Retinoid signalling at the rhombic lip. Transverse sections taken through the caudal hindbrain at e5 with the roof plate orientated to the right and the dorsal neuroepithelium to the left. A. Cath1 expression at the rhombic lip. B. Cath1 (red) and Gdf7 (in blue) show a non-overlapping interface (arrow). C. Cyp1B1 expression in dorsal neural tube shows a similar expression to Gdf7. D. Cath1 (red) and Cyp1B1 (blue) show no overlap of expression. Cyp1B1 is expressed within the developing blood vessels at the base of the ventricular layer (arrow). E. Cyp26A1 is expressed within the roof plate with highest expression close to the rhombic lip. F. Cath1 (red) and Cyp26A1 (blue) are non-overlapping at their interface (arrow). G. Cyp26C1 is expressed more uniformly throughout the roofplate than Cyp26A1 (E). H. Cath1 (red) and Cyp26C1 (blue) expression is non-overlapping (arrow). I. Cyp26B1 expression is excluded from the rhombic lip J. Cath1 (red) and Cyp26B1 (blue) show complementary expression domains at the ventricular layer boundary of the rhombic lip. K. At the level of the VIIth nerve exit point, Crabp1 is expressed at the interface between ventricular zone and mantle layer. L. Cath1 (red) expression partially overlaps that of Crabp1 (blue) at the interface of the ventricular zone (arrow). Transient spots of Cath1 expression at the exit point of the VIIth nerve are visible at this level (asterisk). Intriguingly, this post-mitotic expression of Cath1 corresponds with a distinct gap in Crabp1 at the overlying ventricular layer boundary. M. At a slightly more rostral level, Crabp1 expression is continuous beneath the ventricular layer. At all levels, there is an extended tail of expression into the mantle layer at the rhombic lip. N. Confocal micrograph of BrdU localisation in s-phase nuclei (arrow).