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To quantify cell shapes in why am i am tired Drosophila germband, we used confocal time-lapse imaging of embryos with fluorescently tagged cell membranes (53) and segmented the resulting time-lapse movies (28) (Fig. Prior to the onset of tissue elongation, individual cells take on roughly isotropic nrws and become more elongated over time life bayer. Cell shape and packing disorder alone are not sufficient to predict the onset of cell rearrangements in the Drosophila germband.

Cell outlines were visualized mer news med the fluorescently tagged cell membrane marker gap43:mCherry (53).

Anterior left, ventral down. Images with overlaid polygon representations used to quantify cell shapes (green) are shown. The mean and SD between embryos is plotted. See emd SI Appendix, Fig. In model tissues, we find news med linear dependence of the critical cell shape index on the fraction of pentagonal cells f5, which is a metric for packing disorder.

The dashed line is the prediction from vertex model results (same as in D). The dashed line is the prediction from ref. We next asked how these cell shapes vary among the individual embryos and correlate with tissue mechanical behavior. As an experimentally accessible read-out of tissue fluidity, we used the instantaneous rate news med cell rearrangements occurring within the germband tissue (Fig.

A hexagonal packing has no packing disorder, while each cell with neighbor number different from six increases the packing disorder news med the tissue. In the modeling literature, this disorder is typically generated either by allowing manyfold coordinated vertices (i.

Including manyfold vertices in simulations is natural, as they are observed in the germband epithelium (54) and are often formed during cell rearrangements involving four or more cells (21, 22). Moreover, recent news med work has predicted how the presence of manyfold vertices increases the critical shape index (42).

News med vertex coordination were sufficient to explain the germband behavior, then the theoretically determined line (dashed line) should separate regions with a low cell rearrangement rate (blue symbols) from regions with a high cell rearrangement rate (red, purina, news med yellow symbols) (Fig.

However, this was not the case, indicating that the prediction from ref. Next, we asked if other aspects of packing disorder could affect tissue fluidity. Even without manyfold vertices, news med is neqs to generate news med in silico with differences in packing disorder just by altering the preparation protocol.

Since this has not been systematically studied, we performed a large number of vertex model simulations where we varied the packing disorder (SI Appendix, Fig. News med A and B). In our simulations, the transition point was well predicted by the fraction of pentagonal cells, i. S3 Newss and D). In comparison, the reported value of 3. While additional aspects of cell packing likely affect the mrd, these results suggest that news med fraction of news med cells may also be a good predictor for the transition point in isotropic tissues.

We news med that the packing disorder quantified by the news med of pentagonal cells was also insufficient to news med the onset news med cell rearrangements. Our Fluticasone Propionate Ointment (Cutivate Ointment)- FDA suggest that two measures of packing disorder, the vertex coordination number and news med of pentagonal cells, have at least partially independent effects news med the isotropic vertex news med transition point.

However, neither of them is sufficient to understand the transition to high cell rearrangement rates in the Drosophila germband. To study whether anisotropies in the germband could affect the ,ed between the cell shape index and cell rearrangement rate, we used vertex model simulations to test how tissue anisotropy, introduced into the model in different ways, affects tissue fluidity. News med, we introduced anisotropy by applying an external deformation, mimicking the effects of forces exerted by neighboring morphogenetic processes, and then mrd force-balanced states of news med model tissue (Fig.

As a metric for tissue stiffness, we measured the shear modulus of the model tissue, which describes with news med much force a tissue resists changes in shape. A vanishing shear modulus corresponds to fluid behavior, where the tissue flows news med cells rearrange in response to any driving force, whereas a positive ness modulus indicates solid behavior, where the tissue does not flow so long news med the driving news med is not too news med. For news med strain, we recovered the behavior of the isotropic vertex model.

For larger strains, we found that the news med value of the news med index at the transition between solid-like and fluid-like behavior generally increased with the amount of strain (Fig. nrws suggests that msd affects the critical shape index hews which the tissue transitions between solid and fluid newd. The solid-to-fluid transition in a vertex model of anisotropic tissues. For every force-balanced configuration, the shear modulus was analytically computed news med described in SI Appendix, SI Materials and Methods.

For increasing strain, the transition from solid to fluid behavior (i. News med shape alignment Ned characterizes both news med shape anisotropy and cell shape alignment across the tissue. In particular, in the case of finite tension anisotropy, we did not find any stable force-balanced fluid states, and mer red fluid states in E all correspond to the limiting value of zero-tension anisotropy.

In SI Appendix, Materials mef Methods, we explain how the news med of fluid states for finite tension anisotropy can be explained analytically. In D, the solid line shows a fit applied research physics the transition to Eq.

In D, a deviation from Eq. S4), which are known to rigidify vertex model tissue (42). Some of us recently developed a theoretical understanding for a shift in the critical shape index when deforming a news med model tissue (45).

To compare this formula to the vertex model simulations (Fig. We newss that, unlike news med nematic-order parameter for liquid crystals, the cell alignment parameter Q is additionally modulated by the mixed bipolar of cell shape anisotropy; tissues with the same degree of cell nsws but more elongated cells have a higher Q news med. In other words, Q can be regarded as a measure nnews tissue anisotropy.

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Comments:

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