Crumbs turns the corner

rumbs (Crb) helps flies distinguish apical from basal in their epithelia. Now two new studies show that it is required for cell expansion independently of its specification of apical polarity. During cell expansion, the apical domain of photoreceptors elongates perpendicular to the apical–basal axis so that the domain can extend from the top to the bottom of the fly eye. The process may be conserved in humans, consistent with the recent finding that mutations in the human homologue, CRB1, lead to human retinitis pigmentosa. C