Thyroid hormones embryonic

Ahlgren SC, Wallace H, Bishop J, Neophytou C, Raff MC 1997 Effects of thyroid hormone on embryonic oligodendrocyte precursor cell development in vivo and in vitro. Mol Cell Neurosci 9 420-432... 

Walpita CN, Crawford AD, Janssens EDR, Van der Geyten S, Darras VM (2009) Type 2 iodothyronine deiodinase Is essential for thyroid hormone-dependent embryonic development and pigmentation in zebrafish. Endocrinology 150 530-539... 

Walpita CN, Van der Geyten S, Rurangwa E, Darras VM (2007) The effect of 3,5,3 -triiodothyronine supplementation on zebrafish (Danio rerio) embryonic development and expression of iodothyronine deiodinases and thyroid hormone receptors. Gen Comp Endocrinol 152 206-214... 

The thyroid hormone thyroxine (tetraiodo-thyronine, T4) and its active form triiodothyronine (T3) are derived from the amino acid tyrosine. The iodine atoms at positions 3 and 5 of the two phenol rings are characteristic of them. Post-translational synthesis of thyroxine takes place in the thyroid gland from tyrosine residues of the protein thyro-globulin, from which it is proteolytically cleaved before being released, iodothyronines are the only organic molecules in the animal organism that contain iodine. They increase the basal metabolic rate, partly by regulating mitochondrial ATP synthesis, in addition, they promote embryonic development. 

Thyroid hormone is essential for normal growth and development during embryonic life. Thyroid hormone deficiency during fetal and neonatal development results in mental retardation. There is slowing of physical and mental activity, as well as of cardiovascular, gastrointestinal, and neuromuscular function. Depression may result from untreated hypothyroidism. ... 

A foreign compound which may act in this way is the herbicide nitrofen (2,4-dichloro-4 -mtro diphenyl ether) which causes a variety of malformations lethal to the neonate. There is. no growth retardation or embryolethality at doses which are teratogenic, however (figure 6,18), and therefore this exhibits the first type of dose-response relationship (see above). The mechanism may involve the production of a metabolite which interferes with the thyroid hormone status. The metabolite, which results from reduction and hydroxylation of the parent compound, was detected in embryonic tissue and crossreacted with antibodies to tri-iodothyronine... 

Most hormones interacting with intracellular receptors exert their effects by controlling rates of transcription of specific genes. In this case, the hormone binds to a receptor and the complex migrates to the nucleus, where it interacts with specific DNA sites. Hormones in this class include steroids, thyroid hormones (see here), and the hormonal forms of vitamin D. In addition, retinoids, derived from retinoic acid (related to vitamin A), exert regulatory effects in embryonic development through interactions with intracellular receptors. 

A further analysis of the distribution of T3 receptors in rat cortical cells suggests a preferential localization in neurons [26,30]. A similar finding was reported in embryonic and neonatal chick brain [31]. Studies with pure cultures of neurons and astrocytes from embryonic and neonatal chick brain have confirmed the predominant localization of the receptors in neuronal nuclei [32,33]. It is clear that thyroid hormone receptors are not restricted to neuronal cells, but also appear in glial cells [34,35] suggesting that both cell types are potential targets for thyroid hormones. A direct effect of T3 on protein phosphorylation has indeed been demonstrated in neuronal and glial cells derived from rat cortex [36,37]. 

G. Shanker, N.R. Bhat and R.A. Pieringer. Investigations on myelina-tion in vitro thyroid hormone receptors in cultures of cells dissociated from embryonic mouse brain. Biosci. Rep. 1 289-297 (1981). 

Pure cultured astrocytes were prepared by a modification of the method of Booher and Sensenbrenner (32). Cerebral hemispheres from newborn Wistar rats were mechanically dissociated in Waymouth s medium supplemented with sodium pyruvate (110 mg/ml), antibiotics and 10 % heat-inactivated fetal calf serum. Cells from one brain were seeded in 6 Petri dishes (100 mm diameter) and the cultures were maintained in the serum containing medium for 21 days and then switched for 3 days either to a medium containing thyroid hormone depleted serum (33) or to a serum-free chemically defined medium. This consisted of Waymouth s medium supplemented with 5 pg/ml insulin and 0.5 Mg/ml fatty acid-free bovine serum albumin and antibiotics. Pure cultured astrocytes were also prepared from 14-day-old embryonic chick brain as described above (32). 

N.R. Bhat, L.L. Sarlieve, G. Subba Rao and R.A. Pieringer, Investigations on myelination in vitro. Regulation by thyroid hormone in cultures of dissociated brain cells from embryonic mice, J. Biol. Chem. 254 9342 (1979)-... 

G. Shanker, A.T. Campagnoni and R.A. Pieringer, Investigations on myelinogenesis in vitro developmental expression of myelin basic protein mRNA and its regulation by thyroid hormone in primary cerebral cell cultures from embryonic mice. J. Neurosci. Res. 17 220 (1987). 

These observations suggested that normal brain development requires the availability of both maternal and fetal thyroid hormones,a suggestion which is at variance with earlier reports (9) (14) (15) (16) that the placenta in many mammalian species is relatively impermeable to thyroid hormones and with the suggestion (17) (18) that early mammalian development takes place normally in the absence of thyroid homrones. The observations do agree however with a more recent report (19) that rat embryonic tissues are provided with T and T3 only four days after uterine implantation and well before the onset of fetal thyroid function at 17 days. y also supported by the work of Woods et al (20) who showed that T and T3, when injected into pregnant rats, entered the rat... 

Rey, F. Effects of maternal hypothyroidism on weight and thyroid hormone content of rat embryonic tissues,before and after onset of fetal thyroid function. Endocrinology 117 1890-1900 (1985). 

THYROID HORMONES IN EMBRYONIC TISSUES BEFORE ONSET OF FETAL THYROID FUNCTION... 

Work performed by Weiss and Novak 5 and by Sweney and Shapiroi strongly suggested the possibility that maternal thyroid hormones are available to the rat embryo before onset of fetal thyroid function, despite opinions to the contrary 1 . We decided to re-investigate this possibility by measuring T4 and T3 concentrations in embryonic and fetal tissues. We had developed specific and sensitive RIAs 18, and extensive extraction and purification... 

Shi Y-B, Fu L, Hasebe T, Ishizuya-Oka A (2007) Regulation of extracellular matrix remodeling and cell fate determination by matrix metalloproteinase stromelysin-3 during thyroid hormone-dependent post-embryonic development. Pharmacol Therapeut 116(3 ) 391-400. doi 10.1016/j. pharmthera.2007.07.005... 

Effects of ID on the conceptus. The fetal thyroid starts secreting thyroid hormones at 17.5-18 days of gestation (dg). Contrary to previous statements regarding the impermeability of the mammalian placenta to thyroid hormones, T4 and T3 are found in the early embryonic structures and... 

Thus, under conditions of severe and chronic ID the developing embryo is thyroid hormone deficient both before and after onset of its own thyroid lunction. Before thyroid function embryonic and fetal tissues are entirely dependent on the maternal iodothyronines for their supply of thyroid hormones. As a result of the maternal hypothyroxinemia, the T4 available to the developing LID embryo and fetus is very low. The supply of T3 becomes increasingly deficient. 

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