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Fig. 3. Presence of mesothelium as detected by transmission electron microscopy and
cytokeratins. (A-D) Transmission electron micrographs reveal various
structural components of the plasma membrane at sites of cell-cell contact in
outer cells of the allantois. (A) Ultrathin section through two outer cells
(1,2), and an inner core cell (3) in the proximal region of an early allantoic
bud (EB). The arrow points to a desmosome between the two outer cells, whereas
the arrowheads indicate electron densities, possibly adhesion plaques or
glancing sections through desmosomes, at sites of contact between the outer
cells and an inner cell. Scale bar: 500 nm. (B) Ultrathin section contains a
possible junctional complex between two cells (1,2) in the proximal region of
an early allantoic bud (EB), consisting of a putative tight junction (left of
asterisk), adhesion plaque (arrowhead), and spot desmosome (arrow). Scale bar:
500 nm. (C) Ultrathin section through the proximal region of an EHF stage
allantois shows an isolated adhesion plaque very similar to those previously
described (Batten and Haar,
1979). Scale bar: 100 nm. (D) Ultrathin section through the distal
region of a 4-somite pair (4-s) allantois contains an apparently mature spot
desmosome between two outer cells. Scale bar: 100 nm. (E-G) Brightfield
photomicrographs exhibit immunostaining against cytokeratins (brown color,
arrows) in nascent allantoises of ex vivo specimens. Sections were
counterstained in hematoxylin. (E) EB stage. (F) LB stage. (G) EHF stage.
Other abbreviations as in Fig.
1. Scale bar in G: 50 µm (E-G).
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