CALEB binds via its acidic stretch to the fibrinogen-like domain of tenascin-C or tenascin-R and its expression is dynamically regulated after optic nerve lesion

Recently, we described a novel chick neural transmembrane glycoprotein, whi ch interacts with the extracellular matrix proteins tenascin-C and tenascin -R This protein, termed CALEB, contains an epidermal growth factor-like dom ain and appears to be a novel member of the epidermal growth factor family of growth and differentiation factors. Here we analyze the interaction betw een CALEB and tenascin-C as well as tenascin-ft in more detail, and we demo nstrate that the central acidic peptide segment of CALEB is necessary to me diate this binding. The fibrinogen-like globe within tenascin-C or -R enabl es both proteins to bind to CALEB, We show that two isoforms of CALEB in ch ick and rodents exist that differed in their cytoplasmic segments. To begin to understand the in vivo function of CALEB and since in vitro antibody pe rturbation experiments indicated that CALEB might be important for neurite formation, we analyzed the expression pattern of the rat homolog of CALEB d uring development of retinal ganglion cells, after optic nerve lesion and d uring graft-assisted retinal ganglion cell axon regeneration by in situ hyb ridization. These investigations demonstrate that CALEB mRNA is dynamically regulated after optic nerve lesion and that this mRNA is expressed in most developing and in one-third of the few regenerating (GAP-43 expressing) re tinal ganglion cells.