![]() ![]() Nerve responses were measured as compound action potentials (CAP). *significant difference (p < 0.05) from w 1118 controls: (Kruskal-Wallis test followed by two-tailed Mann-Whitney U-tests with Bonferroni correction). X: not accessible because the nerve response is entirely lost. ( B) Corresponding sensitivity gain due to mechanical amplification, sound particle velocity thresholds of the nerve responses, and maximum amplitudes of the nerve responses extracted from the data in (A) (means ± SD). In w 1118 controls, the antenna’s displacement displays a compressive nonlinearity that aligns with the dynamic range of the nerve response and arises from mechanical amplification by JO neurons (data from N ≥ 5 flies/antennae per strain). Tone frequencies were adjusted to match the mechanical best frequency of the antenna, and lines indicate linear antennal mechanics. ( A) Pure tone-evoked antennal displacement (top) and normalized amplitude of the associated nerve response (bottom) as a function of the sound particle velocity of the tone. Mutant defects in sperm competition suggest that both dyneins also function in sperm motility. This establishes diverse roles of axonemal dyneins in Drosophila auditory neuron function and links auditory neuron motility to primary cilia and axonemal dyneins. Dmdnai2, in addition to being required for amplification, was essential for outer dynein arms in auditory neuron cilia. ![]() Epistasis analysis revealed that Dmdnah3 acts downstream of Nan-Iav channels in controlling the amplificatory gain. Null alleles of both dyneins equally abolished electrical auditory neuron responses, yet whereas mutations in Dmdnah3 facilitated mechanical amplification, amplification was abolished by mutations in Dmdnai2. Promoter fusions revealed that the two axonemal dynein genes Dmdnah3 (=CG17150) and Dmdnai2 (=CG6053) are expressed in chordotonal neurons, including the auditory ones in the fly's ear. Here, we describe two axonemal dynein proteins that are required for Drosophila auditory neuron function, localize to their primary cilia, and differently contribute to mechanical amplification in hearing. Because the neurons bear mechanosensory primary cilia whose microtubule axonemes display dynein arms, we hypothesized that their motility is powered by dyneins. Much like vertebrate hair cells, the chordotonal sensory neurons that mediate hearing in Drosophila are motile and amplify the mechanical input of the ear. ![]()
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