Reply to Krens et al: Cell stretching may initiate cell differentiation

In their letter, Krens et al. (1) question whether our tissue surface tension model can be applied to zebrafish aggregates and explants. They argue that the stretched-out surface cells shown in our manuscript (2) are differentiated squamous epithelial enveloping-layer (EVL) cells, which implies that these zebrafish explants consist of two tissue types and that our model does not apply to these explants. Their data neither contradict our results nor support their claim that “the model as such has very little predictive value for zebrafish explants” (1).