Maternal thyroid hormones are transcriptionally active during embryo-foetal development: results from a novel transgenic mouse model.
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.
Endocrinology Unit, Molecular Endocrinology and Endocrine Cancers laboratory, Department of Internal Medicine, Medical School A. Gemelli, Catholic University, Roma, Italy.
Carmelo
C
Nucera
Patrizia
P
Muzzi
Cecilia
C
Tiveron
Antonella
A
Farsetti
Federico
F
La Regina
Benedetta
B
Foglio
Shou-Ching
SC
Shih
Fabiola
F
Moretti
Linda
L
Della Pietra
Francesca
F
Mancini
Ada
A
Sacchi
Francesco
F
Trimarchi
Alessandro
A
Vercelli
Alfredo
A
Pontecorvi
D000818:Animals; D002490:Central Nervous System / Q000196:embryology / Q000378:metabolism; D047108:Embryonic Development; D005260:Female; D018507:Gene Expression Regulation, Developmental; D015971:Gene Expression Regulation, Enzymologic; D017930:Genes, Reporter; D005818:Genetic Engineering; D007150:Immunohistochemistry; D007763:Lac Operon; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008811:Mice, Inbred DBA; D008822:Mice, Transgenic; D011247:Pregnancy; D011401:Promoter Regions, Genetic; D013963:Thyroid Hormones / Q000235:genetics* / Q000378:metabolism; D015533:Transcriptional Activation; D019076:Transgenes; D001616:beta-Galactosidase / Q000235:genetics / Q000378:metabolism
D013963:Thyroid Hormones; D001616:beta-Galactosidase