title: Tropomodulin 1 Regulation of Actin Is Required for the Formation of Large Paddle Protrusions Between Mature Lens Fiber Cells.
abstract: To elucidate the proteins required for specialized small interlocking protrusions and large paddle domains at lens fiber cell tricellular junctions (vertices), we developed a novel method to immunostain single lens fibers and studied changes in cell morphology due to loss of tropomodulin 1 (Tmod1), an F-actin pointed end-capping protein.
  
  
  
  We investigated F-actin and F-actin-binding protein localization in interdigitations of Tmod1+/+ and Tmod1-/- single mature lens fibers.
  
  
  
  F-actin-rich small protrusions and large paddles were present along cell vertices of Tmod1+/+ mature fibers. In contrast, Tmod1-/- mature fiber cells lack normal paddle domains, while small protrusions were unaffected. In Tmod1+/+ mature fibers, Tmod1, β2-spectrin, and α-actinin are localized in large puncta in valleys between paddles; but in Tmod1-/- mature fibers, β2-spectrin was dispersed while α-actinin was redistributed at the base of small protrusions and rudimentary paddles. Fimbrin and Arp3 (actin-related protein 3) were located in puncta at the base of small protrusions, while N-cadherin and ezrin outlined the cell membrane in both Tmod1+/+ and Tmod1-/- mature fibers.
  
  
  
  These results suggest that distinct F-actin organizations are present in small protrusions versus large paddles. Formation and/or maintenance of large paddle domains depends on a β2-spectrin-actin network stabilized by Tmod1. α-Actinin-crosslinked F-actin bundles are enhanced in absence of Tmod1, indicating altered cytoskeleton organization. Formation of small protrusions is likely facilitated by Arp3-branched and fimbrin-bundled F-actin networks, which do not depend on Tmod1. This is the first work to reveal the F-actin-associated proteins required for the formation of paddles between lens fibers.
authors.affiliation: Department of Cell and Molecular Biology The Scripps Research Institute, La Jolla, California, United States.
authors.forename: Catherine
authors.initials: C
authors.lastname: Cheng
authors.affiliation: Department of Cell and Molecular Biology The Scripps Research Institute, La Jolla, California, United States.
authors.forename: Roberta B
authors.initials: RB
authors.lastname: Nowak
authors.affiliation: Department of Neurobiology, Morehouse School of Medicine, Atlanta, Georgia, United States.
authors.forename: Sondip K
authors.initials: SK
authors.lastname: Biswas
authors.affiliation: Department of Neurobiology, Morehouse School of Medicine, Atlanta, Georgia, United States.
authors.forename: Woo-Kuen
authors.initials: WK
authors.lastname: Lo
authors.affiliation: Department of Cell Biology and Human Anatomy, University of California, Davis, California, United States.
authors.forename: Paul G
authors.initials: PG
authors.lastname: FitzGerald
authors.affiliation: Department of Cell and Molecular Biology The Scripps Research Institute, La Jolla, California, United States.
authors.forename: Velia M
authors.initials: VM
authors.lastname: Fowler
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism; D000199:Actins / Q000235:genetics* / Q000378:metabolism; D000818:Animals; D002386:Cataract / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D002454:Cell Differentiation; D002478:Cells, Cultured; D004247:DNA / Q000235:genetics*; D004252:DNA Mutational Analysis; D004195:Disease Models, Animal; D007908:Lens, Crystalline / Q000378:metabolism / Q000648:ultrastructure*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008855:Microscopy, Electron, Scanning; D009154:Mutation; D051348:Tropomodulin / Q000235:genetics* / Q000378:metabolism
chemical_list: D000199:Actins; C495831:Tmod1 protein, mouse; D051348:Tropomodulin; D004247:DNA