Symmetry analysis of cell nuclei

An algorithm is described that is used to analyze the two‐dimensional spatial symmetry of cell nuclei. The method provides two symmetry features: the symmetry index (SI), which estimates the precise spatial symmetry of a given chromatin component, C n , and the quadrant symmetry index (QSI), which estimates the number of quadrants being occupied by C n . A previous analysis is used to show that age‐related chage in Malpighian tubule nuclei from the adult housefly is associated with significant alterations in the spatial symmetry of low‐, medium‐, and high‐density chromatin components (LDC, MDC, HDC). This included a seven‐fold increase in the spatial symmetry of HDC and a shift in the symmetry profile (from highest to lowest degree of symmetry) from LDC‐MDC‐HDC to MDC‐LDC‐HDC. The increased spatial symmetry of HDC suggests that it occurs at new nuclear sites as the fly ages and that these sites are distributed over approximately 60% of the chromosome population.