Tissue and Cellular Distribution
Being a transcription factor, a protein that binds to specific DNA sites and thereby regulates the activity of specific genes, Tbr1 is localized in the nucleus where the cell’s DNA is located. Tbr1 is expressed in glutamergic neurons rather than GABAergic neurons.
Tbr1 is expressed mainly in early-born postmitotic neurons of the developing cerebral cortex—in particular, the preplate and layer VI neurons. The preplate forms the architectural network of neurons that help developing neurons migrate. Successive migrations of neurons divide the preplate such that its inner cells form the cortical plate while its outer cells form the marginal zone. The cortical plate and the marginal zone eventually develop into six cortical layers, known as the neocortex, present in the mature cerebral cortex. These layers are numbered I-VI with layer VI being the deepest and forming first, while the remaining layers grow outward from it (from V to I). Layers II-VI develop from the cortical plate and layer I forms from the marginal zone. The subplate, intermediate zone, subventricular zone, and ventricular zone are found progressively deeper to these developing cortical layers. High expression of Tbr1 is seen in the marginal zone, cortical plate, and subplate of the developing cortex whereas little expression is seen in the subventricular zone. No Tbr1 expression has been observed in the ventricular zone.
Other regions of Tbr1 expression are: the olfactory bulbs and olfactory nuclei, the lateral hypothalamus region, the entopeduncular nucleus, the eminentia thalami.
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