Localization of a Guanylyl Cyclase to Chemosensory Cilia Requires the Novel Ciliary MYND Domain Protein DAF-25 Victor L. Jensen1, Nathan J. Bialas2, Sharon L. Bishop-Hurley3,4, Laurie L. Molday5, Katarzyna Kida6, Phuong Anh T. Nguyen2, Oliver E. Blacque6, Robert S. Molday5, Michel R. Leroux2, Donald L. Riddle1,7* 1 Medical Genetics, University of British Columbia, Vancouver, Canada, 2 Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, Canada, 3 Division of Biological Sciences, University of Missouri, Columbia, Missouri, United States of America, 4 CSIRO-Livestock Industries, Queensland Biosciences Precinct, Brisbane, Australia, 5 Centre for Macular Research, University of British Columbia, Vancouver, Canada, 6 School of Biomolecular and Biomedical Science, UCD Conway Institute, University College Dublin, Belfield, Dublin, Ireland, 7 Michael Smith Laboratories, University of British Columbia, Vancouver, Canada Abstract In harsh conditions, Caenorhabditis elegans arrests development to enter a non-aging, resistant diapause state called the dauer larva. Olfactory sensation modulates the TGF-b and insulin signaling pathways to control this developmental decision. Four mutant alleles of daf-25 (abnormal DAuer Formation) were isolated from screens for mutants exhibiting constitutive dauer formation and found to be defective in olfaction. The daf-25 dauer phenotype is suppressed by daf-10/IFT122 mutations (which disrupt ciliogenesis), but not by daf-6/PTCHD3 mutations (which prevent environmental exposure of sensory cilia), implying that DAF-25 functions in the cilia themselves. daf-25 encodes the C. elegans ortholog of mammalian Ankmy2, a MYND domain protein of unknown function. Disruption of DAF-25, which localizes to sensory cilia, produces no apparent cilia structure anomalies, as determined by light and electron microscopy. Hinting at its potential function, the dauer phenotype, epistatic order, and expression profile of daf-25 are similar to daf-11, which encodes a cilium-localized guanylyl cyclase. Indeed, we demonstrate that DAF-25 is required for proper DAF-11 ciliary localization. Furthermore, the functional interaction is evolutionarily conserved, as mouse Ankmy2 interacts with guanylyl cyclase GC1 from ciliary photoreceptors. The interaction may be specific because daf-25 mutants have normally-localized OSM-9/TRPV4, TAX-4/ CNGA1, CHE-2/IFT80, CHE-11/IFT140, CHE-13/IFT57, BBS-8, OSM-5/IFT88, and XBX-1/D2LIC in the cilia. Intraflagellar transport (IFT) (required to build cilia) is not defective in daf-25 mutants, although the ciliary localization of DAF-25 itself is influenced in che-11 mutants, which are defective in retrograde IFT. In summary, we have discovered a novel ciliary protein that plays an important role in cGMP signaling by localizing a guanylyl cyclase to the sensory organelle. Citation: Jensen VL, Bialas NJ, Bishop-Hurley SL, Molday LL, Kida K, et al. (2010) Localization of a Guanylyl Cyclase to Chemosensory Cilia Requires the Novel Ciliary MYND Domain Protein DAF-25. PLoS Genet 6(11): e1001199. doi:10.1371/journal.pgen.1001199 Editor: Kaveh Ashrafi, University of California San Francisco, United States of America Received March 9, 2010; Accepted October 7, 2010; Published November 24, 2010 Copyright: 2010 Jensen et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: VLJ was funded by MSFHR (www.msfhr.org) and NSERC (www.nserc-crsng.gc.ca). PATN was funded by CIHR (www.cihr-irsc.gc.ca). DLR was funded by CIHR #MOP-79458. RSM was funded by NIH (www.nih.gov) #EY 02422 and CIHR #RMF-92101. OEB was funded by SFI (www.sfi.ie) #06/Y13/B928. MRL was funded by CIHR #MOP-97956 and the March of Dimes, and is the recipient of a MSFHR senior scholar award. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: driddle@msl.ubc.ca Introduction The dauer larva of Caenorhabditis elegans is an alternate third larval stage where a stress resistant, non-aging life plan is adopted in harsh environmental conditions [1]. Dauer larvae disperse and will resume development when conditions improve. The study of dauer formation has elucidated a complex gene network used to control the decision to go into diapause [2]. The dauer pathway includes well-recognized members in the canonical TGF-b (Transforming Growth Factor-Beta) and Insulin/Insulin-like signaling (IIS) path- ways, as well as proteins affecting olfactory reception, neuron depolarization and peptide hormone secretion. Many mutants isolated as dauer formation defective (Daf-d) or constitutive (Daf-c) have revealed the key signaling components [2]. Here we identify DAF-25, a novel member of the olfactory signaling pathway that is associated with cGMP signaling—a signal transduction pathway with established links to cilia [3]. We show that the mammalian ortholog, Ankmy2, is expressed in ciliary photoreceptors and interacts with a guanylate cyclase (GC1), as predicted from the C. elegans results. The olfactory signaling cascade has been well characterized in the two C. elegans amphids, organs consisting of a set of twelve bilaterally symmetric pairs of ciliated sensory neurons [4,5]. While similar to mammalian olfactory signaling, at least some proteins involved are also homologous to those implicated in mammalian phototransduction [6]. Chemicals are sensed at the afferent, ciliated ends of sensory neurons where they contact the environment through pores in the cuticle. The cilia are required for chemosensation of chemical attractants and repellants, as well as for dauer entry and exit [7]. For many odorants the specific neurons that detect the odor are known [4]. For example, the AWA, AWB and AWC neuron pairs sense volatile odorants such as pyrazine, benzaldehyde, trimethyl thiazole and isoamyl alcohol. The ASH pair of ciliated olfactory neurons can detect changes in osmotic pressure. The connection between dauer formation, chemosensory behavior and cilia is well known [2,8]. C. elegans hermaphrodites only possess non-motile (primary) cilia which are found at the dendritic ends of 60 sensory neurons in the head and tail [5,8]. PLoS Genetics | www.plosgenetics.org 1 November 2010 | Volume 6 | Issue 11 | e1001199