Fig. 1. Tissue overgrowth in the mid- and hindbrain. Wholemount in situ hybridization showing the expression of Sp8 in the central nervous system at E9.5 (A) and E10.5 (B,C). (A-C) Sp8 is found in the forebrain, midbrain, MHB and in the spinal cord. In the spinal cord (B) and in the midbrain, Sp8 is localized to the ventral part of the neuroepithelium, as presented in a frontal section of an E10.5 embryo at the level of the posterior midbrain in situ hybridized with ³⁵S-labeled Sp8 riboprobe (D). At the MHB Sp8 is expressed along the dorsal and ventral neural tube (A,B). Tissue overgrowth occurring in the mid- and hindbrain of Sp8-deficient embryos is apparent on sagittal sections of E11.5 and E12.5 embryos stained with Cresyl Violet (E,F) or Giemsa (G,H). It appears that the tissue thickening which is leading to a reduced aqueduct space, is more prominent in the ventral part of the midbrain and rostral hindbrain.