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Otic vesicle

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Otic vesicle
Gray40.png
Embryo between eighteen and twenty-one days
Formation of the Otic Vesicle.png
General formation of the otic vesicle
Details
Precursorotic placode, auditory pit or otic pit, otic cup,
Gives rise toMembranous labyrinth of the inner ear
Identifiers
Latinvesicula otica
TEvesicle_by_E5.15.1.0.0.0.4 E5.15.1.0.0.0.4
Anatomical terminology

Otic vesicle, or auditory vesicle, consists of either of the two sac-like invaginations formed and subsequently closed off during embryonic development. It is part of the neural ectoderm, which will develop into the membranous labyrinth of the inner ear. This labyrinth is a continuous epithelium, giving rise to the vestibular system and auditory components of the inner ear.[1] During the earlier stages of embryogenesis, the otic placode invaginates to produce the otic cup. Thereafter, the otic cup closes off, creating the otic vesicle. Once formed, the otic vesicle will reside next to the neural tube medially, and on the lateral side will be paraxial mesoderm. Neural crest cells will migrate rostral and caudal to the placode.

The general sequence in formation of the otic vesicle is relatively conserved across vertebrates, although there is much variation in timing and stages.[2] Patterning during morphogenesis into the distinctive inner ear structures is determined by homeobox transcription factors including PAX2, DLX5 and DLX6, with the former specifying for ventral otic vesicle derived auditory structures and the latter two specifying for dorsal vestibular structures.

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Ectoderm

Ectoderm

The ectoderm is one of the three primary germ layers formed in early embryonic development. It is the outermost layer, and is superficial to the mesoderm and endoderm. It emerges and originates from the outer layer of germ cells. The word ectoderm comes from the Greek ektos meaning "outside", and derma meaning "skin".

Epithelium

Epithelium

Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellular matrix. Epithelial tissues line the outer surfaces of organs and blood vessels throughout the body, as well as the inner surfaces of cavities in many internal organs. An example is the epidermis, the outermost layer of the skin.

Vestibular system

Vestibular system

The vestibular system, in vertebrates, is a sensory system that creates the sense of balance and spatial orientation for the purpose of coordinating movement with balance. Together with the cochlea, a part of the auditory system, it constitutes the labyrinth of the inner ear in most mammals.

Auditory system

Auditory system

The auditory system is the sensory system for the sense of hearing. It includes both the sensory organs and the auditory parts of the sensory system.

Otic placode

Otic placode

In embryology, the otic placode is a thickening of the ectoderm on the outer surface of a developing embryo from which the ear develops. The ear, including both the vestibular system and the auditory system, develops from the otic placode beginning the third week of development. During the fourth week, the otic placode invaginates into the mesenchyme adjacent to the rhombencephalon to form the otic pit, which then pinches off from the surface ectoderm to form the otic vesicle.

Paraxial mesoderm

Paraxial mesoderm

Paraxial mesoderm, also known as presomitic or somitic mesoderm is the area of mesoderm in the neurulating embryo that flanks and forms simultaneously with the neural tube. The cells of this region give rise to somites, blocks of tissue running along both sides of the neural tube, which form muscle and the tissues of the back, including connective tissue and the dermis.

Vertebrate

Vertebrate

Vertebrates comprise all animal taxa within the subphylum Vertebrata, including all mammals, birds, reptiles, amphibians and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with currently about 69,963 species described. Vertebrates comprise such groups as the following:jawless fish, which include hagfish and lampreys jawed vertebrates, which include: cartilaginous fish bony vertebrates, which include: ray-fins lobe-fins, which include: coelacanths and lungfish tetrapods

Homeobox

Homeobox

A homeobox is a DNA sequence, around 180 base pairs long, that regulates large-scale anatomical features in the early stages of embryonic development. Mutations in a homeobox may change large-scale anatomical features of the full-grown organism.

PAX2

PAX2

Paired box gene 2, also known as Pax-2, is a protein which in humans is encoded by the PAX2 gene.

DLX5

DLX5

Homeobox protein DLX-5 is a protein that in humans is encoded by the distal-less homeobox 5 gene, or DLX5 gene. DLX5 is a member of DLX gene family.

DLX6

DLX6

Homeobox protein DLX-6 is a protein that in humans is encoded by the DLX6 gene.

Development

The otic vesicle is derived from the cranial placode.[3] The early otic vesicle is characterized as having broad competence and can be subdivided into sensory, non-sensory, and neurogenic components. Sensory epithelial cells and neurons are derived from the proneurosensory domain. This domain can be further sub-categorized into the neurogenic sub-domain and prosensory sub-domain. Prosensory sub-domain eventually gives rise to the support cells and hair cells while the neurogenic sub-domain gives rise to the auditory neuron and vestibular neuron.

The middle part of the otic vesicle develops into the ductus and saccus endolymphaticus.[4] The anterior end of the otic vesicle gradually elongates as a tube and coils upon itself forming the beginnings of the cochlear duct. The vestibular extremity subsequently constricts to form the canalis reuniens. The central part of the otic vesicle represents the membranous vestibule, and is subdivided by a constriction into a smaller ventral part, the saccule, and a larger dorsal and posterior part, the utricle. The dorsal component of the inner ear also consists of what will become the semicircular canals. The utricle and saccule communicate with each other by means of a Y-shaped canal.

Gene signaling

The FGF, Bmp, Wnt and Pax genes are likely to be involved in otic induction.[5] FGF and BMP signals help control patterning in the early otic vesicle. Fgf3 and Fgf10 are suggested to play a role in otic induction in mice, as were Msx genes suggested to play a role in otic vesicle formation in chicks. Pax8 is expressed during the entirety of otic vesicle formation. Other genes found in the otic vesicle across species that may play a role in patterning include Hmx, Fox, Dlx, and Gbx genes.

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Cochlear duct

Cochlear duct

The cochlear duct is an endolymph filled cavity inside the cochlea, located between the tympanic duct and the vestibular duct, separated by the basilar membrane and the vestibular membrane respectively. The cochlear duct houses the organ of Corti.

Saccule

Saccule

The saccule is a bed of sensory cells in the inner ear. It translates head movements into neural impulses for the brain to interpret. The saccule detects linear accelerations and head tilts in the vertical plane. When the head moves vertically, the sensory cells of the saccule are disturbed and the neurons connected to them begin transmitting impulses to the brain. These impulses travel along the vestibular portion of the eighth cranial nerve to the vestibular nuclei in the brainstem.

Utricle (ear)

Utricle (ear)

The utricle and saccule are the two otolith organs in the vertebrate inner ear. They are part of the balancing system in the vestibule of the bony labyrinth. They use small stones and a viscous fluid to stimulate hair cells to detect motion and orientation. The utricle detects linear accelerations and head-tilts in the horizontal plane. The word utricle comes from Latin uter 'leather bag'.

Semicircular canals

Semicircular canals

The semicircular canals or semicircular ducts are three semicircular, interconnected tubes located in the innermost part of each ear, the inner ear. The three canals are the horizontal, superior and posterior semicircular canals.

Fibroblast growth factor

Fibroblast growth factor

Fibroblast growth factors (FGF) are a family of cell signalling proteins produced by macrophages; they are involved in a wide variety of processes, most notably as crucial elements for normal development in animal cells. Any irregularities in their function lead to a range of developmental defects. These growth factors typically act as systemic or locally circulating molecules of extracellular origin that activate cell surface receptors. A defining property of FGFs is that they bind to heparin and to heparan sulfate. Thus, some are sequestered in the extracellular matrix of tissues that contains heparan sulfate proteoglycans and are released locally upon injury or tissue remodeling.

Bone morphogenetic protein

Bone morphogenetic protein

Bone morphogenetic proteins (BMPs) are a group of growth factors also known as cytokines and as metabologens. Originally discovered by their ability to induce the formation of bone and cartilage, BMPs are now considered to constitute a group of pivotal morphogenetic signals, orchestrating tissue architecture throughout the body. The important functioning of BMP signals in physiology is emphasized by the multitude of roles for dysregulated BMP signalling in pathological processes. Cancerous disease often involves misregulation of the BMP signalling system. Absence of BMP signalling is, for instance, an important factor in the progression of colon cancer, and conversely, overactivation of BMP signalling following reflux-induced esophagitis provokes Barrett's esophagus and is thus instrumental in the development of esophageal adenocarcinoma.

Wnt signaling pathway

Wnt signaling pathway

The Wnt signaling pathways are a group of signal transduction pathways which begin with proteins that pass signals into a cell through cell surface receptors. The name Wnt is a portmanteau created from the names Wingless and Int-1. Wnt signaling pathways use either nearby cell-cell communication (paracrine) or same-cell communication (autocrine). They are highly evolutionarily conserved in animals, which means they are similar across animal species from fruit flies to humans.

Pax genes

Pax genes

In evolutionary developmental biology, Paired box (Pax) genes are a family of genes coding for tissue specific transcription factors containing an N-terminal paired domain and usually a partial, or in the case of four family members, a complete homeodomain to the C-terminus. An octapeptide as well as a Pro-Ser-Thr-rich C terminus may also be present. Pax proteins are important in early animal development for the specification of specific tissues, as well as during epimorphic limb regeneration in animals capable of such.

Other animals

Formation of the otic vesicle has been studied extensively in developmental model organisms including chicken, Xenopus, zebrafish, axolotl, and mouse.[6] The transition from the otic placode to the otic vesicle occurs during the 19th somite stage in Zebrafish, Xenopus, and chick. In chick, invagination of the otic placode occurs passively due to the movements of the surrounding placode. The otic placode in zebrafish, on the other hand, occurs by cavitation; the ectodermal placode condenses and forms an ovoid ball directly below the embryo surface. Otic vesicle formation occurs later, during the 25-30 somite stage in mice.

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Model organism

Model organism

A model organism is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the model organism will provide insight into the workings of other organisms. Model organisms are widely used to research human disease when human experimentation would be unfeasible or unethical. This strategy is made possible by the common descent of all living organisms, and the conservation of metabolic and developmental pathways and genetic material over the course of evolution.

Chicken

Chicken

The chicken is a domesticated junglefowl species, with attributes of wild species such as the grey and the Ceylon junglefowl that are originally from Southeast Asia. Rooster and cock are terms for adult male birds, and a younger male may be called a cockerel. A male that has been castrated is a capon. An adult female bird is called a hen, and a sexually immature female is called a pullet. Humans keep chickens primarily as a source of food or as pets. Traditionally they were also bred for cockfighting, which is still practiced in some places. Chickens domesticated for meat are broilers and for eggs are layers.

Xenopus

Xenopus

Xenopus is a genus of highly aquatic frogs native to sub-Saharan Africa. Twenty species are currently described within it. The two best-known species of this genus are Xenopus laevis and Xenopus tropicalis, which are commonly studied as model organisms for developmental biology, cell biology, toxicology, neuroscience and for modelling human disease and birth defects.

Zebrafish

Zebrafish

The zebrafish is a freshwater fish belonging to the minnow family (Cyprinidae) of the order Cypriniformes. Native to South Asia, it is a popular aquarium fish, frequently sold under the trade name zebra danio. It is also found in private ponds.

Axolotl

Axolotl

The axolotl is a paedomorphic salamander closely related to the tiger salamander. It is unusual among amphibians in that it reaches adulthood without undergoing metamorphosis. Instead of taking to the land, adults remain aquatic and gilled. The species was originally found in several lakes underlying what is now Mexico City, such as Lake Xochimilco and Lake Chalco. These lakes were drained by Spanish settlers after the conquest of the Aztec Empire, leading to the destruction of much of the axolotl’s natural habitat.

Mouse

Mouse

A mouse is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse. Mice are also popular as pets. In some places, certain kinds of field mice are locally common. They are known to invade homes for food and shelter.

Somite

Somite

The somites are a set of bilaterally paired blocks of paraxial mesoderm that form in the embryonic stage of somitogenesis, along the head-to-tail axis in segmented animals. In vertebrates, somites subdivide into the dermatomes, myotomes, sclerotomes and syndetomes that give rise to the vertebrae of the vertebral column, rib cage, part of the occipital bone, skeletal muscle, cartilage, tendons, and skin.

Additional images

  • Lateral views of membranous labyrinth and acoustic complex. X 25 dia.

    Lateral views of membranous labyrinth and acoustic complex. X 25 dia.

  • Median views of membranous labyrinth and acoustic complex in human embryos. X 25 dia.

    Median views of membranous labyrinth and acoustic complex in human embryos. X 25 dia.

Source: "Otic vesicle", Wikipedia, Wikimedia Foundation, (2022, October 22nd), https://en.wikipedia.org/wiki/Otic_vesicle.

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Further Reading

Inner ear

Sense of balance

Vestibulocochlear nerve

Semicircular canals

Utricle (ear)

Saccule

Vestibular system

Olfactory epithelium

Ear

Stereocilia (inner ear)

Membranous labyrinth

Eye development

Crista ampullaris

Vestibule of the ear

DLX5

Michel aplasia
References
  1. ^ Freyer L, Aggarwal V, Morrow BE (December 2011). "Dual embryonic origin of the mammalian otic vesicle forming the inner ear". Development. 138 (24): 5403–14. doi:10.1242/dev.069849. PMC 3222214. PMID 22110056.
  2. ^ Park BY, Saint-Jeannet JP (December 2008). "Hindbrain-derived Wnt and Fgf signals cooperate to specify the otic placode in Xenopus". Developmental Biology. 324 (1): 108–21. doi:10.1016/j.ydbio.2008.09.009. PMC 2605947. PMID 18831968.
  3. ^ Appler JM, Goodrich LV (April 2011). "Connecting the ear to the brain: Molecular mechanisms of auditory circuit assembly". Progress in Neurobiology. 93 (4): 488–508. doi:10.1016/j.pneurobio.2011.01.004. PMC 3078955. PMID 21232575.
  4. ^ Brigande JV, Kiernan AE, Gao X, Iten LE, Fekete DM (October 2000). "Molecular genetics of pattern formation in the inner ear: do compartment boundaries play a role?". Proceedings of the National Academy of Sciences of the United States of America. 97 (22): 11700–6. doi:10.1073/pnas.97.22.11700. PMC 34338. PMID 11050198.
  5. ^ Chatterjee S, Kraus P, Lufkin T (July 2010). "A symphony of inner ear developmental control genes". BMC Genetics. 11 (1): 68. doi:10.1186/1471-2156-11-68. PMC 2915946. PMID 20637105.
  6. ^ Noramly S, Grainger RM (November 2002). "Determination of the embryonic inner ear". Journal of Neurobiology. 53 (2): 100–28. doi:10.1002/neu.10131. PMID 12382270.
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