Extended Data Fig. 3: The EC stream forms next to a fused ventricle in humans during gestation.

a, EC stream region at 22 GW stained for Ki-67⁺ and HOPX⁺ cells showing location of insets in b–d. b,c, Ki-67⁺, HOPX⁺, and DCX⁺ cells in the VZ (b) and  outer subventricular zone (c) along the closely opposed walls of the ventricle in the EC stream anlage. d, Staining of an immediately adjacent section for FOXJ1 and vimentin in the region indicated in a shows FOXJ1⁺ cells not contacting the ventricle. e, At 29 GW (top) and birth (bottom), the ventricle has closed in this region which contains a field of DCX⁺ cells at 29 GW and multilayered lamina of coalesced streams at birth between the EC and the V-SVZ. In the wall of the ventricle the ependymal layer contains vimentin⁺ cells in the VZ and Ki-67⁺ cells in the V-SVZ (insets). f, Semithin section stained with toluidine blue showing the EC stream at birth (left), and TEM of cells displaying motile cilia (square inset) and an elongated neuron with ultrastructural features of a migrating cell in the EC stream at birth (right). g, Macaque temporal lobe at 3 and 17 months stained for DCX and vimentin showing open ventricle within the same region where a closed ventricle and the EC stream is found in humans (arrows). Scale bars: 1 mm (g top row), 500 µm (a, e left overviews, f left, g bottom row), 100 µm (d left, e top middle bottom right), 50 µm (b, c, d middle and right), 20 µm (e top right), 2 µm (f right panels). Abbreviations: CGE: caudal ganglionic eminence; EC: entorhinal cortex; HP: hippocampus; tLV: temporal lobe lateral ventricle.