A factor produced by human cells in vitro that changes HeLa cell colonial morphology

Summary Colonies of HeLa cells cultured in media supplemented with human or bovine serum or both can be morphologically described as three types: diffuse, intermediate, and compact, with their modal distribution depending on the serum or sera added to the growth medium. We have observed that for a particular medium or serum system, the percentage of compact colonies remains fairly constant under normal culture conditions, 0.2%, whereas the diffuse and intermediate colonies vary over a much wider range. The presence of certain substances as trypsin, heparin and Darvan in the medium favor the increase of compact colonies at the expense of other types. Furthermore, we have discovered that colonial morphology is influenced by cocultivation of the HeLa cells with human fibroblastlike cells, the compact colonies increasing as the density of the fibroblast element introduced into the mixed cultures is increased. Subsequent investigation revealed that conditioned medium from confluent fibroblast and HeLa cell cultures contained a factor(s), that significantly increased the percentage of compact colonies. The factor is nondialyzable, heat-stable and can be neutralized by serum. Recorded in this presentation are preliminary observations on the kinetics of colony formation and the interaction among the three HeLa cell colony types, the diffuse, the intermediate, and the compact. The factor's effect on HeLa cell colonial morphology is time dependent and rapidly reversed if the factor(s) is removed and fresh medium added.     

Morphological and electrophysiological changes produced by electrical stimulation in cultured neuroblastoma cells.

Electric fields, which were equivalent to those generated by medical devices, were applied to cultured neuroblastoma cells (mouse and human) to test for morphological damage and to establish damage thresholds. Each of two methods of applying fields permitted flow of electrical current and minimized exposure of cells to electrode-breakdown products. One method consisted of a pair of parallel wires in a Petri dish by which current was delivered within a fixed volume of flowing tissue-culture media. With the other method, the cells were held in a confined geometrical chamber and current was applied via agar bridges. Under a given set of stimulation parameters, damage was found to be variable from cell to cell. By changing the strength of the electric field (frequency and duration of stimulation held constant), thresholds of several V/cm were found above which cell damage could be reliably produced. Depending on the intensity of the field, damage took the form of cell lysis or damage to neurites. Intracellular recordings from the mouse neuroblastoma cells revealed a correlation between a decline in resting transmembrane potential and stimulus intensity. Human neuroblastoma cells were less susceptible to damage than were the mouse neuroblastoma cells, given the same strength of applied electric fields.     

Fluctuating and directional asymmetry in natural bird populations exposed to different levels of habitat disturbance, as revealed by mixture analysis

While bilateral trait asymmetry is widely recognized to estimate developmental instability, much controversy exists over which types of asymmetry (fluctuating, directional, and/or antisymmetry) to use. Recently it has been hypothesized that the three types are strongly interrelated, and that increased developmental instability may be reflected in a transition from fluctuating to directional asymmetry and/or antisymmetry. Alternatively, habitat disturbance might change the genetic expression of directional asymmetry. We present herein the first empirical evidence for stress-mediated shifts in types of asymmetry in natural populations, by using mixture analysis to model tarsus asymmetry in bird populations exposed to different levels of habitat disturbance. Observed asymmetry patterns almost exclusively consisted of true fluctuating asymmetry in the least disturbed populations, but became progressively mixed with directional asymmetry under increasing disturbance. Failing to unravel these mixtures of different forms of asymmetry may have critical implications for the analysis and interpretation of asymmetry data.