Sensory structures are often composed of neurons extending their dendrites through a lumen formed by ensheathing epithelia or glia. We have been studying the development of the C. elegans amphid as a model system for sensory organ formation. Previously, we showed that
daf-6 is required for lumen formation by glial cells of the amphid. In
daf-6 mutants, a lumen is not generated, and the ciliated sensory dendrites of the amphid remain trapped within the sheath glia, surrounded by matrix, the material which normally fills the amphid lumen.
daf-6 encodes a Patched-related protein that localizes to the luminal surfaces of the amphid channel, as well as to other tubes, including the excretory cell, vulva, and intestine. Whereas
daf-6 animals are defective only in amphid lumen morphogenesis, animals defective for both
daf-6 and the Dispatched gene
che-14, exhibit defects in all tubular structures that express
daf-6. Furthermore, in mutants with defective sensory endings, DAF-6 localization in the amphid is disrupted, and the amphid channel is malformed. Thus, lumen formation in the amphid may be orchestrated by neuronal cues that regulate the localization of DAF-6 and CHE-14, and their function in controlling vesicle dynamics during tubulogenesis [1]. To further elucidate the role of
daf-6 in amphid lumen morphogenesis, we performed a genetic screen for suppressors of the dye-filling defect of
daf-6 animals. The mutations derived from the screen suppress the morphological defects of
daf-6, as shown by transgenic animals bearing fluorescent markers for amphid neurons and glia, and by EM reconstruction of the suppressed strains. We are currently mapping and cloning the suppressors. In a parallel approach, to explore the link between vesicle dynamics and lumen morphogenesis, we are examining potential genetic interactions between
daf-6 and known components of the endocytosis/exocytosis machinery of C. elegans. Finally, to expand our understanding of amphid morphogenesis, we are assembling a comparative time series of EM reconstructions for wild-type and
daf-6 embryos using high-pressure freezing for sample preparation. [1] Perens, E.A., and Shaham, S. (2005) Dev. Cell 8 893-906.