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Single–base pair differences in a shared motif determine differential Rhodopsin expression

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Science  04 Dec 2015:
Vol. 350, Issue 6265, pp. 1258-1261
DOI: 10.1126/science.aab3417

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Broad versus restricted expression

Color vision in fruit flies requires the restricted expression of light-sensing rhodopsins with different wavelength sensitivities in subsets of photoreceptors. However, all photoreceptors express factors that transduce and amplify the visual signal. Rister et al. found that the distinct expression patterns are determined by a highly tunable regulatory motif. Genes that are broadly expressed have a palindromic variant of the motif. Spatially restricted rhodopsin genes display single-base-pair changes that alter the symmetry of the palindrome and are critical for subtype-specific expression. These findings on the differential regulation of gene expression in fly photoreceptors have implications for the evolution of neuronal subtype diversity.

Science, this issue p. 1258

Abstract

The final identity and functional properties of a neuron are specified by terminal differentiation genes, which are controlled by specific motifs in compact regulatory regions. To determine how these sequences integrate inputs from transcription factors that specify cell types, we compared the regulatory mechanism of Drosophila Rhodopsin genes that are expressed in subsets of photoreceptors to that of phototransduction genes that are expressed broadly, in all photoreceptors. Both sets of genes share an 11–base pair (bp) activator motif. Broadly expressed genes contain a palindromic version that mediates expression in all photoreceptors. In contrast, each Rhodopsin exhibits characteristic single-bp substitutions that break the symmetry of the palindrome and generate activator or repressor motifs critical for restricting expression to photoreceptor subsets. Sensory neuron subtypes can therefore evolve through single-bp changes in short regulatory motifs, allowing the discrimination of a wide spectrum of stimuli.

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