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Cell competition is an evolutionarily conserved quality control process that eliminates suboptimal or potentially dangerous cells. Although differential metabolic states act as direct drivers of competition, how these are measured across tissues is not understood. Here, we demonstrate that vesicular glutamate transporter (VGlut) and autocrine glutamate signaling are required for cell competition and Myc-driven super-competition in the Drosophila epithelia. We find that the loss of glutamate-stimulated VGlut>NMDAR>CaMKII>CrebB signaling triggers loser status and cell death under competitive settings via the autocrine induction of TNF. This in turn drives TNFR>JNK activation, triggering loser cell elimination and PDK/LDH-dependent metabolic reprogramming. Inhibiting caspases or preventing loser cells from transferring lactate to their neighbors nullifies cell competition. Further, in a Drosophila model for premalignancy, Myc-overexpressing clones co-opt this signaling circuit to acquire super-competitor status. Targeting glutamate signaling converts Myc "super-competitor" clones into "losers," highlighting new therapeutic opportunities to restrict the evolution of fitter clones., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Peroxisome dynamics are crucial for intestinal stem cell (ISC) differentiation and gut regeneration. However, the precise mechanisms that govern peroxisome dynamics within ISCs during gut regeneration remain unknown. Using mouse colitis and Drosophila intestine models, we have identified a negative-feedback control mechanism involving the transcription factors peroxisome proliferator-activated receptors (PPARs) and SOX21. This feedback mechanism effectively regulates peroxisome abundance during gut regeneration. Following gut injury, the released free very long-chain fatty acids (VLCFAs) increase peroxisome abundance by stimulating PPARs-PEX11s signaling. PPARs act to stimulate peroxisome fission and inhibit pexophagy. SOX21, which acts downstream of peroxisomes during ISC differentiation, induces peroxisome elimination through pexophagy while repressing PPAR expression. Hence, PPARs and SOX21 constitute a finely tuned negative-feedback loop that regulates peroxisome dynamics. These findings shed light on the complex molecular mechanisms underlying peroxisome regulation in ISCs, contributing to our understanding of gut renewal and repair., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

CRISPR-Cas greatly facilitated the integration of exogenous sequences into specific loci. However, knockin generation in multicellular animals remains challenging, partially due to the complexity of insertion screening. Here, we describe SEED/Harvest, a method to generate knockins in Drosophila, based on CRISPR-Cas and the single-strand annealing (SSA) repair pathway. In SEED (from "scarless editing by element deletion"), a switchable cassette is first integrated into the target locus. In a subsequent CRISPR-triggered repair event, resolved by SSA, the cassette is seamlessly removed. Germline excision of SEED cassettes allows for fast and robust knockin generation of both fluorescent proteins and short protein tags in tandem. Tissue-specific expression of Cas9 results in somatic cassette excision, conferring spatiotemporal control of protein labeling and the conditional rescue of mutants. Finally, to achieve conditional protein labeling and manipulation of short tag knockins, we developed a genetic toolbox by functionalizing the ALFA nanobody., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Retrograde transport of WLS (Wntless) from endosomes to trans-Golgi network (TGN) is required for efficient Wnt secretion during development. However, the molecular players connecting endosomes to TGN during WLS trafficking are limited. Here, we identified a role for Eyes Absent (EYA) proteins during retrograde trafficking of WLS to TGN in human cell lines. By using worm, fly, and zebrafish models, we found that the EYA-secretory carrier-associated membrane protein 3 (SCAMP3) axis is evolved in vertebrates. EYAs form a complex and interact with retromer on early endosomes. Retromer-bound EYA complex recruits SCAMP3 to endosomes, which is necessary for the fusion of WLS-containing endosomes to TGN. Loss of EYA complex or SCAMP3 leads to defective transport of WLS to TGN and failed Wnt secretion. EYA mutations found in patients with hearing loss form a dysfunctional EYA-retromer complex that fails to activate Wnt signaling. These findings identify the EYA complex as a component of retrograde trafficking of WLS from the endosome to TGN., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 Elsevier Inc. All rights reserved.)

During homeostasis, a critical balance is maintained between myeloid-like progenitors and their differentiated progeny, which function to mitigate stress and innate immune challenges. The molecular mechanisms that help achieve this balance are not fully understood. Using genetic dissection in Drosophila, we show that a Wnt6/EGFR-signaling network simultaneously controls progenitor growth, proliferation, and differentiation. Unlike G1-quiescence of stem cells, hematopoietic progenitors are blocked in G2 phase by a β-catenin-independent (Wnt/STOP) Wnt6 pathway that restricts Cdc25 nuclear entry and promotes cell growth. Canonical β-catenin-dependent Wnt6 signaling is spatially confined to mature progenitors through localized activation of the tyrosine kinases EGFR and Abelson kinase (Abl), which promote nuclear entry of β-catenin and facilitate exit from G2. This strategy combines transcription-dependent and -independent forms of both Wnt6 and EGFR pathways to create a direct link between cell-cycle control and differentiation. This unique combinatorial strategy employing conserved components may underlie homeostatic balance and stress response in mammalian hematopoiesis., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 Elsevier Inc. All rights reserved.)

We describe a next-generation Drosophila protein interaction map-"DPIM2"-established from affinity purification-mass spectrometry of 5,805 baits, covering the largest fraction of the Drosophila proteome. The network contains 32,668 interactions among 3,644 proteins, organized into 632 clusters representing putative functional modules. Our analysis expands the pool of known protein interactions in Drosophila, provides annotation for poorly studied genes, and postulates previously undescribed protein interaction relationships. The predictive power and functional relevance of this network are probed through the lens of the Notch signaling pathway, and we find that newly identified members of complexes that include known Notch modifiers can also modulate Notch signaling. DPIM2 allows direct comparisons with a recently published human protein interaction network, defining the existence of functional interactions conserved across species. Thus, DPIM2 defines a valuable resource for predicting protein co-complex memberships and functional associations as well as generates functional hypotheses regarding specific protein interactions., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Organisms have evolved strategies to store resources and overcome periods of low or no nutrient access, including transient shortages or longer non-feeding developmental transitions. Holometabolous insects like Drosophila represent an attractive model to study resource allocation during development because they alternate feeding and non-feeding periods. Amino acids are essential components for tissue growth and renewal, but the strategies used for their storage remain largely unexplored. Here, we characterize the molecular mechanisms for the temporal production, accumulation, and use of specific storage proteins called hexamerins, and demonstrate their role in ensuring tissue formation and adult fitness. Moreover, we show that preventing hexamerin stores enhances the growth of early-developing organs while compromising the emergence of late-forming ones, consequently altering body allometry., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Dynamic changes in three-dimensional cell shape are important for tissue form and function. In the developing Drosophila eye, photoreceptor differentiation requires the progression across the tissue of an epithelial fold known as the morphogenetic furrow. Morphogenetic furrow progression involves apical cell constriction and movement of apical cell edges. Here, we show that cells progressing through the morphogenetic furrow move their basal edges in opposite direction to their apical edges, resulting in a cellular tilting movement. We further demonstrate that cells generate, at their basal side, oriented, force-generating protrusions. Knockdown of the protein kinase Src42A or photoactivation of a dominant-negative form of the small GTPase Rac1 reduces protrusion formation. Impaired protrusion formation stalls basal cell movement and slows down morphogenetic furrow progression and photoreceptor differentiation. This work identifies a cellular tilting mechanism important for the generation of dynamic tissue shape changes and cell differentiation., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

The Hippo pathway is an important regulator of organ growth and cell fate. The major mechanism by which Hippo is known to control transcription is by dictating the nucleo-cytoplasmic shuttling rate of Yorkie, a transcription co-activator, which promotes transcription with the DNA binding protein Scalloped. The nuclear biophysical behavior of Yorkie and Scalloped, and whether this is regulated by the Hippo pathway, remains unexplored. Using multiple live-imaging modalities on Drosophila tissues, we found that Scalloped interacts with DNA on a broad range of timescales, and enrichment of Scalloped at sites of active transcription is mediated by longer DNA dwell times. Further, Yorkie increased Scalloped's DNA dwell time, whereas the repressors Nervous fingers 1 (Nerfin-1) and Tondu-domain-containing growth inhibitor (Tgi) decreased it. Therefore, the Hippo pathway influences transcription not only by controlling nuclear abundance of Yorkie but also by modifying the DNA binding kinetics of the transcription factor Scalloped., Competing Interests: Declaration of interests K.F.H. is a member of the Developmental Cell advisory board., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Epithelial remodeling of the Drosophila retina depends on the pulsatile contraction and expansion of apical contacts between the cells that form its hexagonal lattice. Phosphoinositide PI(3,4,5)P 3 (PIP 3 ) accumulates around tricellular adherens junctions (tAJs) during contact expansion and dissipates during contraction, but with unknown function. Here, we found that manipulations of Pten or PI3-kinase (PI3K) that either decreased or increased PIP 3 resulted in shortened contacts and a disordered lattice, indicating a requirement for PIP 3 dynamics and turnover. These phenotypes are caused by a loss of branched actin, resulting from impaired activity of the Rac1 Rho GTPase and the WAVE regulatory complex (WRC). We additionally found that during contact expansion, PI3K moves into tAJs to promote the cyclical increase of PIP 3 in a spatially and temporally precise manner. Thus, dynamic control of PIP 3 by Pten and PI3K governs the protrusive phase of junctional remodeling, which is essential for planar epithelial morphogenesis., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Neurons must be made in the correct proportions to communicate with the appropriate synaptic partners and form functional circuits. In the Drosophila visual system, multiple subtypes of distal medulla (Dm) inhibitory interneurons are made in distinct, reproducible numbers-from 5 to 800 per optic lobe. These neurons are born from a crescent-shaped neuroepithelium called the outer proliferation center (OPC), which can be subdivided into specific domains based on transcription factor and growth factor expression. We fate mapped Dm neurons and found that more abundant neural types are born from larger neuroepithelial subdomains, while less abundant subtypes are born from smaller ones. Additionally, morphogenetic Dpp/BMP signaling provides a second layer of patterning that subdivides the neuroepithelium into smaller domains to provide more granular control of cell proportions. Apoptosis appears to play a minor role in regulating Dm neuron abundance. This work describes an underappreciated mechanism for the regulation of neuronal stoichiometry., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 Elsevier Inc. All rights reserved.)

The Drosophila larval ventral nerve cord (VNC) shares many similarities with the spinal cord of vertebrates and has emerged as a major model for understanding the development and function of motor systems. Here, we use high-quality scRNA-seq, validated by anatomical identification, to create a comprehensive census of larval VNC cell types. We show that the neural lineages that comprise the adult VNC are already defined, but quiescent, at the larval stage. Using fluorescence-activated cell sorting (FACS)-enriched populations, we separate all motor neuron bundles and link individual neuron clusters to morphologically characterized known subtypes. We discovered a glutamate receptor subunit required for basal neurotransmission and homeostasis at the larval neuromuscular junction. We describe larval glia and endorse the general view that glia perform consistent activities throughout development. This census represents an extensive resource and a powerful platform for future discoveries of cellular and molecular mechanisms in repair, regeneration, plasticity, homeostasis, and behavioral coordination., Competing Interests: Declaration of interests The authors declare no competing interests., (Published by Elsevier Inc.)

The Drosophila lymph gland houses blood progenitors that give rise to myeloid-like blood cells. Initially, blood progenitors proliferate, but later, they become quiescent to maintain multipotency before differentiation. Despite the identification of various factors involved in multipotency maintenance, the cellular mechanism controlling blood progenitor quiescence remains elusive. Here, we identify the expression of nitric oxide synthase in blood progenitors, generating nitric oxide for post-translational S-nitrosylation of protein cysteine residues. S-nitrosylation activates the Ire1-Xbp1-mediated unfolded protein response, leading to G2 cell-cycle arrest. Specifically, we identify the epidermal growth factor receptor as a target of S-nitrosylation, resulting in its retention within the endoplasmic reticulum and blockade of its receptor function. Overall, our findings highlight developmentally programmed S-nitrosylation as a critical mechanism that induces protein quality control in blood progenitors, maintaining their undifferentiated state by inhibiting cell-cycle progression and rendering them unresponsive to paracrine factors., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Epithelial furrowing is a fundamental morphogenetic process during gastrulation, neurulation, and body shaping. A furrow often results from a fold that propagates along a line. How fold formation and propagation are controlled and driven is poorly understood. To shed light on this, we study the formation of the cephalic furrow, a fold that runs along the embryo dorsal-ventral axis during Drosophila gastrulation and the developmental role of which is still unknown. We provide evidence of its function and show that epithelial furrowing is initiated by a group of cells. This cellular cluster works as a pacemaker, triggering a bidirectional morphogenetic wave powered by actomyosin contractions and sustained by de novo medial apex-to-apex cell adhesion. The pacemaker's Cartesian position is under the crossed control of the anterior-posterior and dorsal-ventral gene patterning systems. Thus, furrow formation is driven by a mechanical trigger wave that travels under the control of a multidimensional genetic guide., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Organ size is controlled by numerous factors including mechanical forces, which are mediated in part by the Hippo pathway. In growing Drosophila epithelial tissues, cytoskeletal tension influences Hippo signaling by modulating the localization of key pathway proteins to different apical domains. Here, we discovered a Hippo signaling hub at basal spot junctions, which form at the basal-most point of the lateral membranes and resemble adherens junctions in protein composition. Basal spot junctions recruit the central kinase Warts via Ajuba and E-cadherin, which prevent Warts activation by segregating it from upstream Hippo pathway proteins. Basal spot junctions are prominent when tissues undergo morphogenesis and are highly sensitive to fluctuations in cytoskeletal tension. They are distinct from focal adhesions, but the latter profoundly influences basal spot junction abundance by modulating the basal-medial actomyosin network and tension experienced by spot junctions. Thus, basal spot junctions couple morphogenetic forces to Hippo pathway activity and organ growth., Competing Interests: Declaration of interests K.F.H. is a member of the Developmental Cell advisory board., (Copyright © 2023 Elsevier Inc. All rights reserved.)

During morphogenesis, mechanical forces induce large-scale deformations; yet, how forces emerge from cellular contractility and adhesion is unclear. In Drosophila embryos, a tissue-scale wave of actomyosin contractility coupled with adhesion to the surrounding vitelline membrane drives polarized tissue invagination. We show that this process emerges subcellularly from the mechanical coupling between myosin II activation and sequential adhesion/de-adhesion to the vitelline membrane. At the wavefront, integrin clusters anchor the actin cortex to the vitelline membrane and promote activation of myosin II, which in turn enhances adhesion in a positive feedback. Following cell detachment, cortex contraction and advective flow amplify myosin II. Prolonged contact with the vitelline membrane prolongs the integrin-myosin II feedback, increases integrin adhesion, and thus slows down cell detachment and wave propagation. The angle of cell detachment depends on adhesion strength and sets the tensile forces required for detachment. Thus, we document how the interplay between subcellular mechanochemical feedback and geometry drives tissue morphogenesis., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Tissue homeostasis relies on rewiring of stem cell transcriptional programs into those of differentiated cells. Here, we investigate changes in chromatin occurring in a bipotent adult stem cells. Combining mapping of chromatin-associated factors with statistical modeling, we identify genome-wide transitions during differentiation in the adult Drosophila intestinal stem cell (ISC) lineage. Active, stem-cell-enriched genes transition to a repressive heterochromatin protein-1-enriched state more prominently in enteroendocrine cells (EEs) than in enterocytes (ECs), in which the histone H1-enriched Black state is preeminent. In contrast, terminal differentiation genes associated with metabolic functions follow a common path from a repressive, primed, histone H1-enriched Black state in ISCs to active chromatin states in EE and EC cells. Furthermore, we find that lineage priming has an important function in adult ISCs, and we identify histone H1 as a mediator of this process. These data define underlying principles of chromatin changes during adult multipotent stem cell differentiation., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 The Author(s). Published by Elsevier Inc. All rights reserved.)

Transcription factor combinations play a key role in shaping cellular identity. However, the precise relationship between specific combinations and downstream effects remains elusive. Here, we investigate this relationship within the context of the Drosophila eve locus, which is controlled by gap genes. We measure spatiotemporal levels of four gap genes in heterozygous and homozygous gap mutant embryos and correlate them with the striped eve activity pattern. Although changes in gap gene expression extend beyond the manipulated gene, the spatial patterns of Eve expression closely mirror canonical activation levels in wild type. Interestingly, some combinations deviate from the wild-type repertoire but still drive eve activation. Although in homozygous mutants some Eve stripes exhibit partial penetrance, stripes consistently emerge at reproducible positions, even with varying gap gene levels. Our findings suggest a robust molecular canalization of cell fates in gap mutants and provide insights into the regulatory constraints governing multi-enhancer gene loci., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Germ cells differentiate into oocytes that launch the next generation upon fertilization. How the highly specialized oocyte acquires this distinct cell fate is poorly understood. During Drosophila oogenesis, H3K9me3 histone methyltransferase SETDB1 translocates from the cytoplasm to the nucleus of germ cells concurrently with oocyte specification. Here, we discovered that nuclear SETDB1 is required for silencing a cohort of differentiation-promoting genes by mediating their heterochromatinization. Intriguingly, SETDB1 is also required for upregulating 18 of the ∼30 nucleoporins (Nups) that compose the nucleopore complex (NPC), promoting NPC formation. NPCs anchor SETDB1-dependent heterochromatin at the nuclear periphery to maintain H3K9me3 and gene silencing in the egg chambers. Aberrant gene expression due to the loss of SETDB1 or Nups results in the loss of oocyte identity, cell death, and sterility. Thus, a feedback loop between heterochromatin and NPCs promotes transcriptional reprogramming at the onset of oocyte specification, which is critical for establishing oocyte identity., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 Elsevier Inc. All rights reserved.)

In multicellular lives, the differentiation of stem cells and progenitor cells is often accompanied by a transition from glycolysis to mitochondrial oxidative phosphorylation (OXPHOS). However, the underlying mechanism of this metabolic transition remains largely unknown. In this study, we investigate the role of mechanical stress in activating OXPHOS during differentiation of the female germline cyst in Drosophila. We demonstrate that the surrounding somatic cells flatten the 16-cell differentiating cyst, resulting in an increase of the membrane tension of germ cells inside the cyst. This mechanical stress is necessary to maintain cytosolic Ca 2+ concentration in germ cells through a mechanically activated channel, transmembrane channel-like. The sustained cytosolic Ca 2+ triggers a CaMKI-Fray-JNK signaling relay, leading to the transcriptional activation of OXPHOS in differentiating cysts. Our findings demonstrate a molecular link between cell mechanics and mitochondrial energy metabolism, with implications for other developmentally orchestrated metabolic transitions in mammals., Competing Interests: Declaration of interests The authors declare no competing interests., (Published by Elsevier Inc.)

The retinoblastoma (RB) and Hippo pathways interact to regulate cell proliferation and differentiation. However, the mechanism of interaction is not fully understood. Drosophila photoreceptors with inactivated RB and Hippo pathways specify normally but fail to maintain their neuronal identity and dedifferentiate. We performed single-cell RNA sequencing to elucidate the cause of dedifferentiation and to determine the fate of these cells. We find that dedifferentiated cells adopt a progenitor-like fate due to inappropriate activation of the retinal differentiation suppressor homothorax (hth) by Yki/Sd. This results in the activation of a distinct Yki/Hth transcriptional program, driving photoreceptor dedifferentiation. We show that Rbf physically interacts with Yki and, together with the GAGA factor, inhibits the hth expression. Thus, RB and Hippo pathways cooperate to maintain photoreceptor differentiation by preventing inappropriate expression of hth in differentiating photoreceptors. Our work highlights the importance of both RB and Hippo pathway activities for maintaining the state of terminal differentiation., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Chromatin accessibility is integral to the process by which transcription factors (TFs) read out cis-regulatory DNA sequences, but it is difficult to differentiate between TFs that drive accessibility and those that do not. Deep learning models that learn complex sequence rules provide an unprecedented opportunity to dissect this problem. Using zygotic genome activation in Drosophila as a model, we analyzed high-resolution TF binding and chromatin accessibility data with interpretable deep learning and performed genetic validation experiments. We identify a hierarchical relationship between the pioneer TF Zelda and the TFs involved in axis patterning. Zelda consistently pioneers chromatin accessibility proportional to motif affinity, whereas patterning TFs augment chromatin accessibility in sequence contexts where they mediate enhancer activation. We conclude that chromatin accessibility occurs in two tiers: one through pioneering, which makes enhancers accessible but not necessarily active, and the second when the correct combination of TFs leads to enhancer activation., Competing Interests: Declaration of interests J.Z. owns a patent on ChIP-nexus (no. 10287628). A.K. is on the scientific advisory board of PatchBio, SerImmune, AINovo, TensorBio and OpenTargets, was a consultant with Illumina, and owns shares in Illumina, Deep Genomics, Immunai, and Freenome Inc. All other authors declare no competing interests., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

The Hippo pathway is an evolutionarily conserved regulator of tissue growth that integrates inputs from both polarity and actomyosin networks. An upstream activator of the Hippo pathway, Kibra, localizes at the junctional and medial regions of the apical cortex in epithelial cells, and medial accumulation promotes Kibra activity. Here, we demonstrate that cortical Kibra distribution is controlled by a tug-of-war between apical polarity and actomyosin dynamics. We show that while the apical polarity network, in part via atypical protein kinase C (aPKC), tethers Kibra at the junctional cortex to silence its activity, medial actomyosin flows promote Kibra-mediated Hippo complex formation at the medial cortex, thereby activating the Hippo pathway. This study provides a mechanistic understanding of the relationship between the Hippo pathway, polarity, and actomyosin cytoskeleton, and it offers novel insights into how fundamental features of epithelial tissue architecture can serve as inputs into signaling cascades that control tissue growth, patterning, and morphogenesis., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Post-developmental organ resizing improves organismal fitness under constantly changing nutrient environments. Although stem cell abundance is a fundamental determinant of adaptive resizing, our understanding of its underlying mechanisms remains primarily limited to the regulation of stem cell division. Here, we demonstrate that nutrient fluctuation induces dedifferentiation in the Drosophila adult midgut to drive adaptive intestinal growth. From lineage tracing and single-cell RNA sequencing, we identify a subpopulation of enteroendocrine (EE) cells that convert into functional intestinal stem cells (ISCs) in response to dietary glucose and amino acids by activating the JAK-STAT pathway. Genetic ablation of EE-derived ISCs severely impairs ISC expansion and midgut growth despite the retention of resident ISCs, and in silico modeling further indicates that EE dedifferentiation enables an efficient increase in the midgut cell number while maintaining epithelial cell composition. Our findings identify a physiologically induced dedifferentiation that ensures ISC expansion during adaptive organ growth in concert with nutrient conditions., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 Elsevier Inc. All rights reserved.)

The eukaryotic genome is organized to enable the precise regulation of gene expression. This organization is established as the embryo transitions from a fertilized gamete to a totipotent zygote. To understand the factors and processes that drive genomic organization, we focused on the pioneer factor GAGA factor (GAF) that is required for early development in Drosophila. GAF transcriptionally activates the zygotic genome and is localized to subnuclear foci. This non-uniform distribution is driven by binding to highly abundant GA repeats. At GA repeats, GAF is necessary to form heterochromatin and silence transcription. Thus, GAF is required to establish both active and silent regions. We propose that foci formation enables GAF to have opposing transcriptional roles within a single nucleus. Our data support a model in which the subnuclear concentration of transcription factors acts to organize the nucleus into functionally distinct domains essential for the robust regulation of gene expression., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 Elsevier Inc. All rights reserved.)

The asymmetric divisions of Drosophila neural stem cells (NSCs) produce unequally sized siblings, with most volume directed into the sibling that retains the NSC fate. Sibling size asymmetry results from the preferential expansion of the NSC sibling surface during division. Here, we show that a polarized membrane reservoir constructed by the NSC in early mitosis provides the source for expansion. The reservoir is formed from membrane domains that contain folds and microvilli that become polarized by apically directed cortical flows of actomyosin early in mitosis. When furrow ingression begins and internal pressure increases, the stores of membrane within the apical reservoir are rapidly consumed. Expansion is substantially diminished in NSCs that lack a reservoir, and membrane expansion equalizes when the reservoir is not polarized. Our results suggest that the cortical flows that remodel the plasma membrane during asymmetric cell division function to satisfy the dynamic surface area requirements of unequally dividing cells., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Combinatorial signaling is key to instruct context-dependent cell behaviors. During embryonic development, adult homeostasis, and disease, bone morphogenetic proteins (BMPs) act as dimers to instruct specific cellular responses. BMP ligands can form both homodimers or heterodimers; however, obtaining direct evidence of the endogenous localization and function of each form has proven challenging. Here, we make use of precise genome editing and direct protein manipulation via protein binders to dissect the existence and functional relevance of BMP homodimers and heterodimers in the Drosophila wing imaginal disc. This approach identified in situ the existence of Dpp (BMP2/4)/Gbb (BMP5/6/7/8) heterodimers. We found that Gbb is secreted in a Dpp-dependent manner in the wing imaginal disc. Dpp and Gbb form a gradient of heterodimers, whereas neither Dpp nor Gbb homodimers are evident under endogenous physiological conditions. We find that the formation of heterodimers is critical for obtaining optimal signaling and long-range BMP distribution., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

BMP family ligands can direct cells to divide, differentiate, or die, depending on cell context and specific hetero- or homodimer combinations. In this issue of Developmental Cell, Bauer et al. detect endogenous Drosophila ligand dimers in situ and show that BMP dimer composition affects both signaling range and activity., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Loss of fragile X messenger ribonucleoprotein (FMRP) causes fragile X syndrome (FXS), the most prevalent form of inherited intellectual disability. Here, we show that FMRP interacts with the voltage-dependent anion channel (VDAC) to regulate the formation and function of endoplasmic reticulum (ER)-mitochondria contact sites (ERMCSs), structures that are critical for mitochondrial calcium (mito-Ca 2+ ) homeostasis. FMRP-deficient cells feature excessive ERMCS formation and ER-to-mitochondria Ca 2+ transfer. Genetic and pharmacological inhibition of VDAC or other ERMCS components restored synaptic structure, function, and plasticity and rescued locomotion and cognitive deficits of the Drosophila dFmr1 mutant. Expressing FMRP C-terminal domain (FMRP-C), which confers FMRP-VDAC interaction, rescued the ERMCS formation and mito-Ca 2+ homeostasis defects in FXS patient iPSC-derived neurons and locomotion and cognitive deficits in Fmr1 knockout mice. These results identify altered ERMCS formation and mito-Ca 2+ homeostasis as contributors to FXS and offer potential therapeutic targets., Competing Interests: Declaration of interests B.L. is a cofounder and serves on the scientific advisory board of Cerepeut Inc., (Copyright © 2023 Elsevier Inc. All rights reserved.)

The canonical function of the Hippo signaling pathway is the regulation of organ growth. How this pathway controls cell-fate determination is less well understood. Here, we identify a function of the Hippo pathway in cell-fate decisions in the developing Drosophila eye, exerted through the interaction of Yorkie (Yki) with the transcriptional regulator Bonus (Bon), an ortholog of mammalian transcriptional intermediary factor 1/tripartite motif (TIF1/TRIM) family proteins. Instead of controlling tissue growth, Yki and Bon promote epidermal and antennal fates at the expense of the eye fate. Proteomic, transcriptomic, and genetic analyses reveal that Yki and Bon control these cell-fate decisions by recruiting transcriptional and post-transcriptional co-regulators and by repressing Notch target genes and activating epidermal differentiation genes. Our work expands the range of functions and regulatory mechanisms under Hippo pathway control., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Developmental enhancers bind transcription factors and dictate patterns of gene expression during development. Their molecular evolution can underlie phenotypical evolution, but the contributions of the evolutionary pathways involved remain little understood. Here, using mutation libraries in Drosophila melanogaster embryos, we observed that most point mutations in developmental enhancers led to changes in gene expression levels but rarely resulted in novel expression outside of the native pattern. In contrast, random sequences, often acting as developmental enhancers, drove expression across a range of cell types; random sequences including motifs for transcription factors with pioneer activity acted as enhancers even more frequently. Our findings suggest that the phenotypic landscapes of developmental enhancers are constrained by enhancer architecture and chromatin accessibility. We propose that the evolution of existing enhancers is limited in its capacity to generate novel phenotypes, whereas the activity of de novo elements is a primary source of phenotypic novelty., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Collective cell movements drive normal development and metastasis. Drosophila border cells move as a cluster of 6-10 cells, where the role of the Rac GTPase in migration was first established. In border cells, as in most migratory cells, Rac stimulates leading-edge protrusion. Upstream Rac regulators in leaders have been identified; however, the regulation and function of Rac in follower border cells is unknown. Here, we show that all border cells require Rac, which promotes follower-cell motility and is important for cluster compactness and movement. We identify a Rac guanine nucleotide exchange factor, Cdep, which also regulates follower-cell movement and cluster cohesion. Scribble, Discs large, and Lethal giant larvae localize Cdep basolaterally and share phenotypes with Cdep. Relocalization of Cdep::GFP partially rescues Scribble knockdown, suggesting that Cdep is a major downstream effector of basolateral proteins. Thus, a Scrib/Cdep/Rac pathway promotes cell crawling and coordinated, collective migration in vivo., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2022 The Author(s). Published by Elsevier Inc. All rights reserved.)

Stochastic mechanisms diversify cell fates during development. How cells randomly choose between two or more fates remains poorly understood. In the Drosophila eye, the random mosaic of two R7 photoreceptor subtypes is determined by expression of the transcription factor Spineless (Ss). We investigated how cis-regulatory elements and trans factors regulate nascent transcriptional activity and chromatin compaction at the ss gene locus during R7 development. The ss locus is in a compact state in undifferentiated cells. An early enhancer drives transcription in all R7 precursors, and the locus opens. In differentiating cells, transcription ceases and the ss locus stochastically remains open or compacts. In Ss ON R7s, ss is open and competent for activation by a late enhancer, whereas in Ss OFF R7s, ss is compact, and repression prevents expression. Our results suggest that a temporally dynamic antagonism, in which transcription drives large-scale decompaction and then compaction represses transcription, controls stochastic fate specification., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Developing synapses mature through the recruitment of specific proteins that stabilize presynaptic and postsynaptic structure and function. Wnt ligands signaling via Frizzled (Fz) receptors play many crucial roles in neuronal and synaptic development, but whether and how Wnt and Fz influence synaptic maturation is incompletely understood. Here, we show that Fz2 receptor cleavage via the γ-secretase complex is required for postsynaptic development and maturation. In the absence of γ-secretase, Drosophila neuromuscular synapses fail to recruit postsynaptic scaffolding and cytoskeletal proteins, leading to behavioral deficits. Introducing presenilin mutations linked to familial early-onset Alzheimer's disease into flies leads to synaptic maturation phenotypes that are identical to those seen in null alleles. This conserved role for γ-secretase in synaptic maturation and postsynaptic development highlights the importance of Fz2 cleavage and suggests that receptor processing by proteins linked to neurodegeneration may be a shared mechanism with aspects of synaptic development., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2022 The Author(s). Published by Elsevier Inc. All rights reserved.)

Temporal patterning of neural progenitors is an evolutionarily conserved strategy for generating neuronal diversity. Type II neural stem cells in the Drosophila central brain produce transit-amplifying intermediate neural progenitors (INPs) that exhibit temporal patterning. However, the known temporal factors cannot account for the neuronal diversity in the adult brain. To search for missing factors, we developed NanoDam, which enables rapid genome-wide profiling of endogenously tagged proteins in vivo with a single genetic cross. Mapping the targets of known temporal transcription factors with NanoDam revealed that Homeobrain and Scarecrow (ARX and NKX2.1 orthologs) are also temporal factors. We show that Homeobrain and Scarecrow define middle-aged and late INP temporal windows and play a role in cellular longevity. Strikingly, Homeobrain and Scarecrow have conserved functions as temporal factors in the developing visual system. NanoDam enables rapid cell-type-specific genome-wide profiling with temporal resolution and is easily adapted for use in higher organisms., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2022 The Author(s). Published by Elsevier Inc. All rights reserved.)

During Drosophila melanogaster male germline stem cell (GSC) asymmetric division, preexisting old versus newly synthesized histones H3 and H4 are asymmetrically inherited. However, the biological outcomes of this phenomenon have remained unclear. Here, we tracked old and new histones throughout the GSC cell cycle through the use of high spatial and temporal resolution microscopy. We found unique features that differ between old and new histone-enriched sister chromatids, including differences in nucleosome density, chromosomal condensation, and H3 Ser10 phosphorylation. These distinct chromosomal features lead to their differential association with Cdc6, a pre-replication complex component, and subsequent asynchronous DNA replication initiation in the resulting daughter cells. Disruption of asymmetric histone inheritance abolishes differential Cdc6 association and asynchronous S-phase entry, demonstrating that histone asymmetry acts upstream of these critical cell-cycle progression events. Furthermore, disruption of these GSC-specific chromatin features leads to GSC defects, indicating a connection between histone inheritance, cell-cycle progression, and cell fate determination., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2022 The Author(s). Published by Elsevier Inc. All rights reserved.)

Tissue homeostasis often requires a properly placed niche to support stem cells. Morphogenetic processes that position a niche are just being described. For the Drosophila testis, we recently showed that pro-niche cells, specified at disparate positions during early gonadogenesis, must assemble into one collective at the anterior of the gonad. We now find that Slit and FGF signals emanating from adjacent visceral mesoderm regulate assembly. In response to signaling, niche cells express islet, which we find is also required for niche assembly. Without signaling, niche cells specified furthest from the anterior are unable to migrate, remaining dispersed. The function of such niches is severely disrupted, with niche cells evading cell cycle quiescence, compromised in their ability to signal the incipient stem cell pool, and failing to orient stem cell divisions properly. Our work identifies both extrinsic signaling and intrinsic responses required for proper assembly and placement of the testis niche., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Ribosomal defects perturb stem cell differentiation, and this is the cause of ribosomopathies. How ribosome levels control stem cell differentiation is not fully known. Here, we discover that three DExD/H-box proteins govern ribosome biogenesis (RiBi) and Drosophila oogenesis. Loss of these DExD/H-box proteins, which we name Aramis, Athos, and Porthos, aberrantly stabilizes p53, arrests the cell cycle, and stalls germline stem cell (GSC) differentiation. Aramis controls cell-cycle progression by regulating translation of mRNAs that contain a terminal oligo pyrimidine (TOP) motif in their 5' UTRs. We find that TOP motifs confer sensitivity to ribosome levels that are mediated by La-related protein (Larp). One such TOP-containing mRNA codes for novel nucleolar protein 1 (Non1), a conserved p53 destabilizing protein. Upon a sufficient ribosome concentration, Non1 is expressed, and it promotes GSC cell-cycle progression via p53 degradation. Thus, a previously unappreciated TOP motif in Drosophila responds to reduced RiBi to co-regulate the translation of ribosomal proteins and a p53 repressor, coupling RiBi to GSC differentiation., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Niches maintain a finite pool of stem cells via restricted space and short-range signals. Stem cells compete for limited niche resources, but the mechanisms regulating competition are poorly understood. Using the Drosophila testis model, we show that germline stem cells (GSCs) lacking the transcription factor Chinmo gain a competitive advantage for niche access. Surprisingly, chinmo -/- GSCs rely on a new mechanism of competition in which they secrete the extracellular matrix protein Perlecan to selectively evict non-mutant GSCs and then upregulate Perlecan-binding proteins to remain in the altered niche. Over time, the GSC pool can be entirely replaced with chinmo -/- cells. As a consequence, the mutant chinmo allele acts as a gene drive element; the majority of offspring inherit the allele despite the heterozygous genotype of the parent. Our results suggest that the influence of GSC competition may extend beyond individual stem cell niche dynamics to population-level allelic drift and evolution., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Ribonucleoprotein condensates can exhibit diverse physical states in vitro and in vivo. Despite considerable progress, the relevance of condensate physical states for in vivo biological function remains limited. Here, we investigated the physical properties of processing bodies (P bodies) and their impact on mRNA storage in mature Drosophila oocytes. We show that the conserved DEAD-box RNA helicase Me31B forms viscous P body condensates, which adopt an arrested physical state. We demonstrate that structurally distinct proteins and protein-protein interactions, together with RNA, regulate the physical properties of P bodies. Using live imaging and in situ hybridization, we show that the arrested state and integrity of P bodies support the storage of bicoid (bcd) mRNA and that egg activation modulates P body properties, leading to the release of bcd for translation in the early embryo. Together, this work provides an example of how physical states of condensates regulate cellular function in development., Competing Interests: Declarations of interests S.A. is an advisor on the scientific advisory board of Dew point Therapeutics. A.S.H. is a scientific consultant with Dewpoint Therapeutics., (Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.)

Cancer patients often die from symptoms that manifest at a distance from any tumor. Mechanisms underlying these systemic physiological perturbations, called paraneoplastic syndromes, may benefit from investigation in non-mammalian systems. Using a non-metastatic Drosophila adult model, we find that malignant-tumor-produced cytokines drive widespread host activation of JAK-STAT signaling and cause premature lethality. STAT activity is particularly high in cells of the blood-brain barrier (BBB), where it induces aberrant BBB permeability. Remarkably, inhibiting STAT in the BBB not only rescues barrier function but also extends the lifespan of tumor-bearing hosts. We identify BBB damage in other pathological conditions that cause elevated inflammatory signaling, including obesity and infection, where BBB permeability also regulates host survival. IL-6-dependent BBB dysfunction is further seen in a mouse tumor model, and it again promotes host morbidity. Therefore, BBB alterations constitute a conserved lethal tumor-host interaction that also underlies other physiological morbidities., Competing Interests: Declaration of interests These authors declare no competing interests., (Copyright © 2021 Elsevier Inc. All rights reserved.)

The nuclear lamina is typically associated with transcriptional silencing, and peripheral relocation of genes highly correlates with repression. However, the DNA sequences and proteins regulating gene-lamina interactions are largely unknown. Exploiting the developmentally timed hunchback gene movement to the lamina in Drosophila neuroblasts, we identified a 250 bp intronic element (IE) both necessary and sufficient for relocation. The IE can target a reporter transgene to the lamina and silence it. Endogenously, however, hunchback is already repressed prior to relocation. Instead, IE-mediated relocation confers a heritably silenced gene state refractory to activation in descendent neurons, which terminates neuroblast competence to specify early-born identity. Surprisingly, we found that the Polycomb group chromatin factors bind the IE and are required for lamina relocation, revealing a nuclear architectural role distinct from their well-known function in transcriptional repression. Together, our results uncover in vivo mechanisms underlying neuroblast competence and lamina association in heritable gene silencing., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.)

piRNAs guide Piwi/Panoramix-dependent H3K9me3 chromatin modification and transposon silencing during Drosophila germline development. The THO RNA export complex is composed of Hpr1, Tho2, and Thoc5-7. Null thoc7 mutations, which displace Thoc5 and Thoc6 from a Tho2-Hpr1 subcomplex, reduce expression of a subset of germline piRNAs and increase transposon expression, suggesting that THO silences transposons by promoting piRNA biogenesis. Here, we show that the thoc7-null mutant combination increases transposon transcription but does not reduce anti-sense piRNAs targeting half of the transcriptionally activated transposon families. These mutations also fail to reduce piRNA-guided H3K9me3 chromatin modification or block Panoramix-dependent silencing of a reporter transgene, and unspliced transposon transcripts co-precipitate with THO through a Piwi- and Panoramix-independent mechanism. Mutations in piwi also dominantly enhance germline defects associated with thoc7-null alleles. THO thus functions in a piRNA-independent transposon-silencing pathway, which acts cooperatively with Piwi to support germline development., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Force generation in epithelial tissues is often pulsatile, with actomyosin networks generating contractile forces before cyclically disassembling. This pulsed nature of cytoskeletal forces implies that there must be ratcheting mechanisms that drive processive transformations in cell shape. Previous work has shown that force generation is coordinated with endocytic remodeling; however, how ratcheting becomes engaged at specific cell surfaces remains unclear. Here, we report that PtdIns(3,4,5)P 3 is a critical lipid-based cue for ratcheting engagement. The Sbf RabGEF binds to PIP 3 , and disruption of PIP 3 reveals a dramatic switching behavior in which medial ratcheting is activated and epithelial cells begin globally constricting apical surfaces. PIP 3 enrichments are developmentally regulated, with mesodermal cells having high apical PIP 3 while germband cells have higher interfacial PIP 3 . Finally, we show that JAK/STAT signaling constitutes a second pathway that combinatorially regulates Sbf/Rab35 recruitment. Our results elucidate a complex lipid-dependent regulatory machinery that directs ratcheting engagement in epithelial tissues., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Aging causes stem cell dysfunction as a result of extrinsic and intrinsic changes. Decreased function of the stem cell niche is an important contributor to this dysfunction. We use the Drosophila testis to investigate what factors maintain niche cells. The testis niche comprises quiescent "hub" cells and supports two mitotic stem cell pools: germline stem cells and somatic cyst stem cells (CySCs). We identify the cell-cycle-responsive Dp/E2f1 transcription factor as a crucial non-autonomous regulator required in CySCs to maintain hub cell quiescence. Dp/E2f1 inhibits local Activin ligands through production of the Activin antagonist Follistatin (Fs). Inactivation of Dp/E2f1 or Fs in CySCs or promoting Activin receptor signaling in hub cells causes transdifferentiation of hub cells into fully functional CySCs. This Activin-dependent communication between CySCs and hub regulates the physiological decay of the niche with age and demonstrates that hub cell quiescence results from signals from surrounding stem cells., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.)

Many developmental regulators have complex and context-specific roles in different tissues and stages, making the dissection of their function extremely challenging. As regulatory processes often occur within minutes, perturbation methods that match these dynamics are needed. Here, we present the improved light-inducible nuclear export system (iLEXY), an optogenetic loss-of-function approach that triggers translocation of proteins from the nucleus to the cytoplasm. By introducing a series of mutations, we substantially increased LEXY's efficiency and generated variants with different recovery times. iLEXY enables rapid (t 1/2  < 30 s), efficient, and reversible nuclear protein depletion in embryos, and is generalizable to proteins of diverse sizes and functions. Applying iLEXY to the Drosophila master regulator Twist, we phenocopy loss-of-function mutants, precisely map the Twist-sensitive embryonic stages, and investigate the effects of timed Twist depletions. Our results demonstrate the power of iLEXY to dissect the function of pleiotropic factors during embryogenesis with unprecedented temporal precision., Competing Interests: Declaration of interests E.E.M.F. is a member of the Dev Cell editorial Advisory Board., (Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.)

Cancer tissue often comprises multiple tumor clones with distinct oncogenic alterations such as Ras or Src activation, yet the mechanism by which tumor heterogeneity drives cancer progression remains elusive. Here, we show in Drosophila imaginal epithelium that clones of Ras- or Src-activated benign tumors interact with each other to mutually promote tumor malignancy. Mechanistically, Ras-activated cells upregulate the cell-surface ligand Delta while Src-activated cells upregulate its receptor Notch, leading to Notch activation in Src cells. Elevated Notch signaling induces the transcriptional repressor Zfh1/ZEB1, which downregulates E-cadherin and cell death gene hid, leading to Src-activated invasive tumors. Simultaneously, Notch activation in Src cells upregulates the cytokine Unpaired/IL-6, which activates JAK-STAT signaling in neighboring Ras cells. Elevated JAK-STAT signaling upregulates the BTB-zinc-finger protein Chinmo, which downregulates E-cadherin and thus generates Ras-activated invasive tumors. Our findings provide a mechanistic explanation for how tumor heterogeneity triggers tumor progression via cell-cell interactions., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2021 Elsevier Inc. All rights reserved.)

The presence of a wound triggers surrounding cells to initiate repair mechanisms, but it is not clear how cells initially detect wounds. In epithelial cells, the earliest known wound response, occurring within seconds, is a dramatic increase in cytosolic calcium. Here, we show that wounds in the Drosophila notum trigger cytoplasmic calcium increase by activating extracellular cytokines, Growth-blocking peptides (Gbps), which initiate signaling in surrounding epithelial cells through the G-protein-coupled receptor Methuselah-like 10 (Mthl10). Latent Gbps are present in unwounded tissue and are activated by proteolytic cleavage. Using wing discs, we show that multiple protease families can activate Gbps, suggesting that they act as a generalized protease-detector system. We present experimental and computational evidence that proteases released during wound-induced cell damage and lysis serve as the instructive signal: these proteases liberate Gbp ligands, which bind to Mthl10 receptors on surrounding epithelial cells, and activate downstream release of calcium., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Individual organ development must be temporally coordinated with development of the rest of the organism. As a result, cell division cycles in a developing organ occur on a relatively fixed timescale. Despite this, many developing organs can regenerate cells lost to injury. How organs regenerate within the time constraints of organism development remains unclear. Here, we show that the developing Drosophila hindgut regenerates by accelerating the mitotic cell cycle. This process is achieved by decreasing G1 length and requires the JAK/STAT ligand unpaired-3. Mitotic capacity is then terminated by the steroid hormone ecdysone receptor and the Sox transcription factor Dichaete. These two factors converge on regulation of a hindgut-specific enhancer of fizzy-related, a negative regulator of mitotic cyclins. Our findings reveal how the cell-cycle machinery and cytokine signaling can be adapted to accomplish developmental organ regeneration., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Toll receptors are key determinants of planar polarity during Drosophila gastrulation. Two papers in the current issue of Developmental Cell now identify key features of their downstream signaling that allow cell symmetry to be broken by apparently non-polarized Toll receptors., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2021 Elsevier Inc. All rights reserved.)