Figure 2. Mechanoreceptors of spam mutants undergo dramatic cellular deformation.

Electron micrographs of a typical scolopale MRN in the Johnston's organ. (a) control (cn bw) flies at 37°C and (b) spam homozygous mutants at 21°C have nearly indistinguishable morphology (equivalent results are observed with cn bw flies at 21°C). However, (c) exposure of spam flies to 30 min at 37°C results in major cellular deformation, with the receptor cell cytoplasm expanding to fill the entire scolopale space (importantly, the cells that wrap around the scolopale space are unaffected; data not shown). (d) Placing spam mutants in a high-humidity chamber (>90% RH) prevents the heat-induced deformation. (e-f) cn bw control and spam flies injected with a hyper-osmotic solution to the abdomen. Only spam mutants display dramatic cellular deformation with extensive invasion of the extracellular space. Note that some of the reconstructed EM micrographs show a side view of the scolopale, with only one ciliary root visible (panels a and e), while all others show a front view, with both ciliary roots visible.