neurons differentiated after 3 or 4 days in culture, while for the embryos at stage 9–10, no neuronal differentiation occurred under either condition. The cells remained morphologically undifferentiated and formed aggregates of about 50 cells. Some fibroblasts were found to grow on the collagen matrix.
It is concluded that dissociated cells from embryos at stage 9–10 are incapable of auto differentiation under the present culture conditions. The possible causes of this inability to differentiate are discussed.     

Physiological characteristics of wild Atlantic salmon post-smolts during estuarine and coastal migration

Changes were measured in some of the major physiological variables associated with seawater adaptability, growth and energetics in wild Atlantic salmon Salmo salar smolts and post-smolts migrating from the river and through the estuary, fjord and coastal areas in the River Orkla and the Trondheimsfjord, Norway during late May to early June. Gill Na⁺,K⁺-ATPase activity increased to levels of 12–16 µmol ADP mg protein⁻¹ h⁻¹ in post-smolts caught in higher salinity zones, probably representing long-term levels of Atlantic salmon post-smolts in oceanic conditions. Muscle moisture was regulated within narrow limits (77·7–78·7%) in fish from all zones during both years, suggesting that post-smolts adapt to marine conditions without any long-term disturbance of hydro-mineral balance. Lipid and glycogen content showed a general trend towards depletion from the river, through the fjord and into the ocean. There was, however, no significant change in protein content. The present results confirm that smolts are naturally 'energy deficient' during downstream migration, and suggest that post-smolts also mobilize energy reserves during their early marine phase, while protein is allocated for somatic growth. Plasma growth hormone (GH) levels increased transiently during passage through the estuary and fjord, with lower levels observed in post-smolts caught off-shore, i.e. in fish which were feeding on marine prey and had adapted to the marine environment. These physiological changes may confer substantial selective advantages during the critical early marine phase of anadromous salmonids, and hence are adaptive for long-term survival in sea water.