Identification and characterization of transcripts present at elevated levels in the undifferentiated chick retina

Little is known concerning the genes expressed in the neuro-ectodermal cells of the retina, prior to their differentiation into neurons and glia. An analysis of the transcripts present at early stages of retinal development should lead to the identification of functionally important molecules and increase our understanding of the molecular events involved in tissue maturation. Differential screening of a day 3.5 chick retina cDNA library and Northern blot analysis resulted in the discovery of five mRNAs present at elevated levels in the undifferentiated retina. Tissue maturation was accompanied by a decrease in mRNA signal in all five cases and, with the exception of the brain, transcript levels were higher in the immature retina than in the other tissues tested. Two of the cDNAs, corresponding to brain creatine kinase and carbonic anhydrase-II RNAs, had previously been cloned, while the products encoded by the three remaining RNAs were tentatively identified as the chicken counterparts of mammalian cytosolic aldehyde dehydrogenase, stathmin and a member of the fatty acid binding protein family. The elevated levels of these five RNAs in the undifferentiated retina and the subsequent decrease in transcript levels observed upon tissue maturation indicate that the encoded proteins may play important roles in early retinal development.