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Fig. 6. Dorsal aorta fragments induce Ptf1a in dorsal endoderm explants
from Flk1-/- embryos. (A-C) Dissection of dorsal endoderm
and aorta from E8.5 embryos. (D) RT-PCR analysis of Hnf6 confirms
that the gene is expressed in the endoderm fragments and that there is no
contamination of endodermal cells in the dissected aorta. PCR cycle ranges for
Hnf6, 40-45; actin, 26-30. (E) The endoderm explants were cultured
with (upper panels) or without (lower panels) the dorsal aorta for 24 hours
and photographed. Marked differences in growth were not observed. (F) Analysis
of explant cultures. Hnf6 and Pecam RT-PCR confirm the
existence of endoderm and aorta, respectively, in explants, and Hex
analysis of the dorsal endoderm excludes the possibility of contamination by
ventral pancreas cells (see text). All explants included in the analysis had
the Hnf6, Pecam, Hex and actin expression phenotypes shown. For
wild-type controls (lanes 5, 6), we used: Ptf1a, adult pancreas;
Hnf6, dorsal endoderm from an 8S embryo; Pecam, dorsal aorta
from an 8S embryo; Hex, liver and ventral pancreatic buds from a 20S
embryo. Four out of five Flk1-/- dorsal endoderm explants
cultured with aorta from control embryos expressed Ptf1a, whereas
none of the five Hex-negative explants cultured without the aorta
expressed Ptf1a. PCR cycle ranges: Ptf1a, 40-43,
Hnf6, 39-42; Pecam, 39-42; Hex, 37-40, actin,
28-31. (G) Wt1, a mesenchyme marker
(Armstrong et al., 1992), is
expressed in the dorsal pancreatic region. PCR cycle ranges: Wt1, 40,
43; actin, 26, 29. (H) Wt1-expressing cells do not persistently
contaminate endoderm-aorta explants that induce Ptf1a (RT-PCR
analysis). PCR cycle ranges: Ptf1a, 40-44; Wt1, 38-42;
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