Association of the low-density lipoprotein receptor with caveolae in hamster and rat liver

The association of the low-density lipoprotein (LDL) receptor with detergent resistant hepatic membranes was investigated using discontinuous sucrose gradients. In liver homogenates from both hamsters and rats, the fractions with the highest concentrations of LDL receptor coincided with the location of caveolin-1, a marker of the cholesterol-rich caveolae. Feeding the animals diets enriched in cholesterol slightly shifted both LDL receptor and caveolin-1 to positions of lower density. The cholesterol content of the caveolae fractions was increased 2-fold in animals fed cholesterol-supplemented diets. In homogenates of CHO cells, fractionated in the same manner, the LDL receptor was absent from the caveolae fractions but was present in denser fractions near the bottom of the gradient. Addition of caveolin-1 antibody to solubilized caveolae from liver coimmunoprecipitated the LDL receptor. These observations suggest that in liver, the LDL receptor is mainly located in caveolae. This location contrasts with the clathrin-coated pit location observed in fibroblasts and CHO cells.     

In vivo imaging of the brain cannabinoid receptor

The CB1 cannabinoid receptor is expressed in the brain at levels sufficient to serve as potential target for in vivo imaging using positron emission tomography (PET) or single photon emission computed tomography methodology. To date, the most promising radioligands for the in vivo imaging of this receptor have structures based on that of the cannabinoid antagonist, SR141716A. Rodent data obtained using these in vivo radiotracers has demonstrated that both the behavioral and neurochemical effects of cannabinoids occur at very low levels of receptor occupancy. More recently, an agonist radiotracer based on the structure of aminoalkylindole cannabinoids has also been examined for in vivo labeling of CB1 receptors. Although rodent studies have indicated that in vivo imaging of CB1 receptors is feasible, at the present time this receptor has still to be successful imaged in a human PET study.     

A new species of Thelastomathidae (Nematoda) a parasite of Neocurtilla claraziana Saussure (Orthoptera,Gryllotalpidae) in Argentina

Gryllophila cephalobulata n. sp. (Nematoda, Thelastomatidae) a parasite of the mole cricket Neocurtilla claraziana (Orthoptera, Gryllotalpidae) isolated in Buenos Aires Province, is described and illustrated. It is characterized by cuticle annulated all along the length of the body; the first ring has 4 lobules, the second one has 14 lobules, the others rings are simple, the stoma is short and has 4 small teeth, the genital papillae are arranged in 5 pairs, of which 3 pairs are preanal and 2 pairs are postanal. The tail appendage of the male is long and filiform.     

Brevican isoforms associate with neural membranes

Brevican is a neural-specific proteoglycan of the brain extracellular matrix, which is particularly abundant in the terminally differentiated CNS. It is expressed by neuronal and glial cells, and as a component of the perineuronal nets it decorates the surface of large neuronal somata and primary dendrites. One brevican isoform harbors a glycosylphosphatidylinositol anchor attachment site and, as shown by ethanolamine incorporation studies, is indeed glypiated in stably transfected HEK293 cells as well as in oligodendrocyte precursor Oli-neu cells. The major isoform is secreted into the extracellular space, although a significant amount appears to be tightly attached to the cell membrane, as it floats up in sucrose gradients. Flotation is sensitive to detergent treatment. Brevican is most prominent in the microsomal, light membrane and synaptosomal fractions of rat brain membrane preparations. The association with the particulate fraction is in part sensitive to chondroitinase ABC and phosphatidylinositol-specific phospholipase C treatment. Furthermore, brevican staining on the surface of hippocampal neurons in culture is diminished after hyaluronidase or chondroitinase ABC treatment. Taken together, this could provide a mechanism by which perineuronal nets are anchored on neuronal surfaces.     

HU: promoting or counteracting DNA compaction?

The role of HU in Escherichia coli as both a protein involved in DNA compaction and as a protein with regulatory function seems to be firmly established. However, a critical look at the available data reveals that this is not true for each of the proposed roles of this protein. The role of HU as a regulatory or accessory protein in a number of systems has been thoroughly investigated and in many cases has been largely elucidated. However, almost 30 years after its discovery, convincing evidence for the proposed role of HU in DNA compaction is still lacking. Here we present an extensive literature survey of the available data which, in combination with novel microscopic insights, suggests that the role of HU could be the opposite as well. The protein is likely to play an architectural role, but instead of being responsible for DNA compaction it could be involved in antagonising compaction by other proteins such as H-NS.     

The presence of two UvrB subunits in the UvrAB complex ensures damage detection in both DNA strands

It is generally accepted that the damage recognition complex of nucleotide excision repair in Escherichia coli consists of two UvrA and one UvrB molecule, and that in the preincision complex UvrB binds to the damage as a monomer. Using scanning force microscopy, we show here that the damage recognition complex consists of two UvrA and two UvrB subunits, with the DNA wrapped around one of the UvrB monomers. Upon binding the damage and release of the UvrA subunits, UvrB remains a dimer in the preincision complex. After association with the UvrC protein, one of the UvrB monomers is released. We propose a model in which the presence of two UvrB subunits ensures damage recognition in both DNA strands. Upon binding of the UvrA(2)B(2) complex to a putative damaged site, the DNA wraps around one of the UvrB monomers, which will subsequently probe one of the DNA strands for the presence of a lesion. When no damage is found, the DNA will wrap around the second UvrB subunit, which will check the other strand for aberrations.     

A new species of Cephalobium (Rhabditida,Cephalobiidae), a parasite of Anurogryllus muticus (De Geer) (Orthoptera,Gryllidae) in Argentina

Cephalobium odontolateralis n. sp. (Nematoda, Cephalobiidae) is described and illustrated from the nymphs of Anurogryllus muticus (De Geer) (Orthoptera, Gryllidae) from Buenos Aires province, Argentina. It is characterized by a lateral large tooth in the stoma and by the arrangement and number of the genital papillae in the male; there are 6 pairs of postanal papillae, but none is preanal.     

Comparing the consequences of induced and constitutive plant resistance for herbivore population dynamics

Although it has been suggested that induced and constitutive plant resistance should have different effects on insect herbivore population dynamics, there is little experimental evidence that plant resistance can influence herbivore populations longer than one season. We used a density-manipulation experiment and model fitting to examine the effects of constitutive and induced resistance on herbivore dynamics over both the short and long term. We used likelihood methods to fit population dynamic models to recruitment data for populations of Mexican bean beetles on soybean varieties with no resistance, constitutive resistance, or induced resistance. We compared model configurations that fit parameters for resistance types separately to models that did not account for resistance type. Models representing the hypothesis that the three resistance types differed in their effects on beetle dynamics received the most support. Induced resistance resulted in lower population growth rates and stronger density dependence than no resistance. Constitutive resistance resulted in lower population growth rates and stronger density dependence than induced resistance. Constitutive resistance had a stronger effect on both short-term beetle recruitment and predicted beetle population dynamics than induced resistance. The results of this study suggest that induced and constitutive resistance can differ in their effects on herbivore populations even in a relatively complex system.     

Expression of Drosophila Ten-a,a dimeric receptor during embryonic development

Ten-a and Ten-m are the two Drosophila members of the newly discovered Ten-m family of dimeric type II transmembrane proteins. Here, we report complete cDNA cloning and protein expression patterns of Ten-a. The Ten-a protein, a dimeric receptor of about 500 kDa is mainly expressed on axons of the embryonic central nervous system and on muscle attachment sites.