The term “lamel­lipo­dia” was orig­i­nally coined by Aber­crom­bie to describe the thin cyto­plas­mic sheets extended at the front of mov­ing cells and to dis­tin­guish them from the finger-like pro­jec­tions, termed “filopo­dia”. This sec­tion intro­duces the motile and struc­tural fea­tures of lamel­lipo­dia.

The actin cytoskele­ton of a liv­ing B16 melanoma cell. The cell was trans­feced with a cDNA con­struct of actin tagged with green flu­o­res­cent pro­tein (actin-GFP) allow­ing visu­al­iza­tion of actin in the flu­o­res­cent chan­nel. The lamel­lipodium is seen as a wide band of flu­o­res­cent label at the pro­trud­ing cell front.

The actin cytoskele­ton in a liv­ing fish fibrob­last (CAR cell line) trans­fected as for the cell above. In this cell type the pro­trud­ing cell front fea­tures seg­ments of lamel­lipo­dia between filopo­dia.

The actin cytoskele­ton in a rat 3Y1 fibrob­last that was spread on polyly­sine, fixed and then stained with flu­o­res­cent phal­loidin. A lamel­lipodium bor­ders the entire cell periph­ery and is punc­tu­ated by actin bun­dles that pro­trude only mar­gin­ally beyond the cell edge. We have termed these bun­dles microspikes, to dis­tin­guish them from filopo­dia.

Exper­i­ments with ker­a­to­cytes have shown that frag­ments of lamel­lipo­dia can move on their own, in the absence of a cell body (Euteneuer and Schliwa, 1984; Verk­hovsky et al., 1998).

The auton­omy of the lamel­lipodium is also illus­trated by exper­i­ments show­ing that mechan­i­cal manip­u­la­tion of the ker­a­to­cyte cell body has no influ­ence on lamel­lipodium pro­tru­sion rate (Ander­son et al., 1996):

A smooth micronee­dle is used to give the cell a gen­tle push. The rate of pro­tru­sion of the cell front is unaf­fected.

In the con­verse exper­i­ment the cell body is restrained: again the rate of pro­tru­sion of the cell front is not changed in the short term.

The sheet-like nature of the lamel­lipodium is best illus­trated in elec­tron micro­graphs of cross-sections of cells embed­ded in plas­tic, as shown here. In such images lamel­lipo­dia are found to be in the range of 0.10.3µm thick. (Left) cross-section of a fish ker­a­to­cyte show­ing the thin lamel­lipodium extended from a very large cell body, bar 2.5µm. (Cen­ter) cross sec­tion of a rat 3Y1 fibrob­last spread on polyly­sine, bar 10µm. (Right) enlarged view of the left part of the lamel­lipodium in the cen­ter image, bar 1µm.

Using cor­rel­a­tive light microscopy and con­ven­tional elec­tron microscopy (see Meth­ods) the struc­ture of lamel­lipo­dia in dif­fer­ent states of motil­ity may be ana­lyzed (Figs 4.79), in this exam­ple dur­ing pro­tru­sion (Koestler et al., 2008):

Video frames of a cell express­ing GFP-actin (green) and RFP-VASP (red; see sec­tion Nucle­ation Fac­tors) that was arrested in a phase of pro­tru­sion with a mix­ture of glu­taralde­hyde and Tri­ton X-100 at the time indi­cated (FIX).

Elec­tron micro­graph of the pro­trud­ing zone of the cell shown in the video above, show­ing the diag­o­nal net­work of actin fil­a­ments in lamel­lipo­dia and the bun­dles of actin fil­a­ments that make up the microspikes and filopo­dia. From Koestler et al., 2008.

Enlarge­ment of region from top right in the fig­ure above show­ing details of the lamel­lipodium actin mesh­work and the bun­dled fil­a­ments in the microspikes.

Related Pub­li­ca­tions

  • Ander­son, KI., Wang, YL., Small, JV. (1996). Coor­di­na­tion of pro­tru­sion and translo­ca­tion of the ker­a­to­cyte involves rolling of the cell body. J Cell Biol. 134, 12091218. NCBI PubMed
  • Euteneuer U., and Schliwa M. (1984). Per­sis­tent, direc­tional motil­ity of cells and cyto­plas­mic frag­ments in the absence of micro­tubules. Nature. 511; 310(5972): 5861. NCBI PubMed
  • Koestler, SA., Auinger, S., Vinzenz, M., Rot­tner K., Small, JV. (2008). Dif­fer­en­tially ori­ented pop­u­la­tions of actin fil­a­ments gen­er­ated in lamel­lipo­dia col­lab­o­rate in push­ing and paus­ing at the cell front. Nat Cell Biol. 10, 306313. PDF
  • Verk­hovsky, A., B., Svitk­ina, T., M., Borisy, G., G. (1998). Self-polarization and direc­tional motil­ity of cyto­plasm. Curr. Biol. 9, 1120. NCBI PubMed

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