Master’s-Level Cell Biology & Advanced Molecular Biology Notes

1. Definition

The cytoskeleton is a dynamic intracellular network of protein filaments that determines cell shape, mechanical properties, polarity, intracellular transport, migration, division, and spatial organization.

The three major cytoskeletal systems are:

Actin filaments (microfilaments)
Microtubules
Intermediate filaments

A fourth concept, increasingly important at the Master’s level, is the large group of cytoskeletal regulatory proteins that control filament nucleation, polymerization, depolymerization, cross-linking, severing, stabilization, and interaction with membranes and motor proteins.

                         CYTOSKELETON
                              │
             ┌────────────────┼────────────────┐
             ↓                ↓                ↓
           ACTIN          MICROTUBULES    INTERMEDIATE
         FILAMENTS                         FILAMENTS
             │                │                │
        Cell cortex       Transport       Mechanical
        Migration         Spindle        strength
        Cytokinesis       Polarity
             │                │
             └────────────────┼────────────────┘
                              ↓
                    CELLULAR ORGANIZATION

2. Why Cytoskeletal Regulation Is Necessary

Cytoskeletal filaments are not static structures.

They continuously undergo:

Polymerization
Depolymerization
Remodeling
Branching
Cross-linking
Severing
Stabilization
Reorganization

Therefore, cells require sophisticated regulatory mechanisms to control where, when, and how fast cytoskeletal structures form.

3. Fundamental Principle

A useful way to understand cytoskeletal regulation is:

SIGNAL
  ↓
REGULATORY PROTEIN
  ↓
FILAMENT DYNAMICS
  ↓
CYTOSKELETAL ORGANIZATION
  ↓
CELLULAR RESPONSE

For example:

Growth factor
     ↓
Receptor
     ↓
Rho-family GTPase
     ↓
Actin regulator
     ↓
Actin polymerization
     ↓
Cell migration

4. Major Cytoskeletal Regulatory Processes

Process	Function
Nucleation	Initiates filament formation
Elongation	Increases filament length
Depolymerization	Removes subunits
Capping	Controls filament ends
Severing	Breaks existing filaments
Branching	Creates filament networks
Cross-linking	Connects filaments
Bundling	Produces parallel filament arrays
Stabilization	Prevents excessive disassembly
Motor interaction	Generates force and transport

5. Actin Filament Regulation

Actin exists in two major forms:

G-actin = globular actin

F-actin = filamentous actin

G-actin
  ↓
Nucleation
  ↓
F-actin
  ↓
Elongation
  ↓
Actin network

Actin polymerization is highly regulated because spontaneous nucleation is relatively inefficient.

6. Actin Filament Polarity

Actin filaments have:

Plus/barbed end
Minus/pointed end

BARBED END                         POINTED END
    +                                  −
    │                                  │
    ▼                                  ▼
════════════════════════════════════════
             ACTIN FILAMENT

The two ends have different rates of subunit addition and loss.

7. Actin Polymerization

Actin polymerization involves:

Nucleation
Elongation
Steady-state behavior

       G-actin
          ↓
      Nucleation
          ↓
       Seed
          ↓
    Elongation
          ↓
      F-actin

ATP-bound actin is incorporated preferentially into growing filaments.

ATP is subsequently hydrolyzed to ADP, influencing filament stability.

8. Treadmilling

Actin can undergo treadmilling, where subunits are preferentially added at one end and lost at the other.

              ACTIN FILAMENT

        +                         −
        │                         │
        ↓                         ↓

      Addition                Loss
       of G-actin            of actin
          ↓                     ↓
════════════════════════════════════

This allows rapid remodeling without requiring complete disassembly of the filament.

9. Nucleation-Promoting Factors

Major actin nucleation mechanisms include:

Arp2/3 complex
Formins
Spire proteins
Other nucleators

10. Arp2/3 Complex

The Arp2/3 complex generates branched actin networks.

It nucleates a new filament from the side of an existing filament.

             Parent filament
──────────────────────────────
             \
              \
               \  New branch
                \
                 \

This is particularly important in:

Lamellipodia
Endocytosis
Phagocytosis
Cell migration

11. Formins

Formins promote the formation of long, often unbranched actin filaments.

They are particularly important for:

Filopodia
Stress fibers
Cytokinetic structures
Contractile actin networks

Formin
  ↓
Actin nucleation
  ↓
Linear filament
  ↓
Elongation

12. Arp2/3 vs Formin

Feature	Arp2/3	Formins
Main architecture	Branched	Linear/unbranched
Major structures	Lamellipodia	Filopodia/stress fibers
Mechanism	Branch nucleation	Linear nucleation/elongation
Regulation	NPFs	Rho-family pathways, other signals

13. Actin Capping Proteins

Capping proteins bind filament ends and regulate subunit exchange.

Examples include:

CapZ
Tropomodulin

                 CAP
                  │
                  ▼
═════════════════●
             ACTIN FILAMENT

Capping can prevent uncontrolled elongation or depolymerization.

14. Profilin

Profilin binds G-actin and promotes actin polymerization under appropriate conditions.

It can:

Bind actin
Promote ATP-actin availability
Facilitate actin incorporation into growing filaments
Interact with proline-rich proteins

Profilin
   +
G-actin
   ↓
Actin delivery
   ↓
Filament elongation

15. Cofilin

Cofilin is an important actin-remodeling protein.

It preferentially associates with ADP-actin-containing filaments and promotes:

Filament turnover
Severing
Depolymerization

        F-actin
════════════════════
       ↓ cofilin
══════════╱═════════
         ╱
        ╱
   Fragmentation

Its activity is regulated by phosphorylation.

16. ADF/Cofilin Regulation

A simplified pathway:

LIM kinase
    ↓
Cofilin phosphorylation
    ↓
Reduced actin-severing activity

Conversely, cofilin dephosphorylation promotes its actin-remodeling activity.

Thus:

LIMK ↔ cofilin is an important regulatory axis.

17. Rho-Family GTPases

Three major regulators are:

RhoA
Rac1
Cdc42

They act as molecular switches.

GDP-bound
INACTIVE
   │
   │ GEF
   ↓
GTP-bound
ACTIVE
   │
   ↓
Effector proteins
   │
   ↓
Cytoskeletal remodeling

18. RhoA

RhoA is strongly associated with:

Stress fibers
Actomyosin contractility
Focal adhesion maturation
Cell-body contraction

Simplified pathway:

RhoA-GTP
   ↓
ROCK
   ↓
Myosin light-chain regulation
   ↓
Myosin II activity
   ↓
Contractility

19. Rac1

Rac1 promotes:

Lamellipodia
Branched actin
Cell spreading
Leading-edge formation

Rac1-GTP
   ↓
WAVE complex
   ↓
Arp2/3 activation
   ↓
Branched actin
   ↓
Lamellipodium

20. Cdc42

Cdc42 is particularly important for:

Cell polarity
Filopodia
Directional migration
PAR-complex regulation

Cdc42-GTP
    ↓
WASP
    ↓
Arp2/3
    ↓
Actin remodeling
    ↓
Polarity / protrusion

21. RhoA–Rac–Cdc42 Integration

These GTPases do not operate independently.

                 CELL POLARITY
                       │
          ┌────────────┼────────────┐
          ↓            ↓            ↓
        Cdc42         Rac          RhoA
          ↓            ↓            ↓
       Polarity     Protrusion   Contractility
          │            │            │
          └────────────┼────────────┘
                       ↓
                Cell migration

Their spatial and temporal coordination is essential.

22. Microtubule Regulation

Microtubules are polymers of:

α-tubulin + β-tubulin

They are regulated through:

Nucleation
Polymerization
Dynamic instability
Stabilization
Catastrophe
Rescue
Severing
Microtubule-associated proteins

23. Microtubule Dynamic Instability

Microtubules continuously switch between growth and shrinkage.

Growth
  │
  │
  └──────────┐
             │
         CATASTROPHE
             ↓
         Shrinkage
             │
             │
           RESCUE
             ↑
             │
           Growth

This is called dynamic instability.

24. GTP-Tubulin and Microtubule Stability

Tubulin binds GTP.

During polymerization:

GTP-tubulin
     ↓
Microtubule incorporation
     ↓
GTP hydrolysis
     ↓
GDP-tubulin

A relatively GTP-rich region at the growing end is called the GTP cap.

Loss of this stabilizing state promotes catastrophe.

25. Microtubule-Associated Proteins

MAPs regulate:

Stability
Spacing
Bundling
Polymerization
Interaction with other proteins

Examples include:

Tau
MAP2
MAP4
EB proteins

26. EB Proteins

End-binding proteins, especially EB1, associate with growing microtubule plus ends.

They help recruit other proteins to growing microtubule ends.

                  + END
                    ↓
              [ EB1 ] ●
════════════════════════════
       Microtubule

This creates a dynamic platform for microtubule regulation.

27. Tau and MAP2

Tau is particularly associated with axonal microtubules.

MAP2 is prominent in dendritic compartments.

They contribute to neuronal microtubule organization.

Neuron

Dendrite ── MAP2-associated MTs

Soma
  │
  │
Axon ─────── Tau-associated MTs ─────→

28. Microtubule Severing Proteins

Important severing proteins include:

Katanin
Spastin
Fidgetin

They use ATP-dependent mechanisms to sever microtubules.

══════════════════════════════
             ↓
          Severing
             ↓
═══════             ═════════

Severing can increase the number of microtubule ends and facilitate network remodeling.

29. Microtubule Nucleation

The major nucleation system involves:

γ-tubulin ring complexes (γ-TuRCs)

γ-TuRC
   ↓
Microtubule nucleation
   ↓
Microtubule growth

Major sites include:

Centrosomes
Spindle poles
Golgi-associated MTOCs
Other cellular MTOCs

30. Microtubule Stabilization

Some proteins stabilize microtubules by reducing depolymerization.

Stabilization is important for:

Long-range transport
Cell polarity
Axonal architecture
Mitotic spindle organization

Microtubule dynamics must be balanced rather than simply maximized.

31. Intermediate Filament Regulation

Intermediate filaments differ from actin and microtubules because they do not have the same pronounced plus/minus polarity.

Examples:

Keratins
Vimentin
Desmin
Neurofilaments
Lamins

Their major function is mechanical stability.

32. Intermediate Filament Assembly

A simplified assembly pathway:

Monomer
  ↓
Dimer
  ↓
Tetramer
  ↓
Unit-length filament
  ↓
Intermediate filament

The assembly is highly dynamic despite their mechanical stability.

33. Phosphorylation and Intermediate Filaments

Intermediate filament organization can be regulated by phosphorylation.

For example:

Kinase
  ↓
IF phosphorylation
  ↓
Altered filament organization
  ↓
Reorganization

This is particularly important during:

Mitosis
Cell migration
Stress responses

34. Lamins

Nuclear lamins form the nuclear lamina beneath the inner nuclear membrane.

They provide:

Mechanical support
Nuclear shape
Chromatin organization
Nuclear-envelope organization

      NUCLEUS
┌─────────────────────┐
│ Chromatin           │
│                     │
│                     │
└─────────────────────┘
═══════════════════════
      Nuclear lamina

35. Cytoskeletal Cross-Linkers

Cross-linking proteins connect filaments to one another.

Examples include:

α-actinin
Filamin
Spectrin
Plectin

Actin ═════════════════
          │
       Cross-linker
          │
Actin ═════════════════

Cross-linking produces mechanically and functionally specialized networks.

36. Cytoskeleton–Membrane Linkers

Proteins connect cytoskeletal filaments to the plasma membrane.

Examples:

Spectrin
ERM proteins
Talin
Vinculin
Dystrophin

This allows mechanical and signaling information to be transmitted between the membrane and cytoskeleton.

37. Focal Adhesions

Focal adhesions connect:

Extracellular matrix → integrin → cytoskeleton

      ACTIN
══════════════════
       │
    Vinculin
       │
     Talin
       │
    Integrin
       │
══════════════════
       ECM

They function as both:

Adhesion structures
Mechanosensing/signaling platforms

38. Mechanotransduction

Cells sense mechanical forces through the cytoskeleton.

Mechanical force
       ↓
Integrin / adhesion
       ↓
Actin cytoskeleton
       ↓
Mechanosensitive proteins
       ↓
Signal transduction
       ↓
Gene expression

Thus the cytoskeleton is not simply a structural framework.

It is also a mechanochemical signaling system.

39. Cytoskeleton and Molecular Motors

The cytoskeleton provides tracks for molecular motors.

Microtubules

Kinesin
Dynein

Actin

Myosin

CYTOSKELETON
     │
 ┌───┴───────────┐
 ↓               ↓
Microtubules     Actin
 ↓               ↓
Kinesin          Myosin
Dynein

40. Cytoskeleton and Cell Migration

Migration requires coordination of all three major cytoskeletal systems.

Signal
  ↓
Polarity
  ↓
Actin protrusion
  ↓
Adhesion
  ↓
Microtubule organization
  ↓
Myosin contraction
  ↓
Rear detachment
  ↓
CELL MOVEMENT

41. Cytoskeleton in Cytokinesis

During animal-cell cytokinesis:

      CELL
   ┌─────────┐
   │         │
   │   DNA   │
   │         │
   └────┬────┘
        │
    Actomyosin
     contractile
        ring
        ↓
   Furrow ingression
        ↓
   Two daughter cells

The contractile ring contains:

Actin
Myosin II
Regulatory proteins

42. Cytoskeleton in Mitosis

Microtubules form the mitotic spindle.

Three major categories are:

Kinetochore microtubules
Interpolar microtubules
Astral microtubules

      Centrosome
          ●
         /|\
        / | \
       /  |  \
      /   |   \
     X    X    X
      \   |   /
       \  |  /
        \ | /
         \|/
          ●
      Centrosome

43. Cytoskeleton and Cell Polarity

The cytoskeleton both responds to and establishes polarity.

Polarity signals
      ↓
Rho GTPases
      ↓
Cytoskeletal remodeling
      ↓
Directional transport
      ↓
Cell polarity
      ↓
Localized signaling
      ↓
Further cytoskeletal remodeling

This creates feedback.

44. Cytoskeleton and Cell Signaling

Many signaling pathways directly regulate cytoskeletal dynamics.

Important regulators include:

Rho-family GTPases
PI3K
PAK
ROCK
LIMK
Src-family kinases
FAK

Growth factor
     ↓
Receptor
     ↓
Ras / PI3K / Rho pathways
     ↓
Cytoskeletal regulators
     ↓
Actin / microtubules
     ↓
Cell behavior

45. Temporal and Spatial Regulation

A crucial Master’s-level concept is that cytoskeletal regulation is both:

Spatial

Different regions of the same cell can contain different cytoskeletal structures.

Temporal

The cytoskeleton changes rapidly in response to signals.

                 CYTOSKELETAL REGULATION

                   SPATIAL
                      +
                   TEMPORAL
                      ↓
             DYNAMIC ORGANIZATION
                      ↓
        Precise cellular responses

46. Cytoskeletal Feedback Loops

Cytoskeletal systems regulate signaling, while signaling regulates cytoskeletal systems.

Signal
  ↓
Cytoskeleton
  ↓
Membrane organization
  ↓
Receptor localization
  ↓
Signal amplification
  ↓
More cytoskeletal remodeling

This explains why cytoskeletal organization can become highly polarized and persistent.

47. Actin–Microtubule Crosstalk

Actin and microtubules do not operate independently.

They communicate through:

Cross-linking proteins
+TIP proteins
Motor proteins
Rho-family GTPases
Adhesion complexes

ACTIN ═════════════════
          ╲
           ╲ Crosstalk
            ╲
             ║
             ║
             ║
MICROTUBULE ═════════════

Their coordination is essential for:

Migration
Polarity
Division
Vesicular transport

48. Cytoskeletal Regulation During Migration

A simplified sequence:

External signal
      ↓
Cdc42 establishes polarity
      ↓
Rac activates protrusion
      ↓
Arp2/3 → branched actin
      ↓
Leading edge
      ↓
Adhesion formation
      ↓
Microtubule reorganization
      ↓
RhoA → ROCK → myosin II
      ↓
Rear contraction
      ↓
Migration

49. Pharmacological Regulation

Cytoskeletal dynamics can be experimentally manipulated using drugs.

Actin-associated agents

Cytochalasins
Latrunculins
Jasplakinolide

Microtubule-associated agents

Nocodazole
Colchicine
Taxanes

These compounds are widely used in experimental cell biology.

50. Microtubule Stabilizing vs Destabilizing Agents

Category	Examples	General effect
Microtubule destabilizers	Nocodazole, colchicine	Promote microtubule loss
Microtubule stabilizers	Paclitaxel	Stabilize microtubules
Actin destabilizers	Cytochalasin, latrunculin	Reduce actin polymerization
Actin stabilizing agent	Jasplakinolide	Stabilizes actin filaments

These drugs are useful tools for studying cytoskeletal dynamics.

51. Cytoskeletal Regulation and Disease

Abnormal cytoskeletal regulation is associated with:

Cancer
Neurodegenerative diseases
Muscular disorders
Cardiomyopathies
Ciliopathies
Developmental disorders
Cell-migration abnormalities

52. Cancer

Cancer cells frequently exhibit altered:

Actin organization
Focal adhesion dynamics
Rho GTPase signaling
Microtubule organization
Intermediate filament expression

These changes can promote:

Migration
Invasion
Metastasis
Abnormal division

53. Neurodegeneration

Microtubule-associated proteins are particularly important in neurons.

Abnormal regulation of proteins such as tau can disrupt:

Axonal transport
Microtubule stability
Neuronal architecture

This links cytoskeletal biology to neurodegenerative disease mechanisms.

54. Integrated Cytoskeletal Regulatory Network

                    EXTERNAL SIGNAL
                          │
                          ↓
                      RECEPTOR
                          │
             ┌────────────┼────────────┐
             ↓            ↓            ↓
           PI3K        Rho GTPases     Src/FAK
             │            │            │
             │       ┌────┼────┐       │
             │       ↓    ↓    ↓       │
             │     Cdc42 Rac  RhoA      │
             │       │    │    │        │
             │       ↓    ↓    ↓        │
             │     Actin Actin Myosin   │
             │       │    │    │        │
             └───────┴────┼────┴────────┘
                          ↓
                 CYTOSKELETAL NETWORK
                          │
          ┌───────────────┼────────────────┐
          ↓               ↓                ↓
        ACTIN         MICROTUBULES    INTERMEDIATE
                                        FILAMENTS
          │               │                │
       Shape          Transport        Mechanical
       Migration      Polarity         stability
       Division       Mitosis
          │               │                │
          └───────────────┼────────────────┘
                          ↓
                  CELLULAR BEHAVIOR

55. High-Yield Comparison

Feature	Actin	Microtubules	Intermediate filaments
Subunit	Actin	α/β-tubulin	IF proteins
Diameter	~7 nm	~25 nm	~10 nm
Polarity	Yes	Yes	Generally no
Main ATP/GTP	ATP-actin	GTP-tubulin	No equivalent nucleotide-driven polymerization
Major motor	Myosin	Kinesin/dynein	No conventional motor
Major functions	Shape, migration, contraction	Transport, spindle, polarity	Mechanical strength
Major nucleators	Arp2/3, formins	γ-TuRC	Various assembly mechanisms
Dynamic behavior	High	High	More mechanically stable

56. Master’s-Level Concept: Cytoskeletal Regulation Is Energy Dependent

Cytoskeletal remodeling is coupled to cellular energy metabolism.

ATP
 ↓
Actin dynamics
 ↓
Myosin activity
 ↓
Cellular force generation


GTP
 ↓
Tubulin dynamics
 ↓
Microtubule remodeling

Therefore, cytoskeletal behavior is closely linked to cellular energy status.

57. Master’s-Level Concept: Cytoskeleton as a Signaling Platform

The cytoskeleton is not merely a scaffold.

It can:

Localize signaling molecules
Transmit mechanical forces
Control receptor distribution
Regulate transcription indirectly
Influence organelle positioning
Determine cell shape

Thus:

The cytoskeleton is simultaneously a structural, transport, mechanical, and signaling system.

58. Master’s-Level Concept: Mechanochemical Feedback

Cells convert biochemical signals into mechanical responses and mechanical information back into biochemical signals.

BIOCHEMICAL SIGNAL
       ↓
Cytoskeletal remodeling
       ↓
Mechanical force
       ↓
Mechanosensitive signaling
       ↓
Gene expression / signaling
       ↓
Further cytoskeletal remodeling

This is called mechanochemical feedback.

59. Short Examination Answer

Cytoskeletal Regulation

Cytoskeletal regulation refers to the coordinated control of the assembly, disassembly, organization, stability and interactions of actin filaments, microtubules and intermediate filaments. It is essential for maintaining cell shape, polarity, migration, intracellular transport, mitosis and cytokinesis.

Actin dynamics are regulated by nucleators such as the Arp2/3 complex and formins, capping proteins, profilin, cofilin and Rho-family GTPases. Rac promotes branched actin formation through WAVE–Arp2/3 signaling, Cdc42 regulates polarity and actin remodeling, whereas RhoA promotes actomyosin contractility through ROCK and myosin II.

Microtubule dynamics are regulated by γ-tubulin-dependent nucleation, GTP-dependent polymerization, dynamic instability, microtubule-associated proteins, plus-end tracking proteins and severing proteins such as katanin and spastin. Intermediate filaments provide mechanical stability and are regulated through assembly dynamics and post-translational modifications such as phosphorylation.

Cytoskeletal systems communicate extensively with each other and with membrane-associated signaling complexes. This integration enables cells to convert extracellular signals into spatially and temporally controlled changes in morphology, movement, transport and division.

60. Viva Questions

Q1. What are the three major cytoskeletal systems?
Actin filaments, microtubules and intermediate filaments.

Q2. Which cytoskeletal systems have intrinsic polarity?
Actin filaments and microtubules.

Q3. What is dynamic instability?
The alternating growth and shrinkage of microtubules.

Q4. What is actin treadmilling?
Addition of actin subunits at one end with loss at the other.

Q5. What does Arp2/3 do?
It nucleates branched actin filaments.

Q6. What do formins do?
They promote nucleation and elongation of linear actin filaments.

Q7. What is the function of cofilin?
It promotes actin filament turnover through severing and depolymerization.

Q8. What is the role of profilin?
It regulates G-actin availability and supports actin polymerization.

Q9. What are the three major Rho-family GTPases?
RhoA, Rac and Cdc42.

Q10. Which GTPase is associated with lamellipodia?
Rac.

Q11. Which GTPase promotes actomyosin contractility?
RhoA.

Q12. Which GTPase is strongly associated with polarity?
Cdc42.

Q13. What is γ-TuRC?
A γ-tubulin-containing complex that nucleates microtubules.

Q14. What are kinesin and dynein?
Microtubule-based molecular motors.

Q15. What is the major actin-based motor?
Myosin.

Q16. What is the function of katanin?
Microtubule severing.

Q17. What is mechanotransduction?
Conversion of mechanical forces into biochemical signaling responses.

Q18. Why is cytoskeletal crosstalk important?
It coordinates polarity, migration, trafficking, adhesion and cell division.

61. One-Minute Revision

                         CYTOSKELETAL REGULATION
                                  │
          ┌───────────────────────┼───────────────────────┐
          ↓                       ↓                       ↓
        ACTIN                MICROTUBULES         INTERMEDIATE
                                                   FILAMENTS
          │                       │                       │
     Arp2/3 + formins         γ-TuRC                 Assembly
     Profilin                 MAPs                    Phosphorylation
     Cofilin                  EB proteins             Stability
     Capping                  Katanin
          │                       │
          ↓                       ↓
     RhoA / Rac / Cdc42       GTP dynamics
          │                       │
          ↓                       ↓
      Migration               Transport
      Polarity                Spindle
      Cytokinesis             Polarity
          │                       │
          └───────────┬───────────┘
                      ↓
              CYTOSKELETAL CROSSTALK
                      ↓
       ┌──────────────┼──────────────┐
       ↓              ↓              ↓
   Cell shape      Migration      Transport
       ↓              ↓              ↓
     Division       Polarity      Signaling
                      ↓
               CELL FUNCTION

Core memory rule

Arp2/3 → branched actin
Formin → linear actin
Profilin → actin assembly
Cofilin → actin turnover
Rac → protrusion
Cdc42 → polarity
RhoA → contractility
γ-TuRC → microtubule nucleation
EB1 → growing microtubule ends
Katanin → microtubule severing
Myosin → actin-based force
Kinesin/dynein → microtubule-based transport

Cytoskeletal Regulation

Master’s-Level Cell Biology & Advanced Molecular Biology Notes

1. Definition

2. Why Cytoskeletal Regulation Is Necessary

3. Fundamental Principle

4. Major Cytoskeletal Regulatory Processes

5. Actin Filament Regulation

6. Actin Filament Polarity

7. Actin Polymerization

8. Treadmilling

9. Nucleation-Promoting Factors

10. Arp2/3 Complex

11. Formins

12. Arp2/3 vs Formin

13. Actin Capping Proteins

14. Profilin

15. Cofilin

16. ADF/Cofilin Regulation

17. Rho-Family GTPases

18. RhoA

19. Rac1

20. Cdc42

21. RhoA–Rac–Cdc42 Integration

22. Microtubule Regulation

23. Microtubule Dynamic Instability

24. GTP-Tubulin and Microtubule Stability

25. Microtubule-Associated Proteins

26. EB Proteins

27. Tau and MAP2

28. Microtubule Severing Proteins

29. Microtubule Nucleation

30. Microtubule Stabilization

31. Intermediate Filament Regulation

32. Intermediate Filament Assembly

33. Phosphorylation and Intermediate Filaments

34. Lamins

35. Cytoskeletal Cross-Linkers

36. Cytoskeleton–Membrane Linkers

37. Focal Adhesions

38. Mechanotransduction

39. Cytoskeleton and Molecular Motors

Microtubules

Actin

40. Cytoskeleton and Cell Migration

41. Cytoskeleton in Cytokinesis

42. Cytoskeleton in Mitosis

43. Cytoskeleton and Cell Polarity

44. Cytoskeleton and Cell Signaling

45. Temporal and Spatial Regulation

Spatial

Temporal

46. Cytoskeletal Feedback Loops

47. Actin–Microtubule Crosstalk

48. Cytoskeletal Regulation During Migration

49. Pharmacological Regulation

Actin-associated agents

Microtubule-associated agents

50. Microtubule Stabilizing vs Destabilizing Agents

51. Cytoskeletal Regulation and Disease

52. Cancer

53. Neurodegeneration

54. Integrated Cytoskeletal Regulatory Network

55. High-Yield Comparison

56. Master’s-Level Concept: Cytoskeletal Regulation Is Energy Dependent

57. Master’s-Level Concept: Cytoskeleton as a Signaling Platform

58. Master’s-Level Concept: Mechanochemical Feedback

59. Short Examination Answer

Cytoskeletal Regulation

60. Viva Questions

61. One-Minute Revision

Core memory rule

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