Immunostaining against laminin (LAMA1) indicates the basal polarity of the optic stalk in Arl13b−/− embryos (B), white arrow indicates the optic stalk. In Arl13b+/− embryos, Pax2 is expressed in the central retina and optic stalk (C), instead, in Arl13b−/− embryos in addition to the optic stalk, Pax2 is also ectopically expressed in the proximal segment of the inner layer of the optic cup (C′, C″). Immunohistochemistry against Tbx5 and Pax2 in E10.5 Arl13b+/− (D-D″) and Arl13b
−/− (E-E″) optic cups. In the mutant embryos Pax2 expression is dorsally expanded and that of Tbx5 is missing (white arrowheads indicate the putative dorsal eye territory). Scale bar: 100 μm. (N: 3).