It is well known that biological changes at the molecular level have
morphogenetic consequences, consequences affecting the formation and
differentiation of tissues and organs. It is superfluous to point out that gene mutations and disturbances of the bio-synthetic processes in the
embryo may result in abnormalities in the morphology (structure) of an
organism. However, whereas much is known about causes and consequences at the
molecular level, and in spite of an enormous accumulation of chemical and
morphological data on embryos of various kinds, our understanding of how genes
control morphogenesis is still far from complete. Perhaps one reason for this
is that molecular biologists and morphologists speak different languages.
Whereas the former speak about messenger-RNA and conformational changes of
protein molecules, the latter speak of ectoderms, hypoblasts, and neural
crests.
One solution to this predicament is to try to find some phenomena relevant
to morphogenesis which both the molecular biologist and the morphologist can
understand and discuss. As morphogenesis must be basically the result of
changes in behavior of the individual cells, it seems logical to ask
morphologists to describe the morphogenetic events observed in terms of changes
in cellular contact, changes in the rate of proliferation of cells, or similar
phenomena. Once this is done, it may be appropriate to ask questions about the
molecular background for these changes. One may, for instance, ask whether
variations in cell contact reflect alterations in the populations of molecules
at the cell surface, or one may inquire about the molecular basis for the
increased cell mobility involved in cell dispersion.
Studies of this kind have been carried out with cells released from tissues
in various ways and then allowed to reveal their behavior after being spread
out into a thin layer. In many cases, such cells show the ability to
reaggregate, after which different cell types may sort themselves out into
different layers and even take part in still more intricate morphogenetic
events. But in most cases, the behavior of cells in the intact embryo is
difficult to study because of the thickness and opacity of the cell masses. The
sea urchin embryo, however, has the advantage
that it is so transparent that each cell can be easily observed throughout
development. Thus, by recording the development of a sea urchin embryo with
time-lapse photography, the research scientist might discover previously
unknown features of cellular behavior. Perhaps the study of the sea urchin in
this manner can provide a medium by which the molecular biologist and the
morphologist can begin communicating with each other more effectively about the
way in which genes control morphogenesis.
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