RESEARCH ARTICLE Keratins and plakin family cytolinker proteins control the length of epithelial microridge protrusions Yasuko Inaba*, Vasudha Chauhan, Aaron Paul van Loon, Lamia Saiyara Choudhury, Alvaro Sagasti* Molecular, Cell and Developmental Biology Department and Molecular Biology Institute, University of California, Los Angeles, Los Angeles, United States Abstract Actin filaments and microtubules create diverse cellular protrusions, but intermediate filaments, the strongest and most stable cytoskeletal elements, are not known to directly participate in the formation of protrusions. Here we show that keratin intermediate filaments directly regulate the morphogenesis of microridges, elongated protrusions arranged in elaborate maze-like patterns on the surface of mucosal epithelial cells. We found that microridges on zebrafish skin cells contained both actin and keratin filaments. Keratin filaments stabilized microridges, and overexpressing keratins lengthened them. Envoplakin and periplakin, plakin family cytolinkers that bind F-actin and keratins, localized to microridges, and were required for their morphogenesis. Strikingly, plakin protein levels directly dictate microridge length. An actin-binding domain of periplakin was required to initiate microridge morphogenesis, whereas periplakin-keratin binding was required to elongate microridges. These findings separate microridge morphogenesis into distinct steps, expand our understanding of intermediate filament functions, and identify microridges as protrusions that integrate actin and intermediate filaments. *For correspondence:
[email protected] (YI); Introduction
[email protected] (AS) Cytoskeletal filaments are scaffolds for membrane protrusions that create a vast diversity of cell shapes. The three major classes of cytoskeletal elements—microtubules, actin filaments, and inter- Competing interests: The mediate filaments (IFs)—each have distinct mechanical and biochemical properties and associate authors declare that no with different regulatory proteins, suiting them to different functions.