Organization of the lateral line system in embryonic zebrafish

We describe the organization of lateral line nerves and ganglia in the embryonic zebrafish, Danio rerio. Two lateral line nerves are found anterior to the otic vesicle: the anterodorsal nerve innervates neuromasts of the supraorbital, infraorbital, and otic lines, whereas the anteroventral nerve innervates the mandibular and opercular lines. An additional two lateral line nerves are found posterior to the otic vesicle: the middle lateral line nerve innervates the middle line, whereas the posterior nerve innervates the occipital dorsal and posterior trunk lines. Preotic nerves converge on a single entry zone into the central nervous system at the facial motor root (mVII), as do axons of the octaval nerve. Postotic nerves converge to a posterior entry zone at the glossopharyngeal root. Both lateral line ganglia and neuromasts develop on a stereotypical schedule. To examine the segmental relationships among cranial ganglia, neural crest, and hindbrain, lateral line organization was analyzed in valentino mutants, which have disruptions in the development of rhombomeres 5-7 and in the third arch neural crest, and are missing glossopharyngeal motor neurons. The proposed corresponding lateral line nerve for this head segment, the middle lateral line, appears to develop normally. However, the middle and posterior nerves do not form a posterior entry zone in the absence of a glossopharyngeal root in val mutants, but instead course anteriorly to join the preotic nerves.