Cellular mechanisms of pH tolerance in Rhizobium loti

Seven strains of Rhizobium loti were tested for acid tolerance in yeast-extract mannitol (YEM) broth at pH values ranging from 4.0 to 8.0. The strains that grew at pH 4.0 showed the slowest generation time when grown at pH above 7.0 and also produced the most acid. The acid tolerance was related to the composition and structure of the membrane. pH influenced protein expression in acid-tolerant strains growing at pH 4.0 or 7.0. Acid tolerant strains showed one membrane protein of 49.5 kDa and three soluble proteins of 66.0, 58.0 and 44.0kDa; their expression increased when the cells grew at pH 4.0. It is suggested that acid tolerance in Rhizobium loti involves constitutive mechanisms, such as permeability of the outer membrane together with adaptive responses, including the state of bacterial growth and concomitant changes in protein expression.     

On the Crucial Stages in the Origin of Animate Matter

Theories of the origin of life have proposed hypotheses to link inanimate to animate matter. The theory proposed here derived the crucial stages in the origin of animate matter directly from the basic properties of inanimate matter. It asked what were the general characteristics of the link, rather than what might have been its chemical details. Life and its origin are shown to be one continuous physicochemical process of replication, random variation, and natural selection. Since life exists here and now, animate properties must have been initiated in the past somewhere. According to the theory, life originated from an as yet unknown elementary autocatalyst which occurred spontaneously, then replicated autocatalytically. As it multiplied to macroscopic abundance, its replicas gradually exhausted their reactants. Random chemical drift initiated diversity among autocatalysts. Diversity led to competition. Competition and depletion of reactants slowed down the rates of net replication of the autocatalysts. Some reached negative rates and became extinct, while those which stayed positive ``survived.' Thus chemical natural selection appeared, the first step in the transition from inanimate to animate matter. It initiated the first animate property, fitness, i.e., the capacity to adapt to the environment and to survive. As the environment was depleted of reactants, it was enriched with sequels—namely, with decomposition products and all other products which accompany autocatalysis. The changing environment exerted a selective pressure on autocatalysts to replace dwindling reactants by accumulating sequels. Sequels that were incorporated into the autocatalytic process became internal components of complex autocatalytic systems. Primitive forms of metabolism and organization were thus initiated. They evolved further by the same mechanism to ever higher levels of complexity, such as homochirality (handedness) and membranal enclosure. Subsequent evolution by the same mechanism generated cellular metabolism, cell division, information carriers, and a genetic code. Theories of self-organization without natural selection are refuted. Received: 29 March 1996 / Accepted: 30 May 1996     

Nanomolar Amyloid β Protein-Induced Inhibition of Cellular Redox Activity in Cultured Astrocytes

Abstract: It has been previously reported that Alzheimer's amyloid β protein (Aβ) induces reactive astrocytosis in culture. In the present study, we found that Aβ potently inhibits cellular redox activity of cultured astrocytes, as determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide reduction assay. The following comparative studies revealed several differences between these two actions of Aβ on astrocytes. First, Aβ-induced reactive morphological change was suppressed by the presence of serum or thrombin, and Aβ inhibition of cellular redox activity was observed in either the presence or the absence of serum. Second, micromolar concentrations (10 µ M or more) were required for Aβ to induce reactive astrocytosis, whereas nanomolar concentrations (0.1–100 n M ) were sufficient to inhibit cellular redox activity. Third, the effect of micromolar Aβ was virtually irreversible, but nanomolar Aβ-induced inhibition of cellular redox activity was reversed by washing out Aβ. Furthermore, as it has been reported that Aβ neurotoxicity is mediated by reactive oxygen species, we also examined if similar mechanisms are involved in astrocytic response to Aβ. However, neither Aβ-induced morphological change nor inhibition of redox activity was blocked by antioxidants, suggesting that these effects are not caused by oxidative stress.     

Sexual dimorphism of motorneurons: Timbal muscle innervation in male periodical cicadas and homologous structures in females

Summary Treatment of cultured goldfish xanthophores by hormone (ACTH) or c-AMP induces not only pigment dispersion, but subsequent outgrowth of processes, and pigment translocation into these processes. These latter effects are shown to proceed as follows: First the edge of the cytoplasmic lamellae takes on a scalloped contour with numerous protrusions. These presumably serve as nucleation centers where short microfilament bundles are assembled, Later, the microfilament bundles elongate (grow), often resulting in an extension of the protrusions to become filopodia while the proximal end of the microfilaments penetrates into the thicker portion of the cellular process which now houses the pigment, i.e., the carotenoid droplets. Carotenoid droplets appear to migrate along the microfilament bundles, or cytoplasmic channels associated with them, into the filopodia. Finally, some of the filopodia become broader, thicker and laden with carotenoid droplets and are then recognized by light microscopy as pigmented cellular processes. The microfilaments have been shown to be actin filaments by their thickness, the size of their subunits, and decoration by heavy meromyosin. Evidence is presented which suggests that the growth of these actin filaments may come about by recruitment from short F-actin strands found in random orientation in adjacent areas.     

Fine structure of the ‘Wulst’ region of the domestic fowl in organotypic cultures

Summary Parts of the Wulst region of the chick embryo brain were maintained for 39 days in vitro. Processes of adjacent glial cell form zonulae occludentes and desmosomal junctions in the uppermost stratum of the cultures. Subjacent to this layer, in the neuropil, axodendritic synapses are abundant. 10–20 m below the surface the perikarya of glial cells and neurons are found. The latter form small clusters, plasma membranes of contiguous cells being directly apposed to each other. Axosomatic synapses terminate on the perikarya. Occasionally one terminal synapses on two nerve cells simultaneously. Two types of cilia arise from basal bodies in the cytoplasm of nerve cells. Type I is a slender protrusion of about 0.5 m in diameter, extending into the neuropil. On transverse sections it displays a 9 + 0 pattern of organization of paired micro tubules proximally, and an 8 + 1 configuration more distally. The length of the cilium is approximately 7 m. Type II cilia also originate in the neuronal cytoplasm. The structure of the proximal portion is identical with that of type I cilia. Toward the tip, however, the type II cilium is characterized by a bulbous enlargement which is filled with loosely folded membranes. The fine structural details of this cilium correlate closely to the outer segments of retinal photoreceptor cells during differentiation. The possible role of a light receptor in the Wulst region of birds, controlling biological rhythms, is discussed. Acknowledgements. The authors wish to thank Mrs. H. Frenk for her expert assistance in tissue culture and electron microscopic techniques     

Studies on non-H-2-linked lymphocyte-activating determinants. IV. Ontogeny of the Mls product on murine B cells.

The minor lymphocyte stimulating (Mls) locus codes for lymphocyte activating determinants (LADs) on murine B lymphocytes, but not T lymphocytes. This observation was strengthened by a series of techniques which allow deletion and addition of T and B cells. These included the use of cytotoxic antisera such as anti-Thy 1.2, anti-MTLA, anti-MBLA, and complement, and the use of a goat anti-μ antisera, and finally the use of a fluorescence activated cell sorter (FACS).The studies in this report document the organ distribution and the ontogenetic appearance of the surface LADs on the surface of B lymphocytes from DBA/2N (H-2^d, Mls^a) and CBA/J (H-2^k, Mls^d) mice. Adult-like ability to stimulate H-2 identical BALB/c (H-2^d, Mls^b) and C3H/He (H-2^k, Mls^c) responder cells appeared at about 4–5 weeks of age. Inability of neonatal cells to induce an Mls-defined MLC was found not to be due to a low frequency of B lymphocytes or to the presence of suppressor cells, but due to the absence of the Mls-coded LADs on their surface. These data support the concept that the Mls-coded LADs are present on adult B lymphocytes and are specific markers of B-cell differentiation, which is preceded by membrane IgM and the δ homologue of human IgD, Ia, and the receptor for the third component of complement.     

Analysis of cellular interactions in density-dependent inhibition of 3T3 Cell proliferation

Subpopulations of different proliferative status are determined during cell-density dependent proliferation of 3T3 cells. From these data the probability of conversion of proliferative to quiescent cells is derived and found to correlate well with published data on binding of growth-inhibiting factors secreted from growth-inhibited cells.Based on material presented at the Symposium Intercellular Communication Stuttgart, September 16–17, 1982     

Rapid Cellular Regulation of D-Glucose Transport in Cultured Neural Cells

Previous studies have revealed two different kinds of regulation of glucose utilization in cell lines derived from the nervous system (Keller et al., 1981). We found glucose metabolism of C-6 glioma cells to be limited and regulated by membrane transport. In contrast, glucose utilization of C-1300 neuroblastoma (N2A) cells was limited by the known regulatory enzymes of the Embden-Meyerhof pathway. Under the given experimental conditions the "membrane-limited" C-6 glioma cells were characterized by periodically changing glucose transport rates and very low intracellular glucose concentrations, which remained constant in spite of widely differing transport rates. These findings suggest the close functional coupling between transport and phosphorylation required for the regulation of glucose transport by cellular metabolic needs.     

Studies of vegetative compatibility-incompatibility in higher plants

Summary In order to elucidate the events that lead to cellular autolysis, and thus better understand the mechanism of cellular incompatibility betweenSedum telephoides andSolanum pennellii stems, we have followed the appearance and fate of the hydrolytic enzyme acid phosphatase in both the compatibleSedum autograft and the incompatibleSedum/Solanum heterograft. Acid phosphatase was localized by a modified Gomori-type reaction. Following an initial association with the endoplasmic reticulum and dictyosomes by 6–10 hours after grafting, acid phosphatase activity in the compatibleSedum autograft was associated primarily with the plasmalemma, tonoplast, and vacuole. This strict compartmentation in membranes or organelles and absence of enzyme from the cytosol was maintained throughout the development of the compatible autograft inSedum. Although acid phosphatase activity in the incompatible heterograft betweenSedum andSolanum was initially similar to the compatible autograft inSedum, a marked difference in enzyme localization occurred in the two graft partners over time.Solanum cells accumulated increased amounts of acid phosphatase, but the enzyme remained sequestered in the plasmalemma, tonoplast, and vacuole. In comparableSedum cells, however, there was a dramatic increase in acid phosphatase activity in the cytosol, often without any prior compartmentation within the vacuole. This high activity of acid phosphatase in theSedum cytosol was correlated with cellular autolysis, death, and eventual cell collapse to form the characteristic necrotic layer that insulates the stock from the scion. These results suggest that the lethal cellular senescence associated withSedum cells of the incompatible heterograft is correlated with a cytoplasmic release of acid phosphatase. A similar release of the enzyme does not occur in theSolanum stock or in the compatibleSedum autograft. Thus, while acid phosphatase synthesis and/or activation is induced in both the compatible and incompatible grafts, incompatibility betweenSedum andSolanum involves a failure ofSedum cells to isolate hydrolytic enzymes from the cytosol, which subsequently leads to cellular necrosis.Supported in part by grants from the Academic Senate of UCLA, Sigma Xi, the American Philosophical Society, and the URC of Baylor University.