windbeutel, a gene required for dorsoventral patterning in Drosophila, encodes a protein that has homologies to vertebrate proteins of the endoplasmic reticulum.

The formation of the dorsoventral axis of the Drosophila embryo depends on cell-cell interactions that take place in the female ovary and involve the activation of transmembrane receptors by secreted ligands. The gene windbeutel functions in the somatic follicle cells of the ovary and is required for the generation of a signal that will determine the ventral side of the embryo. This signal originates in the follicle cells during oogenesis, but its actions are only manifested after fertilization, when the egg has already been laid. We have performed a molecular analysis of windbeutel. We have found that windbeutel encodes a putative resident protein of the endoplasmic reticulum, and has homologs in rats and humans. The gene is expressed for a brief period of time in the follicle cells of the ovary, at around the time when the dorsoventral axis of the egg chamber is first established. We propose that Windbeutel is responsible for the folding and/or modification of a specific factor that is secreted from the follicle cells and participates in the activation of the ventralizing signal.