Figure 1: The mechanosensation hypothesis.

a, Much research suggested that cells' primary cilia respond to force through mechanosensation. In this original model, fluid flow pushes the cilium, which triggers the opening of calcium-sensitive channel proteins and so allows calcium ions (Ca²⁺) to enter the cilium. Intracellular signalling cascades are activated by the Ca²⁺ influx, leading to altered gene expression on the left side of the embryo, or promoting water transport in the kidneys. b, Delling et al.¹ find that, contrary to this hypothesis, ciliary bending in response to force does not open Ca²⁺ channels. Instead, the authors propose that the Ca²⁺ influx observed in previous experiments might have been due to diffusion from the cell body, or to damage to cilia in response to extreme levels of force.