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Fig. 3. Expression of Lethal of scute and late Engrailed in midline cells
depends on Hedgehog. (A) At stage 10, midline cells posterior to
the Engrailed domain (En, brown) initiate Lethal of scute (L'sc, black)
expression. (B) In hedgehog mutants, expression of Engrailed
weakens, and Lethal of scute expression in the midline is absent. (C)
At stage 13, Engrailed-positive midline cells (black) form a dense cluster.
(D) In hedgehog mutants, the number of Engrailed-expressing
midline cells is severely reduced. (E) The expression of a 76 kDa
truncation of the signal transducer Cubitus interruptus (Ci76) blocks the
reception of the Hedgehog signal. Blocking Hedgehog reception in all midline
cells leads to a severe reduction in Engrailed-expressing midline cells.
(F) The ectopic expression of Hedgehog (Hh, brown) in midline cells of
hedgehog mutants is sufficient to activate Engrailed (black).
Expression of Engrailed in the midline is limited to Hedgehog-positive cells
but not all midline cells express Hedgehog. (G) Engrailed (red) is
still expressed in a subset of midline cells in a stage 17 embryo. The axons
of midline cells are labelled by expression of tau-GFP (green). (H) In
hedgehog mutants, midline cells (yellow) are not incorporated into
the CNS. Midline cells do not extend axons and the number of midline cells is
severely reduced. Only a few Engrailed-positive midline cells (red) survive.
Arrows indicate cell fragments. (I) The loss of lethal of
scute in the mutant Tp(1;2)sc19 results in a reduction in
Engrailed-positive midline cells, which is comparable to hedgehog
mutants. Ventral views, anterior to the left; brackets outline the
midline.
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