Cell death in regeneration and cell turnover: Lessons from planarians and Drosophila

Programmed cell death plays a crucial role during tissue turnover in all animal species, and it is also essential during regeneration, serving as a key signalling mechanism to promote tissue repair and regrowth. In freshwater planarians, remarkable regenerative abilities are supported by neoblasts, a population of adult stem cells, which enable high somatic cell turnover. Cell death in planarians occurs continuously during regeneration and adult homeostasis, underscoring its critical role in tissue remodeling and repair. However, the exact mechanisms regulating cell death in these organisms remain elusive. In contrast, Drosophila melanogaster serves as a powerful model for studying programmed cell death in development, metamorphosis, and adult tissue maintenance, leveraging advanced genetic tools and visualization techniques. In Drosophila, cell death sculpts tissues, eliminates larval structures during metamorphosis, and supports homeostasis in adulthood. Despite limited regenerative capacity compared to planarians, Drosophila provides unique insights into cell death's regulatory mechanisms. Comparative analysis of these two systems highlights both conserved and divergent roles of programmed cell death in tissue renewal and regeneration. This review synthesizes the latest knowledge of programmed cell death in planarians and Drosophila, aiming to illuminate shared principles and system-specific adaptations, with relevance to tissue repair across biological systems.