Alterations to RGC axon numbers and behaviour at the optic chiasm of PAX77+/+ embryos. (A,B,D) Pax6 immunostaining of E14.5 coronal section. (A) In the wild-type Pax6 expression is not detectable at the optic chiasm (oc) although it is evident in other parts of the brain. Higher magnification of the oc of (B) wild-type and (D) PAX77+/+ embryos show that in neither case is Pax6 immunostaining detectable. (C, E) Horizontal sections showing DiI-labelled retinal axons as they traverse the chiasm, following injections of label into the retina. In both (C) wild-type and (E) PAX77+/+ embryos, retinal axons reach the chiasm along the optic nerve (on) and follow similar trajectories into the optic tract (ot). White dotted lines in (B-E) demarcate the midline. (F) Quantification of RGC projections to the thalamus in wild-type and PAX77+/+ embryos at E16.5 obtained by injecting DiI into the thalamus (on one side only) and counting RGCs retrogradely labelled by DiI in the ipsilateral and contralateral retinae. Note that PAX77+/+ embryos exhibit a dramatic decrease in the number of contralaterally projecting RGCs which is statistically significant (p = 0.008; Mann-Whitney Rank Sum Test). The slight reduction in the number of ipsilaterally projecting RGCs is not significant (p = 0.317; Rank Sum Test). * indicates significant difference (p < 0.05; Mann-Whitney Rank Sum Test). Number of embryos analysed: Pax6+/+ n = 9; PAX77+/+ n = 4. Scale bars: (A) 500 μm; (B-E) 100 μm.
Manuel et al. BMC Developmental Biology 2008 8:59 doi:10.1186/1471-213X-8-59