scholarly journals Mating-Type Locus of Cryptococcus neoformans: a Step in the Evolution of Sex Chromosomes

2002 ◽  
Vol 1 (5) ◽  
pp. 704-718 ◽  
Author(s):  
Klaus B. Lengeler ◽  
Deborah S. Fox ◽  
James A. Fraser ◽  
Andria Allen ◽  
Keri Forrester ◽  
...  
Keyword(s):  
Cryptococcus Neoformans ◽  
Mating Type ◽  
Sex Chromosomes ◽  
Sexual Development ◽  
New Paradigm ◽  
Type Locus ◽  
Mating Type Locus ◽  
Fungal Mating ◽  
Kinase Cascade ◽  
Nonself Recognition

ABSTRACT The sexual development and virulence of the fungal pathogen Cryptococcus neoformans is controlled by a bipolar mating system determined by a single locus that exists in two alleles, α and a. The α and a mating-type alleles from two divergent varieties were cloned and sequenced. The C. neoformans mating-type locus is unique, spans >100 kb, and contains more than 20 genes. MAT-encoded products include homologs of regulators of sexual development in other fungi, pheromone and pheromone receptors, divergent components of a MAP kinase cascade, and other proteins with no obvious function in mating. The α and a alleles of the mating-type locus have extensively rearranged during evolution and strain divergence but are stable during genetic crosses and in the population. The C. neoformans mating-type locus is strikingly different from the other known fungal mating-type loci, sharing features with the self-incompatibility systems and sex chromosomes of algae, plants, and animals. Our study establishes a new paradigm for mating-type loci in fungi with implications for the evolution of cell identity and self/nonself recognition.

scholarly journals Consequences of recombination for the evolution of the mating type locus in Chlamydomonas reinhardtii

2019 ◽  
Author(s):  
Ahmed R. Hasan ◽  
Jaspreet K. Duggal ◽  
Rob W. Ness
Keyword(s):  
Chlamydomonas Reinhardtii ◽  
Gene Conversion ◽  
Mating Type ◽  
Sex Chromosomes ◽  
Purifying Selection ◽  
Recombination Suppression ◽  
Type Locus ◽  
Mating Type Locus ◽  
Sexual Characteristics ◽  
Population Genetic Variation

SummaryRationaleRecombination suppression in sex chromosomes and mating type loci can lead to degeneration due to reduced selection efficacy and Muller’s ratchet effects. However, genetic exchange in the form of non-crossover gene conversions may still take place within crossover-suppressed regions. Recent work has found evidence that gene conversion may explain the low levels of allelic differentiation in the dimorphic mating type locus (MT) of the isogamous alga Chlamydomonas reinhardtii. However, no one has tested whether gene conversion is sufficient to avoid the degeneration of functional sequence within MT.MethodsHere, we calculate levels of linkage disequilibrium (LD) across MT as a proxy for recombination rate and investigate its relationship to patterns of population genetic variation and the efficacy of selection in the region.ResultsWe find that levels of LD predict selection efficacy across MT, and that purifying selection is stronger in shared genes than MT-limited genes to the point of being equivalent to that of autosomal genes.ConclusionsWe argue that isogamous systems without secondary sexual characteristics exhibit reduced selective pressure to differentiate sex chromosomes, and that recombination via gene conversion plays an important role in both reducing differentiation and preventing degeneration of crossover suppressed mating type loci.

scholarly journals Multiple Versions of the A Mating Type Locus of Coprinus cinereus are Generated by Three Paralogous Pairs of Multiallelic Homeobox Genes

Genetics ◽  
1996 ◽  
Vol 144 (1) ◽  
pp. 87-94 ◽  
Author(s):  
Eneida H Pardo ◽  
Suzanne F O'Shea ◽  
Lorna A Casselton
Keyword(s):  
Mating Type ◽  
Sexual Development ◽  
Host Gene ◽  
Coprinus Cinereus ◽  
Type Locus ◽  
Multiple Alleles ◽  
Combined Analysis ◽  
Paralogous Genes ◽  
Mating Type Locus ◽  
Mating Compatibility

Abstract The A mating type locus of Coprinus cinereus determines mating compatibility by regulating essential steps in sexual development. Each A locus contains several genes separated into two functionally independent complexes termed Aα and Aβ, and the multiple alleles of these genes generate an estimated 160 A mating specificities. The genes encode two classes of homeodomain-containing proteins designated HD1 and HD2. In this report we describe two newly cloned loci, A2 and A5, and compare them with A42, A43 and A6 that we have described previously. An Aβ-null locus, retaining just a single active HD1 gene from the α-complex, was generated by mutation. Using this as a transformation host, gene combinations that promote A-regulated development were identified. We demonstrate that each A locus contains members of three paralogous pairs of HD1 and HD2 genes. Different allelic versions of gene pairs are compatible but paralogous genes are incompatible. The genes present in four uncloned A loci were deduced using Southern analyses and transformations with available cloned genes. The combined analysis of nine A factors identifies sufficient A gene alleles to generate at least 72 A mating specificities.

scholarly journals Size variation of the non-recombining region on the mating-type chromosomes in the fungal Podospora anserina species complex

2021 ◽  
Author(s):  
Fanny E Hartmann ◽  
S Lorena Ament-Velásquez ◽  
Aaron A Vogan ◽  
Valérie Gautier ◽  
Stephanie Le Prieur ◽  
...  
Keyword(s):  
Mating Type ◽  
Sex Chromosomes ◽  
Chromosomal Rearrangements ◽  
Size Variation ◽  
Sequence Divergence ◽  
Podospora Anserina ◽  
Strong Linkage Disequilibrium ◽  
Mating Types ◽  
Type Locus ◽  
Mating Type Locus

Abstract Sex chromosomes often carry large non-recombining regions that can extend progressively over time, generating evolutionary strata of sequence divergence. However, some sex chromosomes display an incomplete suppression of recombination. Large genomic regions without recombination and evolutionary strata have also been documented around fungal mating-type loci, but have been studied in only a few fungal systems. In the model fungus Podospora anserina (Ascomycota, Sordariomycetes), the reference S strain lacks recombination across a 0.8 Mb region around the mating-type locus. The lack of recombination in this region ensures that nuclei of opposite mating types are packaged into a single ascospore (pseudo-homothallic lifecycle). We found evidence for a lack of recombination around the mating-type locus in the genomes of 10 P. anserina strains and six closely related pseudo-homothallic Podospora species. Importantly, the size of the non-recombining region differed between strains and species, as indicated by the heterozygosity levels around the mating-type locus and experimental selfing. The non-recombining region is probably labile and polymorphic, differing in size and precise location within and between species, resulting in occasional, but infrequent, recombination at a given base pair. This view is also supported by the low divergence between mating types, and the lack of strong linkage disequilibrium, chromosomal rearrangements, trans-specific polymorphism and genomic degeneration. We found a pattern suggestive of evolutionary strata in P. pseudocomata. The observed heterozygosity levels indicate low but non-null outcrossing rates in nature in these pseudo-homothallic fungi. This study adds to our understanding of mating-type chromosome evolution and its relationship to mating systems.

scholarly journals Serotype AD Strains of Cryptococcus neoformans Are Diploid or Aneuploid and Are Heterozygous at the Mating-Type Locus

2001 ◽  
Vol 69 (1) ◽  
pp. 115-122 ◽  
Author(s):  
Klaus B. Lengeler ◽  
Gary M. Cox ◽  
Joseph Heitman
Keyword(s):  
Cryptococcus Neoformans ◽  
Mating Type ◽  
Yeast Cells ◽  
Sexual Cycle ◽  
Pcr Analysis ◽  
Environmental Isolates ◽  
Type Locus ◽  
Serotype A ◽  
Mating Type Locus ◽  
Normal Meiosis

ABSTRACT Cryptococcus neoformans is a pathogenic basidiomycete with a defined sexual cycle involving mating between haploid yeast cells with a transient diploid state. C. neoformans occurs in four predominant serotypes (A, B, C, and D), which represent different varieties or species. Rare clinical and environmental isolates with an unusual AD serotype have been reported and suggested to be diploid. We found by fluorescence-activated cell sorter analysis that serotype AD strains are aneuploid or diploid. PCR analysis with primers specific for serotype A or D alleles of theCNA1, CLA4, and GPA1 genes revealed that both alleles are often present in serotype AD strains. PCR analysis with primers specific for genes in the MATa orMATα mating-type loci revealed that serotype AD strains are heterozygous for the mating-type locus. Interestingly, in several serotype AD strains, the MATα locus was derived from the serotype D parent and the MATa locus was inherited from a serotype A parent that has been thought to be extinct. Basidiospores from a self-fertile serotype AD strain bearing the putative serotype AMATa locus showed a very low viability (∼5%), and no fertile serotype A MATa strain could be recovered. Serotype AD strains were virulent in a murine model. Hybrid AD strains could readily be isolated following a laboratory cross between a serotype A strain and a serotype D strain. In summary, serotype AD strains ofC. neoformans are unusual aneuploid or diploid strains that result from matings between serotype A and D strains. Self-fertile isolates fail to undergo normal meiosis because of genetic divergence. Our findings further suggest that serotype A MATa strains may exist in nature.

scholarly journals Mitochondria Are Inherited From the MATa Parent in Crosses of the Basidiomycete Fungus Cryptococcus neoformans

Genetics ◽  
2003 ◽  
Vol 163 (4) ◽  
pp. 1315-1325 ◽  
Author(s):  
Zhun Yan ◽  
Jianping Xu
Keyword(s):  
Cryptococcus Neoformans ◽  
Mating Type ◽  
Clinical Strain ◽  
Pathogenic Yeast ◽  
Type Locus ◽  
Mating Type Locus ◽  
Mtdna Inheritance ◽  
Mitochondrial Genotype ◽  
Diploid Cells ◽  
Isogenic Strains

Abstract Previous studies demonstrated that mitochondrial DNA (mtDNA) was uniparentally transmitted in laboratory crosses of the pathogenic yeast Cryptococcus neoformans. To begin understanding the mechanisms, this study examined the potential role of the mating-type locus on mtDNA inheritance in C. neoformans. Using existing isogenic strains (JEC20 and JEC21) that differed only at the mating-type locus and a clinical strain (CDC46) that possessed a mitochondrial genotype different from JEC20 and JEC21, we constructed strains that differed only in mating type and mitochondrial genotype. These strains were then crossed to produce hyphae and sexual spores. Among the 206 single spores analyzed from six crosses, all but one inherited mtDNA from the MATa parents. Analyses of mating-type alleles and mtDNA genotypes of natural hybrids from clinical and natural samples were consistent with the hypothesis that mtDNA is inherited from the MATa parent in C. neoformans. To distinguish two potential mechanisms, we obtained a pair of isogenic strains with different mating-type alleles, mtDNA types, and auxotrophic markers. Diploid cells from mating between these two strains were selected and 29 independent colonies were genotyped. These cells did not go through the hyphal stage or the meiotic process. All 29 colonies contained mtDNA from the MATa parent. Because no filamentation, meiosis, or spore formation was involved in generating these diploid cells, our results suggest a selective elimination of mtDNA from the MATα parent soon after mating. To our knowledge, this is the first demonstration that mating type controls mtDNA inheritance in fungi.

scholarly journals The STE12α Homolog Is Required for Haploid Filamentation But Largely Dispensable for Mating and Virulence in Cryptococcus neoformans

Genetics ◽  
1999 ◽  
Vol 153 (4) ◽  
pp. 1601-1615 ◽  
Author(s):  
Changli Yue ◽  
Lora M Cavallo ◽  
J Andrew Alspaugh ◽  
Ping Wang ◽  
Gary M Cox ◽  
...  
Keyword(s):  
Transcription Factor ◽  
Cryptococcus Neoformans ◽  
Mating Type ◽  
Sexual Cycle ◽  
Type Locus ◽  
Map Kinase Cascade ◽  
Mutant Strains ◽  
Genetic Epistasis ◽  
Kinase Cascade ◽  
Immunocompromised Hosts

Abstract Cryptococcus neoformans is a fungal pathogen that causes meningitis in immunocompromised hosts. The organism has a known sexual cycle, and strains of the MATα mating type are more virulent than isogenic MATa strains in mice, and they are more common in the environment and infected hosts. A C. neoformans homolog of the STE12 transcription factor that regulates mating, filamentation, and virulence in Saccharomyces cerevisiae and Candida albicans was identified previously, found to be encoded by a novel region of the MATα mating type locus, and shown to enhance filamentous growth when overexpressed. We have disrupted the C. neoformans STE12 gene in a pathogenic serotype A isolate. ste12 mutant strains exhibit a severe defect in filamentation and sporulation (haploid fruiting) in response to nitrogen starvation. In contrast, ste12 mutant strains have only modest mating defects and are fully virulent in two animal models compared to the STE12 wild-type strain. In genetic epistasis experiments, STE12 functions in a MAP kinase cascade to regulate fruiting, but not mating. Thus, the C. neoformans STE12α transcription factor homolog plays a specialized function in haploid fruiting, but it is dispensable or redundant for mating and virulence. The association of the MATα locus with virulence may involve additional genes, and other transcription factors that regulate mating and virulence remain to be identified.

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