Background: Even though several studies highlighted the role of maternal thyroid hormones (THs) during embryo-fetal development, direct evidence of their interaction with embryonic thyroid receptors (TRs) is still lacking. Design: We generated a transgenic mouse model ubiquitously expressing a reporter gene tracing TH action during development. We engineered a construct (TRE2x) containing two TH-responsive elements controlling the expression of the LacZ reporter gene, which encodes beta-galactosidase (beta-gal). The specificity of the TRE2x activation by TH was evaluated in NIH3T3 cells by cotransfecting TRE2x along with TRs, retinoic or estrogen receptors in the presence of their specific ligands. TRE2x transgene was microinjected into the zygotes, implanted in pseudopregnant BDF1 mice, and transgenic mouse models were developed. beta-gal expression was assayed in tissue sections of transgenic mouse embryos at different stages of development. Results:In vitro, TRE2x transactivation was observed only following physiological T3 stimulation, mediated exclusively by TRs. In vivo, beta-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 TRE2x transgenic embryos, while the fetal thyroid function (FTF) was still inactive. Immunohistochemistry for TRs essentially colocalized with beta-gal staining. No beta-gal staining was detected in embryos of hypothyroid transgenic mice. Importantly, treatment with T3 in hypothyroid TRE2x transgenic mice rescued beta-gal expression. Conclusions: 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 endpoint assays for new molecules affecting THs action.
Maternal thyroid hormones are transcriptionally active during embryo-fetal development: results from a novel transgenic mouse model
MUZZI, PATRIZIA;VERCELLI, Alessandro;
2010-01-01
Abstract
Background: Even though several studies highlighted the role of maternal thyroid hormones (THs) during embryo-fetal development, direct evidence of their interaction with embryonic thyroid receptors (TRs) is still lacking. Design: We generated a transgenic mouse model ubiquitously expressing a reporter gene tracing TH action during development. We engineered a construct (TRE2x) containing two TH-responsive elements controlling the expression of the LacZ reporter gene, which encodes beta-galactosidase (beta-gal). The specificity of the TRE2x activation by TH was evaluated in NIH3T3 cells by cotransfecting TRE2x along with TRs, retinoic or estrogen receptors in the presence of their specific ligands. TRE2x transgene was microinjected into the zygotes, implanted in pseudopregnant BDF1 mice, and transgenic mouse models were developed. beta-gal expression was assayed in tissue sections of transgenic mouse embryos at different stages of development. Results:In vitro, TRE2x transactivation was observed only following physiological T3 stimulation, mediated exclusively by TRs. In vivo, beta-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 TRE2x transgenic embryos, while the fetal thyroid function (FTF) was still inactive. Immunohistochemistry for TRs essentially colocalized with beta-gal staining. No beta-gal staining was detected in embryos of hypothyroid transgenic mice. Importantly, treatment with T3 in hypothyroid TRE2x transgenic mice rescued beta-gal expression. Conclusions: 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 endpoint assays for new molecules affecting THs action.
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