Analysis of the structural genes encoding M-factor in the fission yeast Schizosaccharomyces pombe: identification of a third gene, mfm3

Effects of rpl1001 Gene Deletion on Cell Division of Fission Yeast and Its Molecular Mechanism

The rpl1001 gene encodes 60S ribosomal protein L10, which is involved in intracellular protein synthesis and cell growth. However, it is not yet known whether it is involved in the regulation of cell mitosis dynamics. This study focuses on the growth, spore production, cell morphology, the dynamics of microtubules, chromosomes, actin, myosin, and mitochondria of fission yeast (Schizosaccharomyces pombe) to investigate the impact of rpl1001 deletion on cell mitosis. RNA-Seq and bioinformatics analyses were also used to reveal key genes, such as hsp16, mfm1 and isp3, and proteasome pathways. The results showed that rpl1001 deletion resulted in slow cell growth, abnormal spore production, altered cell morphology, and abnormal microtubule number and length during interphase. The cell dynamics of the rpl1001Δ strain showed that the formation of a monopolar spindle leads to abnormal chromosome segregation with increased rate of spindle elongation in anaphase of mitosis, decreased total time of division, prolonged formation time of actin and myosin loops, and increased expression of mitochondrial proteins. Analysis of the RNA-Seq sequencing results showed that the proteasome pathway, up-regulation of isp3, and down-regulation of mfm1 and mfm2 in the rpl1001Δ strain were the main factors underpinning the increased number of spore production. Also, in the rpl1001Δ strain, down-regulation of dis1 caused the abnormal microtubule and chromosome dynamics, and down-regulation of hsp16 and pgk1 were the key genes affecting the delay of actin ring and myosin ring formation. This study reveals the effect and molecular mechanism of rpl1001 gene deletion on cell division, which provides the scientific basis for further clarifying the function of the Rpl1001 protein in cell division.

Extending the reach of homology by using successive computational filters to find yeast pheromone genes

The mating of fungi depends on pheromones that mediate communication between two mating types. Most species use short peptides as pheromones, which are either unmodified (e.g., α-factor in Saccharomyces cerevisiae) or C-terminally farnesylated (e.g., a-factor in S. cerevisiae). Peptide pheromones have been found by genetics or biochemistry in a small number of fungi, but their short sequences and modest conservation make it impossible to detect homologous sequences in most species. To overcome this problem, we used a four-step computational pipeline to identify candidate a-factor genes in sequenced genomes of the Saccharomycotina, the fungal clade that contains most of the yeasts: we require that candidate genes have a C-terminal prenylation motif, are shorter than 100 amino acids long, and contain a proteolytic-processing motif upstream of the potential mature pheromone sequence and that closely related species contain highly conserved homologs of the potential mature pheromone sequence. Additional manual curation exploits the observation that many species carry more than one a-factor gene, encoding identical or nearly identical pheromones. From 332 Saccharomycotina genomes, we identified strong candidate pheromone genes in 241 genomes, covering 13 clades that are each separated from each other by at least 100 million years, the time required for evolution to remove detectable sequence homology among small pheromone genes. For one small clade, the Yarrowia, we demonstrated that our algorithm found the a-factor genes: deleting all four related genes in the a-mating type of Yarrowia lipolytica prevents mating.

Pheromone Response and Mating Behavior in Fission Yeast

Most ascomycete fungi, including the fission yeast Schizosaccharomyces pombe, secrete two peptidyl mating pheromones: C-terminally modified and unmodified peptides. S. pombe has two mating types, plus and minus, which secrete two different pheromones, P-factor (unmodified) and M-factor (modified), respectively. These pheromones are specifically recognized by receptors on the cell surface of cells of opposite mating types, which trigger a pheromone response. Recognition between pheromones and their corresponding receptors is important for mate discrimination; therefore, genetic changes in pheromone or receptor genes affect mate recognition and cause reproductive isolation that limits gene flow between populations. Such genetic variation in recognition via the pheromone/receptor system may drive speciation. Our recent studies reported that two pheromone receptors in S. pombe might have different stringencies in pheromone recognition. In this review, we focus on the molecular mechanism of pheromone response and mating behavior, emphasizing pheromone diversification and its impact on reproductive isolation in S. pombe and closely related fission yeast species. We speculate that the "asymmetric" system might allow flexible adaptation to pheromone mutational changes while maintaining stringent recognition of mating partners. The loss of pheromone activity results in the extinction of an organism's lineage. Therefore, genetic changes in pheromones and their receptors may occur gradually and/or coincidently before speciation. Our findings suggest that the M-factor plays an important role in partner discrimination, whereas P-factor communication allows flexible adaptation to create variations in S. pombe. Our inferences provide new insights into the evolutionary mechanisms underlying pheromone diversification.

The asymmetric chemical structures of two mating pheromones reflect their differential roles in mating of fission yeast

In the fission yeast Schizosaccharomyces pombe, the mating reaction is controlled by two mating pheromones, M-factor and P-factor, secreted by M- and P-type cells, respectively. M-factor is a C-terminally farnesylated lipid peptide, whereas P-factor is a simple peptide. To examine whether this chemical asymmetry in the two pheromones is essential for conjugation, we constructed a mating system in which either pheromone can stimulate both M- and P-cells, and examined whether the resulting autocrine strains can mate. Autocrine M-cells responding to M-factor successfully mated with P-factor-lacking P-cells, indicating that P-factor is not essential for conjugation; by contrast, autocrine P-cells responding to P-factor were unable to mate with M-factor-lacking M-cells. The sterility of the autocrine P-cells was completely restored by expressing the M-factor receptor. These observations indicate that the different chemical characteristics of the two types of pheromone, a lipid and a simple peptide, are not essential; however, a lipid peptide might be required for successful mating. Our findings allow us to propose a model of the differential roles of M-factor and P-factor in conjugation of S. pombeThis article has an associated First Person interview with the first author of the paper.

Asymmetric diversification of mating pheromones in fission yeast

In fungi, mating between partners depends on the molecular recognition of two peptidyl mating pheromones by their respective receptors. The fission yeast Schizosaccharomyces pombe (Sp) has two mating types, Plus (P) and Minus (M). The mating pheromones P-factor and M-factor, secreted by P and M cells, are recognized by the receptors mating type auxiliary minus 2 (Mam2) and mating type auxiliary plus 3 (Map3), respectively. Our recent study demonstrated that a few mutations in both M-factor and Map3 can trigger reproductive isolation in S. pombe. Here, we explored the mechanism underlying reproductive isolation through genetic changes of pheromones/receptors in nature. We investigated the diversity of genes encoding the pheromones and their receptor in 150 wild S. pombe strains. Whereas the amino acid sequences of M-factor and Map3 were completely conserved, those of P-factor and Mam2 were very diverse. In addition, the P-factor gene contained varying numbers of tandem repeats of P-factor (4–8 repeats). By exploring the recognition specificity of pheromones between S. pombe and its close relative Schizosaccharomyces octosporus (So), we found that So-M-factor did not have an effect on S. pombe P cells, but So-P-factor had a partial effect on S. pombe M cells. Thus, recognition of M-factor seems to be stringent, whereas that of P-factor is relatively relaxed. We speculate that asymmetric diversification of the two pheromones might be facilitated by the distinctly different specificities of the two receptors. Our findings suggest that M-factor communication plays an important role in defining the species, whereas P-factor communication is able to undergo a certain degree of flexible adaptation–perhaps as a first step toward prezygotic isolation in S. pombe.

An asymmetric pheromone/receptor system in the fission yeast Schizosaccharomyces pombe might allow flexible adaptation of pheromones to mutational changes while maintaining stringent recognition for mating partners, perhaps as a first step toward prezygotic mating isolation.

The emergence of a new species might occur when two groups can no longer mate. Although such reproductive isolation is considered a key evolutionary process, the mechanisms by which it actually occurs have been confined to conjecture. The two sexes (Plus [P] and Minus [M]) of S. pombe each secrete a pheromone (P-factor and M-factor), which binds to a corresponding receptor (mating type auxiliary minus 2 [Mam2] and mating type auxiliary plus 3 [Map3]) on cells of the opposite sex. The interaction between a pheromone and its receptor is essential for successful mating. Here, we explored conservation of the mating pheromone communication system among 150 wild S. pombe strains of different geographical origins and the closely related species S. octosporus. We found that 1) the M-factor/Map3 interaction was completely conserved, whereas the P-factor/Mam2 interaction was very diverse in the strains investigated, and 2) most of the P-factor variants were functional across species. Thus, we have revealed an asymmetric pheromone/receptor system in fungal mating: namely, whereas M-factor communication operates extremely stringently, P-factor communication has the flexibility to create variations, perhaps facilitating prezygotic isolation in S. pombe.

Identification and characterization of the Komagataella phaffii mating pheromone genes

The methylotrophic yeast Komagataella phaffii (Pichia pastoris) is a haploid yeast that is able to form diploid cells by mating once nitrogen becomes limiting. Activation of the mating response requires the secretion of a- and α-factor pheromones, which bind to G-protein coupled receptors on cells of opposite mating type. In K. phaffii, the genes coding for the α-factor (MFα), the pheromone surface receptors and the conserved a-factor biogenesis pathway have been annotated previously. Initial homology-based search failed to identify potential a-factor genes (MFA). By using transcriptome data of heterothallic strains under mating conditions, we found two K. phaffiia-factor genes. Deletion of both MFA genes prevented mating of a-type cells. MFA single mutants were still able to mate and activate the mating response pathway in α-type cells. A reporter assay was used to confirm the biological activity of synthetic a- and α-factor peptides. The identification of the a-factor genes enabled the first characterization of the role and regulation of the mating pheromone genes and the response of K. phaffii to synthetic pheromones and will help to gain a better understanding of the mating behavior of K. phaffii.

Spatial focalization of pheromone/MAPK signaling triggers commitment to cell-cell fusion

Here, Dudin et al. show that cell fusion does not require a dedicated signal but is triggered by spatial focalization of the same pheromone–GPCR–MAPK signaling cascade that drives earlier mating events in Schizosaccharomyces pombe.

Cell fusion is universal in eukaryotes for fertilization and development, but what signals this process is unknown. Here, we show in Schizosaccharomyces pombe that fusion does not require a dedicated signal but is triggered by spatial focalization of the same pheromone–GPCR (G-protein-coupled receptor)–MAPK signaling cascade that drives earlier mating events. Autocrine cells expressing the receptor for their own pheromone trigger fusion attempts independently of cell–cell contact by concentrating pheromone release at the fusion focus, a dynamic actin aster underlying the secretion of cell wall hydrolases. Pheromone receptor and MAPK cascade are similarly enriched at the fusion focus, concomitant with fusion commitment in wild-type mating pairs. This focalization promotes cell fusion by immobilizing the fusion focus, thus driving local cell wall dissolution. We propose that fusion commitment is imposed by a local increase in MAPK concentration at the fusion focus, driven by a positive feedback between fusion focus formation and focalization of pheromone release and perception.

fhl1 gene of the fission yeast regulates transcription of meiotic genes and nitrogen starvation response, downstream of the TORC1 pathway

Environmental changes, such as nutrient limitation or starvation induce different signal transducing pathways, which require coordinated cooperation of several genes. Our previous data revealed that the fhl1 fork-head type transcription factor of the fission yeast could be involved in sporulation, which was typically induced under poor conditions. Since the exact role of Fhl1 in this process was not known, we wanted to identify its downstream targets and to investigate its possible cooperation with another known regulator of sporulation. Gene expression and Northern blot analysis of the fhl1∆ mutant strain revealed the target genes involved in mating and sporulation. Our results also showed that Fhl1 could regulate nutrient sensing, the transporter and permease genes. Since the majority of these genes belonged to the nitrogen starvation response, the possible cooperation of fhl1 and tor2 was also investigated. Comparison of their microarray data and the expression of fhl1 ⁺ from a strong promoter in the tor2-ts mutant cells suggested that one part of the target genes are commonly regulated by Fhl1 and Tor2. Since the expression of fhl1 ⁺ from a strong promoter could rescue rapamycin and temperature sensitivity and suppressed the hyper-sporulation defect of the tor2-ts mutant cells, we believe that Fhl1 acts in TOR signaling, downstream of Tor2. Thus, this work shed light on certain novel details of the regulation of the sexual processes and a new member of the TOR pathway, but further experiments are needed to confirm the involvement of Fhl1 in nutrient sensing.

Local Pheromone Release from Dynamic Polarity Sites Underlies Cell-Cell Pairing during Yeast Mating

Cell pairing is central for many processes, including immune defense, neuronal connection, hyphal fusion, and sexual reproduction. How does a cell orient toward a partner, especially when faced with multiple choices? Fission yeast Schizosaccharomyces pombe P and M cells, which respectively express P and M factor pheromones [1, 2], pair during the mating process induced by nitrogen starvation. Engagement of pheromone receptors Map3 and Mam2 [3, 4] with their cognate pheromone ligands leads to activation of the Gα protein Gpa1 to signal sexual differentiation [3, 5, 6]. Prior to cell pairing, the Cdc42 GTPase, a central regulator of cell polarization, forms dynamic zones of activity at the cell periphery at distinct locations over time [7]. Here we show that Cdc42-GTP polarization sites contain the M factor transporter Mam1, the general secretion machinery, which underlies P factor secretion, and Gpa1, suggesting that these are sub-cellular zones of pheromone secretion and signaling. Zone lifetimes scale with pheromone concentration. Computational simulations of pair formation through a fluctuating zone show that the combination of local pheromone release and sensing, short pheromone decay length, and pheromone-dependent zone stabilization leads to efficient pair formation. Consistently, pairing efficiency is reduced in the absence of the P factor protease. Similarly, zone stabilization at reduced pheromone levels, which occurs in the absence of the predicted GTPase-activating protein for Ras, leads to reduction in pairing efficiency. We propose that efficient cell pairing relies on fluctuating local signal emission and perception, which become locked into place through stimulation.

Distal and proximal actions of peptide pheromone M-factor control different conjugation steps in fission yeast

Mating pheromone signaling is essential for conjugation between haploid cells of P-type (P-cells) and haploid cells of M-type (M-cells) in Schizosaccharomyces pombe. A peptide pheromone, M-factor, produced by M-cells is recognized by the receptor of P-cells. An M-factor-less mutant, in which the M-factor-encoding genes are deleted, is completely sterile. In liquid culture, sexual agglutination was not observed in the mutant, but it could be recovered by adding exogenous synthetic M-factor, which stimulated expression of the P-type-specific cell adhesion protein, Map4. Exogenous M-factor, however, failed to recover the cell fusion defect in the M-factor-less mutant. When M-factor-less cells were added to a mixture of wild-type P- and M-cells, marked cell aggregates were formed. Notably, M-factor-less mutant cells were also incorporated in these aggregates. In this mixed culture, P-cells conjugated preferentially with M-cells secreting M-factor, and rarely with M-factor-less M-cells. The kinetics of mating parameters in liquid culture revealed that polarized growth commenced from the contact region of opposite mating-type cells. Taken together, these findings indicate that M-factor at a low concentration induces adhesin expression, leading to initial cell-cell adhesion in a type of “distal pheromone action”, but M-factor that is secreted directly in the proximity of the adhered P-cells may be necessary for cell fusion in a type of “proximal pheromone action”.

Red1 promotes the elimination of meiosis-specific mRNAs in vegetatively growing fission yeast

Meiosis-specific mRNAs are transcribed in vegetative fission yeast, and these meiotic mRNAs are selectively removed from mitotic cells to suppress meiosis. This RNA elimination system requires degradation signal sequences called determinant of selective removal (DSR), an RNA-binding protein Mmi1, polyadenylation factors, and the nuclear exosome. However, the detailed mechanism by which meiotic mRNAs are selectively degraded in mitosis but not meiosis is not understood fully. Here we report that Red1, a novel protein, is essential for elimination of meiotic mRNAs from mitotic cells. A red1 deletion results in the accumulation of a large number of meiotic mRNAs in mitotic cells. Red1 interacts with Mmi1, Pla1, the canonical poly(A) polymerase, and Rrp6, a subunit of the nuclear exosome, and promotes the destabilization of DSR-containing mRNAs. Moreover, Red1 forms nuclear bodies in mitotic cells, and these foci are disassembled during meiosis. These results demonstrate that Red1 is involved in DSR-directed RNA decay to prevent ectopic expression of meiotic mRNAs in vegetative cells.

Genomewide identification of pheromone-targeted transcription in fission yeast

Background

Fission yeast cells undergo sexual differentiation in response to nitrogen starvation. In this process haploid M and P cells first mate to form diploid zygotes, which then enter meiosis and sporulate. Prior to mating, M and P cells communicate with diffusible mating pheromones that activate a signal transduction pathway in the opposite cell type. The pheromone signalling orchestrates mating and is also required for entry into meiosis.

Results

Here we use DNA microarrays to identify genes that are induced by M-factor in P cells and by P-factor in M-cells. The use of a cyr1 genetic background allowed us to study pheromone signalling independently of nitrogen starvation. We identified a total of 163 genes that were consistently induced more than two-fold by pheromone stimulation. Gene disruption experiments demonstrated the involvement of newly discovered pheromone-induced genes in the differentiation process. We have mapped Gene Ontology (GO) categories specifically associated with pheromone induction. A direct comparison of the M- and P-factor induced expression pattern allowed us to identify cell-type specific transcripts, including three new M-specific genes and one new P-specific gene.

Conclusion

We found that the pheromone response was very similar in M and P cells. Surprisingly, pheromone control extended to genes fulfilling their function well beyond the point of entry into meiosis, including numerous genes required for meiotic recombination. Our results suggest that the Ste11 transcription factor is responsible for the majority of pheromone-induced transcription. Finally, most cell-type specific genes now appear to be identified in fission yeast.

Alternative protein secretion: The Mam1 ABC transporter supports secretion of M-factor linked GFP in fission yeast

To examine whether the fission yeast Mam1 ABC transporter can be used for secretion of heterologous proteins, thereby bypassing the classical secretion pathway, we have analyzed chimeric forms of the M-factor precursor. It was demonstrated that GFP can be exported when fused to both the amino-terminal prosequence from mfm1 and a CaaX motif. This secretion was dependent on the Mam1 transporter and not the classical secretion pathway. The secretion efficiency of GFP, however, was relatively low and most of the reporter protein was trapped in the vacuolar membranes. Our findings suggest that the Mam1 ABC protein is a promiscuous peptide transporter that can accommodate globular proteins of a relatively large size. Furthermore, our results help in defining the sequences required for processing and secretion of natural M-factor.

Comparison of different signal peptides for secretion of heterologous proteins in fission yeast

In the fission yeast Schizosaccharomyces pombe, there are relatively few signal peptides available and most reports of their activity have not been comparative. Using sequence information from the S. pombe genome database we have identified three putative signal peptides, designated Cpy, Amy and Dpp, and compared their ability to support secretion of green fluorescent protein (GFP). In the comparison we also included the two well-described secretion signals derived from the precursors of, respectively, the Saccharomyces cerevisiae alpha-factor and the S. pombe P-factor. The capability of the tested signal peptides to direct secretion of GFP varied greatly. The alpha-factor signal did not confer secretion to GFP and all the produced GFP was trapped intracellular. In contrast, the Cpy signal peptide supported efficient secretion of GFP with yields approximating 10 mg/L. We also found that the use of an attenuated version of the S. cerevisiae URA3 marker substantially increases vector copy number and expression yield in fission yeast.

Isolation and characterization of the Cryptococcus neoformans MATa pheromone gene

Cryptococcus neoformans is a heterothallic basidiomycete with two mating types, MATa and MATalpha. The mating pathway of this fungus has a number of conserved genes, including a MATalpha-specific pheromone (MFalpha1). A modified differential display strategy was used to identify a gene encoding the MATa pheromone. The gene, designated MFa1, is 42 amino acids in length and contains a conserved farnesylation motif. MFa1 is present in three linked copies that span a 20-kb fragment of MATa-specific DNA and maps to the MAT-containing chromosome. Transformation studies showed that MFa1 induced filament formation only in MATalpha cells, demonstrating that MFa1 is functionally conserved. Sequence analysis of the predicted Mfa1 and Mfalpha1 proteins revealed that, in contrast to other fungi such as Saccharomyces cerevisiae, the C. neoformans pheromone genes are structurally and functionally conserved. However, unlike the MFalpha1 gene, which is found in MATalpha strains of both varieties of C. neoformans, MFa1 is specific for the neoformans variety of C. neoformans.

Cellular and molecular mechanisms of sexual incompatibility in plants and fungi

Plants and fungi show an astonishing diversity of mechanisms to promote outbreeding, the most widespread of which is sexual incompatibility. Sexual incompatibility involves molecular recognition between mating partners. In fungi and algae, highly polymorphic mating-type loci mediate mating through complementary interactions between molecules encoded or regulated by different mating-type haplotypes, whereas in flowering plants polymorphic self-incompatibility loci regulate mate recognition through oppositional interactions between molecules encoded by the same self-incompatibility haplotypes. This subtle mechanistic difference is a consequence of the different life cycles of fungi, algae, and flowering plants. Recent molecular and biochemical studies have provided fascinating insights into the mechanisms of mate recognition and are beginning to shed light on evolution and population genetics of these extraordinarily polymorphic genetic systems of incompatibility.

Gene disruption in Schizosaccharomyces pombe using a temperature-sensitive Ura4p

We have generated a temperature-sensitive form of the Ura4p protein from the fission yeast Schizosaccharomyces pombe. A single T-to-C mutation at nucleotide 782 (relative to the initiator ATG codon of ura4) changes the leucine residue at position 261 in Ura4p to a proline. The mutant Ura4p(ts) supports growth at 30 degrees C but is unable to allow growth at 37 degrees C in the absence of uracil when a single copy of the gene is integrated into the host chromosome. Using the ura4(ts) cassette for gene replacements simplifies the identification of transformants in which the disruption construct has undergone homologous integration into the host chromosome, as these individuals contain a single copy of the ura4(ts) gene and fail to grow when replicated to 37 degrees C in the absence of uracil.

The relationship between B-mating-type genes and nuclear migration in schizophyllum commune

Raudaskoski, M. 1998. The relationship between B-mating-type genes and nuclear migration in Schizophyllum commune. Copyright 1998 Academic Press.

FH3, a domain found in formins, targets the fission yeast formin Fus1 to the projection tip during conjugation

Formins are involved in diverse aspects of morphogenesis, and share two regions of homology: FH1 and FH2. We describe a new formin homology region, FH3. FH3 is an amino-terminal domain that differs from the Rho binding site identified in Bni1p and p140mDia. The Schizosaccharomyces pombe formin Fus1 is required for conjugation, and is localized to the projection tip in cells of mating pairs. We replaced genomic fus1+ with green fluorescent protein (GFP)- tagged versions that lacked either the FH1, FH2, or FH3 domain. Deletion of any FH domain essentially abolished mating. FH3, but neither FH1 nor FH2, was required for Fus1 localization. An FH3 domain-GFP fusion protein localized to the projection tips of mating pairs. Thus, the FH3 domain alone can direct protein localization. The FH3 domains of both Fus1 and the S. pombe cytokinesis formin Cdc12 were able to localize GFP to the spindle pole body in half of the late G2 cells in a vegetatively growing population. Expression of both FH3-GFP fusions also affected cytokinesis. Overexpression of the spindle pole body component Sad1 altered the distribution of both Sad1 and the FH3-GFP domain. Together these data suggest that proteins at multiple sites can interact with FH3 domains.

The sxa2-dependent inactivation of the P-factor mating pheromone in the fission yeast Schizosaccharomyces pombe

Haploid cells of the fission yeast Schizosaccharomyces pombe exist in one of two mating types, referred to as M and P. Conjugation occurs between cells of opposite mating type and is controlled by the reciprocal action of diffusible pheromones. Loss of function of the sxa2 gene in M cells causes hypersensitivity to the P-factor mating pheromone and a reduction in mating efficiency. Here we demonstrate the secretion of an sxa2-dependent carboxypeptidase that inactivates P-factor by removal of the C-terminal leucine residue.

Fungal lipopeptide mating pheromones: a model system for the study of protein prenylation

In a variety of fungal species, mating between haploid cells is initiated by the action of peptide pheromones. The identification and characterization of several fungal pheromones has revealed that they have common structural features classifying them as lipopeptides. In the course of biosynthesis, these pheromones undergo a series of posttranslational processing events prior to export. One common modification is the attachment of an isoprenoid group to the C terminus of the pheromone precursor. Genetic and biochemical investigations of this biosynthetic pathway have led to the elucidation of genes and enzymes which are responsible for isoprenylation of other polypeptides including the nuclear lamins, several vesicular transport proteins, and the oncogene product Ras. The alpha-factor of Saccharomyces cerevisiae serves as a model for studying the biosynthesis, export, and bioactivity of lipopeptide pheromones. In addition to being isoprenylated with a farnesyl group, the alpha-factor is secreted by a novel peptide export pathway utilizing a yeast homolog of the mammalian multidrug resistance P-glycoprotein. The identification of putative lipopeptide-encoding loci within other fungi, including the human immunodeficiency virus-associated opportunistic pathogen Cryptococcus neoformans and the plant pathogen Ustilago maydis, has stimulated much interest in understanding possible roles for pheromones in fungal proliferation and pathogenicity. Knowledge of variations within the processing, export, and receptor-mediated signal transduction pathways associated with different fungal lipopeptide pheromones will continue to provide insights into similar mechanisms which exist in higher eukaryotes.

Schizosaccharomyces pombe: a model for molecular studies of eukaryotic genes

Several features of the fission yeast Schizosaccharomyces pombe make it exceptionally well suited for the study of eukaryotic genes. It is a relatively simple eukaryote that can be readily grown and manipulated in the laboratory, using a variety of highly developed and sophisticated methodologies. Schizosaccharomyces pombe cells share many molecular, genetic, and biochemical features with cells from multicellular organisms, making it a particularly useful model to study the structure, function, and regulation of genes from more complex species. For examples, this yeast divides by binary fission, has many genes that contain introns, is capable of using mammalian gene promoters and polyadenylation signals, and has been used to clone mammalian genes by functional complementation of mutants. We present a summary of the biology of S. pombe, useful features that make it amenable to laboratory studies, and molecular techniques available to manipulate the genome of this organism as well as other eukaryotic genes within the fission yeast cellular environment.

Pheromone communication in the fission yeast Schizosaccharomyces pombe

Conjugation between two haploid yeast cells is generally controlled by the reciprocal action of diffusible mating pheromones, cells of each mating type releasing pheromones that induce mating-specific changes in cells of the opposite type. Recent studies into pheromone signalling in the fission yeast Schizosaccharomyces pombe have revealed significant parallels with processes in higher eukaryotes and could provide the opportunity for investigating communication in an organism that is amenable to both biochemical and genetic manipulation.

Assessment of pheromone production and response in fission yeast by a halo test of induced sporulation

We describe a rapid, sensitive and semi-quantitative plate assay for monitoring pheromone activity in the fission yeast Schizosaccharomyces pombe. It is based on the observation that meiosis requires stimulation by pheromone and exploits diploid strains that will only sporulate after addition of exogenous pheromone. The tester strains are heterozygous for mating type, are non-switching, and are mutated in one of the early subfunctions (either mat1-Mc or mat1-Pc), so that meiosis is only induced after exposure to exogenous pheromone (M-factor or P-factor, respectively). Pheromone activity is assessed as an iodine-positive halo of sporulation surrounding the pheromone source, and the width of the halo is related to the amount of pheromone being produced. The assay is sufficiently sensitive to monitor the low amount of M-factor produced by an M mam1 strain, and its sensitivity towards P-factor is greatly increased by using a hyper-sensitive tester strain lacking the Sxa2 protease that is believed to degrade this pheromone. We also demonstrate that the production of P-factor is very much stimulated by exposure of P cells to M-factor.

Mapping of additional markers in fission yeast, especially fus1 and three mfm genes

The following genes of the fission yeast Schizosaccharomyces pombe have been mapped by tetrad analysis--chromosome arm I-L: mfm2, rad24, rad25; I-R: abc1, fus1, mfm1; II-L: mfm3; II-R: mam1, rad13. A hot-spot of meiotic recombination although not quite so active as suggested by previous maps, may be located between rad25 and aro5 on I-L.