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Fig. 7. mRNA expression pattern of fibronectin (Fn1) and its integrin
receptor (Itga5) in the PSM and surrounding tissues. (A-D)
In situ hybridisation for Fn1 on HH12-14 stage chick embryos shows
that Fn1 mRNA is strongly expressed in the ectoderm overlying the PSM
(A-D) and in the posterior part of epithelial somites (A,B,D). Endoderm is
negative posteriorly but expression is detected at the level of anterior PSM
and epithelial somites (B-D). PSM appears negative for Fn1 mRNA
except for a faint staining posteriorly (B,C). (E-I) Removal of
ectoderm before fixation confirms this pattern and shows that Fn1
expression is very strong in the intermediate mesoderm (E,F,G). (J)
However, Fn1 expression is detectable in both the anterior third and
posterior two-thirds of the PSM by RT-PCR. (K) Negative hybridisation
control with Fn1 sense probe. (L-N) In situ hybridisation for
Itga5 shows that it is strongly expressed in the posterior two-thirds
of the PSM and in epithelial somites. Insert (L) shows sense probe control.
Sections of Itga5-hybridised embryos show that the signal in PSM is
faint anteriorly (M), but strong posteriorly (N). Itga5 is also
expressed in notochord, intermediate (arrows) and lateral mesoderm (M,N), and
extraembryonic blood vessels (arrows in L). Faint staining is detectable in
neural tube and ectoderm (arrowheads, M,N). Anterior, up. *,
Epithelial somite; im, intermediate mesoderm; n, notochord; som, somites; ant
PSM, anterior PSM; post PSM, posterior PSM; Ctrl+, positive control (whole
embryo cDNA); RNA, reverse-transcription omitted; water, cDNA omitted. Scale
bars: 500 µm in A,B,E,L; 100 µm in C,D,F-K,M,N.
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