Macrocyst formation in Dictyostelium discoideum: Mating or selfing?

Abstract

It is known from previous work that macrocysts are formed when the two strains of Dictyostelium discoideum (NC4 and V12) are mixed. By culturing NC4 and V12 amoebae together in various ratios and at several densities, and in experiments using vitally stained cells, we have shown that the number of macrocysts formed is directly related to the number of V12 (but not NC4) cells present and that macrocysts may occur without sexual fusion.A starved population of Dictyostelium discoideum amoebae can either develop into asexual fruiting bodies or form macrocysts, depending upon a number of conditions including the appropriate environmental cues (Blaskovics and Raper, '59; Nickerson and Raper, '73), and whether or not amoebae of the opposite mating type are present (Clark et al., '73; Erdos et al., '73). The morphological s e quence leading to macrocyst formation in D. discoideum has been described in some detail by Wallace ('77) and O'Day and Lewis ('81). Briefly, hundreds of amoebae aggregate to form tight cell clusters. Within an aggregate resides the cytophagic giant cell, the putative zygote. A primary wall is secreted around the aggregate transforming it into a precyst. The giant cell proceeds to engulf all of the amoebae in the precyst. In addition to the primary wall, secondary and tertiary walls, rich in cellulose, are formed around the macrocyst thus producing a well-protected, resistant cyst (Erdos et al., '72; Filosa and Dengler, '72; Nickerson and Raper, '73).Because of the obvious importance of genetic studies, it is desirable to know if the two strains, NC4 and V12, of D . discoideum, which produce macrocysts when brought together, are producing zygotes or reproducing asexually possibly by selfing. The extremely low germination efficiency of D. discoideum macrocysts ( < 2%; Wallace and Raper, '79) does not allow one to show that all macrocysts are the results of zygote formation. In this study it is shown that there is macrocyst production without cell fusion of the two mating types. The question of whether there also may be some sexual zygote formation must wait for further analysis. MATERIALS AND METHODS Growth and maintenance of stock culturesStock cultures of D. discoideum strains NC4 and V12M2 were maintained on Escherichia coli Blr as a food source on nutrient agar plates (per liter distilled H,O: 10 g peptone, 10 g dextrose, 0.381 g Na,HPO,, 0.45 g KH,PO,, 20 g difco agar) at 22°C. Stocks were recultured weekly. For long-term storage, spores were lyophilized. Formation of giant cells and macrocystsSpores of NC4 and V12 were washed and heatshocked according to the method of Cotter and Raper ('68) and plated separately on nutrient agar with E. coli Blr. Synchronously developing amoebae could be obtained by harvesting such growth plates 12-18 h after inoculation and separating amoebae from E. coli Blr by differential centrifugation (Bonner, '47). Such NC4 and V12 amoebae, when cultured together on nonnutrient agar and incubated in the dark at 24 k 1 "C, would produce giant cells in approxima...

Genetic structure of a natural population of Dictyostelium discoideum, a cellular slime mould

“…1) in D. discoideum is identical to germinating macrocysts in P. pallidum (Francis et al 1991). Bozzone & Bonner (1982) presented indirect evidence that some macrocysts in D. discoideum contain cells of only one parent. Our results suggest that this is the common pattern in D. discoideum.…”

Signalling and sex in the social amoebozoans

“…The importance of NC4 (type I) as the inducer and V12 (type II) cells as the responders has been supported by other work. Bozzone & Bonner (1982) showed that V12 cells alone can contribute to macrocyst formation when the ratio of V12 to NC4 is extremely high but macrocysts never occur in the absence of NC4 cells. The volatile nature of this inducer verifying it as a true sex pheromone was shown when NC4 cultures induced V12 cells to form macrocysts when both culture dishes were separated by a moat of detergent so that cells could only communicate via a common airspace (O’Day & Lewis, 1975; Lewis & O’Day, 1977).…”

Sexual pheromone accumulation and response in agar plate and liquid cultures of Dictyostelium discoideum

“…A recent study has suggested that cell contact between mating types is essential for macrocyst development (Bozzone and Bonner 1982). In addition, these workers retracted the conclusions from an earlier paper which supported the existence of sexual pheromones in D. discoideum (Machac and Bonner 1975).…”