Cell competition is a conserved phenomenon spanning from arthropods to humans. It involves the elimination of viable yet suboptimal "loser" cells when juxtaposed with their fitter "winner" counterparts. This process has received increased attention for its implications in cancer initiation and progression, neurodegeneration, and ageing. This study investigates the presence of the loser fitness fingerprint Flower LoseB (Fwe LB) and the fitness checkpoint Azot in the optic lobes over a period of 28 days. Notably, the absence of Azot is conventionally linked to the accumulation of loser cells over time. However, our investigation reveals that this accumulation is not perpetual and, intriguingly, Azot is not required for loser cell elimination in this context because loser cells are still eliminated by apoptosis in its absence. Furthermore, we wanted to clarify the percentage of loser cells that are eliminated, and the percentage of dying cells identified as loser during cell competition. We estimate that fewer than 50% of Fwe LB-expressing cells also express Azot and undergo apoptosis. Remarkably, our calculations also demonstrate that over 50% of cells undergoing apoptosis at any given time point are positive for the loser markers Fwe LB and Azot, stressing the relevant role of cell competition in promoting the elimination of suboptimal cells. This comprehensive analysis of fitness marker dynamics over a 28-day timeframe sheds new light on the intricate mechanisms governing Flower-dependent cell competition.

Cell competition is a conserved phenomenon spanning from arthropods to humans. It involves the elimination of viable yet suboptimal “loser” cells when juxtaposed with their fitter “winner” counterparts. This process has received increased attention for its implications in cancer initiation and progression, neurodegeneration, and ageing. This study investigates the presence of the loser fitness fingerprint Flower LoseB (Fwe LB) and the fitness checkpoint Azot in the optic lobes over a period of 28 days. Notably, the absence of Azot is conventionally linked to the accumulation of loser cells over time. However, our investigation reveals that this accumulation is not perpetual and, intriguingly, Azot is not required for loser cell elimination in this context. Furthermore, we estimate that fewer than 50% of Fwe LB-expressing cells also express Azot and undergo apoptosis. Remarkably, our calculations also demonstrate that over 50% of cells undergoing apoptosis at any given time point are positive for the loser markers Fwe LB and Azot. This comprehensive analysis of fitness marker dynamics over a 28-day timeframe sheds new light on the intricate mechanisms governing Flower-dependent cell competition.

Live imaging has been instrumental in understanding cellular dynamics in Drosophila tissues, but technical limitations have prevented long-term visualization of cell competition in adult brains. Here, we describe a simple ex-vivo protocol that enables extended live imaging of adult Drosophila brains for up to 32 hours. The method relies on non-supplemented Schneider’s Drosophila medium and hydrophobic interactions to maintain brain stability during imaging, eliminating the need for complex culture conditions or embedding procedures. We validate this approach by studying cell competition in the optic lobes following traumatic brain injury, where cell competition is expected to occur with a peak at 48 hours after damage. We demonstrate the utility of this method by visualizing the expression of the fitness checkpoint Azot in a loser cell and its subsequent elimination. This protocol offers a versatile platform for studying cell competition and other cellular processes requiring extended observation of the adult Drosophila brain.

Cell competition, a conserved biological process in which cells compete for survival based on relative fitness, has emerged as a critical mechanism in diverse biological contexts. Here, we investigate the role of cell competition in traumatic brain injury (TBI) by characterizing the temporal expression pattern of Azot, a key downstream effector of fitness-based selection, following injury in Drosophila melanogaster . Our findings reveal a distinct temporal profile of Azot expression post-TBI, with TUNEL assays confirming that Azot-expressing cells undergo apoptotic elimination. We demonstrate that following injury, the proportion of dying cells marked as “losers” significantly increases compared to non-injured conditions, indicating that cell competition becomes a predominant elimination mechanism during acute post-injury phases. Contrary to previous findings in neurodegenerative disease models where competition was restricted to neurons, we show that following TBI, both neurons and glia are subject to competitive elimination. Furthermore, in azot knockout conditions, we observe an accumulation of cells attempting to express Azot, suggesting impaired clearance of suboptimal cells. These findings advance our understanding of cellular quality control mechanisms following brain injury and may inform the development of novel therapeutic approaches to enhance functional recovery after TBI.

Competitive interactions between tumor cells and surrounding healthy cells are constantly present during the progression of a solid tumor, and their outcome has been proposed to affect the clinical behavior. Previous studies have described various mechanistic and molecular aspects that characterize this process, overall indicating that cancer cells behave as supercompetitors, which eliminate neighboring healthy cells to gain vital space for growth and infiltration of the tissue. Nevertheless, there is a lack of systematic characterization of these competitive interactions, particularly in the context of cancer in mammals. Furthermore, previous studies in the field of cell competition have primarily focused on homotypic cell competition, involving different clones of the same cell or cells deriving from the same tissue. Data are scarce regarding heterotypic cell competition between two unrelated cell types, which is particularly critical for the understanding of metastatic tumors. In this research, we study cell competition in the context of liver metastases, providing a broad characterization of this process in different relevant scenarios, including cells growing in vitro in 2D and 3D, and in vivo . Results show that in vitro , only a subset of cancer cell lines are coherently strong or moderate competitors against hepatocytes, while the remaining demonstrate poor competitiveness. The competitive proficiency can vary depending on the experimental growth system that is employed, and often predicts the phenotype of liver metastases in terms of aggressiveness and morphology. Finally, our data point towards an involvement of mechanical competition in determining the supercompetitor trait of cancer cells. Altogether, our research provides the first comprehensive characterization of heterotypic cell competition, and indicates that cancer cells possess heterogeneous competitive proficiency towards hepatocytes which can be affected by the growth conditions.