Biology Reference
In-Depth Information
REDUCED CELL PROLIFERATION: AN AID TO
BOUNDARY STABILITY?
Cell proliferation would be a potential source of local stress at a boundary, whatever the
direction of the mitotic spindle. If the spindle were orientated perpendicular to the
boundary, mitosis would push one daughter cell directly at the other compartment
producing a local pressure point. If, on the other hand, the spindle were parallel to the
boundary, accommodation of two cells along the boundary where one was before would
require the breaking of old cell contacts and the making of new ones
d
exactly the sort of
thing that normally allows epithelial cells to move within a plane. Furthermore, the way
that mitosis commandeers much of the microtuble cytoskeleton to make the mitotic spindle,
and much of the actin cytoskeleton to make a cytokinesis ring, would be expected to have
serious effects on the mechanical forces that were being generated and resisted by a cell
before division started.
For these reasons, it is perhaps not surprising that rates of proliferation tend to be mark-
edly reduced along compartment boundaries.
18
Careful observation of boundaries through
time has overthrown an early idea that the non-proliferating cells were somehow set aside
as permanent border guards, and the non-proliferation is now seen more as a mechanism
to avoid unnecessary trouble and stress at the boundary.
19
Boundary formation is in some ways the opposite of a morphogenetic event; it is more
holding morphogenesis in check (although it can be very important for patterning in devel-
opment, which will drive later morphogenetic events). It is nevertheless gaining a great deal
of experimental attention at present, partly to increase our understanding of normal devel-
opment and partly because failure to maintain boundaries is one aspect of cancer
metastasis.
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