Fig. 2. Cellular populations within the E12.5 cerebellar anlage. (A,B,D-F) Paramedial sagittal and (C) lateral sagittal immunostained sections through dorsal r1 at E12.5 in wild-type (A,D,E) and Math1^lacZ/+ (B,C,F) embryos. Markers are indicated. Solid arrowhead in B points to LacZ⁺ cells in the rhombic lip many of which are Lhx2/9 negative. Arrow points to LacZ⁺/Lhx2/9⁺ cells engaged in the RLS. The open arrowheads in B and C indicate LacZ⁺ fibers on the dorsal surface, which belong to LacZ⁺/Lhx2/9⁺ cells. Arrowheads in D inset indicate small numbers of Pft1a⁺/Lhx1/5⁺ double-labeled nuclei. Laterally, the junction (broken line in C) between the pons and cerebellum (Cb) is difficult to distinguish, since the aqueduct (aq in D) no longer separates them. Arrowhead in merge panel E indicates Lmx1a^-/Msx1/2⁺ cells. (G,H) Schematic of the molecular map of roof plate r1 populations in whole-mount (G) and paramedial sagittal section (H). c1 cells extend to the isthmus adjacent to the anterior roof plate. E12.5 cerebellar anlage populations are excluded from this region, defining a negative (neg) zone of gene expression.