April 2014
Volume 55, Issue 13
Free
ARVO Annual Meeting Abstract  |   April 2014
The Cone Conundrum: Intact Cone Signaling Pathways Found in the First Mammalian Rod Monochromat
Author Affiliations & Notes
  • Lorian Elizabeth Schweikert
    Biological Sciences, Florida Institute of Technology, Melbourne, FL
  • Michael S Grace
    Biological Sciences, Florida Institute of Technology, Melbourne, FL
  • Jeffry Fasick
    Biological Sciences, University of South Florida St. Petersburg, St. Petersburg, FL
  • Footnotes
    Commercial Relationships Lorian Schweikert, None; Michael Grace, None; Jeffry Fasick, None
  • Footnotes
    Support None
Investigative Ophthalmology & Visual Science April 2014, Vol.55, 4381. doi:
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      Lorian Elizabeth Schweikert, Michael S Grace, Jeffry Fasick; The Cone Conundrum: Intact Cone Signaling Pathways Found in the First Mammalian Rod Monochromat. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4381.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract
 
Purpose
 

Vision in all mammals occurs through “duplex” retinae containing both rod and cone photoreceptors, the signals from which are processed through cone-and/or rod-specific retinal interneuron pathways. Recent investigations, however, have determined that several cetacean families possess mutations in their single cone opsin gene likely resulting in a condition unique among mammals known as rod monochromacy. Natural and artificial loss-of-function mutations in mammalian opsin genes are reported to cause massive photoreceptor loss and large-scale remodeling of the retina. Here we investigated the cellular organization of the bowhead whale (Balaena mysticetus) retina to determine how this unprecedented functional loss of an entire mammalian photoreceptor class affects light signaling pathways in the retina.

 
Methods
 

Sequencing was performed for cDNA derived from cone opsin mRNA in balaenid whales. Light microscopy, transmission electron microscopy and anti-opsin immunofluorescence were used to characterize retinal architecture and to determine the photoreceptor types in B. mysticetus. In addition, bipolar cell immunofluorescence was used to identify bipolar cell types in the retina.

 
Results
 

Genetic analyses indicate the severe truncation of the single cone opsin mRNA in the B. mysticetus retina, indicating loss of cone cell function, but maintenance of a non-photosensitive, opsin-expressing cone-like cell in the retina. Immunofluorescence, histological and ultrastructural analyses indicate the complete loss of LWS cone outer segments in the balaenid whale retina, suggesting the total loss of cone-based photoreception, but maintenance of cone soma and cone bipolar cells.

 
Conclusions
 

These findings show for the first time a rod-monochromatic mammalian retina, and suggest that despite the loss of cone-mediated photoreception, the associated cone signaling machinery may be functionally maintained for multi-channel rod-based signaling in balaenid whales.

 
 
Bowhead whale (A) and bovine (B) retinal sections labeled with antisera against rhodopsin (red fluorescence), M/LWS cone opsin (green fluorescence), and DAPI nucleic stain (blue).
 
Bowhead whale (A) and bovine (B) retinal sections labeled with antisera against rhodopsin (red fluorescence), M/LWS cone opsin (green fluorescence), and DAPI nucleic stain (blue).
 
Keywords: 693 retinal connections, networks, circuitry • 604 mutations • 648 photoreceptors  
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