Extreme elastic properties of mechanosensory chordotonal organs in Drosophila

Mechanosensory organs in higher organisms, especially propiosensory organs that monitor body movements, are often pre-strained. This allows the organs to adapt to body motions and maintain sensitivity. Some of the tension regulation typically is part of active feedback mechanisms, but it appears that there also are mechanisms that generate persistent prestrain and the corresponding pretension in tissues. How this occurs and how it is regulated, is not understood. Here we study the lateral pentascolopidial organ (lch5), a type of chordotonal organ (ChO), of Drosophila larvae. This organ is a propioceptor constructed as an axial tension sensor that responds to tension changes between two anchoring points in the larval cuticle during body muscle contractions. We performed micromanipulation experiments using glass microneedles to probe the lch5 organ mechanics with calibrated forces. We found that ChO cap cells display extreme elastic properties that create a 400% dynamic range of strain. Furthermore, we show that the extracellular matrix (ECM) surrounding the cap cells is responsible for maintaining the pretension and elasticity of ChOs.