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Figure 12 | Neural Development

Figure 12

From: Sp8 exhibits reciprocal induction with Fgf8 but has an opposing effect on anterior-posterior cortical area patterning

Figure 12

Summary of the Sp8 function related to telencephalic patterning centers and cortical area patterning. (a) Schematic diagram of time-dependent expression domains of Sp8 and Fgf8. At E10.5, Sp8 expression (green) is expressed in both progenitor cells in the cortical VZ (cortex) and within the CoP, where it overlaps with the Fgf8 expression domain (overlapping Sp8 and Fgf8 expression in the CoP is colored yellow). Sp8 expression is gradually excluded from the Fgf8 expression domain (red) at E11.5 and later. (b) Domain-dependent regulation of Sp8 TF activity by Emx2. Sp8 forms a reciprocal induction loop with Fgf8 in the CoP. Emx2 (blue) is expressed in cortical progenitors, but not in the CoP. Although Sp8 is expressed in cortex, Emx2 represses the ability of Sp8 to induce Fgf8, thereby restricting Fgf8 expression to the CoP. (c) Electroporation (EP) of Fgf8 and Sp8 results in opposing shifts in cortical area patterning. In early stages of cortical patterning, Sp8 maintains Fgf8 expression in CoP and the Fgf8 signaling pathway, which imposes anterior identity to cortical progenitors. Anterior EP of Fgf8 expression constructs results in enhanced anterior area identities and a corresponding posterior shift in cortical areas. Anterior EP of Sp8 expression constructs has an opposing effect on area patterning to that of Fgf8, and results in an anterior shift in cortical areas. Posterior EP of either Fgf8 or Sp8 have the opposing effect on area patterning compared to their anterior EP. These opposing effects of ectopic expression of Sp8 on area patterning compared to Fgf8 indicate that Sp8 activates a signaling pathway(s) that can overcome the effect of Fgf8 signaling, perhaps by interfering with Fgf8 signaling or dominating it. Furthermore, Sp8 expression in cortical progenitors may trigger distinct signaling pathways that function to facilitate posterior area identity.

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