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V. Jain, D. Poria, O. Saha, N. K. Dhingra; Expression of Specific Ganglion Cell Proteins by Brn3-Positive Retinal Ganglion Cells in Mouse. Invest. Ophthalmol. Vis. Sci. 2010;51(13):887.
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© ARVO (1962-2015); The Authors (2016-present)
Brn3 family of POU domain transcription factors are required for the development and survival of retinal ganglion cells (RGCs). Interestingly, these proteins are expressed by ~70% of RGCs even in adult retina, raising a possibility that these cells have a defined physiological role. To explore this, we studied the expression by Brn3-positive RGCs of specific ganglion cell proteins, including nonphosphorylated neurofilaments, parvalbumin and melanopsin.
Retinal wholemounts and radial sections from adult C57BL6 mouse were subjected to fluorescent double immunostaining for Brn3 or Brn3a and SMI-32, parvalbumin or melanopsin. Digital images were taken under epifluorescence microscope using two different emissions, and the data analyzed for co-expression of Brn3/Brn3a with the other proteins.
A small proportion of Brn3-positive RGCs expressed SMI-32 or parvalbumin. Approximately 3% of Brn3-positive cells were also positive for SMI-32. However, more than 40% of SMI32-positive RGCs expressed Brn3. Similarly, a subset of parvalbumin-positive cells expressed Brn3. With melanopsin C-terminus antibody that labels predominantly M1 type of intrinsically photosensitive RGCs (ipRGCs), we found that none of the Brn3a-positive RGCs, and a 0.2% of Brn3-positive RGCs expressed melanopsin. However, with melanopsin N-terminus antibody that labels both M1 and M2 type of ipRGCs, we found that none of the Brn3a-positive RGCs, but a relatively larger proportion of Brn3-positive cells expressed melanopsin.
Our study on co-localization of Brn3 and SMI-32 or parvalbumin is consistent with the hypothesis that Brn3-positive RGCs comprise multiple morphological and physiological subtypes, and therfore may not have a single physiological role. The results on coexpression of Brn3/Brn3a and melanopsin suggest that a small subset of Brn3b- and/or Brn3c-, but not Brn3a-positive RGCs coexpress melanopsin, and that the M2, but not the M1 type of ipRGCs preferentially express these Brn3 isoforms.
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