Affiliations: 1) Icahn School of Medicine at Mount Sinai; 2) Faculty of Medicine, University of Chile; 3) Faculty of Sciences, University of Chile
Keywords: a. cytoskeleton; a. cytoskeleton
Actin dynamics are essential in every cell, primarily for cell division, migration, and morphological changes. Actin polymerization can be branched or linear, and it depends on the associated regulatory proteins. There are hundreds of proteins that regulate the actin cytoskeleton dynamics. Competition for actin monomers also occurs between proteins that induce branched or linear actin polymerization. Cell specialization requires actin cytoskeleton transformation to allow the formation of cell structures, like cuticular hairs in Drosophila. This is a well characterized and useful study model to analyze proteins that regulate actin dynamics. Structurally, these hairs are mainly formed by linear actin filaments. A screen was performed to identify wing development regulators. A lethal mutation was found on a gene that was named pelado. Pelado is a protein conserved throughout the animal kingdom but has no clear function. Epithelial mutant cells for pelado shows hair elongation defects. This phenotype was reversed by inducing linear actin polymerization, by reducing branched actin polymerization and by increasing the amount of actin monomers. This suggests that Pelado is involved in the competition for actin monomers. A similar phenomenon occurs in hemocytes, where Pelado is essential to induce filopodia formation in a process that also requires Diaphanous and Profilin. Pelado’s function was also evaluated in A549 human cell line, in a wound healing assay. It has been described that this cell type requires branched actin polymerization to achieve efficient migration. In pelado knockout cells, the wound closes faster and the opposite occurs if we introduce the pelado fly gene in those cells. Immunoprecipitation assays suggests that Pelado is part of a multiprotein complex that includes Scar/WAVE, Diaphanos and Proflin. These data indicate that Pelado’s function in regulating the actin cytoskeleton is conserved, preventing branched actin polymerization at the same time as favoring linear actin polymerization, through actin monomer competition mechanisms that modulate actin cytoskeleton dynamics. To evaluate the domains of Pelado that are important for its function, a C-terminal deletion was generated that can induce filopodia formation but does not rescue hair formation. This indicates that the C-terminal portion of Pelado has a regulatory function that is essential for certain processes, including hair formation in Drosophila.