Demeuldre Mélanie, Hennebert Elise, Bonneel Marie, Lengerer Birgit, Van Dyck Séverine, Wattiez Ruddy, Ladurner Peter, Flammang Patrick
University of Mons, Research Institute for Biosciences, Biology of Marine Organisms and Biomimetics, Mons 7000, Belgium.
University of Mons, Research Institute for Biosciences, Laboratory of Cell Biology, Mons 7000, Belgium.
J Exp Biol. 2017 Jun 1;220(Pt 11):2108-2119. doi: 10.1242/jeb.145706. Epub 2017 Apr 3.
Despite their soft body and slow motion, sea cucumbers present a low predation rate, reflecting the presence of efficient defence systems. For instance, members of the family Holothuriidae rely on Cuvierian tubules for their defence. These tubules are normally stored in the posterior coelomic cavity of the animal, but when the sea cucumber is threatened by a potential predator, they are expelled through the cloacal aperture, elongate, become sticky and entangle and immobilise the predator in a matter of seconds. The mechanical properties (extensibility, tensile strength, stiffness and toughness) of quiescent (i.e. in the body cavity) and elongated (i.e. after expulsion) Cuvierian tubules were investigated in the species using traction tests. Important mechanical differences were measured between the two types of tubules, reflecting adaptability to their operating mode: to ease elongation, quiescent tubules present a low resistance to extension, while elongated tubules present a high toughness to resist tractions generated by the predator. We demonstrate that a mutable collagenous tissue (MCT) is involved in the functioning of these organs: (1) some mechanical properties of Cuvierian tubules are modified by incubation in a cell-disrupting solution; (2) the connective tissue layer encloses juxtaligamental-like cells, a cell type present in all MCTs; and (3) tensilin, a MCT stiffening protein, was localised inside these cells. Cuvierian tubules thus appear to enclose a new type of MCT which shows irreversible stiffening.
尽管海参身体柔软且行动缓慢，但它们的被捕食率很低，这反映出其拥有高效的防御系统。例如，海参科的成员依靠居维叶氏管进行防御。这些管子通常储存在动物的后体腔中，但当海参受到潜在捕食者的威胁时，它们会通过泄殖腔孔被排出，伸长，变得粘稠，并在几秒钟内缠住捕食者并使其无法动弹。利用拉伸试验研究了静止状态（即在体腔内）和伸长状态（即排出后）的居维叶氏管的力学性能（伸展性、拉伸强度、刚度和韧性）。在这两种类型的管子之间测量到了重要的力学差异，这反映了它们对其运作模式的适应性：为便于伸长，静止的管子对伸展的阻力较低，而伸长的管子则具有较高的韧性以抵抗捕食者产生的拉力。我们证明，一种可变胶原组织（MCT）参与了这些器官的功能：（1）居维叶氏管的一些力学性能通过在细胞破碎溶液中孵育而改变；（2）结缔组织层包围着类韧带样细胞，这是所有MCT中都存在的一种细胞类型；（3）张力蛋白，一种MCT硬化蛋白，定位于这些细胞内部。因此，居维叶氏管似乎包围着一种新型的MCT，它表现出不可逆的硬化。
