PERIPHERAL DEVELOPMENT OF CRANIAL NERVES IN A CYCLOSTOME, LAMPETRA-JAPONICA - MORPHOLOGICAL DISTRIBUTION OF NERVE BRANCHES AND THE VERTEBRATE BODY PLAN

The development of peripheral nerves was studied in a Japanese marine lamprey, Lampetra japonica, in whole-mount and sectioned embryos from hatching until the earliest ammocoete. Nerve fibers were immunohistoch emically stained with a monoclonal antibody against acetylated tubulin . Branchiomeric nerves first developed in a simple metamerical pattern , each associated with a single pharyngeal arch. Of those, the ophthal micus profundus, maxillomandibular, and facial nerves later developed a highly modified branching pattern, whereas postotic nerves were less specialized and showed the stereotypical branching pattern of post-tr ematic nerves. The early distribution of melanocytes in myotome-free s pace largely overlapped with the morphology of the cranial nerve and g anglion anlage, and resembled the cephalic crest cell distribution pat tern in the early chick embryo. It was suggested that the cephalic cre st cell distribution, which is also inhibited by myotomes in the lampr ey, would be the common basis for branchiomeric nerve patterning. In l ater development of the lamprey embryo, myotomes 1 through 3, which ha d originated in the postotic region, grew rostrally into the preotic r egion, laterally covering all of the branchiomeric nerves. This result s in a deep position of the cranial nerves, which is not observed in g nathostomes. (C) 1997 Wiley-Liss, Inc.