An increase in nonvertical cleavage plane orientation of mouse aRG has been observed both upon knock-down of Spag5 and when Spag5 mRNA and protein levels in Pax6 mutant mice at midneurogenesis are elevated [ 47 ], suggesting that either too low or too high Spag5 levels perturb the normal, horizontal spindle orientation that is required for aRG vertical cleavage plane orientation.
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