A NEW METHOD FOR ANALYZING ELECTRON MICROSCOPE AUTORADIOGRAPHS USING HYPOTHETICAL GRAIN DISTRIBUTIONS

A new method for the analysis of electron microscope autoradiographs is described which has two advantages over other methods. This method provides estimates for the activity in different regions of the section and takes into account the actual geometrical shape and position of different regions within the section. Use is made of the measured distribution of grains about a thin line source to construct a hypothetical distribution of autoradiographic grains which is then compared with the actual distribution of grains. Different activities are then ascribed to various regions until a satisfactory agreement with the autoradiographic grains is obtained using the χ² significance. In the next paper, an example of the use of this method is given for the distribution of grains in the nucleus of erythroid bone marrow cells labeled with radioactive iron, ⁵⁵Fe.     

C-terminal domain of apolipoprotein CII as both activator and competitive inhibitor of lipoprotein lipase.

In this study we have prepared peptides of the C-terminal domain of apolipoprotein CII (ApoCII) by a solid-peptide-synthesis technique and demonstrated that the C-terminal tetrapeptide, Lys-Gly-Glu-Glu, represents an inhibitor of lipoprotein lipase. The tetrapeptide not only inhibits the basal activity of lipoprotein lipase, but also blocks the activation effect of native ApoCII. The lengthening of this tetrapeptide resulted in a corresponding increase in affinity for lipoprotein lipase. This suggested that amino acids other than those of the C-terminal tetrapeptide also contribute to the binding affinity of ApoCII for lipoprotein lipase. On the basis of an essential requirement of the ApoCII terminal domain for binding to lipoprotein lipase, we suggest that the initial interaction of ApoCII, mediated via the C-terminal tetrapeptide, promotes the proper alignment of ApoCII with lipoprotein lipase, followed by the weak interaction of the ApoCII activator domain with the lipoprotein lipase activator site, enhancing the lipolysis process.     

Mitochondrial gene divergence of Colombian Drosophila pseudoobscura

Isolated populations of drosophila pseudoobscura, separated from North American populations by about 2,400 km, were found in Colombia in 1960. We compared for sequences of the small ribosomal RNA (srRNA) gene on the mitochondria between North American and Colombian D. pseudoobscura in order to clarify the age of the Colombian isolates. The North American populations were not genetically different from each other but were genetically different from the Colombian populations. The Mexican strains represent the area from which the Colombian founders might have come. The estimated net nucleotide divergence between Mexican and Colombian D. pseudoobscura indicates that the Colombian population is not an ancient lineage. Phylogenies using both distance and parsimony methodologies reinforced this conclusion. The Colombian samples group together with both methods but, according to the bootstrap analysis, not significantly. It appears that the populations have not been separated long enough for their DNA sequences to show much divergence.      

Species status of Neisseria gonorrhoeae: evolutionary and epidemiological inferences from multilocus sequence typing

Background  

Various typing methods have been developed for Neisseria gonorrhoeae, but none provide the combination of discrimination, reproducibility, portability, and genetic inference that allows the analysis of all aspects of the epidemiology of this pathogen from a single data set. Multilocus sequence typing (MLST) has been used successfully to characterize the related organisms Neisseria meningitidis and Neisseria lactamica. Here, the same seven locus Neisseria scheme was used to characterize a diverse collection of N. gonorrhoeae isolates to investigate whether this method would allow differentiation among isolates, and to distinguish these three species.     

Complement activation by phospholipids: the interplay of factor H and C1q

Complement proteins in blood recognize charged particles. The anionic phospholipid (aPL) cardiolipin binds both complement proteins C1q and factor H. C1q is an activator of the complement classical pathway, while factor H is an inhibitor of the alternative pathway. To examine opposing effects of C1q and factor H on complement activation by aPL, we surveyed C1q and factor H binding, and complement activation by aPL, either coated on microtitre plates or in liposomes. Both C1q and factor H bound to all aPL tested, and competed directly with each other for binding. All the aPL activated the complement classical pathway, but negligibly the alternative pathway, consistent with accepted roles of C1q and factor H. However, in this system, factor H, by competing directly with C1q for binding to aPL, acts as a direct regulator of the complement classical pathway. This regulatory mechanism is distinct from its action on the alternative pathway. Regulation of classical pathway activation by factor H was confirmed by measuring C4 activation by aPL in human sera in which the C1q:factor H molar ratio was adjusted over a wide range. Thus factor H, which is regarded as a down-regulator only of the alternative pathway, has a distinct role in downregulating activation of the classical complement pathway by aPL. A factor H homologue, β2-glycoprotein-1, also strongly inhibits C1q binding to cardiolipin. Recombinant globular domains of C1q A, B and C chains bound aPL similarly to native C1q, confirming that C1q binds aPL via its globular heads.     

Quirks of dye nomenclature. 8. Methylene blue,azure and violet

Methylene blue was synthesized in 1877 and soon found application in medicine, staining for microscopy and as an industrial dye and pigment. An enormous literature has accumulated since its introduction. Early on, it was known that methylene blue could be degraded easily by demethylation; consequently, the purity of commercial samples often was low. Therefore, demethylation products, such as azures and methylene violet, also are considered here. The names and identity of the components, their varying modes of manufacture, analytical methods and their contribution to biological staining are discussed.     

A tritrophic signal that attracts parasitoids to host-damaged plants withstands disruption by non-host herbivores

Background  

Volatiles emitted by herbivore-infested plants are highly attractive to parasitoids and therefore have been proposed to be part of an indirect plant defense strategy. However, this proposed function of the plant-provided signals remains controversial, and it is unclear how specific and reliable the signals are under natural conditions with simultaneous feeding by multiple herbivores. Phloem feeders in particular are assumed to interfere with plant defense responses. Therefore, we investigated how attack by the piercing-sucking cicadellid Euscelidius variegatus influences signaling by maize plants in response to the chewing herbivore Spodoptera littoralis.