The geometric packing of cells within an epithelial sheet is precise, and the hexagonal shape of the cells helps this organization. A paper from last year has looked at the packing geometry of epithelial fiber cells in the mouse eye lens to determine the role of actin and an associated protein called tropomodulin. The images above are 3D image reconstructions of actin within fiber cells, both in control (left) and tropomodulin mutant (right) lenses. The hexagonal packing of the fiber cells in the mutant is very irregular compared to control cells.
Reference: Roberta B. Nowak, Robert S. Fischer, Rebecca K. Zoltoski, Jerome R. Kuszak, and Velia M. Fowler, .2010. Originally published in Journal of Cell Bioloy. doi: 10.1083/jcb.200905065. Paper can be found here.