1-Methylguanine and 7-methylguanine increase cell agglutinability

Summary 1-Methylguanine and 7-methylguanine, both metabolic products of tRNA degradation, are known to induce transformation of Chinese hamster fibroblasts in culture. The effects of these compounds on the cell membrane have been studied by the method of Concanavalin A-mediated hemadsorption. 1-Methylguanine or 7-methylguanine induced a 50% increase of Con A-mediated hemadsorption within 20 hours of exposure of the cells to the agent at a concentration of 10^-5 M. This alteration was reversed within 13 days when the cells were grown in the control medium. Prolonged treatment with 1-methylguanine or 7-methylguanine resulted in changes which were only slowly reversed during growth of the cells in the control medium. The effect of the methylated purines on the cell membrane could be completely inhibited by simultaneous addition of dibutyryl-cAMP at a concentration of 10^-5 M. The possible mechanism of cell membrane alteration by methylated purines and its relevance to transformation in vitro are discussed.     

A rapid cell membrane permeability test using flourescent dyes and flow cytometry

A reliable and rapid test to detect cytotoxic chemicals which affect cell membranes is described. Fluorescein diacetate freely penetrates intact cells where it is hydrolyzed to its fluorochrome, fluorescein, which is retained in the cell due to its polarity. On the other hand, ethidium bromide is known to be excluded from the intact cell, staining only nucleic acids of membrane-damaged cells. The combination of both fluorochromes results in counter-staining: intact cells fluoresce green (cytoplasm) and membrane-damaged cells fluoresce red (nucleus and RNA). Rat thymocytes freshly isolated without enzyme treatment were incubated simultaneously with test substance and dye solution fluorescein diacetate and ethidium bromide. A two-parameter analysis was performed on a flow cytometer with an on-line computer. Concentration-dependent effects of various detergents and solvents were quantified by measuring the amount of dye retention, i.e., the decrease or increase in fluorescein—fluorescence (peak shift), and the decrease in dye exclusion (increase in ethidium bromide-staining) relative to the untreated control. The assay can be used for rapid monitoring of chemical insults to cell membranes which precede the decrease of the viability measured by pure dye exclusion techniques.Abbreviations DMA dimethyl sulfate - DMSO dimethyl sulfoxide - EB ethidium bromide - F fluorescein - FDA fluorescein diacetate - FS₂₅ concentration of test substance resulting in a F-peak left-shift of 25% from control - PBS phosphate buffered saline - SCT forward light scatter - SDS sodium dodecyl sulfate     

Thymus-independent induction and antigen-dependent recovery of idiotype-specific suppression

BALB/c nude (nu/nu) mice and euthymic (nu/+) littermates were treated as neonates with anti-T15 antibody and challenged at various ages with either a thymus-independent, PC-Brucella abortus (PC-BA), or thymus-dependent, PC-keyhole limpet hemocyanin (PC-KLH), form of phosphorylcholine (PC). Nu/nu mice challenged with PC-KLH received KLH-primed splenic T cells prior to immunization. Neither neonatally anti-idiotype-treated nu/+ nor nu/nu mice responded with the production of T15-positive anti-PC antibodies after challenge with either form of PC antigen. It is concluded that neither induction nor maintenance of a state of T15-specific suppression requires thymus-matured T cells. Recovery of anti-PC responsiveness in suppressed nu/+ or nu/nu mice was similar and was found to be related to the form of antigen used to elicit the response. Immunization with PC-KLH revealed a long-lasting unresponsiveness (up to 16 weeks). In contrast, immunization with PC-BA elicited a full anti-PC response as early as at 6.5 weeks of age.     

Amino acid sequence data on glial fibrillary acidic protein (GFA); implications for the subdivision of intermediate filaments into epithelial and non-epithelial members.

Determination of 50% of the sequence of the astrocyte-specific intermediate filament (IF) protein documents the hypervariable regions as well as parts of the coiled-coil array of glial fibrillary acidic protein (GFA). The results show that the four non-epithelial IF proteins (myogenic desmin, mesenchymal vimentin, GFA and neurofilament 68 K protein) known to form homopolymers are much more closely related than the epithelial keratins, which seem to form heteropolymers only. Of the four non-epithelial proteins, desmin and vimentin are the most closely related, since GFA has a shorter non-alpha-helical array at the amino terminus. We discuss the possibility that the non-alpha-helical terminal arrays, because of their sequence and length variability, are responsible for differences of distinct IF with respect to physical-chemical properties such as the low ionic strength-induced depolymerization into protofilaments.     

Fine structural and enzyme histochemical observations on the dorsal tail tubercle of Mertensiella caucasica (Urodela,Amphibia)

Summary Dorsal tubercle and skin of Mertensiella caucasica have been investigated with the electron microscope and enzyme histochemical methods. The epidermis of the tubercle consists of 8–9 cell layers, that of normal dorsal skin of 5–6. The tubercle is filled with large mucous glands which are surrounded by an almost complete layer of smooth muscle cells (myoepithelial cells). Their glandular cells undergo cyclical changes and are characterized by specific secretory granules, which differ from those of the relatively small mucous glands of the normal dorsal skin.In the connective tissue of the tubercle a relatively rich supply of nerve fibres has been found, which in part contain synaptic and dense core vesicles or accumulations of mitochondria. In the normal dorsal skin nerve fibres occur less frequently.The following enzymes have been demonstrated in the mucous glands of the tubercle: SDH, acid phosphatase, unspecific esterases, E 600 resistant esterase.The tubercle seems to stimulate the female cloaca chemically and mechanically.     

Activity of phenol oxidases at the puparium formation stage in development of nineteen lozenge mutants of Drosophila melanogaster

Phenol oxidase activity of activated A₁ and A₂ (A₃) electrophoretic components from 19 lozenge mutant and three lozenge double mutant strains was compared to that of wild type flies. Melanin production by the activated A components with tyrosine as substrate was compared to activity in the same acrylamide gels with dopa as substrate. Melanin production decreased, first in the A₁ band and then in the A₂ (A₃) band, with increased morphological expression of the mutant genes. No melanin bands were obtained with either substrate in five of the more severely affected mutants. A possible correlation between phenol oxidase activity and quinone production necessary for normal development of eyes, female accessory sex organs, and claws is discussed.Supported by PHS grant AM-08331-05.     

A Model of the Peripheral Auditory System Responding to Low-Frequency Tones

A model of the peripheral auditory system responding to low-frequency tone stimulation is given. The model is of the type previously introduced by Weiss (1966). It includes three interconnected parts: a linear model of the ear's mechanical system, a model of the cochlear transducer, and a stochastic model of an auditory nerve fiber. The output of the model accurately mimics many characteristics of the output of some auditory nerve neurons responding to sinusoidal stimuli but is unable to successfully match all reported aspects of data obtained from other of these neurons. Characteristics of the model neurons are discussed.     

Interactive Effects of CO(2) and O(2) in Soil on Root and Top Growth of Barley and Peas

Barley and pea plants were grown under several regimens of different compositions of soil atmosphere, the O₂ concentration varying from 0 to 21% and the CO₂ concentration from 0 to 8%. In absence of CO₂, the effect of O₂ on root length in barley was characterized by equal root lengths within the range of 21 to 7% O₂ and a steep decline between 7 and 0%. In peas, while showing the same general response, the decline occurred between 14 and 7% O₂. Root numbers of the seminal roots of barley decreased already with reduction in O₂ concentration from 21 to 14%. Dry matter production was affected somewhat differently by O₂ and CO₂ concentration. Dry matter production in barley was reduced at 14% O₂ while root length decreased between 7 and 0%. In peas, dry matter production was favored by low CO₂ concentrations except where there was no oxygen. At 21% O₂, increasing CO₂ concentrations did not seem to affect root length up to concentrations of 2% CO₂. At 8% CO₂, root length was decreased. The inter-active effects of CO₂ and O₂ are characterized by a reduced susceptibility to CO₂ at O₂ values below 7%, and a very deleterious effect of 8% CO₂ at 7% O₂.