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Fig. 8. Analysis of Fgf8 and Bmp4 pathways in E9.5 and E10.5
embryos. (A) Anteroventral head aspects of E10.5 embryos, demonstrating a
reduction of Fgf8 expression in the ventral telencephalon (asterisk)
and an extension from the commissural plate (dotted line) into more dorsal
regions of the midline (arrowhead) in megalin-deficient animals. (B) In-situ
hybridization of lateral head aspects (left panel) Bmp4 expression in
wild types is restricted to the dorsomedial part of the telencephalon and the
dorsal midline of the most anterior diencephalon, whereas in megalin mutants
the Bmp4 expression domain extends along the midline into more caudal
regions of the roof (arrowhead). Coronal sections (right panel) highlight
increased Bmp4 signals in the telencephalon and the anterior
diencephalon of knockout compared with control embryos. (C) Immunodetection of
P-Smad proteins, indicating a signal in E10.5 wild types that is restricted to
the dorsal midline of the tel- and diencephalon (arrowheads) but that is
significantly enhanced and ventrally expanded (arrowheads) in
megalin–/– littermates. P-Smad signals in the spinal
cord are identical in both genotypes. (D) At E9.5, the Fgf8 expression domain
in megalin–/– animals is reduced in the ventral
(asterisk), but extended into the dorsal, region of the telencephalon
(arrowhead). (E-G) At E9.5, expression of Bmp4 is increased in the
rostral and dorsal telencephalon (arrowheads) of
megalin–/– embryos as shown by whole-mount ISH (E, left
panel) or coronal dorsal forebrain sections thereof (E, right panel).
Increases in Bmp4 message result in enhanced phosphorylation of Smad
proteins (F, arrowheads) and induced expression of Bmp4 target gene
Msx1 in the rostral dorsal telencephalon (G, arrowheads).
Msx1 expression in the hindbrain region is unchanged (asterisks). di,
diencephalon; sp, spinal cord; te, telencephalon.
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