Regulation Of Stem Cell Maintenance Research Articles

MTGR1 is required to maintain small intestinal stem cell populations.

Undifferentiated intestinal stem cells (ISCs) are crucial for maintaining homeostasis and resolving injury. Lgr5+ cells in the crypt base constantly divide, pushing daughter cells upward along the crypt axis where they differentiate into specialized cell types. Coordinated execution of complex transcriptional programs is necessary to allow for the maintenance of undifferentiated stem cells while permitting differentiation of the wide array of intestinal cells necessary for homeostasis. Previously, members of the myeloid translocation gene (MTG) family have been identified as transcriptional co-repressors that regulate stem cell maintenance and differentiation programs in multiple organ systems, including the intestine. One MTG family member, myeloid translocation gene related 1 (MTGR1), has been recognized as a crucial regulator of secretory cell differentiation and response to injury. However, whether MTGR1 contributes to the function of ISCs has not yet been examined. Here, using Mtgr1-/- mice, we have assessed the effects of MTGR1 loss specifically in ISC biology. Interestingly, loss of MTGR1 increased the total number of cells expressing Lgr5, the canonical marker of cycling ISCs, suggesting higher overall stem cell numbers. However, expanded transcriptomic and functional analyses revealed deficiencies in Mtgr1-null ISCs, including deregulated ISC-associated transcriptional programs. Ex vivo, intestinal organoids established from Mtgr1-null mice were unable to survive and expand due to aberrant differentiation and loss of stem and proliferative cells. Together, these results indicate that the role of MTGR1 in intestinal differentiation is likely stem cell intrinsic and identify a novel role for MTGR1 in maintaining ISC function.

MAST4 regulates stem cell maintenance with DLX3 for epithelial development and amelogenesis

The asymmetric division of stem cells permits the maintenance of the cell population and differentiation for harmonious progress. Developing mouse incisors allows inspection of the role of the stem cell niche to provide specific insights into essential developmental phases. Microtubule-associated serine/threonine kinase family member 4 (Mast4) knockout (KO) mice showed abnormal incisor development with low hardness, as the size of the apical bud was decreased and preameloblasts were shifted to the apical side, resulting in amelogenesis imperfecta. In addition, Mast4 KO incisors showed abnormal enamel maturation, and stem cell maintenance was inhibited as amelogenesis was accelerated with Wnt signal downregulation. Distal-Less Homeobox 3 (DLX3), a critical factor in tooth amelogenesis, is considered to be responsible for the development of amelogenesis imperfecta in humans. MAST4 directly binds to DLX3 and induces phosphorylation at three residues within the nuclear localization site (NLS) that promotes the nuclear translocation of DLX3. MAST4-mediated phosphorylation of DLX3 ultimately controls the transcription of DLX3 target genes, which are carbonic anhydrase and ion transporter genes involved in the pH regulation process during ameloblast maturation. Taken together, our data reveal a novel role for MAST4 as a critical regulator of the entire amelogenesis process through its control of Wnt signaling and DLX3 transcriptional activity.

YAP and TAZ differentially regulate postnatal cortical progenitor proliferation and astrocyte differentiation.

WW domain-containing transcription regulator 1 (WWTR1, referred to here as TAZ) and Yes-associated protein (YAP, also known as YAP1) are transcriptional co-activators traditionally studied together as a part of the Hippo pathway, and are best known for their roles in stem cell proliferation and differentiation. Despite their similarities, TAZ and YAP can exert divergent cellular effects by differentially interacting with other signaling pathways that regulate stem cell maintenance or differentiation. In this study, we show in mouse neural stem and progenitor cells (NPCs) that TAZ regulates astrocytic differentiation and maturation, and that TAZ mediates some, but not all, of the effects of bone morphogenetic protein (BMP) signaling on astrocytic development. By contrast, both TAZ and YAP mediate the effects on NPC fate of β1-integrin (ITGB1) and integrin-linked kinase signaling, and these effects are dependent on extracellular matrix cues. These findings demonstrate that TAZ and YAP perform divergent functions in the regulation of astrocyte differentiation, where YAP regulates cell cycle states of astrocytic progenitors and TAZ regulates differentiation and maturation from astrocytic progenitors into astrocytes.

Abstract LB047: Pdcd10 is a promising therapeutic target for head and neck squamous cell carcinoma

Abstract Oral cavity squamous cell carcinoma (OCSCC), the most common subtype of head and neck cancer, is a devastating disease, causing substantial morbidity and mortality. Only a handful of targeted therapies are available for OCSCC, and the 5-year overall survival remains ~50%. While strategies are being designed to improve risk assessment, detection, and therapeutic intervention, these approaches are limited by our incomplete understanding of OCSCC biology, particularly in its early development. Thus, it is crucial to identify novel targets of therapeutic interest. Programmed cell death 10 (PDCD10) is a multifaceted protein shown to be overexpressed in several solid malignancies. It was reported that PDCD10 may contribute to tumorigenesis and chemoresistance by promoting cell proliferation, anti-apoptosis, epithelial-mesenchymal transition (EMT), and inhibiting anti-tumor immune responses. Recently it was suggested that PDCD10 is involved in regulating cancer stem cells (CSCs) maintenance in breast and lung cancers. While targeting PDCD10 activity may provide novel strategies for treating HPV- HNSCC, the direct relevance of PDCD10 in regulating head and neck tumorigenesis has not yet been studied. The goal of this study was to evaluate the role of PDCD10 in driving oral malignant transformation and investigate whether PDCD10 inhibition can induce anti-cancer effect. We first generated stable PDCD10 knockdown clones using two human OCSCC cell lines and showed that PDCD10 depletion effects oral cancer cell physiology (such as proliferation, DNA replication, migration, and invasion). We next used organoid models established from normal oral epidermis of tamoxifen inducible Pdcd10F/F and control Pdcd10+/+ mice to investigate the role of PDCD10 in driving oral tumorigenesis and regulating stem cell maintenance following malignant transformation induced by 4NQO treatment. Finally, we used mice with inducible Pdcd10 knockout in tongue epithelia to evaluate the ability of PDCD10 depletion to inhibit the 4NQO induced oral carcinogenesis in vivo. Taken together, our data provide strong evidence that PDCD10 is an oncogene that may promote oral neoplastic progression, posing PDCD10 as a potential therapeutic target for patients with OCSCC. Given the devastating nature of oral cancer and dearth of effective treatment, providing new insights into the cancer driving molecular mechanisms regulated by PDCD10 and using this knowledge for developing therapeutic approaches targeting its activity may ultimately improve patients' prognosis. Citation Format: Manu Sundaresan, Xiangying Cheng, Claudia WIng, Alexander von Kumberg, Elena Jochum, Alka Singh, Joseph Kainov, Piao Zhao, Mohammed Sidahmed, Alexander T. Pearson, Ari J. Rosenberg, Nishant Agrawal, Le Shen, Evgeny Izumchenko. Pdcd10 is a promising therapeutic target for head and neck squamous cell carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB047.

The OsCLV2s-OsCRN1 co-receptor regulates grain shape in rice

The highly conserved CLV–WUS negative feedback pathway plays a decisive role in regulating stem cell maintenance in shoot and floral meristems in higher plants, including Arabidopsis, rice, maize, and tomato. Here, we report the discovery that CLV-like genes directly regulate grain shape in rice. We find significant natural variations in the OsCLV2c, OsCLV2d, and OsCRN1 loci in a genome-wide association study of grain shape in rice. OsCLV2a, OsCLV2c, OsCLV2d, and OsCRN1 negatively regulate grain length–width ratio and show distinctive geographical distribution, indica–japonica differentiation, and artificial selection signatures. Notably, OsCLV2a and OsCRN1 interact biochemically and genetically, suggesting that the two components function in a complex to regulate grain shape of rice. Furthermore, the genetic contributions of the haplotypes combining OsCLV2a, OsCLV2c, and OsCRN1 are significantly higher than those of each single gene alone in controlling key yield traits. These findings identify two groups of receptor-like kinases that may function as distinct co-receptors to control grain size in rice, thereby revealing a previously unrecognized role of the CLV class genes in regulating seed development and proposing a framework to understand the molecular mechanisms of the CLV–WUS pathway in rice and other crops.

Abstract 5636: CUX1 transcriptionally regulates intestinal epithelial homeostasis

Abstract The small intestine digests and absorbs nutrients, a role made possible by specialized secretory and absorptive cells that constantly replenish from the intestinal stem cell niche. Disruption in intestinal epithelium homeostasis has been linked to pathologies including inflammatory bowel disease (IBD) and cancer. However, the processes regulating differentiation in healthy and disease setting are incompletely understood. CUX1 is a highly conserved homeodomain-containing transcription factor that is expressed in small intestinal crypts and has been previously shown to be essential in mice and Drosophila. CUX1 is upregulated upon inflammatory stress conditions, including intestinal damage and in IBD. In addition, CUX1 is predicted to be protective against IBD from genome-wide association studies. The aim of the current work is to determine the mechanistic role of CUX1 in secretory intestinal cells differentiation and epithelial homeostasis. To this end, we have generated transgenic mouse models that modulate CUX1 levels in an inducible manner. Mice with near-null CUX1 levels exhibit rapid weight loss requiring euthanasia while mice with ~50% residual CUX1 halt normal weight gain. Histologic examination of tissues from mice with CUX1 knock-down reveals a lack of mature secretory cells, including goblet and Paneth cells, the latter playing a supportive role to intestinal stem cells. Moreover, mouse intestinal tissues from our knock-down models demonstrated decreased proliferation with increased apoptosis. In transcriptome profiling, we observed downregulation of proliferation, intestinal stem cell, and digestive system developmental gene signatures and decreased levels of key secretory cell regulators, pointing towards a role for CUX1 in stem cell maintenance and differentiation. Indeed, reducing CUX1 levels decreased β-catenin protein levels, while Wnt/β-catenin signaling is required for the organization of the crypt-villus axis. Finally, CUX1 knock-down compromises the ability to form budding organoids, demonstrating the cell intrinsic role for CUX1 in stem cell differentiation. In ongoing studies, we are identifying CUX1 genome-wide binding targets and the epigenetic impact of CUX1 in intestinal epithelium cells. Our findings indicate that CUX1 is a critical regulator of intestinal epithelium homeostasis that has a role in differentiation and potential role in injury-induced de-differentiation in healthy as well as IBD patients. We propose that CUX1 regulates stem cell maintenance and crypt composition by regulating Wnt/β-catenin signaling and inducing fetal-like transcriptomic repair program shown to be coopted by colon cancers. Resolving an intricate network of transcriptional regulation of differentiation in the intestinal crypt holds the potential to successfully target inflammation-related damage in human intestines. Citation Format: Katarzyna Zawieracz, Ningfei An, Megan McNerney. CUX1 transcriptionally regulates intestinal epithelial homeostasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5636.

Chigno/CG11180 and SUMO are Chinmo-interacting proteins with a role in Drosophila testes somatic support cells.

Stem cells are critical for replenishment of cells lost to death, damage or differentiation. Drosophila testes are a key model system for elucidating mechanisms regulating stem cell maintenance and differentiation. An intriguing gene identified through such studies is the transcription factor, chronologically inappropriate morphogenesis (Chinmo). Chinmo is a downstream effector of the Jak-STAT signaling pathway that acts in testis somatic stem cells to ensure maintenance of male stem cell fate and sexual identity. Defects in these processes can lead to infertility and the formation of germ cell tumors. While Chinmo's effect on testis stem cell behavior has been investigated in detail, there is still much to be learned about its structure, function, and interactions with other proteins. Using a two-hybrid screen, we find that Chinmo interacts with itself, the small ubiquitin-like modifier SUMO, the novel protein CG11180, and four other proteins (CG4318, Ova (ovaries absent), Taf3 (TBP-associated factor 3), and CG18269). Since both Chinmo and CG11180 contain sumoylation sites and SUMO-interacting motifs (SIMs), we analyzed their interaction in more detail. Using site-directed mutagenesis of a unique SIM in CG11180, we demonstrate that Chinmo's interaction with CG11180 is SUMO-dependent. Furthermore, to assess the functional relevance of both SUMO and CG11180, we performed RNAi-mediated knockdown of both proteins in somatic cells of the Drosophila testis. Using this approach, we find that CG11180 and SUMO are required in somatic cells of adult testes, and that reduction of either protein causes formation of germ cell tumors. Overall, our work suggests that SUMO may be involved in the interaction of Chinmo and CG11180 and that these genes are required in somatic cells of the adult Drosophila testis. Consistent with the CG11180 knockdown phenotype in male testes, and to underscore its connection to Chinmo, we propose the name Chigno (Childless Gambino) for CG11180.

JMJD3 regulate H3K27me3 modification via interacting directly with TET1 to affect spermatogonia self-renewal and proliferation

BackgroundIn epigenetic modification, histone modification and DNA methylation coordinate the regulation of spermatogonium. Not only can methylcytosine dioxygenase 1 (TET1) function as a DNA demethylase, converting 5-methylcytosine to 5-hydroxymethylcytosine, it can also form complexes with other proteins to regulate gene expression. H3K27me3, one of the common histone modifications, is involved in the regulation of stem cell maintenance and tumorigenesis by inhibiting gene transcription.Methodswe examined JMJD3 at both mRNA and protein levels and performed Chip-seq sequencing of H3K27me3 in TET1 overexpressing cells to search for target genes and signaling pathways of its action.ResultsThis study has found that JMJD3 plays a leading role in spermatogonia self-renewal and proliferation: at one extreme, the expression of the self-renewal gene GFRA1 and the proliferation-promoting gene PCNA was upregulated following the overexpression of JMJD3 in spermatogonia; at the other end of the spectrum, the expression of differentiation-promoting gene DAZL was down-regulated. Furthermore, the fact that TET1 and JMJD3 can form a protein complex to interact with H3K27me3 has also been fully proven. Then, through analyzing the sequencing results of CHIP-Seq, we found that TET1 targeted Pramel3 when it interacted with H3K27me3. Besides, TET1 overexpression not only reduced H3K27me3 deposition at Pramel3, but promoted its transcriptional activation as well, and the up-regulation of Pramel3 expression was verified in JMJD3-overexpressing spermatogonia.ConclusionIn summary, our study identified a novel link between TET1 and H3K27me3 and established a Tet1-JMJD3-H3K27me3-Pramel3 axis to regulate spermatogonia self-renewal and proliferation. Judging from the evidence offered above, we can safely conclude that this study provides new ideas for further research regarding the mechanism of spermatogenesis and spermatogenesis disorders on an apparent spectrum.

Integrated bioinformatics analysis of SEMA3C in tongue squamous cell carcinoma using machine-learning strategies

Tongue squamous cell carcinoma (TSCC) is an aggressive oral cancer with a high incidence of metastasis and poor prognosis. We aim to identify and verify potential biomarkers for TSCC using bioinformatics analysis. To begin with, we examined clinical and RNA expression information of individuals with TSCC from the Gene Expression Omnibus (GEO) database. Differential expression analysis and functional analysis were conducted. Multiple machine-learning strategies were next employed to screen and determine the hub gene, and receiver operating characteristic (ROC) analysis was used to assess diagnostic value. Semaphorin3C (SEMA3C) was identified as a critical biomarker, presenting high diagnostic accuracy for TSCC. In the validation cohorts, SEMA3C exhibited high expression levels in TSCC. The high expression of SEMA3C was a poor prognostic factor in TSCC by the Kaplan–Meier curve. Based on the Gene Ontology (GO) analysis, SEMA3C was mapped in terms related to cell adhesion, positive regulation of JAK-STAT, positive regulation of stem cell maintenance, and positive regulation of NF-κB activity. Single-cell RNA sequencing (ScRNA-seq) analysis showed cells expressing SEMA3C were predominantly tumor cells. Then, we further verified that SEMA3C had high expression in TSCC clinical samples. In addition, the knockdown of SEMA3C suppressed the proliferation, migration, and invasion of TSCC cells in vitro. This study is the first to report the involvement of SEMA3C in TSCC, suggesting that upregulated SEMA3C could be a novel and critical potential biomarker for future predictive diagnostics, prevention, prognostic assessment, and personalized medical services in TSCC.

Human intestinal organoid-derived PDGFRα + mesenchymal stroma enables proliferation and maintenance of LGR4 + epithelial stem cells

BackgroundIntestinal epithelial cells derived from human pluripotent stem cells (hPSCs) are generally maintained and cultured as organoids in vitro because they do not exhibit adhesion when cultured. However, the three-dimensional structure of organoids makes their use in regenerative medicine and drug discovery difficult. Mesenchymal stromal cells are found near intestinal stem cells in vivo and provide trophic factors to regulate stem cell maintenance and proliferation, such as BMP inhibitors, WNT, and R-spondin. In this study, we aimed to use mesenchymal stromal cells isolated from hPSC-derived intestinal organoids to establish an in vitro culture system that enables stable proliferation and maintenance of hPSC-derived intestinal epithelial cells in adhesion culture.MethodsWe established an isolation protocol for intestinal epithelial cells and mesenchymal stromal cells from hPSCs-derived intestinal organoids and a co-culture system for these cells. We then evaluated the intestinal epithelial cells and mesenchymal stromal cells' morphology, proliferative capacity, chromosomal stability, tumorigenicity, and gene expression profiles. We also evaluated the usefulness of the cells for pharmacokinetic and toxicity studies.ResultsThe proliferating intestinal epithelial cells exhibited a columnar form, microvilli and glycocalyx formation, cell polarity, and expression of drug-metabolizing enzymes and transporters. The intestinal epithelial cells also showed barrier function, transporter activity, and drug-metabolizing capacity. Notably, small intestinal epithelial stem cells cannot be cultured in adherent culture without mesenchymal stromal cells and cannot replaced by other feeder cells. Organoid-derived mesenchymal stromal cells resemble the trophocytes essential for maintaining small intestinal epithelial stem cells and play a crucial role in adherent culture.ConclusionsThe high proliferative expansion, productivity, and functionality of hPSC-derived intestinal epithelial cells may have potential applications in pharmacokinetic and toxicity studies and regenerative medicine.

PLZF protein forms a complex with protein TET1 to target TCF7L2 in undifferentiated spermatogonia

The transcription factor promyelocytic leukemia zinc finger (PLZF, also known as ZBTB16) is critical for the self-renewal of spermatogonial stem cells (SSCs). However, the function of PLZF in SSCs is not clear. Here, we found that PLZF acted as an epigenetic regulator of stem cell maintenance and self-renewal of germ cells. The PLZF protein interacts with the ten-eleven translocation 1 (TET1) protein and subsequently acts as a modulator to regulate the expression of self-renewal-related genes. Furthermore, Transcription Factor 7-like 2 (TCF7L2) is promoted by the coordination of PLZF and Tri-methylation of lysine 4 on histone H3 (H3K4me3). In addition, testicular single-cell sequencing indicated that TCF7L2 is commonly expressed in the PLZF cluster. We demonstrated that PLZF directly targets TCF7L2 and alters the landscape of histone methylation in the SSCs nucleus. Meanwhile, the RD domain and Zn finger domain of PLZF synergize with H3K4me3 and directly upregulate TCF7L2 expression at the transcriptional level. Additionally, we identified a new association between PLZF and the histone methyltransferase EZH2 at the genomic level. Our study identified a new association between PLZF and H3K4me3, established the novel PLZF&TET1-H3K4me3-TCF7L2 axis at the genomic level which regulates undifferentiated spermatogonia, and provided a platform for studying germ cell development in male domestic animals.

Loss of Autophagy Disrupts Stemness of Ameloblast-Lineage Cells in Aging

Autophagy is one of the intracellular degradation pathways and maintains cellular homeostasis, regulating the stress response, cell proliferation, and signal transduction. To elucidate the role of autophagy in the maintenance of dental epithelial stem cells and the subsequent enamel formation, we analyzed autophagy-deficient mice in epithelial cells (Atg7f/f;KRT14-Cre mice), focusing on the influence of aging and stress environments. We also performed in vitro cell and organ culture experiments with an autophagy inhibitor. In young Atg7f/f;KRT14-Cre mice, morphological change was not obvious in maxillary incisors, except for the remarkable cell death in the stratum intermedium of the transitional stage. However, under stress conditions of hyperglycemia, the incisor color changed to white in diabetes Atg7f/f;KRT14-Cre mice. Regarding dental epithelial stem cells, the shape of the apical bud region of the incisor became irregular with age, and odontoma was formed in aged Atg7f/f;KRT14-Cre mice. In addition, the shape of apical bud culture cells of Atg7f/f;KRT14-Cre mice became irregular and enlarged atypically, with epigenetic changes during culture, suggesting that autophagy deficiency may induce tumorigenesis in dental epithelial cells. The epigenetic change and upregulation of p21 expression were induced by autophagy inhibition in vivo and in vitro. These findings suggest that autophagy is important for the regulation of stem cell maintenance, proliferation, and differentiation of ameloblast-lineage cells, and an autophagy disorder may induce tumorigenesis in odontogenic epithelial cells.

What a tangled web it weaves: auxin coordination of stem cell maintenance and flower production.

Robust agricultural yields require consistent flower production throughout fluctuating environmental conditions. Floral primordia are produced in the inflorescence meristem, which contains a pool of continuously dividing stem cells. Daughter cells of these divisions either retain stem cell identity or are pushed to the SAM periphery, where they become competent to develop into floral primordia after receiving the appropriate signal. Thus, flower production is inherently linked to regulation of the stem cell pool. The plant hormone auxin promotes flower development throughout its early phases and has been shown to interact with the molecular pathways regulating stem cell maintenance. Here, we will summarize how auxin signaling contributes to stem cell maintenance and promotes flower development through the early phases of initiation, outgrowth, and floral fate establishment. Recent advances in this area suggest that auxin may serve as a signal that integrates stem cell maintenance and new flower production.

Targeting FTO Suppresses Pancreatic Carcinogenesis via Regulating Stem Cell Maintenance and EMT Pathway

N6-methyladenosine (m6A) is the most prevalent post-transcriptional RNA modification regulating cancer self-renewal. However, despite its functional importance and prognostic implication in tumorigenesis, the relevance of FTO, an m6A eraser, in pancreatic cancer (PC) remains elusive. Here, we establish the oncogenic role played by FTO overexpression in PC. FTO is upregulated in PC cells compared to normal human pancreatic ductal epithelial (HPDE) cells. Both RNAi depletion and CS1-mediated pharmacological inhibition of FTO caused a diminution of PC cell proliferation via cell cycle arrest in the G1 phase and p21cip1 and p27kip1 induction. While HPDE cells remain insensitive to CS1 treatment, FTO overexpression confers enhancements in growth, motility, and EMT transition, thereby inculcating tumorigenic properties in HPDE cells. Notably, shRNA-mediated FTO depletion in PC cells impairs their mobility and invasiveness, leading to EMT reversal. Mechanistically, this was associated with impaired tumorsphere formation and reduced expression of CSCs markers. Furthermore, FTO depletion in PC cells weakened their tumor-forming capabilities in nude mice; those tumors had increased apoptosis, decreased proliferation markers, and MET conversion. Collectively, our study demonstrates the functional importance of FTO in PC and the maintenance of CSCs via EMT regulation. Thus, FTO may represent an attractive therapeutic target for PC.

Bmi1 suppresses protein synthesis and promotes proteostasis in hematopoietic stem cells.

The polycomb complex component Bmi1 promotes the maintenance of stem cells in multiple postnatal tissues, partly by negatively regulating the expression of p16Ink4a and p19Arf, tumor suppressors associated with cellular senescence. However, deficiency for p16Ink4a and p19Arf only partially rescues the function of Bmi1-deficient stem cells. We conditionally deleted Bmi1 from adult hematopoietic cells and found that this slowly depleted hematopoietic stem cells (HSCs). Rather than inducing senescence, Bmi1 deficiency increased HSC division. The increased cell division was caused partly by increased Aristaless-related homeobox (ARX) transcription factor expression, which also increased ribosomal RNA expression. However, ARX deficiency did not rescue HSC depletion. Bmi1 deficiency also increased protein synthesis, protein aggregation, and protein ubiquitylation independent of its effects on cell division and p16Ink4a, p19Arf, and ARX expression. Bmi1 thus promotes HSC quiescence by negatively regulating ARX expression and promotes proteostasis by suppressing protein synthesis. This highlights a new connection between the regulation of stem cell maintenance and proteostasis.

PLETHORA-WOX5 interaction and subnuclear localization control Arabidopsis root stem cell maintenance.

Maintenance and homeostasis of the stem cell niche (SCN) in the Arabidopsis root is essential for growth and development of all root cell types. The SCN is organized around a quiescent center (QC) maintaining the stemness of cells in direct contact. The key transcription factors (TFs) WUSCHEL‐RELATED HOMEOBOX 5 (WOX5) and PLETHORAs (PLTs) are expressed in the SCN where they maintain the QC and regulate distal columella stem cell (CSC) fate. Here, we describe the concerted mutual regulation of the key TFs WOX5 and PLTs on a transcriptional and protein interaction level. Additionally, by applying a novel SCN staining method, we demonstrate that both WOX5 and PLTs regulate root SCN homeostasis as they control QC quiescence and CSC fate interdependently. Moreover, we uncover that some PLTs, especially PLT3, contain intrinsically disordered prion‐like domains (PrDs) that are necessary for complex formation with WOX5 and its recruitment to subnuclear microdomains/nuclear bodies (NBs) in the CSCs. We propose that this partitioning of PLT‐WOX5 complexes to NBs, possibly by phase separation, is important for CSC fate determination.

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

ObjectivesAdult 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 MethodsFlies 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.ResultsHere, 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.ConclusionOur 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.

CLE peptides: critical regulators for stem cell maintenance in plants

Plant CLE peptides, which regulate stem cell maintenance in shoot and root meristems and in vascular bundles through LRR family receptor kinases, are novel, complex, and to some extent conserved. Over the past two decades,peptide ligands of the CLAVATA3(CLV3)/Embryo Surrounding Region (CLE) family have been recognized as critical short- and long-distance communication signals in plants, especially for stem cell homeostasis, cell fate determination and physiological responses. Stem cells located at the shoot apical meristem (SAM), the root apical meristem (RAM) and the procambium divide and differentiate into specialized cells that form a variety of tissues such as epidermis, ground tissues, xylem and phloem. In the SAM of Arabidopsis (Arabidopsis thaliana), the CLV3 peptide restricts the number of stem cells via leucine-rich repeat (LRR)-type receptor kinases. In the RAM, root-active CLE peptides are critical negative regulators, while ROOT GROWTH FACTOR (RGF) peptides are positive regulators in stem cell maintenance. Among those root-active CLE peptides, CLE25 promotes, while CLE45 inhibits phloem differentiation. In vascular bundles, TRACHEARY ELEMENT DIFFERENTIATION INHIBITORY FACTOR (TDIF)/CLE41/CLE44 promotes procambium cell division, and prevents xylem differentiation. Orthologs of CLV3 have been identified in liverwort (Marchantia polymorpha), tomato(Solanum lycopersicum), rice (Oryza sativa), maize (Zea mays) and lotus (Lotus japonicas), suggesting that CLV3 is an evolutionarily conserved signal in stem cell maintenance. However, functional characterization of endogenous CLE peptides and corresponding receptor kinases, and the downstream signal transduction has been challenging due to their genome-wide redundancies and rapid evolution.

Djnedd4L Is Required for Head Regeneration by Regulating Stem Cell Maintenance in Planarians.

SUMOylation and ubiquitylation are homologous processes catalyzed by homologous enzymes, and they are involved in nearly all aspects of eukaryotic biology. Planarians, which have the remarkable ability to regenerate their central nervous system (CNS), provide an excellent opportunity to investigate the molecular processes of CNS regeneration in vivo. In this study, we analyzed gene expression profiles during head regeneration with an RNA-seq-based screening approach and found that Djnedd4L and Djubc9 were required for head regeneration in planarians. RNA interference targeting of Djubc9 caused the phospho-H3 mitotic cells to decrease in quantity, or even become absent as a part of the Djubc9 RNAi phenotype, which also showed the collapse of the stem cell lineage along with the reduced expression of epidermal differentiation markers. Furthermore, we found that Djnedd4L RNAi induced increased cell division and promoted the premature differentiation during regeneration. Taken together, our findings show that Djubc9 and Djnedd4L are required for stem cell maintenance in the planarian Dugesia japonica, which helps to elucidate the role of SUMOylation and ubiquitylation in regulating the regeneration process.

Transcriptome Analysis in a Mouse Model of Premature Aging of Dentate Gyrus: Rescue of Alpha-Synuclein Deficit by Virus-Driven Expression or by Running Restores the Defective Neurogenesis.

The dentate gyrus of the hippocampus and the subventricular zone are neurogenic niches where neural stem and progenitor cells replicate throughout life to generate new neurons. The Btg1 gene maintains the stem cells of the neurogenic niches in quiescence. The deletion of Btg1 leads to an early transient increase of stem/progenitor cells division, followed, however, by a decrease during adulthood of their proliferative capability, accompanied by apoptosis. Since a physiological decrease of neurogenesis occurs during aging, the Btg1 knockout mouse may represent a model of neural aging. We have previously observed that the defective neurogenesis of the Btg1 knockout model is rescued by the powerful neurogenic stimulus of physical exercise (running). To identify genes responsible for stem and progenitor cells maintenance, we sought here to find genes underlying this premature neural aging, and whose deregulated expression could be rescued by running. Through RNA sequencing we analyzed the transcriptomic profiles of the dentate gyrus isolated from Btg1 wild-type or Btg1 knockout adult (2-month-old) mice submitted to physical exercise or sedentary. In Btg1 knockout mice, 545 genes were deregulated, relative to wild-type, while 2081 genes were deregulated by running. We identified 42 genes whose expression was not only down-regulated in the dentate gyrus of Btg1 knockout, but was also counter-regulated to control levels by running in Btg1 knockout mice, vs. sedentary. Among these 42 counter-regulated genes, alpha-synuclein (Snca), Fos, Arc and Npas4 showed significantly greater differential regulation. These genes control neural proliferation, apoptosis, plasticity and memory and are involved in aging. In particular, Snca expression decreases during aging. We tested, therefore, whether an Snca-expressing lentivirus, by rescuing the defective Snca levels in the dentate gyrus of Btg1 knockout mice, could also reverse the aging phenotype, in particular the defective neurogenesis. We found that the exogenous expression of Snca reversed the Btg1 knockout-dependent decrease of stem cell proliferation as well as the increase of progenitor cell apoptosis. This indicates that Snca has a functional role in the process of neural aging observed in this model, and also suggests that Snca acts as a positive regulator of stem cell maintenance.