Cover photograph (Copyright © 2006, American Society for Microbiology. All Rights Reserved.): Pancreatic ductal cells (PDC) are derived from wild-type mice (WT-PDC) and K19-K-RAS^G12V transgenic mice, the latter retrovirally transduced with p53^V143A (Ki-RAS^G12V/p53^V143A-PDC). These cells, grown in an extracellular matrix gel, form spheroid cysts with ductal epithelial cells surrounding a lumen. Whereas WT-PDC form normal spheroid cysts, Ki-RAS^G12V/p53^V143A-PDC display cysts with disrupted cellular architecture, loss of normal epithelial polarity, invasion of cells into the lumen, and protrusion of cells from the surface. The cysts are depicted with confocal imaging of immunofluorescence staining for E-cadherin (red) as a basolateral marker, actin (green) as an apical marker, and DAPI counterstaining for nuclei (blue). (See related article on p. 4185.)