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Fig. 5. ngn1 and coe2 expression are independently inhibited by
Her5, but downregulation of one of these targets is sufficient to prevent
neuronal differentiation at the IZ. Expression of coe2 (A-C),
ngn1 (D-F), delB (G-H'), pax2.1 and zn12
(I-N) in wild type (A,D,G,I,I',L), ngn1-/- mutants
(B,C,H,H',J,K) or embryos injected with capped RNA encoding a
dominant-negative form of Coe2 (Xcoe2
DBD) (E,F,M,N).
Embryos injected with MOher5 (C,F,K,N) are compared with
non-injected controls. All views (except I'-K') are flat-mounted
embryos, anterior towards the top, at three somites (A-F), eight somites
(G-H') or 18 somites (I-N). (I'-K') Lateral views of the
tail area of embryos in I-N, anterior leftwards; (G',H')
high-magnification views of the areas boxed in G,H, respectively; red brackets
indicate the IZ. (A-C) coe2 expression in the vcc and r2 is lower in
ngn1-/- mutants (B) but still induced at the IZ in the
absence of Her5 (C, blue arrow). C is a higher magnification of the IZ area
compared with A and B. (D-F) ngn1 expression is lower in the vcc and
r2 when Coe2 activity is reduced, but still induced at the IZ (labelled in red
by pax2.1) in the absence of Her5 (F, blue arrow). (G-H')
Progression of neurogenesis, as revealed by the commitment marker
delB, is fully impaired in the MH area in the absence of Ngn1 (see
G',H'). This contrasts with the maintenance of neurogenesis in
spinal motorneurons (blue arrows) (Cornell
and Eisen, 2002). (I-K') In ngn1-/-
mutants (identified by their lack of sensory neurons in the spinal cord,
compare J', K' and I', arrows), neuronal differentiation in
the MH, revealed by zn12 immunocytochemistry, is fully blocked (brown staining
and brown arrows in I, white arrows to the absence of staining in J). In
addition, in the absence of Her5, neuronal differentiation at the IZ (blue
pax2.1 staining) does not take place (white arrow in K). (L-N)
Neuronal differentiation within the MH (brown staining and brown arrows in L)
is also impaired in the absence of Coe2 function (white arrows in M), and does
not take place at the IZ when Her5 activity is blocked (white arrow in N).
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