Ligand-gated chloride channel subunits encoded by the Haemonchus contortusand Ascaris suum orthologues of the Caenorhabditis elegans gbr-2 (avr-14) gene

The alternatively-spliced Caenorhabditis Elegans gbr-2/avr-14 gene encodes two subunits of the nematode ligand-gated chloride channel family which for ms an important molecular target for the avermectin and related anthelminth ics. We used reverse transcriptase-polymerase chain reaction (RT--PCR) tech niques to isolate cDNAs encoding the products of the gbr-2/avr-14 orthologu es from the parasitic nematodes Haemonchus contortus and Ascaris suum. The predicted polypeptides possess all the characteristics of subunits of the l igand-gated chloride channels, sharing greater than 80% amino-acid identity with their counterparts in C. elegans and with partial sequences from the filarial species Onchocerca volvulus and Dirofilaria immitis. The pattern o f alternative splicing of the gbr-2/avr-14 gene observed in C. elegans is c onserved in H. contortus but may not be in A. suum. Affinity-purified anti- GBR-2 antibodies were used to study the expression of these subunits in adu lt worms and they reacted specifically with the nerve ring, the ventral and dorsal nerve cords, the anterior portion of the dorsal sub-lateral cord an d motor-neuron commissures in H. contortus. Specific immunofluorescence of the nerve cords was confirmed in A. suum; isolated muscle cells did not rea ct with the antibody. (C) 1999 Elsevier science B.V. All rights reserved.