Localization of a fatty acid binding protein and its transcript in the developing chick retina

The undifferentiated chick retina has elevated levels of fatty acid binding protein (R-FABP) mRNA. Tissue maturation is accompanied by a 50-100-fold decrease in transcript levels. To determine the location of the R-FABP transcript and its encoded protein in the developing retina, in situ hybridization and immunohistochemical analyses were carried out using chick embryos at different stages of development. The R-FABP mRNA and protein were found throughout the retina from day 3 to day 7 of incubation. Accumulation of R-FABP in the neurites of ganglion cells could readily be detected at early developmental stages. By day 11, R-FABP transcript levels were considerably reduced in the retina, while the protein was primarily found in the inner nuclear layer, inner plexiform layer and optic nerve fiber layer of the retina. As well, R-FABP mRNA and protein were abundant in the non-pigmented ciliary epithelium, which represents the forward prolongation of the retina in the anterior eye. Immunoelectron microscopy revealed the presence of R-FABP in both the nucleus and cytoplasm of day 4 retinal cells. In the day 13 retina, R-FABP was abundant in the processes of neuronal cells. These results suggest that, early in retinal development, there is a requirement for FABP in the nucleus as well as the cytoplasm of all retinal cells. At later stages, the concentration of R-FABP in the processes of neuronal cells would suggest a biochemical or structural role related to neurite extension and synapse formation.