Decompression and compression experiments support the elasticity-based passive nucleokinesis mechanism.

(A–C) Artificial shrinkage of the process-rich subapical space by laser ablation (at 5 μm deep, as illustrated in A; circularly darkened in FM4-64 imaging, B; see also S3F Fig and S19 Movie) inhibited the initial basal displacement of daughter cells’ nuclei/somata (n = 5 pairs, C) (see also S18 Movie). (D and E) Unidirectional centripetal compression of a cerebral wall (with a device, as shown in D) increased the nuclear density in the subapical space (E; see also S3G Fig and S20 Movie). (F–H) Initial nucleokinesis from the compressed/deformed subapical space (G; H2B-mCherry–labeled) was quicker than that from the uncompressed subapical space (F). Time until departure was 28 ± 8 min for E-IKNM and 60 ± 36 min for L-IKNM when compressed, whereas it was 39 ± 15 min for E-IKNM and 82 ± 39 min for L-IKNM in control (p = 0.00023 for E-IKNM and p = 0.00138 for L-IKNM, Mann–Whitney U test) (summarized in H, n = 59 pairs for control and 43 pairs for the compressed condition) (see also S21 and S22 Movies). (I–K) Compression of single “imprinted” progenitor cells. VZ cells attached to dish base, with their spindle or bipolar in vivo–like morphologies, were pressed perinuclearly by a capillary (illustrated in I, pictured in J), and their nuclei/somata underwent counter-directional displacements (exemplified in J [see also S3H Fig], summarized in K, n = 4 for both control and compression). Scale, 10 μm in B, E, F, G, and J. Underlying data can be found in S1 Data. E-IKNM, early-nucleokinetic; L-IKNM, late-nucleokinetic; VZ, ventricular zone.