• Research Summary

    Survival requires strategies to identify and attract mates. How sensory neurons receive sex- specific signals and how multiple sensory stimuli are integrated to produce innate, stereotyped behaviors is poorly understood. To attack this problem,  the Barr Laboratory studies the molecular basis of sex-specific and sensory behaviors in the nematode Caenorhabditis elegans, which is tractable to molecular genetic, cell biological, and physiological approaches.

  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.

Recent Publications

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.