The Genome of Medicinal Leech (Whitmania pigra) for Exploration of Bioactive Ingredients

Abstract BackgroundLeeches are classic annelids that have a huge diversity and closely related to people, especially medicinal leeches. Medicinal leeches have been widely utilized in medicine based on the pharmacological activities of their bioactive ingredients. The discovery of bioactive ingredients is hindered heavily due to the lack of the genome of medicinal leeches.ResultsTo facilitate this discovery and the research of medicinal leeches, we reported the first genome of the medicinal leech (Whitmania pigra). The assembled genome size of W. pigra is 177 Mbp, close to the estimated genome. Approximately about 23% of the genome was repetitive. A total of 26,743 protein-coding genes were subsequently predicted. There are only 9799 (57%) orthologous genes between W. pigra and Helobdella robusta. And only 16% genes in W. pigra showed syntenic arrangement with H. robusta revealed by gene synteny analysis. Furthermore, W. pigra and H. robusta expanded different gene families enriched in the ‘calcium ion’ and ‘sodium ion’ related functions, respectively. By inspecting genome distribution and gene structure of hirudin, we identified a new hirudin gene g17108 (hirudin_2) with different cysteine pattern. At last, we systematically explored and compared the active substances in the genomes of two leeches. The results showed that W. pigra exceeds H. robusta in both kinds and gene number of active molecules.ConclusionsThis study reported the first genome of the medicinal leech (W. pigra), which provides an important genome resource and new insight into the exploration and development of bioactive molecules of medicinal leeches.