Interchange of apoprotein components between the human plasma high density lipoprotein subclasses HDL2 and HDL3 in vitro.

The major apoproteins of human high density lipoproteins (HDL) labeled with 125I have been shown to exchange between the two major HDL subclasses HDL2 and HDL3 in vitro. This bidirectional exchange process is inhibited by cross-linking with bifunctional reagents and is apparently dependent upon the formation of collision complexes. This exchange has been demonstrated both when the subclasses of HDL are free in solution and also when one of them is covalently bound to Sepharose. Using system involving Sepharose-bound HDL, it could be shown that not only free apoprotein molecules but subunits consisting of lipid-apoprotein combinations were exchanged between HDL2 and HDL3. The rate of exchange in these processes is significant in the lifetime of the protein particles in vivo equalling approximately 2.5% per h for apoprotein exchange. These experiments suggest that there is a dynamic relationship between HDL2 and HDL3 even though each of them exists alone in vitro as stable separate entities; when they are placed together in solution significant interaction occurs between the particles. Apoprotein exchange occurs between HDL2:HDL2 and HDL3:HDL3 as well as between HDL2 and HDL3 molecules. These data also suggest that the interconversion of HDL2 and HDL3 may be affected by the availability of lipids.     

Nicotine decreases agrin signaling and acetylcholine receptor clustering in C2C12 myotube culture

The clustering of acetylcholine receptors (AChRs) in skeletal muscle fibers is a critical event in neuromuscular synaptogenesis. AChRs in concert with other molecules form postsynaptic scaffolds in response to agrin released from motor neurons as motor neurons near skeletal muscle fibers in development. Agrin drives an intracellular signaling pathway that precedes AChR clustering and includes the tyrosine phosphorylation of AChRs. In C2C12 myotube culture, agrin application stimulates the agrin signaling pathway and AChR clustering. Previous studies have determined that the frequency of spontaneous AChR clustering is decreased and AChRs are partially inactivated when bound by the acetylcholine agonist nicotine. We hypothesized that nicotine interferes with AChR clustering and consequent postsynaptic scaffold formation. In the present study, C2C12 myoblasts were cultured with growth medium to stimulate proliferation and then differentiation medium to stimulate fusion into myotubes. They were bathed in a physiologically relevant concentration of nicotine and then subject to agrin treatment after myotube formation. Our results demonstrate that nicotine decreases agrin-induced tyrosine phosphorylation of AChRs and decreases the frequency of spontaneous as well as agrin-induced AChR clustering. We conclude that nicotine interferes with postsynaptic scaffold formation by preventing the tyrosine phosphorylation of AChRs, an agrin signaling event that precedes AChR clustering.     

Preliminary Data on the Behavior,Ecology, and Morphology of Pygmy Tarsiers (<Emphasis Type=Italic>Tarsius pumilus</Emphasis>)

We here present the first behavioral, morphological, and ecological data on a living group of highland pygmy tarsiers, Tarsius pumilus, and compare them with the lowland tarsier species of Sulawesi. Pygmy tarsiers were previously known only from 3 museum specimens and had not been seen alive since the first specimens were collected in 1917 and 1930. As part of a 2-mo exploratory study, we recently located a group consisting of ≥4 pygmy tarsiers in the mossy cloud forest of Lore Lindu National Park, Central Sulawesi, Indonesia. We captured 1 adult female and 2 adult male group members. The tarsiers weighed a mean of 50 g, less than half the weight of adult lowland tarsiers. Our behavioral observations indicate that these tarsiers live in small groups that return to the same sleeping tree each morning. Though our data are preliminary, pygmy tarsier body proportions appear to differ from the lowland Sulawesian tarsier species, with relatively long hind limbs compared to total body length. We also observed differences in grouping and communication behaviors. Unlike lowland tarsiers, pygmy tarsiers possess multiple adult males per group and rarely vocalize or scentmark. These differences may correlate with variables unique to their high altitude habitat, especially a reduction in food and tree resources, given that tree density declined sharply along an altitudinal gradient. Our preliminary study identifies the importance of altitudinal ecological gradients to tarsier behavioral ecology in Central Sulawesi, providing questions and predictions for future research directions.     

Changes in Nitrogen-Fixing and Ammonia-Oxidizing Bacterial Communities in Soil of a Mixed Conifer Forest after Wildfire

This study was undertaken to examine the effects of forest fire on two important groups of N-cycling bacteria in soil, the nitrogen-fixing and ammonia-oxidizing bacteria. Sequence and terminal restriction fragment length polymorphism (T-RFLP) analysis of nifH and amoA PCR amplicons was performed on DNA samples from unburned, moderately burned, and severely burned soils of a mixed conifer forest. PCR results indicated that the soil biomass and proportion of nitrogen-fixing and ammonia-oxidizing species was less in soil from the fire-impacted sites than from the unburned sites. The number of dominant nifH sequence types was greater in fire-impacted soils, and nifH sequences that were most closely related to those from the spore-forming taxa Clostridium and Paenibacillus were more abundant in the burned soils. In T-RFLP patterns of the ammonia-oxidizing community, terminal restriction fragments (TRFs) representing amoA cluster 1, 2, or 4 Nitrosospira spp. were dominant (80 to 90%) in unburned soils, while TRFs representing amoA cluster 3A Nitrosospira spp. dominated (65 to 95%) in fire-impacted soils. The dominance of amoA cluster 3A Nitrosospira spp. sequence types was positively correlated with soil pH (5.6 to 7.5) and NH₃-N levels (0.002 to 0.976 ppm), both of which were higher in burned soils. The decreased microbial biomass and shift in nitrogen-fixing and ammonia-oxidizing communities were still evident in fire-impacted soils collected 14 months after the fire.     

Compact, high performance surface plasmon resonance imaging system

We report the construction and characterization of a new compact surface plasmon resonance imaging instrument. Surface plasmon resonance imaging is a versatile technique for detection, quantification and visualization of biomolecular binding events which have spatial structure. The imager uses a folded light path, wide-field optics and a tilted detector to implement a high performance optical system in a volume 7 in. x 4 in. x 2 in. A bright diode light source and an image detector with fast frame rate and integrated digital signal processor enable real-time averaging of multiple images for improved signal-to-noise ratio. Operating angle of the imager is adjusted by linear translation of the light source. Imager performance is illustrated using resolution test targets, refractive index test solutions, and competition assays for the antiepileptic drug phenytoin. Microfluidic flowcells are used to enable simultaneous assay of three sample streams. Noise level of refractive index measurements was found to decrease proportional to the square root of the number of pixels averaged, reaching approximately 5 x 10(-7) refractive index units root-mean-square for 160 x 120 pixels image regions imaged for 1s. The simple, compact construction and high performance of the imager will allow the device to be readily applied to a wide range of applications.     

New biochip technology for label-free detection of pathogens and their toxins

microSERS is a new biochip technology that uses surface-enhanced Raman scattering (SERS) microscopy for label-free transduction. The biochip itself comprises pixels of capture biomolecules immobilized on a SERS-active metal surface. Once the biochip has been exposed to the sample and the capture biomolecules have selectively bound their ligands, a Raman microscope is used to collect SERS fingerprints from the pixels on the chip. SERS, like other whole-organism fingerprinting techniques, is very specific. Our initial studies have shown that the Gram-positive Listeria and Gram-negative Legionella bacteria, Bacillus spores and Cryptosporidium oocysts can often be identified at the subspecies/strain level on the basis of SERS fingerprints collected from single organisms. Therefore, pathogens can be individually identified by microSERS, even when organisms that cross-react with the capture biomolecules are present in a sample. Moreover, the SERS fingerprint reflects the physiological state of a bacterial cell, e.g., when pathogenic Listeria and Legionella were cultured under conditions known to affect virulence, their SERS fingerprints changed significantly. Similarly, nonviable (e.g., heat- or UV-killed) microorganisms could be differentiated from their viable counterparts by SERS fingerprinting. Finally, microSERS is also capable of the sensitive and highly specific detection of toxins. Toxins that comprised as little as 0.02% by weight of the biomolecule-toxin complex produced strong, unique fingerprints when spectra collected from the complexes were subtracted from the spectra of the uncomplexed biomolecules. For example, aflatoxins B(1) and G(1) could be detected and individually identified when biochips bearing pixels of antibody or enzyme capture biomolecules were incubated in samples containing one or both aflatoxins, and the spectra were then collected for 20 s from an area of the biomolecule pixel approximately 1 microm in diameter. In the future, we plan to investigate the use of hyperspectral imaging Raman microscopy for collecting fingerprints from all the pixels on the biochip, individually yet simultaneously, to enable the rapid detection of diverse pathogens and their toxins in a sample, using a single biochip.     

Assortative Mating and the Reversal of Gender Inequality in Education in Europe: An Agent-Based Model

While men have always received more education than women in the past, this gender imbalance in education has turned around in large parts of the world. In many countries, women now excel men in terms of participation and success in higher education. This implies that, for the first time in history, there are more highly educated women than men reaching the reproductive ages and looking for a partner. We develop an agent-based computational model that explicates the mechanisms that may have linked the reversal of gender inequality in education with observed changes in educational assortative mating. Our model builds on the notion that individuals search for spouses in a marriage market and evaluate potential candidates based on preferences. Based on insights from earlier research, we assume that men and women prefer partners with similar educational attainment and high earnings prospects, that women tend to prefer men who are somewhat older than themselves, and that men prefer women who are in their mid-twenties. We also incorporate the insight that the educational system structures meeting opportunities on the marriage market. We assess the explanatory power of our model with systematic computational experiments, in which we simulate marriage market dynamics in 12 European countries among individuals born between 1921 and 2012. In these experiments, we make use of realistic agent populations in terms of educational attainment and earnings prospects and validate model outcomes with data from the European Social Survey. We demonstrate that the observed changes in educational assortative mating can be explained without any change in male or female preferences. We argue that our model provides a useful computational laboratory to explore and quantify the implications of scenarios for the future.