Parallel activin and BMP signaling coordinates R7/R8 photoreceptor subtype pairing in the stochastic Drosophila retina

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Abstract

Drosophila color vision is achieved by comparing outputs from two types of color-sensitive photoreceptors, R7 and R8. Ommatidia (unit eyes) are classified into two subtypes, known as 'pale' or 'yellow', depending on Rhodopsin expression in R7 and R8. Subtype specification is controlled by a stochastic decision in R7 and instructed to the underlying R8. We find that the Activin receptor Baboon is required in R8 to receive non-redundant signaling from the three Activin ligands, activating the transcription factor dSmad2. Concomitantly, two BMP ligands activate their receptor, Thickveins, and the transcriptional effector, Mad. The Amon TGFβ processing factor appears to regulate components of the TGFβ pathway specifically in pale R7. Mad and dSmad2 cooperate to modulate the Hippo pathway kinase Warts and the growth regulator Melted; two opposing factors of a bi-stable loop regulating R8 Rhodopsin expression. Therefore, TGFβ and growth pathways interact in postmitotic cells to precisely coordinate cell-specific output.

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Brent S Wells

Center for Developmental Genetics, Department of Biology, New York University, New York, United States

Competing interests
The authors declare that no competing interests exist.
Daniela Pistillo

Center for Developmental Genetics, Department of Biology, New York University, New York, United States

Competing interests
The authors declare that no competing interests exist.
Erin Barnhart

Center for Developmental Genetics, Department of Biology, New York University, New York, United States

Competing interests
The authors declare that no competing interests exist.
Claude Desplan

Center for Developmental Genetics, Department of Biology, New York University, New York, United States

For correspondence
cd38@nyu.edu

Competing interests
The authors declare that no competing interests exist.

"This ORCID iD identifies the author of this article:" 0000-0002-6914-1413

Funding

National Eye Institute (EY022843-01)

Brent S Wells

National Eye Institute (EY13012)

Claude Desplan

European Molecular Biology Organization (ALTF 506-2002)

Daniela Pistillo

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

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This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.