A combinatorial cis-regulatory logic restricts color-sensing Rhodopsins to specific photoreceptor subsets in Drosophila

PLoS Genet. 2021 Jun 23;17(6):e1009613. doi: 10.1371/journal.pgen.1009613. eCollection 2021 Jun.

Abstract

Color vision in Drosophila melanogaster is based on the expression of five different color-sensing Rhodopsin proteins in distinct subtypes of photoreceptor neurons. Promoter regions of less than 300 base pairs are sufficient to reproduce the unique, photoreceptor subtype-specific rhodopsin expression patterns. The underlying cis-regulatory logic remains poorly understood, but it has been proposed that the rhodopsin promoters have a bipartite structure: the distal promoter region directs the highly restricted expression in a specific photoreceptor subtype, while the proximal core promoter region provides general activation in all photoreceptors. Here, we investigate whether the rhodopsin promoters exhibit a strict specialization of their distal (subtype specificity) and proximal (general activation) promoter regions, or if both promoter regions contribute to generating the photoreceptor subtype-specific expression pattern. To distinguish between these two models, we analyze the expression patterns of a set of hybrid promoters that combine the distal promoter region of one rhodopsin with the proximal core promoter region of another rhodopsin. We find that the function of the proximal core promoter regions extends beyond providing general activation: these regions play a previously underappreciated role in generating the non-overlapping expression patterns of the different rhodopsins. Therefore, cis-regulatory motifs in both the distal and the proximal core promoter regions recruit transcription factors that generate the unique rhodopsin patterns in a combinatorial manner. We compare this combinatorial regulatory logic to the regulatory logic of olfactory receptor genes and discuss potential implications for the evolution of rhodopsins.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Base Sequence
  • Color Vision / genetics*
  • Drosophila Proteins / genetics*
  • Drosophila Proteins / metabolism
  • Drosophila melanogaster / genetics*
  • Drosophila melanogaster / metabolism
  • Evolution, Molecular
  • Female
  • Gene Expression Regulation
  • Genes, Reporter
  • Green Fluorescent Proteins / genetics
  • Green Fluorescent Proteins / metabolism
  • Photoreceptor Cells, Invertebrate / classification
  • Photoreceptor Cells, Invertebrate / cytology
  • Photoreceptor Cells, Invertebrate / metabolism*
  • Promoter Regions, Genetic*
  • Protein Binding
  • Protein Isoforms / genetics
  • Protein Isoforms / metabolism
  • Rhodopsin / genetics*
  • Rhodopsin / metabolism
  • Transcription Factors / genetics*
  • Transcription Factors / metabolism

Substances

  • Drosophila Proteins
  • Protein Isoforms
  • Rh5 protein, Drosophila
  • Transcription Factors
  • Green Fluorescent Proteins
  • Rhodopsin