Genetic blueprint of the zoonotic pathogen Toxocara canis

Abstract

Toxocara canis is a zoonotic parasite of major socioeconomic importance worldwide. In humans, this nematode causes disease (toxocariasis) mainly in the under-privileged communities in developed and developing countries. Although relatively well studied from clinical and epidemiological perspectives, to date, there has been no global investigation of the molecular biology of this parasite. Here we use next-generation sequencing to produce a draft genome and transcriptome of T. canis to support future biological and biotechnological investigations. This genome is 317 Mb in size, has a repeat content of 13.5% and encodes at least 18,596 protein-coding genes. We study transcription in a larval, as well as adult female and male stages, characterize the parasite’s gene-silencing machinery, explore molecules involved in development or host–parasite interactions and predict intervention targets. The draft genome of T. canis should provide a useful resource for future molecular studies of this and other, related parasites.

The genomic basis of nematode parasitism

“…Transcriptional analysis of the stichosome (compared with the rest of the adult worm) of Trichuris suis shows comparatively greater expression of many genes coding for peptidases and for porins (along with many other genes), consistent with the idea that the stichosome's function is to allow the worm to burrow into host tissue [29,44]. The transcriptional profile of the gut of two parasitic nematodes (H. contortus and T. canis [16,28]) has also shown that genes coding for a range of protease/ peptidases (and protease and peptidase inhibitors), and products involved in binding with and transporting a range of molecules, are comparatively upregulated, consistent with the a priori view of the function of the worm's gut.…”

“…For example, the Ascaris suum genome has 456 peptidase coding genes, with those coding for metallopeptidases and serine proteases predominating. The Toxocara canis genome has many similar genes too-165, 107 and 60 (total 332) coding for metallo, cysteine, and serine peptidases, respectively, together representing 89% of all the predicated peptidase coding genes in this species [28]. In the whipworm Trichuris suis, there are large numbers of genes coding for two classes of peptidases (116 for class S1 and 42 for class S8) [29]; Dictyocaulus viviparus has 478 protease coding genes [30].…”

“…For parasitic adult stages, there is also a comparative increase in the expression of genes coding for a range of enzymes including proteases, peptidases, hydrolases, catalases (for example, in Necator americanus, H. contortus, T. canis and A. suum [16,22,28,32]), and protease inhibitors. Also, consistent with adult stages growing and reproducing, there is a comparative increase in the abundance of transcripts of genes whose products are involved in DNA replication, cuticle formation, and spermatogenesis.…”

“…In many species, proteases and peptidases are predicted to be secreted (A. suum, T. canis, T. suis, S. ratti [19,22,28,29]); in N. americanus, over half (325 of 592) of all proteases fall into this category, and 19% of the 478 of D. viviparus [30]. Some SCP/TAPS proteins are also predicted to be secreted (in A. suum, T. canis, S. ratti, D. viviparus).…”

The barber's pole worm CAP protein superfamily — A basis for fundamental discovery and biotechnology advances

“…americanus (cf. Hawdon et al, 1996, 1999;Datu et al, 2008;Tang et al, 2014;Schwarz et al, 2015), but contrasts with the small numbers of homologous genes inferred from transcriptomic and genomic sequence data sets for some other nematodes studied to date, including Ascaris suum, Toxocara canis and Trichuris suis (see Jex et al, 2011Jex et al, , 2014Zhu et al, 2015). The reason(s) for this apparent difference is unclear, but could relate to differences in developmental and reproductive biology as well as varying modes of host invasion and immune modulation or evasion among nematode species (cf.…”