Abstract
In the Drosophila eye, photoreceptor clusters are arranged with mirror-image symmetry about the dorso-ventral midline. Recent work indicates critical rôles for Wingless and JAK/STAT signalling in setting up long-range gradients of positional information that determine this symmetry. Furthermore, important functions have been elucidated for Notch signalling in specifying the position of the axis of symmetry and then later in development in interpreting gradient information.
