High levels of aldehyde dehydrogenase transcripts in the undifferentiated chick retina

A cDNA clone corresponding to chicken aldehyde dehydrogenase (ALDH) mRNA was isolated from a library representing the polyadenylated RNAs expressed in the retina of day 3.5 chick embryos. The profile of ALDH RNA expression was examined in different tissues as well as at different stages of development in the chick embryo. A notable feature of this analysis was the high level of ALDH transcripts found in the undifferentiated cells of the retina. A 20-fold decrease in ALDH RNA levels was observed upon retinal differentiation, in contrast to the kidney, liver and gut where tissue maturation was accompanied by an increase in ALDH mRNA levels. The observations reported here suggest an important role for the ALDH enzyme in retinal development. One possibility is that retinal, the aldehyde form of vitamin A, serves as a substrate for ALDH in the developing retina, resulting in the formation of retinoic acid which has been implicated in various differentiation processes.