BETA-TUBULIN GENES FROM THE PARASITIC NEMATODE HAEMONCHUS-CONTORTUS MODULATE DRUG-RESISTANCE IN CAENORHABDITIS-ELEGANS

Resistance to antimitotic chemotherapeutics in pathogenic nematodes, f ungi and mammalian cells is closely associated with structural changes in cytoskeletal beta-tubulin. We investigated the possibility of usin g the well-characterised free-living nematode Caenorhabditis elegans a s a model for studying the mechanism of resistance against benzimidazo le (BZ) drugs in the parasitic nematode Haemonchus contortus. Function al analysis of a conserved beta-tubulin isotype (tub-1) mutation near GTP-binding domain II, which is linked to BZ resistance, was carried o ut in C. elegans by heterologous expression of: (1) parasite BZ-sensit ive alleles; (2) BZ-resistant alleles; and (3) in vitro mutagenised be ta-tubulin gene constructs. The injected heterologous gene constructs were not only stably maintained, but also expressed as shown by revers e transcriptase-polymerase chain reaction analysis. The degree of BZ d rug susceptibility of the transformants was assayed and quantified by incubation with both benomyl and thiabendazol. All H. contortus tub-1 constructs, which encoded Phe at position 200, conferred susceptibilit y to thiabendazole in BZ-resistant C. elegans ben-1 mutants. In contra st, constructs carrying Tyr200 did not alter the BZ drug phenotype. Fr om these experiments we conclude that: (1) C. elegans can be used as a n expression host, since injected parasite genes were biologically act ive; and (2) the single Phe to Tyr mutation at position 200 in beta-tu bulin isotype 1 is the cause of BZ resistance in H. contortus.