Regularity and packing of the horizontal cell mosaic in different strains of mice.

The present study describes the relationships between mosaic regularity, intercellular spacing, and packing of horizontal cells across a two-fold variation in horizontal cell density in four strains of mice. We have tested the prediction that mosaic patterning is held constant across variation in density following our recent demonstration that intercellular spacing declines as density increases, by further examination of that dataset: Nearest-neighbor and Voronoi-domain analyses were conducted on multiple fields of horizontal cells from each strain, from which their respective regularity indices were calculated. Autocorrelation analysis was performed on each field, from which the density recovery profile was generated, and effective radius and packing factor were calculated. The regularity indexes showed negative correlations with density rather than being held constant, suggesting that the strong negative correlation between intercellular spacing and density exceeded that required to produce a simple scaling of the mosaic. This was confirmed by the negative correlation between packing factor and density. These results demonstrate that the variation in the patterning present in the population of horizontal cells across these strains is a consequence of epigenetic mechanisms controlling intercellular spacing as a function of density.