Sexuality in the cellular slime mold Dictyostelium giganteum.

Abstract

By pairing of strains of Dictyostelium giganteum in various combinations this species was shown to be heterothallic. Four mating types were identified. Some strains could not be assigned a mating type and others showed no mating reaction. No self-compatible strains were found. Mutations were introduced in several strains and genetic crosses were performed. The results of these crosses show that mating and macrocyst formation are controlled by a single locus-multiple allele incompatibility system. The results also support the view that the myxamoebae that emerge upon germination of the macrocysts are the products of meiosis.In the cellular slime molds the macrocyst is a developmental alternative to the sorocarp. Macrocyst formation begins with the development of a large cell that increases in size as it ingests surrounding myxamoebae (1, 2). Prior to their ingestion the associated myxamoebae have formed the loose, fibrillar primary wall. The ingested myxamoebae are contained in vacuoles of the enlarging macrocyst protoplast. When ingestion is complete, the single large cell forms a rigid secondary wall and a more flexible, trilaminar tertiary wall (2). As the macrocyst matures the ingested amoebae are fragmented into smaller and smaller bodies until they are completely digested, giving the cyst a homogeneous appearance. After an appropriate period of maturation, the time varying with the species, the protoplast of the macrocyst cleaves into myxamoebae which escape when the walls break (3). s adgein th celllar sim mldomeirom a ultrastructural studyofsuch cyn oetI, where late in development meiotic chromosomes were observed (2). It was also shown that the large cell of the nascent macrocyst was at first binucleate but became uninucleate by the time ingestion of the adjacent myxamoebae began. These facts indicated that the macrocyst protoplast arose from the fusion of two cells followed by nuclear fusion and subsequent meiosis,\ thus making the giant cell a zygote.It

Genetic Exchanges in the Macrocysts of Dictyostelium discoideum

“…Recombination among various types of markers has been reported in the progeny from germinated macrocysts of D. mucoroides (MacInnes & Francis, 1974), D. giganteum (Erdos et al, 1975) and Polysphondylium pallidum (Francis, 1975). In all of these studies, arguments are presented favouring a meiotic rather than a parasexual mechanism as operative in macrocysts.…”

Amoebozoans are Secretly but Ancestrally Sexual: Evidence for Sex Genes and Potential Novel Crossover Pathways in Diverse Groups of Amoebae

“…1973a; Goodfellow et al. 1974; Erdos et al. 1975; Schuster 1976; Dacks and Roger 1999a; Goldstein 1999a; Ramesh et al.…”

Macrocyst formation in three dictyostelid species, Dictyostelium monochasioides, Polysphondylium candidum, and P. pseudo-candidum

“…Macrocyst formation is known only in 11 species. Five are heterothallic: Dictyosteliurn giganteum Singh (Erdos et al, 1975), D. lacteum van Tieghem (J. C. Cavender, personal communication), D. mexicanum Cavender, Worley et Raper (Raper, 1984), D. rosarium Raper et Cavender (Chang and Raper, 1981), and Polysphondylium tenuissimum Hagiwara (Hagiwara, 1989). Four are both heterothallic and homothallic: D. discoideum Raper (Erdos et al, 1973b), D. purpureum Olive (Clark et al, 1973;Nickerson and Raper, 1973), P. pallidum Olive (Eisenberg and Francis, 1977), and P. violaceum Brefeld (Clark et al, 1973;Nickerson and Raper, 1973).…”