Cell size homeostasis under the circadian regulation of cell division in cyanobacteria

Bacterial cells maintain their characteristic cell size over many generations. Several rod-shaped bacteria, such as Escherichia coli and the cyanobacteria Synechococcus elongatus, divide after adding a constant length to their length at birth. Through this division control known as the adder mechanism, perturbation in cell length due to physiological fluctuation decays over generations at a rate of 2^-1 per cell division. However, previous experiments have shown that the circadian clock in cyanobacteria reduces cell division frequency at a specific time of day under constant light. This circadian gating should modulate the division control by the adder mechanism, but its significance remains unknown. Here we address how the circadian gating affects cell length, doubling time, and cell length stability in cyanobacteria by using mathematical models. We show that a cell subject to circadian gating grows for a long time, and gives birth to elongated daughter cells. These elongated daughter cells grow faster than the previous generation, as elongation speed is proportional to cell length and divide in a short time before the next gating. Hence, the distributions of doubling time and cell length become bimodal, as observed in experimental data. Interestingly, the average doubling time over the population of cells is independent of gating because the extension of doubling time by gating is compensated by its reduction in the subsequent generation. On the other hand, average cell length is increased by gating, suggesting that the circadian clock controls cell length. We then show that the decay rate of perturbation in cell length depends on the ratio of delay in division by the gating τ_G to the average doubling time τ₀ as [Formula: see text] . We estimated τ_G≈2.5, τ₀≈13.6 hours, and τ_G/τ₀≈0.18 from experimental data, indicating that a long doubling time in cyanobacteria maintains the decay rate similar to that of the adder mechanism. Thus, our analysis suggests that the acquisition of the circadian clock during evolution did not impose a constraint on cell size homeostasis in cyanobacteria.

Adsorbed states of chlorophenol on Cu(110) and controlled switching of single-molecule junctions

A molecular junction of substituted benzene (chlorophenol) is fabricated and controlled by using a scanning tunneling microscope (STM). Prior to the junction formation, the bonding geometry of the molecule on the surface is characterized by STM and electron energy loss spectroscopy (EELS). EELS shows that the OH group of chlorophenol is dissociated on Cu(110) and that the molecule is bonded nearly flat to the surface via an O atom, with the Cl group intact. We demonstrate controlled contact of an STM tip to the "available" Cl group and lift-up of the molecule while it is anchored to the surface via an O atom. The asymmetric bonding motifs of the molecule to the electrodes allow for reversible control of the junction.

Phase I Trial of Nedaplatin and Paclitaxel for Patients with Non-Small Cell Lung Cancer

A phase I study was conducted to evaluate the maximum tolerated dose and feasibility of combination with nedaplatin (NDP) and paclitaxel in patients with non-small cell lung cancer (NSCLC). Fifteen patients under 75 years old, with unresectable NSCLC who had not previously received chemotherapy or radiotherapy, with a performance status of 0-1, were enrolled. The dose escalation levels (NDP/Paclitaxel; mg/m2 day 1) were 80/150 (level 1), 80/180 (level 2), 90/180 (level 3) and repeated every 28 days. All patients receiving level 3 had dose-limiting toxicity. One patient developed grade 4 neutropenia with infection, two had incomplete recovery of neutropenia and thrombocytopenia by the 28th day after the first cycle of chemotherapy. Non-hematologic toxicities, including nephrotoxicity, nausea/vomiting, alopecia, and hypersensitivity reaction, were tolerated. Three of the 15 patients achieved partial responses. We concluded that the recommended dose was paclitaxel 180 and NDP 80 mg/m2 due to the hematologic toxicity.

Imaging sequential dehydrogenation of methanol on Cu(110) with a scanning tunneling microscope

Adsorption of methanol and its dehydrogenation on Cu(110) were studied by using a scanning tunneling microscope (STM). Upon adsorption at 12 K, methanol preferentially forms clusters on the surface. The STM could induce dehydrogenation of methanol sequentially to methoxy and formaldehyde. This enabled us to study the binding structures of these products in a single-molecule limit. Methoxy was imaged as a pair of protrusion and depression along the [001] direction. This feature is fully consistent with the previous result that it adsorbs on the short-bridge site with the C-O axis tilted along the [001] direction. The axis was induced to flip back and forth by vibrational excitations with the STM. Two configurations were observed for formaldehyde, whose structures were proposed based on their characteristic images and motions.

Imaging covalent bonding between two NO molecules on Cu(110)

Using a scanning tunneling microscope, we found metastable upright NO on Cu(110) with the 2π* molecular resonance at the Fermi level. Upon heating above 40 K, it converts to a bent structure with the loss of molecular resonance. By manipulating the distance between two upright NO, we controlled the overlap between 2π* orbitals and observed its splitting below and above the Fermi level, thus visualizing the covalent interaction between them.

Multi-finger structure and pulsed-powering operation scheme for CMOS LSI-based flexible stimulator for retinal prosthesis

Multi-finger structure was proposed to improve flexibility of the CMOS LSI-based multi-chip retinal stimulator. A dual-finger retinal stimulator was fabricated and its functionality was demonstrated in retinal stimulation experiments on rabbit's retina, We also proposed an idea of pulsed-powering operation scheme for the multi-chip flexible retinal stimulator. We compared the pulsed-powering scheme with conventional one in a simulation, and show that the pulsed-powering can be an alternative operation scheme for the neural stimulator that provides an improved safety to the biological tissue.

Light-controlled retinal stimulation on rabbit using CMOS-based flexible multi-chip stimulator

We implemented a light-sensing function on CMOS-based multi-chip stimulator for retinal prosthesis. Using the light-sensing circuitry attached to each stimulation electrode, the flexible multi-chip stimulator is capable of image-based patterned stimulation. We verified the function of the light-controlled decision based on the light intensity measured just beside the stimulation site. We also experimentally demonstrated in vivo retinal stimulation on rabbit's retina with light-controlled decision. The result of the present work is a simplified demonstration for the concept of retinal prosthesis with on-site imaging.

Dehydroascorbic acid reduction in several tissues and cultured hepatocytes of the chicken

Dehydroascorbic acid, the oxidized form of ascorbic acid, is rapidly reduced to ascorbate in living organs (ascorbate recycling). We examined the GSH-dependent dehydroascorbate reductase activity in several tissues of the chicken. The activity was highest in the liver, and second highest in the brain. The activity was localized in the cytosol fraction of the liver. We subsequently examined the dehydroascorbate reduction in separated chicken hepatocytes. The cellular ascorbate concentration was elevated in dehydroascorbate-treated cells. It is thought that hepatocytes incorporated external dehydroascorbate and converted it into ascorbate. These findings suggest that the liver plays an important role in ascorbate recycling by the chicken.

Changes in ascorbic acid content in primary cultured rat hepatocytes exposed to 2,2'-azobis (2-amidinopropane) dihydrochloride, a radical initiator

Changes in ascorbate content in primary cultured rat hepatocytes exposed to oxidative stress derived from water soluble radical initiator 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH) were examined. Cells were exposed to 0.05 and 5 mg/ml of AAPH as 'mild' and severe' oxidative stresses, respectively. Lipid peroxidation in hepatocytes was induced by 'severe' oxidative stress, but not by 'mild' oxidative stress. Ascorbate decreased at 6 hr after administration of both mild' and severe' oxidative stresses, and recovered to the control level after a further 6 hr. In cells treated with 'severe oxidative stress, however, total ascorbate (reduced form plus oxidized form) had increased 24 hr after administration. These results indicated that consumption alone did not account for the increase of ascorbate in hepatocytes under oxidative stress.

Ascorbic acid supplementation to primary culture of chicken hepatocytes with non-serum medium

Chicken liver is lack of ascorbic acid biosynthesis system, different from mammals and highly evoluted birds. Chicken hepatocytes cultured without ascorbate was expected to have lower ascorbate amounts than physiological levels. Intracellular was decreased as compared with intact liver by cell preparation performed with in situ collagenase perfusion. We added ascorbate to a primary culture of chicken hepatocytes in order to restore the amount of ascorbate. Serum-free Leivobitz's L-15 medium which do not contain ascorbate was used for control medium. Cells were cultured with several concentrations of ascorbate for 24 or 48 h. After ascorbate supplementation for 24 to 48 h, cellular ascorbate concentration increased depending on the dose of medium ascorbate. Medium lactate dehydrogenase activity derived from hepatocytes, an index of cell injury, decreased upon 5-100 mg/l of ascorbate supplementation for 48 h. Tyrosine aminotransferase activity, an index of liver function, increased following culture with 50 and 100 mg/l ascorbate for 48 h. The activities, however, decreased by supplementation with 1000 mg/l of ascorbate. In conclusion hepatocytes lost intracellular ascorbate during preparation by in situ collagenase perfusion. Supplementation of ascorbate restored cellular ascorbate concentration, lowered cell injury and raised tyrosine aminotransferase activitv in primary cultured chicken hepatocytes. Ascorbate treatment for 48 h at 50 mg/l was the best combination in this study for primary culture of chicken hepatpcyte with non-serum L-15 medium