Blaxter ML (1993) International C. elegans Meeting "PNDB: a parasitic nematode database."

Blaxter ML

[International C. elegans Meeting, 1993]

Blaxter ML et al. (1998) European Worm Meeting "The phylogenetics of nematodes"

Blaxter ML, Vanfleteren JR, De Ley P, Thomas K, Dorris M, Frisse LM

[European Worm Meeting, 1998]

We are continuing in our quest to define the evolutionary history of the phylum Nematoda using molecular phylogenetic methods. The published analysis (Blaxter et al, Nature 392:71-75 (1998)) has now been complemented with over 100 additional sequenced taxa, arising from our work and that of others (Kampfer et al, Invert. Biol. 117:29-36 (1998) and Aleshin et al, Russ. J. Nematol. in press (1998)). Our analysis continues to support the division of the Nematoda into five major clades, and does not support the division of the phylum into two classes (Adenophorea and Secernentea). The origin of the Secernentea has been more closely defined as residing within the Chromadorida, although a separate chromadorid radiation is now evident. Caenorhabditis remains a close relative of the parasitic strongyles. We are extending the dataset using sequence data derived from fixed museum specimens. Formalin fixation preserves nematode structures very well, but is not good for DNA preservation. We have been able to extract PCR-amplifiable DNA from single 12-year fixed specimens of Strongyloides species using an amino acid titration method. Fragments up to 600 bp are recoverable and sequencable. For specimens preserved in alcohol, even at low temperatures, it has been much more difficult to obtain amplifiable DNAs, but we now have a rehydration-extraction method which works on larger samples. Current projects are focussing on the phylogenetics of the genus Strongyloides, parasites of vertebrate guts which have a facultative free-living generation. This group has turned out to be entertainingly complex, with the species divided into two distinct clades separated by freeliving and parasitic taxa from other genera. We find no correlation between host and parasite phylogenies, suggesting that horizontal transfer between hosts has been common in these parasites. We are examining in detail the coevolution of filarial nematodes and an endosymbiotic Wolbachia-like bacterium. In this case, we have strong evidence for vertical transmission of the endosymbiont within the filarial lineage. We are also providing a phylogenetic framework for comparative EST-based genome projects on additional filarial and other nematode species.

Blaxter ML et al. (1997) International C. elegans Meeting "THE BRUGIA MALAYI GENOME PROJECT"

Blaxter ML, Scott AL, Slatko B, Williams SA, Jayaraman K, Baron L, Jones SJ, Ramzy R, Daub J, Waterfall M

[International C. elegans Meeting, 1997]

Brugia malayi is a filarial nematode, a causative agent of human lymphatic filariasis and elephantiasis. The Brugia genome project aims to aid research on these parasites, particularly research towards new drug targets and vaccines, by a program of gene discovery and gene mapping. cDNA libraries from all lifecycle stages of the parasite have been constructed and EST sequencing performed. Over 7000 sequences have been submitted to dbEST. These correspond to about 4000 genes, or one quarter of the expected number in the parasite. The EST sequences inlude many which are of immediate interest to filarial researchers as well as homologues of a large number of predicted genes from C. elegans. An ACeDB-based database, FilDB, has been developed to handle this data. The Brugia dataset is of value to the C. elegans community for many reasons including: (1) it contains close homologues of C. elegans genes which can confirm otherwise unsupported genefinder genes (2) the stage specific expression patterns of the Brugia genes are known (C. elegans EST sequencing has been from mixed stage libraries in the main).

Blaxter ML (1991) International C. elegans Meeting "SURFACE MOLECULES OF CAENORHABDITIS ELEGANS AND OTHER FREE LIVING NEMATODES: RHABDITOMUCINS ?"

Blaxter ML

[International C. elegans Meeting, 1991]

In the wild, C. elegans is subject both to predation, by other nematodes and nematophagous fungi, and to physical hazards such as dessication. The outer surface of the cuticle is a target for these attacks, and a first line of protection against them. Nematophagous fungi have been shown to recognise and respond to the surface of C. elegans by a lectin-like reactivity to the 'fuzzy coat', a superficial layer on the outside of the cuticle proper. This fuzzy coat has also been linked to the ability of the worms to resist dessication, and may provide some lubrication for locomotion in the soil. Surface-specific 125I labelling with the tyrosine-directed Iodogen reagent reveals a limited set of components on the surface of C. elegans N2. Extraction in mild detergent releases two strongly labelled molecules which resolve on SDS-PAGE at 16 and 5.5 kDa. These are proteinaceous (as judged by protease sensitivity) and do not contain N-linked sugars. In IEF and NEPHGE 2D gel analysis, they do not resolve to a single pI, suggesting that they are variably modified, perhaps by O-linked glycosylation. These two molecules also make up a significant portion of the residual, non-detergent soluble labelled material, indicating that they are also covalently crosslinked to structures in or on the cuticle. My working hypothesis is that they are part of the fuzzy coat, and are a sort of (rhabdito)mucin. Similar strategies applied to parasitic nematodes have also identified limited repertoires of surface accessible proteins, which in some cases (eg Toxocara spp.) are O-glycosylated, excreted glycoproteins localising to the fuzzy coat and having mucin-like properties. This pattem is likely to be primitive to the phylum Nematoda. Labelling of other wild type strains of C. elegans gives the same pattern as N2, except in strains identified as being srf-l by Sam Politz, which lack the smaller molecule. I have also looked at other free-living nematode species: C. brfggsae BO and G 16 (two molecules of 12 and 5.5 kDa), P. redivfvans ( one of 3 kDa), C. oxycerca, R. maupausf and R. terrfcola (no detergent soluble molecules), and a Rhabdftfs sp. from my back garden (three major proteins, significantly larger than those of C. elegans N2).

Blaxter ML et al. (1995) International C. elegans Meeting "NEMATODE GLOBINS: EVOLUTION OF GENE STRUCTURE AND SEQUENCE"

Blaxter ML, Vanfleteren JR, Pizzutto M, Moens L

[International C. elegans Meeting, 1995]

C. elegans unexpectedly expresses a myoglobin-like globin. We have isolated myoglobins and related cuticular globins from the parasites Ascaris suum (gut-dwelling ascarid), Nippostrongylus brasiliensis (gut-dwelling strongylid) and Syngamus trachea (tracheal strongylid). The globins of the gut-dwelling species have high affinities while the affinities of the fully aerobic S. trachea globins are still unknown. Residue B10 has been implicated in the extraordinary affinity of the pseudocoelomic globin from Ascaris: in this unusual isoform B10 is tyrosine and is modeled to offer an extra hydrogen bond to the haem-bound oxygen. All 5 parasite globins, despite their lower affinity, have B10 Tyr suggesting that either it is not available for hydrogen bonding in these proteins or that B10 Tyr is not the sole determinant of affinity. The gene structure of the globins is very variable. Most have the "standard" N-terminal and C-terminal introns also seen in vertebrate genes. The intronless A. suum and single-intron C. elegans myoglobin genes have however lost these. A central intron is present in both pseudocoelomic and myoglobin/cuticle isoform genes but is found in a distinct position (E8, phase 1 versus E3, phase 2) in the two gene families. In the S. trachea cuticle isoform gene a fourth intron is found (EF3, phase 0) which has presumably arisen by a recent insertional event.

Blaxter ML (1993) International C. elegans Meeting "Globin and glutathione peroxidase: C. elegans homologues of parasitic nematode cuticle surface proteins."

Blaxter ML

[International C. elegans Meeting, 1993]

Blaxter ML et al. (1989) International C. elegans Meeting "localization and biosynthesis of cuticular antigens in a parasitic nematode, B Malayi."

Blaxter ML, Maizels RM, Jenkins RE, Cookson E, Gregory B, Selkirk ME, Paxton B, Yazdanbakhsh M

[International C. elegans Meeting, 1989]

Blaxter ML et al. (1997) International C. elegans Meeting "PUTTING C. ELEGANS IN ITS PLACE: A MOLECULAR PHYLOGENY OF THE PHYLUM NEMATODA"

Dorris M, Thomas WK, Scheldeman P, Garey JR, Vanfleteren JR, Liu LX, DeLey P, Vida JT, Blaxter ML, Frisse LM

[International C. elegans Meeting, 1997]

The Phylum Nematoda includes four of every five metazoan animals on the planet. Nematodes are important because of their diversity, ecological significance and impact as parasites of plants, humans and other animals. Morphological studies have failed to provide a unifying phylogenetic framework due to a lack of informative fossils and the limitations of light-microscopy. We present here a phylogenetic analysis using small subunit (SSU) ribosomal DNA sequences from a wide range of nematode taxa. For the first time animal-parasitic, plant-parasitic and free-living taxa can be compared using the same metric. We pinpoint the multiple origins of parasitism within the phylum, identify candidate research models from free-living sister taxa of parasitic clades, and place into context the metazoan research model Caenorhabditis elegans. Our results also suggest that convergent evolution has occurred more frequently in nematodes than hitherto assumed, and that classification will need significant changes.

Blaxter ML et al. (1993) International C. elegans Meeting "Surfin, a heterodimeric cuticle surface protein of C. elegans and other components of the surface."

Silverman MA, Link CD, Blaxter ML

[International C. elegans Meeting, 1993]

Blaxter, M.L. et al. (2017) International Worm Meeting "Nuclear fossils of Wolbachia reveal the complex history of nematode-Wolbachia evolution."

Laetsch, D.R., Blaxter, M.L., Koutsovoulos, G.

[International Worm Meeting, 2017]

Much of the natural world exists in symbiosis. Wolbachia are common, intracellular, maternally transmitted, parasitic symbionts of terrestrial arthropods, causing a variety of reproductive manipulations to assure their own survival. Arthropod Wolbachia can also be beneficial, protecting their hosts from viral and bacterial infections. Filarial nematodes in the Onchocercidae (including human parasites Brugia malayi, Wuchereria bancrofti and Onchocerca volvulus) also carry Wolbachia symbionts, and these are targets for anti-filarial chemotherapeutic interventions. While it was initially believed that onchocercid Wolbachia had a single origin and diversified with their nematode hosts, it is now becoming clear that the history of association between filarial nematodes and their symbionts is more complex. The symbionts of Onchocercidae derive from four Wolbachia supergroups (C, D F and J). Using 15 whole genome sequences of filarial nematodes and their C and D strain Wolbachia, we explored the evolutionary history of this symbiosis. Nematode phylogeny based on nuclear genes places Setaria labiatopapillosa basal to other sequenced species. Within the other Onchocercidae, four species (Onchocerca flexuosa, Acanthocheilonema viteae, Loa loa and Eleaphora elaphi) must have independently lost their infections. We screened the nematode genome sequences for nuclear Wolbachia transfers (NUWTs) -fragments of Wolbachia genomes integrated into the nuclear genome. S. labiatopapillosa had no NUWTs and is therefore primitively uninfected. NUWTs in O. flexuosa, A. viteae, L. loa and E. elaphi confirm these species as being aposymbiotic. We identified the supergroup membership of the Wolbachias from which the NUWTs originated, and found that aposymbotic species carried NUWTs derived from C type genomes, even if their most closely related symbiotic species carried D Wolbachia. Thus the history of Wolbachia in onchocercid nematodes includes not only cospeciation (as observed in the Onchocerca-Dirofilaria group in association with group C Wolbachia) and loss (in the aposymbiotic species), but also symbiont replacement. The supergroup D lineage of Wolbachia, found in the human parasites W. bancrofti and B. malayi, derives from a replacement event. We suggest that the biology of symbiosis may differ strongly in stably symbiotic species compared to those in which symbiont replacement has occurred.