Showing papers by "Max Planck Society published in 1974"

Applications of a theory of biological pattern formation based on lateral inhibition.

Abstract: Model calculations are presented for various problems of development on the basis of a theory of primary pattern formation which we previously proposed. The theory involves short-range autocatalytic activation and longer-range inhibition (lateral inhibition). When a certain criterion is satisfied, self-regulating patterns are generated. The autocatalytic features of the theory are demonstrated by simulations of the determination of polarity in the Xenopus retina. General conditions for marginal and internal activation, and corresponding effects of symmetry are discussed. Special molecular mechanisms of pattern formation are proposed in which activator is chemically converted into inhibitor, or an activator precursor is depleted by conversion into activator. The (slow) effects of primary patterns on differentiation can be included into the formalism in a straightforward manner. In conjunction with growth, this can lead to asymmetric steady states of cell types, cell differentiation and proliferation as found, for instance, in growing and budding hydra. In 2 dimensions, 2 different types of patterns can be obtained. Under some assumptions, a single pattern-forming system produces a ‘bristle’ type pattern of peaks of activity with rather regular spacings on a surface. Budding of hydra is treated on this basis. If, however, gradients develop under the influence of a weak external or marginal asymmetry, a monotonic gradient can be formed across the entire field, and 2 such gradient-forming systems can specify ‘positional information’ in 2 dimensions. If inhibitor equilibrates slowly, a spatial pattern may oscillate, as observed with regard to the intracellular activation of cellular slime moulds. The applications are intended to demonstrate the ability of the proposed theory to explain properties frequently encountered in developing systems.

Perturbations of space--times in general relativity

Abstract: A definition of perturbations of space-times in general relativity is proposed. The definition leads in a natural way to a concept of gauge invariance, and to an extension of a lemma of Sachs (i964). Coupled equations governing linearized perturbations of certain tetrad components of scalar, electromagnetic, and gravitational fields are derived by the use of Geroch, Held & Penrose's (I 973) version of the tetrad formalism of Newman & Penrose (i 962). It is shown that these perturbations are gauge invariant if and only if the unperturbed space-time is vacuum of algebraic type {22} or, equivalently, if and only if the perturbation equations decouple. Finally the maximal subclass of type {22} space-times for which the decoupled perturbation equations can be solved by separation of variables is found. This class comprises all the nonaccelerating type {22} space-times, including that of Kerr, thus elucidating earlier results of Bardeen & Press

The structure of the viscous sublayer and the adjacent wall region in a turbulent channel flow

Abstract: Hot-film anemometer measurements have been carried out in a fully developed turbulent channel flow. An oil channel with a thick viscous sublayer was used, which permitted measurements very close to the wall. In the viscous sublayer between y+ ≃ 0·1 and y+ = 5, the streamwise velocity fluctuations decreased at a higher rate than the mean velocity; in the region y+ [lsim ] 0·1, these fluctuations vanished at the same rate as the mean velocity.The streamwise velocity fluctuations u observed in the viscous sublayer and the fluctuations (∂u/∂y)0 of the gradient at the wall were almost identical in form, but the fluctuations of the gradient at the wall were found to lag behind the velocity fluctuations with a lag time proportional to the distance from the wall. Probability density distributions of the streamwise velocity fluctuations were measured. Furthermore, measurements of the skewness and flatness factors made by Kreplin (1973) in the same flow channel are discussed. Measurements of the normal velocity fluctuations v at the wall and of the instantaneous Reynolds stress −ρuv were also made. Periods of quiescence in the − ρuv signal were observed in the viscous sublayer as well as very active periods where ratios of peak to mean values as high as 30:1 occurred.

Thermoelasticity, pseudoelasticity and the memory effects associated with martensitic transformations

Abstract: The pertinent thermodynamic relations, nucleation and growth and the influence of stress are considered and applied to thermoelasticity and the memory effects.

The development of the macronucleus in the ciliated protozoan Stylonychia mytilus

Abstract: Ciliated protozoa are characterized by generative micronuclei and vegetative polyploid macronuclei. Micronuclei of Stylonychia mytilus contain 1 600 times as much DNA per haploid genome as E. coli. Most of this DNA is shown to be repetitive. The development of the macronucleus involves, as demonstrated by cytology, only 1/3 of the chromosomes which in a first replication phase are polytenized in probably 5 replication steps and appear as giant chromosomes. At this developmental stage considerable amounts of repetitive DNA are still present in the chromosomes. During the subsequent disintegration phase more than 90% of the DNA are eliminated from the macronucleus anlage. The remainder is further replicated five times and composes the final macronucleus. Since this DNA reassociates with a reaction rate almost identical to an ideal second order reaction its kinetic complexity can be determined by comparison with the kinetic complexity of E. coli DNA. Macronuclear DNA reassociates with a kinetic complexity of 26 times the kinetic complexity of E. coli DNA (corrected for GC content) which indicates that macronuclear DNA sequences exist at a ploidy level of 4 096 C. We assume that macronuclear DNA may be present only once per haploid genome. In this case it represents only 1.6% of the DNA in micronuclei or 10% of the DNA in the giant chromosome stage.

An intracellular analysis of visual cortical neurones to moving stimuli: response in a co-operative neuronal network.

Abstract: 1. Responses of cortical cells from the foveal and perifoveal visual field representation in area 17 to moving contrasts were analyzed with intracellular records in anesthetized cats. These intracellularly recorded responses were normal in so far as the cells showed typical orientation/direction sensitivity and only short phasic or no responses to diffuse illumination. 2. With slowly moving bright or dark bars, two types of responses were seen: those with a small excitatory peak and those with a wider excitatory peak. Inhibitory regions outside the excitatory peak were only seen in cells with a small excitatory area. Only very few cells showed inhibitory “flanks” preceding and following the excitation; often inhibition followed the excitation in both the forward and backward direction; sometimes it preceded it in both directions. The inhibition outside the excitatory zone practically always had “dynamic” properties, i.e. was smaller or larger in the two opposite directions of movements. 3. All cells showed strong inhibition (IPSP's) mixed with excitation while the stimulus moved over the excitatory response field. The degree of inhibition was clearly sensitive to the direction of movement (forward or backward) of an optimally oriented moving stimulus, and could also be different at different orientation/ directions. However, the orientation dependence of intracortical inhibition was often less clear than the differences found between the two opposite directions of an optimally oriented stimulus. Inhibition was more marked during binocular than during monocular stimulation. 4. The excitatory areas of cortical cells were mostly slightly elongated, but not systematically along the axis of optimal orientation. The diameters of the excitatory fields were similar along the optimal and the non-optimal orientation axes (mean 1.9±0.78 vs. 2.2±0.92°). 5. It is proposed that the orientation/direction sensitivity of cortical cells is a function of intracortical inhibitory connections with direction/orientation sensitivity rather than only due to the spatial arrangement of excitatory and inhibitory on- or off-center fields. A hypothetical retino-cortical projection map is proposed and it is assumed that direction/orientation sensitive intracortical inhibition is essential for the functional properties of cortical neurones.

Model for Brillouin Scattering in Amorphous Solids

Abstract: An elastic continuum model is presented for Brillouin scattering by an amorphous solid. The assumption that light scatters on distorted plane wave acoustic phonons leads to the prediction that the scattered intensity plotted as a function of the frequency transfer Ωo consists of the usual Brillouin peaks plus a background which, a t room temperature, goes like Ωo; for small Ωo, but rises less steeply for larger Ωo, and may even bend over within the range of the validity of the model, depending on the correlation lengths for spatial fluctuations due to disorder and on the speeds of sound. For the case of a-Si, additional results are obtained with the help of existing experimental measurements. Es wird die Brillouinstreuung in a morphen Snbstanzen an einem elastischen Kontinuums-modell diskutiert. Die Annahme, das Licht an durch deformierte ebene Wellen beschriebenen akustischen Phononen gestreut wird, fiihrt zu folgenden Aussagen. Die Streuintensitiit als Funktion der Frequenzverschiebung besteht aus den ublichen Brillouin-Peaks und einem Hintergrund, der, bei Raumtemperaturen, fur kleine Ωo proportional zu Ω 2o ist. Mit wachsendem Ω o wachst der Hintergrund dam schwacher als Ω2o. Jc nach den Werten der Korrelationslangen fur raumliche Fluktuationen und der Schallgeschwindigkeiten kanner im Giiltigkeitsbereich des Modells sogar nach Erreichen eines Maximums wieder abfallen. ZusaItzliche Aussagen werden fur den Fall von a-Si unter Ausnutzung existierender Messungen gemacht.

The cycle of atmospheric CO.

Abstract: New measurements of the CO-mixing ratio in the two hemispheres with the dissolved CO in surface seawater together with previous results are used to set up a detailed budget of CO in the atmosphere. It is shown that CO is produced by technological and by natural sources. The source strengths of both kinds of sources are of the same magnitude. The total CO-production rate is estimated to be 10 × 10 14 g per year. The corresponding residence time is 0.5 years. From the observed latitudinal CO-distribution between the hemispheres the production of CO by the oxidation of methane in the troposphere is judged to be a minor source. CO is removed by microbiological processes at the soil surfaces, by photochemical consumption in the stratosphere, and probably also by reaction with OH radicals in the troposphere. DOI: 10.1111/j.2153-3490.1974.tb01958.x

Cell cycle kinetics and development of Hydra attenuata. III. Nerve and nematocyte differentiation.

Abstract: The differentiation of nerve cells and nematocytes in Hydra attenuata has been investigated by labelling interstitial cell precursors with [3H]thymidine and following by autoradiography the appearance of labelled, newly differentiated cells. Nematocyte differentiation occurs only in the gastric region where labelled nematoblasts appear 12 h and labelled nematocytes 72-96 h after addition of [3H]thymidine. Labelled nerves appear in hypostome, gastric region, and basal disk about 18 h after addition of [3H]thymidine. The lag in the appearance of labelled cells includes cell division of the precursor as well as differentiation since nerves and nematocytes have 2n postmitotic nuclear DNA content. A cell flow model is proposed for interstitial cells and their differentiated products. Stem cells occur as single interstitial cells or in pairs. Per cell generation about 60 % of the daughter cells of stem cell divisions remain stem cells and about 40 % differentiate nerves and nematocytes. Nerves differentiate directly from stem cells in about 1 day. Nematocyte differentiation requires 5-7 days including proliferation of a cluster of 4, 8, 16 or 32 interstitial cells and differentiation of a nematocyst capsule in each cell. The numbers of interstitial cells and nematoblasts predicted by the cell flow model from the rates of nerve differentiation (900 nerves/day/ hydra), nematocyte differentiation (1760 nematocyte nests/day/hydra) and stem cell proliferation (stem cell cycle = 24 h), agree with the numbers of these cells observed in hydra. The number of stem cells per hydra is 3000-6000 depending on assumptions about the time of determination. The ratio of nematocyte to nerve differentiation averaged over the whole hydra is 3:1. In the hypostome and basal disk interstitial cell differentiation occurs exclusively to nerve cells while in the gastric region the ratio of nematocyte to nerve differentiation is about 7:1.

Three-dimensional structure of adenyl kinase

Abstract: A combination of X-ray data at 3 A resolution and sequence results has yielded the atomic structure of adenyl kinase, a ubiquitous enzyme which catalyses the phosphorylation of AMP by ATP. The abundant secondary structures of the protein and the probable binding sites for ATP and AMP are described.

The influence of proprioceptive feedback on Locust flight co-ordination

Abstract: The right fore wing of a tethered locust (Locusta migratoria) flying in front of a wind tunnel was moved up and down about its normal axis of rotation. The reaction of the animal was measured by recording muscle potentials from the depressor muscles of all wings. The flight rhythm of an animal can be forced to take a preferred phase with regard to the input rhythm, provided the stimulating frequency does not differ by more than 10 to 15% from the wing beat frequency of the non-driven wings. The reaction is apparently due to phasic proprioceptive feedback from the driven wing which influences the flight rhythm within a few wing beats. This proprioceptive feedback normally increases the precision of co-ordination of the wings among themselves.

Serum LH, FSH, prolactin and progesterone from birth to puberty in female and male rats

Abstract: Serum LH, FSH, prolactin and progesterone were determined in male and female prepuberal rats. Neonates of both sexes had high LH and FSH levels, the values in the females being higher than those in the males. Serum prolactin and progesterone were low in neonatal rats. A curious LH secretion pattern occurred in female rats between days 10 and 20; high LH levels were observed in 10–15‰ of the rats during this time, whereas the male rats showed only minor fluctuations. At the same time serum FSH was elevated in both sexes. Again, the values in the females were higher than in the males. Serum prolactin was still low, whereas progesterone rose slightly in both sexes. Serum LH and FSH remained low between days 21 and the immediate peripuberal period (i.e., days 37–45) in males and females, and serum prolactin rose steadily during this period. Progesterone also increased following the prolactin pattern. All hormones (LH, FSH, prolactin and progesterone) were increased during the peripuberal period with cyclic fl...

Crystal and molecular structure of a dimer composed of the variable portions of the Bence-Jones protein REI.

Abstract: The structure of the variable part of a χ-type Bence-Jones protein RE1 has been determined at a resolution of 0.28 nm. It forms a dimer in the crystal related by a local diad, held together by hydrogen bonding interactions of residues Tyr-36, Gln-38, Ala-43, Pro-44, Tyr-87, Gln-89 and Phe-98, which are largely conserved in light chains. The structure consists of two hydrogen-bonded sheets covering a hydrophobic interior made up of mostly conserved amino-acid side chains. Approximately 50% of the residues form β-pleated sheets. Several of the pleated sheet strands are connected by hair-pin bends, which contain glycine residues conserved in most light chains. The arrangement of the hypervariable segments especially in comparison with the Fab structure suggests that the V dimers form a primitive antibody. The folding of the poly-peptide chain and the spatial relationship of the two monomers appear to be the same as in the λ-type Bence-Jones protein dimer and the Fab fragment.

Residence time and variability of tropospheric trace gases

Abstract: It is shown on the basis of theoretical considerations that time and space variations for tropospheric constituents should be approximately inversely proportional to their tropospheric residence time if the distribution of sources and sinks is similar. Compilation of available data seem to verify this. It is pointed out that such a relationship, if confirmed by further data, is a useful tool for atmospheric chemistry. DOI: 10.1111/j.2153-3490.1974.tb01625.x

Somatic hybridisation of plants by fusion of protoplasts

Abstract: Mesophyll protoplasts of “haploids” produced by “anther culture” of two chlorophyll deficient, light sensitive varieties of Nicotiana tabacum, sublethal (s) and virescent (v) are fused with the method of Keller and Melchers (1973). The double heterozygote hybrid of the two recessive genes for light sensitivity complements to normal leaf colour and resistance to high light intensity. By using this complementation obviously 12, possibly 21 independently arisen somatic hybrid plants are selected. Since leaf colour mutations are frequent and light sensitivity of leaf colour mutants is not too rare in higher plants, it is possible to use generally this selection method.

Interaction of Phalloidin with Actin

Abstract: Phalloidin, a toxic bicyclic peptide of rapid action from the toadstool, Amanita phalloides, gives rise to polymerization of G-actin to filamentous structures (Ph-actin) in a medium of low ionic strength. Ph-actin closely resembles the microfilaments found in liver membrane fractions (Ph-filaments) after in vivo or in vitro poisoning. Both phalloidin induced filaments are resistant to 0.6 M KI in contrast to F-actin, and become decorated by heavy meromyosin. After preincubation with cytochalasin B significantly fewer actin filaments are observed.

Putrescine catabolism in mammalian brain.

Abstract: In contrast with putrescine (1,4-diaminobutane), which is a substrate of diamine oxidase, monoacetylputrescine is oxidatively deaminated both in vitro and in vivo by monoamine oxidase. The product of this reaction is N-acetyl-γ-aminobutyrate. The existence of a degradative pathway in mammalian brain for putrescine is shown, which comprises acetylation of putrescine, oxidative deamination of monoacetylputrescine to N-acetyl-γ-aminobutyrate, transformation of N-acetyl-γ-aminobutyrate to γ-aminobutyrate and degradation of γ-aminobutyrate to CO2 via the tricarboxylic acid cycle.

Purine nucleotide metabolism in the cat brain after one hour of complete ischemia.

Abstract: —Complete cerebral ischemia was produced in normothermic anaesthetized cats by clamping the innominate and the left subclavian arteries combined with lowering the blood pressure. After 1 h of ischemia, ATP was no longer present in detectable amounts. Total adenine nucleotides were reduced to 34 per cent of the normal level. The breakdown of guanine nucleotides was less marked, with small amounts of GTP still being present at the end of the ischemic period. In animals with signs of functional recovery after 3–7 h of recirculation, ATP was resynthesized to 62 per cent of the control level. Total adenine nucleotides increased to 68 per cent and the adenylate energy change—[ATP + 1/2 ADP]/[AMP + ADP + ATP]—was re-established to within 7 per cent of the pre-ischemic value. Radiochromatography of nucleotides following intravenous injection of [14C]formate indicated a marked enhancement of postischemic purine de novo synthesis. Purine nucleosides and free bases which accumulated during ischemia, were partially re-utilized by salvage pathways: adenosine was rephosphorylated to AMP by adenosine kinase (EC 2.7.1.20); inosine and hypoxanthine were re-used via IMP in a reaction mediated by hypoxanthine phosphoribosyltransferase (EC 2.4.2.8).

Sensory Transduction in Insect Olfactory Receptors

Abstract: Sensory transduction means the conversion of a physical or chemical stimulus into the excitation of a sensory (or receptor) cell. This process involves a number of steps which can be fully understood only by a combined effort of biophysicists, biochemists, morphologists and physiologists. To study sensory transduction it is also worthwhile to compare sensory systems adapted to different stimulus modalities, since the receptor organs differ considerably depending on their adequate form of stimulus energy.