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ABSTRACT
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.
Acknowledgements
We acknowledge laboratory technicians Ms Marja-Liisa Martimo-Halmetoja and Ms Minna Orreveteläinen for their contribution to the laboratory analyses.
Declaration of interest
None declared in relation to the current article.
Additional information
Notes on contributors
Juuso S. Nissilä
J.S.N., S.K.M., T.T.S., H.J.T., S.Y.O.S., V.J.K., T.E.T., and M.J.T. conceived the project and designed the experiments. Human brain tissue samplings were obtained at forensic autopsies by T.T.S. Brain areas were identified by H.J.T. Western blotting and immunohistochemistry analyses were organized and interpreted by S.K.M. with the help of S.Y.O.S., and H.J.T. also contributed in analysing the results. J.S.N., S.K.M., T.T.S., H.J.T., S.Y.O.S., T.E.T., V.J.K., and M.J.T. took part in writing the initial version of the manuscript. Immunoelectron Microscopy analyses were conducted and interpreted by R.T.S., and H.J.T, S.Y.O.S., as well as S.K.M also contributed in analysing the results. S.K.M prepared the figures. All the authors contributed in interpretation of the results and helped to write the final version of the manuscript. All the authors accepted the final version of the manuscript.
Satu K. Mänttäri
J.S.N., S.K.M., T.T.S., H.J.T., S.Y.O.S., V.J.K., T.E.T., and M.J.T. conceived the project and designed the experiments. Human brain tissue samplings were obtained at forensic autopsies by T.T.S. Brain areas were identified by H.J.T. Western blotting and immunohistochemistry analyses were organized and interpreted by S.K.M. with the help of S.Y.O.S., and H.J.T. also contributed in analysing the results. J.S.N., S.K.M., T.T.S., H.J.T., S.Y.O.S., T.E.T., V.J.K., and M.J.T. took part in writing the initial version of the manuscript. Immunoelectron Microscopy analyses were conducted and interpreted by R.T.S., and H.J.T, S.Y.O.S., as well as S.K.M also contributed in analysing the results. S.K.M prepared the figures. All the authors contributed in interpretation of the results and helped to write the final version of the manuscript. All the authors accepted the final version of the manuscript.
Terttu T. Särkioja
J.S.N., S.K.M., T.T.S., H.J.T., S.Y.O.S., V.J.K., T.E.T., and M.J.T. conceived the project and designed the experiments. Human brain tissue samplings were obtained at forensic autopsies by T.T.S. Brain areas were identified by H.J.T. Western blotting and immunohistochemistry analyses were organized and interpreted by S.K.M. with the help of S.Y.O.S., and H.J.T. also contributed in analysing the results. J.S.N., S.K.M., T.T.S., H.J.T., S.Y.O.S., T.E.T., V.J.K., and M.J.T. took part in writing the initial version of the manuscript. Immunoelectron Microscopy analyses were conducted and interpreted by R.T.S., and H.J.T, S.Y.O.S., as well as S.K.M also contributed in analysing the results. S.K.M prepared the figures. All the authors contributed in interpretation of the results and helped to write the final version of the manuscript. All the authors accepted the final version of the manuscript.
Hannu J. Tuominen
J.S.N., S.K.M., T.T.S., H.J.T., S.Y.O.S., V.J.K., T.E.T., and M.J.T. conceived the project and designed the experiments. Human brain tissue samplings were obtained at forensic autopsies by T.T.S. Brain areas were identified by H.J.T. Western blotting and immunohistochemistry analyses were organized and interpreted by S.K.M. with the help of S.Y.O.S., and H.J.T. also contributed in analysing the results. J.S.N., S.K.M., T.T.S., H.J.T., S.Y.O.S., T.E.T., V.J.K., and M.J.T. took part in writing the initial version of the manuscript. Immunoelectron Microscopy analyses were conducted and interpreted by R.T.S., and H.J.T, S.Y.O.S., as well as S.K.M also contributed in analysing the results. S.K.M prepared the figures. All the authors contributed in interpretation of the results and helped to write the final version of the manuscript. All the authors accepted the final version of the manuscript.
Timo E. Takala
J.S.N., S.K.M., T.T.S., H.J.T., S.Y.O.S., V.J.K., T.E.T., and M.J.T. conceived the project and designed the experiments. Human brain tissue samplings were obtained at forensic autopsies by T.T.S. Brain areas were identified by H.J.T. Western blotting and immunohistochemistry analyses were organized and interpreted by S.K.M. with the help of S.Y.O.S., and H.J.T. also contributed in analysing the results. J.S.N., S.K.M., T.T.S., H.J.T., S.Y.O.S., T.E.T., V.J.K., and M.J.T. took part in writing the initial version of the manuscript. Immunoelectron Microscopy analyses were conducted and interpreted by R.T.S., and H.J.T, S.Y.O.S., as well as S.K.M also contributed in analysing the results. S.K.M prepared the figures. All the authors contributed in interpretation of the results and helped to write the final version of the manuscript. All the authors accepted the final version of the manuscript.
Vesa J. Kiviniemi
J.S.N., S.K.M., T.T.S., H.J.T., S.Y.O.S., V.J.K., T.E.T., and M.J.T. conceived the project and designed the experiments. Human brain tissue samplings were obtained at forensic autopsies by T.T.S. Brain areas were identified by H.J.T. Western blotting and immunohistochemistry analyses were organized and interpreted by S.K.M. with the help of S.Y.O.S., and H.J.T. also contributed in analysing the results. J.S.N., S.K.M., T.T.S., H.J.T., S.Y.O.S., T.E.T., V.J.K., and M.J.T. took part in writing the initial version of the manuscript. Immunoelectron Microscopy analyses were conducted and interpreted by R.T.S., and H.J.T, S.Y.O.S., as well as S.K.M also contributed in analysing the results. S.K.M prepared the figures. All the authors contributed in interpretation of the results and helped to write the final version of the manuscript. All the authors accepted the final version of the manuscript.
Raija T. Sormunen
J.S.N., S.K.M., T.T.S., H.J.T., S.Y.O.S., V.J.K., T.E.T., and M.J.T. conceived the project and designed the experiments. Human brain tissue samplings were obtained at forensic autopsies by T.T.S. Brain areas were identified by H.J.T. Western blotting and immunohistochemistry analyses were organized and interpreted by S.K.M. with the help of S.Y.O.S., and H.J.T. also contributed in analysing the results. J.S.N., S.K.M., T.T.S., H.J.T., S.Y.O.S., T.E.T., V.J.K., and M.J.T. took part in writing the initial version of the manuscript. Immunoelectron Microscopy analyses were conducted and interpreted by R.T.S., and H.J.T, S.Y.O.S., as well as S.K.M also contributed in analysing the results. S.K.M prepared the figures. All the authors contributed in interpretation of the results and helped to write the final version of the manuscript. All the authors accepted the final version of the manuscript.
Seppo Y. O. Saarela
J.S.N., S.K.M., T.T.S., H.J.T., S.Y.O.S., V.J.K., T.E.T., and M.J.T. conceived the project and designed the experiments. Human brain tissue samplings were obtained at forensic autopsies by T.T.S. Brain areas were identified by H.J.T. Western blotting and immunohistochemistry analyses were organized and interpreted by S.K.M. with the help of S.Y.O.S., and H.J.T. also contributed in analysing the results. J.S.N., S.K.M., T.T.S., H.J.T., S.Y.O.S., T.E.T., V.J.K., and M.J.T. took part in writing the initial version of the manuscript. Immunoelectron Microscopy analyses were conducted and interpreted by R.T.S., and H.J.T, S.Y.O.S., as well as S.K.M also contributed in analysing the results. S.K.M prepared the figures. All the authors contributed in interpretation of the results and helped to write the final version of the manuscript. All the authors accepted the final version of the manuscript.
Markku J. Timonen
J.S.N., S.K.M., T.T.S., H.J.T., S.Y.O.S., V.J.K., T.E.T., and M.J.T. conceived the project and designed the experiments. Human brain tissue samplings were obtained at forensic autopsies by T.T.S. Brain areas were identified by H.J.T. Western blotting and immunohistochemistry analyses were organized and interpreted by S.K.M. with the help of S.Y.O.S., and H.J.T. also contributed in analysing the results. J.S.N., S.K.M., T.T.S., H.J.T., S.Y.O.S., T.E.T., V.J.K., and M.J.T. took part in writing the initial version of the manuscript. Immunoelectron Microscopy analyses were conducted and interpreted by R.T.S., and H.J.T, S.Y.O.S., as well as S.K.M also contributed in analysing the results. S.K.M prepared the figures. All the authors contributed in interpretation of the results and helped to write the final version of the manuscript. All the authors accepted the final version of the manuscript.