In vivo, villin is required for Ca2+-dependent F-actin disruption in intestinal brush borders

Villin is an actin-binding protein localized in intestinal and kidney brush borders. In vitro, villin has been demonstrated to bundle and sever F-acti n in a Ca2+-dependent manner. We generated knockout mice to study the role of villin in vivo. In villin-null mice, no noticeable changes were observed in the ultrastructure of the microvilli or in the localization and express ion of the actin-binding and membrane proteins of the intestine. Interestin gly, the response to elevated intracellular Ca2+ differed significantly bet ween mutant and normal mice. In wild-type animals, isolated brush borders w ere disrupted by the addition of Ca2+, whereas Ca2+ had no effect in villin -null isolates. Moreover, increase in intracellular Ca2+ by serosal carbach ol or mucosal Ca2+ ionophore A23187 application abolished the F-actin label ing only in the brush border of wild-type animals. This F-actin disruption was also observed in physiological fasting/refeeding experiments. Oral admi nistration of dextran sulfate sodium, an agent that causes colonic epitheli al injury, induced large mucosal lesions resulting in a higher death probab ility in mice lacking villin, 36 +/- 9.6%, compared with wild-type mice, 70 +/- 8.8%, at day 13. These results suggest that in vivo, villin is not nec essary for the bundling of F-actin microfilaments, whereas it is necessary for the reorganization elicited by various signals. We postulate that this property might be involved in cellular plasticity related to cell injury.