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C Hyver

Publications and source records attributed to C Hyver.

15 recordsLinked to original sources
PubMed1997

Periodic activity of the cortical cytoskeleton of the lymphoblast: modelling by a reaction-diffusion system.

The cytoplasm of cultured human lymphoblasts has a particular organization. A ring formed by actin and myosin delimits a region of the cell where an active membrane veil forms. Depolymerization of the microtubular cytoskeleton releases this ring, which then oscillates between the two poles of the cell. This periodic movement has been studied and described with great precision. We have used these experimental results to model the oscillation of the ring. We have constructed a system of reaction-diffusion equations designed to stimulate the behaviour of the actin and have considered three variables representing, respectively, the proteins involved in actin nucleation, F-actin bound to the plasma membrane and free F-actin, part of which is assumed to constitute the ring, together with myosin. There are two types of results. First, from a theoretical point of view, we have succeeded in simulating a perfect back-and-forth movement of a wave. Second, this model suggests that actin alone, by virtue of its intrinsic properties, can generate an oscillatory movement within the cell, without the need for other oscillators.

Actins↗
PubMed1995

Cortical memory in Paramecium: a theoretical approach to the structural heredity.

Structural heredity is frequently encountered in ciliates. In particular, during division of Paramecium the cortical characteristics of the 2 daughter cells are inherited from those of the mother cell. Genesis of new structures is therefore only possible if there are pre-existing older structures. We attempted to simulate this phenomenon with a model already used to describe the structure and morphogenesis of the cortex of Paramecium. We show that to initiate spatial organization it is enough to choose special starting conditions which comprise the primer of the structure, even if highly localized and at a low concentration of morphogens. This property does not question the basic concepts of genomic heredity.

Animals↗
PubMed1990

MPF and cyclin: modelling of the cell cycle minimum oscillator.

The cell cycle appears to be controlled by the interplay between two protein complexes, MPF and cyclin. Their interactions play an essential role in the structure of the oscillator governing the cell cycle. There seems to be no general agreement on this latter crucial question. Two different mechanisms are proposed: (i) cyclin and p34 kinase combine to form an oligomer with MPF activity; (ii) cyclin enzymatically activates the passage from inactive pre-MPF to active MPF, with the postulate that MPF initiates cyclin degradation. We have modelled these two hypotheses to see whether both actually lead to oscillatory behaviour. The p34-cyclin oligomerization does so without any difficulty. With the second mechanism, however, the strict hypothesis that cyclin degradation is activated by MPF must be re-examined: the system only oscillates if, in disappearing, the MPF and the cyclin react with each other stoichiometrically. The model also demonstrates that it is useless to seek cyclic control of cyclin proteolysis.

Cell Cycle↗
PubMed1985

Biochemical systems as generators of local and global limit cycles.

It has recently been noted (8) that the global limit cycle (hard self-excitation) is apparently not uncommon in nature, especially in biochemical systems. This idea is confirmed by a more detailed study of many biochemical systems with quite different topological structures. The present paper describes some of the cases considered; they were deliberately chosen to be simple, but they almost all have the following properties: for one set of parameters, the linearization method shows that there is a local limit cycle (soft self-excitation); for other parameters, the systems may have global limit cycles.

Biochemical Phenomena↗
PubMed1984

Local and global limit cycles in biochemical systems.

An autonomous periodic behaviour may correspond to a local or global limit cycle. If the cycle is local, the mathematical analysis is fairly easy upon linearizing about a singular point, but there are few mathematical methods for the determination of global limiting cycles. A periodic motion has a priori a 50% chance of being global. This paper describes a method of predicting certain types of global limit cycles. The application of this procedure indicates that there are plenty of biochemical systems with stable singular points but nevertheless oscillatory.

Catalysis↗
PubMed1981

Oscillation of the electrical potential of the frog skin under the effect of Li+: theoretical formulation.

A theoretical model of oscillation is proposed. It is based on the non-linearity introduced in the functioning of the active pump by the presence of lithium. Other plausible causes of oscillation are shown not to interfere in this case. The oscillation is of the local type. Synchronization between the local oscillators is not achieved by diffusional, but by electrical coupling. Numerical calculation shows that the model fits reasonably well to the experimental data.

Animals↗
PubMed1980

[Folds and cusps in biochemical systems].

The example given below, which experimentally demonstrable, shows that the folds and cusps of the catastrophe theory can exist in biochemical systems.

Biochemical Phenomena↗