Name: anaphase start and chromatid release
Uploaded: 2021-04-07T12:12:01.000Z
Duration: 2 min 17 s
Channel: JoVE

K12 Standards

Next Generation Science Standards

High School

Life Science

from-molecules-to-organisms-structures-and-processes

From Molecules to Organisms: Structures and Processes

HS-LS1-4

Separation of Sister Chromatids

中期の終わりに、二配向染色体は中期プレートに整列します。この段階では、コヒーシンタンパク質環複合体が姉妹染色分体をセントロメア領域で一緒に保持し、それらが引き離されるのを防ぎます。
中期から後期への進行は、マルチサブユニットのユビキチンリガーゼ酵素(後期促進複合体、別名シクロソームまたはAPC/C)のサイクリン-Cdk誘導リン酸化によって引き起こされます。リン酸化APC/Cはタンパク質Cdc20に結合し、活性複合体を形成します。
活性APC/C複合体は、セパラーゼと呼ばれるプロテアーゼ酵素に結合したセキュリンと呼ばれる阻害性タンパク質を認識します。この認識に先立ち、セクリンはセパラーゼの活性を阻害します。
活性APC/C複合体は、セキュリンをユビキチンタンパク質にタグ付けし、プロテアソームの分解を標的とします。セクリンが破壊されるとセパラーゼが放出されます。
また、サイクリン-Cdk複合体は、阻害性リン酸化を通じて非結合セパラーゼ活性を負に制御します。
活性APC/C複合体は、サイクリンのユビキチン化を引き起こし、プロテアソームの分解を標的とします。サイクリンが破壊されると、サイクリン依存性キナーゼまたはCdkの酵素活性が除去されます。
Cdksの不活性化により、ホスファターゼ酵素はセパラーゼを脱リン酸化し、Cdkを介したセパラーゼの阻害性再リン酸化を防ぎます。脱リン酸化により、セパラーゼ酵素は、姉妹染色分体を一緒に保持するコヒーシン環複合体を切断することができます。
コヒーシン切断は、姉妹染色分体の凝集性の完全な喪失をもたらし、中期から後期への移行を示します。凝集力の喪失により、姉妹染色分体は分離し、紡錘体の反対側の極に移動することができます。

<ol>
	<li>クレア・アクアビバ、ジョナソン・パインズ。20016.「後期促進複合体/サイクロソーム:APC / C」。細胞科学ジャーナル。119: 2401-2404.[<a href="https://jcs.biologists.org/content/119/12/2401#sec-2">ソース</a>]</li>
	<li>フランク・ウールマン、フリードリヒ・ロッツパイヒ、キム・ナスミス。1999. 「後期発症時の姉妹染色分体の分離は、コヒーシンサブユニット scc の切断によって促進されます。」 Nature 400 (6739)。ネイチャーパブリッシンググループ:37-42。[<a href="https://mcb.berkeley.edu/courses/mcb230/WEB/PAPERS/SCC1.pdf">出典</a>]</li>
	<li>「中期から後期への移行:生産的破壊の事例」 European journal of biochemistry 263, no. 1 (1999): 14-19.</li>
	<li>「後期促進複合体による有糸分裂遷移の制御」 ロンドン王立協会の哲学的取引。シリーズB:生物科学354、no.1389(1999):1583-1590。</li>
</ol>

姉妹染色分体の分離

前期から中期への移行時には、染色体腕に沿った凝集力が減少し、その結果、姉妹染色分体の分離が起こります。 ただし、中期から後期に移行するまで、姉妹染色分体を保持するために残ったコヒーシン結合が残ります。結合が残っているため、姉妹染色分体の早期分離が防止され、娘細胞内の異数性のリスクがブロックされます。

後期の開始時に、タンパク質分解酵素であるセパラーゼが活性化されます。活性化されたセパラーゼは、残留コヒーシン リングのScc1サブユニットを切断し、その結果、凝集が完全に失われます。姉妹染色分体は、それらを保持する力がなくなると分離します。凝集力の欠如により、微小管に沿って緊張する極方向の力が、分離された染色分体を紡錘体極に向かって引っ張ることができます。

有糸分裂の初期では、紡錘体集合チェックポイント(SAC)により、後期促進複合体またはサイクロソーム(APC/C)が、後期に分解が必要なセキュリンやM期サイクリンなどのタンパク質をユビキチン化することが妨げられます。 各染色体が紡錘体上で正しく整列した場合にのみ、SAC は不活性化され、APC/C調節サブユニットであるCDC20およびCDH1のリン酸化と活性化が可能になります。

CDC20はCdk1/サイクリンBによってリン酸化され、活性型APC/C-CDC20を形成します。活性型APC/C-CDC20は、セキュリン、サイクリンA、サイクリンBの分解を触媒し、後期移行を促進します。Cdk活性はサイクリン依存性であるため、サイクリンBの分解によりCdk1活性が失われます。Cdk1/サイクリンB複合体の喪失はAPC/C-CDC20を不活性化しますが、中期から後期への移行の完了を知らせる別の調節サブユニットであるAPC/C-CDH1を活性化します。 活性型APC/C-CDH1は、有糸分裂サイクリンの早期蓄積を防ぐことで有糸分裂終了を促進し、その後のG1期を安定させます。

APC/C-CDC20とAPC/C-CDH1の活性の切り替えは2つの重大な結果をもたらします。第一に、これらの調節サブユニットは、重複しながらも異なる基質特異性を引き起こし、それによって規則正しい細胞周期移行を促進します。第二に、CDC20とCDH1は異なるメカニズムを通じて調節されます。APC/C-CDC20が活性化すると、CDH1はサイクリンB/Cdk1による抑制的リン酸化を受け、APC/Cへの結合が妨げられます。 対照的に、CDC20 活性は、SACによって活性化されるマルチタンパク質(BUBR1、BUB3、CDC20、およびMAD2)である有糸分裂チェックポイント複合体によって阻害されます。

前期から中期への移行では、染色体腕に沿った凝集力が低下し、姉妹の解消につながります...

Education

JoVE Core

Molecular Biology

分子生物学

Unit 2

ユニット2

Cell Division

細胞分裂

KEY TERMS AND CONCEPTS

主要用語と概念

anaphase start and chromatid release

Anaphase starts when sister chromatids are released from one another and pulled toward opposite spindle poles. Before that happens, cohesion along the chromosomal arms is reduced from prophase to metaphase, which helps the sister chromatids resolve. A residual cohesin link still holds them together until the metaphase-to-anaphase transition. This leftover connection helps prevent early separation and reduces the risk of aneuploidy, or the wrong number of chromosomes, in daughter cells.

At the onset of anaphase, separase, a protein-cutting enzyme, becomes active. It cleaves the Scc1 subunit of the remaining cohesin rings. Once that cohesion is lost, the sister chromatids separate without needing a force to pull them apart first. Then the poleward forces along the microtubules can draw the separated chromatids toward the spindle poles.

The spindle assembly checkpoint, or SAC, controls this timing in early mitosis. It blocks the anaphase-promoting complex or cyclosome, called APC/C, from ubiquitinating proteins such as securin and M-phase cyclins until each chromosome is correctly aligned on the mitotic spindle. After alignment, the SAC is turned off. This allows the APC/C regulatory subunits CDC20 and CDH1 to be phosphorylated and activated in sequence.

Phosphorylated CDC20, together with Cdk1/cyclin B, forms active APC/C-CDC20. This complex promotes anaphase by triggering the degradation of securin, cyclin A, and cyclin B. Because Cdk activity depends on cyclins, cyclin B breakdown lowers Cdk1 activity. That loss inactivates APC/C-CDC20 and activates APC/C-CDH1, which signals that the metaphase-to-anaphase transition is complete.

APC/C-CDH1 helps cells exit mitosis and stabilize the next G1 phase by stopping mitotic cyclins from building up too early. The switch between APC/C-CDC20 and APC/C-CDH1 has two important effects. It gives these regulators overlapping but different substrate targets, which helps keep the cell cycle in order. It also reflects different control systems. When APC/C-CDC20 is active, CDH1 is held back by inhibitory phosphorylation from cyclin B/Cdk1. In contrast, CDC20 is blocked by the mitotic checkpoint complex, which includes BUBR1, BUB3, CDC20, and MAD2 and is activated by the SAC.

Anaphase Start and Chromatid Release

mitosis and cytokinesis

Mitosis and Cytokinesis Stages

Mitosis and cytokinesis are the two main steps of cell division. Mitosis is the process that divides the nucleus, while cytokinesis splits the rest of the cell. During mitosis, the cell’s genetic material is separated into two sets. This helps form two new nuclei with the same genetic information. Cytokinesis then completes division by separating the cytoplasm, which creates two daughter cells. These stages work together to make cell division possible in growing and repairing tissues.

duplication of chromatin structure

Chromatin Rebuilding During DNA Replication

Chromatin rebuilding during DNA replication helps cells copy DNA and pass on chromosome structure to daughter cells. During cell division, the genome must be disrupted and then reassembled across the whole chromosome. This process allows chromatin to be inherited, rebuilt, and maintained in new cells. The basic unit of chromatin is the nucleosome. A nucleosome contains DNA wrapped around an octamer of histone proteins, with short linker DNA between neighboring nucleosomes. The histone proteins...

cohesins

Cohesins in Meiosis and Genetic Disorders

Cohesin protein complexes act like molecular glue that keeps sister chromatids together. They are important in both mitosis and meiosis. In mitosis, cohesin complexes are removed from chromosomes before anaphase begins. Meiosis has two rounds of chromosome separation. Meiosis I separates homologous chromosomes, while Meiosis II separates sister chromatids. This process produces four daughter cells. The Meiosis I cohesin complex is made of four subunits: Smc1, Smc3, Rec8, and Scc3. Rec8...

condensins

How Condensins Shape Mitotic Chromosomes

Condensins shape chromosomes during mitosis, the stage when a cell divides. These large protein complexes use ATP, the cell’s energy molecule, to help turn loose post-interphase DNA into compact, separate chromosomes. They organize and segregate chromosomal DNA so it can be passed on correctly. Plant and animal cells contain two condensin complexes: condensin I and condensin II. Each complex has five subunits. Two are SMC, or Structural Maintenance of Chromosomes, subunits. One is a kleisin...

the mitotic spindle

How the Mitotic Spindle Separates Chromosomes

The mitotic spindle is a microtubule-based structure that helps separate chromosomes during cell division. It forms in eukaryotic cells and moves sister chromatids to opposite ends of the parent cell. This leaves each new cell nucleus with the correct genetic material. A bipolar spindle has two poles, and that shape is important for chromosome segregation. In many animal cells, two centrosomes are present when mitosis begins. Each centrosome helps organize a circular set of microtubules at one...

centrosome duplication

Centrosome Duplication in the Cell Cycle

Centrosome duplication is a key part of the animal cell cycle. The centrosome is the main microtubule organizing center, or MTOC, in animal cells. It contains two cylindrical centrioles at its core. Each centriole has nine sets of three microtubules held together by proteins. The two centrioles sit at right angles and are surrounded by the pericentriolar matrix, or PCM, a shapeless protein cloud. Duplication starts early in the cell cycle so each daughter cell can receive a centrosome after...

microtubule instability

Microtubule Growth and Shrinkage

Microtubules are hollow, cylindrical filaments in the cell. They are about 25 nm wide and can range from 200 nm to 25 μm in length. Their main building blocks are GTP-bound tubulin subunits that form αβ-heterodimers, which then assemble into protofilaments. These protofilaments join by lateral bonds to create stable microtubule cylinders. Microtubules are highly dynamic because they repeatedly assemble and break down. They can even grow on one end while shrinking on the other at the same time.

spindle assembly

How the Mitotic Spindle Forms

The mitotic spindle forms through centrosome-mediated, chromatin-mediated, and microtubule-mediated pathways. These pathways often work at the same time. Together, they build a strong spindle apparatus for cell division. In most cells, centrosomes are the main sites where microtubules begin to grow. During the G2 to prophase transition, centrosomes mature and make more microtubules. The growing microtubules extend from both centrosomes, and their plus-ends search for chromosomes by attaching...

attachment of sister chromatids

Kinetochore-Microtubule Binding in Mitosis

Kinetochore-microtubule binding helps chromosomes line up and separate during mitosis. After the nuclear envelope breaks down, condensed chromosomes are exposed to the bipolar microtubules of the mitotic spindle. The kinetochore is a large, disc-shaped protein complex at the centromere region of each sister chromatid, and it serves as the microtubule binding site. Usually, the plus-end of a single microtubule inserts into the kinetochore. In some cases, a kinetochore first makes lateral...

forces acting on chromosomes

Chromosome Movement During Mitosis

Chromosome movement during mitosis depends on several small forces that act at different times and positions in the cell. In prometaphase, these forces help chromosomes move to the equatorial plane and line up at the metaphase plate. Because the forces change with location and stage, chromosome behavior also changes as mitosis continues. Microtubules and motor proteins create two main kinds of force on chromosomes: poleward force and anti-poleward force, also called polar-ejection force.

separation of sister chromatids

Anaphase starts when sister chromatids are released from one another and pulled toward opposite spindle poles. Before that happens, cohesion along the chromosomal arms is reduced from prophase to metaphase, which helps the sister chromatids resolve. A residual cohesin link still holds them together until the metaphase-to-anaphase transition. This leftover connection helps prevent early separation and reduces the risk of aneuploidy, or the wrong number of chromosomes, in daughter cells. At the...

the spindle assembly checkpoint

How Cells Safeguard Chromosome Separation

The spindle assembly checkpoint helps cells safeguard chromosome separation during anaphase. It acts as a molecular surveillance system. The checkpoint checks whether the steps needed for chromosome segregation are complete before the cell moves on. Many proteins work together to control this checkpoint. If mutations affect these proteins, a cell may enter anaphase too early. Chromosomes can then separate before the needed steps are finished. When this happens, the daughter cells may receive...

anaphase a and b

Chromatid Movement by Microtubule Forces

Chromatid movement during anaphase depends on microtubule forces at the spindle. Kinetochore microtubules grow from the spindle poles, and their plus ends attach to kinetochores on sister chromatids. The kinetochore protein complex Ndc80 makes low-affinity links with the microtubule plus end.

the contractile ring

How Cells Build the Contractile Ring

Contractile rings are built from microfilaments and help separate daughter cells during cytokinesis. This ring forms as the cell cycle moves forward, but the exact timing and coordination with other cell cycle events are still not fully understood. RhoA, a small GTPase in the Ras superfamily, controls contractile ring assembly and function. The inactive form of RhoA is bound to GDP. A guanine nucleotide exchange factor, or Rho-GEF, is located in the cortex region, where the next cell division...

determining the plane of cell division

How Cells Set the Division Plane

How cells set the division plane during cell division affects daughter cell size and, in many cases, cell fate. The plane of division is perpendicular to the plane of chromosome segregation. Different organisms use different cues to place it, based on their shape and needs. In animal cells, the cleavage furrow forms along the division plane from the cell cortex, the area just below the plasma membrane. The mitotic spindle is the main guide for this position. If the spindle axis changes, the...

the phragmoplast

How Plant Cells Build a New Wall

Plant cells build a new wall during cytokinesis with help from the phragmoplast. This plant structure forms from the central spindle and related cell parts as the cell finishes dividing. In animal cells, the comparable structure is the midbody, but in plants the phragmoplast expands outward to guide new wall formation. The mature phragmoplast has a donut-like shape. It has an outer leading region, a middle transition zone, and an inner lagging region. New microtubules are assembled...

distribution of cytoplasmic content

How Organelles Are Split During Cytokinesis

Cytokinesis splits a cell’s chromosomes and organelles into two daughter cells. Before cell division, organelles grow and divide. They cannot be made from scratch, so each daughter cell must inherit at least one copy to survive. Many details of this organelle sorting process are still not fully known. The cytoplasm contains organelles, salts, proteins, and water. Small organelles such as peroxisomes and lysosomes can be shared by simple diffusion. Because cells contain many copies of these...

anaphase promoting complex

APC Activates Chromosome Separation

The anaphase-promoting complex, or APC, helps control cell cycle progression by destroying specific proteins at the right time. These proteins are tagged with ubiquitin by ubiquitin ligases and then broken down by the proteasome. The SCF (Skp1/Cullin/F-box) complex and APC are two major ubiquitin ligases involved in this process. SCF stays active throughout the cell cycle, but APC turns on during the metaphase-to-anaphase transition. APC becomes active when Cdc20 or Cdh1 binds to it. These...

key terms and concepts

Learn how the spindle checkpoint, separase, and APC/C control sister chromatid release at anaphase and help prevent chromosome errors in mitosis.

Anaphase Start and Chromatid Release | JoVE K12

molecular biology

JoVE Core 分子生物学は、明確で簡潔なアニメーション ビデオ レッスンを通じて細胞の分子プロセスを紹介します。さらに、科学者の実際のビデオでは、これらの概念の応用が現代の研究室での実際の実験を通じて実証されています。

new-york-state-science-learning-standards

New York State Science Learning Standards

Inheritance and Variation of Traits

HS-LS1-4.

Characteristics of Life

Biology is a natural science that studies life and living organisms, including their structure, function, development, interactions, evolution, ...

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Cell Structure

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The DNA Helix

Nucleic Acids

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Globular and Fibrous Proteins

Translation

Translation is the process of synthesizing proteins from the genetic information carried by messenger RNA (mRNA). Following transcription, it constitutes ...

Intrinsically Disordered Proteins

Ribosomes

Ribosomes translate genetic information encoded by messenger RNA (mRNA) into proteins. Both prokaryotic and eukaryotic cells have ribosomes. Cells that ...

Protein Complex Assembly

Protein and Protein Structures

Conjugated Proteins

Proteins: From Genes to Degradation

Amyloid Fibrils

What are Proteins?

Proteins are polymers of amino acids linked together by peptide bonds. Proteins and polypeptides are interchangeably used to refer to long chains of amino ...

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Protein-Protein Interfaces

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Cofactors and Coenzymes

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Cooperative Allosteric Transitions

Protein Kinases and Phosphatases

GTPases and their Regulation

Covalently Linked Protein Regulators

protein-complexes-with-interchangeable-parts

Protein Complexes with Interchangeable Parts

Mechanical Protein Function

Structural Protein Function

Protein Networks

Construct an explanation based on evidence for how the structure of DNA determines the structure of proteins, which carry out the essential functions of life through systems of specialized cells. [Assessment Boundary: Assessment does not include identification of specific cell or tissue types, whole body systems, specific protein structures and functions, or the biochemistry of protein synthesis.]

HS-LS1-1

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Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms. [Clarification Statement: Emphasis is on functions at the organism system level such as nutrient uptake, water delivery, and organism movement in response to neural stimuli. An example of an interacting system could be an artery depending on the proper function of elastic tissue and smooth muscle to regulate and deliver the proper amount of blood within the circulatory system.] [Assessment Boundary: Assessment does not include interactions and functions at the molecular or chemical reaction level.]

HS-LS1-2

Anaphase Start and Chromatid Release

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