DEVKOTA, RANJAN et al. (2015) International Worm Meeting "Novel regulators of the C. elegans UNC-6/Netrin pathway."

DEVKOTA, RANJAN, Garriga, Gian, Morck, Catarina, CHIEN, JASON

[International Worm Meeting, 2015]

Precise targeting of axons is essential for the proper functioning of the nervous system. Axonal growth cones respond to various guidance cues and navigate through a complex environment to reach their synaptic targets1. Even though many guidance cues and receptors have been identified, there is less knowledge of how axons respond to different cues in different phases of their growth. The aim of this project is to enhance the understanding of axon guidance by focusing on the development of the bilaterally symmetric Hermaphrodite Specific Neurons (HSNs). Each HSN extends a single axon to the ventral nerve cord, which then turns anteriorly and extends to the nerve ring2. The HSNs innervate vulval muscles and the AVF neurons to stimulate hermaphrodite egg laying and locomotion, respectively3,4. We have isolated three mutants whose HSN axons fail to extend ventrally. Our preliminary mapping, complementation and genetic interaction data suggest that these mutations define three genes that function together to antagonize the conserved UNC-6/Netrin signaling pathway. Our initial goal is to identify the underlying mutations with whole genome sequencing and rescue experiments. The identification of these genes will shed light on how the UNC-6/Netrin pathway is modulated for proper axon guidance along the dorsal-ventral axis.References:1. Dickson, B. J. Molecular mechanisms of axon guidance. Science 298, 1959-1964(2002).2. Garriga, G., Desai, C. & Horvitz, H. R. Cell interactions control the direction of outgrowth, branching and fasciculation of the HSN axons of Caenorhabditis elegans. Development 117, 1071-1087(1993).3. Desai, C., Garriga, G., McIntire, S. L. & Horvitz, H. R. A genetic pathway for the development of the Caenorhabditis elegans HSN motor neurons. Nature 336, 638-646(1988).4. Hardaker, L. A., Singer, E., Kerr, R., Zhou, G. & Schafer, W. R. Serotonin modulates locomotory behavior and coordinates egg-laying and movement in Caenorhabditis elegans. J. Neurobiol. 49, 303-313(2001). .

Devkota, Ranjan et al. (2021) International Worm Meeting "A Genetic Titration of Membrane Composition Reveals its Importance for Multiple Cellular and Physiological Traits"

Pilon, Marc, Henricsson, Marcus, DEVKOTA, RANJAN, Kaper, Delaney, Boren, Jan, Bodhicharla, Rakesh

[International Worm Meeting, 2021]

The composition and biophysical properties of cellular membranes must be tightly regulated to maintain the proper functions of myriad processes within cells. To better understand the importance of membrane homeostasis, we assembled a panel of five C. elegans strains that show a wide span of membrane composition and properties, ranging from excessively rich in saturated fatty acids (SFAs) and rigid to excessively rich in polyunsaturated fatty acids (PUFAs) and fluid. The genotypes of the five strain are, from most rigid to most fluid: paqr-1(tm3262) paqr-2(tm3410), paqr-2, N2 (wild-type), mdt-15(et14) nhr-49(et8), and mdt-15(et14) nhr-49(et8) acs-13(et54). We confirmed the excess SFA/rigidity-to-excess PUFA/fluid gradient using the methods of fluorescence recovery after photobleaching (FRAP) and lipidomics analysis. The five strains were then studied for a variety of cellular and physiological traits and found to exhibit defects in: permeability, lipid peroxidation, growth at different temperatures, tolerance to SFA-rich diets, lifespan, brood size, vitellogenin trafficking, oogenesis and autophagy during starvation. The excessively rigid strains often exhibited defects in opposite directions compared to the excessively fluid strains. We conclude that deviation from wild-type membrane homeostasis is pleiotropically deleterious for numerous cellular/physiological traits. The strains introduced here should prove useful to further study the cellular and physiological consequences of impaired membrane homeostasis.

Chien, Jason et al. (2015) International Worm Meeting "Wnt signaling regulates midline guidance in C. elegans."

Morck, Catarina, DEVKOTA, RANJAN, CHIEN, JASON

[International Worm Meeting, 2015]

During the development of the nervous system, axons need to grow in a stereotypical manner in order to form specific connections with their targets. All neurons do not extend axons at the same time; a distinct set of neurons, called the 'pioneers', send out their axons first and serve as scaffolds for other late-outgrowing 'follower' axons. Previous laser ablation studies in C. elegans suggest that the bilaterally symmetric PVP and PVQ axons serve as substrates for the HSN axons in the ventral nerve cord and prevent the HSN axons from crossing over to the opposite sides1,2. However, the molecular mechanisms underlying the midline guidance of these three neurons are not well understood. Through a candidate gene approach we found that 70% of the HSN axons cross over to the other side of the ventral nerve cord in cam-1 mutants. The majority of HSN guidance defects are likely to depend on earlier guidance errors of PVPs and PVQs. CAM-1 is a receptor tyrosine kinase of the Ror family and is implicated in Wnt signaling due to its extracellular Wnt-binding cysteine-rich domain. Wnts belong to a conserved family of secreted glycoproteins that are important for a wide range of developmental processes, but their roles in midline guidance are unclear. Interestingly, combined removal of three of the five Wnts (CWN-1, CWN-2 and EGL-20) results in a crossover phenotype that is indistinguishable from the loss of CAM-1, suggesting that these Wnts signal through the CAM-1 receptor for proper midline guidance. Our preliminary genetic data also indicate that cam-1 interacts with components of other known midline guidance pathways such as Netrin and Slit. We are currently investigating where the Wnts are expressed when the PVPs and PVQs extend and whether CAM-1 acts in these neurons.1Durbin, R. M. (1987). PhD Thesis, University of Cambridge. 2Garriga, G., Desai, C. and Horvitz, H. R. (1993). Development 117, 1071-1087.