A pivotal genetic program controlled by thyroid hormone during the maturation of GABAergic neurons in mice

In mammals, brain development is critically dependent on proper thyroid hormone signaling, via the TRα1 nuclear receptor. However, the downstream mechanisms by which TRα1 impacts brain development are currently unknown, notably because this receptor is expressed ubiquitously from early stages of development. In order to better define the function of TRα1 in the developing brain, we used mouse genetics to induce the expression of a dominant-negative mutation of the receptor specifically in GABAergic neurons, the main inhibitory neurons in the brain, which were previously identified as sensitive to hypothyroidism. This triggered post-natal epileptic seizures, reflecting a profound impairment of GABAergic neuron maturation in different brain areas. Analysis of transcriptome and TRα1 cistrome also allowed us to identify a small set of genes, the transcription of which is upregulated by TRα1 in GABAergic neurons during post-natal maturation of the striatum and which probably play an important role during neurodevelopment. Thus, our results point to GABAergic neurons as direct targets of thyroid hormone during brain development and suggest that many defects seen in hypothyroid brains may be secondary to GABAergic neuron malfunction.