THE PROBLEMS AND PROMISES OF RESEARCH 

 ON THE MOLECULAR ASPECTS OF DEVELOPMENT 



(Workshop Summary) 



Paul 0. P. Ts'o 



Department of Radiological Sciences, The Johns Hopkins University, 

 Baltimore, Maryland 



We have spent three interesting and in- 

 structive days together. I have been much 

 benefited not only by the talks presented in the 

 formal sessions but also by the fruitful discus- 

 sions with many of the participants in this 

 ■workshop. We share a common feeling that at 

 this moment we should review and reflect upon 

 the problems and the progress in the field of 

 developmental biology. Therefore, I shall pre- 

 sent to you certain general consensuses and 

 conclusions which we have reached as a result 

 of our discussions. These conclusions are 

 important to all of us for two reasons. The 

 first is that experimental systems in the field 

 of developmental biology are highly individual- 

 istic and specialized. Few investigators in the 

 field can pick up helpful and specific experi- 

 mental techniques for their own research by 

 examining the work and the experience of 

 others. In most cases each system has its own 

 characteristics not shown by others. There are, 

 to be sure, exceptions such as that demon- 

 strated by the LDH-isozyme story lucidly pre- 

 sented by Dr. Edward Massaro. Experience 

 and working knowledge learned from the iso- 

 zymes' story can certainly be profitably ex- 

 tended to many other biological systems. The 

 most important thing we can learn as a group 

 is' the underlying philosophy and strategy com- 

 mon to all of our research. The second reason 

 is that we are continuously confronted by 

 problems of communication, even as workers 

 in the same field. There are biologists, chem- 

 ists, physicists, biophysicists, etc., in this 

 workshop. This is a very healthy sign reflecting 

 the vigor and the promise of this scientific 

 frontier even though it does bring its own prob- 

 lems. A review of the present status will help 



us with this aspect. 



1 will limit my comments mainly to the 

 unicellular organisms and to a unicellular 

 model. Dr. James Gregg and Dr. Arnold Kahn 

 have presented to us some very interesting and 

 relatively simple systems for the study of 

 multicellular development. In these cases the 

 importance of intercellular reactions must 

 certainly be considered. In higher organisms, 

 hormonal control plays a major role in devel- 

 opment. Nevertheless, concepts developed from 

 the unicellular model will provide the basis for 

 further discussion of more complicated systems. 



Differentiation of a cell clearly implies 

 that the cell is suddenly doing something new, 

 a diversion from what it was doing before. 

 The degree of change, of course, depends upon 

 the experimental system and the monitoring 

 device. At present, however, it remains largely 

 a question of semantics and will until we know 

 more about the ground rules or the basic 

 mechanisms common to all experimental sys- 

 tems. We will, in my opinion, soon reach some 

 agreement that unless the change is sufficiently 

 qualitative and distinctive we will not honor it 

 with the name of "differentiation". Assuming 

 agreement as to what is differentiation, now 

 we are ready to pose the question, "What 

 determines that the cell will change from its 

 present course to a new one?". In this workshop 

 we have loosely described this act as "the 

 decision-making process or processes". I shall 

 try to define and to clarify the concept of "the 

 decision-making process" so that we can dis- 

 cuss it without undue confusion. 



I would like first to define two decision- 

 making bodies in the cell. Their existence is 

 known from cell biology and biochemistry. The 



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