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Fig. 3. Dynamics of endocrine specification and differentiation.
(A-F) Brightfield photomicrographs of Pdx1 immunostaining at various
stages of mouse dorsal pancreas (dp) development. From E11.5-E15.5, Pdx1 is
expressed throughout the pancreatic epithelium (as well as in the posterior
stomach, st), and is subsequently downregulated in acini (ac) and ducts (du)
while being maintained in islet ß-cells (is). (G-L) Confocal
immunofluorescence photomicrographs at equivalent stages, for the
pan-epithelial marker E-cadherin (green) and the islet precursor marker Ngn3
(red). Ngn3 expression is rare at E11.5, dramatically peaks during the
secondary transition (E13.5-E15.5) and declines again at E17.5, becoming
undetectable in neonatal and adult pancreas. Arrowheads indicate proto-acinar
clusters at the periphery of the branched epithelium, from which Ngn3
expression is consistently excluded. (M-R) Confocal detection of
glucagon (green) and insulin (red). Glucagon+ 
-cells are
relatively common at E11.5 and E13.5, wheras large numbers of
insulin+ ß-cells are not detected until after E13.5. From
E17.5 onwards, endocrine cells aggregate into recognizable islets, with
ß-cells at their cores and -cells distributed peripherally. Scale
bar in all images, 50 µm.
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