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The development of hair cells in the embryonic chick's basilar papilla
Insights
Embryonic chick hair cells differentiate into tall and short types by day 11, developing distinct structures and neural connections. This study details the developmental timeline of these crucial auditory sensory cells.
Area of Science:
- Developmental Biology
- Neuroscience
- Otolaryngology
Background:
- Hair cells in the embryonic chick undergo significant morphological changes during development.
- Understanding hair cell differentiation is crucial for auditory system research.
Purpose of the Study:
- To describe the developmental timeline of chick hair cell differentiation.
- To characterize the morphological and synaptic development of hair cells and supporting cells.
Main Methods:
- Light microscopy observation of embryonic chick inner ear development.
- Analysis of hair cell morphology, nuclear positioning, and synaptic formation.
Main Results:
- Hair cell differentiation into tall hair cells (THCs) and short hair cells (SHCs) is evident by day 11.
- Stereocilia and kinocilia develop by day 7, resembling the adult pattern by day 13.
- Synaptic connections between sensory neurons and hair cells form by day 10, with efferent synapses identified by day 19.
- Supporting cells transform into flask-shaped cells and may contribute to the tectorial membrane.
Conclusions:
- The embryonic chick provides a model for studying hair cell development and maturation.
- Distinct morphological and synaptic features of hair cells emerge progressively during development.
- Supporting cell transformation suggests a role in extracellular matrix production for the tectorial membrane.
Abstract:
During the 7th to 21st (hatching) days, hair cells of the embeyonic chick transform from an undifferentiated epithelium into cylindrically-shaped tall hair cells (THCs), pitcher-shaped short hair cells (SHCs), or intermediate hair cells that share structural characteristics of the first two. By the 11th day hair cell types are unambiguous. "Hairs" (stereocilia and a kinocilium) were first identified on the 7th day and resembled the adult pattern the 13th. The nucleus occupies relatively less volume as hair cells increase in size, becoming positioned centrally in THCs and basally in SHCs. Nucleoli, which are prominent throughout development, remain conspicuous even in newly hatched chicks. The cuticular cone begins to form the 11th day. By the 10th day, sensory nerve endings synapse on the bases of the HCs, which by the 11th day develop synaptic bars. Although efferent neurites were in evidence as early as the 11th day, synaptic contacts and their cisterns were identified by the 19th day but may form earlier. Supporting cells transform from cylindrically to flask-shaped cells with constricted necks and may secrete at least a portion of the tectorial membrane.