The <scp>I</scp> ‐ <scp>BAR</scp> Protein <scp>baiap2l1a</scp> Is Required for Protrusion and Lateral Elongation of Microridges

Microridges are laterally elongated membrane protrusions of epithelial cells. Microridges are arranged in maze-like patterns and found on various mucosal epithelia, including the skin of zebrafish, where they are required to maintain mucus. The molecular mechanism that deforms epithelial membranes to create microridges remains unknown. We have found that one of the I-BAR domain proteins, baiap2l1a, which regulate membrane curvature, is required for microridge morphogenesis. Baiap2l1a mutant zebrafish had shorter and wider microridges. Baiap2l1a localized to microridges, and preceded microridge formation. Structure/function experiments revealed that the I-BAR domain could partially rescue microridge length in mutants. A 39 amino acid deletion in the I-BAR domain caused the loss of one α-helix, is sufficient to impair microridge localization and microridge elongation. These results suggest that the intact I-BAR domain structure is required for baiap2l1a microridge localization and function. Eps8like1a genetically interacted with baiap2l1a in microridge elongation. We found that the membrane curvature protein baiap2l1a plays an important role in microridge formation.