Fig. 3: The EC stream extends along a radial scaffold next to a fused extension of the ventricle.

a, At 18 GW, coronal sections show Ki-67⁺SOX2⁺ cells prominent in the CGE and lining the ventricle walls. Ventrally, the medial wall facing the hippocampus and lateral wall facing the cortex are open (dotted line). DG, dentate gyrus. b, At 22 GW, the medial and lateral ventricular zone (VZ) are in close proximity. c, At 22 GW, in an adjacent section (boxed region in b), FOXJ1⁺ cells are present in the medial wall VZ, but not on the opposite wall. Note the network of vimentin⁺ fibres of RG on the lateral wall (inset). d, At birth, the ventricular walls in the EC stream region have fused together, with some remaining FOXJ1⁺ ependymal cells (arrowheads), but no open ventricle. Note the multiple layers of medially oriented DCX⁺ cells flanked by vimentin⁺ fibres turning away from the ventricle (arrow). Right, at seven months, clusters of DCX⁺ cells remain in the EC stream, but have decreased in size. Some FOXJ1⁺ ependymal cells (arrowheads) and vimentin⁺ fibres remain. e, TEM of five ependymal cells (E) in the EC stream at birth, containing multiple long cilia (yellow arrowheads), ciliary basal bodies (magenta arrowheads) and cell–cell junctions typical of ependymal cells (magenta arrows). f, Ultrastructural detail of an immature migratory neuron (red, N) in the EC stream at birth surrounded by glial fibres and cell bodies (blue, A). Adherens junctions (magenta arrows) are visible next to glial fibres (magenta arrowheads). Scale bars, 1 mm (a,b); 100 µm (c left, d); 10 µm (c inset, e left, f top left); 1 µm (e right, f right and bottom).