Showing papers by "Max Planck Society published in 1972"

A theory of biological pattern formation.

Abstract: One of the elementary processes in morphogenesis is the formation of a spatial pattern of tissue structures, starting from almost homogeneous tissue. It will be shown that relatively simple molecular mechanisms based on auto- and cross catalysis can account for a primary pattern of morphogens to determine pattern formation of the tissue. The theory is based on short range activation, long range inhibition, and a distinction between activator and inhibitor concentrations on one hand, and the densities of their sources on the other. While source density is expected to change slowly, e.g. as an effect of cell differentiation, the concentration of activators and inhibitors can change rapidly to establish the primary pattern; this results from auto- and cross catalytic effects on the sources, spreading by diffusion or other mechanisms, and degradation. Employing an approximative equation, a criterium is derived for models, which lead to a striking pattern, starting from an even distribution of morphogens, and assuming a shallow source gradient. The polarity of the pattern depends on the direction of the source gradient, but can be rather independent of other features of source distribution. Models are proposed which explain size regulation (constant proportion of the parts of the pattern irrespective of total size). Depending on the choice of constants, aperiodic patterns, implying a one-to-one correlation between morphogen concentration and position in the tissue, or nearly periodic patterns can be obtained. The theory can be applied not only to multicellular tissues, but also to intracellular differentiation, e.g. of polar cells. The theory permits various molecular interpretations. One of the simplest models involves bimolecular activation and monomolecular inhibition. Source gradients may be substituted by, or added to, sink gradients, e.g. of degrading enzymes. Inhibitors can be substituted by substances required for, and depleted by activation. Sources may be either synthesizing systems or particulate structures releasing activators and inhibitors. Calculations by computer are presented to exemplify the main features of the theory proposed. The theory is applied to quantitative data on hydra — a suitable one-dimensional model for pattern formation — and is shown to account for activation and inhibition of secondary head formation.

The wall region in turbulent shear flow

Abstract: Hot-film measurements in a fully developed channel flow have been made in an attempt to gain more insight into the process of Reynolds stress production. The background for this effort is the observation of a certain sequence of events (deceleration, ejection and sweep) in the wall region of turbulent flows by Corino (1965) and Corino & Brodkey (1969). The instantaneous product signal uv was classified according to the sign of its components u and v, and these classified portions were then averaged to obtain their contributions to the Reynolds stress . The signal was classified into four categories; the two main ones were that with u negative and v positive, which can be associated with the ejection-type motion of Corino & Brodkey (1969), and that with u positive and v negative, associated with the sweep-type motion. It was found that over the wall region investigated, 3·5 [les ] y [les ] 100, these two types of motion give rise to a stress considerably greater than the total Reynolds stress. Two other types of motion, (i) u negative, v negative, corresponding to low-speed fluid deflected towards the wall, and (ii) u positive, v positive, corresponding to high-speed fluid reflected outwards from the wall, were found to account for the ‘excess’ stress produced by the first two categories, which give contributions of opposite sign.The autocorrelations of the classified portions of uv were obtained to determine the relative time scales of these four types of motion. The positive stress producing motions (u 0 and u > 0, v 0, v > 0). It was further surmised that turbulent energy dissipation is associated with the Reynolds stress producing motions, since these result in localized shear regions in which the dissipation is several orders of magnitude greater than the average dissipation at the wall.

Route of passive ion permeation in epithelia.

Abstract: “Tight junctions” between cells in some epithelia actually provide the main route of passive ion permeation. The degree of junctional tightness may underlie important functional differences between different epithelia.

Stationary solitary, snoidal and sinusoidal ion acoustic waves

Abstract: Stix's treatment of zero-damped electrostatic waves in a Maxwellian plasma is extended to the nonlinear regime. Stationary Bernstein-Greene-Krusk almodes which propagate with ion acoustic speed are constructed. This subclass consists of solitary, snoidal (=periodical waves, like ocean waves, which can be written in terms of Jacobian elliptic functions) and sinusoidal waves. A discrimination of those waves can be given by a single parameter, the steepness parameter, which contains nonlinearity, trapping of particles and dispersion. It turns out that Sadgeev's soliton represents a special case of the class solitons having the largest width and the lowest velocity. Hence a modified Korteweg-de-Vries equation must exist with a stronger nonlinearity.

Regeneration of Hydra from Reaggregated Cells

Abstract: Separated cells of hydra reaggregate and develop into normal animals. The regeneration of serially grafted aggregates derived from different parts of hydra tissue demonstrates that the polarity of morphogenesis in hydra is the result of the cellular composition of the tissue, not cellular orientation.

Homogeneous Dynamical Conductivity of Simple Metals

Abstract: Within the jellium model the zero wave vector, frequency-dependent conductivity is expressed in terms of a regular memory function. This quantity is calculated in lowest order in the impurity concentration and the electron-phonon coupling, thus yielding a reasonable approximation for the conductivity valid in the complete frequency regime. The standard results for the static conductivity including vertex corrections are reproduced. Deviations from Drude's formula a because of spin-flip scattering in a magnetic field, because of resonance scattering, because of phonon creation at low temperatures, and because of breaking of the screening cloud attached to charged impurities are discussed.

The route of passive ion movement through the epithelium of Necturus gallbladder.

Abstract: Electrophysiological experiments were performed onNecturus gallbladder to determine whether the main route of passive ion flow was via the cells or via a paracellular shunt path. In the first approach the following values were determined: the transepithelial resistance, the ratio of the voltage deflections across the luminal and basal cell membrane during transepithelial current flow, and the voltage spread within the epithelial cell layer during intracellular application of current pulses. From these data the luminal and basal cell membrane resistances were calculated to be 4,500 and 2,900 Ωcm2, respectively, whereas the transepithelial resistance was only 310 Ωcm2, indicating that approximately 96% of the transepithelial current bypassed the cells. This result was confirmed in a second approach, in which the intracellular voltage deflections were found to remain approximately constant, when the current pulses were passed from a cell into the interstitial compartment with the luminal compartment being empty or when they were passed from the cell into both external compartments simultaneously. In the third approach current was passed through the epithelium and a voltage-scanning microelectrode was moved across the surface of the epithelium to explore the induced electrical field. Significant distortions of the field were observed in the immediate vicinity of the cell borders. This result indicated that the paracellular shunt, which carries the main part of the transepithelial current, leads through the terminal bars and that the terminal bars or “tight” junctions arenot tight for transepithelial movement of small ions in gallbladder epithelium.

In-vitro auxin binding to particulate cell fractions from corn coleoptiles.

Abstract: When low concentrations (e.g. 10-6 M) of labelled 3-indoleacetic acid (14C-IAA) or α-naphthaleneacetic acid (14C-NAA) are added in vitro to homogenates of corn coleoptiles, radioactivity is reversibly bound to pelletable particles. From the saturation kinetics of the binding it is possible to estimate an apparent K M between 10-6 M and 10-5 M and a concentration of specific sites of 10-7–10-6 M per tissue volume. The binding is auxin-specific. Among many compounds tested, only auxins and such auxin analogues that are known to interact directly with auxin in transport and/or growth were found to interfere with this binding. For instance, the growth-active d-dichlorophenoxyisopropionic acid at 10-4 M inhibits 14C-NAA binding more than the less active l-isomer. The auxin-binding fractions are practically free of DNA and cytochrome-C oxidase and contain binding sites for 1-naphthylphthalamic acid. The results are discussed in context with the hyothesis—derived mainly from physiological data—that auxin receptors are localized at the plasma membrane.

Cell cycle kinetics and development of Hydra attenuata. I. Epithelial cells.

Abstract: The cell cycle parameters of epithelial cells of Hydra attenuata are described. Specifically the rate of proliferation and the fraction of proliferating cells have been determined under conditions of defined growth rate. Techniques involved standard methods of cell cycle analysis using histological and tissue maceration preparations; pulse-chase and continuous labelling with [ 3 H]thymidine followed by autoradiographic analysis, and microspectrophotometric determination of nuclear DNA content in single cells. The results indicate that more than 90% of hydra epithelial cells are actively proliferating with a cell cycle duration about equal to the tissue doubling time. In well fed hydra the average cell cycle is about 3 days long. S period is 12-15 h, G 1 0-1 h, and mitosis 1.5 h. Most of the cell cycle consists of a long G 2 period of variable duration (24-72 h). The results provide no evidence for a subpopulation of rapidly proliferating cells as predicted by ‘growth zone’ models of hydra morphogenesis. The results also indicate that the population of epithelial cells is self-sustaining requiring no input by differentiation from other cell types. The long and variable G 2 period means that DNA synthesis and the following cell division are effectively uncoupled such that inhibitors of DNA synthesis may not stop epithelial cell division. The variable nature of the G 2 period suggests it as a possible point of control of hydra growth.

Factors controlling the resealing of the membrane of human erythrocyte ghosts after hypotonic hemolysis.

Abstract: In accordance with former observations of Hoffman (1962a), ghost populations obtained by hypotonic hemolysis and subsequent restoration of isotonicity by the addition of alkali salts, were found to be composed of 3 types of ghosts. For our purposes it was useful to distinguish between: (1) ghosts which reseal immediately after hemolysis (type I); these ghosts are incapable of incorporating alkali ions which are added after hemolysis; (2) ghosts which reseal after the addition of alkali ions (type II); salt added to the hemolysate becomes trapped inside these ghosts in the course of the resealing process at temperatures above 0°C; and (3) ghosts which remain leaky regardless of the experimental condition (type III). The discrimination between the various types of ghosts was partly achieved by a kinetic method first devised by Hoffman (1962a), and partly by sucrose density gradient centrifugation. The relative sizes of the 3 fractions depend on the temperature at which hemolysis took place and on the time interval which elapsed between hemolysis and the addition of salt. At 37°C the resealing process is fast. Many of the ghosts reseal before salt can be added to the hemolysate. Hence, the fraction of type I ghosts is high after hemolysis at that temperature. At 0°C resealing is extremely slow. Hence, salt which has been added to the hemolysate at that temperature will enter the ghosts and become trapped during subsequent incubation at 37°C. There are no ghosts of type I and many ghosts of type II (about 60%). Regardless of the temperature at hemolysis, there are always ghosts which do not reseal even after prolonged incubation at 37°C. A method has been designed which permits the preparation of homogeneous populations of type II ghosts. Complexing agents (ATP, EDTA, 2,3-DPG) may prevent the resealing of the ghost membrane. However, they exert this effect only at elevated temperatures and when present in the medium at the instant of hemolysis. At 0°C, the presence of complexing agents in the medium at the instant of hemolysis has no effect on the subsequent resealing at 37°C. The recovery of the ghost membrane takes place in spite of the continued presence of the agents and eventually leads to trapping of these agents inside the resealed ghosts. The experiments support the contention that the complexing agents interact with a membrane constituent which is neither accessible from the inner nor from the outer surface of the cell membrane but becomes exposed during the hemolytic event when the complexing agents penetrate across the membrane. Apparently, at low tempertrures membrane ligands are more successful in competing with the added complexing agents for this constituent than at higher temperatures. Extending former observations of Hoffman, we found that not only Mg++ but also Ca++ facilitates the resealing process. Perhaps one or the other of the two alkaline earth ions is the membrane constituent which normally participates in the maintenance of the integrity of the red blood cell membrane.

Nature and linkages of the fatty acids present in the lipid-A component of Salmonella lipopolysaccharides.

Abstract: Laurie, myristic, palmitic, and 3-d-(–)-myristic acid in a ratio of about 1:1:1:3 are present in the lipid A part of the glycolipid derived from the Re mutant Salmonella minnesota R595. An additional fatty acid, Δ2-tetradecenoic acid found in larger amounts after alkaline treatment was recognized as an artifact formed by a β-elimination reaction from ester-linked 3-myristoxy-myristic acid. Various methods for the stepwise liberation of fatty acids were used to identify their distribution on the backbone of lipid A which consists of β-1,6-linked glucosamine disaccharide units substituted at position 3′ with 2-keto-3-eoxyoctonate and at positions 1 and 4′ with phosphate. It was found that the amino groups of the glucosamine residues are substituted by 3-D-(–)-hydroxymyristic acid whose hydroxyl group is free. The three available hydroxyl groups at positions 3, 4, and 6′ of the glucosamine dissaccharide are substituted by equal amounts of lauric, palmitic, and 3-D-myristoxymyristic acid and, possibly, by smaller amounts of myristic and unsubstituted 3-D-hydroxymyristic acid. A similar structure of lipid A seems to exist in lipopolysaccharides of other Salmonella species.

Aufschluß biologischer Matrices für die Bestimmung sehr niedriger Spurenelementgehalte bei begrenzter Einwaage mit Salpetersäure unter Druck in einem Teflongefäß

Abstract: Fur die Bestimmung von Spurenelementgehalten (< 10−4%) in biologischen Matrices (Gewebe, Nahrungsmittel, Abwasserschlamme u. a.) bei begrenzten Einwaagen (≤ 500mg) wird ein Druckaufschlus mit HNO3 bzw. HNO3-HF in einem Teflongefas beschrieben. Radiochemische Messungen ergaben, das die Verluste selbst bei Nanogramm-Mengen fluchtiger Elemente (Hg, Se, J u.a.) unter 2% liegen.

Biological Activities of Lipid A Complexed with Bovine‐Serum Albumin

Abstract: Lipid A preparations from the lipopolysaccharides of four Salmonella minnesota R mutants and one Escherichia coli 0100 R mutant were assayed as soluble complexes with bovine serum albumin for lethality in mice, pyrogenicity in rabbits and complement inactivation. Although generally less active than endotoxic lipopolysaccharides, these lipid · albumin complexes nevertheless exhibited strong biological activity. These results indicate that lipid A contains the endotoxic principle of bacterial lipopolysaccharides.

Synthesis of mouse haemoglobin and globin mRNA in leukaemic cell cultures.

Abstract: FRIEND virus infected leukaemic spleen cells, if maintained under tissue culture conditions, differentiate into erythroblasts that incorporate iron and synthesize haem1,2. Addition of dimethyl sulphoxide (DMSO) to these tissue culture cells stimulates their differentiation along the erythrocytic line much further and results in an increased production of haemoglobin3.

The polarity of the proximal tubule cell in rat kidney. Different surface charges for the brush-border microvilli and plasma membranes from the basal infoldings.

Abstract: Two different membrane fractions were obtained from a brush-border fraction of rat kidney cortex by using their different electrical surface charges in preparative free-flow electrophoresis. One membrane fraction contained only morphologically intact microvilli and was characterized by a high specific activity of alkaline phosphatase. The other fraction morphologically resembled classical plasma membranes by possessing junctional complexes and a high Na-K-ATPase activity The contamination of the isolated membrane fractions by other cell organelles was extremely low These two fractions represent the apical (luminal) and the basal (interstitial) area of the renal proximal tubule cell membrane and clearly demonstrate the polarity of this cell.

Affinity Chromatography of DNA‐Binding Enzymes on Single‐Stranded DNA‐Agarose Columns

Abstract: Agarose gels containing immobilized single-stranded circular DNA from phage fd or denatured calf thymus DNA were investigated for their use in the affinity chromatography of DNA-binding enzymes. The DNA content of gel fragments is stable under the conventional conditions of enzyme purification. Single-stranded DNA-agarose columns have a high capacity to bind DNA-specific proteins. They were used to differentiate between similar enzymatic activities in DNA-free extracts from Escherichia coli. Preparative purification is described for the following enzymes: E. coli DNA polymerase I, DNA polymerase II, RNA polymerase, exonuclease III and T4 polynucleotide kinase. Enzyme purification was as high as 200-fold, recovery of enzymatic activity was 75–100%.

Cytological and cytogenetical studies on brain tumors. 4. Identification of the missing G chromosome in human meningiomas as no. 22 by fluorescence technique.

Abstract: Among 70 human meningiomas cytogenetically investigated by us up till now, only 4 tumors showed a hyperdiploidy. 2 of them had a uniform stemline with 47 chromosomes (47,XX,G+ and 47, XY, C(?E)+); the other 2 meningiomas had a stemline with a modal number of 53 (55) chromosomes.

Significance of intracortical inhibition in the visual cortex.

Abstract: OF the cells found at each level of the retinotopically organized retino-geniculo-cortical system of the cat, only those found in the cortex can be specifically sensitive to the orientation of a contrast line and its direction of movement1–3. These cells are arranged in vertical arrays (columns)2 according to their type of trigger feature.

The formation of capillary basement membranes during internal vascularization of the rat's cerebral cortex.

Abstract: The vascularization of the parietal-temporal region of the cerebral hemispheres has been studied in a total of 50 rats from day 11 of gestation up to adults. The first extracerebral vessels constituting the primary perineural vascular network and the first intracerebral vessels on day 12–14 of gestation show sinusoid characteristics, i.e. irregular thickness of the endothelial wall perforated by fenestrations or small holes and showing, if at all, the beginning accumulation of basement membrane (BM) material. No paired vessels have been observed which would be expected if internal vascularization of cortical anlage starts by penetrating loops. Immature capillaries developing by sprouting (and) from the preexistent vessels begin to appear at about day 15 of gestation. The further differentiation of the terminal vascular bed and the establishing of the definitive architecture is accompanied by the maturation of cortical tissue, i.e. diminution of extracellular spaces, differentiation of perivascular, astroglial and neuronal elements including the development of synapses. The continuous process of BM-formation from the first appearance until the postnatal thickening is described by four successive stages: Stage 1. Local accumulations of fine filamentous material between endothelium and opposite perivascular surfaces of sinusoids and sprouts. Stage 2. Delicate networks of filaments attached on endothelial, pericytal and adjacent glial plasma membranes (PM) of immature capillaries, plaques of lamina densa in narrow perivascular clefts. Stage 3. A thin continuous lamina densa adapted to the PM; its filaments are arranged parallel to the cell surface. In this plane they run randomly. In the lamina rara only few filaments run to the PM mainly perpendicular: stage of immature cortical capillaries. Stage 4. Thickened lamina densa, condensed filamentous pattern; narrow zone of lamina rara: stage of mature cortical capillaries. Coincidental with the rapid thickening of BM in the 3rd–4th postnatal week the characteristics of capillary growth change: The intensive sprouting is finished and the capillary length increases nearly proportionally to tissue volume later on. It is suggested that the BM plays a role in regulating differentiation and mitotic division of the adjacent cells.

Chromomeres and genes.

Abstract: The giant cross-banded chromatin “threads” found in the nuclei of various Dipteran cell types had caught the imagination of many cytologists even before their chromosomal nature was established almost forty years ago (Heitz and Bauer, 1933; Painter, 1933; King and Beams, 1934). The revelation that these structures simply presented an enormously magnified but faithful picture of the linear subdivision of the mitotic interphase chromosomes suddenly changed mere curiosity into enthusiasm: In the words of Painter (1934) “it was clear that we had within our grasp the material of which everyone had been dreaming. It was clear... that the highway led to the lair of the gene.” We must admit today that the goal defined in these prophetic words has not yet been reached, and we cannot even claim that the highway towards this goal has been found, in spite of the concerted efforts of two generations of cytologists, cytochemists, and geneticists to localize and characterize genes in polytene chromosomes. This is not the fault of the material itself, nor is it due to lack of skill on the part of the investigators. Progress has been blocked both by problems of methodology and by the difficulty in defining the basic questions of chromosomal and genetic subunits in physical-chemical terms. Adequate micromethods to study the composition and activity of individual genetic units in polytene chromosomes are only now beginning to become available.

Role of F pili in the penetration of bacteriophage fl

Abstract: Early stages of infection of Escherichia coli with the filamentous bacteriophage f1 were examined in the electron microscope. Purified phage-bacteria complexes were prepared at various time intervals after the initiation of synchronous infection. Cells were scored for the total number of F pili, the number of F pili with f1 attached, the number of intact phage particles which occurred at the surface of the cell, and F pilus length. Electron microscope autoradiographs were also prepared at each time interval. The results showed that the average number of F pili with f1 attached decreased with time as phage deoxyribonucleic acid (DNA) entered the cell. Concomitant with this loss, the remaining F pili became shorter. The rate of entry of phage DNA into the cell followed, with a short lag, the rate of loss of F pili with f1 attached. During the lag period, intact phage particles accumulated at the surface of the cell. The results from radioautographs showed that no phage DNA could be located within the F pilus. These results suggest that F pili are resorbed by the cell during infection with the bacteriophage f1. Parallel experiments with noninfected cultures further suggest that pilus resorption may be a normal cellular phenomenon.

Initiation of Deoxyribonucleic Acid Replication in Escherichia coli B/r: Chronology of Events and Transcriptional Control of Initiation

Abstract: Three processes necessary for the initiation of deoxyribonucleic acid replication have been separated in time in synchronously growing Escherichia coli B/r. One can be inhibited with 2 μg of chloramphenicol per ml and occurs about 20 min prior to initiation. A second step, occurring 5 to 10 min prior to initiation, is sensitive to 4 to 30 μg of chloramphenicol per ml. A third process occurs at the time of initiation and can be inhibited with rifampin. The experiments suggest that transcription itself, or the synthesis of a relatively small ribonucleic acid, is required for initiation of replication.

Pupil and Pseudopupil in the Compound Eye of Drosophila

Abstract: An explanation is given of the phenomenon of “deep pseudopupil” in the compound eye of Drosophila. This phenomenon is here exploited as a technique which, combined with that of optical neutralization of the corneal lenslets, permits the real time analysis of the rapid pigment migration occuring in receptor cells 1 to 6 under bright adaptation.