Figure 4

MCT8 expression in neurogenic progenitors. (A–E) Formation of a distinct cell layer containing TBR2+ IPC basal to the VZ in 4.5-week-old organoids. IPC generated by asymmetric RGC divisions in the apical VZ migrate towards more basal positions (see C for migrating TBR2+ IPC within VZ) and IPC located at the basal VZ border show either low SOX2 (arrowheads in D,E) or no SOX2 expression (arrows in D,E). (F–J) Immunostaining of 5-week-old organoid shows strong MCT8 expression in IPCs. White asterisks in (G) mark the cell bodies of TBR2+ IPCs and yellow dots in (G) mark cell bodies of newborn neurons. MCT8 staining intensity was similar in IPC expressing low levels of SOX2 or no SOX2 at all (compare G and J). (K–N) Immunostaining of 7-week-old organoids shows enhanced generation of SOX2+/HOPX+ oRGC and a concurrent expansion of the SVZ. Mitotic figures were frequent among the oRGC population in the SVZ (arrows in N). (O–U) The expanding SVZ was characterized by strong MCT8 expression. Higher magnification views (R–U) of the boxed region in Q show strong membrane MCT8 staining of HOPX+ oRGC. Dashed lines mark the border between VZ and SVZ in (O) and (P). Scale bars: 100 µm (A,B,K,L), 50 µm (C,M,O–Q), 20 µm (F–J,N,R–U), 10 µm (D,E).