Translation and functional expression of cell-cell channel mRNA inXenopus oocytes

Summary mRNA from estrogen-stimulated rat myometrium, a tissue known to upregulate cell-cell channels in response to this hormone, was microinjected intoXenopus laevis oocytes. The oocytes had been freed from covering layers of follicle cells and vitelline to allow direct cell membrane interactions when paired. About 4 hours after the mRNA injection, paired oocytes become electrically coupled. This coupling was due to the presence of typical cell-cell channels characterized by size-limited intercellular tracer flux, the presence of gap junctions at the oocyte-oocyte interface, and the reversible uncoupling that occurred in the presence of carbon dioxide. The induction of new cell-cell channels in the oocyte membrane was observed against a zero background or a low level of endogenous coupling, depending on the maturation stage of the oocytes. The time course of development of cell-cell coupling after the microinjection of mRNA was determined. The mRNA capable of inducing cell-cell coupling was confined to an intermediate size class when fractionated on a sucrose gradient.     

Decreased Cerebrospinal Fluid Glutamine Levels in Patients with Benign Brain Tumors

Abstract: CSF glutamine concentrations were studied in 12 patients with benign brain tumors (meningioma, craniopharyngioma, or osteofibroma), 12 patients with malignant brain tumors (astrocytoma, medulloblastoma, pinealoblastoma, or chondrosarcoma), 9 patients with non-cerebral tumors, and a reference group of 24 patients. The mean ± SD levels in the benign tumor group (424 ± 124 μ M ) were significantly lower (p < 0.0004) than those in the reference group (642 ± 195 μ M ). There was no significant difference between the CSF glutamine concentrations in the malignant cerebral tumor group (643 ± 210 μ M ) or noncerebral tumor group (599 ± 127 μ M ) and those in the reference group. In patients with benign brain tumors there was indication of an inverse linear relationship between the logarithm of CSF glutamine concentration and tumor diameter.     

Cell size and chloroplast size in relation to chloroplast replication in light-grown wheat leaves

As part of an investigation into the control of chloroplast replication the number and size of chloroplasts in mesophyll cells was examined in relation to the size of the cells. In first leaves of Triticum aestivum L. and T. monococcum L. the number of chloroplasts in fully expanded mesophyll cells is positively correlated with the plan area of the cells. The linear relationship between chloroplast number per cell and cell plan area is also consistent over a fivefold range of cell size in isogenic diploid and tetraploid T. monococcum. In T. aestivum the chloroplast number per unit cell plan area varies among cells in relation to the size of the chloroplasts. Those cells containing chloroplasts with a relatively small face area have a correspondingly higher density of chloroplasts, and consequently, the total chloroplast area per unit cell plan area is very similar in all the cells. The results indicate that the proportion of the cell surface area covered by chloroplasts is precisely regulated, and that this is achieved during cell development by growth and replication of the chloroplasts.     

Pilot-scale production of l-phenylalanine from d-glucose

Effects of inoculum size and total sugar content on both l-phenylalanine productivity and titre have been investigated using a tyrosine auxotrophic regulatory mutant of Escherichia coli. Fermentations were carried out in a 500 litre pilot fermenter with intermittent feeding of d-glucose plus phosphate. It was found that the productivity was not greatly affected by inoculum size. However, the l-phenylalanine titre was significantly affected by total sugar content. Relatively high productivities of up to 0.35–0.40 g l-phenylalanine l^?1 h^?1 have been achieved at l-phenylalanine titres of 14–15 g l^?1.     

Effects of monovalent cations on red cell shape and size

Human erythrocytes were incubated in isotonic solutions of different monovalent cations. The apparent size of the red cells measured on scanning electron microscopic pictures decreases in the order Li⁺>Na⁺=K⁺>Rb⁺. These differences in size are abolished after pretreatment with trypsin, which removes a large part of the charges associated with membrane glycoproteins. Shape alterations are also observed. Normal biconcave shapes are visible after Na⁺ or K⁺ incubation, whereas Li⁺ leads to flabby, flattened cells with a certain tendency to crenation, and Rb⁺ causes more pronounced biconcavity with a certain tendency to cupping. The overall effects of pretreatment with trypsin are similar to those of Li⁺. Our results provide evidence that the electrostatic repulsion of glycoproteins and other charged membrane components may play an essential role in maintaining red cell shape.     

Global asymptotic stability of the size distribution in probabilistic models of the cell cycle

Probabilistic models of the cell cycle maintain that cell generation time is a random variable given by some distribution function, and that the probability of cell division per unit time is a function only of cell age (and not, for instance, of cell size). Given the probability density, f(t), for time spent in the random compartment of the cell cycle, we derive a recursion relation for _n(x), the probability density for cell size at birth in a sample of cells in generation n. For the case of exponential growth of cells, the recursion relation has no steady-state solution. For the case of linear cell growth, we show that there exists a unique, globally asymptotically stable, steady-state birth size distribution, _*(x). For the special case of the transition probability model, we display _*(x) explicitly.This work was supported by the National Science Foundation under grants MCS8301104 (to J.J.T.) and MCS8300559 (to K.B.H.), and by the National Institutes of Health under grant GM27629 (to J.J.T.).     

Estimation of the size of freshwater ciliate populations by a sub-sampling technique

A technique is described for the estimation of the size of ciliate populations based on replicated counts. Sample drops were taken by automatic pipettes of different volume from activated sludge and from a small oligotrophic stream. Specific aims were: 1) the estimation of the number of species; 2) the estimation of the number of individual in each species; 3) the selection of a suitable sub-sample size and number of replicates. For each volume the cumulative increase in species taken in successive sub-samples was determined. For each species the minimum permissible sub-sample volume and the number of replicates required for an allowable error of 10% and 25% were determined. Lastly, the relationship between the mean number of individuals counted for each species and the relative coefficient of variation was visualized.     

The response of stream macroinvertebrates to substrate size and heterogeneity

Manipulations of substrate size and components of heterogeneity were designed to test their independent effects and interactions on the abundance and species richness of stream macroinvertebrates. Two components of substrate heterogeneity, variation in size class proportions and number of size classes, had no independent effect on abundance or richness; and in general did not interact with median particle size. Median particle size, stream current, and detritus accounted for most of the significant variation in macroinvertebrates colonizing the experimental substrates. Rocks with high surface heterogeneity (roughness) were colonized by more individuals (but not taxa) than rocks with low surface heterogeneity.     

Predator-mediated habitat use: some consequences for species interactions

Synopsis Behavioral responses to predators can have a major impact on a fishes' diet and habitat choice. Studies with the bluegill sunfish, Lepomis macrochirus, demonstrate that bluegills undergo pronounced shifts in diet and habitat use as they grow in response to changes in their vulnerability to predators. Other species of fish exhibit similar habitat shifts with body size, presumably also in response to changing predation risks and/or foraging gains. An important but little appreciated consequence of this type of predator-mediated habitat use is that predation risk, by structuring size and/or age-specific resource use, may also indirectly affect species interactions. This paper discusses some of the ways in which behavioral responses to predators may affect intra- and interspecific competition in fish. Observational and experimental studies with sunfish (Centrarchidae) provide most of the examples. These studies suggest that the nonlethal effects of predators may be as important as the actual killing of prey.     

Foraging site use and interspecific competition between bluegills and golden shiners

Synopsis Laboratory experiments examined the foraging performances of a dietary generalist, bluegill,Lepomis macrochirus, and a dietary specialist, golden shiner,Notemigonus crysoleucas, as they fed from devices simulating four foraging sites (bottom substrate, water column, submerged macrophytes, and water surface). Fishes foraged in monospecific and mixed-species groups of two and four individuals. For monospecific groups, foraging rates of bluegills did not differ among the four sites, but golden shiners had significantly higher rates on bottom and midwater sites than on plant and surface sites. The size of monospecific groups did not affect foraging rates of either species. In mixed-species trials, bluegills removed more food items than golden shiners from plant and surface sites in two- and four-fish groups and from bottom sites in two-fish groups. Bluegills' foraging performances improved with experience, golden shiners' performances did not. Experimental results are discussed with respect to interactions between bluegills and golden shiners in natural assemblages.