Using protein visualization techniques, cell lines stably expressing GFP-fused full-length and mutant APCs were obtained from cultured Xenopus laevis renal epithelial A6 cells. The use of these cells showed that mutant APCs, whose C-terminal region is absent, induced piling up of cells. Furthermore, piled up cells from mutant APC-expressing cell lines were proven to maintain the intercellular adhesive structure, representing a phenomenon similar to polyp formation in individual organisms (mice).