The Distribution and significance of organically bound iodine in the ascidianCiona intestinalisLinnaeus

Abstract

Some features of the organization of the endostyle of Ciona intestinalis are described. Autoradiographs show that bound iodine is present in a limited area of the epithelium (zone 7), where it is associated with characteristic secretory inclusions which are found only in this zone. These are regarded as providing the molecular basis for the iodination process, and are termed 'thyroidal granules', since they resemble in certain properties the similarly named granules of the endostyle of the ammocoete; it is concluded that they are homologous with these and, through them, with thyroid colloid. Their existence provides evidence that the iodination process is a product of biochemical specialization, and implies that it results in the formation of an hormonal secretion. It is concluded from the distribution of bound iodine over the pharyngeal epithelium and in the food cords that this iodinated secretion is carried in the latter into the intestine. Bound iodine is also present in the cuticle of the test; it is suggested that this may differ from the situation in the endostyle in being a consequence of the iodination of a skeletal protein secretion such as is known to occur in many invertebrates. Prior immersion of the animals in thiouracil solution largely eliminates bound radio-iodine from all of the sites mentioned, although a little may sometimes be detectable in the food cords and cuticle. The results are discussed in the light of recent work on Amphioxus and the ammocoete larva, and attention is drawn to their bearing on current views on the relationship between vertebrates and protochordates.

Ciona intestinalis peroxinectin is a novel component of the peroxidase–cyclooxygenase gene superfamily upregulated by LPS

“…The morphogenesis of this gland, that originates from the embryonic pharyngeal epithelium, supports the homology. In addition, endostyle incorporates iodine (Barrington, 1957(Barrington, , 1958Salvatore, 1969), and the expression of homolog thyroidspecific developmental genes during endostyle development has been reported (McCauley and Bronner-Fraser, 2002; Ogasawara, 2000; Ogasawara and Satoh, 1998; Ogasawara et al, 2001; Venkatesh et al, 1999). The zones 7, 8 and 9 of the C. intestinalis endostyle have been retained the endostyle regions homologs to the vertebrate thyroid (Ogasawara and Satoh, 1998), disclose peroxidase activity (Fujita and Sawano, 1979;Kobayashi et al, 1983), and a specific TPO has been identified in the zone 7 (Ogosawara et al, 1999).…”

The Localization of Organically Bound Iodine in the Endostyle of Amphioxus

“…Such are also to be found in the food cord in the dorsal groove, into which, as is well known, material secreted by the endostyle and gill bars is swept in consequence of the action of the pharyngeal ciliation, while the food cords in the mid-gut and intestine also give strong images. It is always to be remembered that food organisms themselves may bind iodine and contribute to such images (Barrington, 1957), but it seems wholly improbable that this could account for all of the latter; I agree, therefore, with Thomas (1956), who noted similar images in his own preparations, that the iodinated secretion of the endostyle is ultimately incorporated into the food cords.…”

“…At the base of the endostylar groove is a group of cells, here termed' zone 1" which closely resemble the correspondingly placed zone 1 cells of Ciona (Barrington, 1957). They possess slender and densely staining nuclei, long cilia, and a conspicuously striated cell border.…”

Evolution of the thyroid: Anterior–posterior regionalization of theOikopleuraendostyle revealed byOtx,Pax2/5/8, andHox1expression

“…This homology, originally based on the reorganization of the larval endostyle into the adult thyroid in lampreys (Muller, 1873), is supported by iodine binding, peroxidase activity, thyroglobulin, and calcitonin-like cells both in endostyles and in thyroids (Gorbman and Creaser, 1943;Barrington, 1957;Thorpe et al, 1972;Thorndyke, 1978;Thorndyke and Probert, 1979;Kobayashi et al, 1983;Fredriksson et al, 1985Fredriksson et al, , 1988.…”