Extended Data Fig. 1: The methodology of tumour mapping.

(a) Mice were dissected at specific timepoint as indicated for analysis. Representative images of whole brain after dissection were shown. The brain boundary is demarcated by the dashed line. The asterisk indicates the tumour region in the OB. (b) Each brain was serially sectioned. For tumour position analysation, every 14 slices were analysed. For OB tumour volume quantification in Figs. 2, 4, every 4 slices were analysed. Tumour area is demarcated by the dashed line. (c) Tumours were confirmed by co-localization of tdT and Ki67 staining. tdT-labelling efficiency of tumour cells was confirmed by quantification of tdT⁺ cell percentage in Ki67⁺ cells (n = 5 mice). Representative images show the co-localization of tdT and Ki67 staining in the OB rather than other regions such as the subventricular zone (SVZ), the corpus callosum (CC) and the subgranular zone (SGZ) in the hippocampus. (d) Representative haematoxylin and eosin staining (H&E) images of tumours in the OB, cortex and the bottom of the brain (BoB) at different magnifications. Adjacent slices of OB tumours were used for H&E staining, or Ki67 and tdT staining to validate the feasibility of using tdTomato as the surrogate marker to define tumour mass. T, tumour; N, normal; GL, glomerular layer; EPL, external plexiform layer; ML, mitral cell layer; GRL, granule cell layer; LV, lateral ventricle. Scale bars: (b), 10 mm; (c), 300 μm. Data are mean ± s.e.m.

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