De novo transcriptome sequencing of triton shell Charonia lampas sauliae: Identification of genes related to neurotoxins and discovery of genetic markers.

Charonia lampas sauliae (triton snails, triton shells or tritons; Mollusca, Caenogastropoda, Littorinimorpha, Ranellidae) is a marine species with a wide distribution. In Korea, this species is listed as vulnerable and is regionally protected as an endangered species. Here, we report the first comprehensive transcriptome dataset of C. lampas sauliae obtained using the Illumina HiSeq 2500 platform. In total, 97.68% of raw read sequences were processed as clean reads. Of the 577,478 contigs obtained, 146,026 sequences were predicted to contain coding regions. About 89.34% of all annotated unigene sequences showed homologous matches to protein sequences in PANM DB (Protostome database). Further, about one-third of the unigene sequences were annotated using the UniGene, Swiss-Prot, Clusters of Orthologous Groups (COG) and Gene Ontology (GO) databases. In total, 190 enzymes were predicted under key metabolic pathways under stood through Kyoto Encyclopedia of Genes and Genomes (KEGG) database annotation. Repetitive elements such as long terminal repeats (LTRs), short interspersed nuclear elements (SINEs), long interspersed nuclear elements (LINEs), and DNA elements were enriched in the unigene sequences. Among the identified transcripts were the channel proteins, some of which were blocked by tetrodotoxin, which is thought to be synthesized by symbiotic bacteria inhabiting the shells. In addition, conotoxin superfamily peptides, such as B-conotoxin, conotoxin superfamily T and alpha-conotoxin, were identified, which may have relevance to biomedical and evolutionary research. A transcriptome-wide search for polymorphic loci identified 21,568 simple sequence repeats (SSRs) in the unigene sequences. Most SSRs were dinucleotides, among which AC/GT was the dominant SSR type. The molecular and genetic resources revealed in this study could be utilized for investigations on the fitness of the species in the marine environment and sustainability in a changing habitat.