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Satchidananda Panda, Megumi Hatori, Sheena Racheal Keding, Hiep Le; Cellular circuitry of melanopsin function. Journal of Vision 2009;9(14):24-249. doi: 10.1167/9.14.24.
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“Identifying the full complement of melanopsin expressing retinal ganglion cells and understanding their cellular function is critical. However, the existing methods to mark mRGCs and acutely perturb them are insufficient. We have generated a mouse line that expresses Cre recombinase from the native melanopsin locus and used this mouse to comprehensively mark and acutely ablate mRGCs.
We generated a mouse with targeted insertion of Cre-recombinase into the native melanopsin locus. To mark the melanopsin cells, we bred it with a Z/EG mice. This strategy allows Cre-dependent expression of green fluorescent protein (GFP) from a strong b-actin promoter. In the resultant mice melanopsin cells are marked with a GFP marker. In the retina of the resultant reporter mice, GFP expressing cells were mostly found in the ganglion cell layer and in the innermost region of the inner nuclear layer. These cells had extensive dendritic arborization characteristic of the mRGCs. An average of 131 GFP expressing cells/mm2 (±25.4, SD, n = 3) were found in these retina, 42.6% of which also expressed immunologically detectable levels of melanopsin. This revealed that only a subset of mRGCs express enough immunocytochemically detectable level of melanopsin. We also used Cre-inducible diphtheria toxin receptor (iDTR) expression strategy to express the DTR in mRGCs. mRGCs develop normally but can be acutely ablated upon diphtheria toxin administration. The mRGC-ablated mice exhibited normal outer retinal function. However, they completely lacked non-image forming visual responses such as circadian photoentrainment, light modulation of activity, and PLR. These results point to the mRGCs as the site of functional integration of the rod/cone and melanopsin phototransduction pathways and as the primary anatomical site for the divergence of image-forming and non-image forming photoresponses in mammals.”
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