Mechanism and dynamics of conformational ordering in xanthan polysaccharide

The thermally induced order-disorder transition of xanthan (extracellular bacterial polysaccharide from Xanthomonas campestris) has been investigated by optical rotation, differential scanning calorimetry, stopped-flow reaction kinetics and low-angle laser light scattering, and the results have been analysed in terms of Zimm -Bragg helix-coil transition theory. The reciprocal of the transition midpoint temperature (Tm) varies linearly with the logarithm of cation (K+) the salt dependence of Tm, is in agreement with Manning polyelectrolyte theory the ordered structure. The associated increase in cation binding, calculated from the salt dependence of tm, is in agreement with the Manning polyelectrolyte theory for one of the candidate structures from X-ray diffraction, a 5(1) single helix stabilized by packing of side-chains along the polymer backbone, but not for the alternative double-helix structure that has also been proposed. At each salt concentration, the two fundamental parameters of the Zimm -Bragg theory, s and sigma, were calculated. The equilibrium constant for growth of the ordered structure (s) is derived directly from calorimetric measurement of transition enthalpy (delta Hcal ), and sigma, which quantifies the relative instability of the helix nucleus, is derived from the ratio of delta Hcal to the apparent transition enthalpy (delta Happ ) obtained by van't Hoff analysis of the optical rotation data. The temperature course of conformational ordering calculated theoretically is in good quantitative agreement with experimental results from both optical rotation and scanning calorimetry. The calculated average length of stable, ordered chain-sequences increases with decreasing temperature, but equals or exceeds the total chain length from light scattering only at temperatures more than approximately equal to 70 K below Tm, suggesting that ordered and disordered regions may co-exist within the same xanthan molecule. Consistent with this interpretation, the observed rate of conformational ordering increases sharply under conditions where the starting solution for dynamic measurements is partially ordered, suggesting that ordered sequences within each chain may act as helix nuclei for adjacent disordered regions, so that helix growth, rather than the slower nucleation process, becomes rate limiting.     

COMPARISON OF ISOZYMES AMONG TYPHA SPECIES IN THE EASTERN UNITED STATES

Biochemical phenotsypes of four taxa of Typha from the eastern United States were determined by starch gel electrophoresis. The isozyme banding patterns of T. latifolia, T. angustifolia and T. domingensis are distinct and allow unambiguous species identification when morphological characters are inadequate or unsuitable. The fourth form, T. glauca, is not an F₁ hybrid, but it does appear to be intermediate between T. latifolia and T. angustifolia. The status of T. glauca and evolutionary relationships among the four forms may now be clarified by additional sampling because of the distinct and relatively invariant isozyme banding patterns which are described.     

Strength and physical fitness predict the perception of looming sounds

Listeners consistently perceive approaching sounds to be closer than they actually are and perceptually underestimate the time to arrival of looming sound sources. In a natural environment, this underestimation results in more time than expected to evade or engage the source and affords a “margin of safety” that may provide a selective advantage. However, a key component in the proposed evolutionary origins of the perceptual bias is the appropriate timing of anticipatory motor behaviors. Here we show that listeners with poorer physical fitness respond sooner to looming sounds and with a larger margin of safety than listeners with better physical fitness. The anticipatory perceptual bias for looming sounds is negatively correlated with physical strength and positively correlated with recovery heart rate (a measure of aerobic fitness). The results suggest that the auditory perception of looming sounds may be modulated by the response capacity of the motor system.     

The cost of mutualism in a fly-fungus interaction

The movement ability of individuals has become increasingly important to a variety of ecological questions. In this study, I investigate how plant structure and changes in body size through development affect the movement ability of a predaceous stinkbug, Podisus maculiventris, on three species of goldenrod (Solidago spp.) representing a wide range of surface complexities. I adapt existing techniques for quantifying movement in two dimensions to the study of movement on natural plant structures in three dimensions. These experiments indicate that plant structure and insect size are significant factors affecting the movement ability of P. maculiventris. Changes in movement ability due to factors of ontogeny and different habitat structures suggest that the scale of an individual’s ambit or ecological sphere of influence may vary within its lifespan. Considering the influence of ontogeny and habitat structure on movement ability may be useful to investigations of population dynamics, foraging behavior, and pest management. Received: 14 July 1999 / Accepted: 23 March 2000     

There are two gene sequences for human apolipoprotein CI (apo CI) on chromosome 19, one of which is 4 kb from the gene for apo E

A cDNA probe corresponding to the mRNA sequence for apolipoprotein E (apo E) was used to screen two independently-constructed human genomic libraries. Two recombinants (lambda E-2, and lambda E2-1), isolated using the apo E cDNA probe, also contain part or all of the apo CI gene. Hybridisation studies using both apo E and apo CI cDNA probes show that these two genes are in the same orientation and separated by 4 kb.     

Endless forms most stupid,icky, and small: The preponderance of noncharismatic invertebrates as integral to a biologically sound view of life

Big, beautiful organisms are useful for biological education, increasing evolution literacy, and biodiversity conservation. But if educators gloss over the ubiquity of streamlined and miniaturized organisms, they unwittingly leave students and the public vulnerable to the idea that the primary evolutionary plot of every metazoan lineage is “progressive” and "favors" complexity. We show that simple, small, and intriguingly repulsive invertebrate animals provide a counterpoint to misconceptions about evolution. Our examples can be immediately deployed in biology courses and outreach. This context emphasizes that chordates are not the pinnacle of evolution. Rather, in the evolution of animals, miniaturization, trait loss, and lack of perfection are at least as frequent as their opposites. Teaching about invertebrate animals in a “tree thinking” context uproots evolution misconceptions (for students and the public alike), provides a mental scaffold for understanding all animals, and helps to cultivate future ambassadors and experts on these little‐known, weird, and fascinating taxa.     

Multipotent Cancer Stem Cells Derived from Human Malignant Peritoneal Mesothelioma Promote Tumorigenesis

During the progression of malignant peritoneal mesothelioma (MPeM), tumor nodules propagate diffusely within the abdomen and tumors are characterized by distinct phenotypic sub-types. Recent studies in solid organ cancers have shown that cancer stem cells (CSCs) play a pivotal role in the initiation and progression of tumors. However, it is not known whether tumorigenic stem cells exist and whether they promote tumor growth in MPeM. In this study, we developed and characterized a CSC model for MPeM using stably expandable tumorigenic stem cells derived from patient tumors. We found morphologically distinct populations of CSCs that divide asymmetrically or symmetrically in MPeM in vitro cell culture. The MPeM stem cells (MPeMSCs) express stem cell markers c-MYC, NES and VEGFR2 and in the presence of matrix components cells form colony spheres. MPeMSCs are multipotent, differentiate into neuronal, vascular and adipose progeny upon defined induction and the differentiating cells express lineage-specific markers such as TUBB3, an early neuronal marker; vWF, VEGFA, VEGFC and IL-8, endothelial markers; and PPARγ and FABP4, adipose markers. Xenotransplantation experiments using MPeMSCs demonstrated early tumor growth compared with parental cells. Limiting dilution experiments using MPeMSCs and endothelial lineage-induced cells derived from a single MPeMSC resulted in early tumor growth in the latter group indicating that endothelial differentiation of MPeMSCs is important for MPeM tumor initiation. Our observation that the MPeM tumors contain stem cells with tumorigenic potential has important implications for understanding the cells of origin and tumor progression in MPeM and hence targeting CSCs may be a useful strategy to inhibit malignant progression.     

Moving forward with the primate microbiome: Introduction to a special issue of the American Journal of Primatology

Primate microbiome research is a quickly growing field with exciting potential for informing our understanding of primate biology, ecology, and evolution as well as host‐microbe interactions more broadly. This introductory essay to a special section of the American Journal of Primatology provides a cross‐sectional snapshot of current activity in these areas by briefly summarizing the diversity of contributed papers and their relationships to key themes in host‐associated microbiome research. It then uses this survey as a foundation for consolidating a set of key research questions to broadly guide future research. It also argues for the importance of methods standardization to facilitate comparative analyses and the identification of generalizable patterns and relationships. While primatology will benefit greatly from the integration of microbial datasets, it is uniquely positioned to address important questions regarding microbiology and macro‐ecology and evolution more generally. We are eager to see where the primate microbiome leads us.