Expression of Raldh3. A. Raldh3 expression at e3 is localised to the ventral retina of the eye (arrow), Rathke's pouch (white arrow) and the isthmus (white arrowhead). B. En face view of the dissected isthmus (arrow) showing a ring of Raldh2 expression, weakening at its dorsal apex. C. Expression at the isthmus (arrow) and otic vesicle (white arrow) at e6. D. Transverse section through isthmic region (dashed line in C) shows expression concentrated in bilateral foci within the isthmus. E. Transverse section through the presumptive inner ear shows Raldh2 in the endolymphatic duct (white arrow) and saccule (white arrowhead).