Cancer Biology

Planarians are freshwater flatworms, well known for their ability to regenerate a complete organism from any piece of their body. Furthermore, planarians are constantly growing and degrowing throughout their lives, maintaining a functional and proportioned body. These properties rely on the presence of a population of adult stem cells and on the tight control of their cell renewal, which is based on the balance between the proliferation of new cells and their differentiation, and the death of unnecessary cells. Due to the importance of these two processes in planarian biology, over the years, researchers have optimized molecular techniques to detect both cell proliferation and cell death in planarians. Here, we present the two main protocols currently used for cell death detection and quantification in the planarian field: Caspase-3 activity quantification and TUNEL assay.

The mitochondrial pathway of apoptosis involves a complex interplay between dozens of proteins and lipids, and is also dependent on the shape and size of mitochondria. The use of cellular models in past studies has not been ideal for investigating how the complex multi-factor interplay regulates the molecular mechanisms of mitochondrial outer membrane permeabilization (MOMP). Isolated systems have proven to be a paradigm to deconstruct MOMP into individual steps and to study the behavior of each subset of MOMP regulators. In particular, isolated mitochondria are key to in vitro studies of the BCL-2 family proteins, a complex family of pro-survival and pro-apoptotic proteins that directly control the mitochondrial pathway of apoptosis (Renault et al., 2013).

In this protocol, we describe three complementary procedures for investigating in real-time the effects of MOMP regulators using isolated mitochondria. The first procedure is “Liver mitochondria isolation” in which the liver is dissected from mice to obtain mitochondria. “Mitochondria labeling with JC-1 and size fractionation” is the second procedure that describes a method to label, fractionate by size and standardize subpopulations of mitochondria. Finally, the “Real-time MOMP measurements” protocol allows to follow MOMP in real-time on isolated mitochondria. The aforementioned procedures were used to determine in vitro the role of mitochondrial membrane shape at the level of isolated cells and isolated mitochondria (Renault et al., 2015).