Quantitative Test for Mirror Symmetry Relationship between Sister Cells

Abstract

Cell shape determination is a dynamical process modulated by input from genetic and signaling pathways. In order to understand cell morphology as a dynamical system it is critical to determine the degree of spatial inheritance, that is, the degree of influence of spatial organization within a mother cell on the organization of her daughter cells. Visual comparison of symmetry relations between daughters was used by Albrecht-Buehler to probe spatial inheritance in a series of papers published in the 1970's. His results, that sister cells are sometimes mirror images of each other, were interpreted as reflecting spatial inheritance during cell division. We have reinvestigated these claims using quantitative image analysis and several different shape-comparison algorithms to test the symmetry relations between sister cells. Applying these methods to fixed and live RPE-1 and NIH 3T3 cells, we obtained the following results: (A) sister cells are quantitatively more similar in shape than pairs of unrelated cells, (B) When sister cells show a significant degree of shape similarity, they tend to be related by mirror symmetry, (C) the shape similarity between sister cells is highest soon after division and decays on a time scale of several hours, (D) the set-theoretic union of the two sister cell shapes is related to the shape of the mother with a degree of similarity that decays as a function of time before and after division. We have also developed methodologies to compare similarity of internal actin stress fiber organization between sisters and to compare the migration trajectories of sister cells as they move away from the site of division.