The evolutionary radiation of Arvicolinae rodents (voles and lemmings): relative contribution of nuclear and mitochondrial DNA phylogenies

Background  

Mitochondrial and nuclear genes have generally been employed for different purposes in molecular systematics, the former to resolve relationships within recently evolved groups and the latter to investigate phylogenies at a deeper level. In the case of rapid and recent evolutionary radiations, mitochondrial genes like cytochrome b (CYB) are often inefficient for resolving phylogenetic relationships. One of the best examples is illustrated by Arvicolinae rodents (Rodentia; Muridae), the most impressive mammalian radiation of the Northern Hemisphere which produced voles, lemmings and muskrats. Here, we compare the relative contribution of a nuclear marker – the exon 10 of the growth hormone receptor (GHR) gene – to the one of the mitochondrial CYB for inferring phylogenetic relationships among the major lineages of arvicoline rodents.     

Scanning electron microscopy of native biofilms on mung bean sprouts

Native biofilms present on the adaxial surface of cotyledons of mung bean sprouts (Vigna radiata) were studied by use of scanning electron microscopy. Biofilms were abundant on the cotyledon surfaces and were comprised of rod-shaped bacteria, cocci-shaped bacteria, or yeasts, often with one type of microbe predominant. In contrast to our earlier study of biofilms on green sprouts (alfalfa, clover, broccoli, and sunflower), yeast and cocci were abundant on mung bean. Filamentous fungi were not observed. Sheet-like or fibrillar material (presumably composed of secreted microbial polysaccharides, proteins, lipids, and nucleic acids) fully or partially covered the biofilms. Biofilms up to 5 mm in length were observed, and some biofilms were comprised of more than just a monolayer of microbial cells. Native biofilms on sprout surfaces undoubtedly play an important role in the ecology of plant epiphytic microbes and may also afford protected sites for plant and human bacterial pathogens.     

Expression of the IRT1 metal transporter is controlled by metals at the levels of transcript and protein accumulation

Iron, an essential nutrient, is not readily available to plants because of its low solubility. In addition, iron is toxic in excess, catalyzing the formation of hydroxyl radicals that can damage cellular constituents. Consequently, plants must carefully regulate iron uptake so that iron homeostasis is maintained. The Arabidopsis IRT1 gene is the major transporter responsible for high-affinity iron uptake from the soil. Here, we show that the steady state level of IRT1 mRNA was induced within 24 h after transfer of plants to iron-deficient conditions, with protein levels peaking 72 h after transfer. IRT1 mRNA and protein were undetectable 12 h after plants were shifted back to iron-sufficient conditions. Overexpression of IRT1 did not confer dominant gain-of-function enhancement of metal uptake. Analysis of 35S-IRT1 transgenic plants revealed that although IRT1 mRNA was expressed constitutively in these plants, IRT1 protein was present only in the roots when iron is limiting. Under these conditions, plants that overexpressed IRT1 accumulated higher levels of cadmium and zinc than wild-type plants, indicating that IRT1 is responsible for the uptake of these metals and that IRT1 protein levels are indeed increased in these plants. Our results suggest that the expression of IRT1 is controlled by two distinct mechanisms that provide an effective means of regulating metal transport in response to changing environmental conditions.     

The abundance of additional N-acetyllactosamine units in N-linked tetraantennary oligosaccharides of human Tamm-Horsfall glycoprotein is a donor-specific feature

Previously, treatment of Tamm-Horsfall glycoprotein (THp) from different donors with endo-beta-galactosidase has been shown to liberate a tetra- and a Sd(a)-active pentasaccharide, concluding the presence of N-linked carbohydrate chains containing additional N - acetyllactosamine units. These type of oligosaccharides were not found in a detailed structure elucidation of the carbohydrate moiety of THp of one male donor, suggesting a donor-specific feature for these type of structures. Therefore, THp was isolated from four healthy male donors and each subjected to endo-beta-galactosidase treatment in order to release these tetra- and Sd(a)-active pentasaccharide. Differences were observed in the total amount of released tetra- and Sda-active pentasaccharide of the used donors (42, 470, 478, 718 microg/100 mg THp), indicating that the presence of repeating N-acetyllactosamine units incorporated into the N-glycan moiety of THp is donor specific. Furthermore, a higher expression of the Sd(a) determinant on antennae which display N-acetyllactosamine elongation was observed, suggesting a better accessibility for the beta-N-acetylgalactosaminyltransferase. In order to characterize the N-glycans containing repeating N- acetyllactosamine units, carbohydrate chains were enzymatically released from THp and isolated. The tetraantennary fraction, which accounts for more than 33% of the total carbohydrate moiety of THp, was used to isolate oligosaccharides containing additional N - acetyllactosamine units. Five N-linked tetraantennary oligosaccharides containing a repeating N-acetyllactosamine unit were identified, varying from structures bearing four Sd(a) determinants to structures containing no Sd(a) determinant (see below). One compound was used in order to specify the branch location of the additional N- acetyllactosamine unit, and it appeared that only the Gal-6' and Gal-8' residues were occupied by a repeating N -acetyllactosamine unit.      

Differential binding of lectins IL-2 and CSL to candida albicans and cancer cells

The demonstration that interleukin 2 (IL-2) is a lectin specific for oligomannosides allows to understand a new function for this cytokine: as a bifunctional molecule when bound to its receptor ss, IL-2 associates the latter which the CD3/TCR complex, interacting with oligosaccharides of CD3 through its carbohydrate-recognition domain (Zanetta et al. , 1996, Biochem. J., 318, 49-53). This induces the tyrosine phosphorylation of the IL-2R beta by ++p56(lck) , the first step of the IL-2-dependent signaling. Since this specific association is disrupted in vitro by oligomannosides with five and six mannose residues, we made the hypothesis that pathogenic cells or microorganisms could bind IL-2, consequently disturbing the IL-2- dependent response. This study shows that the pathogenic yeast Candida albicans (in contrast with nonpathogenic yeasts) binds high amounts of IL-2 as did cancer cells. In contrast with cancer cells, yeasts do not bind the Man6GlcNAc2-specific lectin CSL, an endogenous "amplifier of activation signals" (Zanetta et al. , 1995, Biochem. J., 311, 629-636).      

STUDIES ON THE SELF-INCOMPATIBILITY RESPONSE OF LILIUM LONGIFLORUM

Removal of substances loosely associated with the wall of Lilium longiflorum pollen did not affect in vitro germination and tube growth, tube growth within compatible styles, or production of viable seeds. Nor was growth of pollen tubes within incompatible styles enhanced by prior removal of the loosely bound materials. Hence, these materials appear not to be recognition factors in the gametophytic self-incompatibility system of Lilium and to have no role in pollen germination. Heat treatment of selected portions of lily pistils prior to pollination indicated that the incompatibility factor(s) was located in the lower half of the style, and that the stigma plays no role in incompatibility.