Synthesis of the sulfate donor PAPS in either the Drosophila germline or somatic follicle cells can support embryonic dorsal-ventral axis formation

The establishment of dorsal-ventral (DV) polarity in the Drosophila embryo depends upon a localized signal that is generated in the perivitelline space of the egg through the action of a serine proteolytic cascade. Spatial regulation of this pathway is determined by the expression of the pipe gene in a subpopulation of ventral follicle cells in the developing egg chamber. The Pipe protein exhibits homology to vertebrate glycosaminoglycan sulfotransferases. In a previous study, we demonstrated that embryonic DV polarity depends upon the sulfotransferase activity of Pipe. Surprisingly, however, our results also indicated that formation of the embryonic DV axis does not require the synthesis of the high-energy sulfate donor, 3'-phosphoadenosine 5'-phosphosulfate (PAPS) in the follicle cells in which Pipe is presumed to function. Here, we resolve this apparent paradox by demonstrating that dorsalized embryos are only produced by egg chambers in which both germline and follicle cells lack PAPS synthetase activity. Thus, PAPS produced either in the germline or in the follicular epithelium can support the requirement for Pipe sulfotransferase activity in embryonic DV patterning. This finding indicates the existence of a conduit for the movement of PAPS between the germline and the follicle cells, which highlights a previously unappreciated mechanism of soma/germline cooperation affecting pattern formation.