Everis Clarke 
Role of Extracellular Matrix Molecules during Development of the Inner Ear
Mentor: Dr. Dwayne Simmons

Extracellular matrix (ECM) is a major component of all tissues and forms the glue-like substance between cells.  The ECM plays a major role in the development of the nervous system.  The ECM is made up of various glycoproteins that can have attractive or repulsive interactions on growing neurons.  The role of ECM during inner ear development is largely unknown. Tenascin-C is a glycoprotein of the ECM that acts in-vitro as both a permissive and a nonpermissive substrate for neurite growth.

We used Sprague Dawley rats as a model system to study the role of tenascin-C in inner ear development and function. The inner ear contains an organ for hearing, the cochlea, and organs for balance, the vestibular system. The cochlea, a spiral-shaped cavity in the petrous portion of the temporal bone, contains the nerve endings essential for hearing.  To investigate the role of tenascin-C, we performed three different assays on rat inner ears.  Using RT-PCR, we designed primers that verified tenascin-C mRNA expression in the inner ear.  Using an oligonucleotide microarray specific for ECM, we compared the expression of 126 different ECM molecules.  Using immunocytochemistry and confocal microscopy, we localized tenascin-C during inner ear development.

The microarray data, while preliminary, displayed differences in the expression of some ECM molecules between postnatal day 0 (P0) and P2 rats and between cochlea and vestibular samples.  We localized tenascin-C below hair cell in the organ of Corti.  Furthermore, tenascin-C expression was high in apical (low frequency) regions and lower in basal (high frequency) regions in P3 rat cochlea.

In conclusion, tenascin-C and other ECM molecules are likely to play a role as an axon guidance molecule in the inner ear since its expression coincides with the development of efferent innervation.