Rapid changes in tissue mechanics regulate cell behaviour in the developing embryonic brain

Abstract

Tissue mechanics is important for development; however, the spatio-temporal dynamics of in vivo tissue stiffness is still poorly understood. We here developed tiv-AFM, combining time-lapse in vivo atomic force microscopy with upright fluorescence imaging of embryonic tissue, to show that during development local tissue stiffness changes significantly within tens of minutes. Within this time frame, a stiffness gradient arose in the developing Xenopus brain, and retinal ganglion cell axons turned to follow this gradient. Changes in local tissue stiffness were largely governed by cell proliferation, as perturbation of mitosis diminished both the stiffness gradient and the caudal turn of axons found in control brains. Hence, we identified a close relationship between the dynamics of tissue mechanics and developmental processes, underpinning the importance of time-resolved stiffness measurements.

Spatial mapping of the collagen distribution in human and mouse tissues by force volume atomic force microscopy

“…Here, we present a design of the force volume AFM experiment, aimed to perform a fast tissue characterization with a standard, non-high-speed AFM setup 6,8,[18][19][20][21][22] . In our experiments, about 30 min are required for characterizing one tissue section, i.e.for the tip positioning in relevant areas of the sample and the mapping of 10 areas of the section, 5 for CE and 5 for CL locations.…”

“…Our results are obtained through a rapid and robust screening, based on the optimization of both the sample preparation method and the scanning parameters, using a conventional (non high-speed) AFM setup. We demonstrate that a standard AFM, equipped with force volume capability, bright field optical imaging capability and without integrated x-y motorized stage 6,8,22 , can be a practical tool for the characterization of tissues exhibiting a structural heterogeneity, due to uneven collagen distribution.…”

Cell Adhesion by Integrins

“…It is striking that most healthy tissues have a stiffness below this point, while fibrotic tissue is stiffer than 5 kPa (see Chapter 9). At the same time, stiffness gradients observed during the development of Xenopus (438) and Drosophila 94 Additionally, work in Drosophila indicates that integrins and talins might experience unique force vectors in different tissues (229). Combined with the findings that specific integrin conformations bind ligands selectively (see above), differential force vectors in tissues might be a mechanism to tune the physiological needs for integrin activation and signaling.…”

Towards brain-tissue-like biomaterials

“…Characterizing the stiffness of the brain with traditional tools is often unreliable, because of the low bending stiffness of brain tissue. Recently, different experimental techniques such as atomic force microscopy 21 , microindentation 22 , 23 , rheology 24 , and magnetic resonance elastography 25 have been used in vivo and ex vivo, under dry and wet conditions, and with different boundary and loading conditions. Using these various techniques the elastic modulus of brain tissue is typically shown to be in the range of few hundreds of Pa to kPa, yet the experimental methods, animal models, and conditions used to conduct these tests diverge substantially from lab to lab, inducing a high degree of variability in measurement outcomes.…”