Subcellular localization of nerve growth factor receptors. Developmental correlations in chick embryo brain

The subcellular distribution of receptors for nerve growth factor (NGF), as assayed by specific binding of the 125I-labeled protein, during the embryonic development of chick brain has been examined. Utilizing differential centrifugation and discontinuous sucrose density gradient centrifugation, it was observed that the majority of the specific NGF receptors are localized in the crude (P2) and purified (B) synaptosomal fractions at all stages of brain development examined. However, during early stages (day 6 to 8) a significant portion of the receptors are also found in the P1 fraction, consistent with their location on dense subcellular structures. Significant 125I-NGF binding is observed in this period of development before the appearance of neurochemical markers (choline acetyltransferase, dopamine-beta-hydroxylase, and 125I-alpha-bungarotoxin binding) which are associated with synaptosomes. The latter stages of development, particularly days 13 to 18, show parallel rapid increases in all neurochemical markers and 125I-NGF binding consistent with the association of nearly all late appearing NGF receptors with synaptosomes. These two apparent classes of NGF receptors may have distinct functional roles in the embryonic development of the chick brain.