Methods to Study Autophagy in Zebrafish.

Autophagy (cellular self-eating) is a highly regulated degradation process of the eukaryotic cell during which parts of the cytoplasm are delivered into, and broken down within, the lysosomal compartment. The process serves as a main route for the elimination of superfluous and damaged cellular constituents, thereby mediating macromolecular and organellar turnover. In addition to maintaining cellular homeostasis, autophagy is involved in various other cellular and developmental processes by degrading specific regulatory proteins, and contributing to the clearance of intracellular pathogens. The physiological roles and pathological involvement of autophagy can be effectively studied in divergent eukaryotic model systems ranging from yeast to mice. Such a tractable animal modelapplied only recently for autophagy researchis the zebrafish Danio rerio, which also facilitates the analysis of more specific biological processes such as tissue regeneration. In this chapter, we overview the main methods and tools that are used to monitor autophagic structures and to assay autophagic responses in this vertebrate organism. We place emphasis on genetic (functional) approaches applied for exploring novel cellular and developmental roles of the autophagic process.

Autophagy is required for zebrafish caudal fin regeneration.

Regeneration is the ability of multicellular organisms to replace damaged tissues and regrow lost body parts. This process relies on cell fate transformation that involves changes in gene expression as well as in the composition of the cytoplasmic compartment, and exhibits a characteristic age-related decline. Here, we present evidence that genetic and pharmacological inhibition of autophagy - a lysosome-mediated self-degradation process of eukaryotic cells, which has been implicated in extensive cellular remodelling and aging - impairs the regeneration of amputated caudal fins in the zebrafish (Danio rerio). Thus, autophagy is required for injury-induced tissue renewal. We further show that upregulation of autophagy in the regeneration zone occurs downstream of mitogen-activated protein kinase/extracellular signal-regulated kinase signalling to protect cells from undergoing apoptosis and enable cytosolic restructuring underlying terminal cell fate determination. This novel cellular function of the autophagic process in regeneration implies that the role of cellular self-digestion in differentiation and tissue patterning is more fundamental than previously thought.