Characterization and expression profile of transient receptor potential channels in sea cucumber Apostichopus japonicus

Abstract

BackgroundIn the past few decades, heat waves and seasonal variation linked with global warming are causing frequent fluctuations of water temperature in aquatic environments, resulting in further challenges for marine organisms. As a poikilothermic marine animal and a temperate species, sea cucumber A. japonicus is also very sensitive to temperature variation and shows a limited ability to adapt to environmental temperature changes. However, the molecular mechanisms by which A. japonicus perceives signals from such a diverse environment including the trigger of aestivation still remain unclear. TRP (transient receptor potential) superfamily, as the great potential “sentinel” of the organism in response to the changes of the external environment signals, perceived little attention and will be the future great candidates for sensory function research in echinoderm.MethodsBLAST program was applied to identify the AjTRPs based on A. japonicus transcriptome database. Gene structure analysis of AjTRPs and phylogenetic analysis of TRPs were performed. The expression profiles of AjTRPs in different tissues and in response to different heat stress treatments (chronic/ acute) were measured using qRT-PCR.ResultsA total of 54 TRPs were identified in A. japonicus. Gene structure analysis showed that the exon numbers and the domains of AjTRPs varied greatly. Phylogenetic analysis indicated that AjTPRs were mainly grouped into six subfamilies: TRPA, TRPM, TRPC, TRPV, TRPML, and TRPP. Copy numbers of each TRP member in marine invertebrates including A. japonicus were more than those in vertebrates, however some TRP channel members were lost in invertebrates. Expression profile detection suggested that the representative 15 AjTRP genes belonging to 6 subfamilies were expressed in all tissues examined.ConclusionOur findings indicate that the plastic evolutionary history of TRP channel genes and suggest that TRPM2-1, TRPM2-2, TRPM3, and TRPC3-1 are potential thermo-TRP proteins involved in thermal regulation in A. japonicus. This work facilitates the knowledge of TRP-mediated sensory systems in echinoderms, provides new insights into the mechanisms of aestivation and global warming adaptation in marine invertebrates.

Thermotaxis in an apolar, non-neuronal animal

“…Temperature responsiveness of TRP channels has been identified across a wide range of organisms. Some examples of TRP channels that have been shown to be temperature-sensitive are TRPM2-1 in Apostichopus japonicus [ 54 ], OSM-9 and OCR-2 TRPV channels in C. elegans [ 55 ], TRPA1 channels in Drosophila melanogaster [ 56 ], TRPM8 channels in Xenopus tropicalis [ 57 ], TRPM2 channels in Nematostella vectensis , and channels such as TRPV4 and TRPM3 in Mus musculus [ 59 , 63 , 64 ]. We found reciprocal best hits in T. adhaerens using blastp and starting with each of these channels, and from the homology tree that we were able to construct using the reciprocal best hits ( figure 5 a ), we are able to see three main groups of hypothetical TRP channels in T. adhaerens .…”

“…In seeking to identify potential sensors mediating the thermotaxis response, we start by looking to TRP channels. TRP channels have diverse known functions; they act as ubiquitous sensors in vertebrates and invertebrates alike and are responsive to numerous chemical and physical stimuli, including temperature [49][50][51][52][53][54][55][56][57][58][59]. These channels are additionally interesting because they are often polymodally activated and are considered an example of signal integration at the level of the sensor itself [53,60].…”