Abstract
The cell adhesion molecule (CAM), Echinoid (Ed), is a transmembrane protein on adherens junctions of Drosophila. The intracellular domain of Ed contains several important motifs, one of them is Nedd4-binding motif, which is related to endocytosis process. In this study, we found that Ed is involved in the normal replacement of abdominal larval epidermal cells (LECs) with adult histoblasts. This process is an important event happened during metamorphosis in Drosophila. At larval stage, the histoblasts are organized in nests and located at lateral sides of each segment. When the embryo reaches pupa stage, histoblast nests will be regulated by various protein signals and proliferate rapidly to expand their territory. At the same time, the original LECs will be pushed away, sink to the basal side and undergo cell death. Finally, all of the abdominal epidermis will be covered by histoblast cells. If we overexpressed the truncated form of ed which Nedd4-binding motif was mutated in LECs, a cleft will form in the midline of the dorsal abdomen. There were remaining LECs in the cleft and some of them had zigzag membrane. This results suggest that Ed with Nedd4-binding motif mutated may have problem undergoing endocytosis and accumulate on membranes of LECs, which strengthens the adhesion of them and prevents them from cell death, thus leaving a cleft on epidermis without the covering of adult histoblasts.