NEARSIGHTED MORPHOGENESIS IN THE DROSOPHI LA RETINA

Drosophila retinal morphogenesis progressively transforms an undiffere ntiated epithelium into a regular array or cristal of approximately 80 0 identical subunits, the ommatidia. This transformation results princ ipally from local and transient intercellular interactions which have been unraveled in great detail thanks to the relative simplicity of th e ommatidial structure and the amenability of Drosophila to genetic an d molecular analyses. At the level of the whole retina, lateral inhibi tion among proneural cells ensures that morphogenesis occurs with spat ial regularity whereas repetitive local interactions between adjacent ommatidia could be responsible for their either ventral or dorsal orie ntation. Within each ommatidium, cells are sequentially recruited arou nd the founding R8 photoreceptor through a stereotypical sequence of l ocal inductions. The development of the Drosophila retina illustrates how the assynchrony of morphogenesis can coordinate essentially short range intercellular communications, allowing the elaboration of a comp lex and regularly arrayed organ with minimal need for global concertat ion or prior paterning.