These nonmuscle cells called cortex cells lie just beneath the plasma membrane. They contain various actin-binding proteins that regulate the polymerization of actin filaments in order to drive cellular processes. Actin filaments polymerize via nucleation and grow through the addition of actin monomers. Various proteins regulate this process by capping filaments, severing filaments, and bundling or cross-linking filaments. Actin polymerization drives cell locomotion, axonal outgrowth, and changes in cell shape during development through formation of structures like lamellipodia.

1. Dumangcas
Durante
Odchimar
Roa, S.

2.  These nonmuscle cells lies just beneath the
plasma membrane
 Arrangements are less ordered, more
labile, and transient unlike muscle
cells/tissues.
 typically restricted to a thin cortex
 ‘cortex’ is an active region of the cell,
responsible for many cellular processes
(e.g. the constriction of a single animal cell into two
cells during cell division.)

3. 1) Nucleating proteins
2) Monomer-sequestering proteins
3) End-blocking (capping) proteins
4) Monomer-polymerizing proteins
5) Actin filament-depolymerizing proteins
6) Cross-linking proteins
7) Filament-severing proteins
8) Membrane-binding proteins

4.  nucleation
Nucleating
protein

5. - prevent polymerizing
by isolation
Monomer-
sequestering
proteins

6. - regulate the length of actin filaments by
binding on an end and blocking a loss or
gain of subunits
Capping
proteins

7. - promote the growth of actin filaments

8. - fragment actin filaments and promote
depolymerization at the pointed end.

9.  promote the formation of loose networks of
filaments
 promote the bundling of actin filaments into
tightly knit, parallel arrays

10.  bind to the side of an existing filament and
break it in two.

11. - Link the actin filaments to the plasma
membrane indirectly, by means of
attachment to a peripheral membrane
protein Membrane-
binding
proteins

15.  Actin Polymerization as a Force-
Generating Mechanism
 Cell Locomotion
• Cells that Crawl over the Substratum
 AxonalOutgrowth
 Changes in Cell Shape during Embryonic
Development

16.  How is the bacterial cell able to induce the
formation of actin filaments at a particular
site on its surface?
• Because Listeria contains a surface protein called
‘ActA’, it recruits and activates a number of host
proteins that work together to direct the process of
actin polymerization. (without the participation of
myosin motors)

18.  Cells that Crawl over the Substratum
• Aided by lamellipodia, it extend out from the
cell as a broad, flattened, veil-like protrusion.
Found by examining its leading edge.

19. Scanning electron micrograph of a mouse fibroblast
crawling over the surface of a culture dish.

22.  Cells that Crawl over the Substratum
• Aided by lamellipodia, it extend out from the
cell as a broad, flattened, veil-like protrusion.
Found by examining its leading edge.
• With these cells can move or analogically can
walk.

23. shows the protrusion of the leading
edge of the cell in the form of a
lamellipodium.
shows the adhesion
of the lamellipodium to the
substratum, to grip the
substratum.
shows
the movement of the bulk of the
cell forward
shows
the rear of the cell has been
pulled forward.

24.  Cells that Crawl over the Substratum
• Aided by lamellipodia, it extend out from the
cell as a broad, flattened, veil-like protrusion.
Found by examining its leading edge.
• With these cells can move or analogically can
walk.
• The protrusion of a lamellipodium is
associated with the nucleation and
polymerization of actin filaments and their
association with various types of actin-binding
proteins.

25. A proposed mechanism
for the movement of a cell in a directed manner

26.  Cells that Crawl over the Substratum
• Lamellipodial movement is a dynamic process.
• As actin filament polymerization and branching
continue at the very front edge of the
lamellipodium, actin filaments are depolymerizing
toward the rear of the lamellipodium.

29. Fluorescence Drawing of a filamentous actin
micrographs of a fish network of the lamellipodium
keratocyte and the actin–myosin
interactions

31.  theexperiment of Ross Harrison provided a
strong evidence that axons develop by a process
of active outgrowth and elongation.
 Thetip of an elongating axon consists of a
growth cone, which resembles a highly motile,
crawling fibroblast and contains several types of
locomotor protrusions, including a lamellipodium,
microspikes, and filopodia.

34.  Changes in cell shape are brought about largely
by changes in the orientation of cytoskeletal
elements within the cells.
 One of the best examples of this phenomenon is
seen in the early stages of the development of
the nervous system.