Schizosaccharomyces pombe
Encyclopedia
Schizosaccharomyces pombe, also called "fission yeast", is a species
of yeast
. It is used as a model organism
in molecular
and cell biology
. It is a unicellular eukaryote
, whose cells
are rod-shaped. Cells typically measure 3 to 4 micrometre
s in diameter and 7 to 14 micrometres in length. Its genome
, which is approximately 14.1 million base pairs, is estimated to contain 4,970 protein-coding genes
and at least 450 non-coding RNAs.
These cells maintain their shape by growing exclusively through the cell tips and divide by medial fission to produce two daughter cells of equal sizes, which makes them a powerful tool in cell cycle
research.
Fission yeast was isolated in 1893 by Lindner from East African millet
beer
. The species name is derived from the Swahili
word for beer (Pombe). It was first developed as an experimental model in the 1950s: by Urs Leupold for studying genetics, and by Murdoch Mitchison
for studying the cell cycle.
The fission yeast researcher Paul Nurse
successfully merged the independent schools of fission yeast genetics and cell cycle research. Together with Lee Hartwell and Tim Hunt
, Nurse won the 2001 Nobel Prize in Physiology or Medicine
for their work on cell cycle regulation.
The sequence of the S. pombe genome
was published in 2002, by a consortium led by the Sanger Institute
, becoming the sixth model eukaryotic organism whose genome
has been fully sequenced. This has fully unlocked the power of this organism, with many genes homologous to human disease genes being identified. In 2006, sub-cellular localization of all the proteins in S. pombe was published using green fluorescent protein
as a molecular tag.
S. pombe has also become an important organism in studying the cellular responses to DNA damage and the process of DNA replication
.
Approximately 120 natural strains of S. pombe have been isolated. These have been collected from a variety of locations including Europe, North and South America and Asia. The majority of these strains have been collected from cultivated fruits such as apples and grapes, or from the various alcoholic beverage
s, such as Brazilian Cachaça
. It is not clear at present whether S. pombe is the major fermenter or a contaminant in such brews. The natural ecology of Schizosaccharomyces
yeasts is not well studied.
The central events of cell reproduction are chromosome duplication, which takes place in S (Synthetic) phase, followed by chromosome segregation and nuclear division (mitosis) and cell division (cytokinesis), which are collectively called M (Mitotic) phase.G1 is the gap between M and S phases, and G2 is the gap between S and M phases. In the budding yeast, the G2 phase is particularly extended, and cytokinesis (daughter-cell segregation) does not happen until a new S (Synthetic) phase is launched.
Fission yeast governs mitosis by mechanisms that are similar to those in multicellular animals. It normally proliferates in a haploid state. When starved, cells of opposite mating types (P and M) fuse to form a diploid zygote that immediately enters meiosis to generate four haploid spores. When conditions improve, these spores germinate to produce proliferating haploid cells.
A spatial gradient is thought to coordinate cell size and mitotic entry in fission yeast.
The Pom1
protein kinase (green) is localized to the cell cortex, with the highest concentration at the cell tips. The cell-cycle regulators Cdr2, Cdr1 and Wee1 are present in cortical nodes in the middle of the cell (blue and red dots). a, In small cells, the Pom1
gradient reaches most of the cortical nodes (blue dots). Pom1
inhibits Cdr2, preventing Cdr2 and Cdr1 from inhibiting Wee1, and allowing Wee1 to phosphorylate Cdk1, thus inactivating cyclin-dependent kinase (CDK) activity and preventing entry into mitosis. b, In long cells, the Pom1
gradient does not reach the cortical nodes (red dots), and therefore Cdr2 and Cdr1 remain active in the nodes. Cdr2 and Cdr1 inhibit Wee1, preventing phosphorylation of Cdk1 and thereby leading to activation of CDK and mitotic entry. (This simplified diagram omits several other regulators of CDK activity.)
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of yeast
Yeast
Yeasts are eukaryotic micro-organisms classified in the kingdom Fungi, with 1,500 species currently described estimated to be only 1% of all fungal species. Most reproduce asexually by mitosis, and many do so by an asymmetric division process called budding...
. It is used as a model organism
Model organism
A model organism is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the organism model will provide insight into the workings of other organisms. Model organisms are in vivo models and are widely used to...
in molecular
Molecular biology
Molecular biology is the branch of biology that deals with the molecular basis of biological activity. This field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry...
and cell biology
Cell biology
Cell biology is a scientific discipline that studies cells – their physiological properties, their structure, the organelles they contain, interactions with their environment, their life cycle, division and death. This is done both on a microscopic and molecular level...
. It is a unicellular eukaryote
Eukaryote
A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear...
, whose cells
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
are rod-shaped. Cells typically measure 3 to 4 micrometre
Micrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...
s in diameter and 7 to 14 micrometres in length. Its genome
Genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
, which is approximately 14.1 million base pairs, is estimated to contain 4,970 protein-coding genes
Gênes
Gênes is the name of a département of the First French Empire in present Italy, named after the city of Genoa. It was formed in 1805, when Napoleon Bonaparte occupied the Republic of Genoa. Its capital was Genoa, and it was divided in the arrondissements of Genoa, Bobbio, Novi Ligure, Tortona and...
and at least 450 non-coding RNAs.
These cells maintain their shape by growing exclusively through the cell tips and divide by medial fission to produce two daughter cells of equal sizes, which makes them a powerful tool in cell cycle
Cell cycle
The cell cycle, or cell-division cycle, is the series of events that takes place in a cell leading to its division and duplication . In cells without a nucleus , the cell cycle occurs via a process termed binary fission...
research.
Fission yeast was isolated in 1893 by Lindner from East African millet
Millet
The millets are a group of small-seeded species of cereal crops or grains, widely grown around the world for food and fodder. They do not form a taxonomic group, but rather a functional or agronomic one. Their essential similarities are that they are small-seeded grasses grown in difficult...
beer
Millet beer
Millet beer, also known as Bantu beer, kaffir beer, or opaque beer, is an alcoholic beverage made from malted millet. This type of beer is common throughout Africa. Related African drinks include maize beer and sorghum beer....
. The species name is derived from the Swahili
Swahili language
Swahili or Kiswahili is a Bantu language spoken by various ethnic groups that inhabit several large stretches of the Mozambique Channel coastline from northern Kenya to northern Mozambique, including the Comoro Islands. It is also spoken by ethnic minority groups in Somalia...
word for beer (Pombe). It was first developed as an experimental model in the 1950s: by Urs Leupold for studying genetics, and by Murdoch Mitchison
Murdoch Mitchison
John Murdoch Mitchison FRS, FRSE was a British zoologist, the son of the Labour politician Dick Mitchison and his wife, the writer Naomi . The biologist J.B.S. Haldane was his uncle, and the physiologist John Scott Haldane was his maternal grandfather...
for studying the cell cycle.
The fission yeast researcher Paul Nurse
Paul Nurse
Sir Paul Maxime Nurse, PRS is a British geneticist and cell biologist. He was awarded the 2001 Nobel Prize in Physiology or Medicine with Leland H. Hartwell and R...
successfully merged the independent schools of fission yeast genetics and cell cycle research. Together with Lee Hartwell and Tim Hunt
Tim Hunt
Sir Richard Timothy "Tim" Hunt, FRS is an English biochemist.Hunt was awarded the 2001 Nobel Prize in Physiology or Medicine with Paul Nurse and Leland H...
, Nurse won the 2001 Nobel Prize in Physiology or Medicine
Nobel Prize in Physiology or Medicine
The Nobel Prize in Physiology or Medicine administered by the Nobel Foundation, is awarded once a year for outstanding discoveries in the field of life science and medicine. It is one of five Nobel Prizes established in 1895 by Swedish chemist Alfred Nobel, the inventor of dynamite, in his will...
for their work on cell cycle regulation.
The sequence of the S. pombe genome
Genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
was published in 2002, by a consortium led by the Sanger Institute
Sanger Institute
The Wellcome Trust Sanger Institute is a non-profit, British genomics and genetics research institute, primarily funded by the Wellcome Trust....
, becoming the sixth model eukaryotic organism whose genome
Genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
has been fully sequenced. This has fully unlocked the power of this organism, with many genes homologous to human disease genes being identified. In 2006, sub-cellular localization of all the proteins in S. pombe was published using green fluorescent protein
Green fluorescent protein
The green fluorescent protein is a protein composed of 238 amino acid residues that exhibits bright green fluorescence when exposed to blue light. Although many other marine organisms have similar green fluorescent proteins, GFP traditionally refers to the protein first isolated from the...
as a molecular tag.
S. pombe has also become an important organism in studying the cellular responses to DNA damage and the process of DNA replication
DNA replication
DNA replication is a biological process that occurs in all living organisms and copies their DNA; it is the basis for biological inheritance. The process starts with one double-stranded DNA molecule and produces two identical copies of the molecule...
.
Approximately 120 natural strains of S. pombe have been isolated. These have been collected from a variety of locations including Europe, North and South America and Asia. The majority of these strains have been collected from cultivated fruits such as apples and grapes, or from the various alcoholic beverage
Alcoholic beverage
An alcoholic beverage is a drink containing ethanol, commonly known as alcohol. Alcoholic beverages are divided into three general classes: beers, wines, and spirits. They are legally consumed in most countries, and over 100 countries have laws regulating their production, sale, and consumption...
s, such as Brazilian Cachaça
Cachaça
Cachaça is a liquor made from fermented sugarcane.It is the most popular distilled alcoholic beverage in Brazil. It is also known as aguardente, pinga, caninha and many other names...
. It is not clear at present whether S. pombe is the major fermenter or a contaminant in such brews. The natural ecology of Schizosaccharomyces
Schizosaccharomyces
Schizosaccharomyces is a genus of fission yeasts. The most well-studied species is S. pombe. At present four Schizosaccharomyces species have been described . Like the distantly related Saccharomyces cerevisiae, S. pombe is a significant model organism in the study of eukaryotic cell biology...
yeasts is not well studied.
Comparison with budding yeast (Saccharomyces cerevisiae)
The yeast species S. pombe and S. cerevisiae are both extensively studied; these two species diverged approximately 300 to 600 million years before present, and are significant tools in molecular and cellular biology. Some of the technical discriminants between these two species are:- S. cerevisiae has approximately 5,600 open reading frameOpen reading frameIn molecular genetics, an open reading frame is a DNA sequence that does not contain a stop codon in a given reading frame.Normally, inserts which interrupt the reading frame of a subsequent region after the start codon cause frameshift mutation of the sequence and dislocate the sequences for stop...
s; S. pombe has approximately 4,970 open reading frames. - Despite similar gene numbers, S. cerevisiae has only about 250 intronIntronAn intron is any nucleotide sequence within a gene that is removed by RNA splicing to generate the final mature RNA product of a gene. The term intron refers to both the DNA sequence within a gene, and the corresponding sequence in RNA transcripts. Sequences that are joined together in the final...
s, while S. pombe has nearly 5,000. - S. cerevisiae has 16 chromosomeChromosomeA chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
s, S. pombe has 3. - S. cerevisiae is often diploid while S. pombe is usually haploid.
- S. cerevisiae is in the G1 phase of the cell cycleCell cycleThe cell cycle, or cell-division cycle, is the series of events that takes place in a cell leading to its division and duplication . In cells without a nucleus , the cell cycle occurs via a process termed binary fission...
for an extended period (consequently, G1-S transition is tightly controlled) while S. pombe remains in the G2 phase of the cell cycle for an extended period (consequently, G2-M transition is under tight control). - Both species share genes with higher eukaryotes that they do not share with each other. S. pombe has RNAi machineryRNAIRNAI is a non-coding RNA that is an antisense repressor of the replication of some E. coli plasmids, including ColE1. Plasmid replication is usually initiated by RNAII, which acts as a primer by binding to its template DNA. The complementary RNAI binds RNAII prohibiting it from its initiation role...
genes like those in vertebrates, while this is missing from S. cerevisiae. S. cerevisiae also has greatly simplified heterochromatin compared to S. pombe. Conversely, S. cerevisiae has well-developed peroxisomes, while S. pombe does not. - S. cerevisiae has small point centromere of 125 bp, and sequence-defined replication origins of about the same size. Conversely, S. pombe has large, repetitive centromeres (40–100 kb) more similar to mammalian centromeres, and degenerate replication origins of at least 1kb.
Life cycle
The fission yeast is a single-celled fungus with simple, fully characterized genome and a rapid growth rate. It has long since been used in brewing, baking and molecular genetics. S. pombe is a rod-shaped cell, approximately 3 µm in diameter, that grows entirely by elongation at the ends. After mitosis, division occurs by the formation of a septum, or cell plate, that cleaves the cell at its midpoint.The central events of cell reproduction are chromosome duplication, which takes place in S (Synthetic) phase, followed by chromosome segregation and nuclear division (mitosis) and cell division (cytokinesis), which are collectively called M (Mitotic) phase.G1 is the gap between M and S phases, and G2 is the gap between S and M phases. In the budding yeast, the G2 phase is particularly extended, and cytokinesis (daughter-cell segregation) does not happen until a new S (Synthetic) phase is launched.
Fission yeast governs mitosis by mechanisms that are similar to those in multicellular animals. It normally proliferates in a haploid state. When starved, cells of opposite mating types (P and M) fuse to form a diploid zygote that immediately enters meiosis to generate four haploid spores. When conditions improve, these spores germinate to produce proliferating haploid cells.
Cytokinesis in fission yeast
The general features of cytokinesis are shown here. The site of cell division is determined before anaphase. The anaphase spindle (in green on the figure) is then positioned so that the segregated chromosomes are on opposite sides of the predetermined cleavage plane.Size control in fission yeast
In fission yeast, where growth governs progression through G2/M, a wee1 mutation causes entry into mitosis at an abnormally small size, resulting in a shorter G2. G1 is lengthened, suggesting that progression through Start (beginning of cell cycle) is responsive to growth when the G2/M control is lost. Furthermore, cells in poor nutrient conditions grow slowly and therefore take longer to double in size and divide. Interestingly enough, low nutrient levels also reset the growth threshold so that cell progresses through the cell cycle at a smaller size. Finally, wee1 mutant fission yeast cells are smaller than wild-type cells, but take just as long to go through the cell cycle. This is possible because small yeast cells grow slower, that is, their added total mass per unit time is smaller than that of normal cells.A spatial gradient is thought to coordinate cell size and mitotic entry in fission yeast.
The Pom1
Pom1
Pom1 is a polarity protein kinase in fission yeast, S. pombe, that localizes to cell ends. The gene pom1 codes for a protein 1087 amino acids long with the protein kinase domain likely located at the carboxyl terminus. Pom1 regulates a signaling pathway that includes Cdk1 and ultimately regulates...
protein kinase (green) is localized to the cell cortex, with the highest concentration at the cell tips. The cell-cycle regulators Cdr2, Cdr1 and Wee1 are present in cortical nodes in the middle of the cell (blue and red dots). a, In small cells, the Pom1
Pom1
Pom1 is a polarity protein kinase in fission yeast, S. pombe, that localizes to cell ends. The gene pom1 codes for a protein 1087 amino acids long with the protein kinase domain likely located at the carboxyl terminus. Pom1 regulates a signaling pathway that includes Cdk1 and ultimately regulates...
gradient reaches most of the cortical nodes (blue dots). Pom1
Pom1
Pom1 is a polarity protein kinase in fission yeast, S. pombe, that localizes to cell ends. The gene pom1 codes for a protein 1087 amino acids long with the protein kinase domain likely located at the carboxyl terminus. Pom1 regulates a signaling pathway that includes Cdk1 and ultimately regulates...
inhibits Cdr2, preventing Cdr2 and Cdr1 from inhibiting Wee1, and allowing Wee1 to phosphorylate Cdk1, thus inactivating cyclin-dependent kinase (CDK) activity and preventing entry into mitosis. b, In long cells, the Pom1
Pom1
Pom1 is a polarity protein kinase in fission yeast, S. pombe, that localizes to cell ends. The gene pom1 codes for a protein 1087 amino acids long with the protein kinase domain likely located at the carboxyl terminus. Pom1 regulates a signaling pathway that includes Cdk1 and ultimately regulates...
gradient does not reach the cortical nodes (red dots), and therefore Cdr2 and Cdr1 remain active in the nodes. Cdr2 and Cdr1 inhibit Wee1, preventing phosphorylation of Cdk1 and thereby leading to activation of CDK and mitotic entry. (This simplified diagram omits several other regulators of CDK activity.)