Studies on the Cellular Basis of Morphogenesis 

 in the Sea Urchin 



T. GUSTAFSON 



The Wenner-Gren Institute for Experimental Biology, 

 University of Stockholm, SzvedeJi 



The task of de\ elopmental physiology is not only to elucidate how the 

 cells in an embryo become biochemically different from each other, e.g. 

 how some cells get the capability to produce and to accumulate heart 

 myosin, cerebrosides, glucose 6-phosphatase, rhodopsin, etc. We also want 

 to understand how the cells become arranged into various well-organized 

 complicated organ structures such as hearts, brains, kidneys, eyes, etc., 

 which in turn are integrated to form whole organisms. 



As a point of departure in our attempt at an analysis we may state that 

 morphogenesis of the organs and the organism as a whole reflects the 

 molecular events going on in its cells. We are permitted to make this 

 statement for many reasons, e.g. treatment of an embryo with agents 

 which interfere with the physical and chemical events in the cells, also 

 brings about characteristic alterations in the anatomical development of 

 the embryo. As an example I may mention that o-iodosobenzoic acid, 

 which is capable of oxidizing certain SH groups, suppresses the develop- 

 ment of the entomesodermal elements in the sea urchin larva, which there- 

 fore only develop into an ectodermal vesicle. A cytosine analogue, 2-thio-5- 

 methyl cytosine, has the same effect. Furthermore, it is generally accepted 

 that genes exert their action by determining the kind of enzymes a cell can 

 form, and we begin to look upon the hereditary morphological deficiencies 

 as the result of disturbances of cellular metabolism. 



The problem we are confronted with is to define how the molecular 

 events are translated into organ structures distributed according to a 

 characteristic and reproducible pattern. We may approach this problem 

 from many different directions. One way is to describe the metabolic 

 pattern of cells in different presumptive organ regions in the embryo. But, 

 even a detailed biochemical dissection of an embryo may — I fear — fail to 

 answer our fundamental questions about morphogenesis, e.g. how a certain 

 part of the blastula wall invaginates to form an archenteron and how the 

 archenteron becomes subdivided into coelomic sacs and other derivatives. 



VOL. n. — 2K 



