Fig. 4. Foxn4 is necessary and sufficient to induce Dll4 in the p2 domain. (A-D1) Double ISH for Dll4 (green) and Foxn4 (red) in wild-type E10.5 mouse embryos, counter-stained with Hoechst to visualise cell nuclei. A and B are transverse and longitudinal sections, respectively, of spinal cord. Foxn4 is expressed in some of the Dll4-positive cells within and outside the VZ (arrows). A significant proportion of double-labelled cells at the ventricular surface are pairs of cells in contact with each other, presumptive daughters of a recent progenitor cell division (e.g. arrows in B). Examples of these are shown at higher magnification in C,D; note the paired nuclei in C1,D1. (E,E') Foxn4-null mouse embryos at E10.5. (E) lacZ expression under Foxn4 control. (E') Dll4 expression in the p2 domain is abolished. (F,F1) Double ISH for Foxn4 (green) and Dll4 (red) showing that Foxn4 induces ectopic expression of Dll4 in electroporated st11-13 chick neural tube.