In this study we investigated the presence and localization of thyroxine in Ciona intestinalis larvae and its involvement in metamorphosis. To date, the mechanisms regulating the metamorphosis of ascidians remain largely unknown. In vivo treatment of swimming larvae with exogenous L-thyroxine and thiourea, and in vitro experiments utilizing high performance liquid chromatography, radioimmunoassay, and immunoperoxidase staining demonstrate the presence of thyroxine at the larval stage. This suggests that this hormone may participate in the control of metamorphosis and thus play a different role from that observed in adults.
Particulate (sheep erythrocytes, ascidian oocytes, stromata, colloidal carbon) or soluble agents (bovine serum albumin or hemoglobin, hemocyanin) were injected in varying doses into the tunic oiCiona intestinalis. This ascidian reacted by producing a capsule and/or tissue injury. Statistical analysis suggests that the two phenomena are independent, probably related to the nature and dose of the irritant.Light histological observations showed granulocyte degranulation in the damaged tissue, suggesting that an acute inflammatory-like process is involved in the tunic reaction.
Larvae of Ascidia malaca, both before and after hatching, were treated with L-thyroxine solutions. The effect of the thyroid hormone was to induce the onset of metamorphosis and then to cause the rate at which body reorganization occurred to increase. In treated larvae the resorption of the tail occurred only few hours after hatching, and a beating heart appeared form 10 to 15 h earlier than in the control larvae. These results are discussed in the context of a probable relationship between the occurrence of a hormonal metamorphic factor and the button cells of the trunk.
Ciona intestinalis L. tunic architecture and cell distribution were investigated with the electron microscope. The observations showed that the ascidian covering is formed by a thin outer cuticle, a subcuticle of variable width and a large single layer of ground substance. “Large granule”, morula, phagocyte and granulocyte are the cellular types encountered; they appear mainly in highly vacuolated states and are distributed throughout the whole tunic. The “large granule” cells, however, are mainly seen in the cuticle layer and the morula cells appear mostly in the outer zone of the ground substance. The role of these cells in tunic construction, repair and regeneration as well as their scavenging function are discussed.
Chemical, histochemical and electron microscopic studies on the fibrous polysaccharide component of the test of Ciona intestinalis L. were made.The results showed cellulose-like fibres to be present in the cuticle layer and in the ground substance. Bundles of fibres varying in diameter from 80 to 600 nm interweave to form a conspicuous network. The bundle appears to be formed of flat fibres, 10-13 nm in width, while the fibre is composed of fibrils 3.5-5 nm; the rectangular cross section of fibres can be supposed. The probable rtile of this polysaccharide is discussed.
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