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Fig. 5. Peptide 4.2-injected embryos show decreased chordin RNA expression during gastrulation and in the chordoneural region
of tail-bud embryos. Chordin mRNA expression in Steinberg’s solution-injected embryos is as reported by Sasai et al. (1994). Chordin
mRNA was restricted to the notochord and prechordal plate (head mesoderm) at stages 13 and 21 (A,D). By stage 32, expression
was restricted to the chordoneural region of the tail-bud (G). In peptide 4.2-injected embryos, the low levels of expression restricted
to the dorsal lip of the blastopore (B) indicate that chordomesoderm involution has been severely compromised. In contrast, LiClinjected
embryos showed chordin RNA expression throughout the notochord, but not in the chordomesoderm (C). By stage 21, the
pattern of chordin expression for peptide 4.2 and LiCl were the same (E,F). Strong expression was visible within the notochord. However,
as with stage 13 embryos, expression is absent from the anterior region. Staining of the lining of the archenteron is an artifact. Although
histological analyses did not indicate any significant morphological differences in trunk development between Steinberg’s solution and
peptide 4.2, expression of chordin was not observed in the chordoneural ridge in tail-bud embryos of peptide 4.2. Thus, the organizer
potential of the tail might be compromised by injection of peptide 4.2 (H). As embryos develop from the late neurula stage, chordin
expression in the notochord decreased and was eventually undetectable by the tail-bud stage, except for the chordoneural ridge
(D,G). However, for LiCl-injected embryos, expression continued in the notochord after sibling control embryos no longer showed
expression (I). Arrow indicates the anterior of the embryos. |