Active cell migration is critical for steady-state epithelial turnover in the gut

Active migration renews gut epithelia Epithelial tissues are continuously renewed throughout adult life, and the gut epithelium is the fastest self-renewing tissue in mammals. Over 3 days or so, epithelial cells migrate from the crypts, where they are born, to the tips of the villi, where they die. It is commonly believed that migration is strictly passive, driven by mitotic pressure in crypts—as cells divide, they push their neighbors upward. Krndija et al. now challenge this concept and show that cells migrate actively, using actin-rich basal protrusions oriented in the direction of migration (see the Perspective by Jansen). Science , this issue p. 705 ; see also p. 642