Quantitative Investigation on the Anterior Pituitary-Thyroid Mechanism During Frog Metamorphosis

Expression of sodium-iodide symporter mRNA in the thyroid gland of Xenopus laevis tadpoles: developmental expression, effects of antithyroidal compounds, and regulation by TSH

“…During spontaneous development, the level of NIS mRNA expression in thyroid glands of X. laevis tadpoles showed distinct changes. The observation of weak mRNA expression of NIS at premetamorphic stages is in accordance with earlier studies that reported low rates of thyroidal iodide uptake in the premetamorphic amphibian thyroid gland (Saxen et al 1957, Regard 1978. Furthermore, the increase in NIS mRNA expression observed during prometamorphosis to peak expression levels at early climax stages followed by a distinct decline towards the end of metamorphosis correlates well with developmental profiles reported for thyroidal iodide uptake (Saxen et al 1957, Regard 1978 and TH levels in X. laevis tadpoles (Leloup & Buscaglia 1977, Krain & Denver 2004).…”

“…The observation of weak mRNA expression of NIS at premetamorphic stages is in accordance with earlier studies that reported low rates of thyroidal iodide uptake in the premetamorphic amphibian thyroid gland (Saxen et al 1957, Regard 1978. Furthermore, the increase in NIS mRNA expression observed during prometamorphosis to peak expression levels at early climax stages followed by a distinct decline towards the end of metamorphosis correlates well with developmental profiles reported for thyroidal iodide uptake (Saxen et al 1957, Regard 1978 and TH levels in X. laevis tadpoles (Leloup & Buscaglia 1977, Krain & Denver 2004). In addition, our own morphometric measurements of follicular cell height, considered as a histological marker of thyroid follicular cell activity (Kalisnik 1972), suggest a relationship between NIS mRNA expression and thyroid follicular cell activity during metamorphosis.…”

“…of NIS mRNA and not the functional protein, our data strongly suggest that the increases in thyroidal iodide uptake during metamorphic development, as observed in previous studies (Saxen et al 1957, Regard 1978, are mediated at least in part by increased transcription of the NIS gene. TSH is the primary hormonal regulator of thyroid gland function and mammalian studies have shown that most effects of TSH are mediated by modulation of thyroid-specific gene expression (Vassart & Dumont 1992, Yamazaki et al 2003.…”

Beyond early development: Xenopus as an emerging model for the study of regenerative mechanisms

“…However it should be noted that this regeneration of the lens in juvenile frogs apparently does not involve transdifferentiation from the cornea or other eye tissues and instead it is thought that the regenerated lens arises from the remaining lens capsule as in mammals. Dent notes that circulating protein bound iodine levels rise sharply at st. 57-58 and decline at the time hypomorphic spikes are formed (Saxen et al, 1957;Dent, 1962) cently, it has also become possible to chemically alter specific molecular pathways by using small molecule inhibitors (so-called "chemical genetics," Section 2.1 and Table 1). While specificity can be an issue with this approach and must be determined for each new compound, molecules are usually added directly to the tadpoles' water, making for a simple assay.…”

Ultrastructural and Cytochemical Studies on the Thyroid Gland of Normal Metamorphosing Frogs (<i>Rana japonica</i> Guenther)

“…Using radio-iodine, thyroid activity in relation to metamorphosis has been studied by a number of workers (GORBMAN and EVANS 1941;SAXEN et al, 1957;KAYE, 1961). They have shown that the thyroid activity at this period is very low.…”