The consequences of ubiquitous expression of the wingless gene in the Drosophila embryo.

The segment polarity gene wingless has an essential function in cell-to-cell communication during various stages of Drosophila development. The wingless gene encodes a secreted protein that affects gene expression in surrounding cells but does not spread far from the cells where it is made. In larvae, wingless is necessary to generate naked cuticle in a restricted part of each segment. To test whether the local accumulation of wingless is essential for its function, we made transgenic flies that express wingless under the control of a hsp70 promoter (HS-wg flies). Uniform wingless expression results in a complete naked cuticle, uniform armadillo accumulation and broadening of the engrailed domain. The expression patterns of patched, cubitus interruptus Dominant and Ultrabithorax follow the change in engrailed. The phenotype of heatshocked HS-wg embryos resembles the segment polarity mutant naked, suggesting that embryos that overexpress wingless or lack the naked gene enter similar developmental pathways. The ubiquitous effects of ectopic wingless expression may indicate that most cells in the embryo can receive and interpret the wingless signal. For the development of the wild-type pattern, it is required that wingless is expressed in a subset of these cells.