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
