Genetics of sex determination in the social amoebae.

The social amoebae possess a sexual cycle that involves transient mutlicellularity: first a zygote attracts surrounding haploid amoebae to form a walled aggregate around it, and then cannibalizes these peripheral cells, eventually forming a dormant single-celled macrocyst. Self-fertile homothallic isolates occur as well as breeding groups of self-infertile heterothallic cells, which commonly have more than two mating types. The mating-type locus of the widely studied model organism Dictyostelium discoideum, which has three mating types, has recently been identified. Two of the three mating types are determined by single putative regulatory genes bearing no mutual similarity, while the third is specified by homologues of both of these genes. This is the first sex-determining locus of an Amoebozoan to be described and, since none of the key regulators show homology to known proteins, may be a first glimpse of a novel mode of regulation used in these organisms. The sexual cycle of dictyostelids has been relatively neglected, but continues to yield much interesting biology as well as having the potential to add to the genetic tools available for the study of these organisms.