DEVELOPMENTAL LOCALIZATION OF RETINA COGNIN SYNTHESIS BY IN-SITU HYBRIDIZATION

Retina cognin (R-cognin) is a 50 kDa protein involved in cell recognit ion and neuronal differentiation during development of the embryonic c hick retina. Initial characterization of a partial cDNA encoding R-cog nin revealed a striking similarity to the cDNA encoding protein disulf ide isomerase (PDI), a 57 kDa multifunctional protein. The exact natur e of the relationship between R-cognin and PDI is not known; however, both proteins appear to be encoded by the same gene. In the present st udy, we developed cRNA probes to examine the expression of R-cognin an d PDI transcripts in embryonic chick retina and liver. In the retina, the amount of transcript decreased with embryonic age, in parallel to a similar decrease in R-cognin protein. In the liver, where PDI is pro minently expressed, the amount of transcript was not developmentally r egulated. The spatial and temporal pattern of expression of the R-cogn in-encoding retinal transcript was examined by in situ hybridization. R-cognin mRNA was expressed in cells across the retina early in retino genesis, but became restricted to the cells of the inner retina later in development. This pattern of expression was the same as the develop mental pattern of R-cognin protein [Dobi et al., Invest. Ophthalmol. V is. Sci. 27, (1986) p. 323-329], thus, demonstrating that this secrete d protein functions at the surface of the cells where it is transcribe d. (C) 1997 Elsevier Science B.V.