Active Movement of the Tunic in Halocynthia roretzi

Abstract

Halocynthia roretzi, a solitary ascidian, can swell and deflate its solid, leather-like tunic largely, but it is not clear whether the tunic deforms actively. Cellulose Iβ, which is predominant in higher plants, is also present in the tunic as a highly crystalline form. The elastic modulus of its whisker crystalline is considerably high. Substantial amounts of chitin sulfate-like, water-soluble polysaccharide were also present. These polysaccharides alone would barely cause tunic deformation. If the tunic's flexible deformation is self-controlled, it would have another element in addition to the polysaccharide, and it would be an ideal model for designing a novel material. The hypothesis of this study was that the H. roretzi tunic has a nervous system, myocytes, and elastic fibers controlling its flexible deformation. Using acetylcholine and touch as stimuli, the tunic samples were found to deform at acetylcholine concentrations ≥20 µM, indicating the existence of a nervous system, and to have mechanosensitivity. The Bodian, Klüver-Barrera, acetylcholinesterase, immunohistochemical (α-smooth muscle actin), and Elastica-Masson staining methods indicated the presence of a nervous system, myocytes, a region rich in α-smooth muscle actin, and elastic fibers, validating the hypothesis. The self-controlled system in the tunic is useful to understand the properties of the tunic and to design a novel actively deforming material.

Active Contraction in the Stable Mechanical Environment of the Tunic of the Ascidian, Halocynthia roretzi, a Polysaccharide-Based Tissue with Blood Circulatory System

“…Active deformation in the tunic due to various stimuli, such as neurotransmitter (acetylcholine) [9], mechanical stimuli [9,10], electrical stimuli [11], and α-chymotrypsin [11], whose substrate is the same as that secreted by the hemocytes of H. roretzi [12]. The nervous system in the tunic has been observed [9,13], which manages the active deformation of the tunic. Also, various secretions by hemocytes have been reported [12,[14][15][16][17][18][19][20], and thus, the condition of the tunic could be controlled by these hemocytes, which move around in the tunic because of its open circulatory system [21].…”

“…Because of its physiological activities, this tunic is not only a cover for the entire body but also comprises tissues with active functions [1,2]. The components of this tunic have been extensively reported, including cellulose Iβ [3][4][5], sulfated chitin [6,7], pseudokeratin [8], α-smooth muscle actin [9], F-actin [9], and elastic fiber [9]. Active deformation in the tunic due to various stimuli, such as neurotransmitter (acetylcholine) [9], mechanical stimuli [9,10], electrical stimuli [11], and α-chymotrypsin [11], whose substrate is the same as that secreted by the hemocytes of H. roretzi [12].…”

“…The components of this tunic have been extensively reported, including cellulose Iβ [3][4][5], sulfated chitin [6,7], pseudokeratin [8], α-smooth muscle actin [9], F-actin [9], and elastic fiber [9]. Active deformation in the tunic due to various stimuli, such as neurotransmitter (acetylcholine) [9], mechanical stimuli [9,10], electrical stimuli [11], and α-chymotrypsin [11], whose substrate is the same as that secreted by the hemocytes of H. roretzi [12]. The nervous system in the tunic has been observed [9,13], which manages the active deformation of the tunic.…”

“…Also, various secretions by hemocytes have been reported [12,[14][15][16][17][18][19][20], and thus, the condition of the tunic could be controlled by these hemocytes, which move around in the tunic because of its open circulatory system [21]. The tunic is composed of an outer region, a middle region, and an inner region: the outer region is the densest among these regions; the middle region is composed of laminar layers; and the inner region comprises loose layers [9]. Without the inner region and most of the middle region, the tunic could still respond to mechanical stimuli and actively deform [9].…”

“…The tunic is composed of an outer region, a middle region, and an inner region: the outer region is the densest among these regions; the middle region is composed of laminar layers; and the inner region comprises loose layers [9]. Without the inner region and most of the middle region, the tunic could still respond to mechanical stimuli and actively deform [9]. During the active deformation of the tunic, changes in mass, which are largely influenced by the influx and efflux of water, have been reported [22].…”