Biomedical Engineering Reference
In-Depth Information
Different branched organs (lung, salivary gland, mammary gland, kidney,
etc.) have very different morphologies. It is possible that the different shapes are
due primarily to mechanical differences in the tissues involved during branching
morphogenesis (39). For example, we found that the viscosity of the surround-
ing mesenchyme affected the cleft shape, with relatively soft mesenchyme lead-
ing to sharper clefts than firmer mesenchyme. It is possible that the wide clefts
of the embryonic lung form because lung mesenchyme is firmer relative to lung
epithelium than salivary mesenchyme is to salivary epithelium. But we do not
know, because no one has measured the viscosities of these specific tissues.
The recombination experiments of Lawson (31-33), Spooner and Wessells
(55), Grobstein (16), Ball (1), and Kratochwil (29) indicate that combinations of
epithelium and mesenchyme from different organs generally lead to morphology
characteristic of the mesenchyme's organ of origin, but that in some cases,
branching does not occur. While differences in growth factors may offer part of
the explanation, it may be that the rest of the explanation lies in simple me-
chanical differences between the mesenchymes. How strong are the epithelia?
How viscous are the mesenchymes?
Measurements of the tissue viscosities and surface tensions of the epithelia
and mesenchymes involved could provide a simple and fascinating key to inter-
preting the large number of facts we have accumulated about branching
morphogenesis. If we really want to understand developmental mechanisms, we
will take mechanical measurements.
5.
ACKNOWLEDGMENTS
This work has been supported by the National Science Foundation and the
National Institutes of Health (DMS 9805611, 0201094).
6.
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