EXPRESSION OF COUP-TFII / NR2F2 AND FOXG1 HELP TO DISTINGUISH THE TELENCEPHALO-OPTO-HYPOTHALAMIC EMBRYONIC DOMAIN AND ITS CONTRIBUTION TO THE AMYGDALA

The transcription factor COUP-TFII (NR2F2) plays a critical role in the development of the amygdala in mammals, being expressed in both pallial and subpallial subdivisions. Previous studies suggested that it is also present in other subdivisions near the telencephalon-hypothalamic frontier or caudal to it, known to produce some neuron subpopulations for the amygdala. One of these domains is the telencephalo-opto-hypothalamic domain (TOH), which expresses the telencephalic transcription factor FOXG1, making it a distinct division of the telencephalon that also produces glutamatergic neurons. To distinguish the TOH from the hypothalamus or from the prethalamic eminence, we combined COUP-TFII labeling (by in situ hybridization or immunohistochemistry) with immunohistochemistry for FOXG1, and analyzed it in mouse and chicken during embryonic development, using different sectioning planes. The results helped to distinguish between TOH (with expression of both COUP-TFII and FOXG1) from the supraopto-paraventricular hypothalamic domain and the prethalamic eminence (with COUP-TFII but not FOXG1). The expression in TOH was observed from early embryonic stages and extended radially from the ventricular zone to the mantle, including part of the medial extended amygdala. In chicken, some COUP-TFII cells also spread tangentially into the central extended amygdala, including the capsular central nucleus. Thus, the medial and central extended amygdala contain a mixture of GABAergic and glutamatergic neurons with different embryonic origins, some of which appear to derive from the TOH. These results open new venues to further investigate the phenotype and function of these different neuron populations on the control of behavior.