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Caspases, well-known for their role in executing apoptosis, also participate in various non-apoptotic processes. Despite this, their involvement in promoting compensatory proliferation - a key aspect of tissue regeneration following extensive cell death - has been a subject of ongoing ambiguity. In our study, we investigate compensatory proliferation in the Drosophila wing imaginal disc following ionizing radiation, a model epithelial tissue that has been a pioneering system for studying this regenerative response. Using a delayed genetic reporter to monitor the activity of the initiator caspase-2/9 ortholog, Dronc, we identified two populations of apoptosis-resistant epithelial cells involved in compensatory proliferation: those that activate Dronc (termed DARE cells) and those that do not (NARE cells). We show that DARE cells pass their apoptosis-resistance trait to their daughter cells, suggesting a molecular memory. We demonstrate that Dronc in DARE cells, but not the apoptosome adapter Dark and the effector caspases, promotes compensatory proliferation both within these cells and in NARE cells through a non-cell-autonomous mechanism. We found that Myo1D, an unconventional myosin interacting with Dronc, is essential for the survival of DARE cells by preventing the lethal activation of effector caspases and subsequent apoptosis. In contrast, Myo7A/Crinkled, another unconventional myosin that interacts with Dronc, promotes effector caspase activation in DARE cells. We demonstrate that the TNFR>JNK signaling pathway in DARE cells directly regulates their proliferation, which in turn influences NARE cell proliferation. Consequently, we show that maintaining proliferative homeostasis between DARE and NARE cells is vital for balanced tissue regeneration. Given the widespread use of ionizing irradiation in cancer treatment and prevention, our findings have potential implications for understanding treatment-resistant cells and cancer recurrence.

RESUMEN

Maintenance of tissue integrity during development and homeostasis requires the precise coordination of several cell-based processes, including cell death. In animals, the majority of such cell death occurs by apoptosis, a process mediated by caspase proteases. To elucidate the role of caspases in tissue integrity, we investigated the behavior of Drosophila epithelial cells that are severely compromised for caspase activity. We show that these cells acquire migratory and invasive capacities, either within 1-2 days following irradiation or spontaneously during development. Importantly, low levels of effector caspase activity, which are far below the threshold required to induce apoptosis, can potently inhibit this process, as well as a distinct, developmental paradigm of primordial germ cell migration. These findings may have implications for radiation therapy in cancer treatment. Furthermore, given the presence of caspases throughout metazoa, our results could imply that preventing unwanted cell migration constitutes an ancient non-apoptotic function of these proteases.

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RESUMEN

There is a need to develop three-dimensional structures that mimic the natural islet tissue microenvironment. Endocrine micro-pancreata (EMPs) made up of acellular organ-derived micro-scaffolds seeded with human islets have been shown to express high levels of key beta-cell specific genes and secrete quantities of insulin per cell similar to freshly isolated human islets in a glucose-regulated manner for more than three months in vitro. The aim of this study was to investigate the capacity of EMPs to restore euglycemia in vivo after transplantation of mouse or human islets in chemically diabetic mice. We proposed that the organ-derived EMPs would restore the extracellular components of the islet microenvironment, generating favorable conditions for islet function and survival. EMPs seeded with 500 mouse islets were implanted intraperitoneally into streptozotocin-induced diabetic mice and reverted diabetes in 67% of mice compared to 13% of controls (p = 0.018, n = 9 per group). Histological analysis of the explanted grafts 60 days post-transplantation stained positive for insulin and exhibited increased vascular density in a collagen-rich background. EMPs were also seeded with human islets and transplanted into the peritoneal cavity of immune-deficient diabetic mice at 250 islet equivalents (IEQ), 500 IEQ and 1000 IEQ. Escalating islet dose increased rates of normoglycemia (50% of the 500 IEQ group and 75% of the 1000 IEQ group, n = 3 per group). Human c-peptide levels were detected 90 days post-transplantation in a dose-response relationship. Herein, we report reversal of diabetes in mice by intraperitoneal transplantation of human islet seeded on EMPs with a human islet dose as low as 500 IEQ.

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RESUMEN

The aim of this work is to obtain significant and regulated insulin secretion from human beta cells ex vivo. Long-term culture of human pancreatic islets and attempts at expanding human islet cells normally result in loss of beta-cell phenotype. We propose that to obtain proper ex vivo beta cell function, there is a need to develop three-dimensional structures that mimic the natural islet tissue microenvironment. We here describe the preparation of endocrine micro-pancreata (EMPs) that are made up of acellular organ-derived micro-scaffolds seeded with human intact or enzymatically dissociated islets. We show that EMPs constructed by seeding whole islets, freshly enzymatically-dissociated islets or even dissociated islets grown first in standard monolayer cultures express high levels of key beta-cell specific genes and secrete quantities of insulin per cell similar to freshly isolated human islets in a glucose-regulated manner for more than 3 months in vitro.

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