Uncoordinated is a specific marker for ciliogenic centrioles and is required for normal axoneme assembly in cilia and flagella. J.D. Baker , M. Kernan. Dept Neurobiology & Behavior, SUNY at Stony Brook, Stony Brook, NY.

   Despite recent progress in identifying the proteins required for centrosome organization and replication, the mechanisms that convert some mitotic centrioles to ciliogenic basal bodies remain obscure. Mutations in uncoordinated (unc) were identified by defects in mechanosensory-dependent behavior - principally, severe uncoordination due to a loss of proprioception. We now find that mutant males do not produce mature sperm. Ultrastructural analysis shows that the flagella in unc testes are often disrupted with split or missing axonemes. Similar defects are seen in ciliated sensory cells. The inner segments of the sensory process of femoral and antennal chordotonal organs of unc flies are normal, but they typically fail to connect to the dendritic cap. At the light microscope level it appears that the ciliated outer segments are missing in these cells. We find that the axonemes of these cilia are either truncated, split, or missing.
    The unc gene encodes a 1386 AA coiled-coil protein expressed only in ciliated sensory neurons and in male germline cells. A functional GFP-tagged Unc protein is localized to the centrioles of primary spermatocytes and at the junction between the nucleus and the flagellum in differentiating spermatids, but disappears from mature sperm. The centrosomal proteins Centrosomin (Cnn) and Gamma-tubulin partially colocalize with Unc-GFP during meiosis and fully overlap in early post-meiotic spermatids. All three of these proteins are undetectable in mature spermatids. In unc mutants Cnn and Gamma-tubulin are properly localized in spermatocytes and in spermatids prior to nuclear reshaping/condensation but are mislocalized thereafter. Hence, both axoneme ultrastructure and the localization of basal body associated proteins are disrupted in unc flies. Current studies aim at the functional dissection of the Unc protein, and the identification of interacting proteins.