The cys-loop ligand-gated ion channel gene superfamily of the red flour beetle, Tribolium castaneum.
BACKGROUND
Members of the cys-loop ligand-gated ion channel (cys-loop LGIC) superfamily mediate chemical neurotransmission and are studied extensively as potential targets of drugs used to treat neurological disorders such as Alzheimer's disease. Insect cys-loop LGICs are also of interest as they are targets of highly successful insecticides. The red flour beetle, Tribolium castaneum, is a major pest of stored agricultural products and is also an important model organism for studying development.


RESULTS
As part of the T. castaneum genome sequencing effort, we have characterized the beetle cys-loop LGIC superfamily which is the third insect superfamily to be described after those of Drosophila melanogaster and Apis mellifera, and also the largest consisting of 24 genes. As with Drosophila and Apis, Tribolium possesses ion channels gated by acetylcholine, gamma-amino butyric acid (GABA), glutamate and histamine as well as orthologs of the Drosophila pH-sensitive chloride channel subunit (pHCl), CG8916 and CG12344. Similar to Drosophila and Apis, Tribolium cys-loop LGIC diversity is broadened by alternative splicing although the beetle orthologs of RDL and GluCl possess more variants of exon 3. Also, RNA A-to-I editing was observed in two Tribolium nicotinic acetylcholine receptor subunits, Tcasalpha6 and Tcasbeta1. Editing in Tcasalpha6 is evolutionarily conserved with D. melanogaster, A. mellifera and Heliothis virescens, whereas Tcasbeta1 is edited at a site so far only observed in the beetle.


CONCLUSIONS
Our findings reveal that in diverse insect species the cys-loop LGIC superfamily has remained compact with only minor changes in gene numbers. However, alternative splicing, RNA editing and the presence of divergent subunits broadens the cys-loop LGIC proteome and generates species-specific receptor isoforms. These findings on Tribolium castaneum enhance our understanding of cys-loop LGIC functional genomics and provide a useful basis for the development of improved insecticides that target an important agricultural pest.
Jones
Andrew K
AK
MRC Functional Genetics Unit, Department of Physiology Anatomy and Genetics, The Sherrington Building, University of Oxford, South Parks Road, Oxford OX1 3QX, UK. andrew.jones@dpag.ox.ac.uk
Sattelle
David B
DB
D000595:Amino Acid Sequence; D000818:Animals; D003545:Cysteine / Q000378:metabolism*; D018698:Glutamic Acid / Q000378:metabolism; D006639:Histidine / Q000378:metabolism; D015640:Ion Channel Gating; D007473:Ion Channels / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D011978:Receptors, Nicotinic / Q000737:chemistry; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D014231:Tribolium / Q000235:genetics*
D007473:Ion Channels; D011978:Receptors, Nicotinic; D018698:Glutamic Acid; D006639:Histidine; D003545:Cysteine