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Updated: Aug 21, 2026

An Ex vivo Culture System to Study Thyroid Development
08:33

An Ex vivo Culture System to Study Thyroid Development

Published on: June 6, 2014

Triiodothyronine rapidly decreases transcription of the thyrotropin subunit genes in thyrotropic tumor explants

M A Shupnik, E C Ridgway

    Endocrinology
    |November 1, 1985
    PubMed

    Insights

    The thyroid hormone T3 directly suppresses thyroid-stimulating hormone (TSH) beta and alpha-subunit mRNA synthesis in thyrotropes. This direct action occurs without requiring new protein synthesis, indicating T3

    Area of Science:

    • Endocrinology
    • Molecular Biology
    • Gene Regulation

    Background:

    • Thyroid hormone (T3) plays a crucial role in regulating thyroid-stimulating hormone (TSH) production.
    • The precise molecular mechanisms by which T3 affects TSH subunit gene expression are not fully elucidated.
    • Thyrotropic tumor cells provide a model system to study direct hormonal effects on TSH gene regulation.

    Purpose of the Study:

    • To investigate the direct impact of the thyroid hormone T3 on the synthesis of TSH beta and alpha-subunit mRNA.
    • To determine if protein synthesis is required for T3-mediated suppression of TSH subunit gene transcription.
    • To correlate T3's transcriptional effects with its nuclear receptor binding kinetics.

    Main Methods:

    • Treatment of TtT 97 thyrotropic tumor explants with T3.
    • Isolation of nuclei and in vitro RNA synthesis labeling with [alpha-32P]UTP.
    • Quantification of newly synthesized TSH beta and alpha-subunit mRNA via cDNA hybridization.
    • Assessment of cycloheximide's effect on T3-mediated gene regulation.

    Main Results:

    • T3 significantly decreased TSH beta and alpha-subunit mRNA synthesis rates in a time-dependent manner.
    • Suppression of mRNA synthesis by T3 correlated with T3 nuclear receptor binding.
    • Decreases in mRNA synthesis preceded changes in steady-state mRNA or protein levels.
    • Cycloheximide did not alter T3's suppressive effects on transcription or mRNA levels.

    Conclusions:

    • T3 directly suppresses TSH beta and alpha-subunit mRNA synthesis at the transcriptional level in thyrotropes.
    • Protein synthesis is not required for the immediate T3-induced downregulation of TSH subunit gene transcription.
    • T3 directly modulates TSH subunit gene expression, likely acting at the gene level.

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