Misexpression of Insc in neuroepithelial cells can induce vertical spindle orientation. Spindle orientation at prometaphase/metaphase was analyzed in neuroepithelial cells at mid third instar (72 hours ALH). (a) In control brains the great majority of neuroepithelial cells have a horizontal spindle axis (arrowhead, enlarged in (a')) (n = 29). Note that neuroepithelial cells do not express Insc. (b) GAL4c855adriven UAS-insc results in apical Insc in neuroepithelial cells and forces spindles into a vertical orientation (n = 42). (c, d) Spindle orientation in control optic lobes (c) and optic lobes misexpressing Insc (d). A horizontal spindle axis is 0°; a vertical spindle axis is 90°. The number of neuroepithelial cells is shown in red within six 15° angle sectors from 0° to 90°.