Monoclonal antibodies against distinct determinants of histone H5 bind to chromatin

A series of monoclonal antibodies specific for distinguishable epitopes in chromosomal protein histone H5 were obtained from mice immunized with either free H5 or H5 . RNA complexes. The antibodies elicited by H5 could be distinguished from those elicited by H5 . RNA by their binding to native or acid-denatured H5, by their interaction with the globular region of H5, and by their cross-reactivity with H1o. The specificity of the antibodies was assessed by enzyme-linked immunosorbent assay (ELISA) and immunoblotting experiments. The antibodies could distinguish between H5 and the closely related histones H1 and H1o. The binding of some of the antibodies to the antigens was dependent on the type of assay used, suggesting nonrandom binding of the antigen to the solid supports used in ELISA and immunoblotting. Competitive ELISA experiments indicate that 8 of the 11 antibodies characterized bind to distinct epitopes. Three monoclonal antibodies bind to epitopes which are in close spatial proximity, causing mutual steric hindrance. The monoclonal antibodies bind to nuclei of fixed cells and to isolated chromatin, indicating that the epitopes are present both in the purified protein and in chromatin-complexed H5. These monoclonal antibodies can be used to study the organization of distinct regions of histones H5 and H1o in chromatin and chromosomes.     

Macrophage Fc receptors control infectivity and neutralization of canine distemper virus-antibody complexes.

Dogs that are persistently infected or that become moribund after exposure to canine distemper virus (CDV) have antibody that neutralized CDV when tested in dog lung macrophage cultures but failed to neutralize CDV when tested in epithelial, fibroblastic, or lymphatic cells. The antibody attached to protein A and was found in the immunoglobulin G fraction. The antibody bound complement and lysed CDV-infected target cells. The neutralizing activity in macrophages could be abolished (i) by pepsin digestion and removal of Fc portions from the antibody, (ii) by blocking the Fc receptors of macrophages with heat-treated normal dog serum, and (iii) by binding of protein A to Fc portions of the antibody. It was concluded that attachment of the CDV-antibody complex to Fc receptors of macrophages was essential for virus neutralization. If this attachment was hindered, the CDV-antibody complex became infectious for macrophages. In contrast, serum from recovering dogs neutralized CDV when tested in epithelial, fibroblastic, or lymphatic cells as well as in macrophages.     

Stimulation of Platelet-derived Growth Factor Receptor β (PDGFRβ) Activates ADAM17 and Promotes Metalloproteinase-dependent Cross-talk between the PDGFRβ and Epidermal Growth Factor Receptor (EGFR) Signaling Pathways

Binding of the platelet-derived growth factor (PDGF)-B to its receptor PDGFRβ promotes proliferation, migration, and recruitment of pericytes and smooth muscle cells to endothelial cells, serving to stabilize developing blood vessels. The main goals of this study were to determine whether the extracellular domain of the PDGFRβ can be proteolytically released from cell membranes and, if so, to identify the responsible sheddase and determine whether activation of the PDGFRβ stimulates its shedding and potentially that of other membrane proteins. We found that the PDGFRβ is shed from cells by a metalloproteinase and used loss-of-function experiments to identify ADAM10 as the sheddase responsible for constitutive and ionomycin-stimulated processing of the PDGFRβ. Moreover, we showed that ligand-dependent activation of the PDGFRβ does not trigger its own shedding by ADAM10, but instead it stimulates ADAM17 and shedding of substrates of ADAM17, including tumor necrosis factor α and transforming growth factor α. Finally, we demonstrated that treatment of mouse embryonic fibroblasts with PDGF-B triggers a metalloproteinase-dependent cross-talk between the PDGFRβ and the epidermal growth factor receptor (EGFR)/ERK1/2 signaling axis that is also critical for PDGF-B-stimulated cell migration, most likely via ADAM17-dependent release and activation of ligands of the EGFR. This study identifies the principal sheddase for the PDGFRβ and provides new insights into the mechanism of PDGFRβ-dependent signal transduction and cross-talk with the EGFR.     

Phylogenetic Correlation Between Male Nuptial Color and Behavioral Responses to Color Across a Diverse and Colorful Genus of Freshwater Fish (Etheostoma spp., Teleostei: Percidae)

Sexual selection theory predicts that preferences in both sexes select for the elaboration of male nuptial coloration, with empirical evidence supporting these predictions. Empirical studies are often limited in their taxonomic inclusiveness, however, and typically do not examine how male and female preferences contribute to macroevolutionary patterns of male color variation across multiple lineages in a clade. This study examined color preferences in a group of dichromatic freshwater fishes known as darters (genus Etheostoma) that vary in the presence of male coloration. The strengths of attraction to black, blue, gray, and red models were tested in females of 18 species, in addition to males of five species. We found a positive association between the presence of red or orange on the body and the amount of time associating with red models, suggesting color variation is at least in part due to variation in female preferences between species. Males also spent more time associating with colors that most closely resembled conspecifics, suggesting that preferential responses to color in males also can contribute to the diversity of nuptial coloration in darters.     

Mechanical properties of peptidoglycan as determined from bacterial thread

Experiments are described in which the tensile strength, the extensibility and the initial Young's modulus of bacterial cell wall have been determined as functions of relative humidity in the range 11-98%. Data on stress relaxation and recovery are also given. Standard fibre-measuring technique has been used on 'bacterial thread', made from a cell-separation-suppressed mutant of Bacillus subtilis. The data show that peptidoglycan, the load bearing polymer in the cell wall, behaves very much like other viscoelastic polymers. Its mechanical behaviour when dry is that of a glassy polymer with tensile strength about 300 MPa and modulus about 20 GPa. When wet, it is weaker and much less stiff with tensile strength about 3 M Pa and modulus 10 M Pa. The relaxation data indicate a wide spectrum of relaxation times. The results are discussed in terms of the structure of peptidoglycan and its orientation in the bacterial cell wall. The way in which mechanical behaviour depends strongly on humidity is compared with that of other biopolymers in terms of possible hydrogen-bond density and the ordering of water molecules. The possibility of a well-defined glass transition is briefly examined.