Individual cell motility studied by time-lapse video recording: influence of experimental conditions

BACKGROUND

Eukaryotic cell motility plays a key role during development, wound healing, and tumour invasion. Computer-assisted image analysis now makes it a realistic task to quantify individual cell motility of a large number of cells. However, the influence of culture conditions before and during measurements has not been investigated systematically.

METHODS

We have evaluated intraassay and interassay variations in determinations of cellular speed of fibroblastoid L929 cells and investigated the effects of a series of physical and biological parameters on the motile behavior of this cell line. Cellular morphology and organization of filamentous actin were assessed by means of phase-contrast and confocal laser scanning microscopy and compared to the corresponding motility data.

RESULTS

Cell dissociation procedure, seeding density, time of cultivation, and substrate concentration were shown to affect cellular speed significantly. pH and temperature of the medium most profoundly influenced cell motility and morphology. Thus, the mean cell speed was 40% lower at pH 7.25 than at pH 7.6; at 29 degrees C, it was approximately four times lower than at 39 degrees C.

CONCLUSION

Of the parameters evaluated, cell motility was most strongly affected by changes in pH and temperature. In general, changes in cell speed were accompanied by alterations in cell morphology and organization of filamentous actin, although no consistent phenotypic characteristics could be demonstrated for cells exhibiting high cell speed.

A simple procedure for quantification of neurite outgrowth based on stereological principles

The molecular mechanisms controlling formation and remodelling of neuronal extensions are of considerable interest for the understanding of neuronal development and plasticity. Determination of neurite outgrowth in cell culture is a widely used approach to investigate these phenomena. This is generally done by a time consuming tracing of individual neurites and their branches. We have used stereological principles to determine the length of neurites. The total neuritic length per cell was estimated by counting the number of intersections between neurites and test lines of an unbiased counting frame superimposed on images of cell cultures obtained by conventional computer-assisted microscopy. The absolute length, L, of neurites per cell was subsequently estimated from the number of neurite intersections, I, per cell by means of the equation L=(pid/2)I describing the relationship between the number of neurite intersections and the vertical distance, d, between the test lines used. When measuring neurite outgrowth from PC12 cells and primary hippocampal neurons, data obtained by counting neuritic intersections correlated statistically significantly with data obtained using a conventional tracing technique. However, information was acquired more efficiently using the stereological approach. Thus, using the described set-up, the stereological procedure was approximately five times less time consuming than the conventional method based on neurite tracing. The study shows that stereological estimation of neuritic length provides a precise and efficient method for the study of neurite outgrowth in cultures of primary neurons and cell lines.

Cell motility is inhibited by the antiepileptic compound, valproic acid and its teratogenic analogues

Valproic acid (VPA) is an established human teratogen that causes neural tube defects in 1-2% of human foetuses exposed to the drug during early pregnancy. In this study, individual cell motility was evaluated using short- and long-term time-lapse video-recording and computer assisted image analysis, and it was found that VPA and selected VPA-analogues inhibited individual cell motility of L-cells in a dose-dependent manner. The compounds caused a decrease in the root-mean-square speed, S, and in the rate of diffusion, R, but an increase in the time of persistence in direction, P. Using short-term recordings and measurements of mean-cell speed, the reduction in the motile behaviour was shown to correlate with the teratogenic potency of the tested compounds. The observed effects of VPA on cell motility was independent of the employed L-cell clone, and could be reproduced in cells containing the neuronal marker NCAM and in the neuronal cell line N2a. Furthermore, the observed effect was independent of culture substratum, being observed for L-cells grown on fibronectin as well as on plastic. Immunofluorescence microscopy revealed that VPA-treatment of mouse L-cells caused a redistribution of F-actin and of a series of focal adhesion proteins, indicating that the effect of VPA on cell motility may be causally related to increased cell-substratum interactions or to alterations in the organisation or dynamics of the actin cytoskeleton.

A simple procedure for morphometric analysis of processes and growth cones of neurons in culture using parameters derived from the contour and convex hull of the object

Morphometric estimation of neuronal processes is currently laborious and time-consuming, since the individual processes (axons and dendrites) have to be traced manually. In order to facilitate the measurement of cellular processes, we have tested a series of parameters derived from the contour and the convex hull of an object and estimated to which extent they reflect process length and number. The parameters included the area, perimeter and form factor of the object and convex hull, their ratios as well as object length, breadth, width, length/width and spreading index. Some new parameters derived from the contour and convex hull of the object, were also computed: process index (the number of areas contained within the convex hull outside the object contour), process domain (the total area contained within the convex hull outside the object contour), their ratio and the square root of the process domain (SR process domain). In total, 18 parameters were estimated. Populations of motoneurons, growth cones of cerebellar granule cells and N2a neuroblastoma cells were utilized due to their diversity in morphological features. The processes of each object were drawn by hand to establish the actual length and number. Total process length per object correlated strongly with object perimeter, process domain and SR process domain. The number of processes per object correlated well with perimeter ratio, process index and form factor, whereas object length, convex hull perimeter and spreading index correlated acceptably with the average process length. Using these parameters for the evaluation of neurite outgrowth in developing of hippocampal neurons in vitro, variables such as object perimeter, process domain and SR process domain were found to be very well suited for estimation of the total length of neurites. We conclude that based on the contour and convex hull of an object it is possible to calculate a series of parameters which may substitute direct measurements of process length.

On the possible physical foundations of health related effects of crystals

I propose a possible physical mechanism to account for widely claimed health related effects of crystals. The hypothesis relates the mechanism of such action to the isotropic diversity of crystals which leads to an enormous information storage capacity of crystal lattices. Sublattices of particular isotopes form an interactive network similar to simulated neural networks based on spin glass models.

Isotopical positional correlations as a possible model for Benveniste experiments

I suggest a hypothetic explanation of recently found 'memory effect' in water (water 'remembers' the presence of some biologically active molecules even when they are diluted to levels less then one molecule per total volume). My explanation is based on isotopic diversity water, namely that some positional correlations of stable isotope (H, D, 16O, 17O and 18O) might work as 'templates' of the originally dissolved molecules. These isotopic correlations are equivalent to the choice of a particular isotopic pattern out of the highly degenerate manyfold of potentially available patterns. This pattern is further reproduced at each next dilution level by some sort of 'locking-in' mechanism. Among possible physical candidates for such locking-in action is the polaronic self-stabilization in non-linear media.

A search for narrow band signals with SERENDIP II: a progress report

Commensal programs for the Search for Extraterrestrial Intelligence (SETI), carried out concurrently with conventional radio astronomical observing programs, can be an attractive and cost-effective means of exploring the large multidimensional search space intrinsic to this effort. Our automated commensal system, SERENDIP II, is a high resolution 131,072 channel spectrometer. It searches for 0.49 Hz signals in sequential 64,700 Hz bands of the IF signal from a radio telescope being used for an astronomical observation. Upon detection of a narrow band signal with power above a preset threshold, the frequency, power, time, and telescope direction are recorded for later study. The system has been tested at the Hat Creek Radio Astronomy Observatory 85 ft telescope and the NASA-JPL Deep Space Station (DSS 14) 64 m telescope. It is currently collecting data at the National Radio Astronomy Observatory 300 ft telescope.

Differential diagnosis of huge abdominal masses visualized on CT scans

Thirty-one consecutive cases of very large abdominal masses (greater than 10 cm in largest dimension) were identified from CT scans on 2145 patients performed over a 15-month period. All were malignant tumors. The most useful information derived from CT scans was the location and organ of origin. The tissue of origin could be predicted from knowledge of the organs expected in each abdominal quadrant or pelvic site. Our results indicate that CT is extremely useful in evaluating very large masses.