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At least 19 recordsLinked to original sources
PubMed1990

Molecular mechanisms underlying erythropoiesis: cycling activity of adult BFU-e relates to their requirement for c-myb function and potential for HbF synthesis.

Highly purified erythroid burst-forming units (BFU-e) from human embryonic liver, adult marrow and blood were manipulated in vitro by cytokine addition in order to explore their requirements for c-myb function and potential for fetal hemoglobin (HbF) synthesis, particularly as related to their cycling activity. c-myb is expressed at a minimal level and functionally required to a limited extent in quiescent adult BFU-e. However, c-myb is actively transcribed and stringently required for differentiation of actively cycling progenitors (embryonic BFU-e, embryonic and adult erythroid colony-forming units). The cycling activity of highly purified adult BFU-e, gradually enhanced by interleukin 3 (IL-3) addition, is strictly and directly related to both their functional requirements for c-myb and the level of myb mRNA expression in the progenitor population. It may be concluded that the transcriptional activity and the functional role of c-myb in early erythropoiesis are dependent upon the cycling activity of the erythroid progenitors. The reactivation of HbF synthesis in normal adult bursts, observed in the standard fetal calf serum-rich (FCS+) clonogenic system, is suppressed in cultures with a drastically limited growth of accessory cells (i.e., in FCS- or FCS+ Mo- conditions). In these cultures, addition of granulocyte/macrophage colony-stimulating factor (GM-CSF) or IL-3 induces a dose-related rise of gamma-chain synthesis, at least in part via a direct action at the BFU-e level. Preliminary studies involving priming of adult BFU-e with IL-3 in liquid phase suggest that the HbF potential is relatively low in quiescent BFU-e, but distinctly higher in actively cycling ones. It is postulated that the in vivo reactivation of HbF synthesis in bone marrow regeneration may be mediated via increased IL-3 and GM-CSF activity, leading to enhanced cycling and differentiation of BFU-e.

Adult↗
PubMed1989

Dependence of the Calvin cycle activity on kinetic parameters for the interaction of non-equilibrium cycle enzymes with their substrates.

Kinetic model studies and control analyses of the Calvin photosynthesis cycle have been performed to characterize the dependence of the cycle activity on maximum velocities and Km values for the interaction of the non-equilibrium cycle enzymes and ATP synthetase with their substrates under conditions of light and carbon dioxide saturation. The results show that Km values have no major influence on the cycle activity at optimal concentrations of external orthophosphate. The maximum cycle activity is controlled mainly by the catalytic capacities of ATP synthetase and sedoheptulose-bisphosphatase, and is close to the maximum cycle flux that can be supported by these two enzymes.

Chloroplasts↗
PubMed1976

Pentose cycle activity of the isolated perfused rat lung.

Pentose cycle activity was estimated in isolated rat lungs under varying conditions of glucose oxidation. Lungs were perfused for 100-120 min with a Krebs-Ringer-bicarbonate buffer, pH 7.4, containing 1-14C- or 6-14C-labeled glucose and ventilated with 95% O2:5% CO2. Based on 14C specific yields in either 14CO2 or perfusate lactate plus pyruvate, pentose cycle flux in control lungs was 5.3 mumol of glucose per hour per gram dry weight (11-12% of glucose utilization). Pentose cycle activity was unaltered by perfusion with 0.8 mM 2,4-dinitrophenol. Perfusion with phenazine methosulfate, an artificial hydrogen acceptor, resulations of the pentose cycle based on 14C yields in tissue lipids (both the fatty acid and deacylated fractions) gave values 2-3 times higher than measurements based on 14CO2. This study indicates that pentose cycle activity in the lung accounts for a significant fraction of glucose utilization and this pathway readily responds to metabolic perturbation.

Animals↗
PubMed1976

Sensitivity to radiation and cycle-active drugs as a function of stem cell compartment repletion.

We have studied the sensitivity of normal mouse hemopoietic tissue to radiation and cycle-active drugs in relation to stem cell compartment repletion. Recovery of erythropoiesis in endogenous spleen colonies, blood reticulocytes, and 30-day survivals were determined in mice after an initial large dose of partial-body irradiation. We found that the normal stem cell compartment is more sensitive to cycle-independent modes of therapy, like radiation and cyclophosphamide, than it is to cycle-active agents like cytosine arabinoside and methotrexate. The depleted stem cell compartment exhibits marked sensitivity to cycle-independent agents but less to cycle-active agents, which, however, suppress its recovery more than they do the normal. The overshoot phase of recovery is relatively resistant to either cycle-independent or cycle-active agents. A reticulocytosis following a reticulocytopenia signals the overshoot phase of stem cell compartment recovery and relatively increased resistance. These findings may prove useful in designing chemotherapy regimens and in anticipating marrow recovery in planning for supportive care in patients with neoplastic disease.

Animals↗
PubMed1976

Physiology and metabolism of pathogenic neisseria: tricarboxylic acid cycle activity in Neisseria gonorrhoeae.

Tricarboyxlic acid cycle activity was examined in Neisseria gonorrhoeae CS-7. The catabolism of glucose in N. gonorrheae by a combination of the Entner-Doudoroff and pentose phosphate pathways resulted in the accumulation of acetate, which was not further catabolized until the glucose was depleted or growth became limiting. Radiorespirometric studies revealed that the label in the 1 position of acetate was converted to CO2 at twice the rate of the label in the 2 position, indicating the presence of a tricarboxylic acid cycle. Growth on glucose markedly reduced the levels of all tricarboxylic acid cycle enzymes except citrate synthase (EC 4.1.3.7). Extracts of glucose-grown cells contained detectable levels of all tricarboxylic acid cycle enzymes except aconitase (EC 4.2.1.3), isocitrate dehydrogenase (EC 1.1.1.42), and a pyridine nucleotide-dependent malate dehydrogenase (EC 1.1.1.37). Extracts of cells capable of oxidizing acetate lacked only the pyridine nucleotide-dependent malate dehydrogenase. In lieu of this enzyem, a particulate pyridine nucleotide-independent malate oxidase (EC 1.1.3.3) was present. This enzyme required flavin adenine dinucleotide for activity and appeared to be associated with the electron transport chain. Radiorespirometric studies utilizing labeled glutamate demonstrated that a portion of the tricarboxylic acid cycle functioned during glucose catabolism. In spite of the presence of all tricarboxylic acid cycle enzymes, N. gonorrhoeae CS-7 was unable to grow in medium supplemented with cycle intermediates.

Acetates↗
PubMed1977

BCNU with and without cyclophosphamide, vincristine, and prednisone (COP) and cycle-active therapy in non-Hodgkin's lymphoma.

Two hundred and ninety-eight evaluable patients with non-Hodgkin's lymphoma were stratified according to histology, treated with either BCNU, cyclophosphamide, Oncovin (vincristine), and prednisone (BCOP) or cyclophosphamide, Oncovin (vincristine), and prednisone (COP), and evaluated at 3 months. Those with a good partial (PR) or complete response (CR) were then separated and randomized to be treated with either cycle-active therapy (methotrexate, cytosine arabinoside, and 6-thioguanine) or more induction therapy with COP or BCOP. Patients not achieving a good PR at 3 months received cycle-active therapy. The results indicate (a) that there is a significant advantage for good over poor histologies with regard to good PRs at 3 months; (b) that the addition of cycle-active therapy (as administered in this study) is of advantage when the tumor has been significantly reduced only for patients receiving COP induction; and (c) that BCOP has an advantage over COP in diffuse histiocytic lymphoma where the percentage of CRs, their durability, and subsequent survival are superior for patients treated with BCOP. Since this lymphoma accounts for about 25% of all non-Hodgkin's lymphoma patients, this regimen represents a useful tool for the chemotherapist.

Carmustine↗
PubMed1991

Antisense myb inhibition of purified erythroid progenitors in development and differentiation is linked to cycling activity and expression of DNA polymerase alpha.

These studies aimed to determine the expression and functional role of c-myb in erythroid progenitors with different cycling activities. In the first series of experiments the erythroid burst-forming unit (BFU-E) and colony-forming unit (CFU-E) populations from adult peripheral blood (PB), bone marrow (BM), and embryonic-fetal liver (FL) were treated with either c-myb antisense oligomers or 3H-thymidine (3H-TdR). A direct correlation was always observed between the inhibitory effect of anti-myb oligomers and the level of cycling activity. Thus, the inhibitory effect of antisense c-myb on the number of BFU-E colonies was 28.3% +/- 15.8% in PB, 53.4% +/- 9.3% in BM, and 68.2% +/- 24.5% in FL. Both adult and embryonic CFU-E were markedly inhibited (73.2% +/- 10.4% and 74.2% +/- 12.7%). Using highly purified PB progenitors, we observed a similar pattern, although with slightly lower inhibitory effects. In the 3H-TdR suicide assay the killing index of BFU-E was 8.9% +/- 4.2% in PB, 29.4% +/- 6.5% in BM, and 40.1% +/- 9.6% in FL. The values for adult and embryonic CFU-E were 55.7% +/- 7.9% and 60.98% +/- 6.6%, respectively. We then investigated the kinetics of c-myb mRNA level during the erythroid differentiation of highly purified adult PB and FL BFU-E, as evaluated in liquid-phase culture by reverse transcription-polymerase chain reaction. Adult erythroid precursors showed a gradual increase of c-myb mRNA from day 4 through day 8 of culture and a sharp decrease at later times, whereas the expression of c-myb mRNA and protein in differentiation embryonic precursors peaked 2 days earlier. In both cases, c-myb mRNA level peaked at the CFU-E stage of differentiation. Finally, highly purified adult PB BFU-E were stimulated into cycling by a 3-day treatment with interleukin-3 in liquid phase: both the sensitivity to c-myb antisense oligomers and the 3H-TdR suicide index showed a gradual, strictly parallel increase. Under the same experimental conditions a progressive increase of the mRNA level of DNA polymerase alpha was observed. These observations suggest that in early erythroid differentiation c-myb activation is associated with the progression of progenitors into the S phase of the cell cycle, as well as to the synthesis of DNA polymerase alpha.

Antisense Elements (Genetics)↗
PubMedDate not supplied

Phase II study of alternating cytoreductive and cycle-active combination chemotherapy for metastatic breast cancer.

Nineteen females with metastatic breast cancer (73% with visceral disease) treated with cyclophosphamide, Adriamycin, and 5-fluorouracil (CAF) cytoreduction followed by, and then alternated with, an intensive "cycle-active" regimen were evaluable. Sixteen of the 19 (84%) patients responded to CAF prior to initiation of the cycle-active regimen, and median remission duration for CAF responders was 50 weeks. The regimen was tolerable and the remission rates and durations were at least as good as those seen with CAF alone. This regimen is now being compared with CAF in a randomized trial of the Southeastern Cancer Study Group.

Adult↗
PubMed1992

Histone H3 transcription in Saccharomyces cerevisiae is controlled by multiple cell cycle activation sites and a constitutive negative regulatory element.

The promoters of the Saccharomyces cerevisiae histone H3 and H4 genes were examined for cis-acting DNA sequence elements regulating transcription and cell division cycle control. Deletion and linker disruption mutations identified two classes of regulatory elements: multiple cell cycle activation (CCA) sites and a negative regulatory site (NRS). Duplicate 19-bp CCA sites are present in both the copy I and copy II histone H3-H4 promoters arranged as inverted repeats separated by 45 and 68 bp. The CCA sites are both necessary and sufficient to activate transcription under cell division cycle control. A single CCA site provides cell cycle control but is a weak transcriptional activator, while an inverted repeat comprising two CCA sites provides both strong transcriptional activation and cell division cycle control. The NRS was identified in the copy I histone H3-H4 promoter. Deletion or disruption of the NRS increased the level of the histone H3 promoter activity but did not alter the cell division cycle periodicity of transcription. When the CCA sites were deleted from the histone promoter, the NRS element was unable to confer cell division cycle control on the remaining basal level of transcription. When the NRS element was inserted into the promoter of a foreign reporter gene, transcription was constitutively repressed and did not acquire cell cycle regulation.

Base Sequence↗
PubMed1977

[Rest-activity-cycle and stereotyped hand waving of a mentally defective child (author's transl)].

Stereotyped acts of a mentally defective girl. 6;6 years old, were observed from 6 a.m. till 8 p.m. during 16 days. Alternating phases of more or less frequent stereotyped hand waving showed a prominent periodicity of about 90 minutes. Sleep stages were also determined polygraphically during 10 nights. As statistically proved the mean peak-to-peak interval of the stereotyped activity at days corresponded to the mean REM- to REM period of nights. This suggests, that the stereotyped behavior of this child was driven by the basic rest activity cycle already described by Kleitman. The mean periodicity of sleep stages was represented by modeled rhythms adapted to the scored sleep stages. If the model rhythms of all 10 nights were extended backward to the preceding days, they paralleled the stereotyped activity. Half periods found in phase with REM stages corresponded to the maxima of the stereotyped activity. It will be discussed that the basic rest activity cycle triggers sensory as well as motor mechanisms characterizing both the phases of enhanced stereotyped activity and REM stages.

Behavior↗
PubMed1990

Plasma melatonin exhibits a diurnal secretion in the common marmoset (Callithrix jacchus): relationship to the rest-activity cycle.

The secretion of plasma melatonin exhibits a diurnal variation in the common marmoset (Callithrix jacchus jacchus) (n = 12) with mean values of 125.8 fmol/ml during darkness and below assay sensitivity (mean 70.5 fmol/ml) during the light period. Both melatonin secretion and the rest activity cycle appeared to be phase advanced with relation to the light dark cycle which is consistent with an endogenous circadian period (tau) of less than 24 h in this species.

Activity Cycles↗
PubMed1977

Basic rest activity cycle and stereotyped behavior of a mentally defective child.

Stereotyped acts of a mentally defective girl, 6 1/2 years old, were observed from 6 a.m. til 8 p.m. during 16 days. Alternating phases of more or less frequent hand waving showed intervals of about 1 1/2 hours. Sleep stages were also determined by polygraphic recordings during 10 nights. As statistically proved the mean peak-to-peak interval of stereotyped activity at days corresponded with the mean REM-to-REM period of consecutive nights. This suggests, that the stereotyped hand waving of this child was driven by the BASIC REST ACTIVITY CYCLE (BRAC) already described by Kleitman. The mean periodicity of sleep cycles was represented by model rhythms adapted to the scored sleep stages. If the model rhythms of all 10 nights were extended backward to the preceding days, they paralleled the stereotyped activity. Thereby half periods found in phase with REM-stages approximatly corresponded to maxima of stereotyped activity. It will be discussed that the BRAC triggers motor and sensory mechanisms characterizing both the phases of enhanced stereotyped activity at day and REM stages at night.

Activity Cycles↗
PubMed1979

Statistical methods for analyzing data on daily activity cycles of primates.

Many field studies on primates have recently been carried out in which quantitative data have been collected using instantaneous scan sampling techniques. However, data collected in this manner are difficult to analyze statistically because of the problem of independence of samples, and a number of investigators have analyzed such data incorrectly. In this paper, we evaluate such analyses and suggest alternative techniques that may be more appropriate. Examples are drawn from data on daily activity cycles of Lemur catta and Lemur fulvus.

Activity Cycles↗
PubMed1992

Effects of prenatal exposure to cocaine on the rest-activity cycle of the preweanling rat.

Either 45 or 60 mg/kg cocaine HCl was administered from days 8-22 of gestation. Pair-fed and nontreated groups served as controls and all treated and control litters were fostered at birth to untreated dams. To examine whether cocaine produces effects on the rest-activity cycle of the offspring, groups of three littermates from each of the treated and control groups were tested for an 8-h observation period on electronic activity monitors at 22 days of age. Neither activity level nor the rest-activity pattern were affected by cocaine. These findings are discussed in relation to previous studies of cannabis and methadone effects on the rest-activity measure.

Animals↗
PubMed1991

Folate-deficient human lymphoblasts: changes in deoxynucleotide metabolism and thymidylate cycle activities.

Peripheral blood lymphocytes of healthy volunteers cultured with phytohaemagglutinin in folate-deficient medium exhibit megaloblastic maturation with reduced intracellular folate content. We have employed this in vitro model for megaloblastic maturation to determine accompanying changes in cellular thymidylate cycle activities and deoxynucleotide levels. Folate-deficient cells exhibit a two-fold increase in thymidine kinase and thymidylate synthase activities. These increased activities were reduced to those of folate-replete cells by co-culture of folate-deficient cells with thymidine. Folate deficiency was accompanied by reduced cellular levels of thymidine triphosphate (TTP) and deoxyguanosine triphosphate (dGTP). Exogenous deoxyuridine produced no increase in the reduced levels of TTP of folate-deficient cells but effected a two-fold increase in cellular deoxycytidine triphosphate. Exogenous thymidine increased the reduced TTP levels of folate-deficient cells and corrected the reduced dGTP level; the increase in cellular TTP accompanying exogenous thymidine was more pronounced in folate-deficient cells. These in vitro findings are compatible with a block in de novo thymidylate synthesis and explain in part the reported in vivo changes for the deoxynucleotide pool in megaloblastic marrow cells due to folate or vitamin B12 deficiency.

Deoxyadenine Nucleotides↗
PubMedDate not supplied

The effects of prenatal exposure to delta-9-tetrahydrocannabinol on the rest-activity cycle of the preweanling rat.

Either 15 or 50 mg/kg of delta-9-tetrahydrocannabinol (delta-9-THC) was administered from Day 2 through Day 22 of gestation. Pair-fed (0 mg/kg) and nontreated groups served as controls and all treated and control litters were fostered at birth to untreated dams. To examine whether delta-9-THC produces effects on the rest-activity cycle of the offspring, groups of 3 littermates from each of the treated and control groups were tested for an 8 hr observation period on electronic activity monitors at 17, 22 and 30 days of age. Whereas all treated and control groups showed age-dependent changes in activity, neither activity level nor the rest-activity pattern were affected by delta-9-THC. These findings are discussed in relation to neurobehavioral studies of activity changes following prenatal exposure to cannabis.

Animals↗
PubMed1992

Repetitive calcium transients and the role of calcium in exocytosis and cell cycle activation in the mouse egg.

The role of calcium in cortical granule exocytosis and activation of the cell cycle at fertilization was examined in the mouse egg using the calcium chelator BAPTA (1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid) and the fluorescent calcium indicator fluo-3. BAPTA and fluo-3 were introduced into zona-free mouse eggs by a 30-min incubation with 0.01-50 microM BAPTA acetoxymethyl ester (AM) and/or 1-20 microM fluo-3 AM prior to in vitro fertilization. Incubation of eggs in greater than or equal to 5.0 microM BAPTA AM inhibited cortical granule exocytosis in all cases. Introduction of the calcium chelator into the egg blocked second polar body formation at greater than or equal to 1.0 microM BAPTA AM. Sperm entry occurred in all eggs regardless of the BAPTA AM concentration. Sperm induce a large transient increase in calcium lasting 2.3 +/- 0.6 min, followed by repetitive transients lasting 0.5 +/- 0.1 min and occurring at 3.4 +/- 1.4-min intervals. Incubation with greater than or equal to 5.0 microM BAPTA AM inhibited all calcium transients. Introduction of BAPTA also inhibited calcium transients, exocytosis, and the resumption of meiosis following application of the calcium ionophore A23187 or SrCl2, which activate eggs. These results demonstrate that the calcium increase at fertilization is required for cortical granule exocytosis and resumption of the cell cycle in a mammalian egg.

Animals↗