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C. elegans PAT-4/ILK Functions as an Adaptor Protein within Integrin Adhesion Complexes

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C. elegans PAT-4/ILK Functions as an Adaptor Protein within Integrin Adhesion Complexes. Mackinnon, C., Qadota, H., Norman, K., Moerman, D., Williams, B. (2002) Current Biology 12: 787-797. The Authors. Dr. Hiroshi Qadota Department of Cell Pharmacology, Nagoya University

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slide1
C. elegans PAT-4/ILK Functions as an Adaptor Protein within Integrin Adhesion Complexes

Mackinnon, C., Qadota, H., Norman, K., Moerman, D., Williams, B. (2002) Current Biology 12: 787-797

slide2
The Authors
  • Dr. Hiroshi Qadota
  • Department of Cell Pharmacology, Nagoya University
  • Protein interactions in C. elegans muscle using Y2H
  • Craig Mackinnon
  • University of Illinois
  • In vivo Protein interactions in muscle attachment structures using FRET
  • Dr. Ken Norman
  • University of Utah?
  • Something to do with Zebra fish
  • Dr. Don Moerman
  • University B.C
  • Something to do with muscle and worms
slide3
Sarcomere assembly andmuscle attachment in C. elegans.

Summary: Muscle sarcomere assembly is a highly orchestrated affair

involving several proteins. The steps involved in initiating the correct

placement of sarcomere substructures are poorly understood. Using mutants in C.elegans we are attempting to dissect the various steps in this process. The model of sarcomere assembly is based on observations that suggest assembly initiates at the plasma membrane and involves proteins within muscle and within the extracellular matrix. This process is remarkably similar to adhesion complex assembly in non muscle cells.

slide4
Why use C. elegans as a model system to study muscle development and sarcomere assembly?
slide6
The Sarcomere

H. sapiens

C. elegans

slide7
Nematode muscle
  • Nematode striated muscle cells do not fuse to form a myotube
  • Adhere tightly to adjacent muscle cells in a quadrant
  • Myofilament lattice anchored to membrane via lateral attachments
  • Adult muscle cell 10 A-bands wide
  • Thin filaments anchor thick filaments to Dense bodies
  • Obliquely striated..not cross striated
slide8
Genes known to function in muscle development
  • Myosin heavy chain A-D= myo-3, unc-54, myo-2, myo-1—required for M-line assembly
  • Mysin head= unc-54—required for filament assembly
  • Myosin light chains: mlc-1, mlc-2, mlc-3—required for calcium of myosin ATPase
  • Paramyosin= unc-15—required for organized body wall muscle; proper assembly of myosin?
  • Twitchin Protein= unc-22—required for proper organization of sarcomeres; regulation of muscle contraction
slide9
Genes known to function in muscle development
  • M-line proteins: UNC-89, creatine kinase, myomesin, skelemin, M protein, titin—required for proper maintenance of the M-line and for holding thick filaments in register
  • Actin filaments: act-5, unc-92, act-1, act-3—required for cell shape; cell movement; muscle contraction
  • Troponin-Tropomyosin: lev-11, pat-10, mup-2—required for viabilty; proper contraction/relaxation
  • Thin filament associated: unc-60, unc-87—required for thin filament assembly
slide10
Genes required for early sarcomere organization
  • Mup class (muscle positioning) and Pat class (paralyzed and arrested elongation at twofold)
  • Dense body & M-line: Deb-1/vinculin; pat-3/ß-integrin, pat-2/α-integrin, unc-52/perlecan
  • Pat class: unc-112, unc-52, myo-3, lev-11
slide11
Sarcomere assembly & membrane

Linkage between myofibril and membrane provided by Dense body

--Major constituents of Dense body: α-actinin, vinculin, talin

--anchor of myofilament lattice: α, β-1 integrin components

--extracellular anchor: perlecan (unc-52)

*Pat mutants studies to date: unc-52, pat-3, unc-112, unc-97, deb-1

This paper focuses on pat-4

slide13
Pat-4 is a homolog of vertebrate ILK
  • RNAi on C29F9.7 98% Pat F1
  • Genomic fragment C29F9.7 rescues pat-4 phenotype
  • a. Localized to LGIIIb. Genomic structure of pat-4 (exons=gray)c. pat-4 point mutations st551, st579d. domain analysis
slide14
PAT-4and βPAT3 Integrin Colocalize at Muscle Attachments
  • pat-4::gfp localizes to dense bodies
  • Abs to βPAT3 integrin
  • Overlay of A, B
  • Detail of body wall muscle (D-F). D=pat-4::yfp; E=pat-3::cfp; F=overlay

Dense bodies (arrows) & M-lines (arrow head)

slide15
PAT-4/ILK required for Dense body & M-line assembly

hypodermis-hypodermis junction

Embryos N2 & pat-4 430min post-fertilization

muscle quadrant

A, B. Normal

C, D. some irregularity; some foci not in tight stripe of attachments

E, F. vinculin does not assemble properly into nascent attachments

G, H. UNC-89, an M-line protein, fails to polarize and remains in clumps in the cytoplasm

slide16
PAT-4/ILK required for UNC-112 assembly into nascent attachments
  • 430 min. post-fertilization, ßPAT3 integrin located in nascent muscle attachments
  • UNC-112::GFP observed in some foci (arrow), but mostly does not colocalize with integrin
slide17
Unc-52, pat-2, unc-112 required for PAT-4/ILK assembly

-Embryo’s stained with Abs to PAT-4/ILK

-Perlecan, Integrin, UNC-112 required for polarization

-Vinculin not required

slide19
PAT-4/ILK acts as an adaptor during attachment assembly
  • ILK functions upstream of vinculin & UNC-89 and downstream of perlecan & integrin
  • Essential function of PAT-4/ILK independent of kinase activity (results not shown)…thus acts primarily as an adaptor
slide20
Summary
  • Pat-4 encodes the sole ILK homolog in C. elegans
  • PAT-4/ILK acts as an adaptor to link proteins at the adhesion complex
  • Absence of PAT-4/ILK blocks sarcomere assembly
  • Y2H identified UNC-112 as an interacting partner of PAT-4/ILK
  • ILK kinase domain is vestigial
  • Proper PAT-4/ILK localization requies perlecan & integrin, but not vinculin
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