Comparative analysis of interspecies diversity in cortical stiffness using atomic force microscopy

초록

The morphology of the brain, especially the cortex, is diverse among species, although it arises from a common structure, the epithelial tissue. Recent studies have shown that tissue deformations driven by cellular dynamics generate distinct mechanical properties of the tissue and provide topographical cues. However, it is still unclear how the mechanical interaction between tissue and cells generates species-specific diversity in cortical morphology. To address this question, we used atomic force microscopy (AFM) to measure the mechanical property "stiffness" of cortical tissue from representative species in evolution. We selected representative amniotes with specific cortical structures, such as reptiles (turtles), birds (chicken), and mammals (mice and ferrets). AFM measurements revealed spatiotemporal stiffness profiles along the apicobasal axis during brain development. In particular, the axon-enriched region, the marginal region in turtles and chickens, and the intermediate zone (IZ) in mammals showed remarkable differences in stiffness. Interestingly, the mammalian IZ showed a remarkable peak in stiffness during brain development. Therefore, we performed the perturbation assay to identify the factor responsible for changes in stiffness during brain development. We found a correlation between the fasciculation of tubulin-rich axon bundles and changes in stiffness in the mouse brain. Laser ablation of the axon bundle in the IZ showed a significant decrease in its stiffness. Taken together, our results suggest that species-specific stiffness patterns generated from different components of the cortical tissue during development may contribute to the formation of cortical structures with unique morphology.