MYO7A — Myosin VIIa

MYO7A — Myosin VIIa

<div class="infobox infobox-gene">
<table>
<tr><td><strong>Gene Symbol</strong></td><td>MYO7A</td></tr>
<tr><td><strong>Full Name</strong></td><td>Myosin VIIa</td></tr>
<tr><td><strong>Chromosome</strong></td><td>11q13.5</td></tr>
<tr><td><strong>NCBI Gene ID</strong></td><td>[4647](https://www.ncbi.nlm.nih.gov/gene/4647)</td></tr>
<tr><td><strong>OMIM</strong></td><td>120650</td></tr>
<tr><td><strong>Ensembl ID</strong></td><td>ENSG00000135624</td></tr>
<tr><td><strong>UniProt ID</strong></td><td>[P12883](https://www.uniprot.org/uniprot/P12883)</td></tr>
<tr><td><strong>Protein Size</strong></td><td>221 kDa, 2,215 amino acids</td></tr>
<tr><td><strong>Associated Diseases</strong></td><td>Usher Syndrome 1B, Deafness, Retinitis Pigmentosa</td></tr>
</table>
</div>

Overview

MYO7A — Myosin VIIa

<div class="infobox infobox-gene">
<table>
<tr><td><strong>Gene Symbol</strong></td><td>MYO7A</td></tr>
<tr><td><strong>Full Name</strong></td><td>Myosin VIIa</td></tr>
<tr><td><strong>Chromosome</strong></td><td>11q13.5</td></tr>
<tr><td><strong>NCBI Gene ID</strong></td><td>[4647](https://www.ncbi.nlm.nih.gov/gene/4647)</td></tr>
<tr><td><strong>OMIM</strong></td><td>120650</td></tr>
<tr><td><strong>Ensembl ID</strong></td><td>ENSG00000135624</td></tr>
<tr><td><strong>UniProt ID</strong></td><td>[P12883](https://www.uniprot.org/uniprot/P12883)</td></tr>
<tr><td><strong>Protein Size</strong></td><td>221 kDa, 2,215 amino acids</td></tr>
<tr><td><strong>Associated Diseases</strong></td><td>Usher Syndrome 1B, Deafness, Retinitis Pigmentosa</td></tr>
</table>
</div>

Overview

Myosin VIIa is an unconventional myosin motor protein encoded by the MYO7A gene that plays critical roles in intracellular transport, particularly in cells with extensive actin-based motility such as retinal photoreceptors and inner ear hair cells [1](https://pubmed.ncbi.nlm.nih.gov/8605169/). This motor protein moves towards the plus (barbed) end of actin filaments and is essential for vision, hearing, and various aspects of cellular function. Mutations in MYO7A cause Usher syndrome type 1B, the most common form of syndromic deafness-blindness.

Gene and Protein Structure

The MYO7A gene spans approximately 39 kb on chromosome 11q13.5 and contains 49 exons encoding a protein of 2,215 amino acids with a molecular weight of approximately 221 kDa [2](https://pubmed.ncbi.nlm.nih.gov/9324766/). The myosin VIIa protein structure includes:

• N-terminal motor domain: Contains the ATPase activity and actin-binding sites responsible for force generation
• Neck region: Contains IQ motifs that bind light chains (calmodulin) for regulation
• Tail domain: Includes a coiled-coil region for dimerization and specific domains for cargo binding

Function

Intracellular Transport

Myosin VIIa functions as a processive motor that transports cargo along actin filaments. It moves towards the plus (barbed) end of actin, which allows it to transport cargo from the cell body towards the periphery in epithelial cells and neurons [4](https://pubmed.ncbi.nlm.nih.gov/10508768/).

Photoreceptor Function

In retinal photoreceptor cells, myosin VIIa is essential for the transport of opsin-containing vesicles from the inner segment to the outer segment [5](https://pubmed.ncbi.nlm.nih.gov/10769040/). The outer segment of photoreceptors is a highly specialized cilium where opsin must be properly localized for phototransduction.

Hair Cell Function

In the inner ear, myosin VIIa is expressed in stereocilia of hair cells where it participates in the transport of proteins essential for stereocilia structure and function [6](https://pubmed.ncbi.nlm.nih.gov/10654948/). It is involved in maintaining the proper localization of proteins necessary for mechotransduction.

Cellular Processes

Myosin VIIa participates in:

• Vesicle transport: Moving endocytic and secretory vesicles
• Organelle positioning: Maintaining proper subcellular distribution of cellular organelles
• Cell polarity: Establishing and maintaining epithelial cell polarity
• Cytokinesis: Contributing to cell division through furrow ingression

Expression Pattern

Myosin VIIa shows a distinctive expression pattern:

• Retina: High expression in photoreceptor cells, particularly in the outer segment
• Inner ear: Expressed in hair cells of the cochlea and vestibular system
• Epithelial tissues: Present in various epithelial cells including kidney, lung, and intestine
• Brain: Low expression in various neuronal populations
• Testis: Expressed in developing sperm cells

Disease Associations

Usher Syndrome Type 1B

Usher syndrome type 1B (USH1B) is caused by recessive mutations in MYO7A. It is the most common form of Usher syndrome, accounting for approximately 50% of all cases [7](https://pubmed.ncbi.nlm.nih.gov/12432094/).

| Feature | Details |
|---------|---------|
| Inheritance | Autosomal recessive |
| Hearing loss | Congenital profound sensorineural deafness |
| Vision loss | Progressive retinitis pigmentosa beginning in childhood |
| Vestibular function | Severe vestibular areflexia (balance problems) |
| Onset | Deafness present at birth; vision loss begins in childhood |

The combination of congenital deafness and progressive blindness makes USH1B particularly debilitating, and patients often benefit from cochlear implants and vision aids.

Deafness (Isolated)

Some MYO7A mutations cause isolated deafness without retinal involvement, demonstrating the phenotypic variability of MYO7A variants [8](https://pubmed.ncbi.nlm.nih.gov/11807148/).

Retinitis Pigmentosa

MYO7A mutations can cause non-syndromic retinitis pigmentosa, where retinal degeneration occurs without hearing loss [9](https://pubmed.ncbi.nlm.nih.gov/10480383/).

Pathogenesis

Mechanotransduction Impairment

In hair cells, myosin VIIa is required for proper organization of stereocilia and the mechanotransduction machinery. Loss of myosin VIIa leads to disorganized stereocilia and impaired hearing [10](https://pubmed.ncbi.nlm.nih.gov/10654948/).

Photoreceptor Degeneration

In photoreceptors, defective opsin transport leads to accumulation of opsin in the inner segment and progressive degeneration of the outer segment [5](https://pubmed.ncbi.nlm.nih.gov/10769040/). This results in the progressive retinal degeneration characteristic of retinitis pigmentosa.

Cellular Transport Defects

The underlying mechanism involves defective transport of various cargoes, including:

• Opsin-containing vesicles in photoreceptors
• Proteins essential for hair bundle structure
• Endocytic vesicles in various cell types

Therapeutic Approaches

Gene Therapy

Adeno-associated virus (AAV)-mediated gene therapy for MYO7A is being developed. Challenges include:

• The large size of MYO7A requiring novel AAV capsids or split-intein approaches
• Delivery to both retina and inner ear
• Timing of intervention before irreversible cell loss

Pharmacological Approaches

• Retinal degeneration: Antioxidants and neuroprotective compounds to slow photoreceptor loss
• Vestibular function: Rehabilitation and balance training

Assistive Devices

• Cochlear implants for profound deafness
• Low vision aids for retinitis pigmentosa

Relationship to Neurodegeneration

While primarily associated with sensory cells, MYO7A research provides insights into general mechanisms of neurodegeneration:

Axonal Transport and Vesicle Trafficking

Myosin VIIa plays a critical role in the transport of cargoes along actin filaments in neuronal cells. In neurons, this motor protein facilitates:

• Synaptic vesicle transport: Myosin VIIa moves synaptic vesicles from the cell body to nerve terminals along actin cytoskeleton[@wang1998]. This process is essential for maintaining synaptic vesicle pools and sustaining neurotransmission.
• Protein sorting: The MyTH4-FERM domain structure in myosin VIIa's tail binds to specific cargo proteins, enabling targeted delivery to distinct cellular compartments.
• Endolysosomal trafficking: Myosin VIIa participates in the movement of endocytic and autophagic vesicles, pathways critical for protein quality control in neurons.

Implications for Alzheimer's Disease

Although MYO7A mutations do not cause AD directly, the protein's trafficking mechanisms inform disease understanding:

• Amyloid precursor protein (APP) trafficking: Similar myosin-based mechanisms govern APP transport in neurons. Understanding myosin VIIa's role helps elucidate APP processing and amyloid-beta production.
• Endosomal sorting: Myosin VIIa participates in endosomal trafficking - a pathway critically impaired in AD where early endosome enlargement is a hallmark.
• Autophagy regulation: Myosin VIIa-mediated transport delivers cargo to autophagosomes. Autophagy impairment in AD neurons may involve similar mechanisms.

Implications for Parkinson's Disease

The transport deficits seen in PD models parallel those in MYO7A-related disorders:

• Synaptic vesicle cycling: Like the transport defects seen in PD-linked genes (like LRRK2), myosin VIIa dysfunction impairs synaptic vesicle replenishment.
• Lysosomal trafficking: Myosin VIIa participates in lysosomal transport.GBA mutations cause PD, and understanding glycosylation pathways informs lysosomal function in PD.
• Axonal maintenance: Myosin VIIa is essential for maintaining axonal integrity. Its study illuminates why axonal degeneration precedes cell body loss in PD.

Therapeutic Insights from Myosin VIIA Research

The study of MYO7A-related disorders provides therapeutic insights applicable to neurodegeneration:

| Approach | Status | Relevance to Neurodegeneration |
|----------|--------|-------------------------------|
| AAV gene therapy | Clinical trials | Vectors developed for MYO7A can deliver neuroprotective genes |
| Small molecule stabilizers | Preclinical | Could stabilize similar transport proteins in AD/PD |
| Gene editing (CRISPR) | Research | Could correct disease-causing mutations in transport genes |
| Protein replacement | Research | Recombinant myosin VIIa delivery techniques inform similar approaches |

Cross-Linked Mechanisms

• [Axonal Transport](/mechanisms/axonal-transport) — Motor protein function in neurons
• [Usher Syndrome](/diseases/usher-syndrome) — Disease category for MYO7A mutations
• [Retinitis Pigmentosa](/diseases/retinitis-pigmentosa) — Associated retinal degeneration
• [Phototransduction](/mechanisms/phototransduction) — Visual signal processing
• [Cytoskeleton](/mechanisms/cytoskeleton) — Actin-based motor function

Key References

External Resources

• [NCBI Gene: MYO7A](https://www.ncbi.nlm.nih.gov/gene/4647)
• [UniProt: P12883](https://www.uniprot.org/uniprot/P12883)
• [OMIM: 120650](https://omim.org/entry/120650)
• [Retina International: Usher Syndrome](https://www.retina-international.org/usher-syndrome/)
• [Usher Syndrome Coalition](https://www.usher-syndrome.org/)

Pathway Diagram

The following diagram shows the key molecular relationships involving MYO7A — Myosin VIIa discovered through SciDEX knowledge graph analysis: