Maternal thyroid hormones are transcriptionally active during embryo–foetal development: results from a novel transgenic mouse model

Abstract

Even though several studies highlighted the role of maternal thyroid hormones (THs) during embryo–foetal development, direct evidence of their interaction with embryonic thyroid receptors (TRs) is still lacking. We generated a transgenic mouse model ubiquitously expressing a reporter gene tracing TH action during development. We engineered a construct (TRE2×) containing two TH-responsive elements controlling the expression of the LacZ reporter gene, which encodes β-galactosidase (β-gal). The specificity of the TRE2× activation by TH was evaluated in NIH3T3 cells by cotransfecting TRE2× along with TRs, retinoic or oestrogen receptors in the presence of their specific ligands. TRE2× transgene was microinjected into the zygotes, implanted in pseudopregnant BDF1 (a first-generation (F1) hybrid from a cross of C57BL/6 female and a DBA/2 male) mice and transgenic mouse models were developed. β-gal expression was assayed in tissue sections of transgenic mouse embryos at different stages of development. In vitro, TRE2× transactivation was observed only following physiological T3 stimulation, mediated exclusively by TRs. In vivo, β-gal staining, absent until embryonic day 9.5–10.5 (E9.5–E10.5), was observed as early as E11.5–E12.5 in different primordia (i.e. central nervous system, sense organs, intestine, etc.) of the TRE2× transgenic embryos, while the foetal thyroid function (FTF) was still inactive. Immunohistochemistry for TRs essentially colocalized with β-gal staining. No β-gal staining was detected in embryos of hypothyroid transgenic mice. Importantly, treatment with T3 in hypothyroid TRE2× transgenic mice rescued β-gal expression. Our results provide in vivo direct evidence that during embryonic life and before the onset of FTF, maternal THs are transcriptionally active through the action of embryonic TRs. This model may have clinical relevance and may be employed to design end-point assays for new molecules affecting THs action.

Regulatory decisions on endocrine disrupting chemicals should be based on the principles of endocrinology

“…The expression profiles of the receptors change throughout development, therefore hormones can have actions in one tissue at one time, and no action in the same tissue at another time. For example, genetic reporter mice designed to show where thyroid hormone receptor is activated indicate that thyroid hormone action is required for the development of the metencephalic and diencephalic vesicles and the ganglia of the cranial nerves on embryonic day (E)11.5 [55]. One day later, thyroid hormone receptor is also expressed in the developing eye.…”

American Thyroid Association Guide to Investigating Thyroid Hormone Economy and Action in Rodent and Cell Models

“…Since at this time, fetal thyroid function in the mouse is still inactive, and these early signals may reflect maternal T 4 or T 3 activity. Early T 3 signaling was observed in the brain (i.e., diencephalic primordia, medulla oblongata) and sense organs primordia (otic vescicle, olfactory epithelium, retina), whereas at late stages (E15.5-E17.5) beta-gal expression was localized in other primordia (i.e., in the bones, follicular nerves of the vibrissae, as well as in the small intestine primordia, but also in the medulla oblongata) (468).…”

Expression of angiogenic switch, cachexia and inflammation factors at the crossroad in undifferentiated thyroid carcinoma with BRAF

“…Slides were rinsed with PBS between incubations. Sections were developed using 3,3-diaminobenzidine (Sigma Chemical Co.) as a substrate and were counterstained with Mayer’s hematoxylin [12] [31] [32]. The IHC markers immunoexpression was assessed semiquantitatively using the following scoring method: 0 (negative), 1+ (1–10% positive cells), 2+ (11–50% positive cells), and 3+ (more than 50% positive cells).…”