ReseaRch highlights

Microbial genetics Social amoebae get ready for sex Most eukaryotic microorganisms asexual developmental cycle upon strain. The resulting strain could carry out during starvation, producing ‘slugs’ that dif- mate with type I cells but not with The identification their life cycles. Although significant ferentiate into fruiting bodies; these type II cells, showing that the expected of the mat locus progress has been made in the study in turn produce that germi- gender switch had occurred. The opens the way of mating for several fungal species, nate to yield new amoebae. However, same locus in type III strains consists little is known about sexual repro- under certain conditions, two cells of two genes, matS and matT, which for the use of duction in protists. Now, writing in of different mating types can fuse to are homologous to matC and matD, sexual genetics in Science, Bloomfield and colleagues yield a diploid zygote that ultimately respectively (their gene products have D. discoideum. report the identification of a genetic forms a dormant . The 50% and 80% identity). locus that determines the three macrocyst undergoes and The authors then expressed mating types in the social numerous mitoses, and finally germi- various mat genes in the matA-null discoideum. nates to release haploid amoebae. mutant and found that mating types I D. discoideum can reproduce by Previous work indicated that and III are determined by a single growth and fission of single cells, a single genetic locus probably gene (either matA or matS, respec- which can also pass through an determines the three mating types tively), whereas the type II system is a (I, II and III) in D. discoideum. When hybrid of the other two and requires the authors separately hybridized the co-expression of matB and matC genomic DNA from four type I and (homologues of matA and matS). six type II D. discoideum strains to a The mat locus of D. discoideum DNA microarray derived from the does not resemble any known sex- of a type I strain, they found determining loci in other organisms, one gene that was present in all although homologous genes are type I organisms and absent from present in related species. all type II strains. This gene, which The identification of the mat locus they called matA, encodes a small opens the way for the use of sexual protein of unknown molecular func- genetics in D. discoideum. These tion. A matA-deficient mutant could findings may therefore represent not form with type II a significant leap forward in those cells. The researchers then sequenced disciplines that use this organism as a the same locus from a type II strain model to study, for example, cell dif- and identified three genes: matB, ferentiation and motility, , matC and matD; matB is homolo- and host–pathogen gous to matA (their gene products interactions. have 60% identity), whereas matC Cesar Sanchez and matD encode unrelated proteins. After confirming that the locus was original researcH PaPer Bloomfield, G. et al. Confocal micrograph of a Dictyostelium discoideum macrocyst, with protective walls >98% identical in all type II strains, Sex determination in the social amoeba surrounding hundreds of cannibalized amoebae trapped in vacuoles inside the Dictyostelium discoideum. Science 330, 1533–1536 cytoplasm of the dormant zygote. Image courtesy of G. Bloomfield, Medical the authors transferred this type II (2010) Research Council, Cambridge, UK. locus into the matA-deleted type I

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