Abstract

The physiological and developmental effects of thyroid hormones are mainly due to the control of gene expression after interaction of T3 with the nuclear receptors. To understand the role of thyroid hormones on cerebral cortex development, knowledge of the genes regulated by T3 during specific stages of development is required. In our laboratory we previously identified genes regulated by T3 in primary cerebrocortical cells in culture. By comparing these data with transcriptomics of purified cell types from the developing cortex, the cellular targets of T3 can be identified. In addition, many of the genes regulated transcriptionally by T3 have defined roles in cortex development, from which the role of T3 can be derived. This review analyses the specific roles of T3-regulated genes in the different stages of cortex development within the physiological frame of the developmental changes of thyroid hormones and receptor concentrations in the human cerebral cortex during fetal development. The data indicate an increase in the sensitivity to T3 during the second trimester of fetal development. The main cellular targets of T3 appear to be the Cajal-Retzius and the subplate neurons. On the other hand T3 regulates transcriptionally genes encoding extracellular matrix proteins, involved in cell migration and the control of diverse signaling pathways.