In situ Structure of Intestinal Apical Surface Reveals Nanosticks on Microvilli

Microvilli are actin bundle-supported membrane protrusions essential for absorption, secretion, and sensation. Microvilli defects cause gastrointestinal disorders; however, mechanisms controlling microvilli formation and organization remain unresolved. Here, we study microvilli by vitrifying the C. elegans larvae with high-pressure freezing, thinning them by cryo-focused ion beam milling, cryo-electron tomography, and sub-tomogram averaging. We uncover that hundreds of previously unrecognized stick-like structures, which we refer to as nanosticks, decorate the lateral surface of microvilli. Nanosticks are 37.5-nm long and 4.5-nm wide, and their formation requires the protocadherin family protein CDH-8. Loss of nanosticks slows down animal growth and increases the number of Y-shaped microvilli, the putative intermediate structures, when a microvillus splits from its tip and separates into two. We suggest that an existing microvillus may divide to form two nascent microvilli with uniformity and that nanosticks may space microvilli.