SELF-RECOGNITION 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 identi fied in several organisms, our knowledge of the molecular basis of sex ual cell recognition is still limited. We have been studying molecular mechanisms of sexual cell fusion using the lower eukaryote Dictyostel ium discoideum. There are homothallic, heterothallic, bisexual and ase xual strains in D. discoideum, and how they distinguish between each o ther to find out proper partners is an interesting and important quest ion. However, analytical studies of sexuality in D. discoideum have be en carried out mostly on heterothallic strains, and the polymorphism o f the mating system has not yet been thoroughly investigated. In the p resent study, we extended our analysis to the bisexual mating phenomen on paying special attention to the mechanism of self-incompatibility. We showed that a bisexual strain WS2162 was self-incompatible at the s tep of sexual cell fusion. Results of antibody inhibition of cell fusi on and detection of gp138, a cell-fusion-related protein found in hete rothallic strains, suggest that a molecular basis for bisexual and het erothallic mating are common. We propose two models to clarify the mec hanisms of self- and non-self discrimination in bisexual mating patter ns of D. discoideum.