9. Mechanisms of cell migration

THE CYTOSKELETAL SYSTEM

2011. 05. 03.

Beáta Bugyi

University of Pécs, Medical School

Department of Biophysics

Cell migration, motility

1. Intracellular - inside the cell muscle contraction

movement of organelles

movement of intracellular pathogens Listeria monocytogenes

Eschericia coli

Rickettsia rickettsii

Shigella

Salmonella

movement of chromosomes

2. Locomotion - displacement of the cell ciliar / flagellar movement

based on a special organelle: cilium, flagellum

pseudopod formation

based on the cytoskeletal filaments

3. Cell shape chages CYTOSKELETON

Listeria monocytogenes Chromosome congression in starfish oocyte

Source: Lénárt Péter és mtsai Nature 436 2005

1. Intracellular movement

move cells through liquid media / move liquid around the cells

fiber-like, flexible, elongated membrane projections of eukaryotic cells (mm - mm)

axonemal structure (0.25 mm): 9+2 microtubules

proteins: microtubules, nexin, dynein, tektin

2. Locomotion - ciliar/flagellar

Cilium

respiratory system (lung epithelium)

Flagellum

spermatozoon

Cilium Flagellum

AXONEME

Tektin

(13)

(9)

2. Locomotion - ciliar/flagellar

flagellum cilium

structure axoneme axoneme

number / cell 1-2 >1000

function propeller-like motion

„waves”

back and forth beating

power stroke – recovery stroke

energy

source ATP ATP

2. Locomotion - ciliar/flagellar

Fibroblast v = 0.5 mm / min

Source: Klemens Rottner Institut für Genetik Universität Bonn

Keratocyte v = 10 mm / min

2. Locomotion – pseudopod formation

0. Stimulus - polarisation chemoatractant, substrate, neighbouring cells

1. Protrusion lamellipodium formation

2. Adhesion formation of new cell-substrate connections

3. Contraction formation of contractile acto-myosin bundles

retratction of the rear of the cell

translocation of the cell body

4. Disassembly of old adhesions

Phases of cell migration

HEP2G adenocarcinoma cells, stimulus: insulin gradient

Cytoskeletal components of cell migration

Lamella

Filopodium

Focal contacts

Lamellipodium

Source: LeClainche és mtsai Physiological Reviews 88 2008.

direction of movement

A simpified scheme of cell migration

PROTRUSION (front) polarised growth of branched actin

filaments (polymerisation)

force generation: actin polymerisation

treadmilling

RETRACTION (rear) antiparallel, linear actin filaments

force generation: acto-myosin

ADHESION support protrusive and contractile forces

mechanical coupling between the

cytoskeleton and the substrate

coupling

↓

efficiency of

cell migration

Lamellipodium (Lp) Lamella (Lm)

actin networks with different structural and dynamic properties at/close to the leading

edge

width / length: 0 – 0.5 mm / 100 – 200 nm

thin, narrow membrane projection width / length: 1 mm/10-20 mm

mechanism WAVE - Arp2/3 komplex

„branching” ?

distance from the

membrace 0 – 0.5 mm > 0.5 mm

dynamics fast turnover

taposómalom egyensúly, treadmilling slow turnover

structutre branched - „dendritic” – filaments linear, non-branched filaments

molecular components capping protein, ADF/cofilin, cortactin, ... tropomyosin, myosin, …

Protrusive actin structures lamellipodium and lamella

Lamellipodium and lamella a possible mechanism

Source: Bugyi Beáta és Marie-France Carlier Annual Reviews in Biophysics 39 2010.

goldfish fibroblast

GFP-actin, vinculin

Focal contacts

classification: size, shape, intracellular localistaion and molecular composition

FOCAL COMPLEXES small, dot-like structure (1 mm2)

near the plasma membrane

dynamic

integrin, talin, paxillin

FOCAL ADHESIONS 2 – 5 mm long strucutre

farther from the plasma membrane

more stable, less dynamic

associated to stress fibers

integrin, talin, paxillin, vinculin, a-aktinin, zyxin, aktopaxin

FIBRILLAR ADHESIONS elongated structure

farthest from the plasma membrane

associated to fibronection fibers

integrin, tenzin

Focal contacts - types, components

Source: LeClainche és mtsai Physiological Reviews 88 2008.

Focal contacts – as molecular clutches

mechanical coupling between the substrate and the cytoskeleton

„disengaged” OFF „engaged” ON

molecular connection between the cytoskeleton and the

substrate

the force generated by actin polymerisation results in

membrance projections at the front of the cell

PROTRUSION the force generated by acto-myosin complexes results in

retraction at the rear of the cell

TRANSLOCATION

no connection between the cytoskeleton and the

substrate

the force generated by actin polymerisation results in

retrograde flow of actin filaments

NO MOVEMENT

Study of actin-based movements in vitro Biomimetic model systems (next…)

N-WASP – Arp2/3 complex formin

mouse fibroblast

t = 3 h

chicken fibroblast

t = 2 h

mouse melanoma cell

t = 20 min

fish epidermal keratocyte

t = 4 min