Pax6/PAX6 gene dosage affects both the total number of RGCs, the number of RGC axons projected to the thalamus and the proportion that project ipsilaterally. (A) Quantification of Brn3a-expressing cells in the retinae of E16.5 Pax6Sey/+, Pax6+/+, PAX77+ and PAX77+/+ embryos. Left, a wholemount retina immunostained with Brn3a antibody (green fluorescence). Dotted circle indicates location of optic nerve head. Boxed area shows location of one of the 160 μm × 160 μm sampling areas, in this case in ventro-temporal retina, used to calculate density of Brn3a-expressing cells (see Methods). The inset is an example of high power image showing individual Brn3a-expressing nuclei. Histogram on right shows the average total number of Brn3a-expressing cells in the retina Sample sizes: Pax6Sey/+ n = 5; Pax6+/+ n = 4; PAX77+ n = 3; PAX77+/+ n = 3. (B) Histogram showing the total numbers of RGCs per retina retrogradely labelled by unilateral injection of DiI into the dorsal thalamus of E16.5 embryos. Each bar is divided into ipsilateral (black) and contralateral (white) components. (C) Histogram showing the percentage of RGCs projecting ipsilaterally calculated from the data presented in (B). Sample sizes in B and C: Pax6Sey/+ n = 4; Pax6+/+ n = 9; PAX77+ n = 5; PAX77+/+ n = 4. In A-C, the embryo genotypes are indicated below each graph and are arranged in order of increasing Pax6/PAX6 gene dosage. In all histograms error bars are s.e.m.s with * indicating a significant difference from Pax6+/+ embryos (p < 0.05 Mann-Whitney Rank Sum test). (E) Cartoon summarising the relationship between Pax6 gene dosage, and the number and location of RGCs generated by the retina (ovals), and whether they project ipsilaterally (filled red) contralaterally (filled yellow) or fail to project (unfilled) to the thalamus. Scale bar in A = 10 μm. Abbreviations: n, nasal; t, temporal, d, dorsal; v, ventral.
Manuel et al. BMC Developmental Biology 2008 8:59 doi:10.1186/1471-213X-8-59