ANTIGEN SYNTHESIS DURING 

 REORGANIZATION IN THE CELLULAR SLIME MOLDS 



James H. Gregg 



Department of Zoology, 

 University of Florida, Gainesville, Florida 



Perhaps most of you are familiar with the 

 details of the development of the slime molds. 

 However, I'd like to emphasize certain steps in 

 their development before continuing with the 

 remainder of the talk. Figure 1 is a diagram 

 of the development of two species of slime mold, 

 Dictyostelium mucoroides and Dictyostelium 

 discoideum. Aggregation of a homogeneous group 

 of D. discoideum vegetative amoebae occurs, 

 which, through morphogenetic movements, forms 

 itself into a migrating pseudoplasmodium or 

 slug. Further morphogenetic movement results 

 in the formation of a mature sorocarp consisting 

 of a small mass of cells supported by a slender 

 stalk. Development is similar in D. mucoroides 

 with the exception that D. mucoroides forms a 

 stalk as it migrates. Eventually, a fruiting body 

 is formed, again consisting of a mass of cells 

 supported by a slender stalk. 



If we examine a fruiting body of D. discoi- 



deum closely, we find that it has developed pro- 

 portionally; that is, regardless of the size of the 

 cell mass, about 70% of the cells differentiate 

 into spores and the remaining 30% differentiate 

 into stalk cells. The basis for this proportional- 

 ity arises by the time of the migration stage. 

 At this time two types of cells have differentiated: 

 the so-called prespores and prestalks. Now, in 

 D. mucoroides as stalk formation occurs con- 

 tinually during migration new prestalk cells 

 are formed from the prespore mass. Thus, at 

 any point during migration there is a constant 

 proportionality between the prespore cells and 

 the prestalk cells, which results in the forma- 

 tion of a proportional sorocarp. 



The question arises, what is the mechanism 

 involved in establishing this proportionality? 

 Obviously it's a problem with the differentiation 

 of two types of cells initially. More specifically, 

 it's a problem in which two types of cells must 



D. mucoroides 



6 







^ 



J}=^ A 



k. 



Vegetotive A«gr«gotlon Migrotion Preculmlnofion Culminotien 



O^ 



Moturt 

 Sportt 



Fig. 1. 

 The developmental stages of D. discoideum and D. mucoroides. 



93 



