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Fig. 5. Alterations of ectoderm specification in embryos and chimeras in which
vegetal signaling is blocked. (A) Co-injection of 
-cadherin
and Antivin results in permanent blastulae with numerous unpatterned
serotonergic neurons in an enlarged animal plate. Inset shows transmitted
light image. (B,C) Embryos co-injected with -cadherin and
BMP. (B) SpNk2.1 is expressed throughout. Inset shows transmitted light image.
(C) Numerous serotonergic neurons are scattered in thickened epithelium.
(D-F) Embryos co-injected with -cadherin and Nodal. SpNk2.1 (D)
and SpHnf6 (E) expression is identical to -cadherin alone. However,
fewer serotonergic neurons form (F). Inset in S shows transmitted light image.
(G,H) Chimeras in which the entire embryo expresses
-cadherin and half co-expresses Antivin (G) and myc as a lineage tracer
or BMP (H) and myc. Serotonergic neurons form in similar numbers as embryos
injected with -cadherin. (I) Chimeras expressing
-cadherin throughout and Nodal in one half have fewer serotonergic
neurons. The serotonergic neurons that form in the half expressing
-cadherin alone are several cell diameters from the interface with
Nodal-expressing cells (arrowhead). (J-L) SpGsc-injected embryos. (J)
SpNk2.1 protein is in all cells of embryos expressing SpGsc. Inset shows
transmitted light image. Neither SpHnf6 (K) nor serotonin (L) are detected.
(M-O) Embryos co-injected with -cadherin and SpGsc. (M) SpNk2.1
is expressed uniformly throughout the embryo. Inset shows transmitted light
image. Neither SpHnf6 (N) nor serotonergic neurons (O) are detected.
(P) In chimeras expressing -cadherin throughout, one half
co-expresses SpGsc (myc-positive). Serotonergic neurons differentiate in the
half of the embryo expressing only -cadherin. The serotonergic neurons
form at the interface with cells expressing SpGsc (arrowhead). (Q)
SB431542-treated -cadherin-injected embryos have a similar number of
unpatterned serotonergic neurons as untreated embryos expressing
-cadherin. (R) Embryos co-expressing -cadherin and Nodal,
then treated with SB431542 form serotonergic neurons. Blocking Nodal receptors
rescues the formation of serotonergic neurons. Scale bar: 20 µm.
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