Transferrin in chick retina: distribution and location during development.

Chick retinas from embryonic day 6 (E6) to 3 weeks post-hatching were examined for the presence and location of endogenous transferrin. Immunocytochemistry revealed that transferrin was differentially distributed in retinal layers. Furthermore, the pattern of transferrin distribution changed with developmental age. At day E6, transferrin was found in 2 distinct bands which were located in the area of the Müller cell end-feet. By day E9, additional regions of transferrin immunoreactivity could be found in the inner and outer plexiform layers (IPL, OPL) and the nerve fiber layer (NFL). These latter 3 bands (IPL, OPL and NFL) became more prominent from E9 until E17 as the synaptic layers and nerve fiber layer increased in density and maturation. Perikarya in the nuclear layers size, density and maturation. Perikarya in the nuclear layers were negative. At day E17 and later, the newly forming outer segments of photoreceptor cells were strongly reactive for transferrin while the somas of the photoreceptor cells, in the ONL, were negative. Retinas from chicks 1 day to 3 weeks post-hatching retained strong immunoreactivity for transferrin in the photoreceptor cell outer segments and OPL, lessened immunoreactivity in the IPL and loss of immunoreactivity in the NFL. Iron distribution in the retina for all ages examined showed only 2 bands that locally corresponded to the Müller cell end-feet. Iron stores were not found in the synaptic layers or photoreceptor cell outer segments. These studies suggest an iron storage function for retinal glia and a role for transferrin in neuronal development and differentiation.