Abstract
Intermediate cells of the stria vascularis are neural crest derived melanocytes. They are essential for the establishment of the endocochlear potential in the inner ear, which allows mechanosensory hair cells to transduce sound into nerve impulses. Despite their importance for normal hearing, how these cells develop and migrate to their position in the lateral wall of the cochlea has not been studied. We find that as early as E10.5 some Schwann cell precursors in the VIIIth ganglion begin to express melanocyte specific markers while neural crest derived melanoblasts migrate into the otic vesicle. Intermediate cells of both melanoblast and Schwann cell precursor origin ingress into the lateral wall of the cochlea starting at around E15.5 following a basal to apical gradient during embryonic development, and continue to proliferate postnatally.
Highlights
The stria vascularis is a specialized epithelium that actively pumps potassium into the scala media to generate the positive endocochlear potential essential for sensory hair cells to transduce sound vibrations into action potentials (Hudspeth, 1989; Steel and Barkway, 1989; Takeuchi et al, 2000; Hibino et al, 2010)
To understand the precise development of intermediate cells in the cochlea, we took advantage of genetic lineage tracing using a Wnt1-Cre2 crossed to Ai3-YFP mouse reporter line to label neural crest cells just before they undergo their epithelial-to-mesenchymal transition and follow their development in the inner ear (Figure 1)
As the cochlea elongates we observe more neural crest cells lining outside the cochlear duct at the site of the future lateral wall, up until E14.5
Summary
The stria vascularis is a specialized epithelium that actively pumps potassium into the scala media to generate the positive endocochlear potential essential for sensory hair cells to transduce sound vibrations into action potentials (Hudspeth, 1989; Steel and Barkway, 1989; Takeuchi et al, 2000; Hibino et al, 2010). This specialized epithelium located on the lateral wall of the cochlea is composed of three different cell types: marginal cells, intermediate cells, and basal cells, each with a distinct embryonic origin. These dark cells express the same channels as marginal cells of the stria vascularis and are in close associations with neural crest derived pigmented cells underneath that are thought to regulate calcium homeostasis (Ciuman, 2009)
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