Ommatidial polarity in the Drosophila eye is determined by the direction of furrow progression and local interactions.

The adult eye of Drosophila is a highly ordered structure. It is composed of about 800 ommatidia, each displaying precise polarity. The ommatidia are arranged about an axis of mirror image symmetry, the equator, which lies along the dorsoventral midline of the eye. We use hedgehog pathway mutants to induce ectopic morphogenetic furrows and use these as a tool to investigate the establishment of ommatidial polarity. Our results show that ommatidial clusters are self-organising units whose polarity in one axis is determined by the direction of furrow progression, and which can independently define the position of an equator without reference to the global coordinates of the eye disc.