Fig. 5. Lineage trees constructed from time-lapse recordings reveal that Numb is expressed at multiple stages in cortical stem cells and neuroblasts. E10-E12 cortical cells were followed with time-lapse video microscopy for up to 7 days then fixed and stained for Numb and ß-tubulin III. The lineages were constructed from the recorded images, and Numb⁺ cells within the trees were identified (indicated by star). (A) A neuroblast clone. Numb was expressed in neuronal progeny generated at various stages within the lineage trees. (B) A stem cell clone. Numb was seen in neurons and also in the dividing ß-tubulin III^– glial progenitor cells found at the end of the lineage. In terminal neuroblast divisions that generated two post-mitotic neurons, Numb could be distributed asymmetrically or symmetrically. Examples are seen in A and B respectively, although both types of distribution occurred in neuroblast and stem cell lineages. N, ß tubulin III⁺ neuron; -, non-neuronal cell; X, cell died; ?, cell migrated out of field.