The Mechanosensory Lateral Line

pp 147-159

Organization and Development of the Zebrafish Posterior Lateral Line

  • Walter K. Metcalfe

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Early studies of the developing lateral lines of amphibians demonstrated that a variety of well-orchestrated cellular behaviors give rise to a rather simple morphological pattern in the embryo. In 1904, Harrison first demonstrated that neuromasts of the posterior lateral lines of frogs (Rana palustris, R. Sylvatica) are derived from cells that migrate from the head region, and that the posterior lateral line nerve connects the posterior lateral line ganglion with the migrating primordium. Later, in studies of the salamander (Ambystoma punctatum) Stone (1922) demonstrated that the posterior lateral line ganglion cells and the primordial cells that form neuromasts both arise from a common postotic placode. Cells in the rostra1 part of the placode become the sensory neurons, and cells in the caudal part form the migratory primordium. As the primordium migrates caudally along the midbody line, clusters of cells are deposited at intervals from the trailing end of the primordium. These cell clusters subsequently differentiate to become the first, or “primary”, neuromasts of the midbody line. Thus, the development of the posterior lateral line involves a variety of fundamentally important but poorly understood cellular activities, such as the formation and differentiation of a placode, initiation and guidance of cell migration, and axon outgrowth and guidance. The posterior lateral line system may prove to be a good model system in which to study these phenomena because of its relative simplicity (being a simple linear array of receptors in the embryo) and accessibility (the receptors are located superficially within the epidermis) and because of the considerable background of information that is already available regarding the development of this system.