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Fig. 1. Liver is specified in Hex-/- embryos but fails to grow
because of a cell proliferation defect. (A) RT-PCR analysis of RNA from
ventral and dorsal foregut domains of 10-somite stage (S) embryos (lanes 3-8).
Albumin and transthyretin were expressed in the hepatic
primordium of Hex-/- embryos at 10S (n=8, two
representative samples depicted). L, embryonic liver mRNA; no RT, not reverse
transcribed RNA; v, ventral; d, dorsal. (B) In situ hybridization for
Albumin and 
-fetoprotein on isolated ventral endoderm
from 2-6S embryos cultured for 48 hours with cardiac mesoderm. Beating cardiac
domains are outlined in red and sometimes lie above or below endoderm domains;
all purple staining is positive, with a subset denoted by arrows. (C-E)
Embryos were exposed in vivo to BrdU for 2 hours, harvested, fixed, sectioned
and stained for BrdU incorporation (purple nuclei). Blue boxes denote lateral
gut endoderm; red boxes denote hepatic endoderm. (F,G) Quantitation of
BrdU-positive endoderm cells relative to total cells in the hepatic (red bars)
and lateral (blue bars) endodermal domains. A total of 24 sections from
wild-type (n=3) and Hex-/-(n=3) embryos
were evaluated; P value was determined by the homoscedastic one tailed t-test.
A lower proliferation rate was detected in the hepatic bud of
Hex-/- embryos. (H,I) TUNEL assay in the hepatic bud of
18S embryos. The regions with a white dotted outline correspond to the blue
and red boxed regions in panels D,E. No evidence for enhanced apoptosis was
detected in Hex-/- embryos; note the positive staining in
the neural tube and amnion in both embryos.
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