Expression of enzymes involved in thyroid hormone metabolism during the early development of Xenopus tropicalis.
BACKGROUND
There are significant indications that amphibians require TH (thyroid hormones) prior to their involvement in the regulation of metamorphosis and before the development of a functional thyroid.


RESULTS
In order to investigate the potential role for TH in pre-metamorphic Xenopus tropicalis we have cloned cDNAs for, and analysed the expression of, TPO (thyroid peroxidase), 5'DII (type II iodothyronine deiodinase) and 5DIII (type III iodothyronine deiodinase), enzymes involved in TH metabolism. Zygotic expression of TPO was detected in neurula stage embryos. Expression was observed in the notochord and later in the thyroid. The notochord was also a common site of expression for 5'DII and 5DIII. Other sites of 5'DII expression are the otic vesicles, retina, liver, blood-forming region, branchial arches and brain. 5DIII is also expressed in the brain, retina, liver, developing pro-nephros, blood-forming region and branchial arches. Embryos exposed to the TPO inhibitor methimazole showed a distinctive dose-dependent phenotype of a crimped notochord and shortened axis, together with alterations in (125)I(-) uptake.


CONCLUSIONS
These data suggest a novel extrathyroidal role for TH during early development, and support the proposal that embryos require thyroid signalling for normal development prior to metamorphosis.
Tindall
Andrew J
AJ
Area 11, Department of Biology, University of York, York YO10 5YW, U.K.
Morris
Ian D
ID
Pownall
Mary E
ME
Isaacs
Harry V
HV
D000818:Animals; D019521:Body Patterning / Q000187:drug effects / Q000235:genetics; D001921:Brain / Q000166:cytology / Q000196:embryology / Q000378:metabolism; D018076:DNA, Complementary / Q000032:analysis / Q000235:genetics; D004625:Embryo, Nonmammalian / Q000196:embryology / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004798:Enzymes / Q000235:genetics*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000235:genetics*; D007453:Iodide Peroxidase / Q000037:antagonists & inhibitors / Q000235:genetics; D007814:Larva / Q000254:growth & development* / Q000378:metabolism; D009672:Notochord / Q000166:cytology / Q000196:embryology / Q000378:metabolism; D009928:Organ Specificity; D013961:Thyroid Gland / Q000166:cytology / Q000196:embryology / Q000378:metabolism; D013963:Thyroid Hormones / Q000096:biosynthesis*; D014781:Viscera / Q000166:cytology / Q000196:embryology / Q000378:metabolism; D014981:Xenopus / Q000196:embryology* / Q000378:metabolism; D000097564:Iodothyronine Deiodinase Type II
D018076:DNA, Complementary; D004791:Enzyme Inhibitors; D004798:Enzymes; D007453:Iodide Peroxidase; D013963:Thyroid Hormones; D000097564:Iodothyronine Deiodinase Type II; C117274:iodothyronine deiodinase type III