Analysis Of Differentially Expressed Genes In The Tube Feet Of Sea Cucumber(Apostichopus Japonicus) Co-exposed To BTEXsby Transcriptome Sequencing

Sea cucumber,Apostichopus japonicus(Selenka), is a common species in the Western Pacific Ocean along the coast of China, Japan, Korea and Russia. In recent years, with the rapid development of coastal petrochemical industry and frequent accidents of marine oil spill, the oil pollution happened occasionally.The marine pollution of benzene series(BTEXs), including benzene, toluene, ethyl benzene and xylene, is mainly from the marine oil spill and coastal petrochemical wastewater discharge. Many studies of sea cucumber have been performed in recent years, but the the effects of BTEXs onA. japonicus is still a new field. By Illumina HiSeqTM 2000 platform, we obtained abundant differentially expressed genes(DEGs) from the tube feet of sea cucumber A. japonicus exposed to 0.0(C), 1.0 mg·L-1 BTEXs(B)for 12 h. Based on the transcriptome data,possible roles of the DEGs played in sea cucumber A. japonicus were discussed. The main conclusions were as follows:(1)Transcriptome analysis of tested and control groups: de novo assembly of the merged transcriptome data from the tube feet of A. japonicus exposed to BTEXs and normal control by Trinity yielded 145675 unigenes with an average length of 657.21 bp. Based on similarity searches with a cut-off E-value of10-5 against protein sequence databases, 35330 of the unigenes(about 24.25%) were matched to known proteins. A total of 8409 unigenes were assigned COG classifications, and the Blast2 GO annotation tool assigned 10532 of the unigenes to 23243 Gene Ontology terms. In addition, 7305 unigenes were assigned to 344 KEGG pathways. Transcriptome analysis based on Illumina paired-end sequencing is a powerful approach for the gene discovery of non-model species.(2)Analysis of the DEGs: By comparing the tested and control groups, 2418 DEGs were identified. Among them, 1049 DEGs were up-regulated and 1369 down-regulated using the criteria |Log2 Fold changes| ≥ 1 and false discovery rate(FDR) ≤ 0.001. GOseq analysis revealed that for B vs. C, 158 DEGs were highly enriched in 149 GO terms including 103 biological processes, 17 cellular component and 29 molecular function terms(p value < 0.05). Pathways associated with BTEXs co-exposed were also mined and indicated that 307 DEGs were enriched in 268 pathways, including signal transduction, cancer, xenobiotics biodegradation and metabolism pathways. The results could be used for screening out the biomarkers of BTEXs on the transcriptome level, and provide the scientific basis to explain the molecular mechanism of toxic effects of BTEXs on sea cucumber A. japonicus.(3)Validation of the DEGs: To confirm the RNA-Seq profiles, qRT-PCR was conducted on four differentially expressed genes(DEGs) that were identified by RNA-Seq.The DEGs from RNA-Seq and qRT-PCR data showed consistent expression patterns. These results provided basic data for gene identification and function studiesof A. japonicus co-exposed to BTEXs.