The effect of the specificity box upon commitment of RPCs is not simply due to possible effects on nuclear localization. (a) The nuclear/cytoplasmic distribution of MYC-XOTX2 and MYC-OTD (as indicated at the left) is shown in lipofected retinal cells, and is compared to cytoplasmic GFP fluorescence; while MYC-XOTX2 shows an exclusively nuclear localization, MYC-OTD is partly cytoplasmic; on the contrary, MYC-OTD/box2 and MYC-OTD/box5b are targeted to the nucleus; a NLS-MYC-OTD fusion protein is forced into the nucleus (bottom row). (b) Endogenous XOTX2 protein distribution is detected by a specific antibody (red fluorescence) in the Xenopus retinal nuclei. (c) Although it forces OTD to the nucleus, a NLS-Myc-otd fusion construct does not have any effect on cell fate of RPCs. Counted cells were as indicated in the histogram (n), from six retinae for GFP, and four retinae for NLS-Myc-otd. PC, photoreceptor cells; HC, horizontal cells; BC, bipolar cells; AC, amacrine cells; GC, ganglion cells. Nuclei are counterstained with Hoechst.