Name: chromosome movement during mitosis
Uploaded: 2021-04-07T12:12:01.000Z
Duration: 2 min 11 s
Channel: JoVE

유사분열 동안, 이중배향 염색체는 방추체 부착을 안정화하기 위해 진동하고 이후에 유사분열 방추체의 적도에서 중기 플레이트를 따라 조립합니다.
염색체가 유사분열 방추체에 부착된 후 염색체에 여러 힘이 작용합니다.
플러스-엔드 탈중합(plus-end de-polymerization)의 결과로 키네토코어-미세소관을 따라 가해지는 주요 극 방향의 힘은 키네토코어와 관련 염색체를 방추체 극 쪽으로 당깁니다. 키네토코어에서 Ndc80 단백질 복합체는 미세소관 측면을 따라 여러 개의 저친화성 부착을 통해 키네토코어를 미세소관에 연결합니다.
미세소관 플러스-엔드 탈중합 동안, Ndc80 부착물은 동체-미세소관 연결을 유지하기 위해 새로운 부위에서 끊어지고 재형성됩니다. 이 메커니즘은 미세소관의 길이가 짧아짐에 따라 염색체를 방추체 기둥 쪽으로 점차 당깁니다.
두 번째 극 방향 힘은 미세소관 플럭스(microtubule flux)에서 발생합니다. 미세소관 마이너스 엔드 탈중합은 마이너스 말단 유도 플럭스를 생성하여 미세소관이 방추극을 향한 이동을 유발합니다. 플러스-엔드 중합을 조정하면 마이너스 말단 해중합을 보상하여 미세소관이 길이를 유지할 수 있습니다.
세 번째 힘인 극 분출력 또는 극 바람은 kinesin-4 및 10 모터 단백질에 의해 생성되어 염색체를 방추극에서 밀어냅니다. Kinesin-4 및 10은 염색체팔을 양극간 미세소관과 연결합니다. 이러한 플러스 엔드 지향 운동 단백질은 염색체를 방추체 적도 쪽으로 이동시킵니다.
이러한 여러 반대 힘의 균형 잡힌 상호 작용은 이중방향 염색체가 염색체 분리를 준비하기 위해 중기 플레이트를 따라 정확하게 정렬할 수 있도록 합니다.

<ol>
	<li>Brouhard, G. J. 및 A. J. Hunt. "유사 분열 염색체의 팔에 대한 미세소관 움직임 : 시험관 내에서 정량화 된 극성 방출 힘." 국립 과학 아카데미 회보 102, no. 39 (2005) : 13903–8. <a href="https://www.pnas.org/content/102/39/13903">[출처]</a></li>
	<li>Dumont, Sophie 및 Timothy J. Mitchison. "유사 분열 방추체의 힘과 길이." Current Biology 19, no. 17 (2009). <a href="https://www.sciencedirect.com/science/article/pii/S096098220901450X">[출처]</a></li>
	<li>Khodjakov, Alexey 및 Tarun Kapoor. "미세소관 플럭스: 무엇에 좋은가?" Current Biology 15, no. 23 (2005). <a href="https://www.sciencedirect.com/science/article/pii/S0960982205013928">[출처]</a></li>
</ol>

염색체에 작용하는 힘

Forces Acting on Chromosomes

유사분열 동안 염색체 이동은 여러 피코뉴턴 수준의 힘의 상호작용을 통해 발생합니다. 전중기에서 이러한 힘은 적도면에서 염색체 조립 또는 회합을 돕고 결국 중기판에서의 정렬로 이어집니다. 염색체에 작용하는 힘은 공간과 시간에 따라 달라집니다. 따라서 세포가 유사분열을 통해 진행됨에 따라 염색체의 위치에 따라 달라집니다.

미세소관과 운동 단백질은 염색체에 두 가지 유형의 힘, 즉 극방향 및 극방향 반대 힘을 가하며, 이는 극성 방출력이라고도 알려져 있습니다. 방추사부착점 미세소관 해중합은 극방향 힘을 생성하고 염색체를 스핀들 극쪽으로 끌어당깁니다. 대조적으로, 동원체-미세소관의 중합은 극성 방출력을 발생시켜 염색체를 세포의 적도 방향으로 밀어냅니다. 크로모키네신 및 키네신-7과 같은 미세소관 플러스 말단 지향 모터 단백질도 염색체를 세포의 적도 방향으로 추진하여 극성 방출력을 생성합니다.

극 방향 힘과 극 방출 힘의 동시적이지만 동일하지 않은 작용은 전중기 동안 염색체의 진동을 유발합니다. 그러나 중기 동안 이중 방향성 자매 염색체는 동일하지만 반대되는 힘을 경험합니다. 이는 스핀들 어셈블리 체크포인트 경로를 침묵시킬 만큼 충분한 장력을 생성하고 세포가 후기 단계로 이동할 수 있도록 합니다. 후기에는 극 방향의 힘이 자매 염색체에 작용하여 딸 세포로 성공적으로 분리됩니다.

위의 힘 외에도 염색체에는 응집력과 분해력도 작용합니다. 코헤신에 의해 발휘되는 응집력은 중기가 끝날 때까지 자매 염색체를 함께 유지합니다. 반면에, 콘덴신에 의해 생성된 분해력은 염색체가 별개의 막대 모양 구조를 형성할 수 있게 하며, 이는 후기 동안 적절한 분리를 돕습니다.

유사분열 동안, 염색체 이동은 여러 피코네톤 수준의 힘의 상호 작용을 통해 발생합니다. 전중기(prometaphase)에서 이러한 힘은 염색체를 돕습니다 ...

Education

교육

JoVE Core

Molecular Biology

분자생물학

Unit 2

제2단원

Cell Division

세포 분열

KEY TERMS AND CONCEPTS

주요 용어 및 개념

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. Poleward force comes from kinetochore microtubule depolymerization, which pulls a chromosome toward the spindle pole. Polar-ejection force comes from kinetochore-microtubule polymerization, which pushes the chromosome toward the cell’s equator.

Motor proteins also help drive chromosomes toward the middle of the cell. Plus-end directed proteins such as chromokinesins and kinesin-7 generate polar-ejection forces. During prometaphase, the unequal balance between poleward and polar-ejection forces makes chromosomes oscillate. In metaphase, the sister chromatids are bioriented, so they experience equal and opposing forces.

That balanced tension is important because it silences the spindle assembly checkpoint pathway. Once this checkpoint is off, the cell can move into anaphase. In anaphase, poleward forces act on sister chromatids and separate them into the daughter cells.

Chromosomes are also controlled by cohesive and resolving forces. Cohesin provides the cohesive force that keeps sister chromatids together until the end of metaphase. Condensins generate the resolving force, which helps chromosomes form distinct rod-shaped structures and supports their proper separation during anaphase.

Chromosome Movement During Mitosis

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 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 poleward and polar-ejection forces move chromosomes during mitosis, align sister chromatids at metaphase, and support separation in anaphase.

Chromosome Movement During Mitosis | JoVE K12

molecular biology

JoVE Core 분자생물학은 명확하고 간결한 애니메이션을 통해 분자 단계에서 일어나는 세포 과정을 설명합니다.또한, 과학자가 직접 실험을 진행하는 실사 영상을 통해 분자생물학 개념의 응용 사례를 보여줍니다.

Chromosome Movement During Mitosis

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