WEBB, J.F.; Villanova University: Development of the Lateral Line System in Teleost Fishes: Zebrafish and Beyond

The lateral line system of teleost fishes provides many opportunities for the investigation of fundamental questions in evolutionary developmental biology. The lateral line system is composed of, not a bilateral pair of cranial sensory organs, but a spatial array of neuromast receptor organs on the head and trunk. In adult fishes, cranial neuromasts are enclosed in lateral line canals that are integrated into a subset of dermatocranial bones, and as such are also a component of the cranial skeleton. Lateral line development commences during embryogenesis with the migration of placode-derived cells from which neuromasts differentiate, and continues through the larval stage (over many weeks) with neuromast maturation and the morphogenesis of the lateral line canals. Neuromast differentiation and distribution, on the trunk has been studied in zebrafish and a handful of other species (e.g., medaka, blind cave fish), and the contributions of this work to our understanding of pattern formation and cell migration will be briefly reviewed. We have compared the pattern and timing of neuromast maturation and the morphogenesis of canal segments in species in 4 teleost clades: Ostariophysi (zebrafish), Scorpaeniformes (greenling), Pleuronectiformes (flatfish) and Perciformes (several cichlids). The unusual morphology of canal neuromasts in zebrafish, and the asymmetry of neuromasts in flatfish, suggest how the pattern and timing of hair cell proliferation during neuromast maturation can be easily altered to generate the diversity of neuromast morphologies documented among teleost fishes. We have also shown that while the pattern of lateral line canal development appears to be conserved, the order and timing of development of individual canal segments is likely the origin of much of the variation in the cranial lateral line canal system among fishes.