Abstract

Drosophila protein tyrosine phosphatase Pez belongs to the FERM superfamily of proteins, many of which interact with the actin cytoskeleton. Due to the presence of the FERM and phosphatase domains, PEZ-class proteins are suspected to play a role in tumor metastasis. The aim of this study is to identify the cellular processes in which Pez participates, using molecular genetic and biochemical approaches. The subcellular distribution of Pez was examined by immunohistochemistry; endogenous Pez cannot be detected, so a transgene that can overexpress Pez in a tissue specific manner was employed to produce detectable amounts of the protein. Pez forms aggregates at the apical surface of epithelial cells. Pez does not colocalize with adherens junction proteins, as seen for human Pez, nor with several cytoskeletal proteins. Ectopic Pez in developing wing epithelia causes a reduction in cell proliferation. Pez does not genetically antagonize tyrosine kinase pathways, as predicted for a phosphatase. Loss-of-function studies show that Pez is required for proper limb development, but not for viability or developmental patterning. A genetic screen was used to identify several regions of the genome that, when present in just one copy, modify the phenotypes due to ectopic Pez in the wings and eyes. Finally, the bimolecular fluorescence complementation assay was used to show that the Drosophila protein Aru can bind Pez in vivo. Together, the findings have ruled out several major hypotheses for Pez function: it does not significantly regulate cell shape or motility, it does not generally counteract tyrosine kinases and is not essential for their patterning functions, and it does not have an abundant binding site in the adherens junction.