DROSOPHILA WINGLESS SUSTAINS ENGRAILED EXPRESSION ONLY IN ADJOINING CELLS - EVIDENCE FROM MOSAIC EMBRYOS

The wingless protein is secreted, but it is not known whether it acts only on cells near to its site of synthesis or whether it has a longer range. Here, we use mosaic Drosophila embryos to estimate the range o f wingless as it acts to maintain expression of the engrailed gene. We find that expression of engrailed is often sustained in those wingles s(-) cells that are located near a wildtype patch of tissue, but this is not invariably so. Also, the numbers of cells maintaining engrailed expression are small. From these findings, we argue that wing less-ex pressing cells sustain engrailed expression only in adjoining cells. T he wingless gene is also needed for maintenance of its own expression; using mosaics, we find that the range of this action is short as well .