UNC-94
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
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.
Videos
Movie 1 (2.1 Mb). 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.
Download MP4
Movie 2 (0.4 Mb). 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 Download MP4