Organ Regeneration Based on Developmental Biology

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semicircular canals and the maculae of the utricle and saccule (Fig. 4.1). Key to the
function of both the auditory and vestibular organs is the mechanosensitive hair cell.
There are four types of hair cells: inner and outer cochlear hair cells and type I and
type II vestibular hair cells. The common feature of all hair cells is the presence of
a hair bundle, an organized array of stereocilia, and a kinocilium, on the apical sur-
face. Mechanical stimuli from sound or positional changes cause deflection of hair
bundles, which is transduced into neural impulses through synaptic contacts at the
basal side of the hair cells (Breneman et al. 2009 ). This electrical signal is transmit-
ted to the brain through primary afferent neurons. In addition to sensory hair cells
and neural components, the inner ear also contains a diverse group of supporting
cells. Supporting cells facilitate ion homeostasis and structural support and have a
potential to help repair injury to sensory hair cells.
The second key to the mammalian inner ear is the inability of mature hair cells
to regenerate when damaged. Thus, inner ear injury generally causes permanent
hearing and/or equilibrium dysfunction. There is a wide spectrum of etiologies
which compromise hair cell function and cause inner ear pathology including con-
genital syndromes, ototoxic medications, noise-induced trauma, and aging. Thus,
establishment of an accurate in  vitro model will allow effective investigation of
various gene and pharmacologic therapies for hearing loss and vestibular dysfunc-
tion (Park 2015 ). Other potential, long-term applications include cell-based
therapies for deafness; for example, introduction of partially differentiated human
fetal auditory stem cells into the cochlea of a gerbil model of neuropathic deafness
demonstrated implantation and survival of transplanted cells in addition to improve-
ments in auditory function (Chen et al. 2012 ).

Hair cell

Supporting

cells

Afferent neuron Efferent neuron

Cochlea

Vestibular

apparatus

Hair bundle

Fig. 4.1 Schematic drawing of the inner ear structure and sensory cells within the inner ear

A.N. Elghouche et al.