Passage 126

It is well known that biological changes atthe molecular level have morphogenetic consequences, consequencesaffecting the formation and differentiation of tissues andorgans. It is superfluous to point out that gene mutations anddisturbances of the bio-synthetic processes in the embryo mayresult in abnormalities in the morphology (structure) of anorganism. However, whereas much is known about causes andconsequences at the molecular level, and in spite of an enormousaccumulation of chemical and morphological data on embryos ofvarious kinds, our understanding of how genes controlmorphogenesis is still far from complete. Perhaps one reason forthis is that molecular biologists and morphologists speakdifferent languages. Whereas the former speak about messenger-RNAand conformational changes of protein molecules, the latter speakof ectoderms, hypoblasts, and neural crests.

One solution to this predicament is to try tofind some phenomena relevant to morphogenesis which both themolecular biologist and the morphologist can understand anddiscuss. As morphogenesis must be basically the result of changesin behavior of the individual cells, it seems logical to askmorphologists to describe the morphogenetic events observed interms of changes in cellular contact, changes in the rate ofproliferation of cells, or similar phenomena. Once this is done,it may be appropriate to ask questions about the molecularbackground for these changes. One may, for instance, ask whethervariations in cell contact reflect alterations in the populationsof molecules at the cell surface, or one may inquire about themolecular basis for the increased cell mobility involved in celldispersion.

Studies of this kind have been carried outwith cells released from tissues in various ways and then allowedto reveal their behavior after being spread out into a thinlayer. In many cases, such cells show the ability to reaggregate,after which different cell types may sort themselves out intodifferent layers and even take part in still more intricatemorphogenetic events. But in most cases, the behavior of cells inthe intact embryo is difficult to study because of the thicknessand opacity of the cell masses. The sea urchin embryo, however,has the advantage that it is so transparent that each cell can beeasily observed throughout development. Thus, by recording thedevelopment of a sea urchin embryo with time-lapse photography,the research scientist might discover previously unknown featuresof cellular behavior. Perhaps the study of the sea urchin in thismanner can provide a medium by which the molecular biologist andthe morphologist can begin communicating with each other moreeffectively about the way in which genes control morphogenesis.