Argosomes: A potential vehicle for the spread of morphogens through epithelia

The formation of morphogen gradients is essential for tissue patterning. Mo rphogens are released from producing cells and spread through adjacent tiss ue; paradoxically, however, many morphogens, including Wingless, associate tightly with the cell membrane. Here, we describe a novel cell biological m echanism that disperses membrane fragments over large distances through the Drosophila imaginal disc epithelium. We call these membrane exovesicles ar gosomes. Argosomes are derived from basolateral membranes and are produced by many different regions of the disc. They travel through adjacent tissue where they are found predominantly in endosomes. Wingless protein colocaliz es with argosomes derived from Wingless-producing cells. The properties of argosomes are consistent with their being a vehicle for the spread of Wingl ess protein.