Fig. 5. Molecular regionalization of the neocortex is perturbed in `mild' Fgf8neo/neo neonates. In situ hybridization performed on sagittal sections of wild-type or Fgf8neo/+ (A,C,E,G,I,K) and Fgf8neo/neo (B,D,F,H,J,L) newborns (A-F) and E18.5 embryos (K-J) with the indicated probes. Note that medial sections (A-F,G,H) of Fgf8neo/neo neonates show the presence of olfactory bulbs. (A-F) Medial sagittal sections of a wild-type brain show Id2 rostral superficial expression (Id2^rs), Id2 parietal expression in layer 5 (Id2⁵) and Id2 occipital superficial expression (Id2^cs). The caudal limit of high Id2^rs (black arrowhead in A) and rostral limit of Id2⁵ (open arrowhead in A) coincide in wild type brains. In Fgf8neo/neo newborns, these two limits still coincide but both move rostrally towards the olfactory bulb (black and open arrowheads in B). The caudal limit of the superficial Cdh8 expression domain (Cdh8^rs) in the frontal neocortex moves rostrally in Fgf8neo/neo newborns (compare black arrowheads in C and D). This modification correlates with a corresponding rostral shift in the high Cdh6 expression domain (black arrowheads in E and F). (G,H) In more lateral sections, Id2 strong caudal expression (Id2^cs) shows a rostral shift in Fgf8neo/neo embryos (black arrowheads). The shift in the rostral Id2 domain is still observed (open arrowheads). (I-L) In medial (I,J) or lateral sections (K,L) there was no consistent changes in Epha7 or RZRß, although minor changes such as an increased spacing between the caudal and rostral Epha7-positive domains (black arrowheads in I,J) were observed in some Fgf8neo/neo embryos. 5, layer 5 expression; cs, caudal superficial expression; GE, ganglionic eminences; Ncx, neocortex; rs, rostral superficial expression; OB, olfactory bulb.