Ethanol tolerances of Drosophila melanogaster populations selected on different concentrations of ethanol supplemented media

Summary Eight recently collected Australasian populations of D. melanogaster were each divided into eight selection lines. Two of these lines from each population were maintained on one of four types of selection media: standard food supplemented with 0%, 3%, 6% and 9% ethanol. After 30 generations the selection lines were tested for tolerance to 9% ethanol medium and after another 20 generations adults were tested for tolerance to concentrated ethanol fumes. Significant differences in tolerance were found among lines selected on different media which were consistent across the eight populations. On the 9% test media, the 6% and 9% selection lines, as compared with the control lines selected on 0% ethanol, were more likely to survive as pre-adults or adults, faster to develop as preadults, and heavier and more productive as adults. However, the tolerance of the 3% lines to the 9% test media was less than that of the 0% control lines in preadult and adult survival, intermediate between that of the 0% and the 6% and 9% lines in productivities, and apparently superior to the 6% and 9% lines in development times and adult weights. The 3%, 6% and 9% lines showed similar tolerances to the ethanol vapour. Previous work showed that 3% ethanol can be a metabolic benefit to D. melanogaster but 6% and 9% are metabolic costs. The present results suggest that the phenotype selected on 3% to obtain a metabolic benefit differs in many respects from that selected on 6% and 9% to minimise their detrimental effects.     

RECOMBINATION AND MIGRATION RATES IN NATURAL POPULATIONS OF BACILLUS SUBTILIS AND BACILLUS MOJAVENSIS

We have investigated the rates of recombination and migration in native populations of two closely related, naturally competent Bacillus species. Native soil isolates of Bacillus subtilis and Bacillus mojavensis were obtained from three continents and, within North America, from populations at a range of geographical distances from one another. The rate of recombination within populations of each species was estimated from restriction-site data for three genes. Recombination was shown to occur within each species at about the same rate as neutral mutation, whatever the geographical scale or phylogenetic scale over which strains were sampled. The rate of migration between populations was estimated by a cladistic analysis and was shown to be high (i.e., Nm > 1), even among populations on different continents. The level of migration within each species is sufficient to prevent neutral geographical divergence within species.     

Genetic exchange and evolutionary divergence in prokaryotes

Recent work shows that genetic exchange in prokaryotes is less frequent but more promiscuous than that in eukaryotes. As a result, genetic exchange plays very different roles in determining the patterns of evolutionary divergence in these major groups. Because sexual isolation is not a prerequisite for divergence in the prokaryotic world, the biological species concept is not appropriate for bacteria. However, there is a species concept that may apply universally.     

The Effect of DNA Sequence Divergence on Sexual Isolation in Bacillus

We have investigated the relationship between sexual isolation and DNA sequence divergence in the transformation (at locus rpoB) of a naturally competent strain of Bacillus subtilis. Using both genomic DNA and a PCR-amplified segment of gene rpoB as donor, we found that the extent of sexual isolation at locus rpoB was closely predicted, over three orders of magnitude, as a log-linear function of sequence divergence at that locus. Because sexual isolation between a recipient and any potential donor may be determined as a general mathematical function of sequence divergence, transformation is perhaps the only sexual system, in either the prokaryotic or the eukaryotic world, in which sexual isolation can be predicted for a pair of species without having to perform the cross. These observations suggest the possibility of a general approach to the indirect prediction of sexual isolation in bacteria recombining principally by natural transformation.     

Cyanobacterial ecotypes in the microbial mat community of Mushroom Spring (Yellowstone National Park, Wyoming) as species-like units linking microbial community composition, structure and function

We have investigated microbial mats of alkaline siliceous hot springs in Yellowstone National Park as natural model communities to learn how microbial populations group into species-like fundamental units. Here, we bring together empirical patterns of the distribution of molecular variation in predominant mat cyanobacterial populations, theory-based modelling of how to demarcate phylogenetic clusters that correspond to ecological species and the dynamic patterns of the physical and chemical microenvironments these populations inhabit and towards which they have evolved adaptations. We show that putative ecotypes predicted by the theory-based model correspond well with distribution patterns, suggesting populations with distinct ecologies, as expected of ecological species. Further, we show that increased molecular resolution enhances our ability to detect ecotypes in this way, though yet higher molecular resolution is probably needed to detect all ecotypes in this microbial community.     

Focal loss of actin bundles causes microtubule redistribution and growth cone turning

It is commonly believed that growth cone turning during pathfinding is initiated by reorganization of actin filaments in response to guidance cues, which then affects microtubule structure to complete the turning process. However, a major unanswered question is how changes in actin cytoskeleton are induced by guidance cues and how these changes are then translated into microtubule rearrangement. Here, we report that local and specific disruption of actin bundles from the growth cone peripheral domain induced repulsive growth cone turning. Meanwhile, dynamic microtubules within the peripheral domain were oriented into areas where actin bundles remained and were lost from areas where actin bundles disappeared. This resulted in directional microtubule extension leading to axon bending and growth cone turning. In addition, this local actin bundle loss coincided with localized growth cone collapse, as well as asymmetrical lamellipodial protrusion. Our results provide direct evidence, for the first time, that regional actin bundle reorganization can steer the growth cone by coordinating actin reorganization with microtubule dynamics. This suggests that actin bundles can be potential targets of signaling pathways downstream of guidance cues, providing a mechanism for coupling changes in leading edge actin with microtubules at the central domain during turning.     

Opinion: Re-evaluating prokaryotic species

There is no widely accepted concept of species for prokaryotes, and assignment of isolates to species is based on measures of phenotypic or genome similarity. The current methods for defining prokaryotic species are inadequate and incapable of keeping pace with the levels of diversity that are being uncovered in nature. Prokaryotic taxonomy is being influenced by advances in microbial population genetics, ecology and genomics, and by the ease with which sequence data can be obtained. Here, we review the classical approaches to prokaryotic species definition and discuss the current and future impact of multilocus nucleotide-sequence-based approaches to prokaryotic systematics. We also consider the potential, and difficulties, of assigning species status to biologically or ecologically meaningful sequence clusters.     

Direct visualization of microtubule flux during metaphase and anaphase in crane-fly spermatocytes

Microtubule flux in spindles of insect spermatocytes, long-used models for studies on chromosome behavior during meiosis, was revealed after iontophoretic microinjection of rhodamine-conjugated (rh)-tubulin and fluorescent speckle microscopy. In time-lapse movies of crane-fly spermtocytes, fluorescent speckles generated when rh-tubulin incorporated at microtubule plus ends moved poleward through each half-spindle and then were lost from microtubule minus ends at the spindle poles. The average poleward velocity of approximately 0.7 microm/min for speckles within kinetochore microtubules at metaphase increased during anaphase to approximately 0.9 microm/min. Segregating half-bivalents had an average poleward velocity of approximately 0.5 microm/min, about half that of speckles within shortening kinetochore fibers. When injected during anaphase, rhtubulin was incorporated at kinetochores, and kinetochore fiber fluorescence spread poleward as anaphase progressed. The results show that tubulin subunits are added to the plus end of kinetochore microtubules and are removed from their minus ends at the poles, all while attached chromosomes move poleward during anaphase A. The results cannot be explained by a Pac-man model, in which 1) kinetochore-based, minus end-directed motors generate poleward forces for anaphase A and 2) kinetochore microtubules shorten at their plus ends. Rather, in these cells, kinetochore fiber shortening during anaphase A occurs exclusively at the minus ends of kinetochore microtubules.     

Chromosome phylogeny of the subfamily Pitheciinae (Platyrrhini,Primates) by classic cytogenetics and chromosome painting

Background  

The New World monkey (Platyrrhini) subfamily Pitheciinae is represented by the genera Pithecia, Chiropotes and Cacajao. In this work we studied the karyotypes of Pithecia irrorata (2n = 48) and Cacajao calvus rubicundus (2n = 45 in males and 2n = 46 in females) by G- and C-banding, NOR staining and chromosome painting using human and Saguinus oedipus whole chromosome probes. The karyotypes of both species were compared with each other and with Chiropotes utahicki (2n = 54) from the literature.     

Direct anti-metastatic efficacy by the DNA enzyme Dz13 and downregulated MMP-2, MMP-9 and MT1-MMP in tumours

The DNA enzyme Dz13, targeted against the oncogene c-Jun, is capable of inhibiting various model tumours in mice albeit in ectopic models of neoplasia. In previous studies using orthotopic models of disease, the inhibitory effects of Dz13 on secondary growth was a direct result of growth inhibition at the primary lesion site. Thus, the direct and genuine effects on metastasis were not gauged. In this study, Dz13 was able to inhibit both locoregional and distal metastasis of tumour cells in mice, in studies where the primary tumours were unaffected due to the late and clinically-mimicking nature of treatment commencement. In addition, the effect of Dz13 against tumours has now been extended to encompass breast and prostate cancer. Dz13 upregulated the matrix metalloproteinase (MMP)-2 and MMP-9, and decreased expression of MT1-MMP (MMP-14) in cultured tumour cells. However, in sections of ectopic tumours treated with Dz13, both MMP-2 and MMP-9 were downregulated. Thus, not only is Dz13 able to inhibit tumour growth at the primary site, but also able to decrease the ability of neoplastic cells to metastasise. These findings further highlight the growing potential of Dz13 as an antineoplastic agent.