Expression of zebrafish fkd6 in neural crest-derived glia.

The zebrafish fkd6 gene is a marker for premigratory neural crest. In this study, we analyze later expression in putative glia of the peripheral nervous system. Prior to neural crest migration, fkd6 expression is downregulated in crest cells. Subsequently, expression appears initially in loose clusters of cells in positions corresponding to cranial ganglia. Double labelling with a neuronal marker shows that fkd6-expressing cells are not differentiated neurones and generally lie peripheral to neurones in ganglia. Later, expression appears associated with the posterior lateral line and other cranial nerves. For the posterior lateral line nerve, we show that fkd6-labeling extends caudally along this nerve in tight correlation with lateral line primordium migration and axon elongation. Expression in colourless mutant embryos is consistent with these cells being satellite glia and Schwann cells.