Generation of Third Dimension: Axial Patterning in the Developing Drosophila Eye

Abstract

Axial patterning, a fundamental process during organogenesis, is required for transition of a single layer organ primordium to a three-dimensional organ in all multi-cellular organisms. Axial patterning involves delineation of antero-posterior (AP), dorsal-ventral (DV), and proximo-distal (PD) axes. Any deviation in this fundamental process of organogenesis results in patterning and growth defects in the organ. The Drosophila eye model has been extensively used to study axial patterning. In the developing Drosophila eye, dorso-ventral (DV) lineage is the first axis to be determined, which is followed by generation of the AP axis. The PD axis is not well defined in the Drosophila eye as the adult eye is located in a socket on the adult head. The default state of the Drosophila early eye primordium is ventral, and the dorsal fate is established by onset of expression of dorsal eye fate selector pannier (pnr) in a group of cells on the dorsal eye margin. The boundary between dorsal and ventral compartments is the site for activation of Notch (N) signaling and is referred to as the equator. Activation of N signaling is crucial for initiating the cell proliferation and differentiation in the developing Drosophila eye imaginal disc. This chapter will focus on (a) how axial patterning occurs in the developing Drosophila eye; (b) how the developing eye field gets divided into dorsal and ventral cell populations, and (c) how dorso-ventral (DV) patterning genes contribute towards the growth and patterning of the fly retina.