An enzyme of bovine retina that catalyzes oxidation of retinaldehyde to retinoic acid was purified to homogeneity and a monoclonal antibody (mAb H-4) was generated. MAb H-4 recognized a single component (Mr = 55,000) in extracts of bovine retina and other bovine tissues. The antibody showed no cross-reactivity with extracts of rat, monkey, or human retinas. A 2067 bp cDNA was selected from a retina cDNA expression library using mAb H-4. The cDNA hybridized with a similarly sized, moderately abundant mRNA prepared from bovine retina. Nucleotide sequence analysis indicated that the cDNA contained a single open reading frame encoding 501 amino acids that have 88% sequence identity with the amino-acid sequence of human hepatic Class 1 aldehyde dehydrogenase. Amino-acid sequence analysis of purified enzyme demonstrated that the cDNA encodes the isolated enzyme. MAb H-4 specifically labeled the somata and processes of a subset of amacrine cells in bovine retinal sections. Labeled amacrine somata were located on both sides of the inner plexiform layer, and their processes ramified into two laminae within the inner plexiform layer. The inner radial processes of Müller (glial) cells were weakly reactive with mAb H-4. Weak immunostaining of amacrine cells was found in monkey retina with mAb H-4, but no signal was detected 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.

Aldehyde Dehydrogenase↗

PubMedDate not supplied

Characterization of aldehyde dehydrogenase-positive amacrine cells restricted in distribution to the dorsal retina.

A class 1 aldehyde dehydrogenase (ALDH) catalyzes oxidation of retinaldehyde to retinoic acid in bovine retina. We used immunocytochemistry and in situ hybridization to localize this enzyme in adult and fetal bovine retinas. Specific ALDH immunoreactivity was present in the cytoplasm of wide-field amacrine cells restricted in distribution to the dorsal part of the adult retina. The somata diameters ranged from approximately 8 microns to approximately 15 microns, and the cells increased in density from approximately 125 cells/mm2 near the horizontal meridian to approximately 425 cells/mm2 in the superior far periphery. The ALDH-positive cells had somata on both sides of the inner plexiform layer (IPL) and processes in two IPL strata. The majority of ALDH-positive cells were unreactive with antibodies against known amacrine cell enzymes and neurotransmitters, including GABA and glycine. The ALDH-positive amacrine cells also did not react with anti-cellular retinoic acid-binding protein, which was present in a subset of GABA-positive amacrine cells. In flat-mounted retinas processed by in situ hybridization, the larger ALDH-positive amacrine cells tended to be more heavily labeled. In addition to amacrine cells, Müller cell processes in the inner retina were weakly immunoreactive for ALDH; however, these glial cells did not contain ALDH mRNA. The pattern of ALDH expression in fetal bovine retinas was documented by immunocytochemistry. No ALDH reactivity was found before 5.5 months; for the remainder of the fetal period, ALDH immunoreactivity was present in amacrine cells similar to those in adult retina. The ALDH-positive amacrine cells in bovine retina are novel, being limited in distribution to the dorsal retina and unlabeled with other amacrine cell-specific markers. Identification of ALDH in amacrine cells provides additional evidence that cells of the inner retina are involved in retinoid metabolism.

Aging↗