EphA4 provides repulsive signals to developing cochlear ganglion neurites mediated through ephrin-B2 and -B3.
The ephrins and Eph receptors make up two large families of bi-directional signaling molecules that are known to play a role in the development of the nervous system. Recently, expression of EphA4 in the developing cochlea was shown, with strong expression in cells lining the osseous spiral lamina (OSL) through which afferent dendrites must pass to reach the organ of Corti (OC). It was also demonstrated that ephrin-B2 and -B3, both of which are known to interact with EphA4, are expressed by spiral ganglion (SG) neurons. To investigate the functional role of EphA4 in the development of inner ear neurons, neonatal rat SG explants were cultured for 72 hours on uniformly coated surfaces or near stripes of EphA4/IgG-Fc-chimera. Control explants were cultured on or near IgG-Fc and EphA1/IgG-Fc-chimera. To assess the roles of ephrin-B2 and -B3 in EphA4 signaling, SG explants were cultured with or without anti-ephrin-B2 and/or -B3 blocking antibodies. Growth patterns of SG neurites at the border of EphA4 receptor stripes showed repulsion, characterized by turning, stopping and/or reversal. In the case of IgG-Fc and EphA1, the neurites grew straight onto the stripes. Treatment with either anti-ephrin-B2 or -B3 blocking antibodies significantly reduced the repulsive effect of an EphA4 stripe. Moreover, when both antibodies were used together, neurites crossed onto EphA4 stripes with no evidence of repulsion. The results suggest that EphA4 provides repulsive signals to SG neurites in the developing cochlea, and that ephrin-B2 and -B3 together mediate this response.
Brors
Dominik
D
Department of Surgery, Division Otolaryngology and Neurosciences, University of California, San Diego School of Medicine and Veterans Administration Medical Center, La Jolla 92093, USA.
Bodmer
Daniel
D
Pak
Kwang
K
Aletsee
Christoph
C
Schäfers
Maria
M
Dazert
Stefan
S
Ryan
Allen F
AF
D000818:Animals; D000831:Animals, Newborn; D000906:Antibodies / Q000494:pharmacology; D002450:Cell Communication / Q000187:drug effects / Q000502:physiology; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology*; D036388:Ephrin-B2 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D036389:Ephrin-B3 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D020439:Growth Cones / Q000378:metabolism / Q000648:ultrastructure; D016501:Neurites / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D009475:Neurons, Afferent / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009924:Organ Culture Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D036122:Receptor, EphA4 / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013136:Spiral Ganglion / Q000166:cytology / Q000254:growth & development* / Q000378:metabolism
D000906:Antibodies; D036388:Ephrin-B2; D036389:Ephrin-B3; D011993:Recombinant Fusion Proteins; D036122:Receptor, EphA4