title: Identification of abundantly expressed novel and conserved genes from the infective larval stage of Toxocara canis by an expressed sequence tag strategy.
abstract: Larvae of Toxocara canis, a nematode parasite of dogs, infect humans, causing visceral and ocular larva migrans. In noncanid hosts, larvae neither grow nor differentiate but endure in a state of arrested development. Reasoning that parasite protein production is orientated to immune evasion, we undertook a random sequencing project from a larval cDNA library to characterize the most highly expressed transcripts. In all, 266 clones were sequenced, most from both 3' and 5' ends, and similarity searches against GenBank protein and dbEST nucleotide databases were conducted. Cluster analyses showed that 128 distinct gene products had been found, all but 3 of which represented newly identified genes. Ninety-five genes were represented by a single clone, but seven transcripts were present at high frequencies, each composing >2% of all clones sequenced. These high-abundance transcripts include a mucin and a C-type lectin, which are both major excretory-secretory antigens released by parasites. Four highly expressed novel gene transcripts, termed ant (abundant novel transcript) genes, were found. Together, these four genes comprised 18% of all cDNA clones isolated, but no similar sequences occur in the Caenorhabditis elegans genome. While the coding regions of the four genes are dissimilar, their 3' untranslated tracts have significant homology in nucleotide sequence. The discovery of these abundant, parasite-specific genes of newly identified lectins and mucins, as well as a range of conserved and novel proteins, provides defined candidates for future analysis of the molecular basis of immune evasion by T. canis.
authors.affiliation: Institute of Cell, Animal and Population Biology, University of Edinburgh, Edinburgh EH9 3JT, Scotland, United Kingdom.
authors.forename: K K
authors.initials: KK
authors.lastname: Tetteh
authors.forename: A
authors.initials: A
authors.lastname: Loukas
authors.forename: C
authors.initials: C
authors.lastname: Tripp
authors.forename: R M
authors.initials: RM
authors.lastname: Maizels
mesh_terms: D020413:3' Untranslated Regions; D000818:Animals; D000975:Antioxidants; D001483:Base Sequence; D019343:Citric Acid; D018509:DNA, Helminth; D004285:Dogs; D010450:Endopeptidases / Q000235:genetics; D020224:Expressed Sequence Tags; D015870:Gene Expression; D017238:Genes, Helminth; D006019:Glycolysis; D015801:Helminth Proteins / Q000096:biosynthesis / Q000378:metabolism; D036341:Intercellular Signaling Peptides and Proteins; D007814:Larva; D037102:Lectins / Q000235:genetics; D008969:Molecular Sequence Data; D009077:Mucins / Q000235:genetics; D000077153:Progranulins; D011498:Protein Precursors / Q000235:genetics; D011499:Protein Processing, Post-Translational; D011950:Receptors, Cholinergic / Q000235:genetics; D012269:Ribosomal Proteins / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D017166:Toxocara canis / Q000235:genetics*; D014764:Viral Proteins / Q000235:genetics
chemical_list: D020413:3' Untranslated Regions; D000975:Antioxidants; D018509:DNA, Helminth; D015801:Helminth Proteins; D036341:Intercellular Signaling Peptides and Proteins; D037102:Lectins; D009077:Mucins; D000077153:Progranulins; D011498:Protein Precursors; D011950:Receptors, Cholinergic; D012269:Ribosomal Proteins; D014764:Viral Proteins; D019343:Citric Acid; D010450:Endopeptidases