Visualizing multiciliated cells in the zebrafish.

Ciliated cells serve vital functions in the body ranging from mechano- and chemo-sensing to fluid propulsion. Specialized cells with bundles dozens to hundreds of motile cilia known as multiciliated cells (MCCs) are essential as well, where they direct fluid movement in locations such as the respiratory, central nervous and reproductive systems. Intriguingly, the appearance of MCCs has been noted in the kidney in several disease conditions, but knowledge about their contributions to the pathobiology of these states has remained a mystery. As the mechanisms contributing to ciliopathic diseases are not yet fully understood, animal models serve as valuable tools for studying cilia development and how alterations in ciliated cell function impacts disease progression. Like other vertebrates, the zebrafish, Danio rerio, has numerous ciliated tissues. Among these, the embryonic kidney (or pronephros) is comprised of both monociliated cells and MCCs and therefore provides a setting to investigate both ciliated cell fate choice and ciliogenesis. Considering the zebrafish nephron resembles the segmentation and function of human nephrons, the zebrafish provide a tractable model for studying conserved ciliogenesis pathways in vivo. In this chapter, we provide an overview of ciliated cells with a special focus on MCCs, and present a suite of methods that can be used to visualize ciliated cells and their features in the developing zebrafish. Further, these methods enable precise quantification of ciliated cell number and various cilia-related characteristics.