| Gene Symbol | MYO7A |
| Full Name | Myosin VIIa |
| Chromosome | 11q13.5 |
| NCBI Gene ID | [4647](https://www.ncbi.nlm.nih.gov/gene/4647) |
| OMIM | 120650 |
| Ensembl ID | ENSG00000135624 |
| UniProt ID | [P12883](https://www.uniprot.org/uniprot/P12883) |
| Protein Size | 221 kDa, 2,215 amino acids |
| Associated Diseases | Usher Syndrome 1B, Deafness, Retinitis Pigmentosa |
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. 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.
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. The myosin VIIa protein structure includes:
The tail region of myosin VIIa contains a unique MyTH4-FERM domain structure that mediates binding to various cargo proteins and organelles 3.
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.
In retinal photoreceptor cells, myosin VIIa is essential for the transport of opsin-containing vesicles from the inner segment to the outer segment 5. The outer segment of photoreceptors is a highly specialized cilium where opsin must be properly localized for phototransduction.
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. It is involved in maintaining the proper localization of proteins necessary for mechotransduction.
Myosin VIIa participates in:
Myosin VIIa shows a distinctive expression pattern:
The expression is highest in tissues requiring extensive membrane trafficking and cell polarity maintenance.
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.
| 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.
Some MYO7A mutations cause isolated deafness without retinal involvement, demonstrating the phenotypic variability of MYO7A variants 8.
MYO7A mutations can cause non-syndromic retinitis pigmentosa, where retinal degeneration occurs without hearing loss 9.
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.
In photoreceptors, defective opsin transport leads to accumulation of opsin in the inner segment and progressive degeneration of the outer segment 5. This results in the progressive retinal degeneration characteristic of retinitis pigmentosa.
The underlying mechanism involves defective transport of various cargoes, including:
Adeno-associated virus (AAV)-mediated gene therapy for MYO7A is being developed. Challenges include:
While primarily associated with sensory cells, MYO7A research provides insights into general mechanisms of neurodegeneration:
Myosin VIIa plays a critical role in the transport of cargoes along actin filaments in neuronal cells. In neurons, this motor protein facilitates:
Dysfunction in myosin VIIa-mediated transport provides a model for understanding transport defects in Alzheimer's disease (where APP transport is impaired), Parkinson's disease (where synaptic vesicle trafficking is disrupted), and Huntington's disease (where mutant huntingtin disrupts axonal transport).
Although MYO7A mutations do not cause AD directly, the protein's trafficking mechanisms inform disease understanding:
The transport deficits seen in PD models parallel those in MYO7A-related disorders:
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 |