Promotion of neurite outgrowth and axon guidance in spiral ganglion cells by netrin-1.
OBJECTIVE
To identify the expression of netrin-1, a diffusible chemoattractive molecule, and its receptor, deleted in colorectal carcinoma (DCC), in the developmentally mature inner ear, and to determine its effects on axon length and guidance in cultured auditory neurons.


METHODS
Messenger RNA (mRNA) and protein expression of netrin-1 and DCC were identified in the organ of Corti and spiral ganglion cells using reverse transcription-polymerase chain reaction (RT-PCR) and fluorescence immunohistochemical analysis. In vitro experiments examined the effects of exogenous netrin-1 on spiral ganglion cell axon length. Auditory neurons were cocultured with a cell line secreting netrin-1 to determine the effect on direction of axon extension.


METHODS
Young C57 mice and posthatched white leghorn chicks.


RESULTS
Netrin-1 and DCC mRNA expression were found in the mouse organ of Corti and spiral ganglion cells by RT-PCR. Application of exogenous netrin-1 led to a dosage-dependent increase in neurite length in cultured spiral ganglion cells. Chick acoustic ganglion cells cocultured with netrin-1-secreting cells demonstrated statistically significant preferential extension toward the source of netrin-1 (P = .04).


CONCLUSIONS
Netrin-1 and DCC are expressed in the organ of Corti and spiral ganglion cells of developmentally mature mice. Exogenous netrin-1 promotes dosage-dependent neurite growth in vitro. Mature auditory neurons preferentially direct neurite extension toward netrin-1 released in culture. These findings may lead to the development of strategies to optimize the interface between electrode arrays and spiral ganglion cells, resulting in improved cochlear implant performance.
Lee
Kenneth H
KH
Department of Otolaryngology-Head and Neck Surgery, University of Texas Southwestern Medical Center at Dallas, Children's Medical Center Dallas, 5323 Harry Hines Blvd, Dallas, TX 75390-9035, USA. kenneth.lee@utsouthwestern.edu
Warchol
Mark E
ME
D000818:Animals; D001369:Axons / Q000187:drug effects*; D002478:Cells, Cultured; D002645:Chickens; D018920:Coculture Techniques; D000075389:DCC Receptor; D007758:Ear, Inner / Q000166:cytology / Q000378:metabolism*; D007150:Immunohistochemistry; D051379:Mice; D008810:Mice, Inbred C57BL; D009414:Nerve Growth Factors / Q000378:metabolism* / Q000494:pharmacology*; D000075388:Netrin-1; D016501:Neurites / Q000187:drug effects; D009925:Organ of Corti / Q000378:metabolism; D012333:RNA, Messenger; D011956:Receptors, Cell Surface / Q000378:metabolism*; D013136:Spiral Ganglion / Q000166:cytology* / Q000187:drug effects; D025521:Tumor Suppressor Proteins / Q000378:metabolism* / Q000494:pharmacology*
D000075389:DCC Receptor; C501910:Dcc protein, mouse; D009414:Nerve Growth Factors; C000617353:Ntn1 protein, mouse; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D025521:Tumor Suppressor Proteins; D000075388:Netrin-1