Septum (cell biology)

Last updated
Septins in Saccharomyces cerevisiae (fluorescent micrograph) * Green: septins (AgSEP7-GFP) * Red: cell outline (phase contrast) * Scale bar: 10 mm S cerevisiae septins.jpg
Septins in Saccharomyces cerevisiae (fluorescent micrograph)
• Green: septins (AgSEP7-GFP )
• Red: cell outline (phase contrast)
• Scale bar: 10 μm

A septum in cell biology is the new cell wall that forms between two daughter cells as a result of cell division. [1] Cell division is an extremely complex process that contains four different subprocesses. [2] These processes included the growth of a cell, DNA replication, the process of allocating replicated chromosomes to daughter cells, and septum formation. [2] Ultimately, the septum is the crucial ending to mitosis, meiosis, and the division of bacterial cells. The formation of the septum (a new cell wall) allows the two daughter cells to be separate from one another and perform their respective functions independently. [3]

Contents

Composition

In Schizosaccharomyces pombe, the primary septum is composed of linear β(1,3)-D-glucan, β(1,6) branches, and α(1,3)-D-glucan. [4] [5] The secondary septum in Schizosaccharomyces pombe is composed of β(1,6)-D-glucan, β(1,6) branches, and α(1,3)-D-glucan. [5] The synthesis of linear β(1,3)-D-glucan for the primary septum is done by the enzyme β(1,3)-D-glucan synthase and regulated by a Rho GTPase. [5] Ags1/Mok1 enzyme is responsible for the synthesis of α(1,3)-D-glucan in the primary septum and secondary septum. [5]

Septum formation during binary fission

The process of bacterial cell division is defined as binary fission, where a bacterium splits to produce two daughter cells. [4] This division occurs during cytokinesis, which in bacteria is made possible due to the divisome (a specific large protein complex) and FtsZ (the ancestor to tubulin for bacteria that drives cytokinesis itself). [4] This protein machinery works to form the barrier known as the septum between the two daughter cells. At the core of this protein complex is the Z-ring- protofilaments that assemble around the cell at the specific site of cell division. [4] The Z-ring formation is made possible due to certain positioning proteins that depend on the species of the cell. [4] The FtsZ portion of the divisome are protofilaments that are tightly attached to the inside of the cytoplasmic membrane by other proteins, for example in E. coli, FtsA and ZipA assist in securing the protofilaments to the membrane. [4] This FtsZ complex and the membrane attachments are termed as the proto-ring. [4] Once the proto-ring is assembled, FtsA (the ancestor to actin for bacteria) connects the Z ring to the other proteins within the divisome and the constriction of the Z-ring and cytoplasmic membrane begins inward. [4] Such inward constriction causes the cells to form a septum and separate from one another, forming two distinct bacteria cells. [4]

Septum formation for eukaryotic cells

Animal Cells

During cytokinesis in animal cells, a contractile ring made up of actin filaments forms, and this ring pinches to divide the cell into two daughter cells. [6] The cells are able to separate due to the formation of a cleavage furrow, which pinches in a centripetal fashion (from the outside of the cell towards the center of the cell). [6] This cleavage furrow is able to pinch together due to the actin filaments that form the contractile ring. [6] Thus, in animal cells it can be observed that the septum is not a true wall, rather the pinching of a cleavage furrow.

Plant Cells

The manner in which plant cells form a septum is drastically different than that of animal cells. This is because in a plant cell there is no cleavage furrow or pinching of the plasma membrane, rather a cell plate forms in the middle of the cell that then allows the division into two daughter cells. [6] The cell plate formation occurs due to vesicles budding from the golgi apparatus [7] and adding to the plant cell in a centrifugal manner thanks to the directed movement of microtubules (from the center to the outside of the cell). [6]

Septum formation in fungi

In yeast, septins form a ring structure, to which other proteins are recruited. [8] In particular, chitin synthase 2 is required, an enzyme that synthesises chitin thereby building up the primary septum. A secondary septum of β-glucans and mannoproteins is then assembled using the enzyme 1,3-Beta-glucan synthase, and the primary septum degraded during cell separation. After degradation of the primary septum, a chitinous bud scar remains on both the mother and daughter cell. [8] [9]

In regard to septum formation related diseases, cancer in eukaryotic cells can occur due to mutations that cause different errors in cytokinesis and in the septum formation itself. [10] This is because defects in cytokinesis can affect the number of sets of chromosomes in the cell, and if a defect occurs that leads to a tetraploid cell, there is a high possibility that aneuploid cells could generate from it. [10] This is an issue because the majority of tumors in humans are made up of aneuploid cells. [10] Additionally, if one of the steps of cytokinesis is negatively affected, the formation of the septum could be made impossible which could lead to the formation of more aneuploid cells. [10] For instance, if the cleavage furrow in an animal cell fails to cleave inwards due to the absence of one of its activators such as polo-like kinase 1, the cell remains with double the amount of chromosomes and could lead to cancerous tumors. [10] Along with this, outside factors could influence cytokinesis and septum formation, such as asbestos fibres. [10] These fibres block the process of cytokinesis of occuring due to their carcinogenic nature. [10] Furthermore, certain breast cancers have been linked to the loss of the adhesion between the cell and the matrix. [10] This causes a process known as entosis to occur, which is the uptake of the cell by cells that neighbor it. [10] Such uptake results in multi-nucleation which can cause human breast cancers. [10]

Since the failure of cytokinesis and septum formation can lead to diseases, researchers were able to discover that blocking the formation of the septum by blocking cytokinesis could treat certain bacterial diseases such as Streptococcus . [11] Researchers found that FtsZ could be used as a target, as it has the ability to stop the division of the cell, which causes diseases such as Streptococcus to halt in cell division, and then lyse, causing the diseased cell to no longer be functional. [11] While some inhibitors of FtsZ have been discovered such as sanguinarine, further work is still required for the majority of these inhibitors to be utilized in a clinical setting. [11]

Related Research Articles

<span class="mw-page-title-main">Cell wall</span> Outermost layer of some cells

A cell wall is a structural layer that surrounds some cell types, found immediately outside the cell membrane. It can be tough, flexible, and sometimes rigid. Primarily, it provides the cell with structural support, shape, protection, and functions as a selective barrier. Another vital role of the cell wall is to help the cell withstand osmotic pressure and mechanical stress. While absent in many eukaryotes, including animals, cell walls are prevalent in other organisms such as fungi, algae and plants, and are commonly found in most prokaryotes, with the exception of mollicute bacteria.

<span class="mw-page-title-main">Cytoskeleton</span> Network of filamentous proteins that forms the internal framework of cells

The cytoskeleton is a complex, dynamic network of interlinking protein filaments present in the cytoplasm of all cells, including those of bacteria and archaea. In eukaryotes, it extends from the cell nucleus to the cell membrane and is composed of similar proteins in the various organisms. It is composed of three main components: microfilaments, intermediate filaments, and microtubules, and these are all capable of rapid growth and or disassembly depending on the cell's requirements.

<span class="mw-page-title-main">Cytokinesis</span> Part of the cell division process

Cytokinesis is the part of the cell division process and part of mitosis during which the cytoplasm of a single eukaryotic cell divides into two daughter cells. Cytoplasmic division begins during or after the late stages of nuclear division in mitosis and meiosis. During cytokinesis the spindle apparatus partitions and transports duplicated chromatids into the cytoplasm of the separating daughter cells. It thereby ensures that chromosome number and complement are maintained from one generation to the next and that, except in special cases, the daughter cells will be functional copies of the parent cell. After the completion of the telophase and cytokinesis, each daughter cell enters the interphase of the cell cycle.

<span class="mw-page-title-main">Cleavage furrow</span> Plasma membrane invagination at the cell division site

In cell biology, the cleavage furrow is the indentation of the cell's surface that begins the progression of cleavage, by which animal and some algal cells undergo cytokinesis, the final splitting of the membrane, in the process of cell division. The same proteins responsible for muscle contraction, actin and myosin, begin the process of forming the cleavage furrow, creating an actomyosin ring. Other cytoskeletal proteins and actin binding proteins are involved in the procedure.

<span class="mw-page-title-main">FtsZ</span> Protein encoded by the ftsZ gene

FtsZ is a protein encoded by the ftsZ gene that assembles into a ring at the future site of bacterial cell division. FtsZ is a prokaryotic homologue of the eukaryotic protein tubulin. The initials FtsZ mean "Filamenting temperature-sensitive mutant Z." The hypothesis was that cell division mutants of E. coli would grow as filaments due to the inability of the daughter cells to separate from one another. FtsZ is found in almost all bacteria, many archaea, all chloroplasts and some mitochondria, where it is essential for cell division. FtsZ assembles the cytoskeletal scaffold of the Z ring that, along with additional proteins, constricts to divide the cell in two.

<span class="mw-page-title-main">Tubulin</span> Superfamily of proteins that make up microtubules

Tubulin in molecular biology can refer either to the tubulin protein superfamily of globular proteins, or one of the member proteins of that superfamily. α- and β-tubulins polymerize into microtubules, a major component of the eukaryotic cytoskeleton. It was discovered and named by Hideo Mōri in 1968. Microtubules function in many essential cellular processes, including mitosis. Tubulin-binding drugs kill cancerous cells by inhibiting microtubule dynamics, which are required for DNA segregation and therefore cell division.

<span class="mw-page-title-main">Filamentation</span> Type of bacteria growth

Filamentation is the anomalous growth of certain bacteria, such as Escherichia coli, in which cells continue to elongate but do not divide. The cells that result from elongation without division have multiple chromosomal copies.

A glucan is a polysaccharide derived from D-glucose, linked by glycosidic bonds. Glucans are noted in two forms: alpha glucans and beta glucans. Many beta-glucans are medically important. They represent a drug target for antifungal medications of the echinocandin class.

Septins are a group of GTP-binding proteins expressed in all eukaryotic cells except plants. Different septins form protein complexes with each other. These complexes can further assemble into filaments, rings and gauzes. Assembled as such, septins function in cells by localizing other proteins, either by providing a scaffold to which proteins can attach, or by forming a barrier preventing the diffusion of molecules from one compartment of the cell to another, or in the cell cortex as a barrier to the diffusion of membrane-bound proteins.

<span class="mw-page-title-main">Prokaryotic cytoskeleton</span> Structural filaments in prokaryotes

The prokaryotic cytoskeleton is the collective name for all structural filaments in prokaryotes. It was once thought that prokaryotic cells did not possess cytoskeletons, but advances in visualization technology and structure determination led to the discovery of filaments in these cells in the early 1990s. Not only have analogues for all major cytoskeletal proteins in eukaryotes been found in prokaryotes, cytoskeletal proteins with no known eukaryotic homologues have also been discovered. Cytoskeletal elements play essential roles in cell division, protection, shape determination, and polarity determination in various prokaryotes.

<span class="mw-page-title-main">Rho-associated protein kinase</span>

Rho-associated protein kinase (ROCK) is a kinase belonging to the AGC family of serine-threonine specific protein kinases. It is involved mainly in regulating the shape and movement of cells by acting on the cytoskeleton.

<span class="mw-page-title-main">Fission (biology)</span> Biological process

Fission, in biology, is the division of a single entity into two or more parts and the regeneration of those parts to separate entities resembling the original. The object experiencing fission is usually a cell, but the term may also refer to how organisms, bodies, populations, or species split into discrete parts. The fission may be binary fission, in which a single organism produces two parts, or multiple fission, in which a single entity produces multiple parts.

<span class="mw-page-title-main">Glucanase</span>

Glucanases are enzymes that break down large polysaccharides via hydrolysis. The product of the hydrolysis reaction is called a glucan, a linear polysaccharide made of up to 1200 glucose monomers, held together with glycosidic bonds. Glucans are abundant in the endosperm cell walls of cereals such as barley, rye, sorghum, rice, and wheat. Glucanases are also referred to as lichenases, hydrolases, glycosidases, glycosyl hydrolases, and/or laminarinases. Many types of glucanases share similar amino acid sequences but vastly different substrates. Of the known endo-glucanases, 1,3-1,4-β-glucanase is considered the most active.

Bacterial morphological plasticity refers to changes in the shape and size that bacterial cells undergo when they encounter stressful environments. Although bacteria have evolved complex molecular strategies to maintain their shape, many are able to alter their shape as a survival strategy in response to protist predators, antibiotics, the immune response, and other threats.

<span class="mw-page-title-main">Min System</span> Mechanism used by E. coli in cell division

The Min System is a mechanism composed of three proteins MinC, MinD, and MinE used by E. coli as a means of properly localizing the septum prior to cell division. Each component participates in generating a dynamic oscillation of FtsZ protein inhibition between the two bacterial poles to precisely specify the mid-zone of the cell, allowing the cell to accurately divide in two. This system is known to function in conjunction with a second negative regulatory system, the nucleoid occlusion system (NO), to ensure proper spatial and temporal regulation of chromosomal segregation and division.

The MinC protein is one of three proteins in the Min system encoded by the minB operon and which is required to generate pole to pole oscillations prior to bacterial cell division as a means of specifying the midzone of the cell. This function is achieved by preventing the formation of the divisome Z-ring around the poles.

<span class="mw-page-title-main">FtsA</span> Bacterial protein that is related to actin

FtsA is a bacterial protein that is related to actin by overall structural similarity and in its ATP binding pocket.

<span class="mw-page-title-main">Actomyosin ring</span> Cellular formation during cytokinesis

In molecular biology, an actomyosin ring or contractile ring, is a prominent structure during cytokinesis. It forms perpendicular to the axis of the spindle apparatus towards the end of telophase, in which sister chromatids are identically separated at the opposite sides of the spindle forming nuclei. The actomyosin ring follows an orderly sequence of events: identification of the active division site, formation of the ring, constriction of the ring, and disassembly of the ring. It is composed of actin and myosin II bundles, thus the term actomyosin. The actomyosin ring operates in contractile motion, although the mechanism on how or what triggers the constriction is still an evolving topic. Other cytoskeletal proteins are also involved in maintaining the stability of the ring and driving its constriction. Apart from cytokinesis, in which the ring constricts as the cells divide, actomyosin ring constriction has also been found to activate during wound closure. During this process, actin filaments are degraded, preserving the thickness of the ring. After cytokinesis is complete, one of the two daughter cells inherits a remnant known as the midbody ring.

<span class="mw-page-title-main">Divisome</span> A protein complex in bacteria responsible for cell division

The divisome is a protein complex in bacteria that is responsible for cell division, constriction of inner and outer membranes during division, and peptidoglycan (PG) synthesis at the division site. The divisome is a membrane protein complex with proteins on both sides of the cytoplasmic membrane. In gram-negative cells it is located in the inner membrane. The divisome is nearly ubiquitous in bacteria although its composition may vary between species.

<span class="mw-page-title-main">FtsK</span> Protein involved in bacterial cell division

FtsK is a protein in E.Coli involved in bacterial cell division and chromosome segregation. It is one of the largest proteins, consisting of 1329 amino acids. FtsK stands for "Filament temperature sensitive mutant K" because cells expressing a mutant ftsK allele called ftsK44, which encodes an FtsK variant containing an G80A residue change in the second transmembrane segment, fail to divide at high temperatures and form long filaments instead. FtsK, specifically its C-terminal domain, functions as a DNA translocase, interacts with other cell division proteins, and regulates Xer-mediated recombination. FtsK belongs to the AAA superfamily and is present in most bacteria.

References

  1. ↑ O'Connor C (2008). "Cell Division: Stages of Mitosis". Nature Education. 1 (1): 188.
  2. 1 2 Cooper, Geoffrey M. (2000), "The Eukaryotic Cell Cycle", The Cell: A Molecular Approach. 2nd edition, Sinauer Associates, retrieved 2024-12-03
  3. ↑ Vicente, Miguel; Rico, Ana Isabel; Martínez-Arteaga, Rocío; Mingorance, Jesús (January 2006). "Septum Enlightenment: Assembly of Bacterial Division Proteins". Journal of Bacteriology. 188 (1): 19–27. doi:10.1128/jb.188.1.19-27.2006. PMC   1317574 . PMID   16352817.
  4. 1 2 3 4 5 6 7 8 9 Haeusser, Daniel P.; Margolin, William (May 2016). "Splitsville: structural and functional insights into the dynamic bacterial Z ring". Nature Reviews Microbiology. 14 (5): 305–319. doi:10.1038/nrmicro.2016.26. ISSN   1740-1534. PMC   5290750 . PMID   27040757.
  5. 1 2 3 4 García Cortés JC, Ramos M, Osumi M, Pérez P, Ribas JC (September 2016). "The Cell Biology of Fission Yeast Septation". Microbiology and Molecular Biology Reviews. 80 (3): 779–91. doi:10.1128/MMBR.00013-16. PMC   4981666 . PMID   27466282.
  6. 1 2 3 4 5 "Difference between Plant and Animal Cytokinesis". BYJUS. Retrieved 2024-12-03.
  7. ↑ "Dissecting Cell Plate Development During Plant Cytokinesis". Janelia Research Campus. Retrieved 2024-12-04.
  8. 1 2 Cabib E, Roh DH, Schmidt M, Crotti LB, Varma A (June 2001). "The yeast cell wall and septum as paradigms of cell growth and morphogenesis". The Journal of Biological Chemistry. 276 (23): 19679–82. doi: 10.1074/jbc.R000031200 . PMID   11309404.
  9. ↑ Lesage G, Bussey H (June 2006). "Cell wall assembly in Saccharomyces cerevisiae". Microbiology and Molecular Biology Reviews. 70 (2): 317–43. doi:10.1128/MMBR.00038-05. PMC   1489534 . PMID   16760306.
  10. 1 2 3 4 5 6 7 8 9 10 Lens, Susanne M. A.; Medema, René H. (January 2019). "Cytokinesis defects and cancer". Nature Reviews Cancer. 19 (1): 32–45. doi:10.1038/s41568-018-0084-6. ISSN   1474-1768.
  11. 1 2 3 Du, Ruo Lan; Sun, Ning; Fung, Yik Hong; Zheng, Yuan Yuan; Chen, Yu Wei; Chan, Pak Ho; Wong, Wing Leung; Wong, Kwok Yin (2021-11-15). "Discovery of FtsZ inhibitors by virtual screening as antibacterial agents and study of the inhibition mechanism". RSC Medicinal Chemistry. 13: 79–89. doi:10.1039/d1md00249j. ISSN   2632-8682.

[1] [2]

NIEHScell.jpg

This cell biology article is a stub. You can help Wikipedia by expanding it.

  1. ↑
  2. ↑
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.