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PubMed1997

Prolactin profiles of pregnant, lactating and non-mated female mink (Mustela vison).

This study was part of an experiment on energy metabolism in pregnant and lactating female mink (Mustela vison). Ten mated and three non-mated female mink were kept in metabolic cages in the laboratory from immediately after mating until the kits were three to four weeks old. Consecutive energy balance experiments with periods each of one week duration, including a 22 h respiration experiment (only three with females that were not mated) were performed, and weekly blood samples were collected for determination of plasma concentrations of thyroid hormones, prolactin, insulin and glucose. Prolactin profiles of pregnant and lactating females had a biphasic pattern: there was an increase in April, a decline immediately before parturition, and peak values were recorded in early May, usually when the females were in the first week of lactation. In females that were not mated plasma concentrations of prolactin did not rise above basal concentration. These females also exhibited a delayed spring moult, and had a lower feed intake. In addition, plasma profiles of thyroid hormones of mated and non-mated animals were different; concentrations of thyroid hormones decreased in April to early May, but the decrease started earlier and was most pronounced in pregnant female mink. These data indicate that prolactin secretion in female mink is regulated by photoperiod, but that other endocrinological events during pregnancy may also be involved.

Animals↗

PubMed2002

Interaction between mating-type proteins from the homothallic fungus Sordaria macrospora.

Mating-type genes control sexual development in ascomycetes. Little is known about their function in homothallic species, which are self-fertile and do not require a mating partner for sexual reproduction. The function of mating-type genes in the homothallic fungus Sordaria macrospora was assayed using a yeast system in order to find properties typical of eukaryotic transcription factors. We were able to demonstrate that the mating-type proteins SMTA-1 and SMTa-1 have domains capable of activating transcription of yeast reporter genes. Two-hybrid analysis for heterodimerization and homodimerization revealed the ability of SMTA-1 to interact with SMTa-1 and vice versa. These two proteins are encoded by different mating types in the related heterothallic species Neurospora crassa. The interaction between SMTA-1 and SMTa-1 was defined by experiments with truncated versions of SMTA-1 and in vitro by means of protein cross-linking. Moreover, we gained evidence for homodimerization of SMTA-1. Possible functions of mating-type proteins in the homothallic ascomycete S. macrospora are discussed.

Amino Acid Sequence↗

PubMed2003

Alpha-pheromone-induced "shmooing" and gene regulation require white-opaque switching during Candida albicans mating.

A 14-mer alpha-pheromone peptide of Candida albicans was chemically synthesized and used to analyze the role of white-opaque switching in the mating process. The alpha-pheromone peptide blocked cell multiplication and induced "shmooing" in a/a cells expressing the opaque-phase phenotype but not in a/a cells expressing the white-phase phenotype. The alpha-pheromone peptide induced these effects at 25 degrees C but not at 37 degrees C. An analysis of mating-associated gene expression revealed several categories of gene regulation, including (i) MTL-homozygous-specific, pheromone stimulated, switching-independent (CAG1 and STE4); (ii) mating type-specific, pheromone-induced, switching-independent (STE2); and (iii) pheromone-induced, switching-dependent (FIG1, KAR4, and HWP1). An analysis of switching-regulated genes revealed an additional category of opaque-phase-specific genes that are downregulated by alpha-pheromone only in a/a cells (OP4, SAP1, and SAP3). These results demonstrate that alpha-pheromone causes shmooing, the initial step in the mating process, only in a/a cells expressing the opaque phenotype and only at temperatures below that in the human host. These results further demonstrate that although some mating-associated genes are stimulated by the alpha-pheromone peptide in both white- and opaque-phase cells, others are stimulated only in opaque-phase cells, revealing a category of gene regulation unique to C. albicans in which alpha-pheromone induction requires the white-opaque transition. These results demonstrate that in C. albicans, the mating process and associated gene regulation must be examined within the context of white-opaque switching.

ATP-Binding Cassette Transporters↗

PubMed1993

The alpha-mating type locus of Cryptococcus neoformans contains a peptide pheromone gene.

The opportunistic fungal pathogen Cryptococcus neoformans has two mating types, MATa and MAT alpha. The MAT alpha strains are more virulent. Mating of opposite mating type haploid yeast cells results in the production of a filamentous hyphal phase. The MAT alpha locus has been isolated in this study in order to identify the genetic differences between mating types and their contribution to virulence. A 138-bp fragment of MAT alpha-specific DNA which cosegregates with alpha-mating type was isolated by using a difference cloning method. Overlapping phage and cosmid clones spanning the entire MAT alpha locus were isolated by using this MAT alpha-specific fragment as a probe. Mapping of these clones physically defined the MAT alpha locus to a 35- to 45-kb region which is present only in MAT alpha strains. Transformation studies with fragments of the MAT alpha locus identified a 2.1-kb XbaI-HindIII fragment that directs starvation-induced filament formation in MATa cells but not in MAT alpha cells. This 2.1-kb fragment contains a gene, MF alpha, with a small open reading frame encoding a pheromone precursor similar to the lipoprotein mating factors found in Saccharomyces cerevisiae, Ustilago maydis, and Schizosaccharomyces pombe. The ability of the MATa cells to express, process, and secrete the MAT alpha pheromone in response to starvation suggests similar mechanisms for these processes in both cell types. These results also suggest that the production of pheromone is under a type of nutritional control shared by the two cell types.

Amino Acid Sequence↗

PubMed1990

The pat1 protein kinase controls transcription of the mating-type genes in fission yeast.

The developmental programme of fission yeast brings about a transition from mitotic cell division to the dormant state of ascospores. In response to nitrogen starvation, two cells of opposite mating type conjugate to form a diploid zygote, which then undergoes meiosis and sporulation. This differentiation process is characterized by a transcriptional induction of the mating-type genes. Conjugation can also be induced in pat1-ts mutants by a shift to a semi-permissive temperature. The pat1 gene encodes a protein kinase, which also functions further downstream in the developmental pathway controlling entry into meiosis. We have analysed transcriptional induction of mating-type genes in various strains--with and without a pat1-ts allele. In wild-type cells of P-mating type derepression occurs in two rounds. First, the mat1-Pc gene is induced in response to nitrogen starvation. Mutants in the map1 gene are defective in this process. In the following step the mat1-Pm gene is expressed in response to a pheromone signal generated by cells of M mating type. Both these controls are derepressed in the pat1-ts mutant at semipermissive temperature. Previous work has established that expression of the mating-type genes in the zygote leads to complete loss of pat1 protein kinase activity causing entry into meiosis. Thus, pat1 can promote its own inactivation. We suggest a model according to which a stepwise inactivation of pat1 leads to sequential derepression of the processes of conjugation and meiosis.

Conjugation, Genetic↗

PubMed1989

Cloning and comparison of A alpha mating-type alleles of the Basidiomycete Schizophyllum commune.

An A alpha mating-type allele (A alpha 4) was isolated by walking the chromosome from the closely linked PAB1 gene. A cosmid clone containing the A alpha 4 allele isolated from the walk was used as a probe to recover the A alpha 1 allele from another cosmid library. Cosmids encoding mating-type activity were identified by transforming Schizophyllum cells and screening for activation of A-regulated development. Putative mating-type transformants were confirmed in mating tests and genetic analyses of progeny. The identity of the specific alleles isolated was demonstrated by showing that their effectiveness in transforming for mating type is limited to recipient strains possessing an A alpha allele different from the one encoded by the cloned sequences. Transforming DNA is active in trans, suggesting that A alpha encodes a diffusible product. Restriction mapping shows that A alpha 1 and A alpha 4 are coded in the same physical region of the genome, but within a subregion that contains extensive sequence divergence. In addition, Southern analyses show that there is only one copy of A alpha 1 or A alpha 4 per haploid genome, and that they do not cross-hybridize to one another or to any of the other A alpha alleles. A alpha 1 and A alpha 4 were subcloned as 2.8 and 1.2 kb fragments, respectively, retaining in transformation all the mating-type activity demonstrated of the original cosmids.

Alleles↗

PubMed1992

DNA damage induced mating type switching in Saccharomyces cerevisiae.

Haploid cells of the yeast Saccharomyces cerevisiae are able to undergo a differentiation-like process: they can switch their mating type between the a and the alpha state. The molecular mechanism of this interconversion of mating types is intrachromosomal gene conversion. It has been shown in a variety of studies that mating type switching in heterothallic strains can be induced by DNA damaging agents, and that different DNA damaging agents differ in the length of incubation after treatment required for induction. Because X-rays induce switching immediately after irradiation and because the DNA double-strand break repair pathway is required for switching, the event initiating heterothallic mating type switching is likely to be a DNA double-strand break. Therefore the assay for heterothallic mating type switching may screen for the induction of DNA double-strand breaks. Several aspects indicating a relationship of mating type switching to mechanisms associated with carcinogenesis are discussed.

DNA Damage↗

PubMed1991

S. cerevisiae alpha pheromone receptors activate a novel signal transduction pathway for mating partner discrimination.

Wild-type S. cerevisiae cells of both mating types prefer partners producing high levels of pheromone and mate very infrequently to cells producing no pheromone. However, some mutants that are supersensitive to pheromone lack this ability to discriminate. In this study, we provide evidence for a novel role of alpha pheromone receptors in mating partner discrimination that is independent of the known G protein-mediated signal transduction pathway. Furthermore, in response to pheromone, receptors become localized to the emerging region of morphogenesis that is positioned adjacent to the nucleus, suggesting that receptor localization may be involved in mating partner discrimination. Actin, myosin 2, and clathrin heavy chain are involved in mating partner discrimination, since strains carrying mutations in the genes encoding these proteins result in a small but significant defect in mating partner discrimination.

Actins↗

PubMed1992

The a mating type locus of U. maydis specifies cell signaling components.

The a mating type locus of the phytopathogenic fungus U. maydis controls fusion of haploid cells and filamentous growth of the dikaryotic mycelium. The a locus exists in two alleles, termed a1 and a2, which are defined by nonhomologous DNA regions comprising 4.5 kb for a1 and 8 kb for a2, flanked by identical sequences. Based on functional assays, mutants, and sequencing, we demonstrate that the mating type in each allele is determined by a set of two genes. One encodes a precursor for a lipopeptide mating factor, and the other specifies the receptor for the pheromone secreted by cells of opposite mating type. Thus, U. maydis employs a novel strategy to determine its mating type by providing the primary determinants of cell-cell recognition directly from the mating type locus.

Alleles↗

PubMed2004

Evolution of the gene encoding mitochondrial intermediate peptidase and its cosegregation with the A mating-type locus of mushroom fungi.

The high level of DNA polymorphism at the mating-type loci of mushroom fungi has made the cloning of mating-type genes difficult. As an alternative to strategies that employ sequence conservation, an approach utilizing conserved gene order could facilitate the cloning of A mating-type genes from mushroom fungi. It has been shown that a gene encoding a mitochondrial intermediate peptidase (MIP) is very close ( < 1 kbp) to the A mating-type locus of two model mushroom species. In this study, the cosegregation of MIP and the A mating-type locus was studied by genotyping progeny of seven additional mushroom species using PCR and genetic crosses. No evidence of any recombination between MIP and the A mating-type locus was detected among all seven species. Phylogenetic analysis of MIP sequences from diverse mushroom species agrees with the current organismal phylogeny, suggesting the sequences are generally orthologous.

Agaricales↗

PubMed2004

Mating-type heterokaryosis and selfing in Cryphonectria parasitica.

Selfing in the chestnut blight fungus, Cryphonectria parasitica, occurs by two different genetic mechanisms. Most self-fertile isolates of C. parasitica are heterokaryotic for mating type, and the progeny from selfing segregate for mating type. Further, we resolved mating-type (MAT) heterokaryons into homokaryons of both mating types by isolating uninucleate asexual spores (conidia). However, because ascospore progeny, with rare exceptions, are not MAT heterokaryons, C. parasitica must lack a regular mechanism to maintain heterokaryosis by selfing. We hypothesize that heterokaryon formation may occur either because of recurrent biparental inbreeding, or by mating-type switching, possibly one involving some kind of parasexual process. The second mechanism found for selfing in C. parasitica occurred less frequently. Three single-conidial isolates (MAT-1 and MAT-2) selfed and produced progeny that did not segregate for mating type. It is currently not known if meiosis occurs during ascospore formation by this mechanism.

Alleles↗

PubMed2001

Mating in mushrooms: increasing the chances but prolonging the affair.

Finding a compatible mating partner is an essential step in the life cycle of most sexually reproducing organisms. Fungi have two or more mating types, and only cells of different mating type combine to produce diploid cells. In mushrooms, this is taken to extremes, with the occurrence of many thousands of mating types. But, having gone to such extraordinary lengths to ensure that almost any two mushroom mycelia in the wild can mate, cell fusion is not followed by nuclear fusion and true diploidy. Instead, the fused cells form a characteristic mycelium, known as the dikaryon, in which haploid nuclei are paired but actively prevented from fusing. The mating-type genes, which encode pheromones, pheromone receptors and homeodomain transcription factors, have crucial roles in regulating the complex developmental programme by which the dikaryon is formed.

Basidiomycota↗

PubMed1999

Role of yeast SIR genes and mating type in directing DNA double-strand breaks to homologous and non-homologous repair paths.

Eukaryotes have acquired many mechanisms to repair DNA double-strand breaks (DSBs) [1]. In the yeast Saccharomyces cerevisiae, this damage can be repaired either by homologous recombination, which depends on the Rad52 protein, or by non-homologous end-joining (NHEJ), which depends on the proteins yKu70 and yKu80 [2] [3]. How do cells choose which repair pathway to use? Deletions of the SIR2, SIR3 and SIR4 genes - which are involved in transcriptional silencing at telomeres and HM mating-type loci (HMLalpha and HMRa) in yeast [4] - have been reported to reduce NHEJ as severely as deletions of genes encoding Ku proteins [5]. Here, we report that the effect of deleting SIR genes is largely attributable to derepression of silent mating-type genes, although Sir proteins do play a minor role in end-joining. When DSBs were made on chromosomes in haploid cells that retain their mating type, sir Delta mutants reduced the frequency of NHEJ by twofold or threefold, although plasmid end-joining was not affected. In diploid cells, sir mutants showed a twofold reduction in the frequency of NHEJ in two assays. Mating type also regulated the efficiency of DSB-induced homologous recombination. In MATa/MATalpha diploid cells, a DSB induced by HO endonuclease was repaired 98% of the time by gene conversion with the homologous chromosome, whereas in diploid cells with an alpha mating type (matDelta/MATalpha) repair succeeded only 82% of the time. Mating-type regulation of genes specific to haploid or diploid cells plays a key role in determining which pathways are used to repair DSBs.

DNA Damage↗

PubMed2003

Chromosomal heteromorphism and an apparent translocation detected using a BAC contig spanning the mating type locus of Phytophthora infestans.

Genetic and physical irregularities associated with the mating type locus of the oomycete, Phytophthora infestans, were revealed by analyzing a contig spanning the locus that was constructed using a bacterial artificial chromosome library. Contigs from both homologs of an A1 strain A/a genotype at mating type locus) had chromosome-specific differences, flanked by regions of similarity. Such heteromorphism was detected within multiple isolates. The mating type locus was narrowed to a 60-70kb interval by genetic mapping of candidate genes, identified using a cDNA library. During these analyses, an unusual isolate of P. infestans was identified in which the mating type determinant had apparently translocated from its location in typical strains. Comparative mapping of the cDNAs between P. infestans and P. parasitica revealed partial synteny between the species however; substantial rearrangements existed and no cDNA was tightly linked to mating type in P. parasitica. These findings add to previous observations of unusual genetic behavior involving mating type in Phytophthora.

Chromosome Mapping↗

PubMed2003

Cloning and characterization of the mating type (MAT) locus from Ascochyta rabiei (teleomorph: Didymella rabiei) and a MAT phylogeny of legume-associated Ascochyta spp.

Degenerate primers designed to correspond to conserved regions of the high mobility group (HMG) protein encoded by the MAT1-2 gene of Cochliobolus heterostrophus, Cochliobolus sativus, and Alternaria alternata were used to amplify the portion of the sequence corresponding to the HMG box motif from Ascochyta rabiei (teleomorph: Didymella rabiei). A combination of TAIL and inverse PCR extended the MAT1-2 sequence in both directions, then primers designed to MAT1-2 flanking DNA were used to amplify the entire MAT1-1 idiomorph. MAT1-1 and MAT1-2 idiomorphs were 2294 and 2693 bp in length, respectively, and each contained a single putative open reading frame (ORF) and intron similar to MAT loci of other loculoascomycete fungi. MAT genes were expressed at high levels in rich medium. MAT-specific PCR primers were designed for use in a multiplex PCR assay and MAT-specific PCR amplicons correlated perfectly to mating phenotype of 35 ascospore progeny from a cross of MAT1-1 by MAT1-2 isolates and to the mating phenotype of field-collected isolates from diverse geographic locations. MAT-specific PCR was used to rapidly determine the mating type of isolates of A. rabiei sampled from chickpea fields in the US Pacific Northwest. Mating type ratios were not significantly different from 1:1 among isolates sampled from two commercial chickpea fields consistent with the hypothesis that these A. rabiei populations were randomly mating. The mating type ratio among isolates sampled from an experimental chickpea field where asexual reproduction was enforced differed significantly from 1:1. A phylogeny estimated among legume-associated Ascochyta spp. and related loculoascocmycete fungi using sequence data from the nuclear ribosomal internal transcribed spacer (ITS) demonstrated the monophyly of Ascochyta/Didymella spp. associated with legumes but was insufficiently variable to differentiate isolates associated with different legume hosts. In contrast, sequences of the HMG region of MAT1-2 were substantially more variable, revealing seven well-supported clades that correlated to host of isolation. A. rabiei on chickpea is phylogenetically distant from other legume-associated Ascochyta spp. and the specific status of A. rabiei, A. lentis, A. pisi, and A. fabae was confirmed by the HMG phylogeny

Amino Acid Sequence↗

PubMed2000

Identification of the MATa mating-type locus of Cryptococcus neoformans reveals a serotype A MATa strain thought to have been extinct.

Cryptococcus neoformans is an opportunistic fungal pathogen with a defined sexual cycle involving mating between haploid MATa and MATalpha cells. Here we describe the isolation of part of the MATa mating-type locus encoding a Ste20 kinase homolog, Ste20a. We show that the STE20a gene cosegregates with the MATa mating type in genetic crosses, maps within the mating-type locus on a 1.8-Mb chromosome, and is allelic with the MATalpha locus. We identify the first MATa isolate of the most common pathogenic variety of C. neoformans (serotype A, variety grubii) which had been thought to be extinct. This serotype A MATa strain is sterile, fails to produce mating pheromone, and is less virulent than a serotype A MATalpha strain in an animal model. Our studies illustrate an association of mating type with virulence and suggest that, like Candida albicans, pathogenic isolates of C. neoformans may be largely asexual.

Amino Acid Sequence↗

PubMed2002

The role of mating type and morphology in Cryptococcus neoformans pathogenesis.

Cryptococcus neoformans is a major fungal pathogen of both humans and animals. The fungus can be divided into two varieties, with each variety being composed of two serotypes. A sexual phase has been identified, which classifies C. neoformans as a bipolar heterothallic fungus with two mating types, MATa and MATalpha. The analysis of mating and mating type in this organism is important for a number of reasons. Both clinical and environmental isolates display a severe bias of the MATalpha mating type over MATa. MATalpha cells are also more virulent than MATalpha cells. Molecular and genetic analyses of the genes that make up the mating pathway have revealed that some of these genes are required for virulence. Finally, although it is well known that infection begins in the lungs after inhalation of infectious particles, it still remains unclear what constitutes the infectious particle. This review will discuss current information about what is known about the role that mating type and morphology play in virulence.

Animals↗

PubMed2000

Fission yeast switches mating type by a replication-recombination coupled process.

Fission yeast exhibits a homothallic life cycle, in which the mating type of the cell mitotically alternates in a highly regulated fashion. Pedigree analysis of dividing cells has shown that only one of the two sister cells switches mating type. It was shown recently that a site- and strand-specific DNA modification at the mat1 locus precedes mating-type switching. By tracking the fate of mat1 DNA throughout the cell cycle with a PCR assay, we identified a novel DNA intermediate of mating-type switching in S-phase. The time and rate of appearance and disappearance of this DNA intermediate are consistent with a model in which mating-type switching occurs through a replication-recombination coupled pathway. Such a process provides experimental evidence in support of a copy choice recombination model in Schizosaccharomyces pombe mating-type switching and is reminiscent of the sister chromatid recombination used to complete replication in the presence of certain types of DNA damage.

DNA Replication↗