title: Identification of candidate infection genes from the model entomopathogenic nematode Heterorhabditis bacteriophora.
abstract: Despite important progress in the field of innate immunity, our understanding of host immune responses to parasitic nematode infections lags behind that of responses to microbes. A limiting factor has been the obligate requirement for a vertebrate host which has hindered investigation of the parasitic nematode infective process. The nematode parasite Heterorhabditis bacteriophora offers great potential as a model to genetically dissect the process of infection. With its mutualistic Photorhabdus luminescens bacteria, H. bacteriophora invades multiple species of insects, which it kills and exploits as a food source for the development of several nematode generations. The ability to culture the life cycle of H. bacteriophora on plates growing the bacterial symbiont makes it a very exciting model of parasitic infection that can be used to unlock the molecular events occurring during infection of a host that are inaccessible using vertebrate hosts.
  
  
  
  To profile the transcriptional response of an infective nematode during the early stage of infection, we performed next generation RNA sequencing on H. bacteriophora IJs incubated in Manduca sexta hemolymph plasma for 9 h. A subset of up-regulated and down-regulated genes were validated using qRT-PCR. Comparative analysis of the transcriptome with untreated controls found a number of differentially expressed genes (DEGs) which cover a number of different functional categories. A subset of DEGs is conserved across Clade V parasitic nematodes revealing an array of candidate parasitic genes.
  
  
  
  Our analysis reveals transcriptional changes in the regulation of a large number of genes, most of which have not been shown previously to play a role in the process of infection. A significant proportion of these genes are unique to parasitic nematodes, suggesting the identification of a group of parasitism factors within nematodes. Future studies using these candidates may provide functional insight into the process of nematode parasitism and also the molecular evolution of parasitism within nematodes.
authors.affiliation: Department of Biological Sciences, George Washington University, Science and Engineering Hall, suite 6000, 800 22nd Street NW, Washington DC, 20052, USA.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Vadnal
authors.affiliation: Department of Microbiology Immunology and Tropical Medicine, George Washington University Medical Center, Washington DC, 20037, USA.
authors.forename: Ramesh
authors.initials: R
authors.lastname: Ratnappan
authors.affiliation: Department of Microbiology Immunology and Tropical Medicine, George Washington University Medical Center, Washington DC, 20037, USA.
authors.forename: Melissa
authors.initials: M
authors.lastname: Keaney
authors.affiliation: Department of Biological Sciences, George Washington University, Science and Engineering Hall, suite 6000, 800 22nd Street NW, Washington DC, 20052, USA.
authors.forename: Eric
authors.initials: E
authors.lastname: Kenney
authors.affiliation: Department of Biological Sciences, George Washington University, Science and Engineering Hall, suite 6000, 800 22nd Street NW, Washington DC, 20052, USA. ioannise@gwu.edu.
authors.forename: Ioannis
authors.initials: I
authors.lastname: Eleftherianos
authors.affiliation: Department of Biological Sciences, George Washington University, Science and Engineering Hall, suite 6000, 800 22nd Street NW, Washington DC, 20052, USA. damienoh@gwu.edu.|Institute for Neuroscience, George Washington University, 636 Ross Hall, 2300 I Street NW, Washington DC, 20052, USA. damienoh@gwu.edu.
authors.forename: Damien
authors.initials: D
authors.lastname: O'Halloran
authors.affiliation: Department of Microbiology Immunology and Tropical Medicine, George Washington University Medical Center, Washington DC, 20037, USA. jhawdon@gwu.edu.
authors.forename: John M
authors.initials: JM
authors.lastname: Hawdon
mesh_terms: D000818:Animals; D019295:Computational Biology / Q000379:methods; D020869:Gene Expression Profiling; D063990:Gene Ontology; D017238:Genes, Helminth; D059014:High-Throughput Nucleotide Sequencing; D054884:Host-Pathogen Interactions; D058977:Molecular Sequence Annotation; D015203:Reproducibility of Results; D017196:Rhabditida Infections / Q000469:parasitology; D017172:Rhabditoidea / Q000235:genetics*; D059467:Transcriptome
keywords: Hemolymph; Heterorhabditis bacteriophora; Nematode; Parasitism; RNA-seq