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Fig. 2. The actin cables are networked within pouch endoderm via insertion into
N-cadherin adherens junctions. The cellular junctions connecting the actin
fibres into supracellular cables were characterised using (A) TEM, (B-D)
N-cadherin in situ hybridisation, and (E-I) confocal analysis of
phalloidin-stained f-actin (green) and anti-N-Cadherin antibody (red). (A) TEM
image of the apical margin of cells within pouch endoderm (stage 17), showing
a bundle of filaments (red arrowhead) running across the cells, just below the
plasma membrane, and connecting via adherens junctions (*). (B,C) Side views
showing N-cadherin expression within pouch endoderm of 1pp and 2pp at
stage 14 (B) and 1pp, 2pp and 3pp at stage 17 (C). (D) Transverse section
through second pouch (2pp) (stage 14); N-cadherin expression is
localised to the apical surface of the pouch endoderm (red arrow). (E) Side
view of a stage 18 embryo showing co-localisation (yellow) of actin (green)
and N-cadherin protein (red) at the apical margin of each pouch (white arrow).
(F) High magnification view of pouch endoderm showing N-cadherin protein (red)
localised to the cellular junctions (white arrow) that support the actin cable
(green). (G) Longitudinal section through a stage 16 embryo, showing an
abundance of N-cadherin protein (red) in the last-to-form pouch (3pp) endoderm
(white arrow). (H,I) Transverse confocal sections through a stage 18 embryo at
the level of (H) the third pouch, indicating the pouch endoderm (PE) and (I)
at lower magnification at the level of the second arch and therefore the
interpouch endoderm (IPE). N-cadherin protein is found in the lateral endoderm
of the pouch (PE in H), but is not apparent in the ventral pharyngeal endoderm
(asterisk in H), or the interpouch endoderm (IPE in I). OV, otic vesicle;
en, endoderm; nc, notochord; aa, arch artery; nt, neural tube; am,
arch mesenchyme; ec, ectoderm. Anterior is towards the left.
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