Barr, MM, Silva M, Haas LA, Morsci NS, Nguyen KCQ, Hall DH, Barr MM.  2014.  C. elegans ciliated sensory neurons release extracellular vesicles that function in animal communication.. Current biology : CB. 24(5):519-25. Abstract
Cells release extracellular vesicles (ECVs) that play important roles in intercellular communication and may mediate a broad range of physiological and pathological processes. Many fundamental aspects of ECV biogenesis and signaling have yet to be determined, with ECV detection being a challenge and obstacle due to the small size (100 nm) of the ECVs. We developed an in vivo system to visualize the dynamic release of GFP-labeled ECVs. We show here that specific Caenorhabdidits elegans ciliated sensory neurons shed and release ECVs containing GFP-tagged polycystins LOV-1 and PKD-2. These ECVs are also abundant in the lumen surrounding the cilium. Electron tomography and genetic analysis indicate that ECV biogenesis occurs via budding from the plasma membrane at the ciliary base and not via fusion of multivesicular bodies. Intraflagellar transport and kinesin-3 KLP-6 are required for environmental release of PKD-2::GFP-containing ECVs. ECVs isolated from wild-type animals induce male tail-chasing behavior, while ECVs isolated from klp-6 animals and lacking PKD-2::GFP do not. We conclude that environmentally released ECVs play a role in animal communication and mating-related behaviors.
Barr, MM, Androwski RJ, Rashid A, Lee H, Lee J, Barr MM.  2013.  Dauer-specific dendrite arborization in C. elegans is regulated by KPC-1/Furin.. Current biology : CB. 23(16):1527-35. Abstract
Dendrites often display remarkably complex and diverse morphologies that are influenced by developmental and environmental cues. Neuroplasticity in response to adverse environmental conditions entails both hypertrophy and resorption of dendrites. How dendrites rapidly alter morphology in response to unfavorable environmental conditions is unclear. The nematode Caenorhabditis elegans enters into a stress-resistant dauer larval stage in response to an adverse environment.
Morsci, NS, Barr MM.  2011.  Kinesin-3 KLP-6 Regulates Intraflagellar Transport in Male-Specific Cilia of Caenorhabditis Elegans. Curr Biol. 21:1239-1244. Abstract
Cilia are cellular sensory organelles whose integrity of structure and function are important to human health [1]. All cilia are assembled and maintained by kinesin-2 motors in a process termed intraflagellar transport (IFT), but they exhibit great variety of morphology and function. This diversity is proposed to be conferred by cell-specific modulation of the core IFT by additional factors, but examples of such IFT modulators are limited [2-4]. Here we demonstrate that the cell-specific kinesin-3 KLP-6 acts as a modulator of both IFT dynamics and length in the cephalic male (CEM) cilia of Caenorhabditis elegans. Live imaging of GFP-tagged kinesins in CEM cilia shows partial uncoupling of the IFT motors of the kinesin-2 family, kinesin-II and OSM-3/KIF17, with a portion of OSM-3 moving independently of the IFT complex. KLP-6 moves independently of the kinesin-2 motors and acts to reduce the velocity of OSM-3 and IFT. Additionally, kinesin-II mutants display a novel CEM cilia elongation phenotype that is partially dependent on OSM-3 and KLP-6. Our observations illustrate modulation of the general kinesin-2-driven IFT process by a cell-specific kinesin-3 in cilia of C. elegans male neurons.
Bae, Y-K, Kim E, L'hernault SW, Barr MM.  2009.  The CIL-1 PI 5-phosphatase Localizes TRP Polycystins to Cilia and Activates Sperm in C. Elegans. Curr Biol. 19:1599-1607. Abstract
C. elegans male sexual behaviors include chemotaxis and response to hermaphrodites, backing, turning, vulva location, spicule insertion, and sperm transfer, culminating in cross-fertilization of hermaphrodite oocytes with male sperm. The LOV-1 and PKD-2 transient receptor potential polycystin (TRPP) complex localizes to ciliated endings of C. elegans male-specific sensory neurons and mediates several aspects of male mating behavior. TRPP complex ciliary localization and sensory function are evolutionarily conserved. A genetic screen for C. elegans mutants with PKD-2 ciliary localization (Cil) defects led to the isolation of a mutation in the cil-1 gene.
Muley, PD, McNeill EM, Marzinke MA, Knobel KM, Barr MM, Clagett-Dame M.  2008.  The atRA-responsive gene Neuron Navigator 2 Functions in Neurite Outgrowth and Axonal Elongation. Dev Neurobiol. 68:1441-1453. Abstract
Neuron navigator 2 (Nav2) was first identified as an all-trans retinoic acid (atRA)-responsive gene in human neuroblastoma cells (retinoic acid-induced in neuroblastoma 1, RAINB1) that extend neurites after exposure to atRA. It is structurally related to the Caenorhabditis elegans unc-53 gene that is required for cell migration and axonal outgrowth. To gain insight into NAV2 function, the full-length human protein was expressed in C. elegans unc-53 mutants under the control of a mechanosensory neuron promoter. Transgene expression of NAV2 rescued the defects in unc-53 mutant mechanosensory neuron elongation, indicating that Nav2 is an ortholog of unc-53. Using a loss-of-function approach, we also show that Nav2 induction is essential for atRA to induce neurite outgrowth in SH-SY5Y cells. The NAV2 protein is located both in the cell body and along the length of the growing neurites of SH-SY5Y cells in a pattern that closely mimics that of neurofilament and microtubule proteins. Transfection of Nav2 deletion constructs in Cos-1 cells reveals a region of the protein (aa 837-1065) that directs localization with the microtubule cytoskeleton. Collectively, this work supports a role for NAV2 in neurite outgrowth and axonal elongation and suggests this protein may act by facilitating interactions between microtubules and other proteins such as neurofilaments that are key players in the formation and stability of growing neurites.
Jauregui, AR, Nguyen KCQ, Hall DH, Barr MM.  2008.  The Caenorhabditis Elegans Nephrocystins act as Global Modifiers of Cilium Structure. J Cell Biol. 180:973-988. Abstract
Nephronophthisis (NPHP) is the most common genetic cause of end-stage renal disease in children and young adults. In Chlamydomonas reinhardtii, Caenorhabditis elegans, and mammals, the NPHP1 and NPHP4 gene products nephrocystin-1 and nephrocystin-4 localize to basal bodies or ciliary transition zones (TZs), but their function in this location remains unknown. We show here that loss of C. elegans NPHP-1 and NPHP-4 from TZs is tolerated in developing cilia but causes changes in localization of specific ciliary components and a broad range of subtle axonemal ultrastructural defects. In amphid channel cilia, nphp-4 mutations cause B tubule defects that further disrupt intraflagellar transport (IFT). We propose that NPHP-1 and NPHP-4 act globally at the TZ to regulate ciliary access of the IFT machinery, axonemal structural components, and signaling molecules, and that perturbing this balance results in cell type-specific phenotypes.
Knobel, KM, Peden EM, Barr MM.  2008.  Distinct Protein Domains Regulate Ciliary Targeting and Function of C. Elegans PKD-2. Exp Cell Res. 314:825-833. Abstract
TRPP2 (transient receptor potential polycystin-2) channels function in a range of cells where they are localized to specific subcellular regions including the endoplasmic reticulum (ER) and primary cilium. In humans, TRPP2/PC-2 mutations severely compromise kidney function and cause autosomal dominant polycystic kidney disease (ADPKD). The Caenorhabditis elegans TRPP2 homolog, PKD-2, is restricted to the somatodendritic (cell body and dendrite) and ciliary compartments of male specific sensory neurons. Within these neurons PKD-2 function is required for sensation. To understand the mechanisms regulating TRPP2 subcellular distribution and activity, we performed in vivo structure-function-localization studies using C. elegans as a model system. Our data demonstrate that somatodendritic and ciliary targeting requires the transmembrane (TM) region of PKD-2 and that the PKD-2 cytosolic termini regulate subcellular distribution and function. Within neuronal cell bodies, PKD-2 colocalizes with the OSM-9 TRP vanilloid (TRPV) channel, suggesting that these TRPP and TRPV channels may function in a common process. When human TRPP2/PC-2 is heterologously expressed in transgenic C. elegans animals, PC-2 does not visibly localize to cilia but does partially rescue pkd-2 null mutant defects, suggesting that human PC-2 and PKD-2 are functional homologs.
Bae, Y-K, Lyman-Gingerich J, Barr MM, Knobel KM.  2008.  Identification of Genes Involved in the Ciliary Trafficking of C. Elegans PKD-2. Dev Dyn. 237:2021-2029. Abstract
Ciliary membrane proteins are important extracellular sensors, and defects in their localization may have profound developmental and physiological consequences. To determine how sensory receptors localize to cilia, we performed a forward genetic screen and identified 11 mutants with defects in the ciliary localization (cil) of C. elegans PKD-2, a transient receptor potential polycystin (TRPP) channel. Class A cil mutants exhibit defects in PKD-2::GFP somatodendritic localization while Class B cil mutants abnormally accumulate PKD-2::GFP in cilia. Further characterization reveals that some genes mutated in cil mutants act in a tissue-specific manner while others are likely to play more general roles in such processes as intraflagellar transport (IFT). To this end, we identified a Class B mutation that disrupts the function of the cytoplasmic dynein light intermediate chain gene xbx-1. Identification of the remaining mutations will reveal novel molecular pathways required for ciliary receptor localization and provide further insight into mechanisms of ciliary signaling.
Bae, Y-K, Barr MM.  2008.  Sensory Roles of Neuronal Cilia: Cilia Development, Morphogenesis, and Function in C. Elegans. Front Biosci. 13:5959-5974. Abstract
In the free-living nematode Caenorhabditis elegans, cilia are found on the dendritic endings of sensory neurons. C. elegans cilia are classified as 'primary' or 'sensory' according to the '9+0' axonemal ultrastructure (nine doublet outer microtubules with no central microtubule pair) and lack of motility, characteristics of '9+2' cilia. The C. elegans ciliated nervous system allows the animal to perceive environmental stimuli and make appropriate developmental, physiological, and behavioral decisions. In vertebrates, the biological significance of primary cilia had been largely neglected. Recent findings have placed primary/sensory cilia in the center of cellular signaling and developmental processes. Studies using genetic model organisms such as C. elegans identified the link between ciliary dysfunction and human ciliopathies. Future studies in the worm will address important basic questions regarding ciliary development, morphogenesis, specialization, and signaling functions.
Liu, T, Kim K, Li C, Barr MM.  2007.  FMRFamide-like Neuropeptides and Mechanosensory Touch Receptor Neurons Regulate male Sexual Turning Behavior in Caenorhabditis Elegans. J Neurosci. 27:7174-7182. Abstract
Caenorhabditis elegans male mating provides a powerful model to study the relationship between the nervous system, genes, and innate sexual behaviors. Male mating is the most complex behavior exhibited by the nematode C. elegans and involves the steps of response, backing, turning, vulva location, spicule insertion, and sperm transfer. Because neuropeptides are important neural regulators of many complex animal behaviors, we explored the function of the FMRFamide-like neuropeptide (flp) gene family in regulating male copulation. We found that peptidergic signaling mediated by FMRF-amide like neuropeptides (FLPs) FLP-8, FLP-10, FLP-12, and FLP-20 is required for the sensory transduction involved in male turning behavior. flp-8, flp-10, flp-12, and flp-20 mutant males significantly increase repetition of substep(s) of turning behavior compared with wild-type males. Genes controlling neuropeptide processing and secretion in general, including egl-3, egl-21, ida-1, and unc-31, are also required for inhibiting repetitive turning behavior. Neuropeptidergic signaling adjusts the repetitiveness of turning independently of serotonergic modulation of the timing of turning. Surprisingly, the mechanosensitive touch receptor neurons are found to be part of the neural circuitry regulating male turning behavior, indicating the existence of functional dimorphisms in the nervous system with regard to sex-specific behaviors.
Hu, J, Wittekind SG, Barr MM.  2007.  STAM and Hrs Down-regulate Ciliary TRP Receptors. Mol Biol Cell. 18:3277-3289. Abstract
Cilia are endowed with membrane receptors, channels, and signaling components whose localization and function must be tightly controlled. In primary cilia of mammalian kidney epithelia and sensory cilia of Caenorhabditis elegans neurons, polycystin-1 (PC1) and transient receptor polycystin-2 channel (TRPP2 or PC2), function together as a mechanosensory receptor-channel complex. Despite the importance of the polycystins in sensory transduction, the mechanisms that regulate polycystin activity and localization, or ciliary membrane receptors in general, remain poorly understood. We demonstrate that signal transduction adaptor molecule STAM-1A interacts with C. elegans LOV-1 (PC1), and that STAM functions with hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs) on early endosomes to direct the LOV-1-PKD-2 complex for lysosomal degradation. In a stam-1 mutant, both LOV-1 and PKD-2 improperly accumulate at the ciliary base. Conversely, overexpression of STAM or Hrs promotes the removal of PKD-2 from cilia, culminating in sensory behavioral defects. These data reveal that the STAM-Hrs complex, which down-regulates ligand-activated growth factor receptors from the cell surface of yeast and mammalian cells, also regulates the localization and signaling of a ciliary PC1 receptor-TRPP2 complex.
Hu, J, Bae Y-K, Knobel KM, Barr MM.  2006.  Casein Kinase II and Calcineurin Modulate TRPP Function and Ciliary Localization. Mol Biol Cell. 17:2200-2211. Abstract
Cilia serve as sensory devices in a diversity of organisms and their defects contribute to many human diseases. In primary cilia of kidney cells, the transient receptor potential polycystin (TRPP) channels polycystin-1 (PC-1) and polycystin-2 (PC-2) act as a mechanosensitive channel, with defects resulting in autosomal dominant polycystic kidney disease. In sensory cilia of Caenorhabditis elegans male-specific neurons, the TRPPs LOV-1 and PKD-2 are required for mating behavior. The mechanisms regulating TRPP ciliary localization and function are largely unknown. We identified the regulatory subunit of the serine-threonine casein kinase II (CK2) as a binding partner of LOV-1 and human PC-1. CK2 and the calcineurin phosphatase TAX-6 modulate male mating behavior and PKD-2 ciliary localization. The phospho-defective mutant PKD-2(S534A) localizes to cilia, whereas a phospho-mimetic PKD-2(S534D) mutant is largely absent from cilia. Calcineurin is required for PKD-2 ciliary localization, but is not essential for ciliary gene expression, ciliogenesis, or localization of cilium structural components. This unanticipated function of calcineurin may be important for regulating ciliary protein localization. A dynamic phosphorylation-dephosphorylation cycle may represent a mechanism for modulating TRPP activity, cellular sensation, and ciliary protein localization.
Bae, Y-K, Qin H, Knobel KM, Hu J, Rosenbaum JL, Barr MM.  2006.  General and Cell-type Specific Mechanisms Target TRPP2/PKD-2 to Cilia. Development. 133:3859-3870. Abstract
Ciliary localization of the transient receptor potential polycystin 2 channel (TRPP2/PKD-2) is evolutionarily conserved, but how TRPP2 is targeted to cilia is not known. In this study, we characterize the motility and localization of PKD-2, a TRPP2 homolog, in C. elegans sensory neurons. We demonstrate that GFP-tagged PKD-2 moves bidirectionally in the dendritic compartment. Furthermore, we show a requirement for different molecules in regulating the ciliary localization of PKD-2. PKD-2 is directed to moving dendritic particles by the UNC-101/adaptor protein 1 (AP-1) complex. When expressed in non-native neurons, PKD-2 remains in cell bodies and is not observed in dendrites or cilia, indicating that cell-type specific factors are required for directing PKD-2 to the dendrite. PKD-2 stabilization in cilia and cell bodies requires LOV-1, a functional partner and a TRPP1 homolog. In lov-1 mutants, PKD-2 is greatly reduced in cilia and forms abnormal aggregates in neuronal cell bodies. Intraflagellar transport (IFT) is not essential for PKD-2 dendritic motility or access to the cilium, but may regulate PKD-2 ciliary abundance. We propose that both general and cell-type-specific factors govern TRPP2/PKD-2 subcellular distribution by forming at least two steps involving somatodendritic and ciliary sorting decisions.
Barr, MM, Garcia RL.  2006.  Male Mating Behavior. WormBook. :1-11. Abstract
Caenorhabditis elegans male mating provides an excellent opportunity to determine how sensory perception regulates behavior and motor programs. The male-specific nervous system and muscles are superimposed over the general nervous system and musculature. Genetic screens and genomic approaches have identified male-specific and male-enriched genes as well as non-sex specific molecules specialized for mating sub-behaviors. In this chapter, we discuss the cellular, genetic, and molecular basis for male mating behavior.
Hu, J, Barr MM.  2005.  ATP-2 Interacts with the PLAT Domain of LOV-1 and is Involved in Caenorhabditis Elegans Polycystin Signaling. Mol Biol Cell. 16:458-469. Abstract
Caenorhabditis elegans is a powerful model to study the molecular basis of autosomal dominant polycystic kidney disease (ADPKD). ADPKD is caused by mutations in the polycystic kidney disease (PKD)1 or PKD2 gene, encoding polycystin (PC)-1 or PC-2, respectively. The C. elegans polycystins LOV-1 and PKD-2 are required for male mating behaviors and are localized to sensory cilia. The function of the evolutionarily conserved polycystin/lipoxygenase/alpha-toxin (PLAT) domain found in all PC-1 family members remains an enigma. Here, we report that ATP-2, the beta subunit of the ATP synthase, physically associates with the LOV-1 PLAT domain and that this interaction is evolutionarily conserved. In addition to the expected mitochondria localization, ATP-2 and other ATP synthase components colocalize with LOV-1 and PKD-2 in cilia. Disrupting the function of the ATP synthase or overexpression of atp-2 results in a male mating behavior defect. We further show that atp-2, lov-1, and pkd-2 act in the same molecular pathway. We propose that the ciliary localized ATP synthase may play a previously unsuspected role in polycystin signaling.
Barr, MM.  2005.  Caenorhabditis Elegans as a Model to Study Renal Development and Disease: sexy Cilia. J Am Soc Nephrol. 16:305-312. Abstract
The nematode Caenorhabditis elegans has no kidney per se, yet ``the worm'' has proved to be an excellent model to study renal-related issues, including tubulogenesis of the excretory canal, membrane transport and ion channel function, and human genetic diseases including autosomal dominant polycystic kidney disease (ADPKD). The goal of this review is to explain how C. elegans has provided insight into cilia development, cilia function, and human cystic kidney diseases.
Jauregui, AR, Barr MM.  2005.  Functional Characterization of the C. Elegans Nephrocystins NPHP-1 and NPHP-4 and Their role in Cilia and male Sensory Behaviors. Exp Cell Res. 305:333-342. Abstract
Autosomal dominant polycystic kidney disease (ADPKD) and nephronophthisis (NPH) share two common features: cystic kidneys and ciliary localized gene products. Mutation in either the PKD1 or PKD2 gene accounts for 95% of all ADPKD cases. Mutation in one of four genes (NPHP1-4) results in nephronophthisis. The NPHP1, NPHP2, PKD1, and PKD2 protein products (nephrocystin-1, nephrocystin-2 or inversin, polycystin-1, and polycystin-2, respectively) localize to primary cilia of renal epithelia. However, the relationship between the nephrocystins and polycystins, if any, is unknown. In the nematode Caenorhabditis elegans, the LOV-1 and PKD-2 polycystins localize to male-specific sensory cilia and are required for male mating behaviors. To test the hypothesis that ADPKD and NPH cysts arise from a common defect in cilia, we characterized the C. elegans homologs of NPHP1 and NPHP4. C. elegans nphp-1 and nphp-4 are expressed in a subset of sensory neurons. GFP-tagged NPHP-1 and NPHP-4 proteins localize to ciliated sensory endings of dendrites and colocalize with PKD-2 in male-specific sensory cilia. The cilia of nphp-1(ok500) and nphp-4(tm925) mutants are intact. nphp-1; nphp-4 double, but not single, mutant males are response defective. We propose that NPHP-1 and NPHP-4 proteins play important and redundant roles in facilitating ciliary sensory signal transduction.
Qin, H, Burnette DT, Bae Y-K, Forscher P, Barr MM, Rosenbaum JL.  2005.  Intraflagellar Transport is Required for the Vectorial Movement of TRPV Channels in the Ciliary Membrane. Curr Biol. 15:1695-1699. Abstract
The membranes of all eukaryotic motile (9 + 2) and immotile primary (9 + 0) cilia harbor channels and receptors involved in sensory transduction (reviewed by). These membrane proteins are transported from the cytoplasm onto the ciliary membrane by vesicles targeted for exocytosis at a point adjacent to the ciliary basal body. Here, we use time-lapse fluorescence microscopy to demonstrate that select GFP-tagged sensory receptors undergo rapid vectorial transport along the entire length of the cilia of Caenorhabditis elegans sensory neurons. Transient receptor potential vanilloid (TRPV) channels OSM-9 and OCR-2 move in ciliary membranes at rates comparable to the intraflagellar transport (IFT) machinery located between the membrane and the underlying axonemal microtubules. OSM-9 motility is disrupted in certain IFT mutant backgrounds. Surprisingly, motility of transient receptor potential polycystin (TRPP) channel PKD-2 (polycystic kidney disease-2), a mechano-receptor, was not detected. Our study demonstrates that IFT, previously shown to be necessary for transport of axonemal components, is also involved in the motility of TRPV membrane protein movement along cilia of C. elegans sensory cells.
Peden, EM, Barr MM.  2005.  The KLP-6 Kinesin is Required for male Mating Behaviors and Polycystin Localization in Caenorhabditis Elegans. Curr Biol. 15:394-404. Abstract
Male mating behavior of the nematode Caenorhabditis elegans offers an intriguing model to study the genetics of sensory behavior, cilia function, and autosomal dominant polycystic kidney disease (ADPKD). The C. elegans polycystins LOV-1 and PKD-2 act in male-specific sensory cilia required for response and vulva-location mating behaviors.
Wang, J, Barr MM.  2005.  RNA Interference in Caenorhabditis Elegans. Methods Enzymol. 392:36-55. Abstract
RNA interference (RNAi) was first discovered in the nematode Caenorhabditis elegans (Fire et al., 1998; Guo and Kemphues, 1995). The completion of the C. elegans genome in 1998 coupled with the advent of RNAi techniques to knock down gene function ushered in a new age in the field of functional genomics. There are four methods for double-stranded RNA (dsRNA) delivery in C. elegans: (1) injection of dsRNA into any region of the animal (Fire et al., 1998), (2) feeding with bacteria producing dsRNA (Timmons et al., 2001), (3) soaking in dsRNA (Tabara et al., 1998), and (4) in vivo production of dsRNA from transgenic promoters (Tavernarakis et al., 2000). In this chapter, we discuss the molecular genetic mechanisms, techniques, and applications of RNAi in C. elegans.
Barr, MM.  2003.  Super Models. Physiol Genomics. 13:15-24. Abstract
Model organisms have been used over a century to understand basic, conserved biological processes. The study of these experimental systems began with genetics and development, moved into molecular and cellular biology, and most recently propelled into functional genomics and proteomics. The goal of this review is simple: to discuss the place of model organisms in ``The Age of the Ome'': the genome, the transcriptome, and the proteome. This review will address the following questions. What exactly is a model organism? What characteristics make an excellent model system? Using the yeast Saccharomyces cerevisiae and the nematode Caenorhabditis elegans as examples, this review will discuss these issues with the aim of demonstrating how model organisms remain indispensable scientific tools for understanding complex biological pathways and human disease.