Mitotic epithelial cells have a dynamic relationship with the layer. Daniel T. Bergstralh, Holly Lovegrove, Daniel St Johnston. Gurdon Inst, Univ Cambridge, Cambridge, United Kingdom.

   Metaphase spindles in the follicle cell epithelium are oriented roughly parallel to the plane of the epithelium. Although prior work suggested that spindle orientation could depend on interaction between spindle poles and APC2, we show that this is not the case. Our results also suggest that apical polarity factors, including aPKC, are not restricted to the apical cortex of dividing cells, and that aPKC does not play a role in spindle orientation in follicle cells. We observe that Pins and Mud, two factors known to participate in spindle orientation in other tissues, are expressed in the ovary and co-localize along the basolateral cortex in dividing cells. Both Pins and Mud are required for orienting spindles in the FCE. We further show that exogenous expression of Inscuteable, a spindle orientation factor found in neuroblast cells, promotes dramatic reorientation of follicle cell spindles. Incorrect orientation of mitotic spindles has been implicated in tumorigenesis in mammals and epithelial disorganization in Drosophila. However, neither the loss of Pins or Mud nor the ectopic expression of Inscuteable leads to disorganization of the follicle cell monolayer. Live imaging reveals that in wild type tissue cells can divide outside the plane of the epithelium then reintegrate back into it. This process also occurs in cells with misoriented spindles. Thus reintegration serves as a robust mechanism for the preservation of a single epithelial layer.