Quantitative analysis of mechanical force required for cell extrusion in zebrafish embryonic epithelia

Abstract

When cells in epithelial sheets are damaged by intrinsic or extrinsic causes, they are eliminated by extrusion from the sheet. Cell extrusion, which is required for maintenance of tissue integrity, is the consequence of contraction of actomyosin rings, as demonstrated by both molecular/cellular biological experimentation and numerical simulation. However, quantitative evaluation of actomyosin contraction has not been performed because of the lack of a suitable direct measurement system. In this study, we developed a new method using a femtosecond laser to quantify the contraction force of the actomyosin ring during cell extrusion in zebrafish embryonic epithelia. In this system, an epithelial cell in zebrafish embryo is first damaged by direct femtosecond laser irradiation. Next, a femtosecond laser-induced impulsive force is loaded onto the actomyosin ring, and the contraction force is quantified to be on the order of kPa as a unit of pressure. We found that cell extrusion was delayed when the contraction force was slightly attenuated, suggesting that a relatively small force is sufficient to drive cell extrusion. Thus, our method is suitable for the relative quantitative evaluation of mechanical dynamics in the process of cell extrusion, and in principle the method is applicable to similar phenomena in different tissues and organs of various species.

Model to Link Cell Shape and Polarity with Organogenesis

“…The factor of 12 = 2 × 6 is due to the hexagonal structure of the cell sheet. Note that our estimate of the extrusion energy is consistent with the finding in Yamada et al (2017) for epithelial cell extrusion. Here, an actomyosin ring is measured to exhibit a contraction force of the order of 1kPa, which results in an extrusion energy of the order 1kPa × 3 ≈ 3 × 10 −13 J.…”

“…In Eskandari & Salcudean (2008), a typical value for the dynamical viscosity µ was reported to be on the order of 250Pa s. This can be related to the coefficient γ by Stokes' Law of viscous drag, γ = 6πµ . We now compare our model with epithelial cell extrusion and use the typical cell speed reported in Yamada et al (2017), v 0 ≈ 1mm h −1 and use the typical cell size reported in Brown & Bron (1987), 2 = 13µm. With these numbers, our model predicts a typical extrusion energy on the order of 12V 0 ≈ 12 × 6πµ 2 v 0 ≈ 2 × 10 −13 J.…”

Model to link cell shape and polarity with organogenesis

“…The factor of 12 = 2 × 6 is due to the hexagonal structure of the cell sheet. Note, that 272 our estimate of the extrusion energy is consistent with the finding in [41] for epithelial 273 cell extrusion. Here, an actomyosin ring is measured to exhibit a contraction force of the 274 order of 1kPa, which results in an extrusion energy of the order 1kPa × Cell proliferation is simulated as a Poisson process by choosing a rate Γ for each cell 281 to divide in each time unit.…”

“…As a starting point for our model, we consider the model suggested 39 in [20] which was used to study directional adhesion mediated by apical-basal (AB) 40 polarity and PCP. The model in [20], however, could not explicitly account for changes 41 in cell shapes. Here, we show that the effect of cell wedging can be modeled within a 42 point-particle representation by modifying cell-cell forces to favor a tilt in AB polarities.…”

“…In [40], a typical value for the dynamical viscosity µ was reported to be on the order of 250Pa s. This can be related to the coefficient γ by Stokes' Law of viscous drag, γ = 6πµ . We now compare our model with epithelial cell extrusion and use the typical cell speed reported in [41], v 0 ≈ 1mm h −1 and use the typical cell size reported in [42], 2 = 13µm. With these numbers, our model predicts a typical extrusion energy on the order of…”