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Figure 6.1 Distribution of E-cadherinGFP (EcadGFP) during initial stages of cell-cell
adhesion in MDCK cells (for details of protein distributions and live cell imaging see
Adams et al., 1998)). (A) Still images from a time-lapse movie of EcadGFP distribution in
live MDCK cells. Note rapid appearance of EcadGFP at initial sites of cell-cell adhesion,
and the subsequent formation of individual puncta as the contact extends. (B) Higher
magnification of a cell-cell contact showing distribution of EcadGFP in puncta along the
contact. (C) Fluorescence recovery after photobleaching (FRAP) of EcadGFP in different
regions of MDCK cells during cell-cell adhesion. Note that the EcadGFP is mobile in the
plasma membrane outside the site of cell-cell contact (grey), less mobile at the newest sites
of cell-cell contact (green) and immobile at the oldest sites of cell-cell contact (beige); for
details, see Adams et al. (1998). (D) Double fluorescence microcopy of two MDCK cells
showing the distribution of E-cadherin (green) and actin filaments (rhodamine-phalloidin);
note close association of actin filaments coming from the cortical bundle with individual
E-cadherin puncta. (A colour reproduction of this figure can be found in the colour plate
section)
surface area of the contact increased, we found that new puncta were inserted
at regularly spaced intervals along the contact, and bundles of actin filaments
become organized perpendicularly to the membrane in association with
each punctum (Adams et al., 1998; see Figure 6.1D). Subsequently, the
circumferential actin cables near cell-cell contact sites separated, and
the resulting two ends of the cable swung outwards to the perimeter of
the contact. Concomitantly, subsets of E-cadherin puncta were also swept
to the margins of the contact where they further coalesced into large
E-cadherin plaques (Adams et al., 1998). The circumferential actin cable was
embedded into each E-cadherin plaque at the contact margin, forming a
continuous actin structure that circumscribed the entire cell couplet. At this
stage, the two cells had achieved maximum contact, a process referred to as
compaction.
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