Drosophila Cappuccino alleles provide insight into formin mechanism and role in oogenesis |
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| Authors: | Haneul Yoo Elizabeth A. Roth-Johnson Batbileg Bor Margot E. Quinlan |
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| Affiliation: | University of California,Santa Barbara;aDepartment of Chemistry and Biochemistry;bMolecular Biology Interdepartmental PhD Program, University of California, Los Angeles, Los Angeles, CA 90095;cMolecular Biology Institute, University of California, Los Angeles, Los Angeles, CA 90095 |
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| Abstract: | During Drosophila development, the formin actin nucleator Cappuccino (Capu) helps build a cytoplasmic actin mesh throughout the oocyte. Loss of Capu leads to female sterility, presumably because polarity determinants fail to localize properly in the absence of the mesh. To gain deeper insight into how Capu builds this actin mesh, we systematically characterized seven capu alleles, which have missense mutations in Capu''s formin homology 2 (FH2) domain. We report that all seven alleles have deleterious effects on fly fertility and the actin mesh in vivo but have strikingly different effects on Capu''s biochemical activity in vitro. Using a combination of bulk and single- filament actin-assembly assays, we find that the alleles differentially affect Capu''s ability to nucleate and processively elongate actin filaments. We also identify a unique “loop” in the lasso region of Capu''s FH2 domain. Removing this loop enhances Capu''s nucleation, elongation, and F-actin–bundling activities in vitro. Together our results on the loop and the seven missense mutations provides mechanistic insight into formin function in general and Capu''s role in the Drosophila oocyte in particular. |
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