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J Exp Biol. 2014 Sep 1;217(Pt 17):3133-45. doi: 10.1242/jeb.107383. Epub 2014 Jun 19.

Opsin expression in Limulus eyes: a UV opsin is expressed in each eye type and co-expressed with a visible light-sensitive opsin in ventral larval eyes.

Author information

  • 1Whitney Laboratory for Marine Bioscience, University of Florida, St Augustine, FL 32080, USA Departments of Neuroscience and Biology, University of Florida, Gainesville, FL 32611, USA Battelle@whitney.ufl.edu.
  • 2Whitney Laboratory for Marine Bioscience, University of Florida, St Augustine, FL 32080, USA Departments of Neuroscience and Biology, University of Florida, Gainesville, FL 32611, USA.
  • 3Department of Ophthalmology, University of Florida, Gainesville, FL 32610, USA.
  • 4Department of Biology, University of Maryland, College Park, MD 20742, USA.

Abstract

The eyes of the horseshoe crab, Limulus polyphemus, are a model for studies of visual function and the visual systems of euarthropods. Much is known about the structure and function of L. polyphemus photoreceptors, much less about their photopigments. Three visible-light-sensitive L. polyphemus opsins were characterized previously (LpOps1, 2 and 5). Here we characterize a UV opsin (LpUVOps1) that is expressed in all three types of L. polyphemus eyes. It is expressed in most photoreceptors in median ocelli, the only L. polyphemus eyes in which UV sensitivity was previously detected, and in the dendrite of eccentric cells in lateral compound eyes. Therefore, eccentric cells, previously thought to be non-photosensitive second-order neurons, may actually be UV-sensitive photoreceptors. LpUVOps1 is also expressed in small photoreceptors in L. polyphemus ventral larval eyes, and intracellular recordings from these photoreceptors confirm that LpUVOps1 is an active, UV-sensitive photopigment. These photoreceptors also express LpOps5, which we demonstrate is an active, long-wavelength-sensitive photopigment. Thus small photoreceptors in ventral larval eyes, and probably those of the other larval eyes, have dual sensitivity to UV and visible light. Interestingly, the spectral tuning of small ventral photoreceptors may change day to night, because the level of LpOps5 in their rhabdoms is lower during the day than during the night, whereas LpUVOps1 levels show no diurnal change. These and previous findings show that opsin co-expression and the differential regulation of co-expressed opsins in rhabdoms is a common feature of L. polyphemus photoreceptors.

© 2014. Published by The Company of Biologists Ltd.

KEYWORDS:

Diurnal rhythms; Limulus photoreceptors; Opsin co-expression; UV opsin; UV sensitivity

PMID:
24948643
[PubMed - indexed for MEDLINE]
PMCID:
PMC4148189
Free PMC Article
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