WASH phosphorylation balances endosomal versus cortical actin network integrities during epithelial morphogenesis

Epithelial cells rely on actin networks to control shape and function. While actin dynamics are well studied, how these networks interact during morphogenesis remains unclear. Prior research has shown that F-actin structures influence cell polarization and motility. However, the coordination between endosomal and cortical actin remains poorly understood. This gap motivated investigations into how actin networks balance during epithelial development. No prior work had resolved the interplay between endosomal and cortical actin in epithelial tube formation. The role of tyrosine phosphatases in this process has not been fully characterized. This paper addresses the lack of understanding about how actin networks are regulated during epithelial morphogenesis. The study focuses on the role of PTPs and Btk29A in epithelial tube development.

The study aimed to clarify how actin networks are coordinated during epithelial morphogenesis. Specifically, it sought to determine how endosomal and cortical actin networks balance in epithelial tube formation. The researchers focused on Drosophila airway development as a model system. They examined the role of receptor tyrosine phosphatases Ptp10D and Ptp4E in this process. The study also investigated how Btk29A and WASH contribute to actin regulation. The goal was to understand how phosphorylation of WASH affects actin dynamics. The researchers wanted to determine if WASH phosphorylation influences both endosomal and cortical actin. The findings would help explain how epithelial cells maintain structural integrity during development.

The researchers used Drosophila as a model to study epithelial tube formation. They generated double mutants lacking Ptp10D and Ptp4E to assess their roles. They observed premature disassembly of apical actin bundles in these mutants. The team also examined the effects of Btk29A and WASH mutations on actin networks. They tested how Btk29A interacts with Ptp10D and WASH in vivo. Phosphorylation of WASH was analyzed using biochemical assays in flies and mice. The researchers assessed endosomal trafficking and cortical actin integrity in mutant conditions. They compared wild-type and mutant phenotypes to determine functional roles of these proteins.

Double mutants of Ptp10D and Ptp4E showed premature disassembly of apical actin bundles. These mutants also exhibited defects in luminal protein clearance and endocytosis. Btk29A and WASH mutations partially rescued these defects. Btk29A forms complexes with Ptp10D and WASH in epithelial cells. Phosphorylation of WASH by Btk29A activates its endosomal function in flies and mice. A phospho-mimetic WASH variant led to endosomal actin accumulation and cortical disassembly. This variant also caused premature luminal endocytosis in epithelial cells. The findings suggest that WASH phosphorylation balances endosomal and cortical actin networks.

The authors propose that PTPs and Btk29A regulate WASH activity to maintain actin network balance. They suggest that WASH phosphorylation activates endosomal function while suppressing cortical actin disassembly. The study supports a model where WASH activity is modulated by phosphorylation state. The findings indicate that endosomal and cortical actin networks are dynamically coordinated. The researchers conclude that this balance is essential for epithelial tube maturation. Their results suggest that PTPs and Btk29A function together to regulate WASH. The study highlights the importance of phosphorylation in actin network regulation. The authors state that this mechanism may be conserved in mammalian systems.