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. Author manuscript; available in PMC: 2012 Oct 1.
Published in final edited form as: Semin Cell Dev Biol. 2011 Jul 23;22(8):842–849. doi: 10.1016/j.semcdb.2011.07.011

Figure 1. Polarity establishment by intrinsic cues, permissive external cues, and instructive external cues.

Figure 1

(A) Some cells align their mitotic spindles independent of external signaling cues.

Polarity domains ‘A’ and ‘B’ are nonspecific and could represent ‘Anterior’ and ‘Posterior’ polarity, ‘Apical’ and ‘Basal’ polarity, ‘Dorsal’ and ‘Ventral’ polarity, etc, depending on the specific cell type.

(B) Permissive external cues: Some cells require an external cue (black arrowheads) for polarization and spindle alignment, but the position of that cue does not convey positional information to cell polarity: moving the cue has no effect on cell polarity or spindle orientation (middle). Absence of these cues leads to polarity defects and defects in spindle orientation (right).

(C) Instructive external cues: Some cells are polarized by instructive external cues (black arrowheads), where changing the position of the cue changes the orientation of polarity and division. Experimentally moving the position of an extrinsic cue differentiates between permissive (B) and instructive (C) functions in spindle orientation.