Myosin 5b is required for proper localization of the intermicrovillar adhesion complex in the intestinal brush border.

BACKGROUND: Intestinal enterocytes have an elaborate apical membrane of actin rich protrusions known as microvilli. The organization of microvilli is orchestrated by the intermicrovillar adhesion complex (IMAC) which connects the distal tips of adjacent microvilli. The IMAC is comprised of CDHR2 and CDHR5 as well as the scaffolding proteins USH1C, ANKS4B and Myosin 7b. To create an IMAC, cells must transport the proteins to the apical membrane. Myosin 5b (MYO5B) is a molecular motor that traffics ion transporters to the apical membrane of enterocytes, and we hypothesized that MYO5B may also be responsible for the localization of IMAC proteins.

METHODS & RESULTS: To address this question, we used 2 different mouse models: (1) neonatal germline MYO5B knockout (MYO5B KO) mice and (2) adult intestinal specific tamoxifen inducible VillinCreERT2 ;MYO5Bflox/flox mice. In control mice, immunostaining revealed that CDHR2, CDHR5, USH1C, and MYO7B were highly enriched at the tips of the microvilli. In contrast, neonatal germline and adult MYO5B deficient mice showed loss of apical CDHR2, CDHR5, and MYO7B in the brush border and accumulation in a subapical compartment. Co-localization analysis revealed decreased Mander's coefficients in adult inducible MYO5B deficient mice compared to control mice for CDHR2, CDHR5, USH1C and MYO7B. Scanning electron microscopy images further demonstrated aberrant microvilli packing in adult inducible MYO5B deficient mouse small intestine.

CONCLUSIONS: These data indicate that MYO5B is responsible for the delivery of IMAC components to the apical membrane.