appears that the presence of the prespore cells 

 in some way inhibits the synthesis of this anti- 

 gen that appears in the isolated prestalk cells. 



Figure 18 shows an isolated D. discoideum 

 prestalk area which was allowed to reorganize 

 for a couple of hours. Again you find a reappear- 

 ance of the antigen in the prestalk cells and in 

 the stalk cells. In D. discoideum prespore cells 

 seem to differentiate more readily. I believe 

 that these are newly differentiated prespore 

 cells and not prespore cells which were acci- 

 dentally removed at the time of the transection. 

 So, I believe that proportional reorganization 

 was initiated in this preparation. 



TS'O: Excuse me, one thing is not very 

 clear to me. Is the rearrangement or reorgani- 

 zation involved with synthesizing new types of 

 cells or transformation of old types to new 

 types? 



GREGG: In an isolated prestalk area, in 

 order for them to regain their proportionality, 

 they must differentiate new prespore cells from 

 existing prestalk cells. 



TS'O: There is new synthesis going on, 

 too, isn't there? Don't you get new cells? 



GREGG: No, there's no increase in cell 

 number. 



TS'O: Then the transected one would be 

 smaller in size? 



GREGG: Oh yes, it would be smaller. The 

 size depends upon the total number of cells 

 isolated. 



Figure 19 shows a reorganizing D. muco- 

 roides posterior prespore area. Now if we fixed 

 and stained this immediately following transac- 

 tion, the entire area would be stained uniformly. 

 After two hours of reorganization the cells at 

 the anterior or uppermost part are beginning to 

 lose their stain or cytoplasmic antigen. Evi- 

 dently, they are forming prestalk cells in order 

 that they can form a stalk and consequently a 

 fruiting body. If we allow reorganization to go 

 on for about five hours, the normal slug shape 

 is regained and the normal proportion of cells 

 is restored. 



In order for a slime mold prestalk isolate 

 to regain its proportionality it must differentiate 

 a certain number of prespore cells. The antigen 

 that reappears must be a necessary entity in the 

 formation of new prespore cells. The prepara- 

 tion in Fig, 20 was stained with antiserum which 

 was absorbed with vegetative amoebae from 

 cultures of about 17 hours of age. We were 

 interested in determining whether nor not the 

 new antigen which reappeared was the same 

 antigen which was present in the cells of an 



earlier age. If it was present in younger cells 

 it probably was necessary in the initial differen- 

 tiation of prespore cells and prespore antigens. 

 However, the absorbed serum produced no stain- 

 ing whatsoever in this preparation. Now, had 

 this preparation contained prespore cells, the 

 prespore cells would be stained to a certain 

 degree. If the antiserum is absorbed with vege- 

 tative amoebae, the prespore staining is not 

 removed. It removes all the staining in the pre- 

 stalk cells, however. 



Figure 21 shows exactly the same section 

 with the exception that it has been stained with 

 the non-absorbed serum simply to show that the 

 antigen had been synthesized in this particular 

 preparation. Now, it was of interest to us that 

 this antigen appeared throughout the entire pre- 

 stalk area. U it is necessary for the slime mold 

 to produce prespore cells to regain their pro- 

 portionality and if this antigen is necessary in 

 the reorganization, it's strange that it was not 

 confined only to a certain number of prestalk 

 cells which would be likely to form prespore 

 cells in the lower area. Thus, it appears that 

 the isolated prestalk cells cannot immediately 

 integrate their size with the necessity to dif- 

 ferentiate a particular number of prespore cells. 

 This is based on the assumption that this antigen 

 is an antigen necessary in the differentiation of 

 prespore cells. 



How does this proportionality arise? Well, 

 I suggest that proportionality arises from the 

 differentiation of prespore cells; and as a result 

 of the differentiation of prespore cells, there is 

 an interaction between the two types of cells 

 which results in an equilibrium. Consequently, 

 in some way, the differentiation of the missing 

 cell types is limited such that the cells are not 

 over-produced. Now, the same idea may be 

 applied to the isolated prespore areas. Their 

 "task", of course, is to produce new prestalk 

 cells. As prestalk cells are produced, again I 

 suggest that there is an interaction between the 

 two cell types which results in a control of cell 

 differentiation and eventually results in pro- 

 portionality being established. 



FERGUS: Would you care to comment on 

 why those prespore amoebae could not increase 

 in number in your transection techniques? 



GREGG: Well, I could not state categori- 

 cally that cell division does not occur. However, 

 attempts have been made to find whether or not 

 the cells increase in number during the normal 

 development, not particularly in transection. 

 There has been no finding which definitely estab- 

 lished that there was a tremendous increase in 



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