Development of the Drosophila melanogaster Eye: from Precursor Specification to Terminal Differentiation

This chapter highlights the processes of formation of Drosophila melanogaster eye and its specification. Even though most processes in eye formation occur during late larval and pupa stages, initial steps of eye disc patterning already take place during early larval life. Clonal analyses of the first instar eye-antennal disc indicate that about 20 cells give rise to the eye, although clone size varies between individuals. During early stages, cells of the eye disc proliferate, leading to disc growth. During early second larval instar, changes in gene expression occur to subdivide the eye-antennal disc into an eye part and an antennal part. Expression of the Pax genes eyeless (ey) and twin of eyeless (toy), two major factors in eye development that are expressed in the entire disc, retracts to the posterior two-thirds while the homeodomain transcription factor Cut starts to be expressed in the anterior third. Ey/Toy expression marks the prospective eye part, whereas Cut expression defines the antenna part. In Drosophila, the specification of the compound eye is controlled by the genes ey, toy, eye gone, sine Oculis, optix, eyes absent, and dachshund that encode nuclear factors.