Comparative transcriptome analysis of salivary glands of Hirudo nipponia in response to starvation

In order to investigate the variations of gene expression of salivary gland in Hirudo nipponia under starvation stress, two libraries of starvation treatment group (D30) and control group (D0) were constructed and sequenced using the Illumina HiSeq 2500 platform (paired-end). After stringent quality control of raw data, 145 981 unigenes were obtained using de novo assembly. The average length of unigenes was 675 bp and N50 length was 1 127 bp. And then all of unigenes were annotated via sequence alignment analysis in CDD, KOG, COG, NR, NT, PFAM, Swissprot, TrEMBL, GO and KEGG databases. The amount of gene expression was also estimated according to TPM (transcripts per million). By comparing the transcriptome data of D30 sample and D0 sample, the differentially expressed genes (DEGs) were screened out with a threshold criteria Q value<0.05 and |Fold Change|> 2. Totally 2 650 DEGs were identified under starvation stress, among which 667 genes were up-regulated and 1 983 genes were down-regulated. Four functional DEGs were selected for qRT-PCR analysis, and the results confirmed that the transcriptome analysis was reliable. In addition, 175 pathways were significantly enriched when all the DEGs were subject to GO enrichment analysis. The results showed that most of the DEGs were involved in cytoplasmic ribosome pathway and ribosome pathway was second. The DEGs were almost down-regulated in these pathways. It was also proved in KEGG enrichment analysis that most DEGs were involved in ribosome pathway was second. The DEGs down-regulated in ribosome pathway can indicate that it reduces protein metabolism under starvation stress. Futhermore, 4 genes were predicted to be involved in anticoagulatory, antithrombotic, antibacterial, anti-inflammatory and antitumor processes, which might play important roles in the treatment of various diseases. The results above mentioned provide important reference information for further study on the molecular mechanism of starvation tolerance of salivary gland and the discovery of pharmaceutical value genes in H. nipponia, and also provide reference for other medicinal leeches.