GISNe - Anatomia, Farmacologia e Medicina Legale

MATERNAL THYROID HORMONES ARE TRANSCRIPTIONALLY ACTIVE DURING
EMBRYONIC DEVELOPMENT: RESULTS FROM A TRANSGENIC MOUSE MODEL
Carmelo Nucera 1,4,6, , Patrizia Muzzi 2 , Cecilia Tiveron 3 , Antonella Farsetti 4,5 , Fabiola Moretti 4,5,
Linda Della Pietra 4 , Francesca Mancini 4 , Ada Sacchi 4 , Laura Tatangelo 3 , Andrea Giaccari 6 ,
Francesco Trimarchi 1 , Francesco Vermiglio 1 , Alessandro Vercelli 2 , Alfredo Pontecorvi 4,6
1 Sezione di Endocrinologia-Dipartimento Clinico-Sperimentale di Medicina e Farmacologia, University of Messina,
Messina (Italy). 2 Dipartimento di Anatomia, Farmacologia e Medicina Legale, University of Torino, Torino (Italy). 3 Centro
Telethon, Istituto Regina Elena, Roma (Italy). 4 Dipartimento di Oncologia Sperimentale, Istituto Regina Elena, Roma
(Italy). 5 Istituto di Neurobiologia e Medicina Molecolare, C.N.R. di Roma (Italy). 6 Istituto di Endocrinologia, Università
Cattolica del Sacro Cuore “A. Gemelli”, Roma (Italy).
Abstract
Even though several studies highlighted the role of maternal thyroid hormones (TH) during
development, direct evidence of their interaction with embryonic thyroid receptors (TRs) is still
lacking. To this end, we generated a transgenic mouse ubiquitously expressing a reporter gene tracing
TH action during embryo-fetal development. We engineered a construct (TRE2x) containing two THresponsive
elements controlling the expression of the LacZ reporter gene which encodes for betagalactosidase
(ß-gal). TRE2x specificity was evaluated in NIH3T3 cells by cotransfecting TRE2x along
with TRs and retinoic or estrogen receptors with their specific ligands. TRE2x transactivation was
observed only upon physiological T3 stimulation, mediated exclusively by TRs. TRE2x microinjected
zygotes were implanted into pseudopregnant BDF1 mice. Transient transgenic embryos were screened
both by ß-gal enzymatic activity assay and polymerase chain reaction (PCR). ß -gal staining, absent up
to embryonic day 9.5 (E9.5), was observed at E11.5-E12.5 until the onset of fetal thyroid function
(FTF) (E17.5) in several tissue primordia. Immunohistochemical TRs localization was essentially
overlapping with ß-gal staining. Interestingly, no ß-gal staining was detected in embryos of
hypothyroid transgenic mice. Our results provide the first in vivo direct evidence that during embryonic
life and before the onset of FTF, maternal TH are transcriptionally functional through the action of
embryonic TRs.