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Virulence attributes and hyphal growth of C. neoformans are quantitative traits and the MATalpha allele enhances filamentation.

Lin X, Huang JC, Mitchell TG, Heitman J - PLoS Genet. (2006)

Bottom Line: We discovered that variation in hyphal length produced during fruiting is a quantitative trait resulting from the combined effects of multiple genetic loci, including the mating type (MAT) locus.Importantly, the alpha allele of the MAT locus enhanced hyphal growth compared with the a allele.MAC1 allelic differences contribute to phenotypic variation, and mac1Delta mutants exhibit defects in filamentation, melanin production, and high temperature growth.

View Article: PubMed Central - PubMed

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

ABSTRACT
Cryptococcus neoformans is a fungal human pathogen with a bipolar mating system. It undergoes a dimorphic transition from a unicellular yeast to hyphal filamentous growth during mating and monokaryotic fruiting. The traditional sexual cycle that leads to the production of infectious basidiospores involves cells of both alpha and a mating type. Monokaryotic fruiting is a modified form of sexual reproduction that involves cells of the same mating type, most commonly alpha, which is the predominant mating type in both the environment and clinical isolates. However, some a isolates can also undergo monokaryotic fruiting. To determine whether mating type and other genetic loci contribute to the differences in fruiting observed between alpha and a cells, we applied quantitative trait loci (QTL) mapping to an inbred population of F2 progeny. We discovered that variation in hyphal length produced during fruiting is a quantitative trait resulting from the combined effects of multiple genetic loci, including the mating type (MAT) locus. Importantly, the alpha allele of the MAT locus enhanced hyphal growth compared with the a allele. Other virulence traits, including melanization and growth at 39 degrees C, also are quantitative traits that share a common QTL with hyphal growth. The Mac1 transcription factor, encoded in this common QTL, regulates copper homeostasis. MAC1 allelic differences contribute to phenotypic variation, and mac1Delta mutants exhibit defects in filamentation, melanin production, and high temperature growth. Further characterization of these QTL regions will reveal additional quantitative trait genes controlling biological processes central to fungal development and pathogenicity.

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Application of QTL Mapping to Melanin Production and Growth at 39 °CThe averaged scores obtained from three independent replicates for melanin production and growth at 39 °C were used as trait values and applied in the WinQTL program. Profiles obtained by CIM are shown. One QTL on Chromosome 7 was identified as responsible for variation in melanin production (A) and two QTLs on Chromosomes 7 and 9 as responsible for growth sensitivity to 39 °C were identified consistently by single marker analysis, IM, CIM, and MIM (B). Other chromosomes without any significant QTL are not shown. Five QTLs responsible for variation of hyphal growth located on Chromosomes 7, 9, 4, 5, and 11 are also shown for comparison (C). The numbers below indicate the percentage of variation accounted for by the corresponding QTLs above according to CIM analyses. LOD threshold for melanin, temperature sensitivity, and filamentation was 7.1, 3.3, and 3.2 respectively.
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pgen-0020187-g009: Application of QTL Mapping to Melanin Production and Growth at 39 °CThe averaged scores obtained from three independent replicates for melanin production and growth at 39 °C were used as trait values and applied in the WinQTL program. Profiles obtained by CIM are shown. One QTL on Chromosome 7 was identified as responsible for variation in melanin production (A) and two QTLs on Chromosomes 7 and 9 as responsible for growth sensitivity to 39 °C were identified consistently by single marker analysis, IM, CIM, and MIM (B). Other chromosomes without any significant QTL are not shown. Five QTLs responsible for variation of hyphal growth located on Chromosomes 7, 9, 4, 5, and 11 are also shown for comparison (C). The numbers below indicate the percentage of variation accounted for by the corresponding QTLs above according to CIM analyses. LOD threshold for melanin, temperature sensitivity, and filamentation was 7.1, 3.3, and 3.2 respectively.

Mentions: In C. neoformans, oxidation of a variety of diphenolic substrates, including the neurotransmitter L-dihydroxyphenylalanine (L-DOPA), can lead to production of melanin [49]. Variation in the rates of melanization confers variation in the shades of brown pigmentation. We compared the degrees of pigmentation among the mapping population and assigned scores from 0 (no pigment) to 4 (the darkest colonies). Assays of this phenotype were repeated three times, and the scores were averaged and used as trait values. Analysis by the WinQTL program revealed only one QTL on Chromosome 7 (Figure 9A). This single QTL accounted for 67.5% of the total variation observed for this population as estimated by CIM analysis. Given the range of phenotypic variation in a single QTL, it is possible that epigenetic mechanisms affect melanization, that minor QTLs account for some of the variation that was not easily detected, or that undetectable QTLs exist in regions not mapped by our markers.


Virulence attributes and hyphal growth of C. neoformans are quantitative traits and the MATalpha allele enhances filamentation.

Lin X, Huang JC, Mitchell TG, Heitman J - PLoS Genet. (2006)

Application of QTL Mapping to Melanin Production and Growth at 39 °CThe averaged scores obtained from three independent replicates for melanin production and growth at 39 °C were used as trait values and applied in the WinQTL program. Profiles obtained by CIM are shown. One QTL on Chromosome 7 was identified as responsible for variation in melanin production (A) and two QTLs on Chromosomes 7 and 9 as responsible for growth sensitivity to 39 °C were identified consistently by single marker analysis, IM, CIM, and MIM (B). Other chromosomes without any significant QTL are not shown. Five QTLs responsible for variation of hyphal growth located on Chromosomes 7, 9, 4, 5, and 11 are also shown for comparison (C). The numbers below indicate the percentage of variation accounted for by the corresponding QTLs above according to CIM analyses. LOD threshold for melanin, temperature sensitivity, and filamentation was 7.1, 3.3, and 3.2 respectively.
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Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC1636697&req=5

pgen-0020187-g009: Application of QTL Mapping to Melanin Production and Growth at 39 °CThe averaged scores obtained from three independent replicates for melanin production and growth at 39 °C were used as trait values and applied in the WinQTL program. Profiles obtained by CIM are shown. One QTL on Chromosome 7 was identified as responsible for variation in melanin production (A) and two QTLs on Chromosomes 7 and 9 as responsible for growth sensitivity to 39 °C were identified consistently by single marker analysis, IM, CIM, and MIM (B). Other chromosomes without any significant QTL are not shown. Five QTLs responsible for variation of hyphal growth located on Chromosomes 7, 9, 4, 5, and 11 are also shown for comparison (C). The numbers below indicate the percentage of variation accounted for by the corresponding QTLs above according to CIM analyses. LOD threshold for melanin, temperature sensitivity, and filamentation was 7.1, 3.3, and 3.2 respectively.
Mentions: In C. neoformans, oxidation of a variety of diphenolic substrates, including the neurotransmitter L-dihydroxyphenylalanine (L-DOPA), can lead to production of melanin [49]. Variation in the rates of melanization confers variation in the shades of brown pigmentation. We compared the degrees of pigmentation among the mapping population and assigned scores from 0 (no pigment) to 4 (the darkest colonies). Assays of this phenotype were repeated three times, and the scores were averaged and used as trait values. Analysis by the WinQTL program revealed only one QTL on Chromosome 7 (Figure 9A). This single QTL accounted for 67.5% of the total variation observed for this population as estimated by CIM analysis. Given the range of phenotypic variation in a single QTL, it is possible that epigenetic mechanisms affect melanization, that minor QTLs account for some of the variation that was not easily detected, or that undetectable QTLs exist in regions not mapped by our markers.

Bottom Line: We discovered that variation in hyphal length produced during fruiting is a quantitative trait resulting from the combined effects of multiple genetic loci, including the mating type (MAT) locus.Importantly, the alpha allele of the MAT locus enhanced hyphal growth compared with the a allele.MAC1 allelic differences contribute to phenotypic variation, and mac1Delta mutants exhibit defects in filamentation, melanin production, and high temperature growth.

View Article: PubMed Central - PubMed

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

ABSTRACT
Cryptococcus neoformans is a fungal human pathogen with a bipolar mating system. It undergoes a dimorphic transition from a unicellular yeast to hyphal filamentous growth during mating and monokaryotic fruiting. The traditional sexual cycle that leads to the production of infectious basidiospores involves cells of both alpha and a mating type. Monokaryotic fruiting is a modified form of sexual reproduction that involves cells of the same mating type, most commonly alpha, which is the predominant mating type in both the environment and clinical isolates. However, some a isolates can also undergo monokaryotic fruiting. To determine whether mating type and other genetic loci contribute to the differences in fruiting observed between alpha and a cells, we applied quantitative trait loci (QTL) mapping to an inbred population of F2 progeny. We discovered that variation in hyphal length produced during fruiting is a quantitative trait resulting from the combined effects of multiple genetic loci, including the mating type (MAT) locus. Importantly, the alpha allele of the MAT locus enhanced hyphal growth compared with the a allele. Other virulence traits, including melanization and growth at 39 degrees C, also are quantitative traits that share a common QTL with hyphal growth. The Mac1 transcription factor, encoded in this common QTL, regulates copper homeostasis. MAC1 allelic differences contribute to phenotypic variation, and mac1Delta mutants exhibit defects in filamentation, melanin production, and high temperature growth. Further characterization of these QTL regions will reveal additional quantitative trait genes controlling biological processes central to fungal development and pathogenicity.

Show MeSH
Related in: MedlinePlus