Final Report Summary - NEUROMAN (Identifying the genes responsible for the expansion of the human cerebral cortex) We made 20 achievements, which are in chronological order:1. We identified basal radial glia as a novel, key progenitor type for neocortical expansion.2. We showed that genes mutated in primary microcephaly alter the orientation of the mitotic spindle.3. We showed that the length of S-phase is a major target of cell cycle regulation of cortical progenitors.4. We showed that midbody release from neural stem cells is differentially affected by proliferation vs. differentiation.5. We showed that progenitor delamination from the ventricular surface is preceded by establishment of a basolateral primary cilium.6. We studied the abundance of basal radial glia in the marmoset, a near-lissencephalic primate.7. We established microinjection of apical radial glia in organotypic slice culture as a novel approach to manipulate the fate of single neural stem cells in tissue.8. We determined for the first time the transcriptomes of human neocortical germinal zones, which led to the suggestion that extracellular matrix is key for progenitor self-renewal.9. We showed that the primary cilium of apical progenitors is not dismantled for mitosis but is endocytosed, providing a cell biological basis for their asymmetric cell division.10. We showed that activation of the thyroid hormone cell surface receptor integrin αvβ3 induces basal progenitor proliferation, which provides an explanation for the neurodevelopmental disorder caused by lack of iodine during pregnancy.11. We showed the critical role of 3' UTR-dependent, miR-92-mediated restriction of Tis21 expression for neocortex size.12. We identified apical-basal astral microtubules as being critical for mitotic spindle orientation of apical progenitors.13. We showed that gyrencephaly is an ancestral mammalian trait, that lissencephaly occurs secondarily during evolution, and that the length of the neurogenic period is key for neocortex size.14. We identified the human-specific gene ARHGAP11B as a key player for basal progenitor amplification and the evolutionary expansion of the neocortex.15. We showed that sustaining Pax6 expression in mouse basal progenitors suffices to generate primate-like basal radial glia in developing mouse neocortex.16. We showed that human cerebral organoids recapitulate human fetal neocortex gene expression programs.17. We showed that the Golgi apparatus in apical radial glia exhibits non-canonical features.18. We established the CRISPR/Cas9 system for gene disruption in developing neocortex of mouse and ferret embryos in vivo.19. We identified metaphase lengthening as a key difference in human as compared to ape apical progenitors.20. We showed that the ability of ARHGAP11B to amplify basal progenitors is due to a single nucleotide substitution that creates a novel splice donor site and thereby causes a reading frame shift leading to the human-specific C-terminal sequence of ARHGAP11B.
