Direct force measurement and loading on developing tissues in intact avian embryos

Developmental morphogenesis is driven by tissue stresses acting on tissue rheology. Direct measurements of forces in small tissues (100μm-1mm) in situ such as in early embryos require high spatial precision and minimal invasiveness. Here we report tissue force microscopy (TiFM) integrating a vertical cantilever probe and live imaging to enable close-loop control of mechanical loading in early chicken embryos. By testing previously qualitatively characterized force-producing tissues in the elongating body axis, we show that TiFM quantitatively captures stress dynamics with high sensitivity. TiFM also provides the capacity of applying a stable, minimally-invasive and physiologically relevant load to drive tissue deformation, which alters morphogenetic progression and cell movements. Together, TiFM addresses a key technological gap in tissue force measurement and manipulation in small developing embryos, and promises to contribute to the quantitative understanding of complex multi-tissue mechanics during development.