Figure 8

Cortical area shifts by ectopic expression of Fgf8 at anterior or posterior sites. Electroporation of a CAG-Fgf8 vector was done at E11.5 and later, at P7, the brains were processed and tangential sections of their cortical areas were visualized by serotonin staining as described in Methods. (a) Ectopic expression of Fgf8 at an anterior site in E11.5 brains causes posterior area shifts with motor (M) area expansion (n = 2 of 2 electroporated cases; this finding replicates that of Fukuchi-Shigomori and Grove [18], therefore we did not perform additional cases) compared to control electroporated brains. (b) In contrast, a posterior electroporation of Fgf8 induces anterior area shifts accompanied by an expansion of V1 (n = 4 of 6 electroporated cases). We also performed electroporations using medial and lateral approaches at mid-posterior levels in an attempt to target the presumptive barrelfield of S1 (posteromedial barrel subfield, PMBSF). (c, d) Medial-posterior electroporation of Fgf8 typically causes an 'elongated' S1 (c) (n = 7 of 10 electroporated cases), whereas lateral-posterior electroporation within the cortical field that would develop as S1 can result in a 'split barrel field' (d) (n = 2 of 9 electroporated cases). The middle of the 'PMBSF' in S1 is pointed to by the line. We did not observe 'duplicate' barrels as reported by Fukuchi-Shigomori and Grove [18]. We assume that duplicated barrels are produced only in a unique situation with an appropriate combination of timing, size and position of the ectopic Fgf8 expression domain, and level of Fgf8 expression, required to partially duplicate the barrel pattern. Arrows indicate targeted locations of the electroporation sites. M, motor areas. Scale bar: 1.0 mm.