Abstract

Drosophila colour vision is achieved by R7 and R8 photoreceptor cells present in every ommatidium. The fly retina contains two types of ommatidia, called 'pale' and 'yellow', defined by different rhodopsin pairs expressed in R7 and R8 cells. Similar to the human cone photoreceptors, these ommatidial subtypes are distributed stochastically in the retina. The choice between pale versus yellow ommatidia is made in R7 cells, which then impose their fate onto R8. Here we report that the Drosophila dioxin receptor Spineless is both necessary and sufficient for the formation of the ommatidial mosaic. A short burst of spineless expression at mid-pupation in a large subset of R7 cells precedes rhodopsin expression. In spineless mutants, all R7 and most R8 cells adopt the pale fate, whereas overexpression of spineless is sufficient to induce the yellow R7 fate. Therefore, this study suggests that the entire retinal mosaic required for colour vision is defined by the stochastic expression of a single transcription factor, Spineless.

1. Center for Developmental Genetics, Department of Biology, New York University, 100 Washington Place, New York, New York 10003, USA
2. Department of Biology, Washington University, Box 1229, 1 Brookings Drive, St Louis, Missouri 63130, USA
3. †Present address: Department of Neurobiology, Stanford University, Fairchild D200, 299 West Campus Drive, Stanford, California 94305, USA
4. *These authors contributed equally to this work

Correspondence to: Claude Desplan¹ Correspondence and requests for materials should be addressed to C.D. (Email: claude.desplan@nyu.edu).

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