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Unisexual reproduction drives meiotic recombination and phenotypic and karyotypic plasticity in Cryptococcus neoformans.

Sun S, Billmyre RB, Mieczkowski PA, Heitman J - PLoS Genet. (2014)

Bottom Line: We found that meiotic recombination operates in a similar fashion during both modes of sexual reproduction.Additionally, we found diploid meiotic progeny were also produced at similar frequencies in the two modes of sexual reproduction, and transient chromosomal loss and duplication likely occurs frequently and results in aneuploidy and loss of heterozygosity that can span entire chromosomes.Our results provide definitive evidence that α-α unisexual reproduction is a meiotic process similar to a-α bisexual reproduction.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, North Carolina, United States of America.

ABSTRACT
In fungi, unisexual reproduction, where sexual development is initiated without the presence of two compatible mating type alleles, has been observed in several species that can also undergo traditional bisexual reproduction, including the important human fungal pathogens Cryptococcus neoformans and Candida albicans. While unisexual reproduction has been well characterized qualitatively, detailed quantifications are still lacking for aspects of this process, such as the frequency of recombination during unisexual reproduction, and how this compares with bisexual reproduction. Here, we analyzed meiotic recombination during α-α unisexual and a-α bisexual reproduction of C. neoformans. We found that meiotic recombination operates in a similar fashion during both modes of sexual reproduction. Specifically, we observed that in α-α unisexual reproduction, the numbers of crossovers along the chromosomes during meiosis, recombination frequencies at specific chromosomal regions, as well as meiotic recombination hot and cold spots, are all similar to those observed during a-α bisexual reproduction. The similarity in meiosis is also reflected by the fact that phenotypic segregation among progeny collected from the two modes of sexual reproduction is also similar, with transgressive segregation being observed in both. Additionally, we found diploid meiotic progeny were also produced at similar frequencies in the two modes of sexual reproduction, and transient chromosomal loss and duplication likely occurs frequently and results in aneuploidy and loss of heterozygosity that can span entire chromosomes. Furthermore, in both α-α unisexual and a-α bisexual reproduction, we observed biased allele inheritance in regions on chromosome 4, suggesting the presence of fragile chromosomal regions that might be vulnerable to mitotic recombination. Interestingly, we also observed a crossover event that occurred within the MAT locus during α-α unisexual reproduction. Our results provide definitive evidence that α-α unisexual reproduction is a meiotic process similar to a-α bisexual reproduction.

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Meiotic progeny disomic for chromosome 4 are produced by α-α unisexual and a-α bisexual reproduction.Top panel: Meiotic progeny from α-α unisexual reproduction between strains 431α and XL280αSS that are disomic for chromosome 4 are shown. Bottom panel: Meiotic progeny from the a-α bisexual reproduction between strains 431α and XL280a that are disomic for chromosome 4 are depicted. The marker numbers in each panel correspond to those listed in Table 2. For simplicity, not all of the markers for α-α unisexual reproduction are shown (please see S3 Table for complete genotyping profiles). The markers located within the MAT locus are highlighted in green, while the markers flanking the centromere are highlighted in red. The values for ploidy were estimated based on FACS analyses and whole genome sequencing (see S1, S2 Figure), where 1N represents haploid and 2N represents diploid. Additionally, the “+” and “−” following 1N or 2N indicate the presence and absence of specific chromosomes, respectively. For example: 2N+22,3 (SSB359-small) represents diploid (2N) with additional two chromosomes (ch. 2 and 3). The small colony from progeny SSB552 appears to be a mixture of individuals with varying ploidy levels (S2 Figure), and is thus designated as “undetermined” here.
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pgen-1004849-g006: Meiotic progeny disomic for chromosome 4 are produced by α-α unisexual and a-α bisexual reproduction.Top panel: Meiotic progeny from α-α unisexual reproduction between strains 431α and XL280αSS that are disomic for chromosome 4 are shown. Bottom panel: Meiotic progeny from the a-α bisexual reproduction between strains 431α and XL280a that are disomic for chromosome 4 are depicted. The marker numbers in each panel correspond to those listed in Table 2. For simplicity, not all of the markers for α-α unisexual reproduction are shown (please see S3 Table for complete genotyping profiles). The markers located within the MAT locus are highlighted in green, while the markers flanking the centromere are highlighted in red. The values for ploidy were estimated based on FACS analyses and whole genome sequencing (see S1, S2 Figure), where 1N represents haploid and 2N represents diploid. Additionally, the “+” and “−” following 1N or 2N indicate the presence and absence of specific chromosomes, respectively. For example: 2N+22,3 (SSB359-small) represents diploid (2N) with additional two chromosomes (ch. 2 and 3). The small colony from progeny SSB552 appears to be a mixture of individuals with varying ploidy levels (S2 Figure), and is thus designated as “undetermined” here.

Mentions: Among the 156 progeny that we recovered from α-α unisexual reproduction, 12 (7.7%; or 14.9% if only unique genotypes are considered) were heterozygous for multiple genetic markers that we employed for genotyping, and the number of heterozygous loci ranging from 8 to 39 (Fig. 6). Similarly, among the 27 basidia that were dissected from a-α bisexual reproduction, we found 4 progeny from two separate basidia (7.4%; or 3.7% is all unique genotypes are considered), basidium No. 5 (progeny SSB889 and SSB904) and basidium No. 24 & 25 (progeny SSC243 and SSC258), that were heterozygous for 8 and 9 of the 17 loci that were analyzed, respectively (Fig. 6). All of these progeny were uninucleate based on DAPI staining, and FACS analyses showed that the nuclei of these progeny had about twice the DNA content as the haploid parental strains (S1 Figure), suggesting these progeny are diploid.


Unisexual reproduction drives meiotic recombination and phenotypic and karyotypic plasticity in Cryptococcus neoformans.

Sun S, Billmyre RB, Mieczkowski PA, Heitman J - PLoS Genet. (2014)

Meiotic progeny disomic for chromosome 4 are produced by α-α unisexual and a-α bisexual reproduction.Top panel: Meiotic progeny from α-α unisexual reproduction between strains 431α and XL280αSS that are disomic for chromosome 4 are shown. Bottom panel: Meiotic progeny from the a-α bisexual reproduction between strains 431α and XL280a that are disomic for chromosome 4 are depicted. The marker numbers in each panel correspond to those listed in Table 2. For simplicity, not all of the markers for α-α unisexual reproduction are shown (please see S3 Table for complete genotyping profiles). The markers located within the MAT locus are highlighted in green, while the markers flanking the centromere are highlighted in red. The values for ploidy were estimated based on FACS analyses and whole genome sequencing (see S1, S2 Figure), where 1N represents haploid and 2N represents diploid. Additionally, the “+” and “−” following 1N or 2N indicate the presence and absence of specific chromosomes, respectively. For example: 2N+22,3 (SSB359-small) represents diploid (2N) with additional two chromosomes (ch. 2 and 3). The small colony from progeny SSB552 appears to be a mixture of individuals with varying ploidy levels (S2 Figure), and is thus designated as “undetermined” here.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4263396&req=5

pgen-1004849-g006: Meiotic progeny disomic for chromosome 4 are produced by α-α unisexual and a-α bisexual reproduction.Top panel: Meiotic progeny from α-α unisexual reproduction between strains 431α and XL280αSS that are disomic for chromosome 4 are shown. Bottom panel: Meiotic progeny from the a-α bisexual reproduction between strains 431α and XL280a that are disomic for chromosome 4 are depicted. The marker numbers in each panel correspond to those listed in Table 2. For simplicity, not all of the markers for α-α unisexual reproduction are shown (please see S3 Table for complete genotyping profiles). The markers located within the MAT locus are highlighted in green, while the markers flanking the centromere are highlighted in red. The values for ploidy were estimated based on FACS analyses and whole genome sequencing (see S1, S2 Figure), where 1N represents haploid and 2N represents diploid. Additionally, the “+” and “−” following 1N or 2N indicate the presence and absence of specific chromosomes, respectively. For example: 2N+22,3 (SSB359-small) represents diploid (2N) with additional two chromosomes (ch. 2 and 3). The small colony from progeny SSB552 appears to be a mixture of individuals with varying ploidy levels (S2 Figure), and is thus designated as “undetermined” here.
Mentions: Among the 156 progeny that we recovered from α-α unisexual reproduction, 12 (7.7%; or 14.9% if only unique genotypes are considered) were heterozygous for multiple genetic markers that we employed for genotyping, and the number of heterozygous loci ranging from 8 to 39 (Fig. 6). Similarly, among the 27 basidia that were dissected from a-α bisexual reproduction, we found 4 progeny from two separate basidia (7.4%; or 3.7% is all unique genotypes are considered), basidium No. 5 (progeny SSB889 and SSB904) and basidium No. 24 & 25 (progeny SSC243 and SSC258), that were heterozygous for 8 and 9 of the 17 loci that were analyzed, respectively (Fig. 6). All of these progeny were uninucleate based on DAPI staining, and FACS analyses showed that the nuclei of these progeny had about twice the DNA content as the haploid parental strains (S1 Figure), suggesting these progeny are diploid.

Bottom Line: We found that meiotic recombination operates in a similar fashion during both modes of sexual reproduction.Additionally, we found diploid meiotic progeny were also produced at similar frequencies in the two modes of sexual reproduction, and transient chromosomal loss and duplication likely occurs frequently and results in aneuploidy and loss of heterozygosity that can span entire chromosomes.Our results provide definitive evidence that α-α unisexual reproduction is a meiotic process similar to a-α bisexual reproduction.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, North Carolina, United States of America.

ABSTRACT
In fungi, unisexual reproduction, where sexual development is initiated without the presence of two compatible mating type alleles, has been observed in several species that can also undergo traditional bisexual reproduction, including the important human fungal pathogens Cryptococcus neoformans and Candida albicans. While unisexual reproduction has been well characterized qualitatively, detailed quantifications are still lacking for aspects of this process, such as the frequency of recombination during unisexual reproduction, and how this compares with bisexual reproduction. Here, we analyzed meiotic recombination during α-α unisexual and a-α bisexual reproduction of C. neoformans. We found that meiotic recombination operates in a similar fashion during both modes of sexual reproduction. Specifically, we observed that in α-α unisexual reproduction, the numbers of crossovers along the chromosomes during meiosis, recombination frequencies at specific chromosomal regions, as well as meiotic recombination hot and cold spots, are all similar to those observed during a-α bisexual reproduction. The similarity in meiosis is also reflected by the fact that phenotypic segregation among progeny collected from the two modes of sexual reproduction is also similar, with transgressive segregation being observed in both. Additionally, we found diploid meiotic progeny were also produced at similar frequencies in the two modes of sexual reproduction, and transient chromosomal loss and duplication likely occurs frequently and results in aneuploidy and loss of heterozygosity that can span entire chromosomes. Furthermore, in both α-α unisexual and a-α bisexual reproduction, we observed biased allele inheritance in regions on chromosome 4, suggesting the presence of fragile chromosomal regions that might be vulnerable to mitotic recombination. Interestingly, we also observed a crossover event that occurred within the MAT locus during α-α unisexual reproduction. Our results provide definitive evidence that α-α unisexual reproduction is a meiotic process similar to a-α bisexual reproduction.

Show MeSH
Related in: MedlinePlus