Ties that bind

In his "Biomechanics" column on the mutable collagenous tissue (MCT) of sea cucumbers and other echinoderms ["Catch and Release," 11/03], Adam Summers remarks that the molecules thought to be responsible for rapidly changing the mechanical properties of MCT "have not been well characterized." But that is only partly true. Jennifer P. Tipper and colleagues recently published the peptide sequence of a stiffening factor called tensilin, obtained from sea cucumber dermis (Matrix Biology 21:625-35, 2002). This protein resembles the molecules in a group known as tissue inhibitors of metalloproteinases, or TIMPs. Metalloproteinases are enzymes that break down connective tissue, and TIMPs play an important role in counteracting their activities.

It is fascinating that a TIMP-like molecule should act as a stiffener in echinoderm MCT. In mammals, too, a TIMP known as TIMP-3 binds strongly to connective tissue components. The properties of tensilin suggest that the mechanism underpinning the mutability of echinoderms evolved from a biochemical system whose original role was to degrade connective tissue. It is also noteworthy that MCT may not be unique to echinoderms. My research collaborators and I have found that the stiffness of the connective tissue in a marine sponge may also be under physiological control.

Iain C. Wilkie

Glasgow, Caledonian University

Glasgow, Scotland

Natural History's e-mail address is nhmag@natural historymag.com

COPYRIGHT 2004 Natural History Magazine, Inc.
COPYRIGHT 2008 Gale, Cengage Learning