R7 photoreceptor specification requires Notch activity

Curr Biol. 2000 Nov 30;10(23):1507-10. doi: 10.1016/s0960-9822(00)00826-5.


The eight photoreceptors in each ommatidium of the Drosophila eye are assembled by a process of recruitment [1,2]. First, the R8 cell is singled out, and then subsequent photoreceptors are added in pairs (R2 and R5, R3 and R4, R1 and R6) until the final R7 cell acquires a neuronal fate. R7 development requires the Sevenless receptor tyrosine kinase which is activated by a ligand from R8 [3]. Here, we report that the specification of R7 requires a second signal that activates Notch. We found that a Notch target gene is expressed in R7 shortly after recruitment. When Notch activity was reduced, the cell was misrouted to an R1/R6 fate. Conversely, when activated Notch was present in the R1/R6 cells, it caused them to adopt R7 fates or, occasionally, cone cell fates. In this context, Notch activity appears to act co-operatively, rather than antagonistically, with the receptor tyrosine kinase/Ras pathway in R7 photoreceptor specification. We propose two models: a ratchet model in which Notch would allow cells to remain competent to respond to sequential rounds of Ras signalling, and a combinatorial model in which Notch and Ras signalling would act together to regulate genes that determine cell fate.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Drosophila / genetics
  • Drosophila / physiology*
  • Drosophila Proteins
  • Eye / growth & development
  • Eye / metabolism
  • Gene Expression Regulation, Developmental
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Photoreceptor Cells, Invertebrate / metabolism*
  • Proteins*
  • Receptors, Notch
  • Repressor Proteins / genetics
  • Repressor Proteins / metabolism
  • Signal Transduction*
  • Transcription, Genetic
  • ras Proteins / genetics
  • ras Proteins / metabolism


  • Drosophila Proteins
  • Membrane Proteins
  • N protein, Drosophila
  • Proteins
  • Receptors, Notch
  • Repressor Proteins
  • ras Proteins