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
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 constitut ...
and
auditory components of the inner ear. 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
Rostral may refer to:
Anatomy
* Rostral (anatomical term), situated toward the oral or nasal region
* Rostral bone, in ceratopsian dinosaurs
* Rostral organ, of certain fish
* Rostral scale
The rostral scale, or rostral, in snakes and other sc ...
and
caudal
Caudal may refer to:
Anatomy
* Caudal (anatomical term) (from Latin ''cauda''; tail), used to describe how close something is to the trailing end of an organism
* Caudal artery, the portion of the dorsal aorta of a vertebrate that passes into the ...
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. Patterning during morphogenesis into the distinctive inner ear structures is determined by
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. For instance, mutations in a homeobox may change large-scale anatomical features of the full-g ...
transcription factors
In molecular biology, a transcription factor (TF) (or sequence-specific DNA-binding factor) is a protein that controls the rate of transcription of genetic information from DNA to messenger RNA, by binding to a specific DNA sequence. The fun ...
including
PAX2
Paired box gene 2, also known as Pax-2, is a protein which in humans is encoded by the ''PAX2'' gene.
Function
The Pax Genes, or Paired-Box Containing Genes, play important roles in the development and proliferation of multiple cell lines, d ...
,
DLX5 and
DLX6
Homeobox protein DLX-6 is a protein that in humans is encoded by the ''DLX6'' gene.
This gene encodes a member of a homeobox transcription factor gene family similar to the Drosophila
''Drosophila'' () is a genus of flies, belonging to the ...
, with the former specifying for ventral otic vesicle derived auditory structures and the latter two specifying for dorsal vestibular structures.
Development
The otic vesicle is derived from the cranial placode. 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. The anterior end of the otic vesicle gradually elongates as a tube and coils upon itself forming the beginnings of the
cochlear duct
The cochlear duct (bounded by the scala media) 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 (Reissner's membrane) resp ...
. 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
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 verticall ...
, 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 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.
Structure
The ...
. 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. 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.
Other animals
Formation of the otic vesicle has been studied extensively in developmental
model organisms including
chicken,
Xenopus
''Xenopus'' () (Gk., ξενος, ''xenos''=strange, πους, ''pous''=foot, commonly known as the clawed frog) is a genus of highly aquatic frogs native to sub-Saharan Africa. Twenty species are currently described within it. The two best-known ...
,
zebrafish
The zebrafish (''Danio rerio'') 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 (and thus often ...
,
axolotl
The axolotl (; from nci, āxōlōtl ), ''Ambystoma mexicanum'', is a paedomorphic salamander closely related to the tiger salamander. Axolotls are unusual among amphibians in that they reach adulthood without undergoing metamorphosis. Instea ...
, and
mouse.
The transition from the otic placode to the otic vesicle occurs during the 19th
somite
The somites (outdated term: primitive segments) 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 in ...
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.
Additional images
File:Gray900.png, Lateral views of membranous labyrinth and acoustic complex. X 25 dia.
File:Gray901.png, Median views of membranous labyrinth and acoustic complex in human embryos. X 25 dia.
References
{{Authority control
Embryology of nervous system