Labeling defined cells or subsets of cells in zebrafish by Kaede photoconversion

The lateral line is a mechanosensory system that comprises a set of discrete sense organs called neuromasts, which are arranged in reproducible patterns on the surface of fish and amphibians. The posterior component of the system, the posterior lateral line (PLL), comprises the neuromasts on the body and tail and its peripheral location makes the PLL accessible and easily visualized by imaging methods. The PLL develops from the migrating primordium and so can be used to examine various aspects of neural development, including the control of long-range, collective cell migration and the mechanisms underlying the establishment of appropriate connectivity. As the PLL develops, the transition from the simple, eight-neuromast-long embryonic system to the juvenile pattern of four lines extending anteroposteriorly and counting about 60 neuromasts involves three processes. First, two new primordia form that also migrate anteroposteriorly, one (primII) along the lateral myoseptum and the other (primD) along the dorsal myoseptum, depositing proneuromasts and interneuromast cells in a manner similar to the embryonic primordium. Second, displacement of differentiated neuromasts occurs along the dorsoventral axis, and third, local proliferation of interneuromast cells occurs to form additional neuromasts. Here we describe the use of Kaede photoconversion to label a chosen cell, or subset of cells, in the migrating primordium. This method can be used to study migration at the level of a single cell, to track cell lineages, or even to determine patterns of innervation.