Cre-dependent GFP labeling and inducible ablation of mRGCs.

<p>Retina of adult <i>Opn4^Cre/+;Z/EG</i> mouse probed with (A) anti-OPN4 or (B) anti-GFP antibodies show staining of a small subset of cells. (C) Only a subset of GFP positive cells also stained with anti-OPN4 antibody. A section of the flat mount retina containing a cell (marked with an arrow) that stained with melanopsin antibody, but did not express detectable level of GFP is shown. (D) Retina of <i>Opn4^Cre/+;R26^iDTR/+</i> showed normal melanopsin immunostaining in a small fraction of RGCs. (E) Two weeks after DT administration, the number of melanopsin-immunoreactive cells were significantly reduced. (F) Average melanopsin immunoreactive cell density in WT and <i>Opn4^Cre/+;R26^iDTR/+</i> retina was comparable. Two weeks after DT administration, the number of cells in WT retina remained unchanged, while that in <i>Opn4^Cre/+;R26^iDTR/+</i> retina reduced from 62.3 mm⁻² to 2.8 mm⁻². No melanopsin immunostaining was observed in <i>Opn4^−/−</i> mice. It is important to note that retina from all DT-treated mice tested by immunostaining still retained a few melanopsin staining cells (arrows), implying incomplete expression of Cre in all mRGCs and/or insufficient level of bioavailable DT. Average cell counts (+SEM, n = 3 to 5 retinas) from each genotype/treatment group are shown. Significant difference in cell numbers (Student's <i>t</i> test, <i>p</i><0.05) between mRGCs without and with DT was highlighted with an asterisk.