Involving Cell Division Research Articles

Purine enzymes and immune function

The term immune function is taken to mean the process by which lymphocytes respond to an antigenic challenge. This response involves cell division and differentiation, which depend on purine nucleotides. The present state of knowledge relating events at the cell surface to the necessarily increased rate of purine de novo synthesis, and the modulation of purine nucleotide interconversions through the mediation of putative intracellular messengers, is reviewed. These physiological processes are related, where possible, to some genetic and pharmacologically induced perturbations of the systems involved.

Model of growth and ergot alkaloid production by Claviceps purpurea

AbstractA growth model for Claviceps purpurea in submerged batch culture is presented. In developing the model, the basic principles of the growth and the morphological properties of C. purpurea are considered. The growth of C. purpurea is assumed to occur in a three‐step manner; the first step involves the assimilation and the growth of cells; the second one involves cell division, and the third one involves transformation of the mature cells to a state where they have no ability to divide but do have the ability to produce ergot alkaloids and then they gradually die. Inorganic phosphate is assumed to be the limiting substrate for the first and the second steps in conditions of carbon source being in excess. The model constants are determined by model simulation and graphical searching techniques to find the minimum value of the absolute difference between the experimental and the simulated curves for biomass, alkaloids, and sucrose.

Molecular signals for initiating protein synthesis in organ hypertrophy.

When chronically provoked to increased physiologic activity, organs increase in mass through augmented protein protein synthesis. This process of compensatory hypertrophy can involve cell division as well as cell growth. To test for molecules that might regulate organ size, by inducing hypertrophy, we performed a series of experiments using isolated, perfused, canine hearts in which the left ventricle was beating but performed no work. Hypertrophying hearts and kidneys as well as normal control organs were extracted and the extracts were perfused through isolated heart preparations. Before and after perfusion, RNA was extracted from fragments of the isolated hearts and translated in cell-free media containing [35S]methionine. Incorporation of methionine into protein was measured by liquid scintillation spectrometry. When perfused through normal hearts, extracts from hypertrophying heart and kidney were able to increase greatly the translational ability of RNA extracted from the normal hearts; corresponding perfusates from nonhypertrophying hearts and kidneys had no effect. Our results indicate that molecules that initiate hypertrophic organ growth are extractable, are generated by the cells of the organ under stress, and are probably similar in heart and kidney and perhaps in many other organs as well.

Hormonal regulation of growth in cultured plant cells.

The group of naturally occurring plant hormones known as the cytokinins are defined by their ability to stimulate cell division in mature, differentiated, mitotically inactive cells in tissue culture. Evidence from the literature suggests that cytokinins play a specific role in regulating the progress of a plant cell through its division cycle;. the hormone appears to trigger the transition from G2 to mitosis. However the cytokinins are capable of evoking an array of physiological and developmental responses (many of which do not involve cell division) from different plant tissues and organs. One biochemical effect of the cytokinins is a dramatic and rapid stimulation of polyribosome formation in cultured soybean, cells which require these hormones for growth. Stationary-phase soybean cells, transferred to a medium containing a cytokinin, double in cell number within 36 hr, but when transferred to a medium of the same composition lacking a cytokinin, they do not grow., In vivo labeling with [35S] methionine and slab-gel electrophoresis demonstrated that cytokinin brings about qualitative changes in the spectrum of proteins synthesized by soybean cells which precede hormone-induced cell division. We have shown that cytokinin-induced polyribosome formation is the result of an effect of the hormone on protein synthesis at the translational level. We propose that, in the absence of the hormone, certain genes are transcribed but their messengers are not translated. These include mRNA's for specific cell division proteins. Cytokinins act as permissive factors, allowing cells to complete a genetically programmed sequence of events which was initiated by other factors.

The interaction of the organizing regions in hydra and its possible relation to the role of the cut end in regeneration

ABSTRACT Regeneration in hydra does not necessarily involve cell division, so that the problem of pattern regulation is essentially one of finding the processes by which a given population of cells are assigned appropriate functions in the correct positions. The restoration and nature of the organizers or ‘dominant regions’ must also be explained. Lateral transplants of the two different organizer tissues (hypostome and basal disc) into the digestive regions of host animals unexpectedly antagonize one another’s inductive ability, suggesting that the heretofore separately studied distal and proximal developmental fields may in fact be interconnected. A model based on this idea, incorporating the extinction results with classical findings, leads to the hypothesis of a role for leakage from the cut surface as a trigger for the regenerative process. This is tested using a ligature technique in which the cut surface is minimized when the hypostome is removed, and the degree of regeneration is found to be significantly lowered, in agreement with prediction. These results are discussed in relation to ‘positional information’ and ‘special substance’ models for pattern formation.

Positional information and pattern regulation in hydra: the effect of γ-radiation

ABSTRACT Hydra exposed to high doses of γ-irradiation (25000 rad) are still capable of regeneration although no normal mitotic figures could be seen for up to 48 h after irradiation. Irradiated heads could still inhibit head formation in other regions in graft combinations. The time for head end determination in irradiated animals appeared to be increased. It is concluded that head end regeneration need not involve cell division.

Bacterial cell model: Cell cycle parameters and macromolecular synthesis

A repliconic Helmstetter type model for the E. coli cell cycle is considered. In this model the syntheses of various enzymes compete for a common precursor and the transcription rate is limited by the cellular quantity of RNA polymerase. Enrichment of the nutritive medium is considered to turn off the synthesis of several enzymes and thus to favour the activity of enzymes directly involving cell division. The model predicts a division rate, μ, inversely proportional to the total genome activation degree, Σ A i ; a cell volume and ploidy constant at low division rates and proportional to μ at high division rates, and explains why size and composition do not depend much on temperature.

DNA synthesis by antibody-forming cells during the primary immune response.

THE mechanism of the rapid increase in specific antibody-producing cells during the primary immune response may involve cell division, cell “recruitment”, or a combination of both. The use of mitotic blocking agents has indicated that very rapid cell division, stimulated by antigen, alone accounts for the rapid increase in haemolytic plaque-forming cells during the primary response by the mouse to sheep erythrocytes1. Several autoradiographic studies were also interpreted to indicate an antigen-stimulated increase in the rate of division by plaque-forming cells during the primary response2,3. One group has, however, interpreted its own and other autoradiographic data to indicate that antigen does not stimulate more rapid division by plaque-forming cells4,5. Two of these studies2,5 involved examination of plaque-forming cells only, sampled on one day. The other two studies3,4 were severely limited in sensitivity by the technique for examining DNA synthesis—continuous exposure to 3H-thymidine from the time of antigen administration to the time of death.

Seedling irradiation of ‘gamma-plantlets’: Demonstration and explanation of a leaf growth stimulation

A dose of 500 krads of gamma rays to dry seeds (‘seed irradiation’) prevents mitosis during germination of wheat seedlings; such seedlings are called ‘gamma-plantlets’. Their growth is relatively little affected by increasing the dose of the seed irradiation beyond 500 krads. As growing seedlings, however, gamma-plantlets are sensitive to additional irradiation (‘seedling irradiation’). Leaf growth is reduced by seedling irradiation doses of 50 krads in intact plants and 25 krads in seedlings excised from the endosperm. The effectiveness of a given dose is decreased by dose fractionation. Consequently some repair mechanisms survive the heavy seed irradiation and can operate independently of processes directly or indirectly involving cell division. Growth stimulation was observed in the first leaf, but not the coleoptile, after a seedling irradiation dose of 25 krads was given to intact gamma-plantlets. Similarly there was a stimulation of second leaf growth but not of stem growth. These growth stimulations were absent when exogenous nutriments were substituted for the endosperm immediately following the seedling irradiation. Associated with the leaf growth stimulation in the intact gamma-plantlets was an accelerated breakdown of endosperm starch to soluble carbohydrate without any greater amylase activity. Comparison of gamma-plantlets from two different varieties of wheat disclosed an apparent correlation between the presence of the leaf growth stimulation and faster breakdown of endosperm starch resulting from the seedling irradiation. We suggest that the leaf growth stimulation, which in this system is not masked by certain inhibitory radiation effects (i.e. decreased mitotic activity and nuclear imbalance resulting from division of cells having chromosomal aberrations), results from the more favorable carbohydrate nutrition caused by an apparently nonspecific promotion of endosperm breakdown.

Short Oommunications Kinins in Germinating Lettuoe Seed

The presence, in plants extracts, of factors capable of promoting cell division has been known for some time (Goldacre and Bottomley 1959; Miller 1961) and such compounds have been partially purified (Miller 1961; Zwar, Bottomley, and Kelford 1963). The germination of seeds normally involves cell division as well as cell enlarge-ment (Mayer and Poljakolf-Mayber 1963). Therefore it seemed of interest to investi-gate whether kinins occur in seeds or are formed during their germination. Lettuce seeds were used because their physiology has been studied extensively. We have also tried to partially characterize their kinins.