Extramitochondrial Porin: Facts and Hypotheses

Mitochondrial porin, or VDAC, is a pore-forming protein abundant in the outer mitochondrialmembrane. Several publications have reported extramitochondrial localizations as well, butthe evidence was considered insufficient by many, and the presence of porin in nonmitochondrialcellular compartments has remained in doubt for a long time. We have now obtained newdata indicating that the plasma membrane of hematopoietic cells contains porin, probablylocated mostly in caveolae or caveolae-like domains. Porin was purified from the plasmamembrane of intact cells by a procedure utilizing the membrane-impermeable labeling reagentNH-SS-biotin and streptavidin affinity chromatography, and shown to have the same propertiesas mitochondrial porin. A channel with properties similar to that of isolated VDAC wasobserved by patch-clamping intact cells. This review discusses the evidence supportingextramitochondrial localization, the putative identification of the plasma membrane porin with themaxi chloride channel, the hypothetical mechanisms of sorting porin to various cellularmembrane structures, and its possible functions.     

Human Oncogenic Viruses: Old Facts and New Hypotheses

Molecular Biology - Numerous studies on the nature of neoplastic growth have demonstrated that oncogenic viruses may be one of the factors causing cancer. According to various estimates,...     

Unconditional Tests of Hypotheses Concerning Relative Risk

The problem of estimation of, and statistical tests for, the relative risk (=α) from samples in which there is matching on covariates have been discussed by various authors (Cox, 1970; MANTEL and HAENSZEL, 1959) using the approach of conditional variates. This paper discusses log LR (likelihood ratio) tests of hypotheses concerning α, as based on one or more sets of matched samples. Approximate X² tests are also developed for the hypotheses concerning α. An example is presented which illustrates the proposed tests of significance (Table 1).     

Hypotheses Concerning Algal Adaptation to Periodic Environmental Factors

A new lower-dimension ecological–evolutionary model of algae was proposed to describe the simultaneous dynamics of variables (population biomass) and parameters (limits of the temperature tolerance interval [a – d, a + d]). In a given periodic temperature regime, the parameters tend to certain final values, which are called evolutionarily stable (ES) values. Calculations showed that ES parameters form a rainbow structure on the plane (a, d); the farthest points of the rainbow correspond to psychrophilic (diatom) and thermophilic (blue–green) algae. Algal adaptation to two periodic environmental factors, temperature and salinity, was carried out within preset temperature and salinity tolerance ranges [a – d, a + d] and [b – c, b + c]. The domain of evolutionarily stable parameters in the plane (a, b) was found to depend on the degree of synchronism of environmental factors. The parameters lay on a linear segment in some cases, while their location on a nonlinear oval was unexpectedly possible in some other cases.

     

Immunofluorescent Localization of Vimentin, Prekeratin and Actin during Odontoblast and Ameloblast Differentiation

The localization of constitutive proteins of different types of cytoskeletal components (prekeratin, vimentin, and actin) was examined in embryonic mouse molars using specific antibodies and immunofluorescence microscopy on frozen sections. Prekeratin and actin were found in the enamel organ. Preameloblasts demonstrated uniform staining, whereas ameloblasts demonstrated an apical accumulation of both prekeratin and actin. Vimentin and actin were observed in the dental papilla. A redistribution of vimentin accompanied the polarization of odontoblasts. A possible transmembranous control of cytoskeletal activities by the extracellular matrix is discussed.     

Basement Membrane Formation in Transfilter Tooth Culture and Its Relation to Odontoblast Differentiation

The mesenchymal cells of the developing tooth differentiate into odontoblasts as a result of an epithelio-mesenchymal interaction. Odontoblast differentiation was studied in vitro by cultivating dental mesenchyme and epithelium with interposed filters. Separation of the two components by enzyme treatment resulted in removal of the basement membrane. When the epithelium was grown alone, or transfilter from killed lens capsule, the basement membrane was not restored. Transfilter cultivation with dental mesenchyme resulted in basement membrane formation, but only if the filter pores allowed penetration of cytoplasmic processes. Hence, a close association between the epithelial and the mesenchymal cells seems to be a prerequisite for the restoration of the basement membrane. Differentiation of odontoblasts took place only in explants in which a basement membrane was formed. Differentiation did not occur when contact of the mesenchymal cells with the basement membrane was prevented by small pore size filters. Further experiments demonstrating an intact basement membrane suggested that membrane contacts between the epithelial and the mesenchymal cells are not needed for odontoblast differentiation. Hence, we suggest that differentiation of odontoblasts is triggered via contact of the mesenchymal cells with the basement membrane.     

Concerning the Differentiation of Bacillus subtilis and Related Species

The results of an investigation involving 45 strains of Bacillus subtilis , 31 strains of B. licheniformis and 29 strains of B. pumilus are reported. The hitherto recognized varieties B. subtilis var. niger and B. subtilis var. aterrimus appear to be only variants of B. subtilis. For a rapid differentiation of B. licheniformis from B. subtilis two tests are recommended—reduction of nitrites and splitting of arginine. The present tests, reduction of nitrate and hydrolysis of starch, are the most suitable for distinguishing between B. pumilus and B. subtilis.     

Odontoblast commitment and differentiation.

Histological and cytological organization confer specificity to the odontoblasts. These postmitotic, neural crest derived, polarized cells are aligned in a single layer at the periphery of the dental pulp and secrete the organic components of predentin-dentin. The developmental history of these cells demands a cascade of epigenetic signalling events comprising the acquisition of odontogenic potential by neural crest cells, their patterning in the developing jaws, the initiation of odontogenesis through interaction with the oral epithelium, commitment, and tooth-specific spatial distribution of competent preodontoblasts able to overtly differentiate. Recent experimental investigations are critically summarized, many open questions are stressed, and current hypotheses concerning the control of terminal odontoblast differentiation are outlined.     

Disruption of Nfic Causes Dissociation of Odontoblasts by Interfering With the Formation of Intercellular Junctions and Aberrant Odontoblast Differentiation

We reported previously that Nfic-deficient mice exhibit short and abnormal molar roots and severely deformed incisors. The objective of this study is to address the mechanisms responsible for these changes using morphological, IHC, and RT-PCR analysis. Nfic-deficient mice exhibited aberrant odontoblasts and abnormal dentin formation in molar roots and the labial crown analog of incisors. The most striking changes observed in these aberrant odontoblasts were the loss of intercellular junctions and the decreased expression of ZO-1 and occludin. As a result, they became dissociated, had a round shape, and lost their cellular polarity and arrangement as a sheet of cells. Furthermore, the dissociated odontoblasts became trapped in dentin-like mineralized tissue, resembling osteodentin in the overall morphology. These findings suggest that loss of the Nfic gene interferes with the formation of intercellular junctions that causes aberrant odontoblast differentiation and abnormal dentin formation. Collectively, these changes in odontoblasts contributed to development of molars with short and abnormal roots in Nfic-deficient mice. (J Histochem Cytochem 57:469–476, 2009)     

The Expression of GM-CSF and Osteopontin in Immunocompetent Cells Precedes the Odontoblast Differentiation Following Allogenic Tooth Transplantation in Mice

Dental pulp elaborates both bone and dentin under pathological conditions such as tooth replantation/transplantation. This study aims to clarify the expression of granulocyte macrophage colony-stimulating factor (GM-CSF) and osteopontin (OPN) in the process of reparative dentin formation by allogenic tooth transplantation using in situ hybridization for OPN and immunohistochemistry for GM-CSF and OPN at both levels of light and electron microscopes. Following the extraction of the mouse molar, the roots and pulp floor were resected and immediately allografted into the sublingual region. On days 1 to 3, immunocompetent cells such as macrophages and dendritic cells expressed both GM-CSF and OPN, and some of them were arranged along the pulp-dentin border and extended their cellular processes into the dentinal tubules. On days 5 to 7, tubular dentin formation commenced next to the preexisting dentin at the pulp horn where nestin-positive odontoblast-like cells were arranged. Until day 14, bone-like tissue formation occurred in the pulp chamber, where OPN-positive osteoblasts surrounded the bone matrix. These results suggest that the secretion of GM-CSF and OPN by immunocompetent cells such as macrophages and dendritic cells plays a role in the maturation of dendritic cells and the differentiation of odontoblasts, respectively, in the regenerated pulp tissue following tooth transplantation.     

Jasmonates,New Regulators of Plant Growth and Development: Many Facts and Few Hypotheses on their Actions

Jasmonates, ubiquitous cyclopentanone compounds, are reviewed as new regulators for plant growth and development. They may complement the group of well-established “classic” phytohormones. Jasmonates influence a multiplicity of plant physiological processes by inhibition, promotion or induction. In many aspects they are similar to abscisic acid, especially in responses to stress. The review contains information on the chemical structures and metabolism of jasmonates, contributes to their biological role and describes possible mode(s) of action at the level of molecular biology and gene expression. In particular, emphasis is placed on the gene expression and accumulation of jasmonate-induced abundant polypeptides as a stress response of the plant cells. A hypothesis is attempted in which endogenous jasmonates represent an integral part of the signal transduction chain between stress signal(s) and stress response(s).     

Rheostat Re-Wired: Alternative Hypotheses for the Control of Thioredoxin Reduction Potentials

Thioredoxins are small soluble proteins that contain a redox-active disulfide (CXXC). These disulfides are tuned to oxidizing or reducing potentials depending on the function of the thioredoxin within the cell. The mechanism by which the potential is tuned has been controversial, with two main hypotheses: first, that redox potential (E_m) is specifically governed by a molecular ‘rheostat’—the XX amino acids, which influence the Cys pK_a values, and thereby, E_m; and second, the overall thermodynamics of protein folding stability regulates the potential. Here, we use protein film voltammetry (PFV) to measure the pH dependence of the redox potentials of a series of wild-type and mutant archaeal Trxs, PFV and glutathionine-equilibrium to corroborate the measured potentials, the fluorescence probe BADAN to measure pK_a values, guanidinium-based denaturation to measure protein unfolding, and X-ray crystallography to provide a structural basis for our functional analyses. We find that when these archaeal thioredoxins are probed directly using PFV, both the high and low potential thioredoxins display consistent 2H⁺:2e^- coupling over a physiological pH range, in conflict with the conventional ‘rheostat’ model. Instead, folding measurements reveals an excellent correlation to reduction potentials, supporting the second hypothesis and revealing the molecular mechanism of reduction potential control in the ubiquitous Trx family.     

Models and Hypotheses

Complex linear appearing structures and networks (e.g. blood vessels, leaf veins, nerves) are formed reproducibly during the development of nearly every organism, but the molecular mechanism leading to such patterns is still unknown. A model is proposed in which a few simple coupled biochemical reactions are able to generate such structures. Among undifferentiated cells, a local peak of differentiation-inducing substance (activator) is formed by autocatalysis and lateral inhibition. The activator peak triggers the differentiation of the cell at that location. Due to changes in metabolism, the differentiated cell repels the activator peak and drives it to a neighbouring cell which then also differentiates. The repulsion between the activator peak and the already differentiated cells forces the activator peak to move ahead of the tip of the extending filament. Long filaments of differentiated cells may be formed, which can split, branch laterally, reconnect with each other and grow towards specific target cells. Partial differential equations describing the mutual interaction of the substances involved were presented and solved with a computer. The resulting patterns show self-regulating properties and other features found in the leaf vascular system, the pattern of tracheae in insect epidermis, and other biological networks.     

Hypotheses and facts

The book, The river, is based on assumptions and not facts. Oral polio vaccine was produced entirely in rhesus monkey kidney cell cultures. Allegations that it was produced in chimpanzee kidneys at the Wistar Institute in Philadelphia or, alternatively, that the vaccine was made in the then Belgian Congo in chimpanzee kidney has no basis in fact. As the only witness to the historical events leading to the development of oral polio vaccine, I have demonstrated in this paper the truthful facts excluding any link between oral polio vaccine and human immunodeficiency virus.