New Clues about the Blood-Clotting Ability of Leeches

Leeches are blood-feeding organisms that have a suite of anticoagulant compounds they secrete from their salivary glands that prevent blood clotting. This allows them to maximize feeding time and blood volume. Leeches are still used in modern medicine, and knowledge about their anticoagulants is important in many ways, from rodent control to understanding host-parasite relationships. A recent study expands our knowledge about the diversity of anticoagulants in two families of leeches.
The authors of an article recently published in the Journal of Parasitology collected leeches from natural and aquarium settings in the United States and Canada. The researchers examined the physical characteristics of each leech to determine their species, dissected the leech salivary glands, extracted the RNA and sequenced the genomic material. Next, they identified the salivary gland components by comparing their sequences with those of other leeches and various animals.
The researchers identified the collected leeches as nine species from the Piscicolidae and Ozobranchidae families, which are composed of saltwater species that feed on fish and turtles, respectively. Despite the fact that these leeches have different host preferences, no differences were found in the diversity of anticoagulants. There was an average of 43 anticoagulants in each species, and the researchers identified several anticoagulants that didn’t match any sequences and others that had never before been linked to leeches. For example, they found sequences that matched ohanin, which is a protein found in king cobra venom. These results suggest that there is a possible connection between anticoagulants in leeches and snake venom and should be explored further.
Michael Tessler, one of the authors of this article, points out why this study is unique among the literature on anticoagulants: “What I believe makes this paper stand out is the broad scope. Our results highlight that looking at individual species is not a great proxy for family-level anticoagulant diversity and that studies need to take a broader look to fully understand what is going on.” Sampling many species and comparing sequences to a broad array of organisms, therefore, could help uncover new information.
The authors also constructed phylogenetic trees, diagrams that show evolutionary relationships, and concluded that leeches may have evolved to have anticoagulants that are beneficial to them. These new leech anticoagulant sequences not only aid in our understanding of the diversity of these compounds, but also provide clues about how leech evolution plays a role in the host-parasite relationship.
http://www.journalofparasitology.org/doi/full/10.1645/17-64