The vertebrate retina is a multilayered tissue acting at the
interface of input light and visual perception. In the mouse,
the formation of this complex structure takes place between
embryonic day E11.5 and post-natal day P8 requiring a
combination of intrinsic and extrinsic factors (1 ). Six
neuronal cell types [retinal ganglion cell (RGC), amacrine,
bipolar, horizontal, rod and cone] and a single glial cell type
(Müller) are formed when actively dividing neuroblasts leave the
cell cycle and commit to cell fates in a temporally ordered
sequence. Differentiation occurs along all three axes. Along the
anterior–posterior axis, uncommitted cells differentiate into
distinct retinal cell types and migrate to their final positions
within either the ganglion, inner nuclear or outer nuclear
layer. Along the dorsal–ventral axis, RGCs and other cell types
acquire a dorsal–ventral pattern that can be observed by
retinotectal projection maps or by molecular markers that
distinguish dorsal axons from ventral axons (2 ). A