Filamentous bacteriophage contract into hollow spherical particles upon exposure to a chloroform-water interface

The bacteriophage M13 is a 1 μm long filament consisting of a circular single-stranded DNA loop firmly held within a tubular protein capsid. We report here that exposure to a chloroform-water interface initiates a 20 fold contraction of each filament into a hollow protein sphere. In these 0.04 μm diameter particles, termed M13 “spheroids,” two thirds of the DNA is apparently extruded through a hole in the wall of the spheroid; the portion of DNA remaining inside the shell centers about the origins of M13 DNA replication. These results suggest that the filament, upon exposure to a membrane environment, undergoes an ordered change whereby the DNA is released into the cell and the coat protein is changed to a form more easily solubilized by the membrane lipids.     

Anti-idiotypic monoclonal antibodies to GM1 identify ganglioside binding proteins

Ganglioside stimulated neurite outgrowth may be due to gangliosidebinding to membrane proteins or to intercalation into the membrane.To test that ganglioside binding proteins could be found onneuronal surfaces, antiidiotypic ganglioside monoclonal antibodies(AIG mAbs) were generated to mimic the biological propertiesof the GM1 ganglioside. The AIG mAbs were identified by theirability to bind to a known GM1 binding protein, the ß-subunit of cholera toxin. For the two AIG mAbs studied, AIG5 andAIG20, binding to ß-CT was blocked most strongly byGM1. This data also suggests that AIG5 and AIG20 mimic differentbut overlapping epitopes of the ganglioside GM1. Western blottingand immunoprecipitation of mammalian tissues reveals four potentialganglioside binding proteins of molecular weight 93, 66, 57,and 45 kDa. Immunocytochemistry demonstrates neuronal surfacelabel with the AIG mAbs, which suggests that gangliosides, enrichedon the neuronal surface membrane, are co-localized with putativeganglioside binding proteins. In bioassays, the AIG mAbs promoteneuronal sprouting. This shows that these antibodies can beused to study the biological effects of ganglioside bindingto neuronal surface proteins, and the role of gangliosides inthe activation of neurite outgrowth. agonist antibody anti-idiotypic antibody gangliosides ganglioside binding proteins     

Transforming growth factor-β1 in reproduction

Expression patterns of TGF-βs during embryogenesis and in adult reproductive organs, as well as the activities of these molecules in in vitro assays of biological processes relating to reproduction and development, have suggested that TGF-βs may play a role in both reproductive function and embryonic development. To investigate the function of TGF-β1 in vivo, the murine TGF-β1 gene was disrupted by gene targeting, and animals that lacked TGF-β1 activity were generated. Homozygous mutant animals were obtained which exhibited a multifocal inflammatory disease. However, the observed numbers of homozygous mutant offspring were less than expected, suggesting the occurrence of some type of prenatal lethality. This paper reviews the proposed role of the TGF-βs in reproductive and developmental processes and discusses observations obtained from the TGF-β1 gene-targeting experiments as they relate to these processes. © 1994 Wiley-Liss, Inc.     

The Influence of Two Naturally Occurring Factors, from the Leaves of Ricinus Communis, on the Fluorescence Induction of Higher Plant Chloroplasts and Intact Algae

Changes in fluorescence induction, brought about by incubation of chloroplasts (Zea mays) in an aqueous extract of Ricinus leaf, have been divided, on the basis of speed of manifestation, into two categories: “fast” changes and “slow” changes (i.e. those observed after 5 min and 1½ hr of incubation, respectively). The former, which include a large increase in the magnitude of the fast component of variable fluorescence and a retardation of decay from maximum to minimum levels of fluorescence, have been ascribed to inhibition of electron transport at a site beyond that of 3-(p-chlorophenyl)-1,1-dimethylurea (CMU)—i.e., towards system I; these changes result from the action of a fraction of the extract consisting of molecules of small size. The latter changes, which include a marked attenuation of the variable part of fluorescence induction, have been associated with system II and may arise from inhibition of electron flow between water and Q or from decrease in number of functional reaction centers; these changes result from the activity of a proteinaceous fraction of the extract, that simultaneously converts the low temperature steady-state emission spectrum of the chloroplasts into a one-banded one, with maximum at 698 nm.     

Evolutionary History of the Grey-Faced Sengi,Rhynchocyon udzungwensis,from Tanzania: A Molecular and Species Distribution Modelling Approach

Rhynchocyon udzungwensis is a recently described and poorly understood sengi (giant elephant-shrew) endemic to two small montane forests in Southern Tanzania, and surrounded in lower forests by R. cirnei reichardi. In this study, we investigate the molecular genetic relationship between R. udzungwensis and R. c. reichardi, and the possible role that shifting species distributions in response to climate fluctuations may have played in shaping their evolutionary history. Rhynchocyon udzungwensis and R. c. reichardi individuals were sampled from five localities for genetic analyses. Three mitochondrial and two nuclear loci were used to construct species trees for delimitation and to determine whether introgression was detectable either from ancient or ongoing hybridization. All species-tree results show R. udzungwensis and R. c. reichardi as distinct lineages, though mtDNA shows evidence of introgression in some populations. Nuclear loci of each species were monophyletic, implying introgression is exclusively historical. Because we found evidence of introgression, we used distribution data and species distribution modelling for present, glacial, and interglacial climate cycles to predict how shifting species distributions may have facilitated hybridization in some populations. Though interpretations are affected by the limited range of these species, a likely scenario is that the mtDNA introgression found in eastern mid-elevation populations was facilitated by low numbers of R. udzungwensis that expanded into lowland heavily occupied R. c. reichardi areas during interglacial climate cycles. These results imply that relationships within the genus Rhynchocyon may be confounded by porous species boundaries and introgression, even if species are not currently sympatric.     

Power analysis of statistical methods for comparing treatment differences from limiting dilution assays

Summary Six different statistical methods for comparing limiting dilution assays were evaluated, using both real data and a power analysis of simulated data. Simulated data consisted of a series of 12 dilutions for two treatment groups with 24 cultures per dilution and 1,000 independent replications of each experiment. Data within each replication were generated by Monte Carlo simulation, based on a probability model of the experiment. Analyses of the simulated data revealed that the type I error rates for the six methods differed substantially, with only likelihood ratio and Taswell's weighted mean methods approximating the nominal 5% significance level. Of the six methods, likelihood ratio and Taswell's minimum Chi-square exhibited the best power (least probability of type II errors). Taswell's weighted mean test yielded acceptable type I and type II error rates, whereas the regression method was judged unacceptable for scientific work.