Cranial nerve growth in birds is preceded by cholinesterase expression during neural crest cell migration and the formation of an HNK-1 scaffold

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Abstract
The expression of the neural crest cell (NCC) markers acetylcholinesterase (AChE) and the HNK-1-epitope is compared from the emigration of cephalic NCC until the formation of the cranial nerves V-X in chicken and quail hindbrain. We show that NCC transiently express acetylcholinesterase (AChE) activity during their emigration; NCC migrate into butyrylcholinesterase (BChE)-positive areas of the cranial mesenchyme. Along these migratory tracks that foreshadow the course of later projecting cranial nerves, BChE increases strongly in cells that may represent immature Schwann cells. Both AChE and BChE, but not HNK-1, are expressed in the ectodermal placodes. In NCC, HNK-1 is expressed strongly only when they approach their destination sites. Their intense expression of HNK-1 then leads to the establishment of tunnel-shaped HNK-1 matrices, within which G4-positive cranial neurites begin to extend. We conclude that AChE and HNK-1 expression in cephalic NCC serve different functions, since AChE is related to their migration, and HNK-1 to their aggregation and the formation of an extracellular neurite scaffold.