Xrp1 and Irbp18 trigger a feed-forward loop of proteotoxic stress to induce the loser status

Cell competition induces the elimination of less-fit “loser” cells by fitter “winner” cells. In Drosophila, cells heterozygous mutant in ribosome genes, Rp/+, known as Minutes, are outcompeted by wild-type cells. Rp/+ cells display proteotoxic stress and the oxidative stress response, which drive the loser status. Minute cell competition also requires the transcription factors Irbp18 and Xrp1, but how these contribute to the loser status is partially understood. Here we provide evidence that initial proteotoxic stress in RpS3/+ cells is Xrp1-independent. However, Xrp1 is sufficient to induce proteotoxic stress in otherwise wild-type cells and is necessary for the high levels of proteotoxic stress found in RpS3/+ cells. Surprisingly, Xrp1 is also induced downstream of proteotoxic stress, and is required for the competitive elimination of cells suffering from proteotoxic stress or overexpressing Nrf2. Our data suggests that a feed-forward loop between Xrp1, proteotoxic stress, and Nrf2 drives Minute cells to become losers

Proteotoxic stress is a driver of the loser status and of cell competition

Cell competition allows “winner” cells to eliminate less fit “loser” cells in tissues. In Minute cell competition, cells heterozygous mutant in ribosome genes, such as RpS3 (+/-) cells, are eliminated by wild-type cells. How cells are primed as losers is partially understood and it has been proposed that reduced translation underpins the loser status of ribosome mutant, or Minute, cells. Here, using Drosophila, we show that reduced translation does not cause cell competition. Instead, we identify proteotoxic stress as the underlying cause of the loser status for Minute competition and competition induced by mahjong, an unrelated loser gene. RpS3 (+/-) cells exhibit reduced autophagic and proteasomal flux, accumulate protein aggregates, and can be rescued from competition by improving their proteostasis. Conversely, inducing proteotoxic stress is sufficient to turn otherwise wild-type cells into losers. Thus, we propose that tissues may preserve their health through a proteostasis-based mechanism of cell competition and cell selection

Proteotoxic stress is a driver of the loser status and cell competition.

Cell competition allows winner cells to eliminate less fit loser cells in tissues. In Minute cell competition, cells with a heterozygous mutation in ribosome genes, such as RpS3+/- cells, are eliminated by wild-type cells. How cells are primed as losers is partially understood and it has been proposed that reduced translation underpins the loser status of ribosome mutant, or Minute, cells. Here, using Drosophila, we show that reduced translation does not cause cell competition. Instead, we identify proteotoxic stress as the underlying cause of the loser status for Minute competition and competition induced by mahjong, an unrelated loser gene. RpS3+/- cells exhibit reduced autophagic and proteasomal flux, accumulate protein aggregates and can be rescued from competition by improving their proteostasis. Conversely, inducing proteotoxic stress is sufficient to turn otherwise wild-type cells into losers. Thus, we propose that tissues may preserve their health through a proteostasis-based mechanism of cell competition and cell selection

Chronic activation of JNK JAK/STAT and oxidative stress signalling causes the loser cell status

Cell competition is a form of cell interaction that causes the elimination of less fit cells, or losers, by wild-type (WT) cells, influencing overall tissue health. Several mutations can cause cells to become losers; however, it is not known how. Here we show that Drosophila wing disc cells carrying functionally unrelated loser mutations (Minute and mahjong) display the common activation of multiple stress signalling pathways before cell competition and find that these pathways collectively account for the loser status. We find that JNK signalling inhibits the growth of losers, while JAK/STAT signalling promotes competition-induced winner cell proliferation. Furthermore, we show that losers display oxidative stress response activation and, strikingly, that activation of this pathway alone, by Nrf2 overexpression, is sufficient to prime cells for their elimination by WT neighbours. Since oxidative stress and Nrf2 are linked to several diseases, cell competition may occur in a number of pathological conditions.Cell competition causes the removal of less fit cells ('losers') but why some gene mutations turn cells into losers is unclear. Here, the authors show that Drosophila wing disc cells carrying some loser mutations activate Nrf2 and JNK signalling, which contribute to the loser status.This work was supported by a Cancer Research UK Programme Grant (A12460) and a Royal Society University Research fellowship to E.P. (UF0905080), a Wellcome Trust PhD studentship to I.K., a Wellcome Trust PhD studentship to M.D. and Core grant funding from the Wellcome Trust (092096) and CRUK (C6946/A14492)

FGFR2 is required for airway basal cell self-renewal and terminal differentiation

Airway stem cells slowly self-renew and produce differentiated progeny to maintain homeostasis throughout the lifespan of an individual. Mutations in the molecular regulators of these processes may drive cancer or degenerative disease, but are also potential therapeutic targets. Conditionally deleting one copy of FGF receptor 2 (FGFR2) in adult mouse airway basal cells results in self-renewal and differentiation phenotypes. We show that FGFR2 signalling correlates with maintenance of expression of a key transcription factor for basal cell self-renewal and differentiation: SOX2. This heterozygous phenotype illustrates that subtle changes in receptor tyrosine kinase signalling can have significant effects, perhaps providing an explanation for the numerous changes seen in cancer.This study was supported by the Medical Research Council (G0900424 to E.R.). Core funders were as follows: Wellcome Trust (092096) and Cancer Research UK (C6946/A14492) supporting the Gurdon Institute; Wellcome Trust and Medical Research Council supporting the Stem Cell Initiative

Mal/SRF Is Dispensable for Cell Proliferation in Drosophila

The Mal/SRF transcription factor is regulated by the level of G-actin in cells and has important roles in cell migration and other actin-dependent processes in Drosophila. A recent report suggests that Mal/SRF and an upstream regulator, Pico, are required for cell proliferation and tissue growth in Drosophila. I find otherwise. Mutation of Mal or SRF does not affect cell proliferation in the fly wing. Furthermore, I cannot reproduce the reported effects of Pico RNAi or Pico overexpression on body size. Nevertheless, I can confirm that overexpression of Pico or Mal causes tissue overgrowth specifically in the fly wing - where SRF is most highly expressed. My results indicate that Mal/SRF can promote tissue growth when abnormally active, but is not normally required for tissue growth during development

The conformational state of Tes regulates its zyxin-dependent recruitment to focal adhesions

The function of the human Tes protein, which has extensive similarity to zyxin in both sequence and domain organization, is currently unknown. We now show that Tes is a component of focal adhesions that, when expressed, negatively regulates proliferation of T47D breast carcinoma cells. Coimmunoprecipitations demonstrate that in vivo Tes is complexed with actin, Mena, and vasodilator-stimulated phosphoprotein (VASP). Interestingly, the isolated NH2-terminal half of Tes pulls out α-actinin and paxillin from cell extracts in addition to actin. The COOH-terminal half recruits zyxin as well as Mena and VASP from cell extracts. These differences suggest that the ability of Tes to associate with α-actinin, paxillin, and zyxin is dependent on the conformational state of the molecule. Consistent with this hypothesis, we demonstrate that the two halves of Tes interact with each other in vitro and in vivo. Using fibroblasts lacking Mena and VASP, we show that these proteins are not required to recruit Tes to focal adhesions. However, using RNAi ablation, we demonstrate that zyxin is required to recruit Tes, as well as Mena and VASP, but not vinculin or paxillin, to focal adhesions

Mechanical cell competition kills cells via induction of lethal p53 levels.

Cell competition is a quality control mechanism that eliminates unfit cells. How cells compete is poorly understood, but it is generally accepted that molecular exchange between cells signals elimination of unfit cells. Here we report an orthogonal mechanism of cell competition, whereby cells compete through mechanical insults. We show that MDCK cells silenced for the polarity gene scribble (scrib(KD)) are hypersensitive to compaction, that interaction with wild-type cells causes their compaction and that crowding is sufficient for scrib(KD) cell elimination. Importantly, we show that elevation of the tumour suppressor p53 is necessary and sufficient for crowding hypersensitivity. Compaction, via activation of Rho-associated kinase (ROCK) and the stress kinase p38, leads to further p53 elevation, causing cell death. Thus, in addition to molecules, cells use mechanical means to compete. Given the involvement of p53, compaction hypersensitivity may be widespread among damaged cells and offers an additional route to eliminate unfit cells.This work was supported by a Cancer Research UK Programme Grant (EP and LW A12460), a Royal Society University Research fellowship to EP (UF0905080), a Wellcome Trust PhD studentship to I.K, a Cambridge Cancer Centre PhD studentship to MG and Core grant funding from the Wellcome Trust (092096) and CRUK (C6946/A14492).This is the final version of the article. It first appeared from Nature Publishing Group via https://doi.org/10.1038/ncomms1137

The influence of gene expression time delays on Gierer-Meinhardt pattern formation systems

There are numerous examples of morphogen gradients controlling long range signalling in developmental and cellular systems. The prospect of two such interacting morphogens instigating long range self-organisation in biological systems via a Turing bifurcation has been explored, postulated, or implicated in the context of numerous developmental processes. However, modelling investigations of cellular systems typically neglect the influence of gene expression on such dynamics, even though transcription and translation are observed to be important in morphogenetic systems. In particular, the influence of gene expression on a large class of Turing bifurcation models, namely those with pure kinetics such as the Gierer–Meinhardt system, is unexplored. Our investigations demonstrate that the behaviour of the Gierer–Meinhardt model profoundly changes on the inclusion of gene expression dynamics and is sensitive to the sub-cellular details of gene expression. Features such as concentration blow up, morphogen oscillations and radical sensitivities to the duration of gene expression are observed and, at best, severely restrict the possible parameter spaces for feasible biological behaviour. These results also indicate that the behaviour of Turing pattern formation systems on the inclusion of gene expression time delays may provide a means of distinguishing between possible forms of interaction kinetics. Finally, this study also emphasises that sub-cellular and gene expression dynamics should not be simply neglected in models of long range biological pattern formation via morphogens