Name: how cells set the division plane
Uploaded: 2021-04-07T12:12:02.000Z
Duration: 2 min 13 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

Determining the Plane of Cell Division

תא מתחלק הקובע במדויק את מישור חלוקת התא שלו חיוני להפרדה מוצלחת של כרומוזומים ולפיזור התוכן הציטופלזמי לתאי הבת שלו.
בבעלי חיים, מישור החלוקה ממוקם בקו המשווה של התא בין הכרומוזומים המופרדים, ומיקומו נקבע במהלך אנאפאזה. מיקרוטובולים היוצרים את הציר המיטוטי מתקשרים עם קליפת התא וממלאים תפקיד מכריע בהגדרת התלם המחשוף.
שלושה מודלים שונים משמשים להסבר קביעת מישור חלוקת התא – מודל הגירוי האסטרלי, מודל ההרפיה הקוטבית ומודל גירוי הציר המרכזי.
במודל הגירוי האסטרלי, מערכים רדיאליים של מיקרוטובולים אסטרליים מתקשרים עם קליפת המוח המשוונית וגורמים להיווצרות התלם המחשוף.
במודל ההרפיה הקוטבי, מיקרוטובולים אסטרליים שולחים אותות מעכבים לקטבי התא ובכך מדכאים את היווצרות התלם בשני הקטבים. זה מוביל להתכווצות קליפת המוח בקו המשווה של התא.
ברגע שהאנאפאזות מתחילות, המיקרוטובולים הבין-קוטביים שנמצאים בין הכרומוזומים המופרדים מתארגנים מחדש למיקרוטובולים האנטי-מקביליים החופפים, הידועים גם בשם הציר המרכזי. במודל גירוי הציר המרכזי, הציר המרכזי מגרה את היווצרות התלם המחשוף בקליפת המוח המשוונית. 
הקונצנזוס הכללי הוא שכל שלושת התהליכים פועלים יחד כדי לקבוע את מישור חלוקת התא. גישה רב-זרועית זו יכולה לגרום למערכת להגיב לתנודות בריכוז החלבונים כמו גם בגודל התא ובכך להגדיל את דיוק חלוקת התא.
תרומתה של כל שיטה תלויה בסוג התא ובגודלו. לדוגמה, בעוברים של C. elegans קיים מערך גדול של מיקרוטובולים אסטרליים ולכן עשויים למלא תפקיד פעיל יותר בקביעת מישור חלוקת התא.

<ol>
	<li>ביולוגיה מולקולרית של התא, אלברטס, מהדורה 6. עמודים 997-999.</li>
	<li>ביולוגיה מולקולרית של התא, לודיש, מהדורה 8. עמודים - 903.</li>
	<li>גילן, דני. "מיקום מישור החלוקה נקבע על ידי אתר חלוקה קורטיקלית בקרום הפלזמה." בתוך ביוטכנולוגיה וחקלאות בת קיימא 2006 ואילך, עמ' 121-124. שפרינגר, דורדרכט, 2007.</li>
	<li>Balasubramanian, Mohan K., Erfei Bi, ו Michael Glotzer. "ניתוח השוואתי של ציטוקינזיס בשמרים ניצנים, שמרי ביקוע ותאי בעלי חיים." ביולוגיה נוכחית 14, מס '18 (2004): R806-R818.</li>
	<li>מזמור, ג'ון. "פיגומים ספטין ומישורי מחשוף בסקרומיצס". תא 84, מס' 2 (1996): 187-190.</li>
	<li>רינקון, סרג'יו א. ואן פאולטי. "Mid1/anillin והוויסות המרחבי של ציטוקינזיס בשמרי ביקוע." Cytoskeleton 69, No. 10 (2012): 764-777.</li>
	<li>גאלי, מטילדה וסנדר ואן דן היובל. "קביעת מישור המחשוף בעוברים מוקדמים של C. elegans". סקירה שנתית של גנטיקה 42 (2008): 389-411.</li>
</ol>

קביעת מישור חלוקת התא

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מיקום מישור חלוקת התא הוא שלב קריטי במהלך התפתחות והתמיינות תאים, במיוחד במהלך מיטוזה כאשר המישור חיוני לקביעת גודלם של שני תאי הבת. מישור חלוקת התא מאונך למישור הפרדת הכרומוזומים, אך לסוגים שונים של אורגניזמים יש מנגנוני חלוקת תאים שונים כדי להתאים למורפולוגיה ולתפקוד שלהם.

תאים של בעלי חיים

בתאי בעלי חיים, תלם המחשוף נוצר לאורך מישור חלוקת התא החל מקליפת התא, האזור שמתחת לממברנת הפלזמה. הציר המיטוטי ממלא תפקיד מכריע בקביעת מישור חלוקת התא; לכן, שינוי בציר של הציר המיטוטי יכול לשנות את מישור החלוקה. אסטרטגיה זו משמשת כמה אורגניזמים איקריוטיים, כגון Caenorhabditis elegans, כדי לעבור מחלוקת תאים סימטרית ואסימטרית. חלוקת תאים סימטרית מייצרת שני תאי בת זהים ולעתים קרובות משמשת לגידול רקמות המכילות רבים מאותו סוג תא. לעומת זאת, חלוקה אסימטרית יוצרת שני תאי בת לא זהים. לדוגמה, תאי נוירו-אפיתל מגדילים בתחילה את מספרם על ידי חלוקות סימטריות. לאחר מכן, הם משתמשים בחלוקה אסימטרית כדי לייצר תאי בת הדומים לתא האב וכן נוירונים מבדילים.

שמרים

בשמרים ניצנים, כגון Saccharomyces cerevisiae, מישור חלוקת התא נקבע בשלב ה-G1 על ידי חלבוני ספטין. ציטוקינזיס מושגת על ידי יצירת תלם מחשוף באזור הצוואר של תאי השמרים הניצנים; עם זאת, המנגנון המיטוטי אינו ממלא תפקיד כלשהו בקביעת מישור חלוקת התא. לעומת זאת, בשמרי ביקוע, כגון Schizosaccharomyces pombe, מיקומו של גרעין הבין-פאזי קובע את מישור חלוקת התא בשלב G2. במהלך אינטרפאזה, החלבון Mid1 ממוקם בעיקר בגרעין; עם זאת, במהלך מיטוזה, Mid1 מיוצא מהגרעין לקליפת התא, שם הוא מגייס רכיבי טבעת אקטומיוזין לאזור המדיאלי של התא. בסופו של דבר זה מביא לכך שתא האם מתחלק לשני תאי בת בגודל דומה.

צמחים

ברוב תאי הצמח, מישור חלוקת התא נקבע לפני שהתא מתחייב למיטוזה. פס קדם-פרופאזה נוצר לאורך קו המשווה של תא האב, המסמן את מישור חלוקת התא. רצועת הקדם-פרופאזה היא מבנה דמוי טבעת המורכב ממיקרוטובולים ו-F-אקטין. היא מולידה צרור מיקרוטובולי הנקרא פרגמופלסט, המספק פיגום מבני להרחבת לוחות התא ומיצובם.
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מיקום מישור חלוקת התא הוא שלב קריטי במהלך התפתחות והתמיינות התא, במיוחד במהלך מיטוזה כאשר המישור הוא ...

Education

JoVE Core

Molecular Biology

ביולוגיה מולקולרית

Unit 2

יחידה 2

Cell Division

חלוקת תאים

KEY TERMS AND CONCEPTS

מונחים ומושגים מרכזיים

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 division plane can change as well. Some eukaryotes, such as Caenorhabditis elegans, use this shift to move from symmetric division to asymmetric division.

Symmetric cell division makes two identical daughter cells and is often used to build tissues with many of the same cell type. Asymmetric division makes two different daughter cells and increases cell diversity. Neuroepithelial cells first divide symmetrically to raise their numbers. They later divide asymmetrically to form a daughter cell like the parent cell and another that will become a neuron.

In budding yeast, such as Saccharomyces cerevisiae, septin proteins decide the plane of division during the G1 phase. The cell then completes cytokinesis by forming a cleavage furrow at the bud neck. In this yeast, the mitotic apparatus does not set the division plane.

In fission yeast, such as Schizosaccharomyces pombe, the interphase nucleus helps decide where the division plane will form during the G2 phase. The Mid1 protein stays mainly in the nucleus during interphase. During mitosis, Mid1 moves to the cell cortex and recruits actomyosin ring components to the middle of the cell. This lets the mother cell divide into two similar-sized daughter cells.

In most plant cells, the division plane is set before the cell enters mitosis. A preprophase band forms along the cell equator and marks where division will occur. This ring-like structure contains microtubules and F-actin. It helps form the phragmoplast, which supports cell plate growth and placement.

How Cells Set the Division Plane

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

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 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 animal cells, yeast, and plant cells position the division plane using the spindle, septins, nucleus, and preprophase band.

How Cells Set the Division Plane | JoVE K12

molecular biology

JoVE Core Molecular Biology showcases the molecular processes of the cell through clear and concise animated video lessons. Additionally, in scientist-in-action videos, these concepts' application is demonstrated through real experiments in modern laboratories.

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New York State Science Learning Standards

Inheritance and Variation of Traits

HS-LS1-4.

Characteristics of Life

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Nucleic Acids

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Globular and Fibrous Proteins

Translation

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Intrinsically Disordered Proteins

Ribosomes

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Protein Complex Assembly

Protein and Protein Structures

Conjugated Proteins

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Cofactors and Coenzymes

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Protein Kinases and Phosphatases

GTPases and their Regulation

Covalently Linked Protein Regulators

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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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Animal and Plant Cell Structure

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An Introduction to the Zebrafish: Danio rerio

Zebrafish (Danio rerio) are small freshwater fish that are used as model organisms for biomedical research. The many strengths of these fish include their ...

Physiology of the Circulatory System

Homeostasis
Conditions in the external environment of an organism can change rapidly and drastically. To survive, organisms must maintain a fairly ...

Anatomy of the Circulatory System

The human circulatory system consists of blood, blood vessels that carry blood away from the heart, around the body, and back to the heart, and the heart ...

Measuring Blood Pressure
ExpandTo prepare for the blood pressure exercise, simply place the appropriate number of alcohol swabs, sphygmomanometers, and ...

Anatomy of the Heart

The human heart is made up of three layers of tissue that are surrounded by the pericardium, a membrane that protects and confines the heart. The ...

Measuring Circulatory System Function in Humans
ExpandBefore starting the experiment go to the front of the room and collect an alcohol swab, a ...

Blood Flow

Blood is pumped by the heart into the aorta, the largest artery in the body, and then into increasingly smaller arteries, arterioles, and capillaries. The ...

What Are Osmoregulation and Excretion?

Organisms must keep bodily fluids at a constant temperature and pH while maintaining specific solute concentrations in order to support life functions. ...

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

How Cells Set the Division Plane

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