Ephexin is downstream of EphA3-regulated-EphA4 forward signaling in the retinotectal mapping formation

MEDORI, MARA; FIORE, LUCIANO; DI SIERVI, NICOLÁS; OLMOS CARREÑO, CINDY; CAVALLERO, GUSTAVO; DI NAPOLI JENNIFER; MALLOU, FLORENCIA; SANCHEZ, VIVIANA; CARRI, NÉSTOR GABRIEL; SCICOLONE, GABRIEL

Huerta Grande,Córdoba.

Congreso; XXVIII Congreso Anual de la Sociedad Argentina de Investigación en Neurociencias; 2013

Sociedad Argentina de Investigación en Neurociencias

EPHEXIN IS DOWNSTREAM OF EPHA3-REGULATED-EPHA4 FORWARD SIGNALING IN THE RETINOTECTAL MAPPING FORMATION.Eph/ephrins are expressed in complementary gradients in the retina and the tectum guiding retinotectal projections. Previously we showed that tectal EphA3 stimulates axon growth of nasal retinal ganglion cells (RGC) toward the caudal tectum preventing them from branching in the rostral tectum. The aim of this work was to study the molecular pathway which mediates the EphA3 action. We postulated that activation of axonal EphA4 rises the level of ephexin phosphorylation and decreases axon growth; tectal EphA3 increases axon growth by reducing axonal EphA4 and ephexin phosphorylation by competing with EphA4 for axonal ephrin-As. We used cultures of retinal explants from chicken embryos treated with EphA3-Fc, Fc, or KYL (EphA4 inhibitor). We analyzed axon length and realized immunocytochemistry and Western blot. We showed that: a) Axonal response to EphA3 is associated to ephrin-A expression, EphA4 phosphorylation and the pattern of phosphorylated ephexin. b) The EphA3 decreases the EphA4 and phexin phosphorylation. c) Inhibition of EphA4 signaling recapitulates the effects of EphA3 on RGC axon growth and branching. The results support the idea of a novel molecular mechanism whereby tectal EphA3 increases axon growth toward the caudal tectum and inhibits axon branching in the rostral tectum by decreasing ephrin-A-mediated-EphA4 forward signaling. Furthermore, it is suggested that regulation of ephexin phosphorylation is downstream of EphA4 activation. Supported by CONICET-UBA.