zone removed, 



Post. 



isolate can produce the missing cell type and 

 produce a fruiting body of normal proportions. 



Bonner et al. (6) following Raper's experi- 

 ment in which they transacted the anterior tip 

 and posterior prespore area in D. discoideum 

 (Fig. 14). They discarded the center section in 

 which the two types of cells were adjacent. I 

 might add that the anterior tip is devoid of 

 nonstarch polysaccharide staining (PAS) but 

 the posterior tip is heavily stained. They allowed 

 the isolated fragments to reorganize for one 

 hour before fixing and staining again. They noted 

 that in the isolated posterior prespore area a 

 margin of cells had begun to lose staining which 

 apparently marked the differentiation of prestalk 

 cells. Later on the prestalk cells are more 

 clearly established, and it appears that pro- 

 portional development has been reestablished. 

 In the isolated anterior tip the staining has begun 

 in the lower region marking the beginning of the 

 formation of prespore cells. By 6 hours pre- 

 spore cell differentiation was well advanced. 

 Thus, it appears that morphological reorgani- 

 zation or regulation of the slime mold occurs 

 simultaneously with regulation of the biochemi- 

 cal entities. 



We performed similar experiments with 

 D, mucoroides and D. discoideum with the idea 

 of staining the fragments with fluorescent anti- 

 body to determine the antigen patterns appearing 

 during reorganization (Fig. l^).laD. discoideum 

 transections we obtained about 2/3 of the an- 

 terior prestalk area and allowed it to reorganize 

 for three hours before fixing it, running it 

 through the sectioning process and staining it 

 with antiserum. In D. mucoroides we isolated 

 the anterior 2/3 of the prestalk area, trying 

 to avoid the region we assumed to be close to 

 the junction of the prestalk-prespore area. You 

 cannot, of course, see the junction of the two 

 types of cells in the living slime mold, unless 

 they have been stained with some sort of vital 

 dye beforehand. In other transections we cut as 

 close as possible to the assumed position of the 

 junction. Each of these fragments was allowed 

 to reorganize for two hours before fixation. 



A third type of transection was made which 

 isolated the entire prestalk area and approxi- 

 mately an equal amount of prespore cells. This 

 type of preparation was allowed to reorganize 

 for two hours before fixation whereas the pos- 

 terior prespore areas reorganized for 2 to 5 

 hours. 



Figure 16 shows an isolated D. mucoroides 

 anterior tip which was allowed to reorganize 

 for about two hours. Now, prespore cells have 



.-«>r .-. ' ... ' . ; ^ ' ' ' " ' ^- ' VVl--^>-.VJ^- ' > ' '- ' jt" 



hour 



6 hours 



Fig. 14. 



A diagram illustrating the experiment In which a par- 

 tially differentiated migrating cell mass is bisected and 

 each portion is examined by the PAS technique after one 

 and 6 hours, respectively. Note that the anterior end of 

 each fragment reversed its PAS staining properties; in 

 one case from the light prestalk condition to the dark 

 prespore condition and vice versa in the other. (Fig. 4, 

 Bonner, Chiquoine and Kolderle, J. Exp. tool. 130, 147, 

 1955; reproduced with permission of the Wlstar Institute 

 of Anatomy and Biology.) 



□ PRESPORES 

 O PRESTALKS 



□ STALKS 



discoideum 



D. mucoroides 



Fig. 15. 



Diagram describing the transection of D. discoideum and 

 D. mucoroides slugs and their developmental stages at- 

 tained before fixation and staining with fluorescent anti- 

 serum. (Fig. 1, Gregg, Devel, Biol. 12, 377, 1965; 

 reproduced with permission of Developmental Biology, 

 published by Academic Press). 



not differentiated in this particular preparation- 

 It appears, although we did not make a detailed 

 study of this, that the number of prespore cells 

 that differentiate seems to depend upon the re- 

 gion in which the transection was made. The 

 closer we get to the junction of the two types of 



101 



