Varying effects of thyrotropin on fetal
thyroid development and function
(March 2003)
The background of the study. The
thyroid gland develops as a thickening of the floor of the pharynx
that then migrates down the neck and divides into two lobes. In
mice, the tissue acquires thyroid functions only after migration
is complete (embryonic day 13). In this study, the development of
the thyroid gland was studied in mice with genetic defects in thyrotropin
(TSH) and the receptor for TSH.
How the study was done. Thyroid
structure and the appearance of the sodium-iodide transporter, thyroglobulin,
and thyroid peroxidase-all needed for thyroid hormone production-were
studied at various stages of development in five groups of mice.
The abnormal groups included mice with complete TSH deficiency,
mice with an abnormal TSH receptor that does not bind TSH well,
and mice with no TSH receptors. In normal mice, iodide-transporting
molecules can be detected at embryonic day 16, thyroglobulin at
day 14.5, and thyroid peroxidase at day 16.
The results of the study. At embryonic
day 17, the size and microscopic structure of the thyroid gland
was similar in the mice with no TSH, the mice with decreased or
no TSH receptors, and normal mice. In contrast, at postnatal age
2 months, the thyroid gland was smaller in the mice with no TSH
or no TSH receptors than it was in normal mice.
At embryonic day 17, the thyroglobulin content was only slightly
lower in the mice with no TSH or decreased TSH receptors, as compared
with normal mice. In contrast, the content of iodide transporters
and thyroid peroxidase was markedly lower or undetectable in the
three groups of abnormal mice.
The conclusions of the study. During
fetal life in mice, TSH and TSH receptors are not important for
thyroid growth and thyroglobulin production, but they are important
for thyroid iodide transport and thyroid peroxidase.
The original article. Postiglione
MP, Parlato R, Rodriguez-Mallon A, Rosica A, Mithbaokar P, Maresca
M, Marians RC, Davies TF, Zannini MS, De Felice M, Di Lauro R. Role
of the thyroid-stimulating hormone receptor signaling in development
and differentiation of the thyroid gland. Proc Soc Natl Acad Sci
U S A 2002;99:15462-7.
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