Fig. 4. Dorsal interneurons that migrate into the ventral horn are lost in Pcdh- null mutant mouse embryos. (A-B') E11.5 control hemicords immunostained with antibodies as indicated. Many dI2-derived FoxD3-positive cells that migrate ventrally coexpress FoxP2 (A; A' shows a magnified view); double-labeled V1 interneurons are also observed. These dorsally derived FoxP2-positive interneurons do not coexpress Pax2 (B,B'); V0/V1-derived double-positive interneurons are, however, observed ventrally. (C) Schematic (left) showing the settling patterns of different populations of FoxP2-positive interneurons. Staining of sections (right) from spinal cords of E17 control and Pcdh- ^del/del mice shows that 50% of the dI2 population (FoxP2-positive Pax2-negative) is lost in mutants. (D) Isl1-positive dI3 interneurons also migrate ventrally, and 50% are lost in Pcdh- ^del/del embryos; note that there is no reduction in Isl1-positive motoneuron pools in mutants. Scale bar: 100µm.