Frontal cortex subdivision patterning is coordinately regulated by Fgf8, Fgf17, and Emx2

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Abstract
The frontal cortex (FC) plays a major role in cognition, movement and behavior. However, little is known about the genetic mechanisms that govern its development. We recently described a panel of gene expression markers that delineate neonatal FC subdivisions and identified FC regionalization defects in Fgf17–/– mutant mice (Cholfin and Rubenstein [2007] Proc. Natl. Acad. Sci. U. S. A. [in press]). In the present study, we applied this FC gene expression panel to examine regionalization phenotypes in Fgf8neo/neo, Emx2–/–, and Emx2–/–;Fgf17–/– newborn mice. We report that Fgf8, Fgf17 and Emx2 play distinct roles in the molecular regionalization of FC subdivisions. The changes in regionalization are presaged by differential effects of rostral patterning center Fgf8 and Fgf17 signaling on the rostral cortical neuroepithelium, revealed by altered expression of Spry1, Spry2, and “rostral” transcription factors Er81, Erm, Pea3, and Sp8. We used Emx2–/–;Fgf17–/– double mutants to provide direct evidence that Emx2 and Fgf17 antagonistically regulate the expression of Erm, Pea3, and Er81 in the rostral cortical neuroepithelium and FC regionalization. We have integrated our results to propose a model for how fibroblast growth factors regulate FC patterning through regulation of regional transcription factor expression within the FC anlage. J. Comp. Neurol. 509:144–155, 2008.