The distribution of melanopsin (OPN4) protein in the human brain.
Until now, melanopsin (OPN4) - a specialized photopigment being responsive especially to blue light wavelengths - has not been found in the human brain at protein level outside the retina. More specifically, OPN4 has only been found in about 2% of retinal ganglion cells (i.e. in intrinsically photosensitive retinal ganglion cells), and in a subtype of retinal cone-cells. Given that Allen Institute for Brain Science has described a wide distribution of OPN4 mRNA in two human brains, we aimed to investigate whether OPN4 is present in the human brain also at protein level. Western blotting and immunohistochemistry, as well as immunoelectron microscopy, were used to analyse the existence and distribution of OPN4 protein in 18 investigated areas of the human brain in samples obtained in forensic autopsies from 10 male subjects (54 ± 3.5 years). OPN4 protein expression was found in all subjects, and, furthermore, in 5 out of 10 subjects in all investigated brain areas localized in membranous compartments and cytoplasmic vesicles of neurons. To our opinion, the wide distribution of OPN4 in central areas of the human brain evokes a question whether ambient light has important straight targets in the human brain outside the retinohypothalamic tract (RHT). Further studies are, however, needed to investigate the putative physiological phototransductive actions of inborn OPN4 protein outside the RHT in the human brain.
a University of Oulu, Center for Life Course Health Research , Oulu , Finland.|b Department of Biology, University of Oulu , Oulu , Finland.
Juuso S
JS
Nissilä
b Department of Biology, University of Oulu , Oulu , Finland.
Satu K
SK
Mänttäri
c University of Oulu , Institute of Diagnostics, Forensic Medicine , Oulu , Finland.
Terttu T
TT
Särkioja
d University of Oulu , Institute of Diagnostics, Pathology , Oulu , Finland.|e Department of Pathology , Oulu University Hospital , Oulu , Finland.
Hannu J
HJ
Tuominen
f Oulu Deaconess Institute , Oulu , Finland.
Timo E
TE
Takala
g Department of Diagnostic Radiology , Oulu University Hospital , Oulu , Finland.
Vesa J
VJ
Kiviniemi
d University of Oulu , Institute of Diagnostics, Pathology , Oulu , Finland.|e Department of Pathology , Oulu University Hospital , Oulu , Finland.|h Biocenter Oulu , University of Oulu , Oulu , Finland.
Raija T
RT
Sormunen
b Department of Biology, University of Oulu , Oulu , Finland.
Seppo Y O
SY
Saarela
a University of Oulu, Center for Life Course Health Research , Oulu , Finland.
Markku J
MJ
Timonen
D001921:Brain / Q000378:metabolism*; D002102:Cadaver; D005786:Gene Expression Regulation / Q000502:physiology*; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D016253:Microscopy, Immunoelectron; D008875:Middle Aged; D021381:Protein Transport; D012160:Retina / Q000378:metabolism; D012165:Retinal Ganglion Cells / Q000502:physiology; D017299:Rod Opsins / Q000235:genetics / Q000378:metabolism*; D014018:Tissue Distribution; D000099210:Melanopsin
D017299:Rod Opsins; D000099210:Melanopsin
Chromophore; OPN4; human brain; melanopsin; non-visual phototransduction; opsin