The key role of autophagy and its relationship with apoptosis in lepidopteran larval midgut remodeling

Cell death is a primary cellular response essential for the development, differentiation, homeostasis, and survival of organisms. This highly heterogeneous process, which includes apoptotic and autophagy-based cell death, can be activated by distinct biochemical cascades, and can display different morphological features. For this reason, a precise characterization of the numerous cell death modalities described so far in eukaryotes, and of their relationships, constitutes a major challenge for current research. Cell death-associated phenomena occur extensively in the larvae of holometabolous insects (i.e. Lepidoptera) during development and metamorphosis to eliminate tissues and organs that the adult does not need. Several larval organs of lepidopteran larvae have been used over the years to study autophagy and apoptosis; however, the current literature is basically fragmentary and confusing. The completion of genome sequencing in Bombyx mori and the development of molecular tools to manipulate the expression of autophagic and apoptotic genes that have now been identified in the silkworm opened up new perspectives and made it possible to analyze in-depth the cell death processes that occur in these insects. This chapter summarizes current knowledge about autophagy research in Lepidoptera. The use of the larval midgut is discussed as a model for studying the roles and regulation of autophagy, and for gaining insight as to how autophagy and apoptosis cooperate in cell death events in lepidopteran larval organs.