Name: how the mitotic spindle separates chromosomes
Uploaded: 2021-04-07T12:12:01.000Z
Duration: 2 min 27 s
Channel: JoVE

有糸分裂紡錘体は、有糸分裂の後期に姉妹染色分体を分離し、それらを細胞の反対側に移動します。
有糸分裂紡錘体の基本的な構造は、微小管と呼ばれる中空の円柱です。2組の微小管は、有糸分裂紡錘体の両端または極に配置されています。
各微小管には、マイナス端とプラス端があります。微小管のマイナス端は、紡錘極の中心で合流します。プラス端はポールから外側に伸びています。
有糸分裂紡錘体における明確な位置と役割を持つ微小管にはさまざまな種類があります。
動原体微小管は、そのプラス端で動原体に付着することにより、染色体を紡錘体極に結合します。キネトコアは、染色分体セントロメアで組み立てられた大きなタンパク質複合体であり、姉妹染色分体をリンクする特殊なDNA配列です。
極間微小管の配置は、握りしめられた一対の手に似ています。極間微小管のプラス端は、反対側の極から伸びる別の極間微小管のプラス端と重なります。モータータンパク質は、極間微小管と結合して紡錘体を組み立てます。
アストラル微小管は、細胞内の紡錘体を固定します。これらの微小管は集合的にスターバーストに似ており、各正の端は紡錘体極から細胞皮質に外側に突き出ています。
ほとんどの動物細胞では、微小管は中心体と呼ばれる細胞小器官の周りに組織化されています。各紡錘極に1つの中心体が存在します。
中心体は、中心小体周囲マトリックスと呼ばれる形のないタンパク質の塊に囲まれた2つの中心小体で構成されています。中心体は、細胞内の微小管を生成、組織化、および固定します。
モータータンパク質の2つのファミリーは、有糸分裂紡錘体の構築と操作に不可欠です:キネシン関連タンパク質とダイニン。通常、キネシン関連タンパク質は微小管のプラス端に向かって移動し、ダイニンはマイナス端に向かって移動します。
有糸分裂紡錘体とその微小管の固有の極性は、染色体の有糸分裂分離を促進し、細胞を分裂させる準備をします。

<ol>
	<li>ヒールド、レベッカ、アレクセイ・ホジャコフ。2015.「検索と捕獲の30年:有糸分裂紡錘体アセンブリの複雑な単純さ」 細胞生物学ジャーナル 211(6):1103–11。<a href="https://doi.org/10.1083/jcb.201510015">https://doi.org/10.1083/jcb.201510015</a>.</li>
	<li>ペトリー、サビーヌ。2016.「有糸分裂紡錘体アセンブリのメカニズム」 生化学の年次レビュー 85(1):659–83。<a href="https://doi.org/10.1146/annurev-biochem-060815-014528">https://doi.org/10.1146/annurev-biochem-060815-014528</a>.</li>
</ol>

有糸分裂紡錘体

The Mitotic Spindle

有糸分裂紡錘体—または紡錘体装置は—微小管と呼ばれる長いタンパク質繊維で構成される真核生物の細胞骨格構造です。 細胞分裂中に形成される紡錘体は姉妹染色分体を分離し、親細胞の反対側の端に移動させます。そこで、個々の染色体が2つの娘細胞の核に分配されます。

有糸分裂紡錘体の双極性構成は染色体の分離を促進し、細胞の分裂の準備をします。双極性有糸分裂紡錘体形成を確実にする機構の1つは中心体に依存しています。

脊椎動物の卵母細胞や高等植物細胞などの一部の細胞には中心体がありません。ただし、ほとんどの動物細胞は、有糸分裂に入ると2つの中心体を持ちます。各中心体は、紡錘体の反対側の端、つまり極にある円形の微小管の配置と会合しています。言い換えれば、中心体は微小管の核を形成します。

モータータンパク質、特にキネシンとダイニンは、通常、微小管の末端または末端付近で機能し、双極性有糸分裂紡錘体の形成と姉妹染色分体の分離を促進します。

たとえば、紡錘体の中間ゾーンにあるキネシン5モーターは、反対側の紡錘体極から伸びる2つの微小管に取り付けられ、スライドして離れます。このプロセスは、スピンドル極を互いに遠ざけることにより、スピンドルの双極性と伸びを促進します。

キネシン5の活性はキネシン14によって相殺されると考えられています。Kinesin-14モーターは、反対側の極から伸びる微小管を引っ張り、効果的に極を結び付けます。これらのモーターの協調動作により、スピンドルを正しく組み立てることができます。

キネシン-4およびキネシン-10はクロモキネシン、つまり有糸分裂染色体と結合できるキネシンです。キネシン4とキネシン10は染色体腕と結合し、染色体と紡錘体極を押し広げます。

ダイニンは細胞のさまざまな部分で微小管を組織します。たとえば、それらはアストラル微小管をアクチン細胞骨格に結びつけ、紡錘体極を互いに遠ざけます。

有糸分裂紡錘体の構造、組織、構成要素により、姉妹染色分体の分離が可能になり、細胞が適切に分裂する準備が整います。

有糸分裂紡錘体(または紡錘体装置)は、微小管と呼ばれる長いタンパク質繊維で構成された真核生物の細胞骨格構造です。形成。。。

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

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 pole, which means centrosomes nucleate microtubules. Some cells, including vertebrate oocytes and higher plant cells, do not have centrosomes.

Motor proteins help build and position the spindle. Kinesins and dynein work at or near microtubule ends and support bipolar spindle formation as well as sister chromatid separation. Kinesin-5 motors at the spindle midzone slide two microtubules apart, which pushes the poles away from each other and helps the spindle elongate.

Kinesin-14 acts in the opposite way. It pulls on microtubules that extend from opposite poles and brings the poles closer together. This balance between kinesin-5 and kinesin-14 helps the spindle assemble correctly. Kinesin-4 and kinesin-10 are chromokinesins, which means they can bind to mitotic chromosomes. They attach to chromosome arms and help push the chromosomes and spindle poles apart.

Dyneins also take part in spindle organization. They link astral microtubules to the actin cytoskeleton and help move the spindle poles away from each other. Together, the spindle structure, its poles, and its motor proteins allow sister chromatids to separate and prepare the cell for proper division.

How the Mitotic Spindle Separates Chromosomes

how-the-mitotic-spindle-separates-chromosomes

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

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 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...

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 mitotic spindle uses microtubules, centrosomes, kinesins, and dynein to separate sister chromatids during cell division.

How the Mitotic Spindle Separates Chromosomes | 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。

How the Mitotic Spindle Separates Chromosomes

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