Abstract
BackgroundTRP (Transient Receptor Potential) channels respond to diverse stimuli and thus function as the primary integrators of varied sensory information. They are also activated by various compounds and secondary messengers to mediate cell-cell interactions as well as to detect changes in the local environment. Their physiological roles have been primarily characterized only in mice and fruit flies, and evolutionary studies are limited. To understand the evolution of insect TRP channels and the mechanisms of integrating sensory inputs in insects, we have identified and compared TRP channel genes in Drosophila melanogaster, Bombyx mori, Tribolium castaneum, Apis mellifera, Nasonia vitripennis, and Pediculus humanus genomes as part of genome sequencing efforts.ResultsAll the insects examined have 2 TRPV, 1 TRPN, 1 TRPM, 3 TRPC, and 1 TRPML subfamily members, demonstrating that these channels have the ancient origins in insects. The common pattern also suggests that the mechanisms for detecting mechanical and visual stimuli and maintaining lysosomal functions may be evolutionarily well conserved in insects. However, a TRPP channel, the most ancient TRP channel, is missing in B. mori, A. mellifera, and N. vitripennis. Although P. humanus and D. melanogaster contain 4 TRPA subfamily members, the other insects have 5 TRPA subfamily members. T. castaneum, A. mellifera, and N. vitripennis contain TRPA5 channels, which have been specifically retained or gained in Coleoptera and Hymenoptera. Furthermore, TRPA1, which functions for thermotaxis in Drosophila, is missing in A. mellifera and N. vitripennis; however, they have other Hymenoptera-specific TRPA channels (AmHsTRPA and NvHsTRPA). NvHsTRPA expressed in HEK293 cells is activated by temperature increase, demonstrating that HsTRPAs function as novel thermal sensors in Hymenoptera.ConclusionThe total number of insect TRP family members is 13-14, approximately half that of mammalian TRP family members. As shown for mammalian TRP channels, this may suggest that single TRP channels are responsible for integrating diverse sensory inputs to maintain the insect sensory systems. The above results demonstrate that there are both evolutionary conservation and changes in insect TRP channels. In particular, the evolutionary processes have been accelerated in the TRPA subfamily, indicating divergence in the mechanisms that insects use to detect environmental temperatures.
Highlights
Transient receptor potential (TRP) (Transient Receptor Potential) channels respond to diverse stimuli and function as the primary integrators of varied sensory information
Conservation of insect TRPV, TRPN, TRPM, and TRPML subfamilies There are 13 identified TRP channel genes in Drosophila [1]; we used them as queries to identify TRP channel genes in the P. humanus, B. mori, T. castaneum, A. mellifera, and N. vitripennis genomes
Phylogenetic analysis of C. elegans, D. melanogaster, and mouse TRPV and TRPM channels demonstrates that C. elegans and mouse independently expanded these subfamily members during their evolution (Fig. 2)
Summary
TRP (Transient Receptor Potential) channels respond to diverse stimuli and function as the primary integrators of varied sensory information. They are activated by various compounds and secondary messengers to mediate cell-cell interactions as well as to detect changes in the local environment. Transient receptor potential (TRP) superfamily members of cation channels share six common transmembrane domains and permeability to cations. Despite these similarities, TRP channels are highly unusual among the known families of ion channels in displaying an impressive diversity of cation selectivities and specific activation mechanisms. TRPC, TRPA, TRPV, and TRPN channels have multiple N-terminal ankyrin repeats [1,2,3]
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