Arrest of cell cycle progression of HeLa cells in the early G1 phase in K+-depleted conditions and its recovery upon addition of insulin and LDL

Cell cycle progression of synchronized HeLa cells was studied by measuring labeling of the nuclei with [³H]thymidine. The progression was arrested in a chemically defined medium in which K⁺ was replaced by Rb⁺ (Rb-CDM) but was restored upon addition of insulin and/or low density lipoprotein (LDL). Cells started DNA synthesis 12 hr after addition of insulin and/or LDL, regardless of the time of arrest, suggesting their arrest early in the G1 phase. After incubation of cells in Rb-CDM containing insulin or LDL singly for 3, 6, or 9 hr, replacement of the medium by that without an addition resulted in marked delay in entry of cells into the S phase, but in its replacement by medium containing both agents, the delay was insignificant. Synthesis of bulk protein, estimated as increase in the cell volume, was not strongly inhibited. From these results we conclude that cell cycle progression of HeLa cells in K^?-depleted CDM is arrested early in the G1 phase and that the arrest is due to lack of some protein(s) required for entry into the S phase that is synthesized in the early G1 phase.     

Loss of chloroplast-localized NAD kinase causes ROS stress in Arabidopsis thaliana

Journal of Plant Research - Chloroplast-localized NAD kinase (NADK2) is responsible for the production of NADP+, which is an electron acceptor in the linear electron flow of photosynthesis. The...     

Control by Light of Hypocotyl Elongation and Levels of Endogenous Gibberellins in Seedlings of Lactuca sativa L.

Four 13-hydroxygibberellins, gibberellin A₁ (GA₁), 3-epi-GA₁,GA₁₉ and GA₂₀ were identified by full-scan GC/MS in extractsof lettuce seedlings (Lactuca sativa L. cv. Grand Rapids). Theresults suggest that the early-13-hydroxylation biosyntheticpathway to GA₁ functions in the lettuce seedlings. It was alsofound that GA₁ is active per se in the control of hypocotylelongation in lettuce seedlings. To investigate the relationshipbetween control by light of hypocotyl elongation and levelsof endogenous GAs in lettuce, endogenous levels of GAs werequantified by radioimmunoassay in seedlings that had been grownfor 5 days in the dark (5D) and in those that had been grownfor 4 days in the dark and then under white light for 1 day(4D1L). The endogenous level of GA₁ in the upper and lower partsof hypocotyls in 5D seedlings was about four times higher thanthat in 4D1L seedlings. The response of explants (hypocotylsegments with cotyledons) from dark-grown seedlings to GA₁ isknown to be similar in the dark and under white light when theexplants are treated with inhibitors of the biosynthesis ofGA. Therefore, the above information suggests that the highlevel of GA₁ in hypocotyls of dark-grown seedlings is responsiblefor the rapid elongation of hypocotyl, while irradiation bywhite light decreases the endogenous level of GA₁ in the hypocotylswith a resultant decrease in the rate of hypocotyl elongation. (Received March 13, 1992; Accepted May 21, 1992)     

Differential regulation of IgA production by TGF-beta and IL-5: TGF-beta induces surface IgA-positive cells bearing IL-5 receptor, whereas IL-5 promotes their survival and maturation into IgA-secreting cells.

Transforming growth factor beta (TGF-beta) and IL-5 have been shown to augment IgA production by LPS-stimulated murine B cells. We investigated the effect of TGF-beta on the expression of surface Ig-isotype and IL-5 receptor on LPS-stimulated B cells. TGF-beta increased the proportion of both surface IgA-positive (sIgA+) B cells and sIgG2b+ B cells and enhanced IgA and IgG2b production by LPS-stimulated B cells. TGF-beta synergized with IL-5 only for IgA production of the seven Ig-isotypes and in combination with IL-5 caused a significant increase in the proportion of sIgA+ B cells up to 17.4%. In contrast, IL-5 decreased the proportion of sIgG2b+ B cells and sIgG3+ B cells and inhibited the production of IgG2b and IgG3 by LPS-stimulated B cells. About 50% of sIgA+ cells induced by TGF-beta expressed IL-5 receptor. They secreted peak levels of IgA and seemed to maintain long viability in the presence of IL-5; whereas TGF-beta had the opposite effects on sIgA+ B cells and down-regulated the IL-5 receptor expression. These results indicate that TGF-beta increases the number of sIgA(+)- and IL-5 receptor-positive B cells which respond to IL-5 giving rise to IgA-secreting cells and also support the notions that TGF-beta preferentially induces switching to sIgA+ B cells and IL-5 induces the maturation of postswitch sIgA+ B cells into IgA-secreting cells in a stepwise fashion.     

Development of human cerebellar nuclei. Morphometric study

The morphometric development of the human cerebellar nuclei was examined in 9 fetuses (16-40 weeks of gestation; WG), an infant (2 months old) and 2 adults (16 and 63 years old). With the morphological observation of serial sections of the brain containing the cerebellar nuclei, the authors measured sections to get several morphometric parameters: the volume of nuclear column and number, packing density and cell body area of neurons. Each nucleus (dentate, emboliform, globose and fastigial nucleus) was recognized even at 16 WG. Nerve cells containing Nissl bodies were observed in all nuclei after 23 WG. Degenerative changes were detected in some neurons for every nucleus at 21 and 23 WG. Three stages were observed in the developmental course of nuclear volume and neuronal packing density: the primary or undifferentiated stage at 16 WG, the secondary stage with variability at 21-32 WG and the tertiary stage with monotonous increase (nuclear volume) or gradual decrease (neuronal packing density) after 35 WG. No significant correlation between neuronal number and gestational age was noticed for every nucleus. The analysis of cell body area (neuronal size) demonstrated that the dentate neurons developed after the intermediate or fastigial neurons. It is concluded that there is a critical period between slightly before 20 WG and slightly after 30 WG, matched with the secondary stage in the development of the cerebellar nuclei.     

Direct evidence that an increase in aortic norepinephrine level in response to insulin-induced hypoglycemia is due to increased adrenal norepinephrine output

This study reports on the major source of circulating norepinephrine that is known to increase, progressively, during sustained hypoglycemia induced by intravenous insulin administration. Plasma concentrations of epinephrine, norepinephrine, and dopamine were simultaneously determined for adrenal venous and aortic blood in dogs anesthetized with sodium pentobarbital. The model used allowed us to perform a functional adrenalectomy (ADRX), while continuously monitoring the adrenal medullary secretory function. Under basal conditions, the net output (micrograms/min) of adrenal epinephrine, norepinephrine, and dopamine were 0.169 +/- 0.074, 0.067 +/- 0.023, and 0.011 +/- 0.003, respectively. Plasma concentrations (ng/mL) of aortic epinephrine, norepinephrine, and dopamine were 0.132 +/- 0.047, 0.268 +/- 0.034, and 0.034 +/- 0.009. Following insulin injection (0.15 IU/kg, i.v.), the net output (micrograms/min) of adrenal epinephrine, norepinephrine, and dopamine increased gradually (p less than 0.05), reaching the values of 0.918 +/- 0.200, 0.365 +/- 0.058, and 0.034 +/- 0.007 30 min after insulin administration. Similarly, aortic epinephrine, norepinephrine, and dopamine concentrations (ng/mL) increased significantly (p less than 0.05) to 0.702 +/- 0.144, 0.526 +/- 0.093, and 0.066 +/- 0.024. The aortic glucose concentration (mg/dL) was diminished from 81.8 +/- 4.1 to 36.9 +/- 3.4 (p less than 0.01). After taking the blood sample at 30 min following insulin administration, ADRX was immediately performed. Five minutes after the onset of ADRX, the net output (micrograms/min) of adrenal epinephrine, norepinephrine, and dopamine increased further to 1.707 +/- 0.374 (p less than 0.05), 0.668 +/- 0.139 (p less than 0.05), and 0.052 +/- 0.017.(ABSTRACT TRUNCATED AT 250 WORDS)     

Growth Characteristics and Intraspecies Host Specificity of a Large Virus Infecting the Dinoflagellate Heterocapsa circularisquama

The growth characteristics and intraspecies host specificity of Heterocapsa circularisquama virus (HcV), a large icosahedral virus specifically infecting the bivalve-killing dinoflagellate H. circularisquama, were examined. Exponentially growing host cells were more sensitive to HcV than those in the stationary phase, and host cells were more susceptible to HcV infection in the culture when a higher percent of the culture was replaced with fresh medium each day, suggesting an intimate relationship between virus sensitivity and the physiological condition of the host cells. HcV was infective over a wide range of temperatures, 15 to 30°C, and the latent period and burst size were estimated at 40 to 56 h and 1,800 to 2,440 infective particles, respectively. Transmission electron microscopy revealed that capsid formation began within 16 h postinfection, and mature virus particles appeared within 24 h postinfection at 20°C. Compared to Heterosigma akashiwo virus, HcV was more widely infectious to H. circularisquama strains that had been independently isolated in the western part of Japan, and only 5.3% of the host-virus combinations (53 host and 10 viral strains) showed resistance to viral infection. The present results are helpful in understanding the ecology of algal host-virus systems in nature.     

Karyotyping by PFGE of clinical isolates of Sporothrix schenckii

Abstract From October 1991 to December 1992 we had eight patients with sporotrichosis at Tsukuba University Hospital in Japan. With 8 strains isolated from these patients, PFGE (pulsed-field gel electrophoresis) analyses were carried out to examine whether the karyotype of S. schenckii is distinguished by our method and whether this molecular approach is a useful means of biotyping of S. schenckii strains. Chromosomes were separated by contour-clamped homogeneous electric field (CHEF) gel electrophoresis. The strains had six to eight chromosomes and a total genome size was approx. 28 Mbp. Although these karyotypes of all the isolates looked closely similar to each other, they were grouped into three types.     

Electronic structures of donor-acceptor polymers based on polythiophene,polyfuran and polypyrrole

Theoretical results on the geometric and electronic structures of some donor-acceptor polymers based on polythiophene (X=S), polyfuran (X=O) and polypyrrole (X=NH) were obtained, using a one-dimensional tight-binding self-consistent field crystal-orbital (SCF-CO) method at the MNDO-AM1 level of approximation. The repeat unit of these polymers consits of a bithiophene, furan or bipyrrole unit bridged by an electron-accepting group or. The optimized geometries of the polymers show a strong dependence on the nature of the electron donating group X. All the polymers studied are predicted to have band gap values ranging between 1 eV and 2 eV. An analysis of their -bond order data and of the patterns of their frontier orbitals shows they have benzenoid-like electronic structures.