Fig. 6. Loss of DI2 interneurons in Bmpr double knockout animals. (A,B,E,F) Foxd3 expression at 11.0 dpc. (A) Foxd3 marks dorsal DI2 neurons (arrow), and ventral V1 neurons in normal animals. (B) Higher magnification of DI2 cells from A (arrowhead). (E) Dorsal Foxd3 expression is reduced in Bmpr double knockouts with a few cells found adjacent to the roof plate (arrow). Ventral expression is unaffected. (F) Magnification of remaining DI2 cells (arrowhead). (C) Lim1/2-positive, Pax2-negative cells of the dorsal neural tube indicate the DI2 (green) population. (D) These cells are markedly reduced in the mutant animals, and are found adjacent to the roof plate (arrow). Lim1/2-positive, Pax2-positive, DI4 (yellow) cells are dorsally expanded. (G,H) Sections from 10.5 dpc mouse embryo labeled with antibodies against Isl1 (green) and Pax2 (red). (G) Double immunostaining demonstrates that Isl1-positive DI3 cells (green) and Pax2-positive DI4 cells (red) are intermingled but represent separate populations. (H) In mutant animals, both of these populations are dorsally expanded, and are found adjacent to the roof plate (arrowhead). (I) Double knockout animals show a complete loss of DI1 neurons and a fourfold decrease in DI2 cells (P<0.001). DI3 and DI4 cells are increased (P<0.01). Single knockout animals do not demonstrate significant differences (data not shown). (J,K) Sections from 11.5 dpc mouse embryo labeled with antibody against phosphorylated histone H3 (phosphoH3, red) and DAPI (blue), demonstrating no change in cell proliferation in mutant animals (K).