Self- and non-self-recognition in bisexual mating of Dictyostelium discoideum

Cell recognition plays a central part in the sexual process. Although cell-surface molecules involved in gamete recognition have been identified in several organisms, our knowledge of the molecular basis of sexual cell recognition is still limited. We have been studying molecular mechanisms of sexual cell fusion using the lower eukaryote Dictyostelium discoideum. There are homothallic, heterothallic, bisexual and asexual strains in D. discoideum, and how they distinguish between each other to find out proper partners is an interesting and important question. However, analytical studies of sexuality in D. discoideum have been carried out mostly on heterothallic strains, and the polymorphism of the mating system has not yet been thoroughly investigated. In the present study, we extended our analysis to the bisexual mating phenomenon paying special attention to the mechanism of self-incompatibility. We showed that a bisexual strain WS2162 was self-incompatible at the step of sexual cell fusion. Results of antibody inhibition of cell fusion and detection of gp138, a cell-fusion-related protein found in heterothallic strains, suggest that a molecular basis for bisexual and heterothallic mating are common. We propose two models to clarify the mechanisms of self- and non-self discrimination in bisexual mating patterns of D. discoideum.