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Identifying the Neuronal Basis of Graviperception in Drosophila melanogaster.  C.J. Johnson¹ , M.T. Texada¹, R. Simonette¹, K.M. Beckingham^{1 1}Dept. of Biochem. And Cell Biol., Rice Univ., Houston, T.X.

   The antenna of Drosophila is used to detect smell and sound.  A mechanosensory organ in the second antennal segment called Johnston's Organ (JO) is responsible for audition.  The array of 200 chordotonal organs (CHO's) in this structure contains stretch responsive neurons.  However, in addition to sound perception, data from our laboratory suggest that the JO also plays a role in graviperception.

   A genetic screen in the Beckingham lab using a gravitaxic maze, has identified mutant flies with altered gravitaxic behavior.   A mutant of the novel gene yuri gargarin  (yuri) identified in this screen indicates that effects on the JO are responsible for its aberrant gravitaxis.  Thus, the mutation appears to alter gravitaxic behavior through effects  in a minor subset of the JO CHO's.  We are testing the hypothesis that there are two functionally distinct classes of CHO's in the JO specialized for either sound or graviperception.  There are two anatomical classes of CHO's in the JO that could serve these two different functions.  We are beginning with studies of the yuri gravitaxic mutant.  If the CHO's affected in this mutant are specialized for graviperception, we hypothesize  i) that these CHO's will correspond to only one of the two anatomical classes previously identified in the JO and ii) the mutant will suffer no hearing loss.  Audition will be studied in collaboration with Dr. M Gopfert, Univ. Koeln Germany.  Detailed studies of the CHO's affected by the yuri mutation are in progress.   Several further mutants isolated from our screen also affect the JO.  Studies are in progress to identify those mutants that affect subsets of CHO's in the JO so that these can also be used to test the hypothesis that the JO serves as a graviperceptor.