CEK5, A TYROSINE KINASE OF THE EPH SUBCLASS, IS ACTIVATED DURING NEURAL RETINA DIFFERENTIATION

The expression of Cek5, a receptor-type tyrosine kinase of the Eph sub class, and its variant form Cek5(+) were examined in the chick neural retina during development. Cek5 is present at high levels at all stage s of retinal development examined, while Cek5(+) is most abundant duri ng differentiation. Cek5 mRNA expression and immunoreactivity are even ly distributed in the undifferentiated retina. With differentiation, C ek5 becomes concentrated in the inner and outer plexiform layers. Whil e only moderate changes in Cek5 protein expression are observed throug hout retinal development, Cek5 phosphorylation on tyrosine in vivo is dramatically increased during differentiation. This suggests that the Cek5 ligand is expressed at high levels and causes Cek5 activation. Th us, Cek5 is likely to play an active role in retinal morphogenesis, pa rticularly during the establishment of interneuronal contacts. (C) 199 4 Academic Press, Inc.