The Notch Intracellular Domain Has an RBPj-Independent Role during Mouse Hair Follicular Development

Notch dimerization provides robustness against environmental insults and is required for vascular integrity

The Notch intracellular domain (NICD) regulates gene expression during development and homeostasis in a transcription factor complex that binds DNA either as monomer, or cooperatively as dimers. Mice expressing Notch dimerization-deficient (NDD) alleles of Notch1 and Notch2 have defects in multiple tissues that are sensitized to environmental insults. Here, we report that cardiac phenotypes and DSS (Dextran Sodium Sulfate) sensitivity in NDD mice can be ameliorated by housing mice under hypo-allergenic conditions (food/bedding). However, compound heterozygote NDD mice (N1RA/-; N2RA/-) in hypo-allergenic conditions subsequently develop severe hydrocephalus and hemorrhages. Further analysis revealed multiple vascular phenotypes in NDD mice including leakage, malformations of brain vasculature, and vasodilation in kidneys, leading to demise around P21. This mouse model is thus a hypomorphic allele useful to analyze vascular phenotypes and gene-environment interactions. The possibility of a non-canonical Notch signal regulating barrier formation in the gut, skin, and blood systems is discussed.

Loss of Notch dimerization perturbs intestinal homeostasis by a mechanism involving HDAC activity

A tri-protein complex containing NICD, RBPj and MAML1 binds DNA as monomer or as cooperative dimers to regulate transcription. Mice expressing Notch dimerization-deficient alleles (NDD) of Notch1 and Notch2 are sensitized to environmental insults but otherwise develop and age normally. Transcriptomic analysis of colonic spheroids uncovered no evidence of dimer-dependent target gene miss-regulation, confirmed impaired stem cell maintenance in-vitro, and discovered an elevated signature of epithelial innate immune response to symbionts, a likely underlying cause for heightened sensitivity in NDD mice. TurboID followed by quantitative nano-spray MS/MS mass-spectrometry analyses in a human colon carcinoma cell line expressing either NOTCH2DD or NOTCH2 revealed an unbalanced interactome, with reduced interaction of NOTCH2DD with the transcription machinery but relatively preserved interaction with the HDAC2 interactome suggesting modulation via cooperativity. To ask if HDAC2 activity contributes to Notch loss-of-function phenotypes, we used the HDAC2 inhibitor Valproic acid (VPA) and discovered it could prevent the intestinal consequences of NDD and gamma secretase inhibitors (DBZ or DAPT) treatment in mice and spheroids, suggesting synergy between HDAC activity and pro-differentiation program in intestinal stem cells.

ASH2L Mediates Epidermal Differentiation and Hair Follicle Morphogenesis through H3K4me3 Modification

The processes of epidermal development in mammals are regulated by complex molecular mechanisms, such as histone modifications. Histone H3 lysine K4 methylation mediated by COMPASS (complex of proteins associated with Set1) methyltransferase is associated with gene activation, but its effect on epidermal lineage development remains unclear. Therefore, we constructed a mouse model of specific ASH2L (COMPASS methyltransferase core subunit) deletion in epidermal progenitor cells and investigated its effect on the development of mouse epidermal lineage. Furthermore, downstream target genes regulated by H3K4me3 were screened using RNA sequencing combined with Cleavage Under Targets and Tagmentation sequencing. Deletion of ASH2L in epidermal progenitor cells caused thinning of the suprabasal layer of the epidermis and delayed hair follicle morphogenesis in newborn mice. These phenotypes may be related to the reduced proliferative capacity of epidermal and hair follicle progenitor cells. ASH2L depletion may also lead to depletion of the epidermal stem cell pools in late mouse development. Finally, genes related to hair follicle development (Shh, Edar, and Fzd6), Notch signaling pathway (Notch2, Notch3, Hes5, and Nrarp), and ΔNp63 were identified as downstream target genes regulated by H3K4me3. Collectively, ASH2L-dependent H3K4me3 modification served as an upstream epigenetic regulator in epidermal differentiation and hair follicle morphogenesis in mice.

Robust reprogramming of glia into neurons by inhibition of Notch signaling and nuclear factor I (NFI) factors in adult mammalian retina

Generation of neurons through direct reprogramming has emerged as a promising therapeutic approach for treating neurodegenerative diseases. In this study, we present an efficient method for reprogramming retinal glial cells into neurons. By suppressing Notch signaling by disrupting either Rbpj or Notch1/2, we induced mature Müller glial cells to reprogram into bipolar- and amacrine-like neurons. We demonstrate that Rbpj directly activates both Notch effector genes and genes specific to mature Müller glia while indirectly repressing expression of neurogenic basic helix-loop-helix (bHLH) factors. Combined loss of function of Rbpj and Nfia/b/x resulted in conversion of nearly all Müller glia to neurons. Last, inducing Müller glial proliferation by overexpression of dominant-active Yap promotes neurogenesis in both Rbpj- and Nfia/b/x/Rbpj-deficient Müller glia. These findings demonstrate that Notch signaling and NFI factors act in parallel to inhibit neurogenic competence in mammalian Müller glia and help clarify potential strategies for regenerative therapies aimed at treating retinal dystrophies.

Progress on the mechanism of natural products alleviating androgenetic alopecia

Androgenetic alopecia (AGA) has become a widespread problem that leads to considerable impairment of the psyche and daily life. The currently approved medications for the treatment of AGA are associated with significant adverse effects, high costs, and prolonged treatment duration. Therefore, natural products are being considered as possible complementary or alternative treatments. This review aims to enhance comprehension of the mechanisms by which natural products treat AGA. To achieve this, pertinent studies were gathered and subjected to analysis. In addition, the therapeutic mechanisms associated with these natural products were organized and summarized. These include the direct modulation of signaling pathways such as the Wnt/β-catenin pathway, the PI3K/AKT pathway, and the BMP pathway. Additionally, they exert effects on cytokine secretion, anti-inflammatory, and antioxidant capabilities, as well as apoptosis and autophagy. Furthermore, the review briefly discusses the relationship between signaling pathways and autophagy and apoptosis in the context of AGA, systematically presents the mechanisms of action of existing natural products, and analyzes the potential therapeutic targets based on the active components of these products. The aim is to provide a theoretical basis for the development of pharmaceuticals, nutraceuticals, or dietary supplements.

The epigenetics orchestra of Notch signaling: a symphony for cancer therapy

The aberrant regulation of the Notch signaling pathway, which is a fundamental developmental pathway, has been implicated in a wide range of human cancers. The Notch pathway can be activated by both canonical and noncanonical Notch ligands, and its role can switch between acting as an oncogene or a tumor suppressor depending on the context. Epigenetic modifications have the potential to modulate Notch and its ligands, thereby influencing Notch signal transduction. Consequently, the utilization of epigenetic regulatory mechanisms may present novel therapeutic opportunities for both single and combined therapeutics targeted at the Notch signaling pathway. This review offers insights into the mechanisms governing the regulation of Notch signaling and explores their therapeutic potential.

Robust reprogramming of glia into neurons by inhibition of Notch signaling and NFI factors in adult mammalian retina

Generation of neurons through direct reprogramming has emerged as a promising therapeutic approach for neurodegenerative diseases. Despite successful applications in vitro , in vivo implementation has been hampered by low efficiency. In this study, we present a highly efficient strategy for reprogramming retinal glial cells into neurons by simultaneously inhibiting key negative regulators. By suppressing Notch signaling through the removal of its central mediator Rbpj, we induced mature Müller glial cells to reprogram into bipolar and amacrine neurons in uninjured adult mouse retinas, and observed that this effect was further enhanced by retinal injury. We found that specific loss of function of Notch1 and Notch2 receptors in Müller glia mimicked the effect of Rbpj deletion on Müller glia-derived neurogenesis. Integrated analysis of multiome (scRNA- and scATAC-seq) and CUT&Tag data revealed that Rbpj directly activates Notch effector genes and genes specific to mature Müller glia while also indirectly represses the expression of neurogenic bHLH factors. Furthermore, we found that combined loss of function of Rbpj and Nfia/b/x resulted in a robust conversion of nearly all Müller glia to neurons. Finally, we demonstrated that inducing Müller glial proliferation by AAV (adeno-associated virus)-mediated overexpression of dominant- active Yap supports efficient levels of Müller glia-derived neurogenesis in both Rbpj - and Nfia/b/x/Rbpj - deficient Müller glia. These findings demonstrate that, much like in zebrafish, Notch signaling actively represses neurogenic competence in mammalian Müller glia, and suggest that inhibition of Notch signaling and Nfia/b/x in combination with overexpression of activated Yap could serve as an effective component of regenerative therapies for degenerative retinal diseases.

Revisiting the role of Notch in nephron segmentation confirms a role for proximal fate selection during mouse and human nephrogenesis

Notch signaling promotes maturation of nephron epithelia, but its proposed contribution to nephron segmentation into proximal and distal domains has been called into doubt. We leveraged single cell and bulk RNA-seq, quantitative immunofluorescent lineage/fate tracing, and genetically modified human induced pluripotent stem cells (iPSCs) to revisit this question in developing mouse kidneys and human kidney organoids. We confirmed that Notch signaling is needed for maturation of all nephron lineages, and thus mature lineage markers fail to detect a fate bias. By contrast, early markers identified a distal fate bias in cells lacking Notch2, and a concomitant increase in early proximal and podocyte fates in cells expressing hyperactive Notch1 was observed. Orthogonal support for a conserved role for Notch signaling in the distal/proximal axis segmentation is provided by the demonstration that nicastrin (NCSTN)-deficient human iPSC-derived organoids differentiate into TFA2B+ distal tubule and CDH1+ connecting segment progenitors, but not into HNF4A+ or LTL+ proximal progenitors.

GJB2 gene therapy and conditional deletion reveal developmental stage-dependent effects on inner ear structure and function

Pathogenic variants in GJB2, the gene encoding connexin 26, are the most common cause of autosomal-recessive hereditary deafness. Despite this high prevalence, pathogenic mechanisms leading to GJB2-related deafness are not well understood, and cures are absent. Humans with GJB2-related deafness retain at least some auditory hair cells and neurons, and their deafness is usually stable. In contrast, mice with conditional loss of Gjb2 in supporting cells exhibit extensive loss of hair cells and neurons and rapidly progress to profound deafness, precluding the application of therapies that require intact cochlear cells. In an attempt to design a less severe Gjb2 animal model, we generated mice with inducible Sox10iCre ^ERT2 -mediated loss of Gjb2. Tamoxifen injection led to reduced connexin 26 expression and impaired function, but cochlear hair cells and neurons survived for 2 months, allowing phenotypic rescue attempts within this time. AAV-mediated gene transfer of GJB2 in mature mutant ears did not demonstrate threshold improvement and in some animals exacerbated hearing loss and resulted in hair cell loss. We conclude that Sox10iCre ^ERT2 ;Gjb2 ^flox/flox mice are valuable for studying the biology of connexin 26 in the cochlea. In particular, these mice may be useful for evaluating gene therapy vectors and development of therapies for GJB2-related deafness.

Comprehensive transcriptome and methylome analysis delineates the biological basis of hair follicle development and wool-related traits in Merino sheep

Background

Characterization of the molecular mechanisms underlying hair follicle development is of paramount importance in the genetic improvement of wool-related traits in sheep and skin-related traits in humans. The Merino is the most important breed of fine-wooled sheep in the world. In this study, we systematically investigated the complexity of sheep hair follicle development by integrating transcriptome and methylome datasets from Merino sheep skin.

Results

We analysed 72 sequence datasets, including DNA methylome and the whole transcriptome of four gene types, i.e. protein-coding genes (PCGs), lncRNAs, circRNAs, and miRNAs, across four embryonic days (E65, E85, E105, and E135) and two postnatal days (P7 and P30) from the skin tissue of 18 Merino sheep. We revealed distinct expression profiles of these four gene types across six hair follicle developmental stages, and demonstrated their complex interactions with DNA methylation. PCGs with stage-specific expression or regulated by stage-specific lncRNAs, circRNAs, and miRNAs were significantly enriched in epithelial differentiation and hair follicle morphogenesis. Regulatory network and gene co-expression analyses identified key transcripts controlling hair follicle development. We further predicted transcriptional factors (e.g. KLF4, LEF1, HOXC13, RBPJ, VDR, RARA, and STAT3) with stage-specific involvement in hair follicle morphogenesis. Through integrating these stage-specific genomic features with results from genome-wide association studies (GWAS) of five wool-related traits in 7135 Merino sheep, we detected developmental stages and genes that were relevant with wool-related traits in sheep. For instance, genes that were specifically upregulated at E105 were significantly associated with most of wool-related traits. A phenome-wide association study (PheWAS) demonstrated that candidate genes of wool-related traits (e.g. SPHK1, GHR, PPP1R27, CSRP2, EEF1A2, and PTPN1) in sheep were also significantly associated with dermatological, metabolic, and immune traits in humans.

Conclusions

Our study provides novel insights into the molecular basis of hair follicle morphogenesis and will serve as a foundation to improve breeding for wool traits in sheep. It also indicates the importance of studying gene expression in the normal development of organs in understanding the genetic architecture of economically important traits in livestock. The datasets generated here are useful resources for functionally annotating the sheep genome, and for elucidating early skin development in mammals, including humans.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-021-01127-9.

BRAFV600E Overrides NOTCH Signaling in Thyroid Cancer

Background: Several mechanisms likely cooperate with the mitogen-activated protein (MAP)-kinase pathway to promote cancer progression in the thyroid. One putative pathway is NOTCH signaling, which is implicated in several other malignancies. In thyroid cancer, data regarding the role of the NOTCH pathway are insufficient and even contradictory. Methods: A BRAF^V600E-driven papillary thyroid carcinoma (PTC) mouse model was subjected to NOTCH pathway genetic alterations, and the tumor burden was followed by ultrasound. Further analyses were performed on PTC cell lines or noncancerous cells transfected with NOTCH^IC or BRAF^V600E, which were then subjected to pharmacological treatment with MAP-kinase or NOTCH pathway inhibitors. Results: The presence of the BRAF^V600E mutation coupled with overexpression of the NOTCH intracellular domain led to significantly bigger thyroid tumors in mice, to a more aggressive carcinoma, and decreased overall survival. Although more cystic, the tumors did not progress into anaplastic thyroid carcinomas. On the contrary, the deletion of RBP-jκ (a major cofactor involved in NOTCH signaling) did not alter the phenotype in mice. BRAF^V600E-mutated PTC cell lines were resistant to pharmacological inhibition of the NOTCH pathway. Inhibition of MEK1/2 uncovered a predominant effect on Hes1/Hey1 transcription compared with NOTCH inhibition in BRAF^V600E-mutated cell lines. Finally, γ-secretase activity and γ-secretase subunit transcription levels were dependent on ERK activation. Our findings suggest that MAP-kinase activity overrides the NOTCH pathway in the context of thyroid cancer. Conclusions: The interaction between the BRAF and NOTCH pathways demonstrates that the BRAF^V600E mutation might bypass NOTCH and exert a strong positive effect on NOTCH downstream targets in thyroid carcinoma.

Targeting the Notch Signaling Pathway in Chronic Inflammatory Diseases

The Notch signaling pathway regulates developmental cell-fate decisions and has recently also been linked to inflammatory diseases. Although therapies targeting Notch signaling in inflammation in theory are attractive, their design and implementation have proven difficult, at least partly due to the broad involvement of Notch signaling in regenerative and homeostatic processes. In this review, we summarize the supporting role of Notch signaling in various inflammation-driven diseases, and highlight efforts to intervene with this pathway by targeting Notch ligands and/or receptors with distinct therapeutic strategies, including antibody designs. We discuss this in light of lessons learned from Notch targeting in cancer treatment. Finally, we elaborate on the impact of individual Notch members in inflammation, which may lay the foundation for development of therapeutic strategies in chronic inflammatory diseases.

Deficiency of Rbpj Leads to Defective Stress-Induced Hematopoietic Stem Cell Functions and Hif Mediated Activation of Non-canonical Notch Signaling Pathways

Deregulated notch signaling has been associated with human pathobiology. However, functions of notch pathways in hematopoiesis remain incompletely understood. Here, we ablated canonical notch pathways, through genetic deletion of Rbpj, in hematopoietic stem cells (HSCs). Our data identified that loss of canonical notch results in normal adult HSC pool, at steady state conditions. However, HSC maintenance and functions in response to radiation-, chemotherapy-, and cytokine- induced stress were compromised in the absence of canonical notch. Rbpj deficient HSCs exhibit decreased proliferation rates and elevated expression of p57^Kip2. Surprisingly, loss of Rbpj resulted in upregulation of key notch target genes and augmented binding of Hes1 to p57 and Gata2 promoters. Further molecular analyses identified an increase in notch activity, elevated expression and nuclear translocation of Hif proteins, and augmented binding of Hif1α to Hes1 promoter in the absence of Rbpj. These studies, for the first time, identify a previously unknown role for non-canonical notch signaling and establish a functional link between Hif and Notch pathways in hematopoiesis.

Notch signalling defines dorsal root ganglia neuroglial fate choice during early neural crest cell migration

Background

The dorsal root ganglia (DRG) are a critical component of the peripheral nervous system, and function to relay somatosensory information from the body’s periphery to sensory perception centres within the brain. The DRG are primarily comprised of two cell types, sensory neurons and glia, both of which are neural crest-derived. Notch signalling is known to play an essential role in defining the neuronal or glial fate of bipotent neural crest progenitors that migrate from the dorsal ridge of the neural tube to the sites of the DRG. However, the involvement of Notch ligands in this process and the timing at which neuronal versus glial fate is acquired has remained uncertain.

Results

We have used tissue specific knockout of the E3 ubiquitin ligase mindbomb1 (Mib1) to remove the function of all Notch ligands in neural crest cells. Wnt1-Cre; Mib1^fl/fl mice exhibit severe DRG defects, including a reduction in glial cells, and neuronal cell death later in development. By comparing formation of sensory neurons and glia with the expression and activation of Notch signalling in these mice, we define a critical period during embryonic development in which early migrating neural crest cells become biased toward neuronal and glial phenotypes.

Conclusions

We demonstrate active Notch signalling between neural crest progenitors as soon as trunk neural crest cells delaminate from the neural tube and during their early migration toward the site of the DRG. This data brings into question the timing of neuroglial fate specification in the DRG and suggest that it may occur much earlier than originally considered.

Electronic supplementary material

The online version of this article (10.1186/s12868-019-0501-0) contains supplementary material, which is available to authorized users.

Endoderm Jagged induces liver and pancreas duct lineage in zebrafish

Liver duct paucity is characteristic of children born with Alagille Syndrome (ALGS), a disease associated with JAGGED1 mutations. Here, we report that zebrafish embryos with compound homozygous mutations in two Notch ligand genes, jagged1b (jag1b) and jagged2b (jag2b) exhibit a complete loss of canonical Notch activity and duct cells within the liver and exocrine pancreas, whereas hepatocyte and acinar pancreas development is not affected. Further, animal chimera studies demonstrate that wild-type endoderm cells within the liver and pancreas can rescue Notch activity and duct lineage specification in adjacent cells lacking jag1b and jag2b expression. We conclude that these two Notch ligands are directly and solely responsible for all duct lineage specification in these organs in zebrafish. Our study uncovers genes required for lineage specification of the intrahepatopancreatic duct cells, challenges the role of duct cells as progenitors, and suggests a genetic mechanism for ALGS ductal paucity.The hepatopancreatic duct cells connect liver hepatocytes and pancreatic acinar cells to the intestine, but the mechanism for their lineage specification is unclear. Here, the authors reveal that Notch ligands Jagged1b and Jagged2b induce duct cell lineage in the liver and pancreas of the zebrafish.

Notch Signaling in Development, Tissue Homeostasis, and Disease

Notch signaling is an evolutionarily highly conserved signaling mechanism, but in contrast to signaling pathways such as Wnt, Sonic Hedgehog, and BMP/TGF-β, Notch signaling occurs via cell-cell communication, where transmembrane ligands on one cell activate transmembrane receptors on a juxtaposed cell. Originally discovered through mutations in Drosophila more than 100 yr ago, and with the first Notch gene cloned more than 30 yr ago, we are still gaining new insights into the broad effects of Notch signaling in organisms across the metazoan spectrum and its requirement for normal development of most organs in the body. In this review, we provide an overview of the Notch signaling mechanism at the molecular level and discuss how the pathway, which is architecturally quite simple, is able to engage in the control of cell fates in a broad variety of cell types. We discuss the current understanding of how Notch signaling can become derailed, either by direct mutations or by aberrant regulation, and the expanding spectrum of diseases and cancers that is a consequence of Notch dysregulation. Finally, we explore the emerging field of Notch in the control of tissue homeostasis, with examples from skin, liver, lung, intestine, and the vasculature.

The Varied Roles of Notch in Cancer

Notch receptors influence cellular behavior by participating in a seemingly simple signaling pathway, but outcomes produced by Notch signaling are remarkably varied depending on signal dose and cell context. Here, after briefly reviewing new insights into physiologic mechanisms of Notch signaling in healthy tissues and defects in Notch signaling that contribute to congenital disorders and viral infection, we discuss the varied roles of Notch in cancer, focusing on cell autonomous activities that may be either oncogenic or tumor suppressive.