Abstract
Echinoid (Ed) is a transmembrane protein which is a member of immunoglobulin superfamily of cell adhesion molecule (CAM) on adherens junctions. The intracellular domain of Ed contains a non-typical PDZ-binding motif interacting with Actin filaments through Canoe, and it also comprises Nedd4- and AP-2 binding motif related to endocytosis process. In Drosophila embryos, Ed is expressed throughout the lateral epidermis at early stage and then is gradually undetectable in the amnioserosa cells. In this study, we found that Ed is internalized through AP-2 and Nedd4-mediated endocytosis during germ band retraction which leads to Ed clearance in the amnioserosa. The results demonstrate that Nedd4 is more crucial to this process by ectopically expressing the truncated forms of ed which Nedd4 and AP-2 binding motifs deleted. We further found that overexpression of defective Nedd4 and AP-2 binding motifs of ed also affects the cell morphology and causes different levels of cell constriction. It has previously been shown that overexpression of ed in the amnioserosa results in apical constriction and irregular accumulation of actin, suggesting that Ed might recruit some actin-associated proteins interacting with actin and further lead to apical constriction during this process.