Altered Membrane Structure and Surface Potential in Homozygous Hemoglobin C Erythrocytes

Background

Hemoglobin C differs from normal hemoglobin A by a glutamate-to-lysine substitution at position 6 of beta globin and is oxidatively unstable. Compared to homozygous AA erythrocytes, homozygous CC erythrocytes contain higher levels of membrane-associated hemichromes and more extensively clustered band 3 proteins. These findings suggest that CC erythrocytes have a different membrane matrix than AA erythrocytes.

Methodology and Findings

We found that AA and CC erythrocytes differ in their membrane lipid composition, and that a subset of CC erythrocytes expresses increased levels of externalized phosphatidylserine. Detergent membrane analyses for raft marker proteins indicated that CC erythrocyte membranes are more resistant to detergent solubilization. These data suggest that membrane raft organization is modified in CC erythrocytes. In addition, the average zeta potential (a measure of surface electrochemical potential) of CC erythrocytes was ≈2 mV lower than that of AA erythrocytes, indicating that substantial rearrangements occur in the membrane matrix of CC erythrocytes. We were able to recapitulate this low zeta potential phenotype in AA erythrocytes by treating them with NaNO₂ to oxidize hemoglobin A molecules and increase levels of membrane-associated hemichromes.

Conclusion

Our data support the possibility that increased hemichrome deposition and altered lipid composition induce molecular rearrangements in CC erythrocyte membranes, resulting in a unique membrane structure.     

Timosaponin AIII Is Preferentially Cytotoxic to Tumor Cells through Inhibition of mTOR and Induction of ER Stress

The aqueous extract of Anemarrhena asphodeloides (BN108) induces apoptosis in various cancer cell lines but is significantly less cytotoxic in non-transformed cells. Chemical fractionation of BN108 showed that its cytotoxicity is associated with timosaponins, steroidal saponins of coprostane type. Timosaponin BII (TBII) is a major saponin in BN108, but it shows little cytotoxicity. A much less abundant TAIII induces cell death in tumor cells but not in normal cells, reproducing the selectivity of the total extract BN108. Glycosidase treatment, by removing the extra sugar moiety in TBII, converts it to TAIII and confers cytotoxic activity. Analysis of the mechanisms of death induced by TAIII revealed activation of two distinct pro-apoptotic pathways: first, inhibition of mTORC1 manifested in much reduced phosphorylation of mTORC1 targets; second, induction of endoplasmic reticulum stress culminating in phosphorylation of eIF2α and activation of caspase 4. These pro-apoptotic pathways are activated by TAIII selectively in tumor cells but not in normal cells. Both pathways play a causative role in TAIII cytotoxicity, as restoration of either mTOR activity or relief of ER stress alone offer only partial protection from TAIII. Inhibition of mTORC1 and induction of ER stress apparently contribute to the induction of the previously reported autophagic response in TAIII-treated cells. TAIII induced autophagy plays a protective role in TAIII induced death signaling, and failure to mount autophagic response is associated with heightened sensitivity to TAIII induced apoptosis. The multiple death-promoting and apparently tumor-selective responses to TAIII, its ability to inhibit mTORC1, and the possibility of further enhancing its cytotoxicity by pharmacological inhibition of autophagy, make TAIII an attractive candidate for development as a cancer therapeutic agent.     

Characterization of 18 microsatellite marker loci in the white-collared lemur (Eulemur cinereiceps)

The white-collared lemur (Eulemur cinereiceps) is found in southeastern Madagascar. This species is endangered due to the loss and fragmentation of its natural habitat and hunting. Eighteen nuclear microsatellite loci were isolated from genomic DNA derived from an animal from Mahabo Forest in Madagascar. Population genetic parameters were estimated from a population of white-collared lemur sampled at Vevembe Forest 7 years apart to evaluate the potential utility of this marker suite.     

Catchment Liming to Restore Degraded, Acidified Heathlands and Moorland Pools

Current restoration measures of degraded, acidified heathland ecosystems have not always been successful in the Netherlands. Positive effects of a restored hydrology are often counteracted by acidification of the soil and the local groundwater system. Liming of the heathlands in the catchment of moorland pools might contribute to the restoration of both habitats. Experimental catchment liming was carried out in two degraded Dutch heathlands, with doses varying between 2 and 6 tons/ha. Catchment liming resulted in increased pH and base cation concentrations in the highest elevated limed parts, as well as in the lower situated, nonlimed heath areas and moorland pools. Generally, catchment liming created suitable conditions for the return of heathland target species, and the positive effects lasted for at least 6 years. The response of the heathland vegetation to the liming has, however, been slow because only a small number of endangered plant species increased in abundance. In contrast, four Red List soft‐water macrophytes strongly increased in abundance in the moorland pool. Our results show that, even with the slow return of Red List plant species, catchment liming can be a successful management tool for the restoration of the acidified heathland landscape.     

Elemental characterization of the exoskeleton in the whipscorpions Mastigoproctus giganteus and Typopeltis dalyi (Arachnida: Thelyphonida)

The arthropod cuticle is a structurally diverse secretion that is largely composed of lipids, proteins, and α‐chitin that function together in protection, prey capture, and as a skeletal framework for efficient and diverse means of locomotion. Aquatic, aerial, and terrestrial arthropods are well known to enrich their cuticles with trace elements that are proposed to strengthen or otherwise enhance specific regions of the exoskeleton. In this study, we provide evidence that whipscorpions (vinegaroons) enrich their exoskeleton with up to 14 trace elements. We use energy‐dispersive x‐ray spectroscopy (EDS) to provide the first comparisons of trace element composition in two species of Thelyphonida: Mastigoproctus giganteus (female) and Typopeltis dalyi (female and male). We analyzed the chemical composition of eight regions that have sensory, locomotory, taxonomic, protective, and/or predatory significance: the flagellum, prosoma, tarsal claws of the walking legs, tarsi of the antenniform legs, chelicerae, and the terminal three segments of the pedipalps. Our results reveal the presence of 14 trace elements across both species (12 elements in T. dalyi, 10 elements in M. giganteus), and only four elements are present at significant levels (≥1% weight): Si, Cl, Ca, and Zn. The flagellum, antenniform leg tarsi, and prosoma keel lack these elements in both species, while the chelicerae of all species are enriched with Ca, Zn, and Cl, and the tarsal claws are enriched with Zn. Significantly, we note the presence of Si in the prosomal carapace (but not the keel) of males and females of Typopeltis only, which appears to be the first evidence of this transition metal in the arthropod exoskeleton. We discuss the significance of these chemical enrichments in whipscorpions and provide hypotheses about their functional significance.     

Characterization of 21 microsatellites developed from Propithecus deckeni deckeni

Decken's sifaka (Propithecus deckeni deckeni) is found between the Mahavavy and Manambolo Rivers, in western Madagascar. Twenty‐one polymorphic nuclear microsatellite loci were isolated from genomic DNA derived from a P. d. deckeni, from Tsingy de Bemaraha National Park. Population genetic parameters were estimated on 10 individuals each, sampled from Tsingy de Bemaraha National Park and Tsiombikibo Classified Forests. Significant null alleles were detected in seven loci which were dropped before population genetic parameters were re‐estimated and compared to the full marker suite.     

Kinetic model for lamellipodal actin-integrin ‘clutch’ dynamics

In migrating cells, with especial prominence in lamellipodial protrusions at the cell front, highly dynamic connections are formed between the actin cytoskeleton and the extracellular matrix through linkages of integrin adhesion receptors to actin filaments via complexes of cytosolic “connector” proteins. Myosin-mediated contractile forces strongly influence the dynamic behavior of these adhesion complexes, apparently in two counter-acting ways: negatively as the cell-generated forces enhance complex dissociation, and at the same time positively as force-induced signaling can lead to strengthening of the linkage complexes. The net balance arising from this dynamic interplay is challenging to ascertain a priori, rendering experimental studies difficult to interpret and molecular manipulations of cell and/or environment difficult to predict. We have constructed a kinetics-based model governing the dynamic behavior of this system. We obtained ranges of parameter value sets yielding behavior consistent with that observed experimentally for 3T3 cells and for CHO cells, respectively. Model simulations are able to produce results for the effects of paxillin mutations on the turnover rate of actin/integrin linkages in CHO cells, which are consistent with recent literature reports. Overall, although this current model is quite simple it provides a useful foundation for more detailed models extending upon it.Key words: cell migration, cytoskeleton, contractile force, paxillin     

Green nesting material has a function in mate attraction in the European starling

The function of fresh green nest material has long been debated. It has been suggested that it reduces the number of ectoparasites in nests and on nestlings (nest protection hypothesis), or is used by males to signal condition and paternal quality (male quality hypothesis) or is used as a sexually selected ornament to attract females (courtship hypothesis). We simultaneously tested these three hypotheses in the European starling, Sturnus vulgaris, in the field. Green material was carried by male starlings only, and mainly during nest building. It was not used to reduce ectoparasites. Males nesting in nestboxes that were experimentally contaminated with ectoparasites did not carry more green nest material than males nesting in control boxes, and experimental removal and addition of green material had no effect on the number of ectoparasites on the nestlings or on their body mass. Furthermore, the amount of green material carried into a nestbox was not associated with male body mass, paternal incubation attendance or nestling food provisioning. There is two-fold experimental evidence that males use green plant material to attract mates. First, removal of greenery resulted in a significantly lower percentage of nestboxes containing a clutch than the control or addition treatment. Second, unpaired male starlings sang more and carried more greenery into a nestbox when a caged female was positioned adjacent to the nestbox than when a caged male or an empty cage was present. Paired males, when subjected to the same experimental design, did not respond.     

Riparian Butterfly (Papilionoidea and Hesperioidea) Assemblages Associated with Tamarix-Dominated, Native Vegetation–Dominated, and Tamarix Removal Sites along the Arkansas River, Colorado, U.S.A.

We studied butterfly assemblages at eight riparian sites over five years. Sites included Tamarix spp.–dominated riparian areas; sites where mechanical means or biological control agents (Diorhabda elongata deserticola) were used to limit Tamarix; sites that were mixtures of native woody vegetation (e.g., Populus and Salix) and Tamarix; and native vegetation sites. We identified a gradient in butterfly community composition that changed from treated Tamarix sites, through mixed vegetation, to native vegetation sites. Tamarix sites had lower butterfly metric (riparian butterfly index [RBI]) values than did native vegetation sites. The RBI is based on a combination of richness measures and the presence of specific species and groups of butterflies. There was no significant change in the RBI over sampling periods at any sites, including both Tamarix eradication sites. The RBI at sites where Tamarix control took place did not approach restoration goals based on values at unimpacted sites. Positive effects on riparian butterfly assemblages were not linked to any Tamarix control efforts, nor did we detect a decline from initial butterfly metrics at Tamarix sites. Direct ordination provided information on environmental variables, such as amount of nectar and herbaceous plant richness, which may be important in riparian restoration efforts.