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Cell Motility
Lecture 24
BSCI 420/421
Nov 21, 2002
“ A university is a group of faculty and student entrepreneurs,
united by a common opposition to parking policies.”
- C. Kerr
1. Microfilament-based motility
2. Microtubule-based motility
1. Microfilament-based motility
a. Contractility (mainly Myosin II and actin)
1) Skeletal and cardiac muscle (last lecture)
2) Smooth muscle
3) Cytokinesis (after mitosis)
4) Phagocytosis
5) Non-muscle cell contraction
b. Cell migration along surfaces
c. Cytoplasmic streaming in plants and protist
All except muscle are inhib by cytochalasin and phalloidin.
2) Smooth muscle
Involves formation of myosin filaments from ind myosin II mols.
MLCK is activated by
Calmodulin, activated
By Ca2+ release.
5) Non-muscle cell contraction
E.g., contraction of terminal web of neural tube cells:
(attached by
adherens
jxs)
b) Cell migration along surfaces, e.g. fibroblasts & growth cones
of axons
(Fig 99).
2. Microtubule-based motility
Three different mechanisms:
a) Assembly and disassembly
b) Transport along MTs by motor proteins
c) Sliding of MTs
a) Assembly and disassembly (including DI)
E.g., formation of neurites, the projections from neurons.
formation of cilia and flagella,
formation of axopodia of protists.
Movement of poles and chromosomes during mitosis.
MT inhibitors colchicine & nocodazole inhibit these processes.
b) Transport along MTs by motor proteins
Kinesin (+) toward the cell surface. (Anterograde)
e.g. Secr. Ves, ER
Dynein (-) toward the cell center. (Retrograde)
e.g. Golgi ves
How do we know which direction motors move in axons?
When axons are cooled locally, MTs break down and
transport stops at the ends of Mts. Kinesin and Kinesintransported cargo stops at the near edge of the gap,
and dynein and dynein transported cargo stops at the far
edge of the gap.
dynein
multivesicular bodies
kinesin
neurotrans ves
mitochondria
small amt of
dynein
c) Sliding of MTs
1) Sliding apart of mitotic spindle polar MTs
by bipolar KLP (Bim C), discovered as a mutation
in Drosophila.
2) Beating of cilia & flagella
Sliding of Flagellar axoneme Mts w & w/o digestion of
linker proteins.