FRINGE IS ESSENTIAL FOR MIRROR SYMMETRY AND MORPHOGENESIS IN THE DROSOPHILA EYE

An early event in Drosophila eye development is the division of the ey e disc into dorsoventral domains. The dorsoventral pattern is displaye d in the adult compound eye as a distinct mirror symmetry across the d orsoventral midline or equator(1,2). The dorsoventral axis is also imp licated in organizing early development of the eye, as retinal differe ntiation is initiated at the posterior dorsoventral midline(3). Here w e show that Fringe is expressed specifically in the ventral half of th e undifferentiated eye disc, thus creating a dorsoventral boundary. Ec topic Fringe borders that are generated by clones of fringe(-) cells c an reverse the planar polarity of photoreceptor clusters, indicating t hat the Fringe boundary is crucial for the induction of mirror symmetr y. Lack of a Fringe boundary disrupts equatorial expression of Notch s ignalling proteins and causes a complete failure of eye development. O ur results indicate that the formation of the Fringe boundary and subs equent Notch signalling at the equator are essential for organizing mi rror symmetry and eye morphogenesis.