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Fig. 8. Model for extrinsic signaling. During the cell cycle, the neuroblast
receives positional cues from the epithelium, to polarize along the apicobasal
embryonic axis, and during mitosis this allows for the basal placement of all
GMC daughters and their progeny after cytokinesis. At late G2, extrinsic
signaling indicates the position on the neuroblast cortex to establish Par
apical polarity. During prophase, apical Par crescents are forming at this
pre-selected position, independently of centrosome behavior. The position of
the apical crescents determines spindle orientation at prometaphase and
spindle position is maintained throughout mitosis, ensuring the reproducible
basal placement of all GMCs. Extrinsic cues also maintain centrosome(s)
position at the epithelial/neuroblast contact site throughout the cell cycle.
See Discussion for further details.
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