A mathematical model to study the dynamics of epithelial cellular networks.

Epithelia are sheets of connected cells that are essential across the animal kingdom. Experimental observations suggest that the dynamical behavior of many single-layered epithelial tissues has strong analogies with that of specific mechanical systems, namely large networks consisting of point masses connected through spring-damper elements and undergoing the influence of active and dissipating forces. Based on this analogy, this work develops a modeling framework to enable the study of the mechanical properties and of the dynamic behavior of large epithelial cellular networks. The model is built first by creating a network topology that is extracted from the actual cellular geometry as obtained from experiments, then by associating a mechanical structure and dynamics to the network via spring-damper elements. This scalable approach enables running simulations of large network dynamics: the derived modeling framework in particular is predisposed to be tailored to study general dynamics (for example, morphogenesis) of various classes of single-layered epithelial cellular networks. In this contribution, we test the model on a case study of the dorsal epithelium of the Drosophila melanogaster embryo during early dorsal closure (and, less conspicuously, germband retraction).

Where's the naevus? Inter-operator variability in the localization of melanocytic lesion border.

BACKGROUND: The first step in the analysis of a dermatoscopically imaged melanocytic lesion is segmentation--informally, isolating those points in the image belonging to the lesion from those belonging to the surrounding non-lesional skin. Although typically studied in the context of automated analysis, segmentation is a necessary step even for human operators who plan to evaluate quantitative features of a lesion (such as diameter or asymmetry). METHODS: In a double blind evaluation of the segmentation of 77 digital dermatoscopic images, we observed a significant inter-operator variability. RESULTS: The area of the disagreement region was on average 15.28% of the area of the lesion itself, and in 10% of the cases it was more than 28%. More experienced dermatologists showed greater agreement among themselves than with less experienced dermatologists, and a slight tendency toward 'tighter' segmentations. CONCLUSION: The evaluation methodology addresses a number of crucial difficulties encountered in previous studies and may be of independent interest. Our results underscore the necessity of taking into account inter-operator variability in large epidemiological studies, in particular those involving less experienced dermatologists, and of striving toward techniques allowing greater standardization and replicability in the evaluation of the fundamental visual parameters of lesions.