myoblast fusion

Definition

Target type: biologicalprocess

A process in which non-proliferating myoblasts fuse to existing fibers or to myotubes to form new fibers. A myoblast is a mononucleate cell type that, by fusion with other myoblasts, gives rise to the myotubes that eventually develop into skeletal muscle fibers. [CL:0000056, GOC:mtg_muscle]

Myoblast fusion is a complex process that is essential for the formation of skeletal muscle. It involves the coordinated interaction of multiple signaling pathways and cellular processes, leading to the fusion of individual myoblasts into multinucleated myotubes. This process is tightly regulated and is influenced by a variety of factors, including growth factors, transcription factors, and extracellular matrix components. Here is a detailed description of the biological process of myoblast fusion:

**1. Commitment and Activation:**

Myoblasts, the precursors of muscle fibers, are committed to the myogenic lineage and express specific myogenic transcription factors, such as MyoD and Myf5. These factors activate the expression of genes involved in myoblast proliferation and differentiation.

**2. Cell Cycle Exit and Differentiation:**

As myoblasts differentiate, they exit the cell cycle and begin to express genes involved in myoblast fusion. This includes the expression of cell adhesion molecules, such as integrins and cadherins, which mediate cell-cell interactions.

**3. Alignment and Contact:**

Myoblasts align themselves along the long axis of the developing muscle fiber. This alignment is facilitated by cell-cell interactions mediated by cell adhesion molecules. Once aligned, myoblasts make contact with each other through specialized fusion sites.

**4. Fusion Pore Formation:**

At the fusion sites, the plasma membranes of two myoblasts come into close proximity. Fusion pores form at these sites, allowing for the merging of the two cells. The formation of fusion pores is a complex process that involves the recruitment of specific proteins, including fusogens (e.g., Myomaker, Myomerger) and regulatory proteins (e.g., MFGE8, Syncytin-1).

**5. Membrane and Cytoplasm Merging:**

Once fusion pores are formed, the plasma membranes of the two myoblasts fuse, allowing for the merging of their cytoplasm and organelles. The nuclei of the two myoblasts remain distinct within the newly formed myotube.

**6. Myotube Maturation:**

The newly formed myotubes continue to grow and differentiate. They synthesize and assemble muscle-specific proteins, such as myosin and actin, which form the contractile apparatus of muscle fibers. The myotubes also align themselves along the long axis of the muscle fiber, forming organized bundles of muscle fibers.

**7. Formation of Mature Muscle Fiber:**

As the myotubes mature, they fuse with other myotubes to form larger, multinucleated muscle fibers. This process continues until the muscle fiber reaches its final size and shape.

**Factors Affecting Myoblast Fusion:**

* **Growth Factors:** Growth factors, such as fibroblast growth factor (FGF) and insulin-like growth factor (IGF), play a role in stimulating myoblast proliferation and differentiation, which are essential for myoblast fusion.
* **Transcription Factors:** Myogenic transcription factors, such as MyoD and Myf5, activate genes involved in myoblast fusion, and their expression is regulated by growth factors and other signaling pathways.
* **Extracellular Matrix Components:** Extracellular matrix components, such as laminin and fibronectin, provide structural support and guidance to myoblasts, and they also play a role in regulating myoblast fusion.
* **Cytoskeletal Dynamics:** The cytoskeleton plays an essential role in myoblast alignment, cell-cell contact, and fusion pore formation.
* **Signaling Pathways:** Various signaling pathways, such as the Wnt, MAPK, and PI3K pathways, regulate myoblast fusion by controlling the expression of fusion-related genes and the activity of fusion proteins.

**Consequences of Defective Myoblast Fusion:**

Defects in myoblast fusion can lead to various muscle disorders, including muscular dystrophies. These disorders are characterized by muscle weakness, degeneration, and atrophy.

In summary, myoblast fusion is a highly regulated and complex process that is essential for the formation of functional skeletal muscle. It involves a coordinated interplay of various signaling pathways, cellular processes, and molecular components.'
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Proteins (10)

Compounds (272)