Iodine binding and peroxidase activity in the endostyle of Salpa fusiformis, Thalia democratica, Dolioletta gegenbauri and Doliolum nationalis (Tunicata, Thaliacea)

Abstract

The protothyroid region in the endostyles of four species of tunicates was examined by means of autoradiography and cytochemistry, at both the light and electron-microscopic levels. To reveal the primary binding site for iodine, autoradiography was carried out on endostylar tissue from animals that had been incubated with high activity 125I over a short period of time. The specific iodine binding enzyme, a peroxidase, was traced by its reaction with DAB. In accordance with previous findings, the iodine-binding cells proved to be the same as those containing the peroxidase. There were also strong indications of a secondary uptake of iodinated compounds and subsequent release into the body fluid. Together with the ultrastructural features, the data provided strong evidence indicating that these cells constitute a protothyroid region, which partly functions as an endocrine organ, possibly homologous with the vertebrate thyroid gland. Since the number of zones varied between the species, the numeration of the protothyroid region also varied. However, in all the examined endostyles, the protothyroid region was seen to be situated dorsolaterally to the glandular regions of the endostyle concerned with food capture.

Thyroglobulin: A Master Regulator of Follicular Function via Transcriptional Suppression of Thyroid Specific Genes.

“…In the thyroid, the follicular lumen, not the follicular cell is believed to the primary source of thyroid hormones secreted into the blood stream; the follicle is the source, the cells surrounding the follicle the individual processing agents. In some sea fish, such as lamprey, thyroglobulin (TG) and thyroid hormones are synthesized, stored, and secreted by specialized cells in the endostyle, and there is no follicular structure [5,36]. A large follicular space appears, therefore, to be required by land-based animals in order to efficiently utilize and store the essential component of the thyroid hormones, i.e.…”

Restricted expression of NADPH oxidase/peroxidase gene (Duox) in zone VII of the ascidian endostyle

“…CiTPO and Ci-Duox expression, together with the iodine-binding and catalytic activities of TPO, are however excluded from the ventralmost part of zone VII, suggesting a different molecular background of the various regions within zone VII, with only its dorsal part being homologous to the thyroid. This topological relationship of thyroidal features might be conserved among urochordates as summarized by Fredriksson et al (1988). Furthermore, the expression of Ci-Duox and CiTPO have not been observed in the dorsal and ventral ends of zone VII, and Ci-Duox expression is shifted dorsally compared with the expression domain of CiTPO (this study; Ogasawara et al 1999), HrTPO (Ogasawara et al 1999), and Ci-FoxE, which is an ortholog of the mammalian gene thyroid transcription factor-2 (TTF-2; Ogasawara and Satou 2003).…”

Ultrastructural studies of cilia formation during thyroid gland differentiation in grass snake embryos

“…The endostyle consists of several kinds of cells and some of them have an iodine-concentrating activity (Fujita and Nanba, 1971;Thorpe et al, 1972;Dunn, 1974;Wright et al, 1980). These iodine-binding cells of the endostyle seem to produce thyroglobulin and partly share the same enzymatic machinery as the thyroid gland of vertebrate species (Fujita and Honma, 1969;Fujita, 1972;Fujita and Sawano, 1979;Suzuki and Kondo, 1973;Fredriksson et al, 1985Fredriksson et al, , 1988. Moreover, during evolution iodine-binding cells originated from the endostyle, lost their multiciliated character and occasionally have one, two or five cilia per cell in the thyroid of vertebrate species, although these cilia are found mainly in the developmental period (Nunez and Gershon, 1976;Martin et al, 1988).…”