cDNA-AFLP analysis in levamisole-resistant Haemonchus contortus reveals alternative splicing in a nicotinic acetylcholine receptor subunit.

The cDNA-AFLP (cDNA-amplified fragment length polymorphism) method comparing transcripts from levamisole-resistant and susceptible Haemonchus contortus isolates has led to the successful identification of a number of potentially useful levamisole-resistance markers. In the present study, we report the characterization of the transcript-derived fragment (TDF) named HAX which was confirmed to be specifically expressed in three levamisole-resistant isolates by RT-PCR experiments. Cloning and sequencing of the full-length cDNA sequence of HAX revealed high similarity to the Caenorhabditis elegans acr-8 gene and its putative H. contortus orthologue encoding a nicotinic acetylcholine receptor subunit. This Hco-acr-8b short isoform corresponded to a spliced variant of Hco-acr-8 mRNA containing the two first exons and a part of intron 2. As nicotinic acetylcholine receptors constitute the pharmacological target of levamisole, Hco-acr-8b may potentially be involved in the molecular mechanisms leading to levamisole-resistance acquisition in H. contortus.