Peak Of Mitotic Activity Research Articles

Thermal stress and selection for growth affect myogenic satellite cell lipid accumulation and adipogenic gene expression through mechanistic target of rapamycin pathway.

Satellite cells (SCs) are multipotential stem cells having the plasticity to convert to an adipogenic lineage in response to thermal stress during the period of peak mitotic activity (the first week after hatch in poultry). The mechanistic target of rapamycin (mTOR) pathway, which regulates cellular function and fate of SCs, is greatly altered by thermal stress in turkey pectoralis major muscle SCs. The objective of the present study was to determine the effects of thermal stress, selection for growth, and the role of the mTOR pathway on SC intracellular lipid accumulation and expression of adipogenic regulatory genes. These effects were analyzed using SCs isolated from the pectoralis major muscle of 1-wk-old modern faster-growing commercial turkey line (NC) selected for increased growth and breast muscle yield as compared with SCs of a historic slower-growing Randombred Control Line 2 (RBC2) turkey. Heat stress (43 °C) of SCs during proliferation increased intracellular lipid accumulation (P < 0.001), whereas cold stress (33 °C) showed an inhibitory effect (P < 0.001) in both lines. Knockdown of mTOR reduced the intracellular lipid accumulation (P < 0.001) and suppressed the expression of several adipogenic regulatory genes: peroxisome proliferator-activated receptor-γ (PPARγ; P < 0.001), CCAAT/enhancer-binding protein-β (C/EBPβ; P < 0.001), and neuropeptide-Y (NPY; P < 0.001) during both proliferation and differentiation. The NC line SCs showed fewer reductions in lipid accumulation compared with the RBC2 line independent of temperature. Both intracellular lipid accumulation (P < 0.001) and PPARγ expression (P < 0.001) were greater at 72 h of proliferation than at 48 h of differentiation in both the RBC2 and NC lines independent of temperature. Thus, hot and cold thermal stress affected intracellular lipid accumulation in the pectoralis major muscle SCs, in part, through the mTOR pathway in wea growth-dependent manner. Altered intracellular lipid accumulation could eventually affect intramuscular fat deposition, resulting in a long-lasting effect on the structure and protein to fat ratio of the poultry pectoralis major muscle.

The liver regeneration of land snail Helix lucorum

Study of regenerative peculiarities in organisms standing on the various steps of phylogenesis is important in order to establish the common biological meaning and basic pattern of regeneration.The aim of the work was to study the regeneration characters of the mollusc liver so called hepatopancreas which is the analogue of vertebrate liver.Experiments were carried out on a land snail Helix lucorum using the experimental model elaborated by us. The transcriptional activities within the liver cell nuclei were studied using by test‐system of RNA‐synthesis. To evaluate the mitotic activity of the liver tissue 5–7 μm paraffin sections were used under the light microscope.The rhythmic character of RNA‐synthesis was revealed in the liver cells of intact snail during the day. The live resection induced the growth control genes activation like in rodents. The peak of transcriptional activity of these genes was appeared at 9th hour after the operation. Thereby the first peak of mitotic activity within the liver tissue was observed at 27th hour after the operation. The liver mass was regenerated after a week from the resection. The quantitative correlation of the main cell types (digestive, calcium and excretory ‐ 8:1:1) within the liver lobes remained stable.On the basis of our results we conclude that the initial stages of reparative processes carry the similar character in phylogenetically distant organisms.

Mitotic Activity in the Dermis of Mice During Graft Versus Host Disease: The Role of Fibroblast Replication in Dermal Fibrosis

When immunocompetent cells are transferred to an allogeneic, immunologically compromised host a complex series of cellular events are initiated, referred to as graft versus host disease. This results in widespread organ damage with fibrosis being a prominent feature. The pathologic fibrosis may result from an increase in fibroblast numbers, an increase in collagen produced from individual fibroblasts, or a combination of the two processes. The relative contribution of fibroblast replication to the pathologic fibrosis seen in graft versus host disease has not been directly determined previously, and this is the main object of this paper. Graft versus host disease was induced by the transfer of lymphoid cells from B10D2 mice to irradiated Balb/c recipients. In order to study the mitotic activity of dermal cells following bone marrow transplantation, a thymidine anologue, bromo-deoxyuridine (BrDU), was administered to mice using an osmotically driven, implantable infusion device. The labeled cells were visualized immuno-histochemically and studied at weekly intervals. There is intense mitotic activity in the basal layer of the epidermis and the acrosyringal epithelium from the second week. Evidence of increased mitotic activity in the epidermis persisted until the fifth week post-transplantation. Fibroblast replication was seen from the end of the third post-transplant week. Dermal collagen deposition also occurred at this time. Peak mitotic activity was present at the end of the fourth week and was less pronounced by the fifth week. It was especially evident in the upper dermis where the developing collagen layer was being deposited. To our knowledge this is the first direct demonstration of fibroblast proliferation in an immunologically mediated fibrotic disorder. It is concluded that fibroblast replication is an important mechanism leading to the pathologic fibrosis seen in graft versus host disease and, by analogy, probably other types of immunologically mediated fibrosis.

Elastin and collagen in the fetal sheep lung. I. Ontogenesis.

The ontogenesis of elastin (desmosine), collagen (hydroxyproline), and DNA concentrations and their rates of increase were studied in fetal sheep lungs from day 60 until term. Elastin increased 13-, 17-, 63- and 11- fold in nondissected parenchyma, dissected (free of tubular structures of greater than 0.1 mm diameter) parenchyma, pleura, and trachea, respectively. Collagen increased 2.1-, 1.8-, 5- and 3-fold, respectively, in the four tissues. A sharp rise in elastin occurred after day 100. The rate of increase in elastin was greater in dissected than in nondissected parenchyma while the reverse was true for collagen. The steepest rise of elastin concentration occurred in the pleura after day 125. DNA concentration peaked on day 125 and was lowest at term. These findings are consistent with 1) the onset of a steep rise in elastin accumulation during the canalicular period, 2) the development of a rigid, mainly collagenous structure of the central airways and blood vessels and a distensible peripheral "gas-exchange tissue," rich in elastin, 3) an important role of elastin in the function of the visceral pleura, and 4) a peak of mitotic activity during the early alveolar period.

Cell cycle parameters of adult rat hepatocytes in a defined medium. A note on the timing of nucleolar DNA replication.

Hepatocytes, isolated from adult (250-350 g) rats, attached and survived well in primary culture on highly diluted (less than 1 microgram/cm2) collagen gel in a synthetic medium without serum or hormones. About 20% of the cells "spontaneously" entered S phase during the first 4 days of culturing, and mitoses were easily demonstrated at the near physiological concentration (1.25 mM) of Ca++ prevailing in the medium. Cultures given 9 nM epidermal growth factor (EGF) and 20 nM insulin 20 h after inoculation showed vigorous DNA synthesis and mitotic activity. Autoradiography of such cells exposed to [3H]thymidine allowed the determination of the following cell cycle parameters: Lag period from EGF/insulin stimulation till onset of increased DNA synthesis, 17 h; rate of entry into S phase (kG1/S), 0.028/h; duration of S phase, 8.4 h; duration of G2 phase, 2.7 h. The peak DNA synthesis (pulse labelling index, 24%) and peak mitotic activity (mitotic index, 1.7%) occurred 35 and 43 h, respectively, after the stimulation with EGF/insulin. These values are comparable to those reported during the in vivo compensatory hyperplasia following partial hepatectomy of adult rats. A marked variation of the intranuclear [3H]thymidine pulse labelling pattern was noted: During the first 1.5 h of the S phase, the labelling was extranucleolar and during the last 1.5 h chiefly nucleolar. The cells survived well in the absence of glucocorticoid, whose effect on cell cycle parameters therefore could be studied. Dexamethasone (25-250 nM) did not appreciably affect the durations of S phase and G2 phase or the pattern of preferential extranucleolar and nucleolar DNA synthesis within the S phase.

La morphogenèse du limbe des Dicotylédones

In this unique and comprehensive article, Dr. Cusset presents a historical review of ideas and theories on leaf development, a detailed description and critique of the classical model, a discussion...

Topographic distribution of dividing hepatocytes in the regenerating liver lobule during peak mitotic activity

Topographic distribution of dividing hepatocytes in the regenerating liver lobule during peak mitotic activity

The circadian optimal time for hepatectomy in the study of liver regeneration.

Standardized (light from 0600 to 1800) C3HS mice, hepatectomized at different circadian stages, were killed at 1400 (the peak time of mitotic activity in intact mice). The higher values of mitotic index were those of mice operated at 1400, 48 hr before. The curve of mitotic activity of the regenerating liver of mice operated at 1400 and that of mice operated at 0200 (an opposite time in the circadian stage) are, both, grossly in phase with the curves of mitotic index in young and adult mice liver. The amplitude of the first peak of mitotic activity in mice operated at 0200 was dramatically lower than that of animals operated at 1400. The same applies to hepatocytes as well as to the sinusoid litoral population of cells. It is concluded that 1400 hr, as contrast to 0200 hr, is an optimal time for hepatectomy if one wants to obtain the highest mitotic index first peak during regeneration in a normal phase position (the position of the mitotic index peak in the liver of normal young and adult mice).

A second peak in uptake of gentamicin by rat kidney after cessation of treatment

Gentamicin was administered s.c. to rats once daily for 7 days at 5 mg kg-1. At the end of this period renal concentrations of gentamicin declined from day 1 to day 5 postdosing, but showed a second peak on day 8, after which they declined again through days 16 and 22. This second peak coincided with a peak of mitotic activity in the kidney, suggesting that this organ, while recovering from gentamicin-induced damage, passes through a temporary phase during which it has increased affinity for gentamicin.

Mitotic rate of rat thyroid follicular cells in vivo in response to a single injection of thyrotropin (TSH).

The mitotic rate of thyroid follicular cells was assessed by a stathmokinetic method at intervals from 15 min to 24 hr after a single injection of 1 iu/kg of thyrotropin (TSH). The mitotic rate was increased 15 min after TSH and remained elevated for 3 hr. Two further peaks of mitotic activity were present at 9 hr and 24 hr after TSH. Serum TSH concentrations were increased from 5 min to 3 hr with a maximum at 1 hr.

Cold synchronization for the study of peripheral blood and bone marrow chromosomes in leukemias and other hematologic disease states.

A method of cold-shock synchronization of immature granulocytic cells from peripheral blood or bone marrow is described. It is shown that this method provides an increased yield of early metaphases and offers advantages over others currently employed. The peaks of mitotic activity following the cold-shock treatment differ for patients with acute nonlymphoblastic leukemia (ANLL) and patients with chronic myeloid leukemia (CML) by an interval of 2 h. This method is considered to be suitable for routine cytogenetic studies on hematological patients.

Inhibition of mitotic activity of the corneal epithelium during chronic pyrogenal-induced stress in albino rats

Injection of pyrogenal daily for 5 days caused no change in the diurnal index of labeled nuclei (ILN): it was 67.0% in the cornea of control rats and 69.1% in stressed rats. Cytophotometric analysis with a control for section thickness showed that chronic exposure to stress led to a significant increase in the number of tetraploid nuclei from 3.2 to 7.7%. There were no significant changes in the percentages of the other classes of nuclei. Neither polyploidization nor evidence of accumulation of cells in the G2-phase was found. The absence of a progressive increase in the number of tetraploid nuclei or of more marked polyploidization against the background of prolonged depression of cell division and a stable ILN can be explained by the circadian nature of the response of mitotic activity to stress. Even during chronic exposure to stress the depression of cell division which was observed in the afternoon and evening was not found in the morning, at the peak of mitotic activity. This circadian shunt contributes to maintenance of the modal ploidy of the corneal nuclei.

Liver sinusoidal cell ultrastructure in partially hepatectomized rats

Two-thirds of the liver was removed from male Wistar rats weighing 160–200 g. In response to the operation phasic changes occurred in the structure of the lysosomal apparatus in the Kupffer cells. The number of primary lysosomes in the Kupffer cells was increased 2.5 h after partial hepatectomy, and the size and polymorphism of the lysosomes were increased after 9 h. At the peak of mitotic activity of the hepatocytes (30 h after partial hepatectomy) mainly secondary lysosomes were identified in the Kupffer cells, but 48 h after the operation, on the other hand, their number was reduced, although “young” forms of primary lysosomes appeared. Manifestations of fatty infiltration predominated in the endothelial cells and reached a maximum at the peak of mitosis of the hepatocytes. The results are evidence that ultrastructural changes in the sinusoidal cells depend on the phases of reparative regeneration of the liver.

Diurnal rhythm of mitosis in the corneal epithelium after splenectomy

Splenectomy was performed on CBA mice and the diurnal rhythm of mitotic activity in the corneal epithelium studied 5 days later, after preliminary injection of colcemid into the animals 3 h before sacrifice. In that part of the 24-h period that is characterized by a high mitotic index (from 3 a.m. to 3 p.m.) the index of c-mitoses in the experimental mice was significantly lower than in the control and the peak of mitotic activity was postponed. The duration of the phase of an increase in the number of cell divisions was shortened. The total number of c-mitoses in the control animals in the course of the 24-h period was 72.3% of the control number. The rate of physiological regeneration of the corneal epithelium was reduced in the splenectomized mice. It is suggested that the lymphoid system affects the entry of cells into mitosis in epithelial tissue and the formation of the wave of mitosis during the period of increased mitotic activity.

Repair and reorganization of minced cardiac muscle in the adult newt (Notophthalmus viridescens).

AbstractStudies of the response of adult mammalian and amphibian ventricle to injury have indicated the formation of a connective tissue scar in the place of the wounded or amputated muscle. It has been demonstrated that amphibian myocytes adjacent to a wound surface, unlike mammalian myocytes, have a proliferative capacity. In the present study, a minced cardiac muscle graft was placed into the adult newt ventricle in order to increase the number of myocytes near a wound surface. With such an increased number of reactive myocytes, it was thought a new wall consisting primarily of muscle might be formed. One‐sixteenth to one‐eighth of the ventricular apex was removed, minced and returned to the amputation surface of the ventricle. General histological and autoradiographic studies were conducted on two sham‐operated animals and on five experimental animals which were killed at 5, 10, 20, 30, 50 and 70 days after surgery. Major events of the repair and reorganization of minced cardiac muscle included blood clot formation followed by necrosis of the blood clot and much of the muscle graft. By ten days, an apparent coalescence of muscle fragments and continuity of ventricular and graft lumina were observed, although the graft area never formed an integrated unit with the wounded ventricular wall. The peak of mitotic activity (3.19%) and thymidine labeling (28.1%) of graft cells, including many cells which resembled cardiac myocytes, was observed at 20 days. At 30 days, the graft was observed as a continuous wall composed primarily of muscle fibers. Several 30‐, 50‐ and 70‐day grafts had rhythmic contractions. These results suggest that amphibian cardiac muscle has histogenetic and proliferative capacities not attributable to mammalian cardiac muscle.

A circadian rhythm of mitotic activity in the uterine luminal epithelium of the rat: effect of estrogen.

The study was designed to determine whether or not the rat uterine luminal epithelium exhibits a mitotic circadian rhythm and to ascertain the effect of estrogen treatment at different time periods on the uterine epithelial mitotic response. Immature rats were injected with either sesame oil (controls) or 60 ng of estradiol-17 beta at eight time periods and were necropsied 24 hours after treatment. Colchicine was administered IP two hours before autopsy. Peak mitotic activity was observed during the nocturnal phase (0300) for both the control and estrogen-treated rats. The nadirs were recorded during the diumal phase (1800 and 1200 for the control and estrogen groups, respectively). The differences between low and high values were 1100% for the control rhythm and 101% for the estrogen animals. The data demonstrate the existence of overt circadian rhythms in the uterine epithelium for both control and estrogentreated rats.

Mitotic reduction in rat liver exposed to ultrasound.

AbstractLivers in anesthetized rats were exposed to 1.90 mHz, 60 mW/cm2 (spatial average) continuous wave ultrasound for five minutes. Subsequent mitotic activity was stimulated by partial hepatectomy. About thirty hours following stimulation (the time of peak mitotic activity in control animals), exposed animals had mean mitotic indices ranging from 20 to 80% of control values.

Regeneration of rat tracheal epithelium after mechanical injury. I. The relationship between mitotic activity and cellular differentiation.

SummaryThe time of appearance of cytologic specialization in cells of regenerating rat tracheal epithelium was compared to the time of maximal mitotic response. Trauma sufficient to lethally injure most cells reaching the surface but sparing most basal cells resulted in a peak of mitotic activity from the 26th to the 30th hour following injury. The cells in the hyperplastic regenerating epithelium at the peak of mitosis had high nuclear-cytoplasmic ratios with little cytoplasmic or surface specialization. Ciliogenesis and mucinogen formation were not. seen in most cells until the 60th hr after the injury and there was little cell division at that time or later. Since cessation of mitosis does not follow or even coincide with the replenishment of the ciliated or goblet cell populations, the data does not support the hypothesis that control of cell division resides in the elaboration or release of a suppressor substance by the mature cells.

Ultrasonic Reduction of Mitotic Activity in Regenerating Rat Liver

In the adult rat liver there is ordinarily little cell division, but in response to an urgent demand for cells (as occurs after partial liver removal) large numbers of cells divide. The purpose of this study was to measure levels of mitotic activity (stimulated by partial hepatectomy) after ultrasonic treatment of the intact liver. Anesthetized male Charles River rats were treated with ultrasound and their mitotic indices compared with control animals. A continuous 2-MHz 100-mW/cm2 unfocused sound beam was oriented to impinge on the liver. The transducer was placed on the abdomen for a treatment time of five minutes. Temperature rises were less than 5°C at the transducer-abdomen junction and less than 1°C in the liver. Within two hours of treatment about 70% of the liver was surgically removed. Twenty-eight to 30 hours after partial hepatectomy (the time of peak mitotic activity in control animals) the mitotic index of the regenerating liver tissue was observed. Treated animals showed a reduction in mitotic index to about one-half that for controls. Statistical analysis showed the results to be significant at the 1% level. [This work was supported in part by grants from R. J. Reynolds Industries, Inc., and the USPHS, Food and Drug Administration, Grant RL-00129.]

Circadian rhythms in mitotic activity and 3H‐thymidine uptake in the duodenum: Effect of isoproterenol on the mitotic rhythm

AbstractMitotic activity in the duodenum of the rat and mouse exhibits a circadian periodicity with a peak in the rat between 1200 and 1500 hours and a sustained trough between 1800 and 0600. Scintillation counts revealed a similar rhythm in the total uptake of 3H‐thymidine by the rat duodenum with a sustained but fluctuating crest occurring between 0800 and 1800 and a trough between 1900 and 0100. In the mouse the peak mitotic activity occurred at 0900 and the trough at 1700. Isoproterenol completely abolishes the rhythm in mitosis in mouse duodenum, when injected exactly 28 hours previous to sacrifice. The results are discussed in relation to reports that deny a circadian rhythm in mitotic activity in the duodenum.