Windbeutel is required for function and correct subcellular localization of the Drosophila patterning protein Pipe

Drosophila embryonic dorsal-ventral polarity originates in the ovarian foll icle through the restriction of pipe gene expression to a ventral subpopula tion of follicle cells, Pipe, a homolog of vertebrate glycosaminoglycan-mod ifying enzymes, directs the ventral activation of an extracellular serine p roteolytic cascade which defines the ventral side of the embryo, When pipe is expressed uniformly in the follicle cell layer, a strong ventralization of the resulting embryos is observed, Here, we show that this ventralizatio n is dependent on the other members of the dorsal group of genes controllin g dorsal-ventral polarity, but not on the state of the Epidermal Growth Fac tor Receptor signal transduction pathway which defines egg chamber polarity . Pipe protein expressed in vertebrate tissue culture cells localizes to th e endoplasmic reticulum, Strikingly, coexpression of the dorsal group gene windbeutel in those cells directs Pipe to the Golgi, Similarly, Pipe protei n exhibits an altered subcellular localization in the follicle cells of fem ales mutant for windbeutel. Thus, Windbeutel protein enables the correct su bcellular distribution of Pipe to facilitate its pattern-forming activity.