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Fig. 2. Expression of AmphiHox1 (A-L) and AmphiWnt3 (M-R) in
amphioxus embryos treated as follows: DMSO control (A-D,M,N), 1 x
10-6 M RA (E-H,O,P) and 1 x 10-6 M BMS009 (a RA
antagonist) (I-L,Q,R). Anterior to left. Whole mounts viewed from the left
side and frontal sections in C, G, K viewed from dorsal side. The `x' in B,F,J
shows the level of the section in C,G,K, respectively. Arrowheads indicate the
anterior limit of expression in the endoderm. Scale bars=50 µm. (A) In
15-hour control neurulae, AmphiHox1 is expressed in the posterior
half of the endoderm and overlying ectoderm with the highest expression
localizing to the middle third. (B-D) At 20 hours (B,C) and 30 hours (D) of
development, the anterior limit of endodermal and ectodermal expression is
just posterior to the pharynx. (E-H) RA upregulates expression of
AmphiHox1 in endoderm and ectoderm and expands it anteriorly. By 30
hours (H) expression in the endoderm is restricted to the extreme anterior end
of the larva. (I-L) Treatments with the RA antagonist BMS009 downregulate
AmphiHox1 and shift expression posteriorly in both the ectoderm and
endoderm. (M,N) In mid-neurulae and early larvae of amphioxus,
AmphiWnt3 is expressed in the ventral endoderm just posterior to the
pharynx. (O,P) Treatment with RA initially shifts endodermal expression of
AmphiWnt3 anteriorly and subsequently leads to a downregulation of
expression by 30 hours of development (P). (Q,R) In BMS009-treated embryos,
AmphiWnt3 expression is expanded posteriorly.
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