The Mutable Collagenous Tissue of Echinoderms: From Biology to Biomedical Applications

Abstract

The mutable collagenous tissue (MCT) of echinoderms (starfish, sea-urchins and their close relations) has the capacity to drastically alter its mechanical properties within a timescale of seconds under the control of the nervous system. MCT is of central importance to the biology of echinoderms: postural fixation of the body or its appendages depends on passive MCT stiffening and all autotomy (defensive self-detachment) mechanisms involve irreversible MCT destabilisation. This chapter reviews research on the biology and biomedical applications of MCT. It focuses on recent advances in knowledge of its organisation, biomechanics, molecular mechanisms of tensile change and neural control, and demonstrates that MCT has attracted interest as a source of constituents for the construction of novel materials with potential biomedical applications and as a source of inspiration for the design of entirely artificial materials with adaptable and controllable mechanical properties.

EchinoDB: an update to the web-based application for genomic and transcriptomic data on echinoderms

“…Another echinoderm-specific phenomenon is the capacity of the connective tissue structures to rapidly change their tensile strength under the control of the central nervous system [ 5 , 41 , 42 ]. A subset of neurosecretory cells is thought to release proteins that can either stiffen or soften the extracellular collagenous matrix.…”

“…To demonstrate the practical utility of the new version of EchinoDB [ 18 ] and its associated resources - OphiuroidDB [ 22 ] and EchinoidDB [ 23 ] – we illustrate how EchinoDB is used in retrieving key components of the Notch and Wnt signaling pathways, that are crucial for tissue regeneration in echinoderms [ 16 , 28 – 32 ]. In addition, we describe the use of SequenceServer (BLAST tool) [ 27 , 33 , 26 ] integrated within EchinoDB to find the putative homologs of the skeleton matrix proteins [ 4 , 34 – 37 ] and tensilin (a protein that controls tensile strength of mutable collagenous tissues) [ 5 , 38 – 40 , 41 , 42 ], previously reported in sea urchins (Echinodermata:Echinoidea) and sea cucumbers (Echinodermata: Holothuroidea).…”

“…It contains five extant classes: Asteroidea, Ophiuroidea, Holothuroidea, Echinoidea, and Crinoidea [1]. Echinoderms share a number of unique characteristics such as: pentaradial body symmetry (or modifications thereof ) in adults, a skeleton composed of numerous ossicles formed of stereom (a calcium carbonate material), a water-vascular system, and a mutable collagenous tissue [2][3][4][5]. However, the most astonishing feature of echinoderms is their capacity to regenerate complex internal organs following injury or autotomy [6][7][8][9][10][11][12][13].…”

Flexible sutures reduce bending moments in shells: from the echinoid test to tessellated shell structures

“…Considering the sutural collagen bundles, it is also important to emphasize that, apart from rare exceptions, the vast majority of connective tissues in living echinoids and in all the other echinoderms consist of peculiar collagenous tissues, called mutable collagenous tissues (MCT), characterized by unique mechanical behaviour [ 52 , 53 ]: in fact, they can modulate their passive mechanical properties (tensile strength, stiffness and viscosity) passing from a rigid state to a semi-flexible or to an even very pliant condition according to the functional needs and under direct neural control [ 52 , 53 ]. MCTs are ubiquitous in all extant echinoderms most of all in the form of dermal connective tissue in the body wall, articular ligaments interconnecting skeletal components and tendons linking muscles to skeletal elements [ 52 , 53 ]: in all these cases, MCTs present analogous functional roles as dermis, ligaments and tendons in vertebrates, but their mechanical properties do change in an exceptionally rapid (less than 1 s) and drastic way (up to two orders of magnitude, e.g. in spines) [ 52 ].…”

“…In order to verify if the collagenous sutures of the echinoid test consisted of MCTs and were therefore subjected to dynamic mutability phenomena, preliminary tests with elevated K + concentrations (100 mM K + in seawater) were carried out; this treatment has been usually employed in biomechanical tests to neurally induce stiffening in MCTs [ 52 , 53 , 56 ]. For this reason, the sutural collagenous ligaments were tested in two experimental conditions: (i) normal filtered seawater; and (ii) seawater with 100 mM K + , which was expected to modify the mechanical state of MTCs [ 52 ].…”