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Fig. 3. Ptc1
loop2 affects
cell-fate specification in a radial manner. (A) `Haloes' of
PHOX2A-negative/Ptc1
loop2-negative
(uncolored) cells surround
Ptc1
loop2+/PHOX2A-negative
(blue) cells. (B) Cross-section through whole-mount shown in A,
demonstrating that the `haloes' are columns of
PHOX2A-negative/Ptc1
loop2-negative
cells radially associated with more-pially located
Ptc1
loop2+ cells. (C)
Ptc1
loop2-electroporated
embryos at E4 display midbrain columns in cross-section. (C, inset) Magnified
view of a single column of cells (indicated by arrowhead). Individual cells
are marked by asterisks. (D) Cross-section through an E4 embryo
electroporated with low concentrations of EGFP, displaying
bipolar-radial glia-like midbrain progenitors. Note that, when multiple cells
are present in a single column, they are cytoplasmically continuous
(arrowhead). (E) Close-up of boxed area in D, highlighting the radial
glial-like morphology of the midbrain progenitors, including the presence of
end-feet at the ventricular surface. (F) Demonstration of dye-coupling
through gap junctions among three ventral midbrain cells following the
injection of Alexa-Fluor 488 into the central cell (*). H&H
stage 10 explant presented in whole-mount view (rostral is to the top and
ventricular surface faces the viewer; orientation is the same as in
Fig. 1A). Each cell is
approximately 7.5 µm across and the cells are spaced approximately 5 µm
apart. The central cell is ventricular with respect to the other two cells.
H&H, embryonic stages according to Hamburger and Hamilton
(Hamburger and Hamilton,
1951); rFP, rostral floor plate.