The neural basis of Drosophila gravity-sensing and hearing

Abstract

Footnote S1. Amplitude of gravity-induced receiver deflections. It has not been known whether the antennal receiver may really be deflected by gravity. The gravitational force imposed on objects near the earth's surface is F = m   X , where m is the mass of the object and X & & is the acceleration due to gravity (ca. 9.8 m/s 2 ). The apparent mass of the fly's antennal receiver is ca. Footnote S2. Stimulus amplitude and receiver vibrations. The pulse songs of courting males reach particle velocities of up to ca. 2.8 mm/s (95 dB) 3 . Following a previous report 4 , we presented the songs at pressure amplitudes of up to ca. 100 dB, which, under far-field conditions, corresponds to particle velocities of up to ca. 5 mm/s. This latter particle velocity will displace the arista-tip by ca. 1 m (See Göpfert et al. 5 ).Footnote S3. Hyperpolarisation of JO neurons. We found that JO neurons are not only activated (depolarised) when stretched but are also deactivated (hyperpolarised) when compressed. This deactivation is consistent with the correlations of transducer gating in the antennal receiver's mechanics 2 , which suggests that the stationary open probability of the transducer channels in JO neurons is ca. 0.5. Accordingly, deflecting the receiver forwards increase the transducer open probability in the JO neurons of the anterior region while reducing the probability in the posterior region. Together, auditory anatomy and transducer characteristics suffice to account for the opposing calcium signals observed in response to static receiver deflections.Footnote S4. Distribution of the flies in the counter-current apparatus. In the negative gravitaxis assay, flies were distributed into six tubes by being asked five times to climb up or to stay (Fig. 3a). If the population of the flies is genetically homogeneous and if each fly acts independently and has a constant probability of climbing up in all trials, the final distribution of the flies is expected to match a binomial distribution 6 . By comparing measured distributions to binomial distributions with the measured partition coefficient Cf (the probability of fly's climbing at each trial), we confirmed that the distribution of intact wild-type flies and flies with ablated where n is the number of tubes (6), and Nk is the number of the flies in the k th tube 6 . Footnote S5. Definition of aberrant gravitaxis. We used two criteria to define abnormal gravitaxis (Fig. 3b, c and Supplementary Fig. S4b). First, statistically significant changes in negative gravitaxis were determined from the differences in the partition coefficient Cf between the four data sets (negative gravitaxis and phototaxis of the flies with and without neuronal silencing, judged by RM-ANOVA and Student's t-test). If alterations in negative gravitaxis in flies with selectively silenced JO neurons were due to the general locomotion defects, similar alterations would be observed also in phototaxis behaviour, i.e.,

TRPA channels distinguish gravity sensing from hearing in Johnston's organ

“…Drosophila appears to be Johnston's organ (1). This organ is located in the second antennal segment.…”

“…Of note, the TRPN gene no mechanoreceptor potential C (nompC) (19,20) and the TRPV genes nanchung (nan) and inactive (iav) (21,22) are expressed in Johnston's organ chordotonal neurons and are required for normal hearing. Moreover, a nan mutant reduced the Ca 2ϩ elevations in Johnston's organ neurons that occur with antennal movement (1). The TRPA genes painless (pain) (23) and pyrexia (pyx) (24) are also expressed in Johnston's organ, although their function there is unknown.…”

“…It was proposed that the third segment may also be deflected by gravity (7), and the geometry of Johnston's organ suggests it could respond to gravity irrespective of head orientation (2). Indeed, recent work indicates that Johnston's organ can also respond to gravity, as well as to wind (1,8). Thus, Johnston's organ may detect multiple different mechanosensory stimuli, and investigations of specific molecular mechanisms underlying these sensory functions may benefit our understanding of other polymodal sensory structures such as the inner ear and dorsal root ganglion in mammals.…”

Separate TRP channels mediate amplification and transduction in drosophila

“…Therefore, we extended our observations by measuring generator currents while using a rigid, piezoelectrically-actuated probe to rotate the distal antennal segment. In this recording configuration, step rotations produce short-latency currents which decay over tens of milliseconds; the rapid adaptation to the static step is further evidence that the GFN is postsynaptic to the fast-adapting AB JONs and not the slow-adapting CE JONs [8].…”

“…NompC or TRPN1 was proposed as a candidate member of the transduction complex that converts mechanical force into an electrical signal in Drosophila auditory receptor neurons, in part due to its requirement for active amplification of sound-induced antennal motion [2,3,8,11,13]. NompC is present in arthropod, fish, and amphibian genomes but absent from those of birds and mammals.…”