Cryptocaryon irritans is an obligate parasitic ciliate protozoan that can infect various commercially important mariculture fish species and cause high lethality and economic loss. Current methods of controlling this parasite with chemicals or antibiotics are widely considered to be environmentally harmful. Piscidins with broad spectrum antibacterial, antifungal and antiviral activities were found to have potent activity against C. irritans. Little, however, has been understood about the killing mechanisms of piscidins in parasites. In total, 57.12, 50.44, 55.86 and 47.87 million raw reads were generated from untreated theront and trophont, and piscidin (Lc-pis) treated theront and trophont libraries, respectively. After de novo assembly, 966,609 unigenes were generated with an average length of 420 bp: among these, 618,629 unigenes showed identity with sequences in one or more databases, with some showing to be significantly manipulated by Lc-pis treatment. The species classification showed that more than 25.8% unigenes from trophonts were homologous to the large yellow croaker (Larimichthys crocea) and less than 3.8% unigenes from theronts were matched. The homologous unigenes demonstrated that the tissue from host could exist in trophonts and might be transported to parasite via vesicular transports. Our analysis showed that regulatory transcripts were involved in vesicular trafficking. Among transcripts induced by Lc-pis, most genes up-regulated in treated and untreated theronts were involved in cell migration and apoptosis related pathways. Few transcripts were found to be down-regulated in treated and untreated trophonts related to cell structure and migration after treatment. This is the first transcriptome analysis of C. irritans exposed to Lc-pis, which enhanced the genomic resources and provided novel insights into molecular mechanisms of ciliates treated by cationic antimicrobial peptide. Our comprehensive transcriptome analysis can facilitate the identification of potential drug targets and vaccines candidates for controlling this devastating fish pathogen.

BackgroundNeuropeptide pedal peptide (PP) and orcokinin (OK) are related active peptides that have been widely discovered in invertebrates. They have complex structures, and play key roles in various physiological process. Till now, there were no any reports in cephalopods with highly differentiated multi-lobular brain.MethodsThe partial cDNA sequence of neuropeptide PP in Sepiella japonica (termed as Sj-PP) was identified from a transcriptome, the full-length cDNA was obtained by rapid amplification cDNA ends (RACE) method. The bioinformatic analysis was performed through associated softwares. The tissue distribution profile and spatio-temporal expression were detected out by semi-quantitative RT-PCR and quantative Real-time PCR (qRT-PCR) assay, respectively. The tissue location was carried out with in situ hybridization (ISH).ResultsThe putative precursor of Sj-PP encodes 22 mature peptides, of which, only tridecapeptides could be post-translationally amidated at C-terminus. Each tridecapeptide owns the most conserved and frequent N-terminus DSI. The sequence analysis showed PPs shared low identity, and Sj-PP might be a PP3 member. The quantitative data showed Sj-PP widely distributed in various tissues, and the content in brain, optic lobe, liver and nidamental gland continuously increased till gonad maturation during the whole growth and development stages. In situ hybridization (ISH) detected Sj-PP positive signals in almost all regions of optic lobe except plexiform zone, all functional lobes in brain, epithelial cells and outer membrane layer of accessary nidamental gland, which hinted it is likely to be involved in the regulation of reproduction, such as vitellogenin synthesis, restoration, and ova encapsulation.ConclusionsThe results declared Sj-PP was involved in the neuroendocrine regulation in cephalapod, and provided a basic theoretical data for further studying regulatory role in the reproduction.