Probable chaperone protein involved in dorsoventral axis patterning in early embryos. Probably acts by folding and targeting pipe (pip) into the Golgi. Homodimer. Interacts directly with pip. Briefly expressed in the follicle cells of the ovary, at around the time when the dorsoventral axis of the egg chamber is first established. Expressed in ovaries, early embryo (0-4 hours) and adult males. Almost undetectable in female carcasses. In ovaries, it is not detected in the germarium or early stage egg-chambers and is first detectable in the follicle cells of stage 8 egg-chambers. The peak of expression occurs in the follicle cells of stages 9 and early 10, and it disappears completely before stage 11. Not expressed in the germline cells (nurse cells and oocyte), with the possible exception of late stage 10 nurse cells. The CXXC motif was initially thought to constitute the active site of a potential protein disulfide isomerase activity. However, such motif is not essential, suggesting that it has no disulfide isomerase activity. Its precise role remains unclear. 'Windbeutel' means 'profiteroles' in German.