Cell surface and cell division

Oxidative stress and gene regulation

Reactive oxygen species are produced by all aerobic cells and are widely believed to play a pivotal role in aging as well as a number of degenerative diseases. The consequences of the generation of oxidants in cells does not appear to be limited to promotion of deleterious effects. Alterations in oxidative metabolism have long been known to occur during differentiation and development. Experimental perturbations in cellular redox state have been shown to exert a strong impact on these processes. The discovery of specific genes and pathways affected by oxidants led to the hypothesis that reactive oxygen species serve as subcellular messengers in gene regulatory and signal transduction pathways. Additionally, antioxidants can activate numerous genes and pathways. The burgeoning growth in the number of pathways shown to be dependent on oxidation or antioxidation has accelerated during the last decade. In the discussion presented here, we provide a tabular summary of many of the redox effects on gene expression and signaling pathways that are currently known to exist.

Quantized cell cycle times: interaction between a relaxation oscillator and ultradian clock pulses

Control of the timing of cell division is considered to result from a relaxation cell cycle oscillator: this has one slow and one rapid component and obeys a system of two ordinary differential equations. Interactions of the slow component with an ultradian oscillator leads to quantization of cell cycle times when the free parameters of the cell cycle oscillator are chosen close to its bifurcation point. This model fits the experimental results previously reported.

Oxidative influence on development and differentiation: an overview of a free radical theory of development

Metabolic gradients exist in developing organisms and are believed to influence development. It has been postulated that the effects of these gradients on development result from differential oxygen supplies to tissues. Oxygen has been found to influence the course of development. Cells and tissues in various stages of differentiation exhibit discrete changes in their antioxidant defenses and in parameters of oxidation. Metabolically generated oxidants have been implicated as one factor that directs the initiation of certain developmental events. Also implicated as factors that modulate developmental processes are the cellular distribution of ions and the cytoskeleton both of which can be influenced by oxidants. The interaction of oxidants with ion balance and cytoskeleton is discussed.

Thymocyte membrane changes and modifications of interphase death

A reduction in the rate of interphase death of X-irradiated thymocytes is observed when they are previously treated with triton X-100 or trypsin at low concentrations. The data obtained demonstrate the importance of the structural integrity of the cell surface in the initiation of processes leading to interphase death of lymphoid cells.

Phospholipase activity and plasma membrane homeostasis

Cyclic changes in the physiochemical state of the plasma membrane appear to be necessary for the normal functioning of the cell, especially with respect to division and differentiation. Such changes require a flexible membrane lipid composition to permit the necessary sequence of physicochemical changes to occur during these cellular events. This flexibility can be lost as a result of peroxidation-induced cross linking of membrane constituents, which prevents the normal physico-chemical membrane changes from occurring, resulting in abnormal cellular function. It is proposed that phospholipase A2 and C form a mutually regulatory enzyme system playing an important role with respect to the maintenance of membrane composition and flexibility.

The role of cytoskeletal integrity in cellular transformation

The cytoskeleton appears to function as a linkage between the nuclear and the plasma membranes, permitting environmental stimuli acting at the cell membrane to be transmitted to the nucleus for initiation of an appropriate response. This interplay can account for cases of temporary phenotypic reversions in transformed cell lines, where a deficient cytoskeleton prevents the cell membrane and nucleus from acting in a coordinated manner. Implications for the clinical aspects of cancer therapy are briefly discussed.

The role of lipid and antioxidant exchanges in cell division synchronization (mathematical model)

Cell-cycle synchronization of two diffuse-coupled cells has been studied in the framework of the membrane model for the cell division cycle, proposed by Chernavskii et al. (1977). It has been shown semi-analytically (using the averaging principle) and by computer stimulation that a) if the duration of the G1-phase (TG1) for two identical cells is comparable with the duration of the remaining cycle (TS + G2 + M), the lipid (L)-exchange results in a synchronization with phase difference phi = 0. The antioxidant (A)-exchange leads to a phase-locking with phi = T0/2 (where T0 is the cell cycle period; b) if TG1 much greater than TS + G2 + M (or TG1 much less than TS + G2 + M) the L-exchange makes synchronization possible both with phi = 0 and phi = T0/2 while the A-exchange results in phase-locking with phi confined to the region 0 to T0/2; c) for non-identical cells differing in the values of kinetic parameters, the locking band narrows as the population density increases (when some model parameters are close to the bifurcation thresholds). We expect that the cells selected artificially at a definite phase of cycle might maintain the synchronous division for a long time if the lipid exchange between cells were stimulated.