Cell Fusion Promoting Factor Common to Homothallic and Heterothallic Mating Systems in Dictyostelium discoideum : (sexual cell fusion/Dictyostelium discoideum/conditioned medium/mating system).

Cellular slime mould Dictyostelium discoideum propagates as single haploid cells and under certain environmental conditions enters into a sexual cycle called macrocyst formation. There are homothallic and heterothallic strains reported, the former being able to form macrocysts in clonal cell populations while the latter to do so only in the presence of opposite mating-type strains. Molecular basis for differential mating systems is an intersting subject totally unknown yet. In the present study, sexual cell interactions in AC4, a homothallic strain of D. discoideum, was studied in comparison with the heterothallic mating system. The conditoned medium of AC4 cells was found to promote the sexual cell fusion among themselves. In addition, it also enhanced the cell fusion between heterothallic strains. Furthermore, the conditioned medium obtained from the mated culture of heterothallic strains reported to induce the sexual cell fusion in the heterothallic strains (Saga and Yanagisawa, 1983) was found also to promote the cell fusion in AC4. These results suggest that common regulatory mechanisms operate for sexual cell fusion among different mating systems in D. discoideum.