Cell size and cell division of the anterior pituitary: time course in the growing rat

Pituitary cells increase their numbers more than 3-fold during the 1st 10 days of life while maintaining the same cell size ratios. In the 25-day-old animal, the rate of cell division slows and there is a slight increase in the number of large cells. An increase in adult weight is attributed to hyperplasia and a shift to a population of larger cells.     

Quantitative ultrastructural features of maturing mononuclear phagocytes in rat peritoneal fluids.

Ultrastructural features of the in vivo transformation of macrophage congeners in resident and adjuvant-induced peritoneal populations are evaluated by sterological methods. Maturation involves an increase in cell size by the differential hypertrophy of subcellular compartments, notably remaining cytoplasm, nucleus and lysosome-like granules. Larger cells have more and larger granules, more mitochondria and a greater plasmalemmal surface. In contrast, adjuvant activation tends to produce fewer granules and a nett loss of surface membrane.     

Quantitative ultrastructural features of maturing mononuclear phagocytes in rat peritoneal fluids

Summary Ultrastructural features of the in vivo transformation of macrophage congeners in resident and adjuvant-induced peritoneal populations are evaluated by stereological methods. Maturation involves an increase in cell size by the differential hypertrophy of subcellular compartments, notably remaining cytoplasm, nucleus and lysosome-like granules. Larger cells have more and larger granules, more mitochondria and a greater plasmalemmal surface. In contrast, adjuvant activation tends to produce fewer granules and a nett loss of surface membrane.I wish to thank Professor R. Barer for his advice and helpful criticism. Thanks are also due to the Wellcome Trust for financial support.     

Regulation of the type III InsP3 receptor and its role in beta cell function

The type III inositol 1,4,5-trisphosphate receptor (InsP3R) is an important intracellular calcium (Ca2+) release channel in the pancreatic beta cell. Pancreatic beta cells secrete insulin following a characteristic change in membrane potential that leads to an increase in cytoplasmic Ca2+. Both extracellular Ca2+ and Ca2+ mobilized from InsP3-sensitive stores contribute to this increase. RIN-m5F cells, an insulin-secreting beta cell line, preferentially express the type III InsP3R. These cells have been useful in determining the regulatory properties of the type III InsP3R and the role of this isoform in an intact cell. The type III InsP3R is ideal for signal initiation because high cytoplasmic Ca2+ does not inhibit its activity. Altered insulin secretion, the result of changes in Ca2+ handling by the beta cell, has significant clinical consequences.     

Unscheduled CDK1 activity in G1 phase of the cell cycle triggers apoptosis in X-irradiated lymphocytic leukemia cells

Cyclin-dependent kinase 1 (CDK1) is a major component of the cell cycle progression engine. Recently, several investigations provided evidence demonstrating that unscheduled CDK1 activation may also be involved in apoptosis in cancerous cells. In this article, we demonstrate that X-ray irradiation induced G1 arrest in MOLT-4 lymphocytic leukemia cells, the arrest being accompanied by reduction in the activity of CDK2, but increased CDK1 activity and cell apoptosis in the G1 phase. Interestingly, this increase in CDK1 and apoptosis by ionizing radiation was prevented by pretreatment with the CDK1 inhibitor, roscovitine, suggesting that CDK1 kinase activity is required for radiation-induced apoptotic cell death in this model system. Furthermore, cyclin B1 and CDK1 were detected co-localizing and associating in G1 phase MOLT-4 cells, with the cellular lysates from these cells revealing a genotoxic stress-induced increase in CDK1 phosphorylation (Thr-161) and dephosphorylation (Tyr-15), as analyzed by postsorting immunoprecipitation and immunoblotting. Finally, X-irradiation was found to increase Bcl-2 phosphorylation in G1 phase cells. Taken together, these novel findings suggest that CDK1 is activated by unscheduled accumulation of cyclin B1 in G1 phase cells exposed to X-ray, and that CDK1 activation, at the wrong time and in the wrong phase, may directly or indirectly trigger a Bcl-2-dependent signaling pathway leading to apoptotic cell death in MOLT-4 cells. Received 30 March 2006; received after revision 23 June 2006; accepted 24 August 2006 J. Wu and Y. Feng contributed equally to this work.     

Cellular control of the tick-borne virus antigen production in persistently infected cell culture

Summary The influence of inhibition or stimulation of cellular DNA synthesis on tick-borne virus antigen production in persistently infected cell culture was studied. Either mitomycin C or cytosine-arabinoside caused cessation of antigen-containing cell number increase. Stimulation of cellular DNA synthesis by growth medium change increased the level of antigen-containing cells. When HEp-2-Sof culture was synchronized, a correlation was observed between the entrance of cells into DNA synthesis phase and the increase of proportion of antigen-containing cells.     

Novel oscillations in cell suspensions ofDictyostelium discoideum

Summary With a light-scattering technique, two novel rhythms were discovered in cell suspensions ofDictyostelium discoideum. One is a damped oscillation with a period of 2 to 2.5 min (at 23°C) induced by folate in EDTA-dissociated undifferentiated cells. The other is a sinusoidal oscillation with a period of about 12 min occasionally observed with late differentiated cells. Obviously, the repertoire of rhythms of this simple eukaryotic organism is larger than previously assumed.     

Regulation of caldesmon activity by Cdc2 kinase plays an important role in maintaining membrane cortex integrity during cell division

To study the mitosis-specific phosphorylation of caldesmon (CaD), we generated a mutant of the C-terminal fragment (amino acids 244–538) of human fibroblast CaD (CaD39-6F), as well as a mutant of the full-length CaD (CaD-6F), in which all six potential phosphorylation sites for Cdc2 kinase were abolished. The mitotic CaD39-6F-overexpressing cells required more time to progress from anaphase start to 50% cytokinesis, exhibited larger size, and abnormally formed numerous small blebs. In contrast, overexpression of the wild-type C-terminal fragment of CaD (CaD39) did not result in abnormal bleb formation, but led to larger size and prolonged the time requirement between anaphase start and 50% cytokinesis. Similar abnormal blebs were also observed in the CaD-6F-overexpressing cells. CaD-6F-overexpressing cells did not show larger size but required more time to progress from anaphase start to 50% cytokinesis. These results suggest that mitosis-specific phosphorylation of CaD plays a role in inhibiting bleb formation and that the N-terminal fragment of CaD is required for cell size determination. Received 4 September 2002; received after revision 25 November 2002; accepted 4 December 2002     

The subcommissural organ of the lizardLacerta s. sicula raf. ultrastructure during the winter

Summary The secretory activity of the SCO cells ofLacerta s.sicula Raf. is strongly reduced during the winter. Such reduction is documented by the decrease of the number of secretory granules type A and B described in previous papers in the summer SCO cells. Also the sacks of RER filled with electron-dense material (type C secretion) are very few; in their place there are, in the basal region of the cells, large vacuoles. In the distal region of the cells, at the free cell surface, a pronounced increase in the number of microvilli is noticed.     

Cellular control of the tick-borne virus antigen production in persistently infected cell culture.

The influence of inhibition or stimulation of cellular DNA synthesis on tick-borne virus antigen production in persistently infected cell culture was studied. Either mitomycin C or cytosine-arabinoside caused cessation of antigen-containing cell number increase. Stimulation of cellular DNA synthesis by growth medium change increased the level of antigen-containing cells. When HEp-2-Sof culture was synchronized, a correlation was observed between the entrance of cells into DNA synthesis phase and the increase of proportion of antigen-containing cells.     

Activation-induced cellular accumulation of histamine in immature but not mature murine mast cells

Mast cell activation involves the rapid release of inflammatory mediators, including histamine, from intracellular granules. The cells are capable of regranulation and multiple rounds of activation. The goal of this study was to determine if there are changes in the content of pre-formed mast cell mediators after a round of activation. After 24 h, the histamine content of bone marrow-derived mast cells (BMMC), but not that of peritoneal mast cells, exceeded the amount in resting cells. Accumulation of histamine in BMMC peaked at 72 h of activation, and returned toward preactivation levels by 96 h. The increase in histamine content was accompanied by an increase in the gene expression of histidine decarboxylase. No increases in beta hexosaminidase or murine mast cell protease-6 were observed. These findings indicate that BMMC respond to activation by increasing total cell-associated histamine content. This increase may be important to the response of these cells upon subsequent exposure to antigens.     

Histochemical response of alkaline phosphatase activity during the healing of cutaneous wounds in a cat-fish

Summary The activity of alkaline phosphatase in the various tissue components of the regenerating skin of a cat-fish has been studied. A marked increase in alkaline phosphatase activity in the cells of migrating epithelium has been correlated with their highly active state. High alkaline phosphatase in the basal cells after 2 days has been found to have played an important role in cell multiplication and differention. The functional significance of this enzyme is discussed in relation to the granulation tissue formation.     

Immunohistochemical individualization of adenohypophyseal thyrotropic cells in the monkey Macaca irus, using a human anti-beta-TSH antibody

Using the indirect immunofluorescence technique and an antiserum against the specific beta subunit of human TSH, selective immunocytochemical staining was localized in a cell population of the pars distalis of the monkey Macaca irus. These thyrotropic cells, which were positive to aldehyde fuchsin, Alcian blue, and PAS, were localized on the one hand in the ventro-medial zone of the pars distalis, especially alongside the large vessels of this region, and on the other in the zona tuberalis, i. e. at the bottom of the pars tuberalis. Some cells, sparsely distributed, were seen in the posterior part of the lateral lobes of the pars distalis, in the vicinity of the pars intermedia. No thyrotropic cells were encountered in pars tuberalis. Pars intermedia and posterior lobe contained no cells immunoreactive to beta-hTSH. In females, the thyrotropic cells were more numerous and larger than in males. Generally the thyrotropic cells were round or oval in shape, sometimes they were polygonal.     

Lipid peroxidation caused by chinoform-ferric chelate in cultured neural retinal cells

Incorporation of chinoform-ferric chelate was demonstrable in cultured neural retinal cells of chick embryos after 1 h of incubation, and the lipid peroxide level in the cells was increased strikingly 1 h thereafter. On the other hand, free ferric ions were scarcely incorporated into the cells, and a significant increase in the lipid peroxide level in the cells was not observed. These data indicate that chinoform is carrier of iron for its passage through cell membranes and that the incorporated iron induces lipid peroxidation which in turn leads to neural cell degeneration.     

Differential interaction of 2,4,6-trinitrobenzenesulfonic (TNBS) and 2,4-dinitrobenzenesulfonic (DNBS) acids on mouse lymphocytes]

Modifications of lymphoid cells with dinitro-2,4 phenylsulfonic acid (DNBS) or trinitro-2,4,6 phenylsulfonic acid (TNBS) have been studied. TNBS action always produces an electrophoretic mobility increase in relation with the amount of amino-groups, according to the cell type. DNBS action produces an electrophoretic mobility increase for B cells of spleen and a decrease for T cells of spleen and thymic cells. The hydrophobic fluorescent probe 1-anilino-8-naphthalene sulphonate used to study conformational changes of cells revealed a slight fluorescence decrease for TNP-modified cells and an important fluorescence increase for DNP-modified cells.     

Survival of BSC-1 cells through the maintenance of cell volume brought about by epidermal growth factor depends on attachment to the substratum

Addition of epidermal growth factor to culture medium without calf serum suppressed the increase in cell volume and then enhanced the survival of BSC-1 cells attached to culture dishes. However, these effects of epidermal growth factor were not observed in the case of cells on dishes coated with heat-denatured bovine serum albumin.     

Morphological effects of serotonin and ketanserin on embryonic chick skin in vitro

Cell and organotypical cultures are used to study the direct effect of serotonin and of ketanserin, a serotonin antagonist, on dermal and epidermal cells of embryonic chick skin. Ketanserin stimulates the increase in cell number and inhibits the differentiation, whereas serotonin stimulates differentiation and inhibits the increase in cell number.     

Survival of BSC-1 cells through the maintenance of cell volume brought about by epidermal growth factor depends on attachment to the substratum

Summary Addition of epidermal growth factor to culture medium without calf serum suppressed the increase in cell volume and then enhanced the survival of BSC-1 cells attached to culture dishes. However, these effects of epidermal growth factor were not observed in the case of cells on dishes coated with heat-denatured bovine serum albumin.     

Effects of gonadotropin-releasing hormone (LH-RH) on the pars distalis and testis of the Skipper frog,rana cyanophlyctis (Schn.)

Summary Administration of LH-RH to adult male Skipper frogs resulted in marked hypertrophy and degranulation of basophils-2 (B2) in the pars distalis of the pituitary and a significant increase in their nuclear and cellular area. Concomitantly, there is a significant increase in the relative weight of the testes, in the number of cell nests containing secondary spermatogonia and primary spermatocytes, and in the nuclear diameter of the Leydig cells. There is also an increase in the ⁵-3-hydroxysteroid dehydrogenase and glucose-6-phosphate dehydrogenase activities in the Leydig cells. The results indicate that the B2 cells are gonadotrops and the hormone(s) secreted by B2 cells regulate the spermatogenetic and steroidogenic activity of the testis inR. cyanophlyctis.The free gift of LH-RH from NIH is gratefully acknowledged. Authors are grateful to CSIR, New Delhi, for the award of a SRF to the first author and to Karnatak University, Dharwad for providing laboratory facilities.     

Regulation of the cell cycle following DNA damage in normal and Ataxia telangiectasia cells

A proportion of the population is exposed to acute doses of ionizing radiation through medical treatment or occupational accidents, with little knowledge of the immedate effects. At the cellular level, ionizing radiation leads to the activation of a genetic program which enables the cell to increase its chances of survival and to minimize detrimental manifestations of radiation damage. Cytotoxic stress due to ionizing radiation causes genetic instability, alterations in the cell cycle, apoptosis, or necrosis. Alterations in the G1, S and G2 phases of the cell cycle coincide with improved survival and genome stability. The main cellular factors which are activated by DNA damage and interfere with the cell cycle controls are: p53, delaying the transition through the G1-S boundary; p21^WAF1/CIPI, preventing the entrance into S-phase; proliferating cell nuclear antigen (PCNA) and replication protein A (RPA), blocking DNA replication; and the p53 variant protein p53as together with the retinoblastoma protein (Rb), with less defined functions during the G2 phase of the cell cycle. By comparing a variety of radioresistant cell lines derived from radiosensitive ataxia talangiectasia cells with the parental cells, some essential mechanisms that allow cells to gain radioresistance have been identified. The results so far emphasise the importance of an adequate delay in the transition from G2 to M and the inhibition of DNA replication in the regulation of the cell cycle after exposure to ionizing radiation.