Avalilação PREreview de Eph-ephrin-mediated differential persistence as a mechanism for cell sorting

The preprint Eph-ephrin-mediated differential persistence as a mechanism for cell sorting by Bothe et al. investigates whether enhanced persistence of the motion of cells upon heterotypic contacts in a two species model enables sorting into distinct patches of individual species.

Using a computational model of interacting ABPs, the authors could recreate scenarios in which differential persistence enables cell sorting, measured with an increased demixing index, which has also been found in experiments where differential persistence was identified. They also tested the influence of other mechanisms known to induce cell sorting, such as differential adhesion and contact inhibition of locomotion. Eventually, they identify that each mechanism performs best in different parameter regimes, e.g., differential persistence works best at low density, but improves the performance of contact inhibition of locomotion at high density.

Major issues

• The authors specify that, in experiments, after heterotypic interactions, there is transiently increased persistence. However the duration of this transient state is never measured. Instead, they claim that persistence is enhanced for about 12 minutes. Importantly, this is nothing more than the persistence time inferred by the ABP. This persistence time of 12 minutes describes the strength of persistence but not the duration of enhanced persistence.

• Instead of an ABP, the authors should consider using a modified ABP model that takes into account transiently enhanced persistence for fitting the MSD. This would require an analytical solution. At least, it should be noted that in the simulations, there are two parameters, $\tau^+$ and $\tau_p$, hence it would be useful for a thorough comparison to also be able to parameterize the experiments accordingly. When performing the MSD fit with the current model, the total time over which the fit is performed determines the fit parameters.

• Connected to this, it should be clarified how interactions in the simulations affect the MSD, for example by measuring the MSD in the simulations. Also, it would be interesting to compare the persistence time with the typical time between collisions.

• It is unclear why $D^+$ is scanned for only in scenarios with additional CIL and not before, given that it is a key parameter that was before assumed to be 0. This would also connect closer to the experiment, where the (transiently) enhanced persistence is not infinite. These insights could potentially improve the match between the rotational diffusivity in experiment and simulation.

• The distribution of exit angles after heterotypic contacts in Fig. S1A is described as narrow. Its variance is reported to be 93°. From the incorrect dimension (degree instead of degree squared) and visually, one can conclude that this should mean standard deviation instead of variance. While it is certainly narrower than the corresponding distribution after homotypic contacts, which was shown with the p value, an angle distribution with a standard deviation of 93° should not be described as narrow.

• The way how differential persistence and differential adhesion are implemented does not match the common idea of differential properties in cell sorting literature. Usually, it refers to each of multiple species having different properties, and not to one of them in response to heterotypic contacts. In the case of CIL, the authors correctly state that this is non-differential.

• In the experiments, interactions between three or more cells should be somehow characterized. It would at least be useful if the authors commented on what influence these interactions have.

Minor issues

• List concerns that would improve the overall flow or clarity but are not critical to the understanding and conclusions of the research.

• Plots of MSDs should have logarithmic axes, at least in an additional supplementary figure. Especially Fig. 2C would benefit from this, as dynamical regimes become more easily recognizable then.

• Considering an athermal ABP as the foundation of the experimental model would be fine, given that the mapping of the MSD to an athermal ABP was already successful.

• The symbol $v^+$ is used but never introduced.

• The statement that the optimal value of $\tau_p$ is proportional to the inverse Pe should be backed by results shown in the paper.

• In Fig. 1 it looks like more area is covered after 400 mins. It would be useful if the authors could comment on whether cells proliferate. Also, the density could be measured and compared.

• For improved readability, the snapshots B-E should be marked in the parameter space in panel A in both Figs. 5 and 6.

• In Fig. 6, it would be insightful to see a snapshot within the dark purple region.

Competing interests

The authors declare that they have no competing interests.

Use of Artificial Intelligence (AI)

The authors declare that they did not use generative AI to come up with new ideas for their review.