Wednesday, September 3, 2008

Leech Cocoons

In a series of papers, recently, Dan Shain (Rutgers University) and his colleagues have been carefully examining the structural and chemical properties of leech cocoons. As background, these cocoons are egg-cases that are secreted by the clitellum of leeches and they show some striking diversity. Brooding glossiphoniid leeches have a membraneous cocoon, erpobdellids and fish-leeches (below) cement their hardened cocoons to surfaces, and the medicinal leech cocoons (above) are pretty spongy looking. If you think about it, the material that goes into making these eggs cases must be pretty strange. First, whatever is secreted must adhere and polymerize quickly underwater and without any light or heat. Secondly, there's eveidence that leech cocoons are highly
resistant to denaturation or degredation; so much so that they seem to be showing up in Jurassic and Triassic deposits (e.g., Manum et al., 1991. Zoologica Scripta 20: 347-366; Jansson, et al. In Press, Early Jurassic leech cocoons from eastern Australia. Alcheringa). The work led by Shain has covered a variety of perspectives including the molecular composition of the proteins involved (one seems to belong to the same family as the factor Xa anticoagulants!), the structure of the cocoons and their biophysical properties.