CHARACTERIZATION AND LOCALIZATION OF AN ALDEHYDE DEHYDROGENASE TO AMACRINE CELLS OF BOVINE RETINA

An enzyme of bovine retina that catalyzes oxidation of retinaldehyde t o retinoic acid was purified to homogeneity and a monoclonal antibody (mAb H-4) was generated. MAb H-4 recognized a single component (M(r) = 55,000) in extracts of bovine retina and other bovine tissues. The an tibody showed no cross-reactivity with extracts of rat, monkey, or hum an retinas. A 2067 bp cDNA was selected from a retina cDNA expression library using mAb H-4. The cDNA hybridized with a similarly sized, mod erately abundant mRNA prepared from bovine retina. Nucleotide sequence analysis indicated that the cDNA contained a single open reading fram e encoding 501 amino acids that have 88% sequence identity with the am ino-acid sequence of human hepatic Class 1 aldehyde dehydrogenase. Ami no-acid sequence analysis of purified enzyme demonstrated that the cDN A encodes the isolated enzyme. MAb H-4 specifically labeled the somata and processes of a subset of amacrine cells in bovine retinal section s. Labeled amacrine somata were located on both sides of the inner ple xiform layer, and their processes ramified into two laminae within the inner plexiform layer. The inner radial processes of Muller (glial) c ells were weakly reactive with mAb H-4. Weak immunostaining of amacrin e cells was found in monkey retina with mAb H-4, but no signal was det ected in rat or human retina. The results provide further evidence for metabolism and function of retinoids within cells of the inner retina and define a novel class of retinal amacrine cells.