Fig 2: RAB6A/B double knockout causes microcephaly A Schematic representation of cortical neurogenesis. Apical radial glial (aRG) cells are epithelial cells and the main neuronal progenitors in mouse. Basal radial glial (bRG) cells are rare in mouse but are the most abundant progenitor population in human. They have delaminated from the neuroepithelium. I.P.: Intermediate Progenitor.B Western blot analysis of RAB6A/A' and RAB6B protein levels in WT, Emx1-Cre; RAB6 loxP/loxP (RAB6A KO), RAB6B -/- (RAB6B KO) and Emx1-Cre; RAB6A loxP/loxP ; RAB6B -/- (RAB6A/B dKO) E15.5 cortical extracts.C P0 WT and RAB6A/B dKO brains. A cortical hemisphere is circled (dotted lines).D Cortical area in WT (N = 13 brains), RAB6A KO (N = 3 brains), RAB6B KO (N = 5 brains), and RAB6A/B dKO (N = 5 brains) at P0.E WT and RAB6A/B dKO brains stained for layer II/III marker CDP at P0. Scale bar = 100 µm.F Cortical thickness (µm) in WT (N = 6 brains), RAB6A KO (N = 3 brains), RAB6B KO (N = 3 brains) and RAB6A/B dKO (N = 4 brains) at P0.G Immunostaining for cleaved Caspase 3 (cCAS3) in WT and RAB6A/B dKO brains at P0. Scale bar = 50 µm. Data information: (D, F) Kruskal–Wallis test with a Dunn post-hoc test and Benjamini–Hochberg procedure. All error bars indicate SD.

Fig 3: RAB6 A/B dKO leads to ectopic TBR2-negative basal progenitors A RAB6A/A' and RAB6B expression in the developing brain and at P2.B Ventricular zone (VZ) thickness normalized to total cortical thickness in N = 6 WT brains and N = 3 RAB6A/B dKO. Mann–Whitney U test, *P = 0.05.C PAX6 and TBR2 staining in RAB6A/B dKO E15.5 brains. Arrows indicate detached PAX6+/TBR2- cells. Scale bar = 25 µm.D Percentage of ectopic PAX6+/TBR2- cells in RAB6A/B dKO E15.5 brains. RAB6A/B dKO: 470 cells from N = 3 brains.E P-VIM and TBR2 staining in RAB6A/B dKO E15.5 brains. Arrows indicate detached P-VIM+/TBR2- cells. Scale bar = 25 µm.F Percentage of ectopic P-VIM+/TBR2- cells in RAB6A/B dKO E15.5 brains. RAB6A/B dKO: 99 cells from N = 3 brains.G Percentage of ectopic P-VIM+ cells that maintained a basal process in RAB6A/B dKO E15.5 brains. RAB6A/B dKO: 99 cells from N = 3 brains.H Schematic representation of in utero electroporation and live imaging procedure in the mouse developing cortex. Data information: All error bars indicate SD.