A Go-type opsin mediates the shadow reflex in the annelid Platynereis dumerilii

BMC Biol. 2018 Apr 18;16(1):41. doi: 10.1186/s12915-018-0505-8.


Background: The presence of photoreceptive molecules outside the eye is widespread among animals, yet their functions in the periphery are less well understood. Marine organisms, such as annelid worms, exhibit a 'shadow reflex', a defensive withdrawal behaviour triggered by a decrease in illumination. Herein, we examine the cellular and molecular underpinnings of this response, identifying a role for a photoreceptor molecule of the Go-opsin class in the shadow response of the marine bristle worm Platynereis dumerilii.

Results: We found Pdu-Go-opsin1 expression in single specialised cells located in adult Platynereis head and trunk appendages, known as cirri. Using gene knock-out technology and ablation approaches, we show that the presence of Go-opsin1 and the cirri is necessary for the shadow reflex. Consistently, quantification of the shadow reflex reveals a chromatic dependence upon light of approximately 500 nm in wavelength, matching the photoexcitation characteristics of the Platynereis Go-opsin1. However, the loss of Go-opsin1 does not abolish the shadow reflex completely, suggesting the existence of a compensatory mechanism, possibly acting through a ciliary-type opsin, Pdu-c-opsin2, with a Lambdamax of approximately 490 nm.

Conclusions: We show that a Go-opsin is necessary for the shadow reflex in a marine annelid, describing a functional example for a peripherally expressed photoreceptor, and suggesting that, in different species, distinct opsins contribute to varying degrees to the shadow reflex.

Keywords: Platynereis dumerilii; annelid; behaviour; evolution; marine; non-visual; opsins; peripheral photoreceptors; shadow reflex.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Annelida / classification
  • Annelida / genetics*
  • Evolution, Molecular
  • Opsins / genetics*
  • Phylogeny


  • Opsins