ACTIN BINDING PROTEINS ARE THE factorsthat govern the rates of assembly, numbers, lengths, and spatial patterns of actin filaments.
(a) Fluorescence micrograph of a portion of a cell infected with the bacteriumL. monocytogenes. The bacteria appear as red-stained objects justin front of the green-stained filamentous actin tails. (b) Electron micrographof a cell infected with the same bacterium as in a, showing theactin filaments that form behind the bacterial cell and push it throughthe cytoplasm. The actin filaments have a bristly appearance becausethey have been decorated with myosin heads. Bar at the upper left,0.1 m.
Figure 9.68 shows a single fibroblast that was in theprocess of moving toward the lower right corner of the field when it was prepared for microscopy.Cell locomotion, as exhibited by the fibroblast in Figure 9.68, shares properties with other types of locomotion, for example, walking animals (with legs).
The repetitive sequence of activities that occurs as a cellcrawls over the substratum
Distribution of traction forces within a migratingfibroblast.
Left photo - Fluorescence micrographs of a fish keratocyte moving over a culture dish by means of a broad, flattened lamellipodium.Right- A schematic drawing depicting the filamentous actin network of the lamellipodium and the actin–myosin interactions toward the rear of the lamellipodium.
Dumangcas Durante Odchimar Roa, S.
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.)
- fragment actin filaments and promote depolymerization at the pointed end.
promote the formation of loose networks of filaments promote the bundling of actin filaments into tightly knit, parallel arrays
bind to the side of an existing filament and break it in two.
- Link the actin filaments to the plasmamembrane indirectly, by means ofattachment to a peripheral membraneprotein Membrane- binding proteins
Actin Polymerization as a Force- Generating Mechanism Cell Locomotion • Cells that Crawl over the Substratum AxonalOutgrowth Changes in Cell Shape during Embryonic Development
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)
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.
Scanning electron micrograph of a mouse fibroblastcrawling over the surface of a culture dish.
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.
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. showsthe movement of the bulk of the cell forward shows the rear of the cell has been pulled forward.
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.
A proposed mechanismfor the movement of a cell in a directed manner
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.
Fluorescence Drawing of a filamentous actinmicrographs of a fish network of the lamellipodiumkeratocyte and the actin–myosin interactions
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.
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.