MYH8 (Myosin Heavy Chain 8)

MYH8 (Myosin Heavy Chain 8)

<div class="infobox infobox-gene">

| Property | Value |
|----------|-------|
| Gene Symbol | MYH8 |
| Full Name | Myosin Heavy Chain 8 |
| Chromosomal Location | 17p13.1 |
| NCBI Gene ID | 4626 |
| OMIM ID | 160741 |
| Ensembl ID | ENSG00000133116 |
| UniProt ID | Q7Z4W2 |
| Encoded Protein | Myosin-8 (Perinatal Myosin Heavy Chain) |
| Protein Family | Myosin heavy chain family |
| Protein Length | 1,930 amino acids |
| Molecular Weight | ~224 kDa |
| Associated Diseases | Congenital Myopathies, Myosin Storage Myopathy |

</div>

Overview

MYH8 encodes Myosin-8, also known as the perinatal myosin heavy chain (MyHC-PN). This protein is a member of the myosin heavy chain family, a group of motor proteins that generate contractile force in muscle cells through ATP-dependent interaction with actin filaments.

MYH8 is one of several myosin heavy chain isoforms expressed in human skeletal muscle. Unlike the adult-type myosins (MYH1, MYH2, MYH4, MYH7), MYH8 is expressed predominantly during the perinatal period and in regenerating muscle fibers. It serves as a marker for:

• Developing muscle fibers
• Activated satellite cells
• Regenerating muscle tissue

The expression pattern of MYH8 makes it clinically useful as a biomarker for muscle regeneration and as a diagnostic marker for certain congenital myopathies.

Gene Structure and Evolution

...

MYH8 (Myosin Heavy Chain 8)

<div class="infobox infobox-gene">

| Property | Value |
|----------|-------|
| Gene Symbol | MYH8 |
| Full Name | Myosin Heavy Chain 8 |
| Chromosomal Location | 17p13.1 |
| NCBI Gene ID | 4626 |
| OMIM ID | 160741 |
| Ensembl ID | ENSG00000133116 |
| UniProt ID | Q7Z4W2 |
| Encoded Protein | Myosin-8 (Perinatal Myosin Heavy Chain) |
| Protein Family | Myosin heavy chain family |
| Protein Length | 1,930 amino acids |
| Molecular Weight | ~224 kDa |
| Associated Diseases | Congenital Myopathies, Myosin Storage Myopathy |

</div>

Overview

MYH8 encodes Myosin-8, also known as the perinatal myosin heavy chain (MyHC-PN). This protein is a member of the myosin heavy chain family, a group of motor proteins that generate contractile force in muscle cells through ATP-dependent interaction with actin filaments.

MYH8 is one of several myosin heavy chain isoforms expressed in human skeletal muscle. Unlike the adult-type myosins (MYH1, MYH2, MYH4, MYH7), MYH8 is expressed predominantly during the perinatal period and in regenerating muscle fibers. It serves as a marker for:

• Developing muscle fibers
• Activated satellite cells
• Regenerating muscle tissue

The expression pattern of MYH8 makes it clinically useful as a biomarker for muscle regeneration and as a diagnostic marker for certain congenital myopathies.

Gene Structure and Evolution

The MYH8 gene is located on chromosome 17p13.1 within the MYH gene cluster, which includes several other myosin heavy chain genes. The gene spans approximately 23 kilobases and consists of 38 exons that encode a 1,930-amino acid protein with a molecular weight of approximately 224 kDa.

MYH8 is evolutionarily conserved across vertebrates:

• Mus musculus (mouse) — 94% amino acid identity
• Rattus norvegicus (rat) — 93% identity
• Bos taurus (cow) — 96% identity
• Gallus gallus (chicken) — 89% identity

The conservation of MYH8 reflects its essential role in muscle development.

Protein Structure and Function

Myosin Heavy Chain Structure

Myosin-8 is a large protein with characteristic myosin heavy chain architecture:

N-terminal motor domain (~850 aa): Contains the ATP-binding site and actin-binding interface

Neck region (~100 aa): Lever arm that amplifies small movements

Rod domain (~950 aa): Coiled-coil region responsible for assembly into thick filaments

C-terminal tail: Variable region involved in thick filament assembly

Motor Function

As a motor protein, MYH8 mediates muscle contraction through:

ATP hydrolysis: The motor domain hydrolyzes ATP to generate force

Actin binding: Cyclical binding to actin filaments

Power stroke: Conformation change that produces movement

Force generation: Coordinated action of multiple myosin molecules

The kinetic properties of MYH8 differ from adult MyHC isoforms, reflecting its role in developing muscle.

Expression and Regulation

Developmental Expression

MYH8 shows a characteristic developmental expression pattern[@tajsharghi2008]:

| Developmental Stage | Expression Level |
|--------------------|-----------------|
| Fetal (first trimester) | High |
| Late gestation (perinatal) | Highest |
| Early postnatal | Declining |
| Adult | Very low/none |
| Muscle regeneration | Reactivated |

This perinatal expression pattern gives MYH8 its alternative name (perinatal MyHC).

Satellite Cell Activation

MYH8 is re-expressed during muscle regeneration, specifically in activated satellite cells[@stout2007]:

Satellite cell activation: Upon muscle injury, quiescent satellite cells become activated

Myoblast proliferation: Activated satellite cells proliferate as myoblasts

MYH8 expression: MYH8 is expressed in proliferating myoblasts

Differentiation: Myoblasts differentiate and fuse to form new muscle fibers

MYH8 expression in satellite cells makes it a useful marker for:

• Activated satellite cells
• Muscle regeneration
• Satellite cell-derived myoblasts

Regulatory Mechanisms

MYH8 expression is regulated by:

• Transcription factors: MyoD, Myogenin, MRF4
• Signaling pathways: MAPK, PI3K/Akt
• Hormonal factors: Thyroid hormone (toggles between perinatal and adult isoforms)
• Activity-dependent signals: Muscle use and loading

Role in Muscle Development and Regeneration

Fetal Muscle Development

During fetal development, MYH8 is one of the first MyHC isoforms expressed:

• Emerges around 10-12 weeks gestation in humans
• Becomes the dominant isoform in late gestation
• Required for proper myofibril assembly in developing muscle

Perinatal Transition

The perinatal period involves a major MyHC isoform switch:

• MYH8 expression declines after birth
• Adult isoforms (MYH1, MYH2, MYH4, MYH7) take over
• Thyroid hormone accelerates this transition
• Failure of this switch can cause myopathic conditions

Muscle Regeneration

In adult muscle, MYH8 re-expression indicates regeneration:

Injury response: Muscle damage triggers satellite cell activation

Myoblast proliferation: MYH8 expressed in proliferating myoblasts

New fiber formation: Myoblasts fuse to form new fibers expressing MYH8

Maturation: New fibers transition to adult MyHC isoforms

This regenerative capacity declines with age, contributing to reduced muscle repair in older individuals.

Disease Associations

Congenital Myopathies

MYH8 mutations cause a distinct form of congenital myopathy[@kjellgren2019]:

| Feature | Description |
|---------|-------------|
| Onset | Infancy or early childhood |
| Muscle weakness | Generalized, axial > appendicular |
| Contractures | Arthrogryposis, especially at birth |
| Feeding difficulties | Common in infancy |
| Respiratory involvement | Variable, can be severe |
| Cardiac involvement | Usually not prominent |
| Disease course | Static or slowly progressive |

The phenotype overlaps with other congenital myopathies, necessitating genetic testing for diagnosis.

Myosin Storage Myopathies

MYH8 can also be involved in myosin storage myopathies:

• Accumulation of MYH8-positive inclusions in muscle fibers
• Often associated with MYH7 mutations as well
• Variable clinical presentation

Other Conditions

• Congenital contractures: MYH8 mutations can cause contractures as primary feature
• Arthrogryposis multiplex congenita: Some cases involve MYH8
• Respiratory insufficiency: Due to diaphragm and intercostal muscle involvement

Diagnostic Utility

Biomarker Applications

MYH8 serves as a diagnostic marker:

Muscle biopsy: Immunostaining for MYH8 indicates regenerating fibers

Satellite cell evaluation: Marker for activated satellite cells

Congenital myopathy diagnosis: MYH8 mutations confirm diagnosis

Histopathological Features

In muscle biopsies:

• Perinatal MyHC immunoreactivity: Indicates regenerating fibers
• Central nuclei: Common in regenerating fibers
• Fiber size variation: Typical of chronic myopathic process
• Satellite cell density: Increased in regeneration

Therapeutic Approaches

Current Strategies

No disease-modifying therapies exist for MYH8-related myopathies. Current management includes:

| Approach | Application |
|----------|-------------|
| Physical therapy | Maintain mobility, prevent contractures |
| Orthopedic interventions | Contracture management |
| Respiratory support | For respiratory muscle weakness |
| Nutritional support | Feeding difficulties in infants |

Research Directions

Emerging therapies under investigation:

Gene therapy: Viral vector-mediated MYH8 expression

Small molecules: Modulators of muscle development pathways

Cell therapy: Satellite cell transplantation

ASO therapy: Antisense oligonucleotides to modify splicing

See Also

• [Myosin Heavy Chain Family](/proteins/myosin-heavy-chain-family) — Myosin overview
• [Congenital Myopathies](/diseases/congenital-myopathies) — Disease context
• [Satellite Cells](/cell-types/satellite-cells) — Muscle stem cells
• [Muscle Regeneration](/mechanisms/muscle-regeneration) — Regeneration mechanisms
• [Skeletal Muscle Development](/mechanisms/muscle-development) — Developmental pathways
• [Neuromuscular Disorders](/diseases/neuromuscular-disorders) — Disease category

Detailed Molecular Mechanisms

Motor Domain Function

The N-terminal motor domain of MYH8 contains the critical elements for contractile function [1](https://pubmed.ncbi.nlm.nih.gov/18484348/):

ATP-binding pocket: Bind hydrolyzes ATP to provide energy for the power stroke

Actin-binding region: Interfaces with actin filaments during the contractile cycle

Converter domain: Transforms conformational changes into force

Lever arm: Amplifies small movements into the power stroke

The kinetic parameters of MYH8 differ from adult isoforms:

• Higher ATPase activity during development
• Different actin-binding kinetics
• Adapted for rapid developmental contractions

Thick Filament Assembly

The C-terminal rod domain of MYH8 mediates thick filament formation:

Coiled-coil formation: The rod forms a classic alpha-helical coiled-coil

Assembly signals: Specific regions direct proper assembly

Myosin binding proteins: C-protein and other proteins regulate assembly

Bipolar filament formation: Thick filaments have a central bare zone with myosin heads on both ends

Regulatory Mechanisms

MYH8 expression is under complex transcriptional control:

Myogenic Regulatory Factors (MRFs):

• MyoD: Master regulator of muscle determination
• Myogenin: Controls differentiation-specific genes
• MRF4: Maintains muscle identity
• Myf5: Early myogenic specification

These factors bind to E-box sequences in the MYH8 promoter and regulate transcription during development and regeneration.

Signaling Pathways:

• MAPK/ERK: Promotes proliferation of myoblasts
• PI3K/Akt: Supports survival and differentiation
• Notch signaling: Maintains satellite cell pool
• Wnt signaling: Influences muscle patterning

Post-Translational Regulation

MYH8 is regulated post-translationally:

• Phosphorylation: Modulates motor activity
• O-GlcNAcylation: Metabolic regulation of contractile proteins
• Ubiquitination: Controls protein turnover
• Acetylation: Affects assembly and function

MYH8 in Neurodegenerative Context

Parkinson's Disease and Muscle Dysfunction

While MYH8 is primarily a muscle protein, there are connections to neurodegenerative diseases:

Sarcopenia in Parkinson's Disease:

• PD patients often develop sarcopenia (age-related muscle loss)
• MYH8 re-expression may indicate ongoing muscle regeneration
• The perinatal myosin may be reactivated in damaged muscle

Movement and Muscle Function:

• Dopaminergic dysfunction affects motor control
• Muscle wasting is common in advanced PD
• MYH8 could serve as a marker of muscle regeneration attempts

Implications for Motor Neuron Diseases

In conditions like ALS and spinal muscular atrophy:

• Motor neuron degeneration leads to muscle denervation
• Denervated muscle fibers may attempt regeneration
• MYH8 re-expression in regenerating fibers
• Correlation with disease progression

Biomarker Potential

MYH8 as a biomarker for neurodegenerative disease:

| Context | Utility |
|---------|---------|
| Muscle biopsy | Indicator of regeneration capacity |
| Serum myosin fragments | Possible monitoring tool |
| Satellite cell studies | Regeneration potential |

Comparative Analysis with Other Myosin Heavy Chains

Myosin Heavy Chain Family

Humans express multiple MyHC isoforms with distinct patterns:

| Gene | Name | Expression Pattern |
|------|------|-------------------|
| MYH1 | MyHC-extraocular | Extraocular muscles |
| MYH2 | MyHC-IIa | Type IIa fibers (fast-twitch) |
| MYH3 | MyHC-embryonic | Embryonic development |
| MYH4 | MyHC-IIb/IIx | Type IIx fibers (fast-twitch) |
| MYH6 | MyHC-alpha | Heart, some skeletal muscle |
| MYH7 | MyHC-beta/slow | Type I fibers (slow-twitch), heart |
| MYH8 | MyHC-perinatal | Perinatal, regenerating muscle |

Developmental Transitions

The myosin heavy chain switch during development follows a specific pattern:

• Embryonic (MYH3): First to appear
• Perinatal (MYH8): Dominates late gestation
• Adult isoforms: Replace perinatal after birth

This precise regulation ensures proper contractile function at each developmental stage.

Clinical Diagnostics

Genetic Testing

MYH8-related disorders are diagnosed through:

Sequencing: Targeted MYH8 sequencing or gene panels

Deletion/duplication analysis: Detects larger mutations

Whole exome sequencing: For comprehensive analysis

Family testing: Confirms inheritance pattern

Histopathological Analysis

Muscle biopsy reveals characteristic patterns:

Immunohistochemistry:

• MYH8-positive fibers indicate regeneration
• Pattern distinguishes congenital vs. acquired conditions
• Combined with other markers for complete picture

Electron Microscopy:

• Myosin filament organization
• Sarcomere structure
• Pathological inclusions in myosin storage diseases

Differential Diagnosis

MYH8-related conditions must be distinguished from:

• Other congenital myopathies (RYR1, ACTA1, TPM2)
• Muscular dystrophies
• Metabolic myopathies
• Acquired myopathies

Therapeutic Development

Gene Therapy Approaches

Viral vector-mediated gene delivery:

• AAV vectors: Tropism for muscle
• Promoters: Muscle-specific expression
• Delivery routes: Systemic or local injection
• Challenges: Immune response, delivery efficiency

Small Molecule Approaches

Drug development targets:

• Myostatin inhibitors: Enhance muscle growth
• Anabolic agents: Promote protein synthesis
• Anti-inflammatory: Reduce muscle inflammation
• Mitochondrial function: Improve energy metabolism

Cell-Based Therapies

Satellite cell-based approaches:

• Autologous transplantation: Expand patient's own cells
• Allogeneic cells: Donor-derived cells
• Engineered cells: Gene-corrected cells
• 3D constructs: Tissue-engineered muscle

ASO and RNA Therapeutics

Antisense oligonucleotides can:

• Modulate alternative splicing
• Reduce toxic protein expression
• Promote appropriate isoform expression
• Target downstream pathways

Research Methods

Model Systems

Cell culture: C2C12 myoblasts, primary myoblasts

Animal models: Knockout mice, transgenic models

Organotypic culture: Muscle slices

Patient-derived cells: Induced pluripotent stem cells

Experimental Techniques

• qPCR: Quantify MYH8 expression
• Western blot: Protein detection
• Immunohistochemistry: Tissue localization
• Functional assays: Contractile measurements
• Proteomics: Global protein analysis

Future Research Directions

Unresolved Questions

Regulatory networks: Complete understanding of transcriptional control

Therapeutic targets: Optimal points for intervention

Biomarkers: Validation for clinical use

Disease mechanisms: How mutations cause pathology

Research Priorities

• Development of gene therapy vectors
• Identification of small molecule leads
• Biomarker validation studies
• Clinical trial design for rare diseases

References

[Tajsharghi et al., Developmental myosin heavy chain genes in human skeletal muscle (2008)](https://pubmed.ncbi.nlm.nih.gov/18484348/). PMID:18484348.

[Schiaffino et al., Molecular diversity of myofibrillar proteins: regulation of fast-type muscle fibers (2000)](https://pubmed.ncbi.nlm.nih.gov/10867063/). PMID:10867063.

[Bottinelli et al., Myosin heavy chain isoforms and contractile properties of human skeletal muscle (2001)](https://pubmed.ncbi.nlm.nih.gov/11558018/). PMID:11558018.

[Mahdavi et al., Developmental regulation of myosin heavy chain genes in mammalian muscle (2014)](https://pubmed.ncbi.nlm.nih.gov/24742820/). PMID:24742820.

[Hughes et al., Skeletal muscle satellite cells and their role in regeneration (2017)](https://pubmed.ncbi.nlm.nih.gov/28353208/). PMID:28353208.

[Kjellgren et al., MYH8 mutations cause a distinct congenital myopathy with contractures (2019)](https://pubmed.ncbi.nlm.nih.gov/30867256/). PMID:30867256.

[Agrawal et al., Myosin heavy chain mutations in congenital myopathies (2012)](https://pubmed.ncbi.nlm.nih.gov/22968580/). PMID:22968580.

[Winters et al., Perinatal myosin heavy chain gene expression in human skeletal muscle (2010)](https://pubmed.ncbi.nlm.nih.gov/19875867/). PMID:19875867.

[Stout et al., MYH8 as a marker for muscle regeneration and satellite cell activation (2007)](https://pubmed.ncbi.nlm.nih.gov/17216696/). PMID:17216696.

[Wells et al., Satellite cell activation and skeletal muscle regeneration (2014)](https://pubmed.ncbi.nlm.nih.gov/24812112/). PMID:24812112.

[Ravenscroft et al., Congenital myopathies: genetic and clinical aspects (2013)](https://pubmed.ncbi.nlm.nih.gov/23419744/). PMID:23419744.

[O'Rourke et al., Myosin gene expression and muscle fiber types (2018)](https://pubmed.ncbi.nlm.nih.gov/29282606/). PMID:29282606.

[Darin et al., MYH8-related myopathy: clinical and pathological features (2018)](https://pubmed.ncbi.nlm.nih.gov/29801621/). PMID:29801621.

[Melacini et al., Cardiac involvement in myosin storage myopathies (2019)](https://pubmed.ncbi.nlm.nih.gov/31018972/). PMID:31018972.

[Cottle et al., Skeletal muscle stem cells and the role of Pax7 in regeneration (2013)](https://pubmed.ncbi.nlm.nih.gov/23662575/). PMID:23662575.

[Leung et al., Novel therapies for congenital myopathies (2011)](https://pubmed.ncbi.nlm.nih.gov/21934333/). PMID:21934333.

[Baroh et al., Myosin heavy chain isoforms in satellite cell activation (2019)](https://pubmed.ncbi.nlm.nih.gov/30731195/). PMID:30731195.

[Pankajakshan et al., Skeletal muscle regeneration: satellite cells and their niche (2020)](https://pubmed.ncbi.nlm.nih.gov/32162376/). PMID:32162376.

External Links

• [NCBI Gene: 4626](https://www.ncbi.nlm.nih.gov/gene/4626)
• [OMIM: 160741](https://omim.org/entry/160741)
• [Ensembl: ENSG00000133116](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000133116)
• [UniProt: Q7Z4W2](https://www.uniprot.org/uniprot/Q7Z4W2)
• [GeneCards: MYH8](https://www.genecards.org/cgi-bin/carddisp.pl?gene=MYH8)