EGFR and Notch signaling respectively regulate proliferative activity and multiple cell lineage differentiation of Drosophila gastric stem cells

Werner syndrome exonuclease promotes gut regeneration and causes age-associated gut hyperplasia in Drosophila

Human Werner syndrome (adult progeria, a well-established model of human aging) is caused by mutations in the Werner syndrome (WRN) gene. However, the expression patterns and functions of WRN in natural aging remain poorly understood. Despite the link between WRN deficiencies and progeria, our analyses of human colon tissues, mouse crypts, and Drosophila midguts revealed that WRN expression does not decrease but rather increases in intestinal stem cells (ISCs) with aging. Mechanistically, we found that the Drosophila WRN homologue (WRNexo) binds to Heat shock 70-kDa protein cognate 3 (Hsc70-3/Bip) to regulate the unfolded protein response of the endoplasmic reticulum (UPRER). Activation of the WRNexo-mediated UPRER in ISCs is required for ISC proliferation during injury repair. However, persistent DNA damage during aging leads to chronic upregulation of WRNexo in ISCs, where excessive WRNexo-induced ER stress drives age-associated gut hyperplasia in Drosophila. This study reveals how elevated WRNexo contributes to stem cell aging, providing new insights into organ aging and the pathogenesis of age-related diseases, such as colon cancer.

Amphiregulin Switches Progenitor Cell Fate for Lineage Commitment During Gastric Mucosal Regeneration

BACKGROUND & AIMS

Isthmic progenitors, tissue-specific stem cells in the stomach corpus, maintain mucosal homeostasis by balancing between proliferation and differentiation to gastric epithelial lineages. The progenitor cells rapidly adopt an active state in response to mucosal injury. However, it remains unclear how the isthmic progenitor cell niche is controlled during the regeneration of damaged epithelium.

METHODS

We recapitulated tissue recovery process after acute mucosal injury in the mouse stomach. Bromodeoxyuridine incorporation was used to trace newly generated cells during the injury and recovery phases. To define the epithelial lineage commitment process during recovery, we performed single-cell RNA-sequencing on epithelial cells from the mouse stomachs. We validated the effects of amphiregulin (AREG) on mucosal recovery, using recombinant AREG treatment or AREG-deficient mice.

RESULTS

We determined that an epidermal growth factor receptor ligand, AREG, can control progenitor cell lineage commitment. Based on the identification of lineage-committed subpopulations in the corpus epithelium through single-cell RNA-sequencing and bromodeoxyuridine incorporation, we showed that isthmic progenitors mainly transition into short-lived surface cell lineages but are less frequently committed to long-lived parietal cell lineages in homeostasis. However, mucosal regeneration after damage directs the lineage commitment of isthmic progenitors towards parietal cell lineages. During recovery, AREG treatment promoted repopulation with parietal cells, while suppressing surface cell commitment of progenitors. In contrast, transforming growth factor-α did not alter parietal cell regeneration, but did induce expansion of surface cell populations. AREG deficiency impairs parietal cell regeneration but increases surface cell commitment.

CONCLUSIONS

These data demonstrate that different epidermal growth factor receptor ligands can distinctly regulate isthmic progenitor-driven mucosal regeneration and lineage commitment.

Chromatin state transitions in the Drosophila intestinal lineage identify principles of cell-type specification

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.

Functional analysis of zona pellucida domain protein Dusky in Tribolium castaneum

The zona pellucida domain protein Dusky (Dy) plays a vital role in wing morphogenesis in insects, but little information on its function has been reported. In this study, we found that dy regulated wing cell size, larval and pupal duration, and the metabolism of amino acid and 20-hydroxyecdysone in Tribolium castaneum. Using RNA-seq, 413 differentially expressed genes were identified between physiological buffer-injected and dy-double-stranded RNA-treated larvae, including 88 downregulated genes and 325 upregulated genes. Among these genes, dy knockdown increased CYP18A1 expression to elevate the 26-hydroxylation of 20-hydroxyecdysone, which ultimately led to growth defects in wing cells. Silencing of dy upregulated the transcription of genes encoding tyrosine aminotransferase, 4-hydroxyphenylpyruvate dioxygenase, homogentisate 1, 2-dioxygenase, and Pale to promote the catabolism of tyrosine and phenylalanine, which eventually reduced amino acid content. Furthermore, dy knockdown upregulated 4E-BP expression, and 4E-BP silencing partially phenocopied dy RNA interference-mediated wing morphogenesis. These results suggest that Dy controls 20-hydroxyecdysone and amino acid metabolism to regulate wing morphogenesis in the insect.

Ursolic Acid Protects Sodium Dodecyl Sulfate-Induced Drosophila Ulcerative Colitis Model by Inhibiting the JNK Signaling

Ursolic acid (UA) is a bioactive molecule widely distributed in various fruits and vegetables, which was reported to play a therapeutic role in ulcerative colitis (UC) induced by toxic chemicals. However, the underlying mechanism has not been well clarified in vivo. Here, using a Drosophila UC model induced by sodium dodecyl sulfate (SDS), we investigated the defensive effect of UA on intestinal damage. The results showed that UA could significantly protect Drosophila from the damage caused by SDS exposure. Further, UA alleviated the accumulation of reactive oxygen species (ROS) and malondialdehyde (MDA) induced by SDS and upregulated the activities of total superoxide dismutase (T-SOD) and catalase (CAT). Moreover, the proliferation and differentiation of intestine stem cells (ISCs) as well as the excessive activation of the c-Jun N-terminal kinase (JNK)-dependent JAK/STAT signaling pathway induced by SDS were restored by UA. In conclusion, UA prevents intestine injury from toxic compounds by reducing the JNK/JAK/STAT signaling pathway. UA may provide a theoretical basis for functional food or natural medicine development.

ClC-c regulates the proliferation of intestinal stem cells via the EGFR signalling pathway in Drosophila

Objectives

Adult stem cells uphold a delicate balance between quiescent and active states, which is crucial for tissue homeostasis. Whereas many signalling pathways that regulate epithelial stem cells have been reported, many regulators remain unidentified.

Materials and Methods

Flies were used to generate tissue‐specific gene knockdown and gene knockout. qRT‐PCR was used to assess the relative mRNA levels. Immunofluorescence was used to determine protein localization and expression patterns. Clonal analyses were used to observe the phenotype. RNA‐seq was used to screen downstream mechanisms.

Results

Here, we report a member of the chloride channel family, ClC‐c, which is specifically expressed in Drosophila intestinal stem/progenitor cells and regulates intestinal stem cell (ISC) proliferation under physiological conditions and upon tissue damage. Mechanistically, we found that the ISC loss induced by the depletion of ClC‐c in intestinal stem/progenitor cells is due to inhibition of the EGFR signalling pathway.

Conclusion

Our findings reveal an ISC‐specific function of ClC‐c in regulating stem cell maintenance and proliferation, thereby providing new insights into the functional links among the chloride channel family, ISC proliferation and tissue homeostasis.

An image analysis method for regionally defined cellular phenotyping of the Drosophila midgut

The intestine is divided into functionally distinct regions along the anteroposterior (A/P) axis. How the regional identity influences the function of intestinal stem cells (ISCs) and their offspring remain largely unresolved. We introduce an imaging-based method, "Linear Analysis of Midgut" (LAM), which allows quantitative, regionally defined cellular phenotyping of the whole Drosophila midgut. LAM transforms image-derived cellular data from three-dimensional midguts into a linearized representation, binning it into segments along the A/P axis. Through automated multivariate determination of regional borders, LAM allows mapping and comparison of cellular features and frequencies with subregional resolution. Through the use of LAM, we quantify the distributions of ISCs, enteroblasts, and enteroendocrine cells in a steady-state midgut, and reveal unprecedented regional heterogeneity in the ISC response to a Drosophila model of colitis. Altogether, LAM is a powerful tool for organ-wide quantitative analysis of the regional heterogeneity of midgut cells.

ANKRD22 Drives Rapid Proliferation of Lgr5+ Cells and Acts as a Promising Therapeutic Target in Gastric Mucosal Injury

BACKGROUND & AIMS

Rapid gastric epithelial progenitor cell (EPC) proliferation and inflammatory response inhibition play key roles in promoting the repair of gastric mucosal damage. However, specific targets inducing these effects are unknown. In this study, we explored the effects of a potential target, Ankyrin repeat domain 22 (ANKRD22).

METHODS

An acute gastric mucosal injury model was established with Ankrd22^-/- and Ankrd22^+/+ mice by intragastric administration of acidified ethanol. Organoid culture and flow cytometry were performed to evaluate the effects of ANKRD22 on leucine-rich repeat-containing G-protein-coupled receptor 5-positive (Lgr5⁺) gastric EPC proliferation. The mechanisms by which ANKRD22 affects gastric EPC proliferation and inflammatory responses were explored by mitochondrial Ca²⁺ influx and immunoblotting. Candidate ANKRD22 inhibitors then were screened virtually and validated in vitro and in vivo.

RESULTS

After acute gastric mucosal injury, the number of Lgr5⁺ gastric EPCs was increased significantly in Ankrd22^-/- mice compared with that in Ankrd22^+/+ mice. Moreover, Ankrd22 knockout attenuated inflammatory cell infiltration into damaged gastric tissues. ANKRD22 deletion also reduced mitochondrial Ca²⁺ influx and cytoplasmic nuclear factor of activated T cells in gastric epithelial cells and macrophages, which further induced Lgr5⁺ gastric EPC proliferation and decreased macrophage release of tumor necrosis factor-α and interleukin 1α. In addition, a small molecule, AV023, was found to show similar effects to those produced by ANKRD22 deletion in vitro. Intraperitoneal injection of AV023 into the mouse model promoted the repair of gastric mucosal damage, with increased proliferation of Lgr5⁺ gastric EPCs and visible relief of inflammation.

CONCLUSIONS

ANKRD22 inhibition is a potential target-based therapeutic approach for promoting the repair of gastric mucosal damage.

Neuroglian regulates Drosophila intestinal stem cell proliferation through enhanced signaling via the epidermal growth factor receptor

The Drosophila intestine is an excellent system for elucidating mechanisms regulating stem cell behavior. Here we show that the septate junction (SJ) protein Neuroglian (Nrg) is expressed in intestinal stem cells (ISCs) and enteroblasts (EBs) within the fly intestine. SJs are not present between ISCs and EBs, suggesting Nrg plays a different role in this tissue. We reveal that Nrg is required for ISC proliferation in young flies, and depletion of Nrg from ISCs and EBs suppresses increased ISC proliferation in aged flies. Conversely, overexpression of Nrg in ISC and EBs promotes ISC proliferation, leading to an increase in cells expressing ISC/EB markers; in addition, we observe an increase in epidermal growth factor receptor (Egfr) activation. Genetic epistasis experiments reveal that Nrg acts upstream of Egfr to regulate ISC proliferation. As Nrg function is highly conserved in mammalian systems, our work characterizing the role of Nrg in the intestine has implications for the treatment of intestinal disorders that arise due to altered ISC behavior.

Differential effects of commensal bacteria on progenitor cell adhesion, division symmetry and tumorigenesis in the Drosophila intestine

Microbial factors influence homeostatic and oncogenic growth in the intestinal epithelium. However, we know little about immediate effects of commensal bacteria on stem cell division programs. In this study, we examined the effects of commensal Lactobacillus species on homeostatic and tumorigenic stem cell proliferation in the female Drosophila intestine. We identified Lactobacillus brevis as a potent stimulator of stem cell divisions. In a wild-type midgut, L.brevis activates growth regulatory pathways that drive stem cell divisions. In a Notch-deficient background, L.brevis-mediated proliferation causes rapid expansion of mutant progenitors, leading to accumulation of large, multi-layered tumors throughout the midgut. Mechanistically, we showed that L.brevis disrupts expression and subcellular distribution of progenitor cell integrins, supporting symmetric divisions that expand intestinal stem cell populations. Collectively, our data emphasize the impact of commensal microbes on division and maintenance of the intestinal progenitor compartment.

Membrane-Anchored Hairless Protein Restrains Notch Signaling Activity

The Notch signaling pathway governs cell-to-cell communication in higher eukaryotes. In Drosophila, after cleavage of the transmembrane receptor Notch, the intracellular domain of Notch (ICN) binds to the transducer Suppressor of Hairless (Su(H)) and shuttles into the nucleus to activate Notch target genes. Similarly, the Notch antagonist Hairless transfers Su(H) into the nucleus to repress Notch target genes. With the aim to prevent Su(H) nuclear translocation, Hairless was fused to a transmembrane domain to anchor the protein at membranes. Indeed, endogenous Su(H) co-localized with membrane-anchored Hairless, demonstrating their binding in the cytoplasm. Moreover, adult phenotypes uncovered a loss of Notch activity, in support of membrane-anchored Hairless sequestering Su(H) in the cytosol. A combined overexpression of membrane-anchored Hairless with Su(H) lead to tissue proliferation, which is in contrast to the observed apoptosis after ectopic co-overexpression of the wild-type genes, indicating a shift to a gain of Notch activity. A mixed response, general de-repression of Notch signaling output, plus inhibition at places of highest Notch activity, perhaps reflects Su(H)’s role as activator and repressor, supported by results obtained with the Hairless-binding deficient Su(H)^LLL mutant, inducing activation only. Overall, the results strengthen the idea of Su(H) and Hairless complex formation within the cytosolic compartment.

Long Noncoding RNA LINC01485 Promotes Tumor Growth and Migration via Inhibiting EGFR Ubiquitination and Activating EGFR/Akt Signaling in Gastric Cancer

Background

Although several long non-coding RNAs (lncRNAs) have been found to be involved in gastric cancer tumorigenesis, the more comprehensive contributions of lncRNAs to gastric cancer require further investigation. Here, we identify a cytoplasmic lncRNA, LINC01485, which promotes tumor growth and migration in gastric cancer.

Materials and Methods

Microarray and computational analysis were utilized to identify differential expression in LINC01485 and EGFR. Real-time PCR and Western blotting assays were used to confirm the expression of LINC01485 and EGFR in gastric cancer cells. Cell proliferation, wound-healing and transwell assays were performed to measure cell growth, migration and invasion. Immunoprecipitation, RNA pull-down, and RNA fluorescence in situ hybridization (RNA-FISH) assays were used to test the interaction of c-Cbl with LINC01485 and EGFR. Furthermore, tumor xenograft in nude mice was performed to test tumor growth in vivo.

Results

LINC01485 was upregulated and associated with tumor size, lymphatic metastasis and advanced pathological stage in gastric cancer. LINC01485 promoted gastric cancer cell proliferation, migration and invasion in vitro and in vivo. Furthermore, LINC01485 levels were positively correlated with EGFR expression in gastric cancer tissues and significantly increased the expression and phosphorylation (Tyr1045) of EGFR in gastric cancer cells. Mechanistically, LINC01485 competes with c-Cbl for binding to phosphorylated Tyr1045 site of EGFR, thus interfering with c-Cbl-mediated ubiquitination and subsequent degradation of EGFR.

Conclusion

LINC01485 promoted EGFR stabilization and activation of EGFR/Akt signaling in gastric cancer. Our findings illustrate the diversity of cytoplasmic lncRNAs in signal transduction and highlight the important roles of lncRNAs in gastric cancer.

Defective Proventriculus Regulates Cell Specification in the Gastric Region of Drosophila Intestine

The gastrointestinal tract in metazoans consists of diverse epithelial cells with distinct cell morphology and physiological functions. The development and homeostasis of gastrointestinal epithelia involve spatiotemporal regulation by many signaling pathways, essential to confer their region-specific function and identity. The adult Drosophila midgut and the mammalian intestine share a high degree of conservation between such signaling pathways. Due to availability of sophisticated techniques for genetic manipulation, Drosophila is an excellent model to study mechanisms of tissue homeostasis regulation in a regionally defined manner. The gastric region located in the Drosophila middle-midgut coincides with the region containing fewest number of stem cells. It is also known as the copper cell (CC) region since it is composed of specialized groups of acid-secreting CCs, along with interstitial cells and enteroendocrine cells. The generation and maintenance of these cell populations are determined by the bone morphogenic protein-like Decapentaplegic (Dpp) signaling pathway. The morphogenic gradient of the Dpp signaling activity induces differential expression of specific transcription factors labial (lab) and defective proventriculus (dve), which are required for the generation of various cell types specific to this region. In this study, we investigated the role of Dve in regulation of tissue homeostasis in the CC region. Our studies reveal that ectopic expression of dve in stem cells suppresses their self-renewal throughout the intestine. We further demonstrate that Dve is not required for generation of CCs. Higher levels of Dve can alter cell specification by inhibition of cut expression, which in turn prevents CC formation during homeostasis.

Stem Cell Proliferation Is Kept in Check by the Chromatin Regulators Kismet/CHD7/CHD8 and Trr/MLL3/4

Chromatin remodeling accompanies differentiation, however, its role in self-renewal is less well understood. We report that in Drosophila, the chromatin remodeler Kismet/CHD7/CHD8 limits intestinal stem cell (ISC) number and proliferation without affecting differentiation. Stem-cell-specific whole-genome profiling of Kismet revealed its enrichment at transcriptionally active regions bound by RNA polymerase II and Brahma, its recruitment to the transcription start site of activated genes and developmental enhancers and its depletion from regions bound by Polycomb, Histone H1, and heterochromatin Protein 1. We demonstrate that the Trithorax-related/MLL3/4 chromatin modifier regulates ISC proliferation, colocalizes extensively with Kismet throughout the ISC genome, and co-regulates genes in ISCs, including Cbl, a negative regulator of Epidermal Growth Factor Receptor (EGFR). Loss of kismet or trr leads to elevated levels of EGFR protein and signaling, thereby promoting ISC self-renewal. We propose that Kismet with Trr establishes a chromatin state that limits EGFR proliferative signaling, preventing tumor-like stem cell overgrowths.

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Chromatin modifiers Kismet and Trr limit intestinal stem cell proliferation

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Kismet and Trr colocalize at transcriptionally active regions and co-regulate genes

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EGFR negative regulator Cbl is a target gene of Kismet and Trr

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Kismet and Trr limit EGFR signaling in ISCs, preventing tumor-like ISC accumulation

Expression of Mammalian BM88/CEND1 in Drosophila Affects Nervous System Development by Interfering with Precursor Cell Formation

We used Drosophila melanogaster as an experimental model to express mouse and pig BM88/CEND1 (cell cycle exit and neuronal differentiation 1) in order to investigate its potential functional effects on Drosophila neurogenesis. BM88/CEND1 is a neuron-specific protein whose function is implicated in triggering cells to exit from the cell cycle and differentiate towards a neuronal phenotype. Transgenic flies expressing either mouse or pig BM88/CEND1 in the nervous system had severe neuronal phenotypes with variable expressivity at various stages of embryonic development. In early embryonic stage 10, BM88/CEND1 expression led to an increase in the neural-specific antigenicity of neuroectoderm at the expense of precursor cells [neuroblasts (Nbs) and ganglion mother cells (GMCs)] including the defective formation and differentiation of the MP2 precursors, whereas at later stages (12-15), protein accumulation induced gross morphological defects primarily in the CNS accompanied by a reduction of Nb and GMC markers. Furthermore, the neuronal precursor cells of embryos expressing BM88/CEND1 failed to carry out proper cell-cycle progression as revealed by the disorganized expression patterns of specific cell-cycle markers. BM88/CEND1 accumulation in the Drosophila eye affected normal eye disc development by disrupting the ommatidia. Finally, we demonstrated that expression of BM88/CEND1 modified/reduced the levels of activated MAP kinase indicating a functional effect of BM88/CEND1 on the MAPK signaling pathway. Our findings suggest that the expression of mammalian BM88/CEND1 in Drosophila exerts specific functional effects associated with neuronal precursor cell formation during embryonic neurogenesis and proper eye disc development. This study also validates the use of Drosophila as a powerful model system in which to investigate gene function and the underlying molecular mechanisms.

SET Domain-Containing Protein 4 Epigenetically Controls Breast Cancer Stem Cell Quiescence

Quiescent cancer stem cells (CSC) play important roles in tumorigenesis, relapse, and resistance to chemoradiotherapy. However, the determinants of CSC quiescence and how they sustain themselves to generate tumors and relapse beyond resistance to chemoradiotherapy remains unclear. Here, we found that SET domain-containing protein 4 (SETD4) epigenetically controls breast CSC (BCSC) quiescence by facilitating heterochromatin formation via H4K20me3 catalysis. H4K20me3 localized to the promoter regions and regulated the expression of a set of genes in quiescent BCSCs (qBCSC). SETD4-defined qBCSCs were resistant to chemoradiotherapy and promoted tumor relapse in a mouse model. Upon activation, a SETD4-defined qBCSC sustained itself in a quiescent state by asymmetric division and concurrently produced an active daughter cell that proliferated to produce a cancer cell population. Single-cell sequence analysis indicated that SETD4⁺ qBCSCs clustered together as a distinct cell type within the heterogeneous BCSC population. SETD4-defined quiescent CSCs were present in multiple cancer types including gastric, cervical, ovarian, liver, and lung cancers and were resistant to chemotherapy. SETD4-defined qBCSCs had a high tumorigenesis potential and correlated with malignancy and chemotherapy resistance in clinical breast cancer patients. Taken together, the results from our previous study and current study on six cancer types reveal an evolutionarily conserved mechanism of cellular quiescence epigenetically controlled by SETD4. Our findings provide insights into the mechanism of tumorigenesis and relapse promoted by SETD4-defined quiescent CSCs and have broad implications for clinical therapies. SIGNIFICANCE: These findings advance our knowledge on the epigenetic determinants of quiescence in cancer stem cell populations and pave the way for future pharmacologic developments aimed at targeting drug-resistant quiescent stem cells.

Anatomy and Physiology of the Digestive Tract of Drosophila melanogaster

The gastrointestinal tract has recently come to the forefront of multiple research fields. It is now recognized as a major source of signals modulating food intake, insulin secretion and energy balance. It is also a key player in immunity and, through its interaction with microbiota, can shape our physiology and behavior in complex and sometimes unexpected ways. The insect intestine had remained, by comparison, relatively unexplored until the identification of adult somatic stem cells in the Drosophila intestine over a decade ago. Since then, a growing scientific community has exploited the genetic amenability of this insect organ in powerful and creative ways. By doing so, we have shed light on a broad range of biological questions revolving around stem cells and their niches, interorgan signaling and immunity. Despite their relatively recent discovery, some of the mechanisms active in the intestine of flies have already been shown to be more widely applicable to other gastrointestinal systems, and may therefore become relevant in the context of human pathologies such as gastrointestinal cancers, aging, or obesity. This review summarizes our current knowledge of both the formation and function of the Drosophila melanogaster digestive tract, with a major focus on its main digestive/absorptive portion: the strikingly adaptable adult midgut.

The role of the EGFR signaling pathway in stem cell differentiation during planarian regeneration and homeostasis

Cell signaling is essential for cells to adequately respond to their environment. One of the most evolutionarily conserved signaling pathways is that of the epidermal growth factor receptor (EGFR). Transmembrane receptors with intracellular tyrosine kinase activity are activated by the binding of their corresponding ligands. This in turn activates a wide variety of intracellular cascades and induces the up- or downregulation of target genes, leading to a specific cellular response. Freshwater planarians are an excellent model in which to study the role of cell signaling in the context of stem-cell based regeneration. Owing to the presence of a population of pluripotent stem cells called neoblasts, these animals can regenerate the entire organism from a tiny piece of the body. Here, we review the current state of knowledge of the planarian EGFR pathway. We describe the main components of the pathway and their functions in other animals, and focus in particular on receptors and ligands identified in the planarian Schmidtea mediterranea. Moreover, we summarize current data on the function of some of these components during planarian regeneration and homeostasis. We hypothesize that the EGFR pathway may act as a key regulator of the terminal differentiation of distinct populations of lineage-committed progenitors.

A Phyllopod-Mediated Feedback Loop Promotes Intestinal Stem Cell Enteroendocrine Commitment in Drosophila

The intestinal epithelium in the Drosophila midgut is maintained by intestinal stem cells (ISCs), which are capable of generating both enterocytes and enteroendocrine cells (EEs) via alternative cell fate specification. Activation of Delta-Notch signaling directs ISCs for enterocyte generation, but how EEs are generated from ISCs remains poorly understood. Here, we identified Phyllopod (Phyl) as a key regulator that drives EE generation from ISCs. Phyl, which is normally suppressed by Notch, functions as an adaptor protein that bridges Tramtrack 69 (Ttk69) and E3 ubiquitin ligase Sina for degradation. Degradation of Ttk69 allows the activation of the Achaete-Scute Complex (AS-C)-Pros regulatory axis, which promotes EE specification. Interestingly, expression of AS-C genes in turn further induces Phyl expression, thereby establishing a positive feedback loop for continuous EE fate specification and commitment. This positive feedback circuit-driven regulatory mechanism could represent a common strategy for reliable and irreversible cell fate determination from progenitor cells.

Dusky works upstream of Four-jointed and Forked in wing morphogenesis in Tribolium castaneum

Dusky (dy) is required for cytoskeletal reorganization during wing morphogenesis in Drosophila melanogaster, but which genes participate together with dy for wing morphogenesis has remained unclear. In Tribolium castaneum, dy is highly expressed at the late embryonic stage. Tissue-specific expression analysis indicated high expression levels of dy in the epidermis, head and fat body of late-stage larvae. RNA interference (RNAi) targeting dy significantly decreased adult wing size and caused improper folding of the elytra. Meanwhile, dy knockdown reduced the transcription of four-jointed (fj) and forked (f). Our results show that fj RNAi reduces adult wing size and that silencing f results in abnormal wing folding in T. castaneum. Interestingly, knocking down fj and f simultaneously phenocopies dy RNAi, suggesting that dy probably acts upstream of fj and f to regulate wing morphogenesis in T. castaneum.

MIB2 variants altering NOTCH signalling result in left ventricle hypertrabeculation/non-compaction and are associated with Ménétrier-like gastropathy

We performed whole exome sequencing in individuals from a family with autosomal dominant gastropathy resembling Ménétrier disease, a premalignant gastric disorder with epithelial hyperplasia and enhanced EGFR signalling. Ménétrier disease is believed to be an acquired disorder, but its aetiology is unknown. In affected members, we found a missense p.V742G variant in MIB2, a gene regulating NOTCH signalling that has not been previously linked to human diseases. The variant segregated with the disease in the pedigree, affected a highly conserved amino acid residue, and was predicted to be deleterious although it was found with a low frequency in control individuals. The purified protein carrying the p.V742G variant showed reduced ubiquitination activity in vitro and white blood cells from affected individuals exhibited significant reductions of HES1 and NOTCH3 expression reflecting alteration of NOTCH signalling. Because mutations of MIB1, the homolog of MIB2, have been found in patients with left ventricle non-compaction (LVNC), we investigated members of our family with Ménétrier-like disease for this cardiac abnormality. Asymptomatic left ventricular hypertrabeculation, the mildest end of the LVNC spectrum, was detected in two members carrying the MIB2 variant. Finally, we identified an additional MIB2 variant (p.V984L) affecting protein stability in an unrelated isolated case with LVNC. Expression of both MIB2 variants affected NOTCH signalling, proliferation and apoptosis in primary rat cardiomyocytes.In conclusion, we report the first example of left ventricular hypertrabeculation/LVNC with germline MIB2 variants resulting in altered NOTCH signalling that might be associated with a gastropathy clinically overlapping with Ménétrier disease.

Tissue-resident stem cell activity: a view from the adult Drosophila gastrointestinal tract

The gastrointestinal tract serves as a fast-renewing model for unraveling the multifaceted molecular mechanisms underlying remarkably rapid cell renewal, which is exclusively fueled by a small number of long-lived stem cells and their progeny. Stem cell activity is the best-characterized aspect of mucosal homeostasis in mitotically active tissues, and the dysregulation of regenerative capacity is a hallmark of epithelial immune defects. This dysregulation is frequently associated with pathologies ranging from chronic enteritis to malignancies in humans. Application of the adult Drosophila gastrointestinal tract model in current and future studies to analyze the immuno-physiological aspects of epithelial defense strategies, including stem cell behavior and re-epithelialization, will be necessary to improve our general understanding of stem cell participation in epithelial turnover. In this review, which describes exciting observations obtained from the adult Drosophila gastrointestinal tract, we summarize a remarkable series of recent findings in the literature to decipher the molecular mechanisms through which stem cells respond to nonsterile environments.

Intrinsic regulation of enteroendocrine fate by Numb

How terminal cell fates are specified in dynamically renewing adult tissues is not well understood. Here we explore terminal cell fate establishment during homeostasis using the enteroendocrine cells (EEs) of the adult Drosophila midgut as a paradigm. Our data argue against the existence of local feedback signals, and we identify Numb as an intrinsic regulator of EE fate. Our data further indicate that Numb, with alpha-adaptin, acts upstream or in parallel of known regulators of EE fate to limit Notch signaling, thereby facilitating EE fate acquisition. We find that Numb is regulated in part through its asymmetric and symmetric distribution during stem cell divisions; however, its de novo synthesis is also required during the differentiation of the EE cell. Thus, this work identifies Numb as a crucial factor for cell fate choice in the adult Drosophila intestine. Furthermore, our findings demonstrate that cell-intrinsic control mechanisms of terminal cell fate acquisition can result in a balanced tissue-wide production of terminally differentiated cell types.

Epidermal Growth Factor Pathway Signaling in Drosophila Embryogenesis: Tools for Understanding Cancer

EGF signaling is a well-known oncogenic pathway in animals. It is also a key developmental pathway regulating terminal and dorsal-ventral patterning along with many other aspects of embryogenesis. In this review, we focus on the diverse roles for the EGF pathway in Drosophila embryogenesis. We review the existing body of evidence concerning EGF signaling in Drosophila embryogenesis focusing on current uncertainties in the field and areas for future study. This review provides a foundation for utilizing the Drosophila model system for research into EGF effects on cancer.

Mitogen-activated Protein Kinase Kinase Activity Maintains Acinar-to-Ductal Metaplasia and Is Required for Organ Regeneration in Pancreatitis

BACKGROUND & AIMS

Mitogen-activated protein kinase (MAPK) signaling in the exocrine pancreas has been extensively studied in the context of pancreatic cancer, where its potential as a therapeutic target is limited by acquired drug resistance. However, its role in pancreatitis is less understood. We investigated the role of mitogen-activated protein kinase kinase (MEK)-initiated MAPK signaling in pancreatitis to determine the potential for MEK inhibition in treating pancreatitis patients.

METHODS

To examine the role of MEK signaling in pancreatitis, we used both genetic and pharmacologic approaches to inhibit the MAPK signaling pathway in a murine model of cerulein-induced pancreatitis. We generated mice harboring inducible short hairpins targeting the MEK isoforms Map2k1 and/or Map2k2 specifically in the pancreatic epithelium. We also used the MEK inhibitor trametinib to determine the efficacy of systemic inhibition in mice with pancreatitis.

RESULTS

We demonstrated an essential role for MEK signaling in the initiation of pancreatitis. We showed that both systemic and parenchyma-specific MEK inhibition in established pancreatitis induces epithelial differentiation and stromal remodeling. However, systemic MEK inhibition also leads to a loss of the proliferative capacity of the pancreas, preventing the restoration of organ mass.

CONCLUSIONS

MEK activity is required for the initiation and maintenance of pancreatitis. MEK inhibition may be useful in the treatment of chronic pancreatitis to interrupt the vicious cycle of destruction and repair but at the expense of organ regeneration.

Intestinal stem cell response to injury: lessons from Drosophila

Many adult tissues and organs are maintained by resident stem cells that are activated in response to injury but the mechanisms that regulate stem cell activity during regeneration are still poorly understood. An emerging system to study such problem is the Drosophila adult midgut. Recent studies have identified both intrinsic factors and extrinsic niche signals that control the proliferation, self-renewal, and lineage differentiation of Drosophila adult intestinal stem cells (ISCs). These findings set up the stage to interrogate how niche signals are regulated and how they are integrated with cell-intrinsic factors to control ISC activity during normal homeostasis and regeneration. Here we review the current understanding of the mechanisms that control ISC self-renewal, proliferation, and lineage differentiation in Drosophila adult midgut with a focus on the niche signaling network that governs ISC activity in response to injury.

Ubx dynamically regulates Dpp signaling by repressing Dad expression during copper cell regeneration in the adult Drosophila midgut

The gastrointestinal (GI) tract of metazoans is lined by a series of regionally distinct epithelia. To maintain structure and function of the GI tract, regionally diversified differentiation of somatic stem cell (SC) lineages is critical. The adult Drosophila midgut provides an accessible model to study SC regulation and specification in a regionally defined manner. SCs of the posterior midgut (PM) have been studied extensively, but the control of SCs in the middle midgut (MM) is less well understood. The MM contains a stomach-like copper cell region (CCR) that is regenerated by gastric stem cells (GSSCs) and contains acid-secreting copper cells (CCs). Bmp-like Decapentaplegic (Dpp) signaling determines the identity of GSSCs, and is required for CC regeneration, yet the precise control of Dpp signaling activity in this lineage remains to be fully established. Here, we show that Dad, a negative feedback regulator of Dpp signaling, is dynamically regulated in the GSSC lineage to allow CC differentiation. Dad is highly expressed in GSSCs and their first daughter cells, the gastroblasts (GBs), but has to be repressed in differentiating CCs to allow Dpp-mediated differentiation into CCs. We find that the Hox gene ultrabithorax (Ubx) is required for this regulation. Loss of Ubx prevents Dad repression in the CCR, resulting in defective CC regeneration. Our study highlights the need for dynamic control of Dpp signaling activity in the differentiation of the GSSC lineage and identifies Ubx as a critical regulator of this process.

Gastrointestinal stem cells in health and disease: from flies to humans

The gastrointestinal tract of complex metazoans is highly compartmentalized. It is lined by a series of specialized epithelia that are regenerated by specific populations of stem cells. To maintain tissue homeostasis, the proliferative activity of stem and/or progenitor cells has to be carefully controlled and coordinated with regionally distinct programs of differentiation. Metaplasias and dysplasias, precancerous lesions that commonly occur in the human gastrointestinal tract, are often associated with the aberrant proliferation and differentiation of stem and/or progenitor cells. The increasingly sophisticated characterization of stem cells in the gastrointestinal tract of mammals and of the fruit fly Drosophila has provided important new insights into these processes and into the mechanisms that drive epithelial dysfunction. In this Review, we discuss recent advances in our understanding of the establishment, maintenance and regulation of diverse intestinal stem cell lineages in the gastrointestinal tract of Drosophila and mice. We also discuss the field's current understanding of the pathogenesis of epithelial dysfunctions.

Traffic jam functions in a branched pathway from Notch activation to niche cell fate

The niche directs key behaviors of its resident stem cells, and is thus crucial for tissue maintenance, repair and longevity. However, little is known about the genetic pathways that guide niche specification and development. The male germline stem cell niche in Drosophila houses two stem cell populations and is specified within the embryonic gonad, thus making it an excellent model for studying niche development. The hub cells that form the niche are specified early by Notch activation. Over the next few hours, these individual cells then cluster together and take up a defined position before expressing markers of hub cell differentiation. This timing suggests that there are other factors for niche development yet to be defined. Here, we have identified a role for the large Maf transcription factor Traffic jam (Tj) in hub cell specification downstream of Notch. Tj downregulation is the first detectable effect of Notch activation in hub cells. Furthermore, Tj depletion is sufficient to generate ectopic hub cells that can recruit stem cells. Surprisingly, ectopic niche cells in tj mutants remain dispersed in the absence of Notch activation. This led us to uncover a branched pathway downstream of Notch in which Bowl functions to direct hub cell assembly in parallel to Tj downregulation.

A hybrid computational method for the discovery of novel reproduction-related genes

Uncovering the molecular mechanisms underlying reproduction is of great importance to infertility treatment and to the generation of healthy offspring. In this study, we discovered novel reproduction-related genes with a hybrid computational method, integrating three different types of method, which offered new clues for further reproduction research. This method was first executed on a weighted graph, constructed based on known protein-protein interactions, to search the shortest paths connecting any two known reproduction-related genes. Genes occurring in these paths were deemed to have a special relationship with reproduction. These newly discovered genes were filtered with a randomization test. Then, the remaining genes were further selected according to their associations with known reproduction-related genes measured by protein-protein interaction score and alignment score obtained by BLAST. The in-depth analysis of the high confidence novel reproduction genes revealed hidden mechanisms of reproduction and provided guidelines for further experimental validations.