Insight into the role of thyroid hormone on neocortex development through global transcriptome analysis of primary cerebrocortical cells: Identification of genes regulated directly and indirectly by triiodothyronine in specific cell types

Thyroid hormones, thyroxine and triiodothyronine (T3) are crucial for cerebral cortex development acting through regulation of gene expression. To define the transcriptional program under T3 regulation we have performed RNA-Seq of T3-treated and untreated primary mouse cerebrocortical cells. The expression of 1,145 genes or 7.7% of expressed genes was changed upon T3 addition, of which 371 responded to T3 in the presence of cycloheximide indicating direct transcriptional regulation. The results were compared with available transcriptomic datasets of defined cellular types. In this way we could identify genomic targets of T3 in astrocytes and neurons, and in neuron subtypes, such as layer-specific neurons, and neurons expressing specific markers such as prepronociceptin, cholecystokinin, or cortistatin. T3 up-regulates mostly genes related to cell membrane events, such as G-protein signaling, neurotransmission, and ion transport, and down-regulates genes involved in nuclear events, such as cell division, M phase of cell cycle, and chromosome organization and segregation. Remarkably the transcriptomic changes induced by T3 sustain the transition from embryonic to adult patterns of gene expression. The results allowed us to define in molecular terms the elusive role of thyroid hormones on neocortical development. Overall design: Pregnant dams were euthanized on gestational day 17.5, and the fetuses were extracted and euthanized by decapitation. The cerebral cortices were dissected, disaggregated and finally the cells were suspended in culture medium. After 9 days incubation cells were incubated for 24 hours before adding T3 at a final concentration of 10 nM. The cells were harvested 24 hours later. Cells without T3 were incubated in parallel. Cerebral cortices from individual fetuses originated two replicas for the cell culture, one with T3 and another without T3. Number of samples: 6.

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Gil-Ibañez P, García-García F, Dopazo J, Bernal J, Morte B