Drawing lines in the Drosophila wing: initiation of wing vein development

It has been proposed that wing veins in Drosophila form at boundaries betwe en discrete sectors of cells that subdivide the anterior-posterior axis of the developing wing primordium. Recently, analysis of events underlying ini tiation of vein formation suggests that there is a general developmental me chanism for drawing lines between adjacent domains of cells, which is refer red to as 'for-export-only-signaling'. In this model, cells in one domain p roduce a short range signal to which they cannot respond. As a consequence of this constraint, cells lying in a narrow line immediately outside the si gnal-producing domain are the only cells that can respond to the signal by activating expression of vein-promoting genes.