Function of Oncogenes in Early Embryogenesis 
identical to the segment polarity gene wingless. 
This observation has allowed us to study the in- 
teractions of Wnt-\/ wingless with other segmen- 
tation genes. 
The basic body plan of the fruit fly is estab- 
lished by several classes of genes that progres- 
sively divide the embryo into smaller compart- 
^-ments: the gap genes, the pair-rule genes, and the 
segment polarity genes. Whereas the gap and 
pair-rule genes encode nuclear proteins and are 
active before the Drosophila embryo becomes 
cellularized, the segment polarity genes are the 
first that control cell-cell interactions. The wing- 
less gene is a good example, encoding a secreted 
factor, but other segment polarity genes are 
thought to interact with wingless. To study the 
properties of the wingless protein, we have made 
antibodies that recognize it in whole-mount em- 
bryos and in individual cells. The protein is seen 
on the surface of cells and in intracellular vesicu- 
lar structures. We have characterized the distri- 
bution of the wingless protein in embryos that 
are mutant for wingless itself and have obtained 
evidence that lack of secretion of the protein is 
the primary defect in these mutants. 
In an additional approach, we have overex- 
pressed the wingless gene in embryos, from a 
heat-shock promoter. The phenotype of the heat- 
shock wingless embryos is the opposite of the 
phenotype of embryos lacking wingless. Surpris- 
ingly, heat-shock wingless embryos are very simi- 
lar to embryos that are mutant for two other 
segment polarity genes, called naked and zeste- 
white-3, suggesting common biochemical path- 
ways of wingless and those genes. 
We have also found that wingless in Drosoph- 
ila is part of a gene family, with at least two addi- 
tional members. These genes, called DWnt-2 and 
T>Wnt-5 for the time being, are also expressed 
during early embryogenesis, in characteristic pat- 
terns that differ from wingless. Mutants at these 
genes have not yet been obtained, but the un- 
usual character of the DWnt-5 protein, which is 
three times as long as other Wnt proteins, may 
give us new clues as to the biochemical mecha- 
nism of action of the genes. 
In the future we hope to extrapolate our in- 
creasing understanding of the function of the 
Wnt genes in embryogenesis to the mechanism of 
action of the genes in cancer. 
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