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A mechanical bottleneck explains the variation in cup growth during FcgammaR phagocytosis.

van Zon JS, Tzircotis G, Caron E, Howard M - Mol. Syst. Biol. (2009)

Bottom Line: Here, we study the internalization of immunoglobulin G-coated particles in cells transfected with Fcgamma receptors (FcgammaRs) through the formation of an enveloping phagocytic cup.We explain these observations in terms of a mechanical bottleneck using a simple mathematical model of the overall process of cup growth.Our analysis gives a coherent explanation for the importance of geometry in phagocytic uptake and provides a unifying framework for integrating the key processes, both biochemical and mechanical, occurring during cup growth.

View Article: PubMed Central - PubMed

Affiliation: Centre for Integrative Systems Biology Imperial College (CISBIC), South Kensington Campus, Imperial College London, London, UK.

ABSTRACT
Phagocytosis is the process by which cells internalize particulate material, and is of central importance to immunity, homeostasis and development. Here, we study the internalization of immunoglobulin G-coated particles in cells transfected with Fcgamma receptors (FcgammaRs) through the formation of an enveloping phagocytic cup. Using confocal microscopy, we precisely track the location of fluorescently tagged FcgammaRs during cup growth. Surprisingly, we found that phagocytic cups growing around identical spherical particles showed great variability even within a single cell and exhibited two eventual fates: a cup either stalled before forming a half-cup or it proceeded until the particle was fully enveloped. We explain these observations in terms of a mechanical bottleneck using a simple mathematical model of the overall process of cup growth. The model predicts that reducing F-actin concentration levels, and hence the deforming force, does not necessarily lead to stalled cups, a prediction we verify experimentally. Our analysis gives a coherent explanation for the importance of geometry in phagocytic uptake and provides a unifying framework for integrating the key processes, both biochemical and mechanical, occurring during cup growth.

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(A) Distribution of phagocytic cup sizes as a function of time for cells with WT FcγRs (gray bars, n>35 for all panels). A cup size of S=πR≈4.7 μm corresponds to a fully formed cup. Model simulations (red line), in which we plot the distribution of cup sizes for 100 particles with the force per unit of actin number used in Figure 2H multiplied by a factor drawn from a Gaussian distribution with mean 0.95 and s.d. 0.30. All other parameters take their WT values. (B) Phagocytic cup size as a function of time for solutions of our model in which the force per unit of actin number is multiplied by the specified factor. The cup size corresponding to a half-cup is indicated by a dotted line and that corresponding to a full cup by a dashed line.
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f3: (A) Distribution of phagocytic cup sizes as a function of time for cells with WT FcγRs (gray bars, n>35 for all panels). A cup size of S=πR≈4.7 μm corresponds to a fully formed cup. Model simulations (red line), in which we plot the distribution of cup sizes for 100 particles with the force per unit of actin number used in Figure 2H multiplied by a factor drawn from a Gaussian distribution with mean 0.95 and s.d. 0.30. All other parameters take their WT values. (B) Phagocytic cup size as a function of time for solutions of our model in which the force per unit of actin number is multiplied by the specified factor. The cup size corresponding to a half-cup is indicated by a dotted line and that corresponding to a full cup by a dashed line.

Mentions: However, we find great variability in the rate of cup progression from one particle to another, even within the same cell. This variability might partially reflect imperfect synchronization of phagocytosis in our experiments, but is likely to be an intrinsic property of phagocytic cup formation. To quantify the amount of variability in cup progression, we focus on a single parameter: the phagocytic cup size S, which measures the distance from the center of the phagocytic cup to its rim along the surface of the particle as defined by the distribution of the GFP-tagged FcγR (see Figure 2G). The cup size ranges from S=0, for the undeformed cell membrane, to S=πR, for a fully formed phagocytic cup, where R is the radius of the enveloped particle. In Figure 3A, we plot the distribution of cup sizes as a function of time for WT FcγR-transfected cells phagocytosing 3-μm diameter particles. We find that already at t=0 min, phagocytic cups show a wide distribution of cup sizes.


A mechanical bottleneck explains the variation in cup growth during FcgammaR phagocytosis.

van Zon JS, Tzircotis G, Caron E, Howard M - Mol. Syst. Biol. (2009)

(A) Distribution of phagocytic cup sizes as a function of time for cells with WT FcγRs (gray bars, n>35 for all panels). A cup size of S=πR≈4.7 μm corresponds to a fully formed cup. Model simulations (red line), in which we plot the distribution of cup sizes for 100 particles with the force per unit of actin number used in Figure 2H multiplied by a factor drawn from a Gaussian distribution with mean 0.95 and s.d. 0.30. All other parameters take their WT values. (B) Phagocytic cup size as a function of time for solutions of our model in which the force per unit of actin number is multiplied by the specified factor. The cup size corresponding to a half-cup is indicated by a dotted line and that corresponding to a full cup by a dashed line.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2736656&req=5

f3: (A) Distribution of phagocytic cup sizes as a function of time for cells with WT FcγRs (gray bars, n>35 for all panels). A cup size of S=πR≈4.7 μm corresponds to a fully formed cup. Model simulations (red line), in which we plot the distribution of cup sizes for 100 particles with the force per unit of actin number used in Figure 2H multiplied by a factor drawn from a Gaussian distribution with mean 0.95 and s.d. 0.30. All other parameters take their WT values. (B) Phagocytic cup size as a function of time for solutions of our model in which the force per unit of actin number is multiplied by the specified factor. The cup size corresponding to a half-cup is indicated by a dotted line and that corresponding to a full cup by a dashed line.
Mentions: However, we find great variability in the rate of cup progression from one particle to another, even within the same cell. This variability might partially reflect imperfect synchronization of phagocytosis in our experiments, but is likely to be an intrinsic property of phagocytic cup formation. To quantify the amount of variability in cup progression, we focus on a single parameter: the phagocytic cup size S, which measures the distance from the center of the phagocytic cup to its rim along the surface of the particle as defined by the distribution of the GFP-tagged FcγR (see Figure 2G). The cup size ranges from S=0, for the undeformed cell membrane, to S=πR, for a fully formed phagocytic cup, where R is the radius of the enveloped particle. In Figure 3A, we plot the distribution of cup sizes as a function of time for WT FcγR-transfected cells phagocytosing 3-μm diameter particles. We find that already at t=0 min, phagocytic cups show a wide distribution of cup sizes.

Bottom Line: Here, we study the internalization of immunoglobulin G-coated particles in cells transfected with Fcgamma receptors (FcgammaRs) through the formation of an enveloping phagocytic cup.We explain these observations in terms of a mechanical bottleneck using a simple mathematical model of the overall process of cup growth.Our analysis gives a coherent explanation for the importance of geometry in phagocytic uptake and provides a unifying framework for integrating the key processes, both biochemical and mechanical, occurring during cup growth.

View Article: PubMed Central - PubMed

Affiliation: Centre for Integrative Systems Biology Imperial College (CISBIC), South Kensington Campus, Imperial College London, London, UK.

ABSTRACT
Phagocytosis is the process by which cells internalize particulate material, and is of central importance to immunity, homeostasis and development. Here, we study the internalization of immunoglobulin G-coated particles in cells transfected with Fcgamma receptors (FcgammaRs) through the formation of an enveloping phagocytic cup. Using confocal microscopy, we precisely track the location of fluorescently tagged FcgammaRs during cup growth. Surprisingly, we found that phagocytic cups growing around identical spherical particles showed great variability even within a single cell and exhibited two eventual fates: a cup either stalled before forming a half-cup or it proceeded until the particle was fully enveloped. We explain these observations in terms of a mechanical bottleneck using a simple mathematical model of the overall process of cup growth. The model predicts that reducing F-actin concentration levels, and hence the deforming force, does not necessarily lead to stalled cups, a prediction we verify experimentally. Our analysis gives a coherent explanation for the importance of geometry in phagocytic uptake and provides a unifying framework for integrating the key processes, both biochemical and mechanical, occurring during cup growth.

Show MeSH
Related in: MedlinePlus