De Novo Transcriptome Sequencing of the Octopus vulgaris Hemocytes Using Illumina RNA-Seq Technology: Response to the Infection by the Gastrointestinal Parasite Aggregata octopiana

Abstract

Background Octopus vulgaris is a highly valuable species of great commercial interest and excellent candidate for aquaculture diversification; however, the octopus’ well-being is impaired by pathogens, of which the gastrointestinal coccidian parasite Aggregata octopiana is one of the most important. The knowledge of the molecular mechanisms of the immune response in cephalopods, especially in octopus is scarce. The transcriptome of the hemocytes of O. vulgaris was de novo sequenced using the high-throughput paired-end Illumina technology to identify genes involved in immune defense and to understand the molecular basis of octopus tolerance/resistance to coccidiosis.ResultsA bi-directional mRNA library was constructed from hemocytes of two groups of octopus according to the infection by A. octopiana, sick octopus, suffering coccidiosis, and healthy octopus, and reads were de novo assembled together. The differential expression of transcripts was analysed using the general assembly as a reference for mapping the reads from each condition. After sequencing, a total of 75,571,280 high quality reads were obtained from the sick octopus group and 74,731,646 from the healthy group. The general transcriptome of the O. vulgaris hemocytes was assembled in 254,506 contigs. A total of 48,225 contigs were successfully identified, and 538 transcripts exhibited differential expression between groups of infection. The general transcriptome revealed genes involved in pathways like NF-kB, TLR and Complement. Differential expression of TLR-2, PGRP, C1q and PRDX genes due to infection was validated using RT-qPCR. In sick octopuses, only TLR-2 was up-regulated in hemocytes, but all of them were up-regulated in caecum and gills.ConclusionThe transcriptome reported here de novo establishes the first molecular clues to understand how the octopus immune system works and interacts with a highly pathogenic coccidian. The data provided here will contribute to identification of biomarkers for octopus resistance against pathogens, which could improve octopus farming in the near future.

An updated molecular basis for mussel immunity

“…Some core components of the complement system are present in Protostomes and even in cnidarians, hence, established more than 1000 MYA [81]. Proteins showing sequence homology to some components of the complement system have been also reported in molluscs [22,23,82].…”

Understanding the cephalopod immune system based on functional and molecular evidence

“…The molecular basis of the O. vulgaris immune system has been recently provided At the same time, this result suggests that potentially novel genes might be awaiting identification and validation, including those involved in immune response. Even thought, 3% of predicted proteins related to an immune function were identified [98], a small but acceptable quantity compared to 10% recorded in bivalves like Ruditapes decussatus [99], which is presumably better represented in public databases than the common octopus.…”

Early life stage bottlenecks of carnivorous molluscs under captivity: a challenge for their farming and contribution to seafood production

“…Blood samples could be obtained from the cephalic aorta (following Castellanos‐Martínez et al . ,) but it will be necessary to develop molecular tools for detecting male and female hormones from available samples without sacrificing octopuses (Larson & Anderson ).…”

“…All these defence strategies have recently been studied in S. officinalis and O. vulgaris (Castellanos‐Martínez et al . ,; Gestal & Castellanos‐Martínez ), which opens other study strategy to determine the effect of diets, productive management and stress, on the innate immunity of cephalopods.…”