MCB 2210 Lecture Notes - Lecture 29: Endocytosis, Cdc42, Baud
3 Apr 2016
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Actin: membrane protrusion (lamellipodia and filopodia) The leading edge regularly extends thin sheet-like structures called lamellipodia and thin needle-like projections or spikes called filopodia. After protruding forward, they adhere to the substrate or sweep over the top of a cell as a ruffle. Also contain long cables of actin called stress fibers that function in cell adhesion and contraction. Actin actively polymerizes near the leading edge. The behavior of actin filaments in lamellipodia and filopodia can be traced by microinjecting the cells with fluorescently labeled actin. Immediately after injection, fluorescent actin is incorporated into filaments at the extreme leading edge: indicates that actin polymerization takes place. After actin filaments are nucleated at the leading edge of a fibroblast: the entire network of filaments fluxes backward towards the interior of the cell. Depolymerization of filaments begins so retrograde flow is coupled to depolymerization. Cofilin= thought the be major actin depolymerizing activity behind leading edge.
