which are characterized by the loss of prestalk 

 antigens in the prestalk cells and the synthesis 

 of additional antigens in the prespores. To what 

 this may be attributed is a little bit of a puzzle. 

 However, we know from previous work that 

 antigens are synthesized during the transition 

 from the amoebae to the pseudoplasmodium. 

 Also, antigens are lost during this transition. 

 Some of these antigens which are lost may be 

 the antigens from the prestalk cells, resulting 

 in the loss of standing capacity in the prestalk 

 area, whereas the additional antigens which are 

 synthesized during the transition may be repre- 

 sented by the prespore antigens which are syn- 

 thesized in the prespore cells. Additional anti- 

 gens are lost and also synthesized in the 

 transition from the slug to the mature spores. 



Now, Sonneborn et al. (5) have shown that 

 mucopolysaccharide begins to increase, begin- 

 ning at about the late aggregation stage in 

 D. discoideum, and reaches a peak during cul- 

 mination. Perhaps the synthesis of prespore 

 antigen is represented by a rise in mucopoly- 

 saccharide. However, this is speculation. Bonner 

 et al. (6) have shown that such polysaccharides 

 are confined to the prespore cells with very 

 little polysaccharide staining in the prestalk 

 cells. So, it's possible that some of the antigens 

 we're dealing with are polysaccharides and that 

 accounts for the particular staining we find with 

 fluorescent antibody in the slug. 



Now, there are some mutant forms of slime 

 molds which appear to be inhibited in their abil- 

 ity to form prespore cells and prestalk cells. 

 Filosa (3) isolated the mutant MV from D. mu- 

 coroides-ll, which is characterized by the fact 

 that it forms a relatively small slug. D. muco- 

 roides-11 migrates long distances before form- 

 ing the spore mass, whereas MV may migrate 

 without forming a stalk or may migrate for a 

 short distance and form a short stalk bearing a 

 small spore mass. Thus MV appears to be in- 

 hibited in their migrating ability, and this may 

 be tied up with the fact that they are inhibited 

 in their ability to form prestalk cells and pre- 

 spore cells. Figure 13 is a cross section of an 

 MV slug, which in this instance has begun to 

 produce a small stalk. Now, when we stain MV 

 slugs with either MV serum or with wild type 

 antiserum, we observe essentially the same 

 staining pattern. Generally, the staining pattern 

 is not as intensive as in the wild type and, on 

 many occasions, the staining is spotty and gives 

 a patchy appearance. There is no sharp delinea- 

 tion between the prestalk cells and the prespore 

 cells. It appears that the normal complement of 



prestalk cells has not differentiated, at least by 

 this stage. 1 might add that the antiserum pro- 

 duced by the MV will stain the wild type per- 

 fectly normally. So it appears that there are 

 similar antigens in MV which can result in 

 antiserum which will stain the wild type nor- 

 mally; but there apparently are not a sufficient 

 number of antigens in the MV to enable it to 

 stain intensively. 



There is a mutant form of D. discoideum 

 known as Fr-17 which is similar to MV in that 

 it fails to develop normally (5). Usually it forms 

 amorphous mounds of cells but under certain 

 circumstances it forms an aberrant looking 

 fruiting body, a stalk bearing a small spore 

 mass. They have found this mutant, Fr-17, 

 produces mucopolysaccharide in normal quan- 

 tities but at a much earlier stage than the 

 normal wild type. In other words, the production 

 of mucopolysaccharide appears to be accelerated 

 in the Fr-17. Incidentally, the mucopolysaccha- 

 ride is antigenic, also (5). They've tested it with 

 spore antiserum. So there's a possibility, since 

 this polysaccharide(s) is antigenic, that we are 

 dealing with polysaccharide as well as protein. 



Now, Takeuchi (1) has reported that MV 

 cells removed from the interphase stage, that 

 is just prior to aggregation, still retain, what 

 he terms, their ring-like staining. This means 

 that they have more or less of a diffuse staining 

 at interphase, whereas the wild type cell will 

 have developed small granules which stain 

 prominently. There appears to be a delay inMV 

 at the interphase stage in the synthesis of these 

 small granules. Whether this has anything to do 

 with the polysaccharide synthesis we cannot say 

 at the moment, but it appears that the differen- 

 tiation of these cells into prestalk and prespores 

 may be related in some way to the fact that they 

 have delayed formation of these small granules 

 which is normal to the wild type. 



Most of the material that I've presented so 

 far was a necessary prelude to the main point 

 which I hope to make. I had to study normal 

 development first in order to interpret the 

 transection experiments which I shall discuss 

 now. 



Raper (7) performed an experiment with 

 D. discoideum in which he transected prestalk 

 cells and a portion of the prespore area and 

 isolated the two fragments. If he allowed suffi- 

 cient time to go by, each of these portions (the 

 prespore area and the prestalk area) regulated 

 to form a normal fruiting body. This means that 

 each of these portions of the slime mold has the 

 capacity to regulate. Consequently, each type of 



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