Early localization of alpha-fetoprotein in the developing nervous system of the chicken.

The intracellular presence of alpha-fetoprotein (AFP) and serum albumin (SA) has been recently demonstrated in the developing brain of primates, rats and mice. We report here the morphologic localization by immunocytochemical methods of AFP, SA, ovalbumin (OA) and immunoglobulin G (IgG) in the nervous system of chicken embryos. AFP was detected inside cells of the neural crest as soon as 48 hours after fertilization. Subsequently, the protein could be localized in many other neural structures, including cerebral cortex, brain stem nuclei, sensory retina, spinal cord and dorsal root ganglia. Disappearance of AFP inside the nervous system was observed 15 to 17 days after fertilization. The localization pattern of SA was similar to that of AFP, with the only difference being a short (2 to 3 days) displacement in time. On the contrary, OA and IgG were not found in the developing nervous system throughout the period examined. This provides support to the selectivity of the neural internalization of AFP and SA, and seems to exclude a mechanism of passive diffusion to explain such incorporation.