Multivalency of Sonic hedgehog conjugated to linear polymer chains modulates protein potency

A potently active multivalent form of the protein Sonic hedgehog (Shh) was produced by bioconjugation of a modified recombinant form of Shh to the linear polymers poly(acrylic acid) (pAAc) and hyaluronic acid (HyA) via a two-step reaction exploiting carboimiide and maleimide chemistry. Efficiency of the conjugation was approximately 75% even at stoichiometric ratios of 30 Shh molecules per linear HyA chain (i.e., 30:1 Shh/HyA). Bioactivity of the conjugates was tested via a cellular assay across a range of stoichiometric ratios of Shh molecules to HyA linear chains, which was varied from 0.6:1 Shh/HyA to 22:1 Shh/HyA. Results indicate that low conjugation ratios decrease Shh bioactivity and high ratios increase this activity beyond the potency of monomeric Shh, with approximately equal activity between monomeric soluble Shh and conjugated Shh at 7:1 Shh/HyA. In addition, high-ratio constructs increased angiogenesis determined by the in vivo chick chorioallantoic membrane (CAM) assay. These results are captured by a kinetic model of multiple interactions between the Shh/HyA conjugates and cell surface receptors resulting in higher cell signaling at lower bulk Shh concentrations.     

The “Beauty Myth” Is No Myth

The phenomenon of apparently greater emphasis on human female physical attractiveness has spawned an array of explanatory responses, but the great majority can be broadly categorized as either evolutionary or social constructivist in nature. Both perspectives generate distinct and testable predictions. If, as Naomi Wolf (The beauty myth: How images of female beauty are used against women. New York: William Morrow, [originally published in 1991], 2002) and others have argued, greater emphasis on female attractiveness is part of a predominantly Western “beauty myth,” then an analysis of a culturally diverse sample should reveal marked fluctuation in gendered attractiveness emphasis: there should be significant numbers of cultures in which male and female attractiveness are equally emphasized, and cultures in which male attractiveness receives more emphasis. On the other hand, an evolutionary perspective suggests that disproportionate emphasis on female attractiveness will be a universal or near-universal phenomenon. To test these hypotheses, we tallied references to male versus female attractiveness in 90 collections of traditional folktales from 13 diverse cultural areas. The results are consistent with the evolutionary predictions and inconsistent with the constructivist predictions. Across culture areas information on physical attractiveness was much more likely to be conveyed for female characters. Together with other recent studies, these results suggest that the main elements of the beauty myth are not myths: there are large areas of overlap in the attractiveness judgments of diverse populations, and cross-cultural emphasis on physical attractiveness appears to fall principally upon women.     

Oncogenic activities of metabotropic glutamate receptor 1 (Grm1) in melanocyte transformation

Previously, we reported a transgenic mouse line, TG-3, that develops spontaneous melanoma with 100% penetrance. We demonstrated that ectopic expression of Grm1 in melanocytes was sufficient to induce melanoma in vivo. In this present study, the transforming properties of Grm1 in two cultured immortalized melanocytes were investigated. We showed that, in contrast to parental melanocytes, these Grm1-clones have lost their requirement of TPA supplement for proliferation and have acquired the ability to form colonies in semi-solid medium. Xenografts of these cells formed robust tumors in both immunodeficient nude and syngeneic mice with a short latency (3-5 days). The malignancy of these cells was demonstrated by angiogenesis and invasion to the muscle and the intestine. The requirement of Grm1 expression for the maintenance of transformation was demonstrated by an inducible siRNA system. Induction of expression of siRNA for Grm1 reduced the number of proliferating/viable cells in vitro and suppressed in vivo xenografted tumor growth in comparison with control. Taken together, these results showed that expression of exogeneously introduced Grm1 is sufficient to induce full transformation of immortalized melanocytes.     

Towards better cardiovascular journals

In their never-ending search for truth, science and medical research rely heavily on data published in peer-reviewed journals. Subsequent publication of incorrect scientific data may interfere with the process of implementation of new treatment modalities and insights and understanding of disease processes. This may be caused by simple mistakes or involuntary misinterpretation without overt scientific misconduct or fraudulent publication.     

Modelling the effects of loss of soil biodiversity on ecosystem function

There are concerns about whether accelerating worldwide loss of biodiversity will adversely affect ecosystem functioning and services such as forage production. Theoretically, the loss of some species or functional groups might be compensated for by changes in abundance of other species or functional groups such that ecosystem processes are unaffected. A simulation model was constructed for carbon and nitrogen transfers among plants and functional groups of microbes and soil fauna. The model was based on extensive information from shortgrass prairie, and employed stabilizing features such as prey refuges and predator switching in the trophic equations. Model parameters were derived either from the literature or were estimated to achieve a good fit between model predictions and data. The model correctly represented (i) the major effects of elevated atmospheric CO₂ and plant species on root and shoot biomass, residue pools, microbial biomass and soil inorganic nitrogen, and (ii) the effects on plant growth of manipulating the composition of the microbial and faunal community. The model was evaluated by comparing predictions to data not used in model development. The 15 functional groups of microbes and soil fauna were deleted one at a time and the model was run to steady state. Only six of the 15 deletions led to as much as a 15% change in abundance of a remaining group, and only two deletions (bacteria and saprophytic fungi) led to extinctions of other groups. Functional groups with greater effect on abundance of other groups were those with greater biomass or greater number of consumers, regardless of trophic position. Of the six deletions affecting the abundance of other groups, only three (bacteria, saprophytic fungi, and root‐feeding nematodes) caused as much as 10% changes in indices of ecosystem function (nitrogen mineralization and primary production). While the soil fauna as a whole were important for maintenance of plant production, no single faunal group had a significant effect. These results suggest that ecosystems could sustain the loss of some functional groups with little decline in ecosystem services, because of compensatory changes in the abundance of surviving groups. However, this prediction probably depends on the nature of stabilizing mechanisms in the system, and these mechanisms are not fully understood.     

Field and Microcosm Studies of Decomposition and Soil Biota in a Cold Desert Soil

In the extreme cold desert soil of the McMurdo Dry Valleys of Antarctica, we studied the effects of changing moisture and temperature on rates of decomposition and the activity and abundance of soil organisms. Our objective was to understand how moisture and temperature structure invertebrate communities and control important ecosystem processes and soil biotic activity in this extreme environment. First, in a field experiment, we manipulated soil moisture and temperature and compared cotton strip decomposition rates at two dry valley sites with different moisture regimes. At both sites, live nematode abundance and activity were unchanged by soil treatments over the 2-year study. In the same plots, the cotton strips did not decompose, despite soil warming and the addition of moisture. The results suggest that biological activity in the McMurdo Dry Valleys is severely limited and that soil organisms are not responsive to improving environmental conditions. Second, in microcosms, we manipulated dry valley soil moisture at a constant temperature of 10°C and measured the rates of key soil processes. Soil respiration, nitrification, and the decomposition of cotton strips were all greater in dry valley soils that were wetted to 10% moisture content, as compared to soils at 0.6%. These results indicate that the decomposition potential for dry valley soils is high when moisture and temperature limitations are removed. In the field, however, this process was extremely slow, and biota did not respond to improving environmental conditions. Soil processes appear to be limited primarily by the extreme desiccation of the dry valleys. Ecosystems processes are likely restricted to the brief periods following infrequent snowfall, melt, and soil wetting that permit the activity of soil microbes and biota. Received 23 May 2001; Accepted 7 September 2001.     

Analysis of IgA1 N-glycosylation and its contribution to FcalphaRI binding

The IgA isotype of human antibodies triggers inflammatory responses via the IgA-specific receptor FcalphaRI (CD89). Structural studies have suggested that IgA1 N-glycans could modulate the interaction with FcalphaRI. We have carried out detailed biophysical analyses of three IgA1 samples purified from human serum and recombinant IgA1-Fc and compared their binding to FcalphaRI. Analytical ultracentrifugation revealed wide variation in the distribution of polymeric species between IgA1 samples, and Fourier transform ion cyclotron resonance mass spectrometry showed overlapping but distinct populations of N-glycan species between IgA1 samples. Kinetic and equilibrium data from surface plasmon resonance experiments revealed that variation in the IgA1 C H2 N-glycans had no effect on the kinetics or affinity constants for binding to FcalphaRI. Indeed, complete enzymatic removal of the IgA1 N-glycans yielded superimposable binding curves. These findings have implications for renal diseases such as IgA nephropathy.     

Interaction between uranium and the cytochrome c 3 of Desulfovibrio desulfuricans strain G20

Cytochrome c₃ of Desulfovibrio desulfuricans strain G20 is an electron carrier for uranium (VI) reduction. When D. desulfuricans G20 was grown in medium containing a non-lethal concentration of uranyl acetate (1 mM), the rate at which the cells reduced U(VI) was decreased compared to cells grown in the absence of uranium. Western analysis did not detect cytochrome c₃ in periplasmic extracts from cells grown in the presence of uranium. The expression of this predominant tetraheme cytochrome was not detectably altered by uranium during growth of the cells as monitored through a translational fusion of the gene encoding cytochrome c₃ (cycA) to lacZ. Instead, cytochrome c₃ protein was found tightly associated with insoluble U(IV), uraninite, after the periplasmic contents of cells were harvested by a pH shift. The association of cytochrome c₃ with U(IV) was interpreted to be non-specific, since pure cytochrome c₃ adsorbed to other insoluble metal oxides, including cupric oxide (CuO), ferric oxide (Fe₂O₃), and commercially available U(IV) oxide.An erratum to this article can be found at     

Sex-biased evolutionary forces shape genomic patterns of human diversity

Comparisons of levels of variability on the autosomes and X chromosome can be used to test hypotheses about factors influencing patterns of genomic variation. While a tremendous amount of nucleotide sequence data from across the genome is now available for multiple human populations, there has been no systematic effort to examine relative levels of neutral polymorphism on the X chromosome versus autosomes. We analyzed ~210 kb of DNA sequencing data representing 40 independent noncoding regions on the autosomes and X chromosome from each of 90 humans from six geographically diverse populations. We correct for differences in mutation rates between males and females by considering the ratio of within-human diversity to human-orangutan divergence. We find that relative levels of genetic variation are higher than expected on the X chromosome in all six human populations. We test a number of alternative hypotheses to explain the excess polymorphism on the X chromosome, including models of background selection, changes in population size, and sex-specific migration in a structured population. While each of these processes may have a small effect on the relative ratio of X-linked to autosomal diversity, our results point to a systematic difference between the sexes in the variance in reproductive success; namely, the widespread effects of polygyny in human populations. We conclude that factors leading to a lower male versus female effective population size must be considered as important demographic variables in efforts to construct models of human demographic history and for understanding the forces shaping patterns of human genomic variability.