The uncoordinated gene encodes a novel coiled-coil protein required for mechanoreceptor function and spermatogenesis. J.D. Baker , S. Adhikarakunnathu , M. Kernan. Dept Neurobiology & Behavior, SUNY at Stony Brook, Stony Brook, NY.

   Flies sense mechanical stimuli such as touch and sound with external bristles, campaniform sensilla and chordotonal organs, collectively known as type I mechanoreceptors. In each type, mechanical signals are transduced by a bipolar sensory neuron with a ciliated sensory ending that contacts the specialized extracellular structures. Genetic screens for mutations causing severe uncoordination and touch insensitivity identified many mutations affecting mechanotransduction (Kernan et al., 1994), including several new alleles of uncoordinated (unc). Electrophysiological recordings from unc mutants show that, as in other mechanosensory mutants, both touch-evoked bristle mechanoreceptor potentials and sound-evoked antennal chordotonal potentials are absent. In addition, unc mutants have a late defect in spermatogenesis: sperm elongate but never become motile. Because type I sensory endings and the sperm flagella are both ciliary structures, we suspect that Unc is involved in the construction or operation of sensory and other cilia.
    We have used positional cloning to identify a 4.5kb unc cDNA, predicted to encode a novel 1386 amino-acid protein with two coiled-coil regions and a nucleotide-binding p-loop. A construct including 3.9kb of the predicted promoter and gene fused in the third exon to the unc cDNA, rescues the behavioral, electrophysiological and sperm immotility phenotypes in germline transformants. To establish and understand the role of Unc in ciliary differentiation or transduction we are now determining its cellular and subcellular location, and are using site directed mutagenesis to test the functional requirement for nucleotide binding.