RETINAL FABP PRINCIPALLY LOCALIZES TO NEURONS AND NOT TO GLIAL-CELLS

The presence of fatty acid-binding protein (FABP) in the embryonic chi ck retina may be linked to the demand for polyunsaturated fatty acids in this developing neural tissue. There is a decline in the overall le vel of FABP as the retina matures, suggesting a role for FABP in cellu lar differentiation. However, this pattern is not present in the chick brain, indicating a unique function for FABP in the retina. Immunohis tochemical staining of paraffin sections of chick retina from embryoni c day 21 revealed immunopositive photoreceptor inner segments, outer n uclear layer, 'radial processes' in the inner nuclear layer, a subpopu lation of cells in the ganglion cell layer, and inner limiting membran e. This pattern suggested that FABP positive cells were photoreceptors , Muller (glial) cells, and possibly ganglion cells. Staining of secti ons for glutamine synthetase, an enzyme specific for Muller cells, was similar but not identical to the pattern observed with FABP; thus ide ntification of these cells as FABP-positive was not conclusive. Howeve r, in retinal cells dissociated from day E14 embryos and cultured for one week, staining with FABP was more intense in the neurons than in t he 'flat' cells (presumed to be derived from the Muller cells). Retina l FABP thus appears to be localized predominantly in neurons, and may serve to sequester fatty acids in preparation for neurite outgrowth as the retinal cells differentiate.