Myosin VIIA is

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respon ...

that in humans is encoded by the ''MYO7A''

gene In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...

. Myosin VIIA is a member of the unconventional

myosin Myosins () are a superfamily of motor proteins best known for their roles in muscle contraction and in a wide range of other motility processes in eukaryotes. They are ATP-dependent and responsible for actin-based motility. The first myosin (M ...

superfamily of proteins. Myosins are

actin Actin is a protein family, family of Globular protein, globular multi-functional proteins that form microfilaments in the cytoskeleton, and the thin filaments in myofibril, muscle fibrils. It is found in essentially all Eukaryote, eukaryotic cel ...

binding molecular motors that use the enzymatic conversion of ATP - ADP + inorganic phosphate (Pi) to provide the energy for movement. Myosins are mechanochemical proteins characterized by the presence of a motor domain, an

actin-binding domain Actin-binding proteins (also known as ABPs) are proteins that bind to actin. This may mean ability to bind actin monomers, or polymers, or both. Many actin-binding proteins, including α-actinin, β-spectrin, dystrophin, utrophin and fimbrin, do ...

, a neck domain that interacts with other proteins, and a tail domain that serves as an anchor. Myosin VIIA is an unconventional myosin with the longest tail (1360 aa). The tail is expected to dimerize, resulting in a two-headed molecule. Unconventional myosins have diverse functions in

eukaryotic Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bact ...

cells and are primarily thought to be involved in the movement or linkage of intra-cellular membranes and

organelles In cell biology, an organelle is a specialized subunit, usually within a cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts of cells, as organs are to the body, hence ''organelle,'' th ...

to the actin cytoskeleton via interactions mediated by their highly divergent tail domains. MYO7A is expressed in a number of mammalian tissues, including

testis A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primarily testoster ...

kidney The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; bloo ...

, lung, inner ear,

retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then ...

and the ciliated epithelium of the nasal

mucosa A mucous membrane or mucosa is a membrane that lines various cavities in the body of an organism and covers the surface of internal organs. It consists of one or more layers of epithelial cells overlying a layer of loose connective tissue. It is ...

Clinical significance

Mutations in the ''MYO7A'' gene cause the

Usher syndrome Usher syndrome, also known as Hallgren syndrome, Usher–Hallgren syndrome, retinitis pigmentosa–dysacusis syndrome or dystrophia retinae dysacusis syndrome, is a rare genetic disorder caused by a mutation in any one of at least 11 genes result ...

type 1B, a combined deafness/blindness disorder. Affected individuals are typically profoundly deaf at birth and then undergo progressive retinal degeneration.

Model organisms

Model organisms have been used in the study of MYO7A function. A spontaneous mutant mouse line, called ''Myo7a^sh1-6J'' was generated. Male and female animals underwent a standardized

phenotypic screen In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological prop ...

to determine the effects of deletion. Twenty three tests were carried out on

mutant In biology, and especially in genetics, a mutant is an organism or a new genetic character arising or resulting from an instance of mutation, which is generally an alteration of the DNA sequence of the genome or chromosome of an organism. It ...

mice and ten significant abnormalities were observed. Male

homozygous Zygosity (the noun, zygote, is from the Greek "yoked," from "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism. Mo ...

mice displayed a decreased body weight, a decrease in body fat, improved

glucose tolerance Prediabetes is a component of the metabolic syndrome and is characterized by elevated blood sugar levels that fall below the threshold to diagnose diabetes mellitus. It usually does not cause symptoms but people with prediabetes often have obesit ...

and abnormal

pelvic girdle The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton). The ...

bone morphology. Homozygous mutant mice of both sex displayed various abnormalities in a modified

SHIRPA SHIRPA is a standardized set of experimental procedures used by scientists to characterize the phenotype of genetically modified laboratory mice. The protocols are designed to test muscle function, cerebellar function, sensory function and neuropsy ...

test, including abnormal gait, tail dragging and an absence of

pinna reflex The posterior auricular muscle is a muscle behind the auricle of the outer ear. It arises from the mastoid part of the temporal bone, and inserts into the lower part of the cranial surface of the auricle of the outer ear. It draws the auricle ...

, a decrease in

grip strength Grip strength is the force applied by the hand to pull on or suspend from objects and is a specific part of hand strength. Optimum-sized objects permit the hand to wrap around a cylindrical shape with a diameter from one to three inches. Stair rai ...

, an increased thermal

pain threshold The threshold of pain or pain threshold is the point along a curve of increasing perception of a stimulus at which pain begins to be felt. It is an entirely subjective phenomenon. A distinction must be maintained between the stimulus (an externa ...

, severe

hearing impairment Hearing loss is a partial or total inability to hear. Hearing loss may be present at birth or acquired at any time afterwards. Hearing loss may occur in one or both ears. In children, hearing problems can affect the ability to acquire spoken ...

and a number of abnormal

indirect calorimetry Indirect calorimetry calculates heat that living organisms produce by measuring either their production of carbon dioxide and nitrogen waste (frequently ammonia in aquatic organisms, or urea in terrestrial ones), or from their consumption of oxyg ...

and

clinical chemistry Clinical chemistry (also known as chemical pathology, clinical biochemistry or medical biochemistry) is the area of chemistry that is generally concerned with analysis of bodily fluids for diagnostic and therapeutic purposes. It is an appli ...

parameters.

References

External links

GeneReviews/NCBI/NIH/UW entry on Usher Syndrome Type I
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Clinical significance

Model organisms

References

External links

Further reading