Reporter Gene Constructs Suggest That the Caenorhabditis Elegans Avermectin Receptor β-Subunit is Expressed Solely in the Pharynx

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Abstract
Gene promoter/LacZ reporter constructs were made in order to analyse the expression of the beta-subunit of the Caenorhabditis elegans glutamate-gated Cl- channel (Glu-Cl) receptor. Southern blot analysis of the C. elegans cosmid C35E8 identified a 4kbp EcoRI fragment which contained the 5' portion of the Glu-Cl beta coding sequence together with 5' flanking sequences. This was subcloned and used as the template for polymerase chain reaction (PCR) amplification of a DNA fragment encoding the first 24 amino acid residues of Glu-Cl beta together with 1.4 kbp of 5' genomic sequence. The fragment was subcloned into the LacZ expression vector pPD22.11 to form a translational reporter fusion. After injection of the construct into worms, six stably transformed lines were established and assayed for beta-galactosidase activity. Stained nuclei were observed in the pharyngeal metacorpus in adults and in all larval stages, and stained nuclei were seen in many embryos undergoing morphogenesis. Additional stained nuclei towards the terminal bulb of the pharynx were observed in larval stages. These results provide further evidence that the Glu-Cl receptor mediates the glutamatergic inhibition of pharyngeal muscle via the M3 motor neurone and point to inhibition of pharyngeal pumping as a major mode of action for avermectins.