Functional opsin patterning for Drosophila color vision is established through signaling pathways in adjacent object-detection neurons

Vision is mainly based on two different tasks, object detection and color discrimination through activities of photoreceptor (PR) cells. Drosophila compound eye consists of [~]800 ommatidia. Every ommatidium contains eight PR cells; six outer cells (R1-R6) and two inner cells (R7 and R8) by which object detection and color vision are achieved, respectively. Expression of opsin genes in R7 and R8 is highly coordinated through the instructive signal from R7 to R8, and two major ommatidial subtypes are distributed stochastically; pale type expresses Rh3/Rh5, while yellow type expresses Rh4/Rh6 in R7/R8. The homeodomain protein Defective proventriculus (Dve) is expressed in yellow-type R7 and in six outer PRs, and it is involved in Rh3 repression to specify the yellow-type R7. dve mutant eyes exhibited atypical coupling, Rh3/Rh6 and Rh4/Rh5, indicating that the Dve activity is required for proper opsin coupling. Surprisingly, Dve activity in R1 is required for instructive signal, whereas those in R6 and R7 block the signal. Our results indicate that functional coupling of two different neurons is established through signaling pathways from adjacent neurons that are functionally different. Summary StatementDve activity is required for proper opsin coupling of two neurons that is established through signaling pathways from adjacent neurons that are functionally different.