Biology Reference
In-Depth Information
FIGURE 27.1
Verna's use of a tissue-engineered abstract system to discriminate between two rival hypotheses
to account for the innervation of the dermal layer of the skin, but not the epidermal layer, by sensory axons. The
hypotheses were: (a) strong attraction by the dermis, and (b) strong repulsion by the epidermis. A sensory ganglion
(SG) was placed on a coated surface about 1 mm from an explant of either dermis (DER) or epidermis (EPI). The
dermis explant had no effect on the progress of growth cones (indicated by the axons they left behind) whereas the
epidermis was avoided, supporting hypothesis (b).
by chondroitin sulphate:
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because work in each species has concentrated so far on only one of
these molecules, it is not yet clear whether the control really is different in birds andmammals
or whether each animal really uses both types of molecule.
Another example of tissue engineering being used to discriminate between rival hypoth-
eses concerns the development of glandular organs that arise as derivatives of the gut. There
are several of these
d
lung, liver and pancreas are examples
d
and all have a common archi-
tecture of a branched epithelium surrounded by mesenchymal cells. That said, the
morphology of the epithelium varies in detail between the organs so that they may be easily
distinguished by the shape of the tree. Two rival hypotheses placed control of this detailed
morphology either in the epithelium itself or in the surrounding mesenchyme, which
exchanges signals with the epithelium. The hypotheses were tested by engineering chimaeric
organs using the unbranched epithelium from one organ rudiment and the mesenchyme
from another.
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Control organs, in which an isolated epithelium received its own mesen-
chyme, grew organotypically (
Figure 27.2
). In chimaeric organs, the morphology developed
by the epithelium was characteristic of the organ that was the source of the mesenchyme, not
the organ that was the source of the epithelium itself. If mesenchyme from a non-branching
epithelium such as trachea was used instead, the epithelium did not branch at all.
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