Incorporation of Labeled Precursors into the RNA and Proteins of Lactic Dehydrogenase Virus

Lactic dehydrogenase virus was grown in primary mouse embryo cells and labeled with (3)H-uridine and (3)H-amino acids. Concentrated and purified virus was banded by isopycnic centrifugation in sucrose gradients, and infectivity and radioactivity were found to correspond at a density of 1.17 g/cm(3). The extracted viral RNA was resolved by electrophoresis in polyacrylamide-agarose mixed gels, and the mol wt was estimated to be 6.0 x 10(6).     

Intra-individual variation in the vocalized frequency of the Taiwanese leaf-nosed bat, Hipposideros terasensis, influenced by conspecific colony members

We examined the intra-individual variation in resting frequency of the constant-frequency component of the second harmonic of the pulse (F _rest) over 4 years in a laboratory colony of the Taiwanese leaf-nosed bat (Hipposideros terasensis). Patterns of change in F _rest were observed when individuals were added to or removed from the colony so that we investigated whether F _rest was affected by neighboring colony members. F _rest of each bat continually showed a long-term gradual change throughout the year, and all bats in the colony increased or decreased their F _rest in the same direction as a group non-seasonally. The greatest short-term changes were observed when new bats with a relatively low F _rest joined the colony and F _rest of new bats converged with those of the original colony members around 8 –16 days after their introduction. Conversely, a single individual showed sudden short-term decrease in F _rest after its isolation from other colony members. These findings strongly indicate that F _rest is flexible according to the presence of neighboring conspecific bats. We suggest that the audio-vocal feedback for conspecific pulses appears to be involved in the short- or long-term intra-individual variation in F _rest other than factors previously thought such as age or season.     

Signal transduction of betacellulin in growth and migration of vascular smooth muscle cells

Epidermal growth factor (EGF) family ligands have been implicated in cardiovascular diseases because of their enhanced expression in vascular lesions and their promoting effects on growth and migration of vascular smooth muscle cells (VSMCs). Betacellulin (BTC), a novel EGF family ligand, has been shown to be expressed in atherosclerotic lesions and to be a potent growth factor of VSMCs. However, the molecular mechanisms downstream of BTC involved in mediating vascular remodeling remain largely unknown. Therefore, the aim of this study was to examine the effects of BTC on signal transduction, growth, and migration in VSMCs. We found that BTC stimulated phosphorylation of EGF receptor (EGFR) at Tyr1068, which was completely blocked by an EGFR kinase inhibitor, AG-1478. BTC also phosphorylated ErbB2 at Tyr877, Tyr1112, and Tyr1248 and induced association of ErbB2 with EGFR, suggesting their heterodimerization in VSMCs. In postreceptor signal transduction, BTC stimulated phosphorylation of extracellular signal-regulated kinase (ERK)1/2, Akt, and p38 mitogen-activated protein kinase (MAPK). Moreover, BTC stimulated proliferation and migration of VSMCs. ERK and Akt inhibitors suppressed migration markedly and proliferation partially, whereas the p38 inhibitor suppressed migration partially but not proliferation. In addition, we found the presence of endogenous BTC in conditioned medium of VSMCs and an increase of BTC on angiotensin II stimulation. In summary, BTC promotes growth and migration of VSMCs through activation of EGFR, ErbB2, and downstream serine/threonine kinases. Together with the expression and processing of endogenous BTC in VSMCs, our results suggest a critical involvement of BTC in vascular remodeling. epidermal growth factor receptors; ErbB2; migration; signal transduction     

Osmoelastic coupling in biological structures: decrease in membrane fluidity and osmophobic association of phospholipid vesicles in response to osmotic stress

Poly(ethylene glycol)- (PEG-) induced change in membrane fluidity and aggregation of phospholipid vesicles were studied. A threshold concentration of PEG was required to induce the aggregation. This concentration increased with a decrease in the molecular weight of PEG, e.g., from 5% (w/w) with PEG 6000 (PEG with an average molecular weight of 7500) to more than 30% (w/w) with PEG 200. The aggregation was reversible upon dilution of PEG if the initial PEG concentration was smaller than a certain value, e.g., 22% (w/w) for PEG 6000. Addition of PEG caused a decrease in membrane fluidity of the vesicles detected by fluorescence anisotropy of diphenylhexatriene and by electron spin resonance of a spin-labeled fatty acid. The anisotropy change of diphenylhexatriene fluidity change had an inflection point at approximately 5% (w/w) of PEG 6000, which might suggest that the aggregation would make the decrease of membrane fluidity smaller. Transfer of lipid molecules between phospholipid vesicles was enhanced by the PEG-induced aggregation. The enhancement occurred not only upon direct addition of PEG to the suspending medium, but also upon dialysis of the vesicle suspension against a high concentration of PEG. All these features are consistent with osmoelastic coupling in the phospholipid membranes and the subsequent osmophobic association of the vesicles. The imbalance of osmolarity between the region adjacent to the vesicle surface (exclusion layer) and the bulk aqueous phase, which results from the preferential exclusion of PEG from the exclusion layer in the case of direct addition of PEG, exerts an osmotic stress on the vesicles.(ABSTRACT TRUNCATED AT 250 WORDS)