Cells In Synthesis Phase Research Articles

Cell cycle parameters and ornithine decarboxylase activity in the red bone marrow of hibernating ground squirrels Urocitellus undulatus

During the hibernation season, the values for the parameters of the cell cycle of red bone marrow cells in the hibernating ground squirrels Urocitellus undulatus, when they return to an active-like state between periods of torpor and interbout arousal, do not differ from those observed in summer-active animals. In animals that enter a state of torpor, the cumulative percentage of cells in the resting phase (G0 phase) and pre-synthesis phase (G1 phase) increased from 71.8 to 76.0%, the percentage of cells in the synthesis phase (S phase) decreased from 19.3 to 15.3% compared to those animals that return to an active-like state between periods of torpor and interbout arousal. The cumulative percentage of cells in the post DNA synthesis phase (G2 phase) and mitosis (M) does not change, but (G2 + M)/S ratio increases. When animals enter a state of torpor, changes in parameter values are observed when the animal’s body temperature drops below 25°C, this effect refers to a system whose thermal relaxation time is a nonmonotonic function of the initial temperature. The activity of the key enzyme of polyamine synthesis ornithine decarboxylase, a marker of cell activation and proliferation during interbout arousal does not significantly differ from that observed in summer-active animals; the enzymatic activity decreases sharply, when animals decrease their body temperature below 25°C and enter a state of torpor, and this activity remains at a low level during hibernation and arousal until body temperature reaches 30°C. The role of changes in the parameter values associated with proliferative activity in adaptation of hematopoietic tissue during hibernation of the Yakutian ground squirrel is discussed.

Passage determines toxicity and neuronal markers expression in PC12 cells with altered phenotype

PC12 cells, a catecholaminergic cell line widely used in neurotoxicology, developed variants that have lost some of their characteristic features such as response to NGF and controlled cell division. The present study was undertaken to evaluate the responses obtained between two passages (early and late) of PC12 cells with altered phenotype in viability, percentage of cells in synthesis phase and expression of tyrosine hydroxylase. We hypothesized that being unaware of working with a cell line bearing an altered phenotype could be responsible for the high variability reported in viability assays in the scientific literature. We used sodium arsenite (5–1000 μg L−1), lead acetate (5–1000 μg dL−1), 3-nitropropionic acid (100–5000 μM) and 6-hydroxydopamine (50–300 μM) for viability assays. The results showed that PC12 cells with altered phenotype do not respond uniformly to a variety of stimuli, therefore the requirement to ascertain the true identity of cell lines before testing hypothesis is an important issue to be addressed.

Experimental necrosis and arrest of proliferation of Schwann cells by cytosine arabinoside.

In developing rat cervical sympathetic trunks, Schwann cells proliferate intensely during the first week after birth but axonal populations do not increase. Thus, experimental inhibition of DNA synthesis should affect Schwann cells and spare axons whose cell bodies are not dividing. The present investigation was aimed at determining the effects of an inhibitor of DNA synthesis-cytosine arabinoside (ara-C)--on axons and Schwann cells in developing nerves. Ara-C (60 mg kg(-1) body weight) was injected subcutaneously to newborn rats every six hours for 36 hours. At intervals from 2--4 days of age, animals were given tritiated thymidine (4 muCi per gram body weight) to label Schwann cells in synthesis phase. One hour later rats were killed by systemic perfusion of phosphate buffered glutaraldehyde. Cervical sympathetic trunks (CST's) and sciatic nerves were removed and processed for radioautography and electron microscopy (EM). Labelled and unlabelled Schwann cell nuclei were counted to determine the labelling index (LI%) for each nerve. By the end of ara-C treatment there was almost complete absence of labelling but LI's rose sharply 24 hours after discontinuing ara-C. By EM axons appeared normal; Schwann cells, however, showed prominent nuclear and cytoplasmic changes consisting of nuclear degeneration, dilatation of rough endoplasmic reticulum and increased cytoplasmic density. Ara-C, by suppressing proliferation and causing necrosis of Schwann cells but sparing axons, results in a developmental alteration of axon-Schwann cell relationships. It is suggested that the pathogenetic mechanism involves an inbalance in DNA/RNA synthesis metabolism.

Experimental and cytopathological studies on the nucleic acid synthesis of murine hepatocytes.

Acute changes in nucleic acid synthesis of murine hepatocytes after application of some kinds of agents were studied cytopathologically. The quantity of DNA in almost all normal liver cells shows accurate euploidy, such as 2c, 4c, 8c, etc., by microspectrophotometry (UMSPI, Carl Zeiss). This result corresponds with that of karyometry. Intranuclear quantity of RNA of the mouse and the rat is 15% of DNA. By using such normal in vivo liver cell, the following results were obtained. (A) Toxins or agents which injure DNA transiently reduce the extinction of DNA at a wave length of 260 nm. Microscopically the heterochromatin of the nucleus decreases and becomes thin. On the contrary, the nucleus of the cells in synthesisphase shows that the chromocentrums are reduced, the heterochromatin forms rather a fine network with the euchromatin, and the nucleoli become vague or unrecognizable. (B) On RNA-syn-thesis: (a) The liver cells in which RNA synthesis is decreased: In the case of the cells in which DNA-dependent RNA synthesis is relatively purely disturbed, intranuclear RNA decreases. Microscopically, the nucleoli become smaller and/or disappear and eosinophilic substance appears secondarily in the karyoplasm. In the case of the cells in which the ergastoplasm of the cytoplasm is disturbed first and migration of RNA from the karyplasm into the cytoplasm is stopped, intranuclear RNA increases markedly. Microscopically, the so-called giant nucleolus appears, but its stainability reduces. Distribution of the basophilic substance of the cytoplasm becomes markedly irregular. In the case of the cells in which both DNA and the cytoplasm are injured, intranuclear RNA increases. Microscopically most of the nucleoli become enlarged and their stainability is reduced. The nucleolus-associated chromatin decreases, especially markedly. (b) The liver cells, in which RNA synthesis is accelerated: Intranuclear RNA is normal or decreases. Microscopically the nucleoli become smaller and their stainability increases, that is, the nucleoli are concentrated. The nucleolus-associated chromatin becomes wider. The basophilic substance of the cytoplasm is distributed diffusely and “schollig”. (c) At the early stage after hepatectomy, intranuclear RNA increases and microscopically the nucleoli become larger, but more edematous and RNA synthesis are reduced, then intranuclear RNA decreases gradually. Microscopically, the nucleoli become smaller and the basophilic substance of the cytoplasm increases when RNA synthesis is just accelerated. Enlargement of the nucleolus at the latter stage is thought to be the true “reparative swelling”.