B cell genomics behind cross-neutralization of SARS-CoV-2 variants and SARS-CoV

1. Download : Download high-res image (219KB)
2. Download : Download full-size image

     

Can landscape properties predict occurrence of grey-sided voles?

There has been a long-term decline in spring and fall numbers of Clethrionomys rufocanus in boreal Sweden in 1971–2005. Previous studies on permanent sampling plots in the centre of 2.5 × 2.5 km landscapes suggested that habitat fragmentation (sensu destruction) could have contributed to the decline. Therefore, we tested these findings in a field study and compared trapping results on the central sampling plots of landscapes with a low degree of fragmentation (LDF) and of “hot spot” type with trapping results in managed forest landscapes with a high degree of fragmentation (HDF). We predicted that C. rufocanus would be more common on the LDF plots. We used our permanent plots supplemented with a new sample of plots, mainly of the rare LDF type, inside or just outside the long-term study area. Very few voles were trapped on both plot types, and no difference was found. However, a subsequent pilot study with trapping in a national park with large areas of pristine, unfragmented forest yielded more voles than in the managed, more fragmented, areas. Consequently, the initial field study data and some other recent data were also re-analysed from a “local patch quality” perspective. This alternative approach revealed the positive importance of large focal patches of forest >60 years old and their content of old-growth (pine) forest (>100 years). Interestingly, at the landscape level, the frequency distribution of patches of forest >60 years old, old-growth (>100 years), and especially of old-growth pine forest (>100 years), relative to the properties of plots with C. rufocanus, suggested that there are few forest patches left that are suitable for C. rufocanus. Our current results suggest that habitat fragmentation cannot be excluded as a contributing cause to the long-term decline of C. rufocanus in boreal Sweden.     

Entrapment Bias of Arthropods in Miocene Amber Revealed by Trapping Experiments in a Tropical Forest in Chiapas,Mexico

All entomological traps have a capturing bias, and amber, viewed as a trap, is no exception. Thus the fauna trapped in amber does not represent the total existing fauna of the former amber forest, rather the fauna living in and around the resin producing tree. In this paper we compare arthropods from a forest very similar to the reconstruction of the Miocene Mexican amber forest, and determine the bias of different trapping methods, including amber. We also show, using cluster analyses, measurements of the trapped arthropods, and guild distribution, that the amber trap is a complex entomological trap not comparable with a single artificial trap. At the order level, the most similar trap to amber is the sticky trap. However, in the case of Diptera, at the family level, the Malaise trap is also very similar to amber. Amber captured a higher diversity of arthropods than each of the artificial traps, based on our study of Mexican amber from the Middle Miocene, a time of climate optimum, where temperature and humidity were probably higher than in modern Central America. We conclude that the size bias is qualitatively independent of the kind of trap for non–extreme values. We suggest that frequent specimens in amber were not necessarily the most frequent arthropods in the former amber forest. Selected taxa with higher numbers of specimens appear in amber because of their ecology and behavior, usually closely related with a tree–inhabiting life. Finally, changes of diversity from the Middle Miocene to Recent time in Central and South America can be analyzed by comparing the rich amber faunas from Mexico and the Dominican Republic with the fauna trapped using sticky and Malaise traps in Central America.     

Rate-Dependent Behavior of the Amorphous Phase of Spider Dragline Silk

The time-dependent stress-strain behavior of spider dragline silk was already observed decades ago, and has been attributed to the disordered sequences in silk proteins, which compose the soft amorphous matrix. However, the actual molecular origin and magnitude of internal friction within the amorphous matrix has remained inaccessible, because experimentally decomposing the mechanical response of the amorphous matrix from the embedded crystalline units is challenging. Here, we used atomistic molecular dynamics simulations to obtain friction forces for the relative sliding of peptide chains of Araneus diadematus spider silk within bundles of these chains as a representative unit of the amorphous matrix in silk fibers. We computed the friction coefficient and coefficient of viscosity of the amorphous phase to be in the order of 10⁻⁶ Ns/m and 10⁴ Ns/m², respectively, by extrapolating our simulation data to the viscous limit. Finally, we used a finite element method for the amorphous phase, solely based on parameters derived from molecular dynamics simulations including the newly determined coefficient of viscosity. With this model the time scales of stress relaxation, creep, and hysteresis were assessed, and found to be in line with the macroscopic time-dependent response of silk fibers. Our results suggest the amorphous phase to be the primary source of viscosity in silk and open up the avenue for finite element method studies of silk fiber mechanics including viscous effects.     

The preparation and characterization of liposomes containing X-ray contrast agents

Unilamellar phospholipid vesicles loaded with the water-soluble, ionic X-ray contrast agent diatrizoate (Hypaque, Renografin) were manufactured by reverse-phase evaporation for use as organ-enhancing agents in X-ray computed tomography. Encapsulation efficiency was determined as a function of various diatrizoate concentrations in vesicles of varying lipid composition. Loss of encapsulated diatrizoate over 24 h was examined in vesicles composed of several egg phosphatidylcholine/cholesterol ratios. Size estimates for loaded vesicles were obtained by negative-stain electron microscopy, Millipore filtration and light microscopy. Intravenous in vivo injection of loaded vesicles in the rat resulted in significant enhancement of both spleen and liver on subsequent scans. Vesicles were similarly prepared with the water-soluble, nonionic agent metrizamide (Amipaque). Encapsulation efficiency was determined, and in vivo behavior was observed.     

On lipid droplets in renal interstitial cells

Summary By ultracentrifugation of homogenates of rat renal papillae, a low density layer composed of small primary fluorescing lipid droplets was isolated. Probably the isolated lipid material originates mainly from the primary fluorescing lipid droplets of the renal interstitial cells. The isolated lipid droplets were mainly triglycerides, cholesterol esters and free longchain fatty acids. The long-chain fatty acid composition of the main components differed markedly from that of the analogous components of plasma and depot fat. The findings suggest that the complex lipids of the isolated lipid droplets are synthetized by the renal papilla and probably by the renal interstitial cells. The prostaglandin precursor arachidonic acid constitutes a significant fraction of the triglyceride long-chain fatty acids. Usually also small quantities of prostaglandins were present. Altogether the results suggest that the lipid droplets of the renal interstitial cells may function as a storage site for prostaglandin precursor.This work was supported by a grant from the Danish State Research Foundation. — The authors wish to acknowledge the support and inspiration given by E. Bojesen, M.D., Ph.D., the Institute of Experimental Medicine, Division of Endocrinology. — The authors wish to thank Dr. John E. Pike of the Upjohn Company, Kalamazoo, Michigan, for supplying the Prostaglandins used in this study.