Fig. 2.

Transmission electron micrographs of the normal and RA-free quail spinal cord at the forelimb level. (A,B) The floor plate region of the normal spinal cord showing numerous microvilli (mv) projecting into the lumen and many cell junctional complexes at the apical surfaces of the cells lining the lumen (white arrows). (C,D) The floor plate region of the RA-free spinal cord showing a much wider lumenal surface and a decrease in the number of microvilli and junctional complexes. (E,F,G) The roof plate region of the normal spinal cord, which is about two cells in height with few microvilli and junctional complexes at the lumenal surface. (H,I,J) The roof plate region of the RA-free spinal cord showing an increased height (arrowed line) accompanied by a very narrow lumen with an increased number of microvilli and junctional complexes present at the lumenal surfaces of the ependymal cells. Bars in A,C = 2 mm; bars in B,D,G,J = 500 nm; bars in E,H = 5 µm; bars in F,I = 1 µm.