Convergent evolution of a parasite-encoded complement control protein-scaffold to mimic binding of mammalian TGF-ß to its receptors, TßRI and TßRII.

The mouse intestinal helminth Heligmosomoides polygyrus modulates host immune responses by secreting a transforming growth factor (TGF)-ß mimic (TGM), to expand the population of Foxp3+ Tregs. TGM comprises five complement control protein (CCP)-like domains, designated D1-D5. Though lacking homology to TGF-ß, TGM binds directly to the TGF-ß receptors TßRI and TßRII and stimulates the differentiation of naïve T-cells into Tregs. However, the molecular determinants of binding are unclear. Here, we used surface plasmon resonance, isothermal calorimetry, NMR spectroscopy, and mutagenesis to investigate how TGM binds the TGF-ß receptors. We demonstrate that binding is modular, with D1-D2 binding to TßRI and D3 binding to TßRII. D1-D2 and D3 were further shown to compete with TGF-ß(TßRII)2 and TGF-ß for binding to TßRI and TßRII, respectively. The solution structure of TGM-D3 revealed that TGM adopts a CCP-like fold but is also modified to allow the C-terminal strand to diverge, leading to an expansion of the domain and opening potential interaction surfaces. TGM-D3 also incorporates a long structurally ordered hypervariable loop, adding further potential interaction sites. Through NMR shift perturbations and binding studies of TGM-D3 and TßRII variants, TGM-D3 was shown to occupy the same site of TßRII as bound by TGF-ß using both a novel interaction surface and the hypervariable loop. These results, together with the identification of other secreted CCP-like proteins with immunomodulatory activity in H. polygyrus, suggest that TGM is part of a larger family of evolutionarily plastic parasite effector molecules that mediate novel interactions with their host.

Redescription of Heligmosomoides neopolygyrus, Asakawa and Ohbayashi, 1986 (Nematoda: Heligmosomidae) from a Chinese rodent, Apodemus peninsulae (Rodentia: Muridae); with comments on Heligmosomoides polygyrus polygyrus (Dujardin, 1845) and related species in China and Japan.

Heligmosomoides neopolygyrus, Asakawa and Ohbayashi, 1986 (Nematoda, Heligmosomoidea) is redescribed from Apodemus peninsulae from Rangtang, Sichuan, China. A morphological review of the Heligmosomoides spp. belonging to the "polygyrus line" proposed by Asakawa (1988) is made using new characters. This enabled us to distinguish two subspecies in Mus musculus (Heligmosomoides polygyrus bakeri from Japan and H. p. polygyrus from China) and two valid species in Apodemus spp. (H. neopolygyrus from Japan (in A. peninsulae) and from China (in A. agrarius) and H. asakawae from China (in A. uralensis)). Three parasite species of A. agrarius and A. peninsulae, previously identified by Asakawa et al. (1993) as H. neopolygyrus, are considered to be Heligmosomoides incertae sedis. This is the first report of H. neopolygyrus in A. peninsulae from China.

Heligmosomoides bakeri: a new name for an old worm?

A popular model system for exploring the host-parasite relationship of gastrointestinal nematodes is commonly known as Heligmosomoides polygyrus bakeri. Recently, this parasite was raised to full species level as H. bakeri, to distinguish it from a close relative, H. polygyrus sensu stricto, the dominant intestinal nematode of wood mice in Western Europe, which is unable to infect laboratory mice (Mus sp.) without the aid of powerful immunosuppressants. Herein, the argument is presented that it is necessary to rename this parasite, and that H. bakeri is the correct name for the species used widely throughout the world as a laboratory research model. Supporting this claim, key evidence is presented demonstrating that H. bakeri and H. polygyrus are two quite distinct species.

Molecular evidence that Heligmosomoides polygyrus from laboratory mice and wood mice are separate species.

The gastro-intestinal (GI) nematode Heligmosomoides polygyrus is an important experimental model in laboratory mice and a well-studied parasite of wood mice in the field. Despite an extensive literature, the taxonomy of this parasite in different hosts is confused, and it is unclear whether laboratory and field systems represent the same or different Operational Taxonomic Units (OTUs). Molecular analyses reveal high sequence divergence between H. p. bakeri (laboratory) and H. p. polygyrus (field); 3% difference in the ribosomal DNA Internal Transcribed Spacers (ITS) and 8.6% variation in the more rapidly evolving mitochondrial cytochrome c oxidase I (COI) gene. The COI sequence of U.K. H. p. polygyrus is more similar to H. glareoli from voles than to H. p. bakeri, while a single isolate of H. p. polygyrus from Guernsey confirms the extent of genetic variation between H. p. polygyrus populations. Analysis of molecular variance demonstrated that mtCOI sequence variation is associated primarily with groups with distinct ITS2 sequences, and with host identity, but is not partitioned significantly with a single combined taxon H. polygyrus incorporating European and North American isolates. We conclude therefore that the laboratory OTU should be raised to the level of a distinct species, as H. bakeri from the laboratory mouse Mus musculus, and we reject the hypothesis that H. bakeri has diverged from H. polygyrus in the recent past following introduction into America. However, we are unable to reject the hypothesis that H. polygyrus and H. bakeri are sister taxa, and it may be that H. polygyrus is polyphyletic or paraphyletic.

Metabolic labelling of wild and laboratory subspecies of the trichostrongyle nematode Heligmosomoides polygyrus.

The immunological, biochemical and taxonomic relationship between wild and laboratory subspecies of Heligmosomoides polygyrus was studied by metabolically labelling parasite proteins with [35S]-methionine. Much variability, both in content and synthesis of proteins was observed between the two subspecies. Laboratory female worms had a higher protein content and incorporated more radioactive label into somatic proteins than their wild counterparts. Incorporation of radioactivity into excretory/secretory (ES) proteins, predicted to contain important antigens, demonstrates a major reduction in synthesis of proteins with molecular weights 66, 55, 43, 41, 40, 39, 37, 28 and 16 kDa by laboratory females. These differences in protein synthesis might explain the differing infectivities of the two subspecies when passaged in inbred laboratory (Mus musculus) and wild (Apodemus sylvaticus) mice.

Genomic variability within laboratory and wild subspecies of Heligmosomoides polygyrus.

Genomic DNA extracted from laboratory and wild subspecies of the trichostrongyle nematode Heligmosomoides polygyrus were compared using RFLP and DNA/DNA hybridization techniques. Eight restriction endonuclease digests of the genomic DNA of the two subspecies were hybridized with heterologous ribosomal DNA probes and the total radio-isotope labelled DNA of the laboratory subspecies. DNA hybridization of the two subspecies of H. polygyrus yielded different banding patterns when probed with the rDNA clones in Pvu II digests and when total genomic DNA was used as the probe in Hind III and Pvu II digests. The remaining hybridization profiles of both subspecies were identical.