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

有丝分裂纺锤体在有丝分裂的后期将姐妹染色单体分开并移向细胞的两极。
有丝分裂纺锤体的基本结构是称为微管的中空圆柱体。两组微管分别排列在有丝分裂纺锤体的相对两端，即两极。
每根微管都有一个负端和一个正端。微管的负端在纺锤体极的中心处汇聚，正端则从两极向外延伸。
在有丝分裂纺锤体中，存在不同类型的微管，它们具有特定的位置和功能。
动粒微管通过其正端与动粒结合，将染色体连接到纺锤体极。动粒是在染色单体着丝粒上组装的大型蛋白质复合物，着丝粒是一种特殊的DNA序列，负责连接姐妹染色单体。
极间微管的排列方式类似于一对紧握的手。一条极间微管的正端与来自相对极的另一条极间微管的正端相互重叠。运动蛋白与极间微管结合，调控纺锤体的组装。
星体微管将纺锤体锚定在细胞内。这些微管整体呈星爆状，每条微管的正端从纺锤体极向外延伸至细胞皮层。
在大多数动物细胞中，微管围绕一种称为中心体的细胞器进行排列。每个纺锤体极含有一个中心体。
中心体由两个中心粒组成，周围围绕着一团无定形的蛋白质结构，称为中心粒周围基质。中心体负责在细胞内产生、组织并锚定微管。
两类运动蛋白对有丝分裂纺锤体的构建和功能至关重要：驱动蛋白相关蛋白和动力蛋白。通常，驱动蛋白相关蛋白向微管的正端移动，而动力蛋白则向微管的负端移动。
有丝分裂纺锤体及其微管的固有极性有助于染色体的有丝分裂分离，为细胞分裂做好准备。

<ol>
	<li>Heald、Rebecca 和 Alexey Khodjakov。2015. "三十年的搜索和捕获:有丝分裂纺锤体组装的复杂简单性。"细胞生物学杂志 211 （6）:1103-11。<a href="https://doi.org/10.1083/jcb.201510015">https://doi.org/10.1083/jcb.201510015</a>.</li>
	<li>佩特里，萨宾。2016. "有丝分裂纺锤体组装的机制。"生物化学年鉴 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>

有丝分裂纺锤体

The Mitotic Spindle

有丝分裂纺锤体——或称纺锤器——是一种真核细胞的细胞骨架结构，由称为微管的长蛋白纤维组成。纺锤体在细胞分裂期间形成，将姐妹染色单体分离并移动到母细胞的两端，然后各自成为单独的染色体，分配到两个子细胞的细胞核中

 有丝分裂纺锤体的双极结构有利于染色体分离，为细胞分裂做好准备。 确保双极有丝分裂纺锤体形成的一种机制依赖于中心体。

一些细胞，例如脊椎动物卵母细胞和高等植物细胞，缺乏中心体； 然而，大多数动物细胞在进入有丝分裂时都有两个中心体。 每个中心体都与有丝分裂纺锤体两端—或两极—上的微管圆形排列相关。 换句话说，中心体是微管的成核部位。

运动蛋白—尤其是驱动蛋白和动力蛋白—通常在微管末端或附近起作用，促进双极有丝分裂纺锤体的形成和姐妹染色单体的分离。

例如，纺锤体中区的驱动蛋白 5 马达附着并在来自相对的纺锤体极延伸的两个微管，并将它们分开； 该过程通过将纺锤极彼此推开来促进纺锤体双极性和延长。

驱动蛋白 5 的活性被认为可以被驱动蛋白 14 抵消。 Kinesin-14 电机拉动从相反两极延伸的微管，有效地将两极聚集在一起。 这些电机的协调活动使主轴能够正确组装。

驱动蛋白 4 和驱动蛋白 10 是染色驱动蛋白，可以与有丝分裂染色体相关的驱动蛋白结合。 驱动蛋白 4 和驱动蛋白 10 与染色体臂结合，将染色体和纺锤体极推开。

动力蛋白在细胞的各个部分组织微管。 例如，它们将星体微管与肌动蛋白细胞骨架连接起来，使纺锤体两极彼此远离。

有丝分裂纺锤体的结构、组织和成分允许姐妹染色单体分离，为细胞的正常分裂做好准备。

有丝分裂纺锤体——或称纺锤体装置——是一种真核生物的细胞骨架结构，由称为微管的长蛋白纤维组成。形成……

Education

教育

JoVE Core

Molecular Biology

分子生物学

Unit 2

第二单元

Cell Division

细胞分裂

KEY TERMS AND CONCEPTS

关键术语与概念

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 分子生物学通过清晰简洁的动画视频课程展示了细胞的分子过程。此外，在科学家在行动的视频中，这些概念的应用是通过现代实验室中的真实实验演示的。

How the Mitotic Spindle Separates Chromosomes

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