Name: how cells build the contractile ring
Uploaded: 2021-04-07T12:12:02.000Z
Duration: 2 min 15 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

The Contractile Ring

تسمى الخطوة الأخيرة من دورة الخلية التي تقسم الخلية إلى خليتين ابنتيتين بالحركة الخلوية. يبدأ الحركية الخلوية بعد فصل الكروموسوم في الانقسام وينتهي عندما تنقسم الخلية.
تتميز بداية الحركية الخلوية بظهور تجعد يسمى ثلم الانقسام. بدءا من الطور ، يتعمق الأخدود وينتشر لتشكيل حلقة حول الخلية. يتم إنشاء هذا الضغط ، الذي يقسم الخلية في النهاية إلى قسمين ، بواسطة الحلقة الانقباضية.
بروتين يسمى RhoA هو المنظم الرئيسي لتجميع الحلقة المقلصة ووظيفتها. لضمان تكوين الحلقة الانقماشية في المكان المناسب ، يتم تنشيط RhoA محليا في قشرة الخلية ، بالقرب من خط الاستواء للخلية. يضمن RhoA ، جنبا إلى جنب مع ألياف مغزل الطور ، أيضا تشكيل الحلقة الانقماشية في الوقت المناسب ، بعد فصل الكروموسوم.
تتكون الحلقة الانقماشية من بروتينات هيكلية ، بما في ذلك خيوط الأكتين وخيوط الميوسين II. ينتج عن نشاط RhoA تجميع الميوسين II وخيوط الأكتين المضادة للموازي في بنية الحلقة الانقباضية. يعزز RhoA بلمرة خيوط الأكتين الموضعية الضرورية لتكوين الحلقة المقلصة.
تولد مكونات الحلقة الانقباضية القوة اللازمة لتقسيم الخلية. تتضمن إحدى آليات الانكماش النشاط الحركي للميوسين. هنا ، تتحرك خيوط الميوسين نحو الطرف الزائد لخيوط الأكتين المضادة للتوازي المجاورة. يسحب هذا النشاط الأكتين المضاد للتوازي ، مما يجعلها تنزلق عبر بعضها البعض ، وتتقلص الحلقة.
يستمر تقلص الحلقة حتى تقرص خليتين جديدتين. تتحلل الحلقة بمجرد تكوين الخلايا الجديدة.
يمكن أن يؤدي عدم كفاءة أو عدم وجود تكوين حلقة انقباضية إلى انقسام غير طبيعي للخلايا وضعف النمو واحتمال تكوين الورم.

<ol>
	<li>البيولوجيا الجزيئية للخلية ، ألبرتس ، الطبعة السادسة. الصفحة 996-997</li>
	<li>ميلر ، آن ل. "الحلقة الانقباضية". علم الأحياء الحالي 21 ، رقم 24 (2011): R976-R978. <a href="https://www.cell.com/current-biology/pdf/S0960-9822(11)01205-X.pdf">[مصدر المقال]</a></li>
	<li>تشانغ وفريد وديفيد بورجيس. "الحلقة الانقباضية". علم الأحياء الحالي 13 ، رقم 18 (2003): R692-R693. <a href="https://www.cell.com/current-biology/pdf/S0960-9822(03)00641-9.pdf">[مقالة المصدر]</a></li>
	<li>جرين ، ريبيكا أ. ، جوناثان آر مايرز ، شاوهي وانغ ، ليندسي لويلين ، أرشد ديساي ، أنجون أوديا ، وكارين أوجيما. "حلقة منتصف الجسم تغلق آلية الانفصال في حالة عدم وجود أنابيب دقيقة في منتصف الجسم." مجلة بيولوجيا الخلية 203 ، العدد 3 (2013): 505-520.</li>
	<li>كريم ، صبريا سي ، أمل كيشاد ، وجيل آر إكس هيكسون. "الحركية الخلوية للخلايا الحيوانية: الحلقة الانقباضية المعتمدة على rho actomyosin-anilloseptin كآلة لتجميع وضغط وفرز المجال المجهري للغشاء." الحدود في علم الأحياء الخلوي والتنموي 8 (2020).</li>
</ol>

الحلقة المقلصة

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تتكون الحلقات المتقلصة من خيوط دقيقة وهي مسؤولة عن فصل الخلايا الوليدة أثناء التحريك الخلوي. يستمر تجميع الحلقة المتقلصة جنبًا إلى جنب مع أحداث دورة الخلية الأخرى؛ ومع ذلك، لا يُعرف سوى القليل جدًا من التفاصيل الآلية حول توقيت وتنسيق الحلقات المقلصة مع دورة الخلية.

يتحكم GTPase الصغير، RhoA، في وظيفة وتجميع الحلقة المقلصة. ينتمي RhoA إلى عائلة البروتينات Ras الفائقة. يؤدي تنشيط الفورمينات بواسطة RhoA إلى تعزيز تكوين خيوط الأكتين، في حين أن تنشيط كينازات البروتين المتعددة بواسطة RhoA يحفز تجميع وانكماش الميوسين II. تقوم الكينازات بتفسفر سلسلة ضوء الميوسين وتحفز تكوين الخيوط والنشاط الحركي. بالإضافة إلى الأكتين والميوسين II (الأكتوميوسين)، تشارك خيوط الحاجز أيضًا في تكوين الحلقة الانقباضية. تعمل خيوط Septin على تثبيت الحلقة المقلصة وتلعب دورًا مهمًا في الحركة الخلوية للخميرة.

يتم تنظيم تنشيط RhoA بواسطة عامل تبادل النوكليوتيدات الجواني (Rho-GEF). تم العثور على هذا البروتين في منطقة القشرة، وهي موقع انقسام الخلايا في المستقبل. يرتبط الشكل غير النشط من RhoA بثنائي فوسفات الغوانوزين (GDP). يقوم Rho-GEF بتبادل ثنائي فوسفات الغوانوزين (GDP) المرتبط بـ RhoA مع GTP. يؤدي الربط GTP إلى تنشيط RhoA، والذي بدوره يؤدي إلى تكوين حلقات مقلصة.

ينظم RhoA أيضًا نشاط بروتين السقالة الأنيلين، وهو لاعب أساسي في تكوين الحلقة الانقباضية. بينما يعتبر RhoA المنشط الرئيسي لتجميع الحلقة المقلصة، يعمل الأنيلين كمنظم رئيسي للحلقة من خلال الارتباط بالأكتين، والميوسين II، والدهون فوسفاتية الغشائية، والسبتين، والمكونات الهيكلية والتنظيمية الأخرى المشاركة في تكوين الحلقة المقلصة.

الانكماش المستمر للحلقة المقلصة يعني أنها تحتاج تدريجيًا إلى عدد أقل من خيوط الأكتوميوسين لتشكيل حلقة بنفس السمك؛ لذلك، يحدث التفكيك المصاحب لخيوط الأكتوميوسين عندما تنقبض الحلقة. خلال المراحل النهائية من التحريك الخلوي، تنضج الحلقة المقلصة والمغزل المركزي الذي يحتوي على أنابيب دقيقة مدمجة لتشكل الجسم الأوسط وحلقة الجسم الأوسط. تقوم حلقة الجسم الوسطى بعد ذلك بفصل الخلية الأم، مما يؤدي إلى تكوين خليتين ابنتين.

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تتكون الحلقات الانقباضية من خيوط دقيقة وهي مسؤولة عن فصل الخلايا الوليدة أثناء الحركة الخلوية. تجميع حلقة الانقباض ...

Education

JoVE Core

Molecular Biology

البيولوجيا الجزيئية

Unit 2

الوحدة الثانية

Cell Division

انقسام الخلية

KEY TERMS AND CONCEPTS

المصطلحات والمفاهيم الأساسية

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 will occur. Rho-GEF swaps GDP for GTP, and this activates RhoA.

Once active, RhoA promotes actin filament formation by activating formins. It also stimulates several protein kinases, which phosphorylate the myosin light chain. This helps myosin II form filaments and increases motor activity. Along with actin and myosin II, septin filaments also support contractile ring formation. Septins help stabilize the ring and are especially important in yeast cytokinesis.

RhoA also regulates anillin, a scaffold protein that organizes the ring. Anillin binds actin, myosin II, membrane phospholipids, septin, and other structural and regulatory components involved in contractile ring formation. As the ring shrinks, it needs fewer actomyosin filaments to keep the same thickness. Because of this, actomyosin filaments disassemble at the same time the ring contracts.

In the final stage of cytokinesis, the contractile ring and the central spindle, which contains compact microtubules, mature into the midbody and the midbody ring. The midbody ring then carries out abscission, the final split of the parent cell. This creates two daughter cells.

How Cells Build the Contractile Ring

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 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

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 RhoA, actin, myosin II, septins, and anillin work together to build the contractile ring and complete cytokinesis in dividing cells.

How Cells Build the Contractile Ring | JoVE K12

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HS-LS1-2

How Cells Build the Contractile Ring

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