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Parasexual genetic analysis of the cellular slime mold Dictyostelium discoideum A3
Abstract:
Haploid strain A3 of the cellular slime mold Dictyostelium discoideum is valuable for biochemical studies because it is capable of axenic growth. Mutants of A3 temperature-sensitive for growth and resistant to the drugs cycloheximide, acriflavin, or methanol were isolated.--Heterozygous diploid recombinants, formed at low frequency by cell and nuclear fusion, were isolated by selecting temperature-resistant progeny of mixed cultures of two nonallelic temperature-sensitive haploids (LOOMIS 1969). Each drug-resistant mutation was found to be recessive. Two independently isolated methanol-resistant mutants were in one complementation group.--Diploids of A3 heterozygous for drug resistance formed drug-resistant segregants with a frequency of approximately 10(-4). Segregants selected for resistance to a single drug were either haploid or diploid; the fraction which was haploid varied from 0.11 to 0.86, depending on the selected marker. Segregants selected for resistance to two or three drugs were almost all haploid.--Using this parasexual cycle of diploid formation and haploidization, linkage of these temperature-sensitive and drug-resistance mutations to each other and to mutations studied by KATZ and SUSSMAN (1972) and by WILLIAMS, KESSIN and Newell (1974b) was analyzed. The methanol-resistant mutants were found to be partially resistant to acriflavin, and unlinked to the mutant selected for acriflavin resistance, which was methanol-sensitive. Of the expected seven linkage groups in D. discoideum, five, and a possible sixth, have been marked.--Linkage analysis of a mutant abnormal in morphogenesis showed that its phenotype results from two unlinked chromosomal mutations.
Insights
This study utilized the parasexual cycle in Dictyostelium discoideum to map drug-resistance mutations. Researchers successfully marked five, possibly six, of the seven linkage groups, advancing genetic understanding of this organism.
Area of Science:
- Cellular and Molecular Biology
- Genetics
- Developmental Biology
Background:
- Haploid strain A3 of Dictyostelium discoideum is crucial for biochemical studies due to its axenic growth capability.
- Drug-resistant and temperature-sensitive mutants were generated to facilitate genetic analysis.
Purpose of the Study:
- To utilize the parasexual cycle of Dictyostelium discoideum for genetic mapping of mutations.
- To analyze the linkage of temperature-sensitive and drug-resistance mutations.
- To mark additional linkage groups in Dictyostelium discoideum.
Main Methods:
- Isolation of temperature-sensitive and drug-resistant mutants (cycloheximide, acriflavin, methanol).
- Formation and isolation of heterozygous diploid recombinants through cell and nuclear fusion.
- Selection of drug-resistant segregants from diploid strains to determine ploidy and linkage.
Main Results:
- Drug-resistant mutations were found to be recessive.
- Methanol-resistant mutants exhibited partial resistance to acriflavin and were unlinked to acriflavin-resistant mutants.
- Five, and potentially a sixth, of the seven expected linkage groups in Dictyostelium discoideum were marked.
- A mutant with abnormal morphogenesis was shown to result from two unlinked chromosomal mutations.
Conclusions:
- The parasexual cycle is an effective tool for genetic mapping in Dictyostelium discoideum.
- Linkage analysis revealed new genetic markers and relationships between mutations.
- The study significantly advanced the genetic map of Dictyostelium discoideum, marking multiple linkage groups.