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Robust patterns in the stochastic organization of filopodia.

Husainy AN, Morrow AA, Perkins TJ, Lee JM - BMC Cell Biol. (2010)

Bottom Line: Filopodia are highly dynamic structures that show a rich diversity in appearance and behavior.While there are several mathematical models of filopodia initiation and growth, testing the capacity of these theoretical models in predicting empirical behavior has been hampered by a surprising shortage of quantitative data related to filopodia.Neither is it clear how quantitatively robust the cellular filopodial network is and how perturbations alter it.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biochemistry, Microbiology & Immunology, University of Ottawa, 451 Smyth Road, Ottawa, Ontario K1H 8M5, Canada.

ABSTRACT

Background: Filopodia are actin-based cellular projections that have a critical role in initiating and sustaining directional migration in vertebrate cells. Filopodia are highly dynamic structures that show a rich diversity in appearance and behavior. While there are several mathematical models of filopodia initiation and growth, testing the capacity of these theoretical models in predicting empirical behavior has been hampered by a surprising shortage of quantitative data related to filopodia. Neither is it clear how quantitatively robust the cellular filopodial network is and how perturbations alter it.

Results: We have measured the length and interfilopodial separation distances of several thousand filopodia in the rodent cell line Rat2 and measured these parameters in response to genetic, chemical and physical perturbation. Our work shows that length and separation distance have a lognormal pattern distribution over their entire detection range (0.4 μm to 50 μm).

Conclusions: We find that the lognormal distribution of length and separation is robust and highly resistant to perturbation. We also find that length and separation are independent variables. Most importantly, our empirical data is not entirely in agreement with predictions made based on existing theoretical models and that filopodial size and separation are an order of magnitude larger than what existing models suggest.

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Related in: MedlinePlus

The actin cytoskeleton in Rat2 cells. Rat2 fibroblast cell stained for actin (white) and DNA (blue). The leftmost panel shows transverse actin stress fibers (S) and filopodia (F) as hair-like projections from the cell perimeter. The central panel shows counting of individual filopodia lengths (L1, L2, L3, L4) and distance separation (D1, D2, D3). The right panel shows a mitotic cell with retraction fibers (R) indicated. The red scale bar is 10 μm.
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Figure 1: The actin cytoskeleton in Rat2 cells. Rat2 fibroblast cell stained for actin (white) and DNA (blue). The leftmost panel shows transverse actin stress fibers (S) and filopodia (F) as hair-like projections from the cell perimeter. The central panel shows counting of individual filopodia lengths (L1, L2, L3, L4) and distance separation (D1, D2, D3). The right panel shows a mitotic cell with retraction fibers (R) indicated. The red scale bar is 10 μm.

Mentions: Filopodia span a wide range of observable lengths and individual cells show high variability in the size and number of filopodia they possess. To understand filopodia in their cellular context, we observed filopodia production in rodent fibroblast Rat2 cells. We chose this cell line because it is non-cancerous and individual cells have filopodia that span nearly two orders of magnitude in length. The appearance of the actin cytoskeleton in typical Rat2 cells is shown in Figure 1. In interphase, two types of linear actin polymers are commonly seen, stress fibers (S) and filopodia (F). Stress fibers traverse the cell in a lengthwise manner. Filopodia, on the other hand, are visible as linear projections from the cell body that emanate from multiple places and proceed in multiple directions. Filopodia are distinguishable from the less frequently observed and visibly similar retraction fibers. Retraction fibers are seen primarily in mitotic cells but also appear in cells in interpahse, at the trailing edge during migration. Based on our previously published work with living Rat2 cells [23], filopodia can be visually distinguished from retraction fibers (R) based on their relative thickness and extended presence behind the plasma membrane. We have purposely excluded mitotic cells from our analysis to avoid potential confusion between filopodia and retraction fibers. Moreover, Rat2 cells are relatively non-migratory so they have very few retraction fibers relative to filopodia in non-mitotic cells.


Robust patterns in the stochastic organization of filopodia.

Husainy AN, Morrow AA, Perkins TJ, Lee JM - BMC Cell Biol. (2010)

The actin cytoskeleton in Rat2 cells. Rat2 fibroblast cell stained for actin (white) and DNA (blue). The leftmost panel shows transverse actin stress fibers (S) and filopodia (F) as hair-like projections from the cell perimeter. The central panel shows counting of individual filopodia lengths (L1, L2, L3, L4) and distance separation (D1, D2, D3). The right panel shows a mitotic cell with retraction fibers (R) indicated. The red scale bar is 10 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2992051&req=5

Figure 1: The actin cytoskeleton in Rat2 cells. Rat2 fibroblast cell stained for actin (white) and DNA (blue). The leftmost panel shows transverse actin stress fibers (S) and filopodia (F) as hair-like projections from the cell perimeter. The central panel shows counting of individual filopodia lengths (L1, L2, L3, L4) and distance separation (D1, D2, D3). The right panel shows a mitotic cell with retraction fibers (R) indicated. The red scale bar is 10 μm.
Mentions: Filopodia span a wide range of observable lengths and individual cells show high variability in the size and number of filopodia they possess. To understand filopodia in their cellular context, we observed filopodia production in rodent fibroblast Rat2 cells. We chose this cell line because it is non-cancerous and individual cells have filopodia that span nearly two orders of magnitude in length. The appearance of the actin cytoskeleton in typical Rat2 cells is shown in Figure 1. In interphase, two types of linear actin polymers are commonly seen, stress fibers (S) and filopodia (F). Stress fibers traverse the cell in a lengthwise manner. Filopodia, on the other hand, are visible as linear projections from the cell body that emanate from multiple places and proceed in multiple directions. Filopodia are distinguishable from the less frequently observed and visibly similar retraction fibers. Retraction fibers are seen primarily in mitotic cells but also appear in cells in interpahse, at the trailing edge during migration. Based on our previously published work with living Rat2 cells [23], filopodia can be visually distinguished from retraction fibers (R) based on their relative thickness and extended presence behind the plasma membrane. We have purposely excluded mitotic cells from our analysis to avoid potential confusion between filopodia and retraction fibers. Moreover, Rat2 cells are relatively non-migratory so they have very few retraction fibers relative to filopodia in non-mitotic cells.

Bottom Line: Filopodia are highly dynamic structures that show a rich diversity in appearance and behavior.While there are several mathematical models of filopodia initiation and growth, testing the capacity of these theoretical models in predicting empirical behavior has been hampered by a surprising shortage of quantitative data related to filopodia.Neither is it clear how quantitatively robust the cellular filopodial network is and how perturbations alter it.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biochemistry, Microbiology & Immunology, University of Ottawa, 451 Smyth Road, Ottawa, Ontario K1H 8M5, Canada.

ABSTRACT

Background: Filopodia are actin-based cellular projections that have a critical role in initiating and sustaining directional migration in vertebrate cells. Filopodia are highly dynamic structures that show a rich diversity in appearance and behavior. While there are several mathematical models of filopodia initiation and growth, testing the capacity of these theoretical models in predicting empirical behavior has been hampered by a surprising shortage of quantitative data related to filopodia. Neither is it clear how quantitatively robust the cellular filopodial network is and how perturbations alter it.

Results: We have measured the length and interfilopodial separation distances of several thousand filopodia in the rodent cell line Rat2 and measured these parameters in response to genetic, chemical and physical perturbation. Our work shows that length and separation distance have a lognormal pattern distribution over their entire detection range (0.4 μm to 50 μm).

Conclusions: We find that the lognormal distribution of length and separation is robust and highly resistant to perturbation. We also find that length and separation are independent variables. Most importantly, our empirical data is not entirely in agreement with predictions made based on existing theoretical models and that filopodial size and separation are an order of magnitude larger than what existing models suggest.

Show MeSH
Related in: MedlinePlus