EST sequencing of the parasitic nematode Haemonchus contortus suggests a shift in gene expression during transition to the parasitic stages

Expressed sequence tags from the parasitic nematode Haemonchus contortus we re generated in order to identify anchor loci for comparative mapping betwe en nematode genomes and candidate targets for future control measures. In t otal, 370 SL1 trans-spliced cDNAs from different developmental stages repre senting 195 different genes were partially sequenced. From these expressed sequence tags 50% were similar to genes with a known or predicted function and 19% were similar to nematode sequences with no ascribed function. From the first, free-living L1 and L3 stages relatively many cDNAs matched to ho usekeeping genes, and 11% (L1) or 23% (L3) of the encoded proteins were pre dicted to contain signal peptides. In contrast, no function could be ascrib ed to most of the cDNAs from the early L5 and adult parasitic stages, but f or 30% (L5) or 55% (adult) of the encoded proteins a signal sequence was pr edicted. This limited analysis suggests that during the transition from the free-living to parasitic stages gene expression shifts towards the synthes is of less conserved extracellular proteins. These proteins offer the best perspectives for vaccine development and the development of anthelmintic dr ugs. III contrast, cDNAs from the first larval stages may be most suitable for comparative mapping with the free-living nematode Caenorhabditis elegan s. (C) 2000 Elsevier Science B.V. All rights reserved.