Abstract:The outstanding characteristics of the marine invertebrate chordates, ascidians, are a sessile adult stage and cellulose production. These characteristics are not seen in other chordate groups. Molecular studies have suggested that these two characteristics are tightly linked. Ascidians possess the gene encoding cellulose synthase in their genomes. The disruption of the cellulose synthase gene results in abnormal metamorphosis and failure in adhesion, suggesting that cellulose is necessary for starting and con… Show more
“…They are in fact the only animals capable of synthesizing cellulose, thanks to a single horizontal gene transfer event that introduced the Cellulose synthase ( celA ) gene from some ancient prokaryote into the genome of the ancestral tunicate [204, 229, 282]. It is possible that the newly acquired ability of the epidermis to synthesize a protective mantle allowed tunicates to eschew the mobility or reclusiveness of their presumed vermiform ancestors [281]. Fig.…”
For more than a century, studies on tunicate muscle formation have revealed many principles of cell fate specification, gene regulation, morphogenesis, and evolution. Here, we review the key studies that have probed the development of all the various muscle cell types in a wide variety of tunicate species. We seize this occasion to explore the implications and questions raised by these findings in the broader context of muscle evolution in chordates.
“…They are in fact the only animals capable of synthesizing cellulose, thanks to a single horizontal gene transfer event that introduced the Cellulose synthase ( celA ) gene from some ancient prokaryote into the genome of the ancestral tunicate [204, 229, 282]. It is possible that the newly acquired ability of the epidermis to synthesize a protective mantle allowed tunicates to eschew the mobility or reclusiveness of their presumed vermiform ancestors [281]. Fig.…”
For more than a century, studies on tunicate muscle formation have revealed many principles of cell fate specification, gene regulation, morphogenesis, and evolution. Here, we review the key studies that have probed the development of all the various muscle cell types in a wide variety of tunicate species. We seize this occasion to explore the implications and questions raised by these findings in the broader context of muscle evolution in chordates.
“…Cellulose is contained in the cell wall of plants with lignin and is thought to be the most abundant polysaccharide from all the organisms on earth. It is also produced by bacteria [13], but not by animals other than ascidians [14]. It is used as biomaterials such as dialysis membranes and a scaffold in tissue engineering [15].…”
Biopolymers, including extracellular matrix proteins and polysaccharides, are used as substrates for cell culture and scaffolds in tissue engineering. Ionizing radiation, for example with gamma rays or electron beams, is used to sterilize materials and to modify the physical and chemical properties of materials. The principles of the effect of ionizing radiation on biopolymers are discussed in this review article. Among the types of ionizing radiation, gamma rays and electron beams are widely used to sterilize biomaterials and construct medical devices. Water molecules are split by irradiation with ionizing radiation to give hydrated electrons, proton radicals and hydroxyl radicals. These reactive molecular species react with polymer chains to provoke scission or crosslinking reactions. Both the scission and crosslinking of the polymer chains can occur, depending on the types of polymer and irradiation conditions. Sterilization of materials is necessary if they are used in medical devices and implants. The advantages and disadvantages of ionizing radiation in comparison with other methods of sterilization are also discussed. Irradiations with strong gamma rays on the three types of biopolymers-Type I collagen, wool keratin and alginate-are described as examples of biopolymers. Ionizing radiation is a very useful tool for sterilizing materials and constructing medical devices, but it is important that we know its merits and demerits, as well as the limitations, safety and risks, of its applications.
“…Presumably, this ancestral chordate pattern was also present in the common ancestor of tunicates and vertebrates, but disappeared during tunicate evolution. Tunicates have lost all trace of a collagenous dermis, probably as a consequence of acquiring bacterial cellulose synthase through horizontal gene transfer (Sasakura, 2018) and evolving cellulose skeletons for body support-intraepidermally in appendicularians and supraepidermally in ascidians (Hirose et al, 2011).…”
Section: A Dense Peripheral Layer Of Dermis With Fenestrae May Be Ancestral In Chordatesmentioning
Serial blockface scanning electron microscopy (SBSEM) is used to describe the sensory peripheral nervous system (PNS) in the tail of a cephalochordate, Asymmetron lucayanum. The reconstructed region extends from the tail tip to the origin of the most posterior peripheral nerves from the dorsal nerve cord. As peripheral nerves ramify within the dermis, all the nuclei along their course belong to glial cells. Invaginations in the glial cell cytoplasm house the neurites, an association reminiscent of the nonmyelinated Schwann cells of vertebrates. Peripheral nerves pass from the dermis to the epidermis via small fenestrae in the sub-epidermal collagen fibril layer; most nerves exit abruptly, but a few run obliquely within the collagen fibril layer for many micrometers before exiting. Within the epidermis, each nerve begins ramifying repeatedly, but the branches are too small to be followed to their tips with SBSEM at low magnification (previous studies on other cephalochordates indicate that the branches end freely or in association with epidermal sensory cells). In Asymmetron, two morphological kinds of sensory cells are scattered in the epidermis, usually singly, but sometimes in pairs, evidently the recent progeny of a single precursor cell. The discussion considers the evolution of the sensory PNS in the phylum Chordata. In cephalochordates, Retzius bipolar neurons with intramedullary perikarya likely correspond to the Rohon-Beard cells of vertebrates. However, extramedullary neurons originating from ventral epidermis in cephalochordates (and presumably in ancestral chordates) contrast with vertebrate sensory neurons, which arise from placodes and neural crest.
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