Fig. 2: Morphological changes of C. elegans embryos upon indentation for different eggshell treatments.

a Schematic cross-sectional views of the eggshell in its untreated and degraded forms. The untreated eggshell has a trilaminar structure, consisting of an outer vitelline layer, a middle chitin layer and an inner chondroitin proteoglycan layer (ai). Treatment with sodium hypochlorite solution (bleach) selectively removes the VL, but may also attack the underlying CL (aii). Chitinase treatment is applied after bleach treatment to strip away the CL from the embryo shell (aiii). b Frontal and lateral schematic cross-sections of an embryo, illustrating the shape changes in width Δw and length Δl upon indentation with a depth Δz. c Bright field microscopy images in relaxed and poked states of a live, bleach-treated embryo in the twitching stage. A lateral extension Δw upon indentation with respect to the relaxed egg width w is well visible (F_z = 5 µN). d Scatter plot of embryo elongation Δl and widening Δw as derived from microscopy images upon indentation. Widening is more prominent than the elongation changes for all eggs and conditions. Paired t-test was applied to calculate p between l and l + Δl and w & w + Δw, respectively (**p ≤ 0.01; ****p ≤ 0.0001; ns not significant). Force values are F_z = 5.0 µN for untreated and bleached eggs and F_z = 0.5 µN for chitinase-treated eggs. e Scatter plot of the embryo ellipticity (ratio l/w) in relaxed and poked states for treated and untreated conditions. Very soft chitinase-treated eggs tend to shorten slightly and show stronger widening, but also larger deviation from mean values than untreated and bleached eggs