Two Opsin 3-Related Proteins in the Chicken Retina and Brain: A TMT-Type Opsin 3 Is a Blue-Light Sensor in Retinal Horizontal Cells, Hypothalamus, and Cerebellum

PLoS One. 2016 Nov 18;11(11):e0163925. doi: 10.1371/journal.pone.0163925. eCollection 2016.


Opsin family genes encode G protein-coupled seven-transmembrane proteins that bind a retinaldehyde chromophore in photoreception. Here, we sought potential as yet undescribed avian retinal photoreceptors, focusing on Opsin 3 homologs in the chicken. We found two Opsin 3-related genes in the chicken genome: one corresponding to encephalopsin/panopsin (Opn3) in mammals, and the other belonging to the teleost multiple tissue opsin (TMT) 2 group. Bioluminescence imaging and G protein activation assays demonstrated that the chicken TMT opsin (cTMT) functions as a blue light sensor when forced-expressed in mammalian cultured cells. We did not detect evidence of light sensitivity for the chicken Opn3 (cOpn3). In situ hybridization demonstrated expression of cTMT in subsets of differentiating cells in the inner retina and, as development progressed, predominant localization to retinal horizontal cells (HCs). Immunohistochemistry (IHC) revealed cTMT in HCs as well as in small numbers of cells in the ganglion and inner nuclear layers of the post-hatch chicken retina. In contrast, cOpn3-IR cells were found in distinct subsets of cells in the inner nuclear layer. cTMT-IR cells were also found in subsets of cells in the hypothalamus. Finally, we found differential distribution of cOpn3 and cTMT proteins in specific cells of the cerebellum. The present results suggest that a novel TMT-type opsin 3 may function as a photoreceptor in the chicken retina and brain.

MeSH terms

  • Animals
  • Brain / cytology
  • Brain / metabolism*
  • Calcium / metabolism
  • Cerebellum / cytology
  • Cerebellum / metabolism
  • Chickens
  • Exons
  • Gene Expression
  • Genomics
  • Hypothalamus / cytology
  • Hypothalamus / metabolism
  • Introns
  • Light
  • Multigene Family
  • Phylogeny
  • Protein Transport
  • RNA Transport
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • Retina / cytology
  • Retina / metabolism*
  • Retinal Horizontal Cells / physiology
  • Rod Opsins / genetics
  • Rod Opsins / metabolism*


  • RNA, Messenger
  • Rod Opsins
  • Calcium

Grant support

Olympus Corporation is not a funder in this study. This commercial affiliation provided support in the form of salaries for an author [TS], but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of this author are articulated in the ‘author contributions’ section. The funders, KAKENHI (grant numbers 15H00812 to Takahiro Yamashita; 16H02515 to Yoshinori Shichida; 24500382 and 22657057 to Hideyo Ohuchi) and Pfizer Japan Inc. (to Hideyo Ohuchi), as stated previous and revised versions, had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript, either.