The Hardin Lab - UNC-94/Tmod

Tropomodulin protects α-catenin-dependent junctional actin networks under stress during epithelial morphogenesis

Elisabeth A. Cox-Paulson,1 Elise Walck-Shannon,2 Allison M. Lynch,3 Sawako Yamashiro,4,5 Ronen Zaidel-Bar,3,6 Celeste C. Eno,2 Shoichiro Ono,4 and Jeff Hardin2,3

1Department of Biology, State University of New York at Geneseo, 353 Integrated Science Center, 1 College Circle, Geneseo, NY 14454, USA
2Program in Genetics, University of Wisconsin–Madison, 1117 W. Johnson Street, Madison, WI 53706, USA
3Department of Zoology, University of Wisconsin–Madison, 1117 W. Johnson Street, Madison, WI 53706, USA
4Department of Pathology, Emory University, Whitehead Research Building, Room 105N, Atlanta, GA 30322, USA
5Present address: Laboratory of Single-Molecule Cell Biology, Tohoku University Graduate School of Life Sciences, 6-3 Aoba, Aramaki-Aza, Aoba-ku, Sendai, Miyagi 980-8578, Japan
6Present address: Mechanobiology Institute Singapore, T-Lab, 5A Engineering Drive 1, National University of Singapore, Singapore 117411, Singapore

Supplemental material for the following paper:
Cox-Paulson, E., Walck-Shannon, E., Lynch, A., Yamashiro, S., Zaidel-Bar, R., Celeste C. Eno, C., Ono, S., and Hardin, J. (2012). Tropomodulin protects α-catenin-dependent junctional actin networks under stress during epithelial morphogenesis. Curr. Biol. 22:1500-1505. PubMed

Summary
Supplemental data and methods
Video sequence 1
Video sequence 2

Summary
α-catenin is central to recruitment of actin networks to the cadherin-catenin complex, but how such networks are subsequently stabilized against stress applied during morphogenesis is poorly understood. To identify proteins that functionally interact with α-catenin in this process, we performed enhancer screening using a weak allele of the C. elegans α-catenin, hmp-1, thereby identifying UNC-94/ tropomodulin. Tropomodulins (Tmods) cap the minus ends of F-actin in sarcomeres. They also regulate lamellipodia, can promote actin nucleation, and are required for normal cardiovascular development and neuronal growth-cone morphology. Tmods regulate the morphology of cultured epithelial cells, but their role in epithelia in vivo remains unexplored. We find that UNC-94 is enriched within a HMP-1-dependent junctional-actin network at epidermal adherens junctions subject to stress during morphogenesis. Loss of UNC-94 leads to discontinuity of this network, and high-speed filming of hmp-1(fe4);unc- 94(RNAi) embryos reveals large junctional displacements that depend on the Rho pathway. In vitro, UNC-94 acts in combination with HMP- 1, leading to longer actin bundles than with HMP-1 alone. Our data suggest that Tmods protect actin filaments recruited by α-catenin from minus-end subunit loss, enabling them to withstand the stresses of morphogenesis.

Supplemental data and methods (0.9 Mb; PDF)

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Videos


Movie 1 (2.1 M; AVI). Elongation in Wild-Type, unc-94(RNAi), hmp-1(fe4), and hmp-1(fe4);unc-94(RNAi) Embryos. Frames were collected every 2 min for 180 min. The display rate was 8.57 frames per s.
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Movie 2 (0.4 Mb; AVI). Adherens-Junction Dynamics in an Elongating Wild-Type, hmp-1(fe4), and hmp-1(fe4);unc-94(RNAi) Embryo. Frames were collected every 10 s for 5 min. Images are projections of 12–16 focal planes. The display rate was ten frames per s.
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