Kinetic cell-cycle analysis of a cultured mammalian cell population

Some inequalities for moments and coefficients of variation for a large class of probability functions

Some inequalities for moments and coefficients of variation of probability densities over the positive real line are obtained by means of simple geometrical relationships. As an illustrative application rigorous bounds are obtained for the ratio of weight average to number average molecular weight for a large class of distributions of macromolecules, giving a more precise characterization of this empirical measure of heterogeneity.

Measuring diameters of rod-shaped bacteria in vivo with polarized light scattering

The angular function for elements of the Mueller matrix for polarized light scattering from suspensions of microorganisms is known to be reproducible for different growths of a given bacterial strain in the log (or exponential) phase of growth. The reason for this, the stability of the size and shape distribution for cells, is briefly discussed. Experiments were performed using suspensions of two different strains of Escherichia coli cells in log phase and measuring the angular dependence of the Mueller matrix ratio S34/S11. Calculations were then performed using the coupled dipole approximation to model electromagnetic scattering from particles where the shape of an individual cell was approximated by a cylinder capped with hemispheres of the same radius as the cylinder. Using previously measured values for the length distribution and index of refraction of the cells, the calculated scattering curve was found to fit the measured curve very well. The values obtained for the cell diameters were quite close to diameters previously measured by optical microscopy. Thus this method provides a rapid and convenient method for monitoring bacterial diameters in vivo even when there is an appreciable distribution of bacterial lengths in the population.

A dynamic simulation model of tissue growth and cell patterning

The distributions of cells in tissues of experimental chimaeras and mosaics can serve as tests of mechanisms and rules by which single cells organize themselves into complex, multicellular structures during embryogenesis. We have devised a dynamic, computer simulation model of tissue growth and cell patterning which is directly applicable to the analysis of chimaeras and mosaics. In the model, schematized cells possess a small behavioral repertoire and simple rules for the carrying out of these behaviors. Populations of such cells evolve tissue patterns in real-time that are very similar to those seen in experimental animals. In particular, we have modeled the major pattern features seen in amphibian and mammalian eye chimaeras and mosaics. We have demonstrated that cell mixing can be a passive concomitant of interstitial cell division, a result which alleviates the need to postulate active cell mixing in such mammalian systems. We expect this approach to be a valuable addition to methods of pattern analysis in development.

Influence of the existence of a resting state on the decay of synchronization in cell culture

General relationships between the distribution of cell doubling times and the growth pattern of an initially synchronized cell population are applied to the model proposed by Smith and Martin (1973) in which the mitotic cycle or "B" phase is preceded by a random-exit resting "A" state. Results show that culture synchronization decays so rapidly as to be virtually unobservable unless the time spent by a cell in the B phase is at least equal to that spent in the A state. If synchronization persists over several mitotic cycles, the growth pattern is determined to a much greater extent by variation in the duration of the B phase than by the probability of exit from the A state. Accordingly the growth pattern of a cell population, like the doubling time distribution which governs the pattern, is of limited usefulness in detecting the existence of a resting state.

The effect of post-UV dark incubation on survival of chick-embryo fibroblasts after photoreactivation

A survival assay with chick-embryo fibroblasts was used to study photoreactivation of ultraviolet (UV) irradiation-induced damage. The kinetics of the photoreactivation was studied as a function of the length of a post UV dark incubation period of from 0 to 18 h at 38.5 degrees C. The logarithmic survival curve with no photoreactivation had a Do of about 4.3 J/m2 giving approximately 0.8% relative plating efficiency after a UV dose of 21 J/m2. At this dose the efficiency of photoreactivation (survival increase per unit blacklight dose) increased with post UV incubation time reaching a maximum at 4-6 h, then declining until there was little photoreactivation observed for times longer than about 11 h. The possibility that this effect was produced by pre-UV perturbations of the cell cycle was eliminated by the fact that the same results were achieved after several rather different trypsinization protocols. The shape of the photoreactivation vs. blacklight curve at the time of peak efficiency showed a threshold up to about 3 kJ/m2, a rising portion and a plateau after 12-16 kJ/m2 when the survival increased by a factor of roughly 8.

Motility of mouse fibroblasts in tissue culture

The growth and motion of mouse L-cells in vitro have been studied by means of time-lapse photography. In particular, the mitotic period and the motility, defined in terms of [R2], the mean square displacement of an ensemble of cells, have been measured as a function of temperature. The motility is a function of the phase of the cell cycle. For approximately the first one-eighth of the mitotic period the motility is well described as a random walk with persistence, the duration of the persistence being determined by the time of extension of the filopodic spindle. The temperature dependence of the diffusion constant follows the Arrhenius factor. The mitotic period, which varies exponentially as (1/T), exhibits a large variance, and the time difference in replication of daughter pairs follows approximately a Poisson distribution with a mean difference of 138 min at T = 37 degrees C. There is no evidence of mirror symmetry in the motion of daughter pairs for fibroblast cells plated in vitro in Corning tissue culture flasks.

Sensitivity to ultraviolet radiation as a function of DNA content in Escherichia coli B/r

Populations of Escherichia coli B/r A were grown to log phase at various growth rates determined by the richness of the medium. The genome content, G, was calculated from log phase doubling times by means of the Cooper-Helmstetter formula. Cell volumes were measured and found to vary linearly with this genome content. Cells with various DNA contents were prepared for ultraviolet irradiation and plated for dark repair under similar conditions. The resulting logarithmic survival curves were all similar in shape: convex up, with straight line portions having approximately the same slope (D0 = 11.4 +/- 0.2 J/m2). The shoulders however increase in width with calculated DNA content giving an extrapolation number which varies roughly as exp(G) or exp (0.6 Gmax).

An approximation method for estimating cell loss from a growing tumor

A simple self-consistent calculational scheme is developed for estimating cell loss for a growing tumor (or other population) when the growth fraction can be estimated at regular intervals. This is applied to published data for a particular much-studied Ehrlich ascites tumor. The loss rate is found to be substantially higher than that estimated by previous, less precise means.

Some inequalities for moments and coefficients of variation for a large class of probability functions

Some inequalities for moments and coefficients of variation of probability densities over the positive real line are obtained by means of simple geometrical relationships. As an illustrative application rigorous bounds are obtained for the ratio of weight average to number average molecular weight for a large class of distributions of macromolecules, giving a more precise characterization of this empirical measure of heterogeneity.