De novo assembly and analysis of tissue-specific transcriptomes revealed the tissue-specific genes and profile of immunity from Strongylocentrotus intermedius

• Tissues-specific transcriptome of Strongylocentrotus intermedius was sequenced for the first time.
• In total 96,764 contigs within 24,778 gene families in S. intermedius were annotated.
• Potential tissue-specific pathways progressed in different tissues were annotated.
• In S. intermedius, 1074 (4.3% of all genes) genes were annotated as defending genes.
• Coelomocytes is the main immune monitor, complement is very important in S. intermedius.

Strongylocentrotus intermedius is an important marine species in north China and Japan. Recent years, diseases are threating the sea urchin aquaculture industry seriously. To provide a genetic resource for S. intermedius as well as overview the immune-related genes of S. intermedius, we performed transcriptome sequencing of three cDNA libraries representing three tissues, coelomocytes, gut and peristomial membrane respectively. In total 138,421 contigs were assembled from all sequencing data. 96,764 contigs were annotated according to bioinformatics databases, including NT, nr, Swiss-Prot, KEGG, COG. 49,336 Contigs were annotated as CDS. In this study, we obtained 24,778 gene families from S. intermedius transcriptome. The gene expression analysis revealed that more genes were expressed in gut, more high expression level genes in coelomocytes when compared with other tissues. Specific expressed contigs in coelomocytes, gut, and peristomial membrane were 546, 1136, and 1012 respectively. Pathway analysis suggested 25, 17 and 36 potential specifically pathways may specific progressed in peristomial membrane, gut and coelomocytes respectively. Similarities and differences between S. intermedius and other echinoderms were analyzed. S. intermedius was more homology to Strongylocentrotus purpuratus than others sea urchin. Of 24,778 genes, 1074 genes are immune-related, immune genes were expressed with a higher level in coelomocytes than other tissues. Complement system may be the most important immune system in sea urchin. We also identified 2438 SSRs and 16,236 SNPs for S. intermedius. These results provide a transcriptome resource and foundation to study molecular mechanisms of sea urchin immune system.