Current versus historical population sizes in vertebrate species with high gene flow: a comparison based on mitochondrial DNA lineages and inbreeding theory for neutral mutations

Using inbreeding theory as applied to neutral alleles inherited maternally, we generate expected probability distributions of times to identity by descent for random pairs of mitochondrial genotypes within a population or within an entire species characterized by high gene flow. For comparisons with these expectations, empirical distributions of times to most recent common ancestry were calculated (by conventional mtDNA clock calibrations) from mtDNA haplotype distances observed within each of three vertebrate species--American eels, hardhead catfish, and redwinged blackbirds. These species were chosen for analysis because census population size in each is currently large and because both genetic and life-history data are consistent with the postulate that historical gene flow within these species has been high. The observed molecular distances among mtDNA lineages were two to three orders of magnitude lower than predicted from census sizes of breeding females, suggesting that rate of mtDNA evolution is decelerated in these species and/or that long-term effective population size is vastly smaller than present-day population size. Several considerations point to the latter possibility as most likely. The genetic structure of any species is greatly influenced by historical demography; even for species that are currently abundant, mtDNA gene lineages appear to have been channeled through fairly small numbers of ancestors.      

Developmental and wound-, cold-, desiccation-, ultraviolet-B-stress-induced modulations in the expression of the petunia zinc finger transcription factor gene ZPT2-2

The ZPT2-2 gene belongs to the EPF gene family in petunia (Petunia hybrida), which encodes proteins with TFIIIA-type zinc-finger DNA-binding motifs. To elucidate a possible function for ZPT2-2, we analyzed its pattern of expression in relation to different developmental and physiological stress signals. The activity of the ZPT2-2 promoter was analyzed using a firefly luciferase (LUC) reporter gene, allowing for continuous measurements of transgene activity in planta. We show that ZPT2-2::LUC is active in all plant tissues, but is strongly modulated in cotyledons upon germination, in leaves in response to desiccation, cold treatment, wounding, or ultraviolet-B light, and in petal tissue in response to pollination of the stigma. Analysis of mRNA levels indicated that the modulations in ZPT2-2::LUC expression reflect modulations in endogenous ZPT2-2 gene expression. The change in ZPT2-2::LUC activity by cold treatment, wounding, desiccation, and ultraviolet-B light suggest that the phytohormones ethylene and jasmonic acid are involved in regulating the expression of ZPT2-2. Although up-regulation of expression of ZPT2-2 can be blocked by inhibitors of ethylene perception, expression in plants is not induced by exogenously applied ethylene. The application of jasmonic acid does result in an up-regulation of gene activity and, thus, ZPT2-2 may play a role in the realization of the jasmonic acid hormonal responses in petunia.     

Rafting on wrack as a mode of dispersal for plants in coastal marshes

Here, I examine the potential for dead plant material, or wrack, to act as a vector of dispersal for plants among coastal marshes along the Palmer River in New England, USA. Three hundred mats of wrack floating along a 2.5 km section of river spanning tidal fresh, brackish and salt marshes were sampled for propagules of plants from May 1997 to October 1998. Thirty species of plants and 2 species of algae were associated with the wrack, and 24 of the plant species were viable under greenhouse conditions. Common and abundant species of tidal fresh, brackish and salt marshes were found in the wrack, as well as introduced and invasive species. Wrack contained plants suited to different modes of dispersal, including water, wind and adherence to animals. Measurements of the movement of individual mats of wrack along a 200 m section of the river indicated that wrack travelled at speeds ranging from 1.1 to 2.6 km h⁻¹, which translates to potential dispersal distances ranging from 6.5 to 15.9 km for one ebb or flood tide of 6 h duration. Tagged mats of wrack tracked for one ebb or flood tide travelled at least 2.5 km along the river. These results suggest that wrack may be an important agent of plant dispersal among coastal marshes in estuaries.     

Characterization of a new degradable polymer scaffold for regeneration of the dermis: In vitro and in vivo human studies

Full thickness skin wounds in humans heal with scars, but without regeneration of the dermis. A degradable poly(urethane urea) scaffold (PUUR), Artelon® is already used to reinforce soft tissues in orthopaedics, and for treatment of osteoarthritis of the hand, wrist and foot. In this paper we have done in vitro experiments followed by in vivo studies to find out whether the PUUR is biocompatible and usable as a template for dermal regeneration. Human dermal fibroblasts were cultured on discs of PUUR, with different macrostructures (fibrous and porous). They adhered to and migrated into the scaffolds, and produced collagen. The porous scaffold was judged more suitable for clinical applications and 4 mm Ø, 2 mm-thick discs of porous scaffold (12% w/w or 9% w/w polymer solution) were inserted intradermally in four healthy human volunteers. The implants were well tolerated and increasing ingrowth of fibroblasts was seen over time in all subjects. The fibroblasts stained immunohistochemically for procollagen and von Willebrand factor, indicating neocollagenesis and angiogenesis within the scaffolds. The PUUR scaffold may be a suitable material to use as a template for dermal regeneration.Key words: dermal regeneration, tissue engineering, polymer scaffold, wound healing, in vitro, in vivo, guided tissue regeneration, human, burns     

SIMPROT: Using an empirically determined indel distribution in simulations of protein evolution

Background  

General protein evolution models help determine the baseline expectations for the evolution of sequences, and they have been extensively useful in sequence analysis and for the computer simulation of artificial sequence data sets.     

Carbogen breathing after irradiation enhances the effectiveness of tirapazamine in SiHa tumors but not SCCVII tumors in mice

The penetration of anticancer agents into tumor tissue has recently attracted considerable attention. This study examines the effect of carbogen breathing on the antitumor activity of tirapazamine combined with radiation. Our hypothesis is based on the observation that the diffusion of tirapazamine through tissue is dependent on oxygen tension. We postulated that carbogen breathing might enhance the ability of tirapazamine to diffuse to hypoxic cells located distal to functional blood vessels in tumors. We first determined that carbogen breathing caused no significant change in the pharmacokinetics of tirapazamine, suggesting that any effect of carbogen breathing on the activity of tirapazamine is not attributable to modulation of pharmacokinetics. Cell survival in SCCVII and SiHa tumors after 10 Gy X rays alone was similar. However, when tirapazamine was administered 30 min after radiation treatment under air-breathing conditions, cell killing was greater in SCCVII tumors compared to SiHa tumors. Carbogen breathing during the exposure to tirapazamine did not change the cell survival in SCCVII tumors, but it enhanced cell killing in the SiHa tumors. Interestingly, carbogen breathing during radiation treatment produced greater cell killing in the SiHa tumors than in the SCCVII tumors. The vascular architecture and type of hypoxia in the two tumors probably underlie the differences in the responses of the two tumors. These findings suggest that the effectiveness of tirapazamine and other hypoxic cytotoxins may be dependent on tumor type.     

Detecting impacts of non‐native species on associated invertebrate assemblages depends on microhabitat

Invasive plants that displace native floral communities can cause changes to associated invertebrate species assemblages. Using a mini‐review of the literature and our own data we add to the still considerable debate about the most effective methods for testing community‐level impacts by invasive species. In endangered saltmarshes of southeast Australia, the non‐native rush Juncus acutus L. is displacing its native congener J. kraussii Hochst., with concurrent changes to floral and faunal assemblages. In two coastal saltmarshes, we tested the hypothesis that the ability to detect differences in the invertebrate assemblage associated with these congeneric rushes depends on the microhabitat of the plant sampled. We used three sampling methods, each targeting specific microhabitats: sweep netting of the plant stems, vacuum sampling of the plant tussock, and vacuum sampling of the ground directly below the plants. Over 3800 individuals and 92 morphospecies were collected across four main taxa: gastropods, crustaceans, hexapods and arachnids. Detection of differences in invertebrate density, richness and composition associated with native compared with non‐native rushes was dependent on the microhabitat sampled and these differences were spatially variable. For example, at one saltmarsh the stems and tussock of J. acutus had a lower density and richness of total invertebrates and hexapods than those of the native J. kraussii. In contrast, crustaceans on the ground were in greater abundance below J. acutus than J. kraussii. This study demonstrates that on occasions where overall differences in the assemblage are not detected between species, differences may become apparent when targeting different microhabitats of the plant. In addition, separately targeting multiple microhabitats likely leads to a greater probability of detecting impacts of invasion. Comparing the invertebrate assemblage without differentiating between or sampling an array of microhabitats can fail to determine the impact of invasive species. These results highlight that a combination of methods targeting different microhabitats is important for detecting differences within the invertebrate community, even for phylogenetically related species.     

The effects of salbutamol on epithelial ion channels depend on the etiology of acute respiratory distress syndrome but not the route of administration

Introduction

We investigated the effects of intravenous and intratracheal administration of salbutamol on lung morphology and function, expression of ion channels, aquaporin, and markers of inflammation, apoptosis, and alveolar epithelial/endothelial cell damage in experimental pulmonary (p) and extrapulmonary (exp) mild acute respiratory distress syndrome (ARDS).

Methods

In this prospective randomized controlled experimental study, 56 male Wistar rats were randomly assigned to mild ARDS induced by either intratracheal (n = 28, ARDSp) or intraperitoneal (n = 28, ARDSexp) administration of E. coli lipopolysaccharide. Four animals with no lung injury served as controls (NI). After 24 hours, animals were anesthetized, mechanically ventilated in pressure-controlled mode with low tidal volume (6 mL/kg), and randomly assigned to receive salbutamol (SALB) or saline 0.9% (CTRL), intravenously (i.v., 10 μg/kg/h) or intratracheally (bolus, 25 μg). Salbutamol doses were targeted at an increase of ≈ 20% in heart rate. Hemodynamics, lung mechanics, and arterial blood gases were measured before and after (at 30 and 60 min) salbutamol administration. At the end of the experiment, lungs were extracted for analysis of lung histology and molecular biology analysis. Values are expressed as mean ± standard deviation, and fold changes relative to NI, CTRL vs. SALB.

Results

The gene expression of ion channels and aquaporin was increased in mild ARDSp, but not ARDSexp. In ARDSp, intravenous salbutamol resulted in higher gene expression of alveolar epithelial sodium channel (0.20 ± 0.07 vs. 0.68 ± 0.24, p < 0.001), aquaporin-1 (0.44 ± 0.09 vs. 0.96 ± 0.12, p < 0.001) aquaporin-3 (0.31 ± 0.12 vs. 0.93 ± 0.20, p < 0.001), and Na-K-ATPase-α (0.39 ± 0.08 vs. 0.92 ± 0.12, p < 0.001), whereas intratracheal salbutamol increased the gene expression of aquaporin-1 (0.46 ± 0.11 vs. 0.92 ± 0.06, p < 0.001) and Na-K-ATPase-α (0.32 ± 0.07 vs. 0.58 ± 0.15, p < 0.001). In ARDSexp, the gene expression of ion channels and aquaporin was not influenced by salbutamol. Morphological and functional variables and edema formation were not affected by salbutamol in any of the ARDS groups, regardless of the route of administration.

Conclusion

Salbutamol administration increased the expression of alveolar epithelial ion channels and aquaporin in mild ARDSp, but not ARDSexp, with no effects on lung morphology and function or edema formation. These results may contribute to explain the negative effects of β2-agonists on clinical outcome in ARDS.     

Habitat fragmentation leads to reduced pollinator visitation,fruit production and recruitment in urban mangrove forests

Mangrove forests worldwide undergo anthropogenic fragmentation that may threaten their existence, and yet there have been few tests of the effects of fragmentation on demographic processes critical for mangrove regeneration. Predicting the effects of habitat fragmentation on mangroves is problematic as pollinators may move more freely across water than terrestrial habitat, and propagules can be widely dispersed by water. Here, within each of two estuaries, we compared pollinator diversity and activity, reproductive effort and output, and rates of recruitment for sets of three large (>1500 trees), medium (300–500) and small (<50) stands. As predicted, most measures of reproductive activity and success were inversely related to stand size with large stands typically producing significantly more and larger fruit, and significantly more seedlings. Most strikingly, we found the effect of fragmentation on the abundance of pollinators (honeybees), the production and quality of fruit and the survival rate of seedlings to be similar, showing significant reduction of recruitment in small stands. This study provides the first rigorous evidence that recruitment of mangroves, like for many terrestrial plants, is negatively impacted by habitat fragmentation. From a management perspective, we argue that in the short term our data imply the importance of conserving the largest possible stands. However, additional work is needed to determine (1) the proportion of recruits within small stands that originate within large stands, (2) how seedling performance varies with fruit size and genotype, and (3) how seedling size and performance vary with the abundance and diversity of pollen.     

Radiosensitization of a mouse tumour by Ro 03-8799: acute and protracted administration

The nitroimidazole Ro 03-8799 has been tested as a sensitizer of hypoxic tumour cells, using regrowth delay of a mouse mammary carcinoma. This drug has a short biological half-life and has previously proved to be less promising in tumour experiments than was predicted from in vitro studies and from artificially hypoxic skin. The postulate that this might result from the delay in penetrating to poorly vascularized tumour regions has been tested by maintaining constant blood and tumour levels for 2 hours before irradiation, using an infusion pump. For equivalent gross tumour concentrations at the time of irradiation there was no significant difference in the radiosensitization achieved with a single dose or with prolonged administration. This indicates that slow penetration of the drug is not a problem.