Comparative transcriptomic analysis reveals the mechanism of leech environmental adaptation.

The medicinal leeches have been widely utilized in medical procedures for thousands of years. Recently, there were more and more transcriptomes of leech published online including the medicinal leech (Hirudo medicinalis) and some other leeches. However, leech's genetic backgrounds are still largely unknown. In this report, transcriptomes of three phylogenetically close leeches (Poecilobdella javanica, Whitmania pigra, and Haemadipsa cavatuses) were established by RNA-seq technique for studying their genetic mechanisms of environmental adaption. Over 110 million high-quality reads were generated and assembled into unique transcriptome (reads = 200 bp). 27,138 out of de novo assembled transcripts (41.77%) were assigned to one or more GO terms. Additionally, the transcripts were detected in 217 predicted KEGG pathways. The enriched genes were involved in protein metabolism, GPCRs and pathogen-resistant pathways. The results showed that the great variations existed in gene expression of olfactory transduction pathway among three leech species. The comparisons of leech species hinted at the underlying mechanism of leeches adapting well in various environments. Our study will provide useful rationales for future studies of leeches and other annelid species.