Physical interaction of Delta1, Jagged1, and Jagged2 with Notch1 and Notch3 receptors

Airway epithelial STAT3 is required for allergic inflammation in a murine model of asthma

The STAT3 transcription factor is critical for cytokine signaling and the acute phase response, but its role in allergic asthma is largely undefined. To investigate the role of STAT3 in mediating allergic inflammation, we used chemical and genetic approaches to inactivate STAT3 in the airway epithelium of mice. In a murine model of chronic asthma, we demonstrate that the administration of house dust mite (HDM) leads to robust STAT3 activation in the airway epithelium, smooth muscle, and immune cells in the lungs of C57BL/6 mice. To investigate the role of STAT3 in HDM-induced airway inflammation, a conditional knockout of STAT3 in the airway epithelium was generated, e-STAT3-/-. We determined that e-STAT3-/- mice had a significant decrease in HDM-induced airway eosinophilia, lung Th2 accumulation, and chemokines compared with wild-type animals. Importantly, the e-STAT3-/- mice had a significant decrease in airway hyperresponsiveness to methacholine. The administration of two STAT kinase inhibitors diminished STAT3 activation and markedly abrogated the HDM-induced lung inflammation. These findings suggest that STAT3 acts as a novel epithelial regulator of the allergic response by altering Th2 cell recruitment and effector function, and thus, targeting this molecule may provide the basis for a novel asthma therapy.

Bone marrow-derived hemopoietic precursors commit to the T cell lineage only after arrival in the thymic microenvironment

T lymphocytes develop in the thymus from hemopoietic precursors that commit to the T cell lineage under the influence of Notch signals. In this study, we show by single cell analyses that the most immature hemopoietic precursors in the adult mouse thymus are uncommitted and specify to the T cell lineage only after their arrival in the thymus. These precursors express high levels of surface Notch receptors and rapidly lose B cell potential upon the provision of Notch signals. Using a novel culture system with complexed, soluble Notch ligands that allows the titration of T cell lineage commitment, we find that these precursors are highly sensitive to both Delta and Jagged ligands. In contrast, their phenotypical and functional counterparts in the bone marrow are resistant to Notch signals that efficiently induce T cell lineage commitment in thymic precursors. Mechanistically, this is not due to differences in receptor expression, because early T lineage precursors, bone marrow lineage marker-negative, Sca-1-positive, c-Kit-positive and common lymphoid progenitor cells, express comparable amounts of surface Notch receptors. Our data demonstrate that the sensitivity to Notch-mediated T lineage commitment is stage-dependent and argue against the bone marrow as the site of T cell lineage commitment.

Disruption of the somitic molecular clock causes abnormal vertebral segmentation

Somites are the precursors of the vertebral column. They segment from the presomitic mesoderm (PSM) that is caudally located and newly generated from the tailbud. Somites form in synchrony on either side of the embryonic midline in a reiterative manner. A molecular clock that operates in the PSM drives this reiterative process. Genetic manipulation in mouse, chick and zebrafish has revealed that the molecular clock controls the activity of the Notch and WNT signaling pathways in the PSM. Disruption of the molecular clock impacts on somite formation causing abnormal vertebral segmentation (AVS). A number of dysmorphic syndromes manifest AVS defects. Interaction between developmental biologists and clinicians has lead to groundbreaking research in this area with the identification that spondylocostal dysostosis (SCD) is caused by mutation in Delta-like 3 (DLL3), Mesoderm posterior 2 (MESP2), and Lunatic fringe (LFNG); three genes that are components of the Notch signaling pathway. This review describes our current understanding of the somitic molecular clock and highlights how key findings in developmental biology can impact on clinical practice.

Jagged1-selective notch signaling induces smooth muscle differentiation via a RBP-Jkappa-dependent pathway

The Notch signaling pathway plays a crucial role in specifying cellular fates by interaction between cellular neighbors; however, the molecular mechanism underlying smooth muscle cell (SMC) differentiation by Notch signaling has not been well characterized. Here we demonstrate that Jagged1-Notch signaling promotes SMC differentiation from mesenchymal cells. Overexpression of the Notch intracellular domain, an activated form of Notch, up-regulates the expression of multiple SMC marker genes including SMC-myosin heavy chain (Sm-mhc) in mesenchymal 10T1/2 cells, but not in non-mesenchymal cells. Physiological Notch stimulation by its ligand Jagged1, but not Dll4, directly induces Sm-mhc expression in 10T1/2 cells without de novo protein synthesis, indicative of a ligand-selective effect. Jagged1-induced expression of SM-MHC was blocked bygamma-secretase inhibitor, N-(N-(3,5-difluorophenyl)-l-alanyl)-S-phenylglycine t-butyl ester, which impedes Notch signaling. Using Rbp-jkappa-deficient cells and site-specific mutagenesis of the SM-MHC gene, we show that such an induction is independent of the myocardin-serum response factor-CArG complex, but absolutely dependent on RBP-Jkappa, a major mediator of Notch signaling, and its cognate binding sequence. Of importance, Notch signaling and myocardin synergistically activate SM-MHC gene expression. Taken together, these data suggest that the Jagged1-Notch pathway constitutes an instructive signal for SMC differentiation through an RBP-Jkappa-dependent mechanism and augments gene expression mediated by the myocardin-SRF-CArG complex. Given that Notch pathway components are expressed in vascular SMC during normal development and disease, Notch signaling is likely to play a pivotal role in such situations to modulate the vascular smooth muscle cell phenotype.

Dll4-selective Notch signaling induces ephrinB2 gene expression in endothelial cells

The Notch pathway is involved in multiple aspects of vascular development, including arterial-venous differentiation. Here, we show that Notch stimulation instructively induces arterial characteristics in endothelial cells (EC). Forced expression of Notch intracellular domain (NICD, activated form of Notch) induced mRNA expression for a subset of arterial-specific markers such as ephrinB2, connexin40, and HERP1 only in EC but not other cell lines. In co-culture experiments using EC and either Dll4- or Jagged1-expressing cells, we found that Dll4 stimulation but not Jagged1 markedly induced ephrinB2 expression. An inducible expression of HERP1 and HERP2 by NICD has no measurable effects on expression of ephrinB2 and venous marker EphB4 although either HERP1 or HERP2 overexpression exerts potent inhibitory effects on EphB4 expression without ephrinB2 induction. We also found no functional interaction between Notch and TGF-beta-ALK1 signalings in an induction of ephrinB2 expression. These results suggest that Dll4-stimulated Notch signaling induces a part of arterial characteristics only in EC via HERP-independent mechanism. Our data provide new insight into the molecular mechanism of ligand-selective Notch activation during differentiation of arterial EC.

Notch ligands with contrasting functions: Jagged1 and Delta1 in the mouse inner ear

Each of the sensory patches in the epithelium of the inner ear is a mosaic of hair cells and supporting cells. Notch signalling is thought to govern this pattern of differentiation through lateral inhibition. Recent experiments in the chick suggest, however, that Notch signalling also has a prior function - inductive rather than inhibitory - in defining the prosensory patches from which the differentiated cells arise. Several Notch ligands are expressed in each patch, but their individual roles in relation to the two functions of Notch signalling are unclear. We have used a Cre-LoxP approach to knock out two of these ligands, Delta1 (Dll1) and Jagged1 (Jag1), in the mouse ear. In the absence of Dll1, auditory hair cells develop early and in excess, in agreement with the lateral inhibition hypothesis. In the absence of Jag1, by contrast, the total number of these cells is strongly reduced, with complete loss of cochlear outer hair cells and some groups of vestibular hair cells, indicating that Jag1 is required for the prosensory inductive function of Notch. The number of cochlear inner hair cells, however, is almost doubled. This correlates with loss of expression of the cell cycle inhibitor p27(Kip1) (Cdkn1b), suggesting that signalling by Jag1 is also needed to limit proliferation of prosensory cells, and that there is a core part of this population whose prosensory character is established independently of Jag1-Notch signalling. Our findings confirm that Notch signalling in the ear has distinct prosensory and lateral-inhibitory functions, for which different ligands are primarily responsible.

Target selectivity of vertebrate notch proteins. Collaboration between discrete domains and CSL-binding site architecture determines activation probability

All four mammalian Notch proteins interact with a single DNA-binding protein (RBP-jkappa), yet they are not equivalent in activating target genes. Parallel assays of three Notch-responsive promoters in several cell lines revealed that relative activation strength is dependent on protein module and promoter context more than the cellular context. Each Notch protein reads binding site orientation and distribution on the promoter differently; Notch1 performs extremely well on paired sites, and Notch3 prefers single sites in conjunction with a proximal zinc finger transcription factor. Although head-head sites can elicit a Notch response on their own, use of CBS (CSL binding site) in tail-tail orientation is context-dependent. Bias for specific DNA elements is achieved by interplay between the N-terminal RAM (RBP-jkappa-associated molecule/ankyrin region), which interprets CBS proximity and orientation, and the C-terminal transactivation domain that interacts specifically with the transcription machinery or nearby factors. To confirm the prediction that modular design underscores the evolution of functional divergence between Notch proteins, we generated a synthetic Notch protein (Notch1 ankyrin with Notch3 transactivation domain) that displayed superior signaling strength on the hes5 promoter. Consistent with the prediction that "preferred" targets (Hes1) should respond faster and at lower Notch concentration than other targets, we showed that Hes5-GFP was extinguished fast and recovered slowly, whereas Hes1-GFP was inhibited late and recovered quickly after a pulse of DAPT in metanephroi cultures.

Notch ligands Delta-like1, Delta-like4 and Jagged1 differentially regulate activation of peripheral T helper cells

The Notch pathway is involved in cell differentiation processes in various organs and at several developmental stages. The importance of Notch for early T lymphocyte development is well established. Recently, Notch has been implicated in directing naive T helper cell differentiation towards the Th1, Th2 or regulatory T cell lineages. However, the molecular events underlying these processes are poorly understood. We show that the Notch ligands Delta-like1, Delta-like4 and Jagged1 differentially affect early T cell activation and proliferation following T cell receptor cross-linking. Delta-like1 and Jagged1 induce a dose-dependent inhibition of early activation markers CD69 and CD25, as well as inhibition of proliferation after anti-CD3 stimulation of purified CD4+ T cells. Similarly, the rapid activation of transcription factors NF-AT, AP-1 and NF-kappaB is suppressed. In contrast, triggering of Notch by Delta-like4 enhances T cell activation and proliferation. The observed effects are dependent on simultaneous cross-linking of TCR and Notch but independent of gamma-secretase-mediated cleavage of Notch. These data suggest direct interference between Notch and early TCR signal transduction events, independent of the classical Notch pathway via release of the Notch intracellular domain. A Notch-mediated alteration of TCR signaling strength may contribute to the recently described modulation of naïve T cell differentiation by Notch ligands.

Functional analysis of a recurrent missense mutation in Notch3 in CADASIL

BACKGROUND

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is an inherited vascular dementia characterised by recurrent ischemic strokes in the deep white matter. Mutations in the gene encoding the cell surface receptor, Notch3, have been identified in CADASIL patients, and accumulation of the extracellular domain of Notch3 has been demonstrated in affected vessels. Almost all CADASIL mutations alter the number of cysteine residues in the epidermal growth factor (EGF)-like repeats in the extracellular domain of the protein.

OBJECTIVES

To understand the functional consequences of a recurrent CADASIL mutation on furin processing, cell surface expression, ligand binding, and activation of a downstream effector CBF1 by the Notch3 receptor.

METHODS

We expressed wild type and mutant Notch3 receptors in cultured cells and examined cell surface expression of the proteins. We also applied a new flow cytometry based approach to semi-quantitatively measure binding to three Notch ligands. Additionally, we used a well characterised co-culture system to examine ligand dependent activation of transcription from a CBF1-luciferase reporter construct.

RESULTS

These studies revealed subtle abnormalities in furin processing of the mutant receptor, although both heterodimeric and full length receptors are present on the cell surface, are capable of interacting with soluble forms of three ligands, Delta1, Delta4, and Jagged1, and retain the ability to activate CBF1 in a ligand dependent manner.

CONCLUSIONS

By comparison with other mutant forms of Notch3, these data indicate that individual CADASIL mutations can have disparate effects on Notch3 expression and function.

The Notch ligands DLL1 and JAG2 act synergistically to regulate hair cell development in the mammalian inner ear

The mammalian auditory sensory epithelium, the organ of Corti, contains sensory hair cells and nonsensory supporting cells arranged in a highly patterned mosaic. Notch-mediated lateral inhibition is the proposed mechanism for creating this sensory mosaic. Previous work has shown that mice lacking the Notch ligand JAG2 differentiate supernumerary hair cells in the cochlea, consistent with the lateral inhibitory model. However, it was not clear why only relatively modest increases in hair cell production were observed in Jag2 mutant mice. Here, we show that another Notch ligand, DLL1, functions synergistically with JAG2 in regulating hair cell differentiation in the cochlea. We also show by conditional inactivation that these ligands probably signal through the NOTCH1 receptor. Supernumerary hair cells in Dll1/Jag2 double mutants arise primarily through a switch in cell fate, rather than through excess proliferation. Although these results demonstrate an important role for Notch-mediated lateral inhibition during cochlear hair cell patterning, we also detected abnormally prolonged cellular proliferation that preferentially affected supporting cells in the organ of Corti. Our results demonstrate that the Notch pathway plays a dual role in regulating cellular differentiation and patterning in the cochlea, acting both through lateral inhibition and the control of cellular proliferation.

Functional redundancy of the Notch gene family during mouse embryogenesis: analysis of Notch gene expression in Notch3-deficient mice

The Notch3 gene, a member of the Notch gene family, is expressed in a wide variety of tissues during development. We generated and analyzed Notch3-deficient mice to assess the in vivo role of the Notch3 gene. Consistent with previous observation of Krebs et al. [Characterization of Notch3-deficient mice: normal embryonic development and absence of genetic interactions with a Notch1 mutation, Genesis 37 (3) (2003) 139-143], the Notch3-/- mice were viable, fertile, and developed normally despite abundant expression of Notch3 in various embryonic tissues. We examined the details of Notch1, 2, and 4 expressions in the Notch3-/- embryos compared with those in wild-type embryos. As a result, we found that a deficiency in Notch3 did not affect the expression of Notch1, 2, and 4, and that either Notch1 or Notch2, or sometimes both, was always expressed in all Notch3-expressing tissues examined. These results support the idea that other Notch genes functionally compensate for Notch3 during embryonic development. We also surveyed the adult tissues of Notch3-/- mice and found significantly fewer thymocytes in 10-week-old mice. Therefore, the thymus might be a target tissue affected by Notch3 deficiency.

Notch governing mature T cell differentiation

The differentiation of naive T cells to effector/memory T cells is regulated by a variety of factors. The recent advance of the contribution of Notch signaling in this differentiation step has provided a new path to better understand the acquisition or persistence of effector function of mature T cells. In this review, we summarize emerging and, in some points, conflicting evidence for Notch signaling on mature T cell activation and differentiation.

dlk acts as a negative regulator of Notch1 activation through interactions with specific EGF-like repeats

The protein dlk, encoded by the Dlk1 gene, belongs to the Notch epidermal growth factor (EGF)-like family of receptors and ligands, which participate in cell fate decisions during development. The molecular mechanisms by which dlk regulates cell differentiation remain unknown. By using the yeast two-hybrid system, we found that dlk interacts with Notch1 in a specific manner. Moreover, by using luciferase as a reporter gene under the control of a CSL/RBP-Jk/CBF-1-dependent promoter in the dlk-negative, Notch1-positive Balb/c 14 cell line, we found that addition of synthetic dlk EGF-like peptides to the culture medium or forced expression of dlk decreases endogenous Notch activity. Furthermore, the expression of the gene Hes-1, a target for Notch1 activation, diminishes in confluent Balb/c14 cells transfected with an expression construct encoding for the extracellular EGF-like region of dlk. The expression of Dlk1 and Notch1 increases in 3T3-L1 cells maintained in a confluent state for several days, which is associated with a concomitant decrease in Hes-1 expression. On the other hand, the decrease of Dlk1 expression in 3T3-L1 cells by antisense cDNA transfection is associated with an increase in Hes-1 expression. These results suggest that dlk functionally interacts in vivo with Notch1, which may lead to the regulation of differentiation processes modulated by Notch1 activation and signaling, including adipogenesis.

The intracellular domain of X-Serrate-1 is cleaved and suppresses primary neurogenesis in Xenopus laevis

The Notch ligands, Delta/Serrate/Lag-2 (DSL) proteins, mediate the Notch signaling pathway in a numerous developmental processes in multicellular organisms. Although the ligands induce the activation of the Notch receptor, the intracellular domain-deleted forms of the ligands cause dominant-negative phenotypes, implying that the intracellular domain is necessary for the Notch signal transduction. Here we examined the role of the intracellular domain of Xenopus Serrate (XSICD) in Xenopus embryos. X-Serrate-1 has the putative nuclear localization sequence (NLS) in downstream of the transmembrane domain. Biochemical analysis revealed that XSICD fragments are cleaved from the C-terminus side of X-Serrate-1. Fluorescence microscopic analysis showed that the nuclear localization of XSICD occurs in the neuroectoderm of the embryo injected with the full-length X-Serrate-1/GFP. Overexpression of XSICD showed the inhibitory effect on primary neurogenesis. However, a point mutation in the NLSs of XSICD inhibited the nuclear localization of XSICD, which caused the induction of a neurogenic phenotype. The animal cap assay revealed that X-Serrate-1 suppresses primary neurogenesis in neuralized animal cap, but X-Delta-1 does not. Moreover, XSICD could not activate the expression of the canonical Notch target gene, XESR-1 in contrast to the case of full-length X-Serrate-1. These results suggest that the combination of XSICD-mediated intracellular signaling and the extracellular domain of Notch ligands-mediated activation of Notch receptor is involved in the primary neurogenesis. Moreover, we propose a bi-directional signaling pathway mediated by X-Serrate-1 in Notch signaling.

Fringe glycosyltransferases differentially modulate Notch1 proteolysis induced by Delta1 and Jagged1

Fringe O-fucose-beta1,3-N-acetylglucosaminyltransferases modulate Notch signaling by potentiating signaling induced by Delta-like ligands, while inhibiting signaling induced by Serrate/Jagged1 ligands. Based on binding studies, the differential effects of Drosophila fringe (DFng) on Notch signaling are thought to result from alterations in Notch glycosylation that enhance binding of Delta to Notch but reduce Serrate binding. Here, we report that expression of mammalian fringe proteins (Lunatic [LFng], Manic [MFng], or Radical [RFng] Fringe) increased Delta1 binding and activation of Notch1 signaling in 293T and NIH 3T3 cells. Although Jagged1-induced signaling was suppressed by LFng and MFng, RFng enhanced signaling induced by either Delta1 or Jagged1, underscoring the diversity of mammalian fringe glycosyltransferases in regulating signaling downstream of different ligand-receptor combinations. Interestingly, suppression of Jagged1-induced Notch1 signaling did not correlate with changes in Jagged1 binding as found for Delta1. Our data support the idea that fringe glycosylation increases Delta1 binding to potentiate signaling, but we propose that although fringe glycosylation does not reduce Jagged1 binding to Notch1, the resultant ligand-receptor interactions do not effectively promote Notch1 proteolysis required for activation of downstream signaling events.

Notch ligands Delta 1 and Jagged1 transmit distinct signals to T-cell precursors

Signaling through the Notch pathway plays an essential role in inducing T-lineage commitment and promoting the maturation of immature thymocytes. Using an in vitro culture system, we show that 2 different classes of Notch ligands, Jagged1 or Delta1, transmit distinct signals to T-cell progenitors. OP9 stromal cells expressing either Jagged1 or Delta1 inhibit the differentiation of DN1 thymocytes into the B-cell lineage, but only the Delta1-expressing stromal cells promote the proliferation and maturation of T-cell progenitors through the early double-negative (DN) stages of thymocyte development. Whereas the majority of bone marrow-derived stem cells do not respond to Jagged1 signals, T-cell progenitors respond to Jagged1 signals during a brief window of their development between the DN1 and DN3 stages of thymic development. During these stages, Jagged1 signals can influence the differentiation of immature thymocytes along the natural killer (NK) and gamma delta T-cell lineages.

Hereditary Vascular Anomalies

Increased understanding of the mechanisms of angiogenesis and lymphangiogenesis has provided a glimpse at some of the molecules involved in the pathophysiology of hemangiomas and vascular malformations. This review focuses on recent advances in our understanding of the mechanisms of angiogenesis/lymphangiogenesis and the differentiation of arterial, venous, and lymphatic vessels. We integrate this knowledge with new data obtained from genetic studies in humans, which have revealed a number of heretofore-unsuspected candidates involved in the development of familial vascular anomalies. We present a common infantile vascular tumor, hemangioma, and then focus on hereditary familial vascular and lymphatic malformations. We also summarize transgenic mouse models for some of these malformations. It seems reasonable to believe that novel therapeutic strategies will soon emerge for the treatment of hemangiomas and vascular malformations.

Characterization of Notch3-deficient mice: normal embryonic development and absence of genetic interactions with a Notch1 mutation

The Notch signaling pathway is an evolutionarily conserved signaling mechanism and mutations in its components disrupt cell fate specification and embryonic development in many organisms. To analyze the in vivo role of the Notch3 gene in mice, we created a deletion allele by gene targeting. Embryos homozygous for this mutation developed normally and homozygous mutant adults were viable and fertile. We also examined whether we could detect genetic interactions during early embryogenesis between the Notch3 mutation and a targeted mutation of the Notch1 gene. Double homozygous mutant embryos exhibited defects normally observed in Notch1-deficient embryos, but we detected no obvious synergistic effects in the double mutants. These data demonstrate that the Notch3 gene is not essential for embryonic development or fertility in mice, and does not have a redundant function with the Notch1 gene during early embryogenesis.

Distribution of presenilin 1 and 2 and their relation to Notch receptors and ligands in human embryonic/foetal central nervous system

Notch signaling in vertebrates is mediated by four Notch receptors (Notch-1, -2, -3, and -4) that are activated by interacting with at least five different Notch ligands, Jagged-1, Jagged-2, Delta-1, -2, and -3. Recent studies have shown that the gamma-secretase-like intramembranous cleavage of Notch receptors to release their cytoplasmic signaling domains requires the presenilin (PS) proteins 1 and 2 (PS1 and PS2). Here, we used immunohistochemistry to compare the distribution of all four Notch receptor proteins and three ligands in the context of co-localization with PS1 and PS2 in first trimester human central nervous system (CNS). In addition, we investigated Notch receptors and ligands expression by Western blotting. The study was performed on the forebrain and spinal cord of human embryonic/foetal CNS (5-11 gestational weeks). Results showed a divergent distribution of the different Notch receptor proteins with only Notch-1 being co-localized with PS1 and PS2. Notch-2 was only seen occasionally within the developing cortex and spinal cord. Notch-3 expression was restricted to neuroepithelial cells of the spinal cord and endothelial cells in blood vessels of both developing cerebral cortex and spinal cord. The weak, punctate staining of Notch-4 in the neuroepithelium of the spinal cord could not be confirmed with Western blotting. Neither Notch-2, nor -3 showed overlap with either PS1 or PS2 immunoreactivity. The ligand Jagged-1 was found sporadically in the neuroepithelial cell layer in cerebral cortex of the earlier stages of development and of the spinal cord during the first trimester while Jagged-2 was not detected. Jagged-1 and Jagged-2 immunoreactivities were not found in the 9-11-week cortex. No co-distribution of Jagged-1 and PS1 or PS2 was found. Delta-1 ligand expression was detected in neuroepithelial cells of the ventricular zone of the cerebral cortex, and also in maturating neurons in the cortical plate and ventral horns of the developing spinal cord. The presence of Notch-1, Delta-1 and Jagged-1 in the neuroepithelium of developing CNS indicates that Notch signaling in proliferating human progenitor cells only involves these two receptor ligands and that cleavage of Notch-1 is mediated both by PS1 and PS2. The strong immunoreactivity of Notch-1, Delta-1 and PS1 in the cortical plate and in maturating neurons of the spinal cord also suggests that these proteins may regulate the maturation processes of post-mitotic neurons. The pronounced PS1 immunoreactivity in neurites in the hindbrain and spinal cord without detectable expression of any Notch receptor or ligand suggests that a possible role for PS1 in neurite growth involves either gamma-secretase-mediated cleavage of other substrates or gamma-secretase-independent mechanisms.

Instruction of distinct CD4 T helper cell fates by different notch ligands on antigen-presenting cells

Antigen-presenting cells (APC) tailor immune responses to microbial encounters by stimulating differentiation of CD4 T cells into the Th1 and Th2 lineages. We demonstrate that APC use the Notch pathway to instruct T cell differentiation. Strikingly, of the two Notch ligand families, Delta induces Th1, while Jagged induces the alternate Th2 fate. Expression of these different Notch ligands on APC is induced by Th1- or Th2-promoting stimuli. Th2 differentiation has been considered a default process as APC-derived instructive signals are unknown. We demonstrate that Jagged constitutes an instructive signal for Th2 differentiation, which is independent of IL4/STAT6. Th2 differentiation induced by APC is abrogated in T cells lacking the Notch effector RBPJkappa. Notch directs Th2 differentiation by inducing GATA3 and by directly regulating il4 gene transcription through RBPJkappa sites in a 3' enhancer.

The human Delta-like 1 homologue is implicated in the progression of liver fibrosis in biliary atresia

Advanced liver cirrhosis frequently occurs in infants with biliary atresia despite early surgical correction. The aetiology is unknown, but may involve many cytokines and liver cells including hepatic stellate cells (HSCs). A cytokine expression array and real-time quantitative reverse transcription-polymerase chain reaction (QRT-PCR) were used to study cytokine expression during the progression of liver fibrosis in biliary atresia. A Delta-like 1 homologue (DLK1) gene was identified and this gene was up-regulated during the early stage, and down-regulated during the late stage, of biliary atresia, similar to the expression pattern of the procollagen alpha1(I) gene. Further characterization with immunohistochemistry, confocal microscopy, and in situ hybridization revealed that the DLK1 protein was mainly present in the cytoplasm of smooth muscle actin-positive mesenchymal cells that were morphologically and immunohistochemically identical to activated HSCs/myofibroblasts, whereas DLK1 mRNA was present only in hepatocytes. As DLK1 is a negative regulator of adipocyte differentiation and may control cell fate during differentiation, overexpression of DLK1 protein in HSCs in the early stage of biliary atresia suggests that DLK1 may be implicated in the transformation of HSCs from fat-storing cells to myofibroblasts and in fibrogenesis associated with biliary atresia.

Activated Notch1 associates with a presenilin-1/gamma-secretase docking site

Presenilin-1 (PS1), implicated as the active component of the gamma-secretase enzymatic complex, is known to cleave the cell surface receptor Notch1 after ligand binding. Here we directly visualize Notch1-PS1 interactions using a novel fluorescence lifetime imaging microscopy assay to monitor fluorescence resonance energy transfer. We demonstrate that endogenous Notch1 and PS1 move into close proximity at the cell surface after activation of Notch1 by the Delta1 ligand. A constitutively active N-terminally truncated form of Notch1, an immediate substrate of the gamma-secretase complex, similarly is found in close proximity to PS1. Interestingly, this interaction remains in the presence of a potent gamma-secretase active site inhibitor. Thus ligand binding to Notch1 appears to result in access of truncated Notch1 to a putative docking site on the PS1-gamma-secretase complex. These results suggest a novel mechanism of ligand binding-mediated signal transduction of Notch1.

Patterns of Jagged1, Jagged2, Delta-like 1 and Delta-like 3 expression during late embryonic and postnatal brain development suggest multiple functional roles in progenitors and differentiated cells

The Notch-DSL signaling system, consisting of multiple receptors and ligands, inhibits neurogenesis and promotes gliogenesis during embryonic development, but the specific function of the various ligands and receptors at later developmental stages are unknown. Here, we examined the expression pattern of four Delta, Serrate and Lag-2 (DSL) ligands, Jagged1, Jagged2, Delta-like1 (Dl1) and Delta-like 3 (Dl3), in late embryonic and postnatal rat brain by in situ hybridization. In late embryos, Jagged1, Dl1 and Dl3 mRNAs were present in the periventricular germinal epithelia, but this expression diminished during postnatal ages. Jagged1 mRNA was also expressed in the inner aspect of the dentate gyrus at early postnatal times. Dl3 was detectable in the external granule cell layer (EGL) of the cerebellum, another site of postnatal neurogenesis. Jagged2 mRNA was expressed in virtually all postnatal neurons. Jagged1 mRNA was highly expressed in several brain nuclei during postnatal development, with lower levels of expression in other grey matter regions. In white matter, Dl1 and Dl3 mRNAs were expressed during the first week of postnatal development but only the expression of Dl1 mRNA persisted through the second week. Dl1 mRNA was present at lower levels throughout grey matter during the first few weeks of development. Jagged1 mRNA was expressed in blood vessels, choroid plexus, and menninges throughout development and in the adult. Jagged2 mRNA was transiently expressed in cerebral blood vessels and choroid plexus during the first postnatal week. Taken together, these results support multiple and differing roles for the various ligands during and after central nervous system (CNS) development.

Delta1-Notch3 Interactions Bias the Functional Differentiation of Activated CD4+ T Cells

Following activation by antigen, naive CD4+ T helper precursor cells execute distinct genetic programs that result in their differentiation toward the type 1 or type 2 helper T cell (Th1 or Th2) phenotype. Although the differentiation and function of these Th subsets has been well studied, little is known about the contribution to these differentiation events of cell surface receptors other than those for soluble cytokines, such as IL-12 or IL-4. Here, we provide direct evidence that the Delta1 interaction with Notch3 on CD4+ T cells transduces signals, promoting development toward the Th1 phenotype. The positive role of Notch signaling in effector cell differentiation was dose dependent, with high levels of stimulation resulting in reduced T cell activation. Our data revealed a clear contribution of Notch pathways to Th1 versus Th2 fate decisions, while also providing insight into another mechanism for inhibition of CD4+ T cell activation.

Active form of Notch members can enforce T lymphopoiesis on lymphoid progenitors in the monolayer culture specific for B cell development

The in vitro induction of T lymphopoiesis needs the precise stereoscopic structure of thymus tissues as seen in fetal thymus organ culture. In this study, we demonstrated for the first time that the introduction of the intracellular region of Notch1 can induce T cells expressing TCR without any thymic environment. In the coculture on the monolayer of OP-9, which was originally known to support B cell specific development, hemopoietic progenitors developed into Thy-1(+)CD25(+) T lineage cells if the progenitor cells were infected with the retrovirus containing Notch1 intracellular domains. The Thy-1(+) cells progressed to a further developmental stage, CD4 and CD8 double-positive cells expressing TCR on the cell surface, if they were further cultured on OP-9 or in the thymus. However, T cell induction by intracellular Notch1 failed unless both OP-9 and IL-7 were present. It is notable that Notch2 and Notch3 showed an effect on T lymphopoiesis similar to that of Notch1. These results indicate that in vitro T lymphopoiesis is inducible by signaling via Notch family members in a lineage-specific manner but shares other stroma-derived factors including IL-7 with B lymphopoiesis.

Delta-Notch signaling controls the generation of neurons/glia from neural stem cells in a stepwise process

We examined the role of Notch signaling on the generation of neurons and glia from neural stem cells by using neurospheres that are clonally derived from neural stem cells. Neurospheres prepared from Dll1(lacZ/lacZ) mutant embryos segregate more neurons at the expense of both oligodendrocytes and astrocytes. This mutant phenotype could be rescued when Dll1(lacZ/lacZ) spheres were grown and/or differentiated in the presence of conditioned medium from wild-type neurospheres. Temporal modulation of Notch by soluble forms of ligands indicates that Notch signaling acts in two steps. Initially, it inhibits the neuronal fate while promoting the glial cell fate. In a second step, Notch promotes the differentiation of astrocytes, while inhibiting the differentiation of both neurons and oligodendrocytes.

The C-terminal PDZ-ligand of JAGGED1 is essential for cellular transformation

JAGGED1 is a member of the Delta/Serrate/Lag-2 (DSL) family of proteins that are cell-bound ligands for Notch receptors. Initiation of Notch signaling occurs through a series of proteolytic events upon the binding of Notch to a DSL protein presented on neighboring cells. Whether DSL proteins themselves are capable of initiating an intrinsic signaling mechanism within the cell they are expressed is not known. Aberrant misexpression of JAGGED1 and DELTA1 has been documented in several human tumors; however, the mechanism by which misexpression of JAGGED1 contributes to oncogenesis has not been elucidated. We report that expression of human JAGGED1 transforms RKE cells in culture, therefore providing a model system to elucidate the function of DSL proteins. JAGGED1-mediated transformation occurs in a dose-dependent manner and requires a PDZ-ligand at the C terminus. Mutation of the PDZ-ligand did not affect the ability of JAGGED1 to initiate Notch signaling in neighboring cells. However, the PDZ-ligand is required for changes in the expression of JAGGED1 target genes and transcriptional activation of luciferase reporter constructs. Our data indicate the existence of a novel PDZ-dependent signaling pathway intrinsic to JAGGED1. We propose a bi-directional signaling model such that DSL proteins may have two distinct functions: to initiate Notch signaling in a neighboring cell and to initiate a PDZ-dependent signaling mechanism in the DSL-expressing cell. Moreover, we conclude that this intrinsic signaling mechanism of JAGGED1 may partly provide a link between aberrant misexpression of JAGGED1 and tumorigenesis.

HES-1 preserves purified hematopoietic stem cells ex vivo and accumulates side population cells in vivo

Mouse long-term hematopoietic reconstituting cells exist in the c-Kit+Sca-1+Lin- (KSL) cell population; among them, CD34(low/-) cells represent the most highly purified population of hematopoietic stem cells in the adult bone marrow. Here, we demonstrate that retrovirus-mediated transduction of CD34(low/-)c-Kit+Sca-1+Lin- (34-KSL) cells with the HES-1 gene, which encodes a basic helix-loop-helix transcription factor functioning downstream of the Notch receptor, and is a key molecule for the growth phase of neural stem cells in the embryo, preserves the long-term reconstituting activity of these cells in vitro. We also show that cells derived from the HES-1-transduced 34-KSL population produce progenies characterized by negative Hoechst dye staining, which defines the side population, and by CD34(low/-) profile in the bone marrow KSL population in each recipient mouse at ratios 3.5- and 7.8-fold those produced by nontransduced 34-KSL-derived competitor cells. We conclude that HES-1 preserves the long-term reconstituting hematopoietic activity of 34-KSL stem cells ex vivo. Up-regulation of HES-1 protein in the 34-KSL population before unnecessary cell division, that is, without retrovirus transduction, may represent a potent approach to absolute expansion of hematopoietic stem cells.

Notch1 and Jagged1 expression by the developing pulmonary vasculature

The molecular mechanisms of pulmonary vascular development are poorly understood. Cell-specific developmental pathways are influenced by cell-cell signaling. Notch signaling molecules are highly conserved receptors active in many cell-fate determination systems. Recent observations of Notch molecules and a Notch ligand, Jagged1, suggest their importance in vascular morphogenesis, and particularly pulmonary vascular development. We performed a systematic evaluation of Notch1/Jagged1 gene and protein expression in the developing mouse lung from embryonic day 11 until adulthood by using quantitative PCR, immunofluorescence, and electron microscopic analysis. mRNA transcripts for Notch1-4 and Jagged1 increased progressively from early to later lung development, accompanied by a simultaneous rise in endothelial cell-specific gene expression, a pattern not seen in other organs. Notch1 mRNA was identified on both epithelial and mesenchymal structures of the embryonic lung. Immunofluorescence staining revealed the progressive acquisition of Notch1 and Jagged1 proteins by the emerging endothelium. Notch1 and Jagged1 were seen initially on well-formed, larger vessels within the embryonic lung bud and progressively on finer vascular networks. Each was also expressed on surrounding nonvascular structures. The localization of Notch1 and Jagged1 on endothelial cell surface membranes within the alveolar microvasculature was confirmed by immuno-electron microscopy. These temporal and spatial patterns in Notch1/Jagged1 gene and protein expression suggest multiple potential paths of cell-cell signaling during lung development and vascular morphogenesis.

Determinants of Notch-3 receptor expression and signaling in vascular smooth muscle cells: implications in cell-cycle regulation

The Notch family of receptors and ligands plays an important role in cell fate determination, vasculogenesis, and organogenesis. Mutations of the Notch-3 receptor result in an arteriopathy that predisposes to early-onset stroke. However, the functional role of the Notch signaling pathway in adult vascular smooth muscle cells (VSMCs) is poorly characterized. This study documents that the Notch-3 receptor, the ligand Jagged-1, and the downstream transcription factor, HESR-1, are expressed in the normal adult rat carotid artery, and that this expression is modulated after vascular injury. In cultured VSMCs, both angiotensin II and platelet-derived growth factor (PDGF) markedly downregulated Notch-3 and Jagged-1 through ERK-dependent signaling mechanisms and prevented the glycosylation of Jagged-1. The downregulation of Jagged-1 and Notch-3 was associated with a decrease in CBF-1-mediated gene transcription activation and a fall in the mRNA levels of the downstream target transcription factor HESR-1. To test the hypothesis that the Notch pathway was coupled to growth regulation, we generated VSMC lines overexpressing the constitutively active form of Notch-3 (A7r5-N3IC). These cells exhibited a biphasic growth behavior in which the growth rate was retarded during the subconfluent phase and failed to decelerate at postconfluence. The lack of cell-cycle arrest in postconfluent A7r5-N3IC was associated with an attenuated upregulation of the cell-cycle inhibitor p27(kip) relative to control cells. This study documents the regulation of the Jagged-1 and Notch-3 genes in VSMCs by growth factor stimulation as well as a role for Notch-3 as a determinant of VSMC growth.

Down-regulation of Delta by proteolytic processing

Notch signaling regulates cell fate decisions during development through local cell interactions. Signaling is triggered by the interaction of the Notch receptor with its transmembrane ligands expressed on adjacent cells. Recent studies suggest that Delta is cleaved to release an extracellular fragment, DlEC, by a mechanism that involves the activity of the metalloprotease Kuzbanian; however, the functional significance of that cleavage remains controversial. Using independent functional assays in vitro and in vivo, we examined the biological activity of purified soluble Delta forms and conclude that Delta cleavage is an important down-regulating event in Notch signaling. The data support a model whereby Delta inactivation is essential for providing the critical ligand/receptor expression differential between neighboring cells in order to distinguish the signaling versus the receiving partner.

A secreted Delta1-Fc fusion protein functions both as an activator and inhibitor of Notch1 signaling

Signaling induced through interactions between DSL (Delta, serrate, LAG-2) ligand-signaling cells and Notch-responding cells influences the developmental fate of a wide variety of invertebrate and vertebrate cell types. Consistently with a requirement for direct cell-cell interactions, secreted DSL ligands expressed in flies do not appear to activate Notch signaling but rather produce phenotypes reminiscent of losses in Notch signaling. In contrast, secreted DSL ligands expressed in Caenorhabditis elegans or supplied to mammalian cells in culture produce effects indicative of Notch activation. In fact, engineered secreted DSL ligands have been used to study Notch signaling in neurogenesis, gliogenesis, hematopoeisis, neurite morphogenesis and ligand-induced nuclear translocation of the Notch intracellular domain. Using a recombinant, secreted form of the DSL ligand Delta1, we found that antibody-induced oligomerization (termed "clustering") was required for this soluble ligand to bind specifically to Notch1-expressing cells, undergo internalization, and activate downstream signaling. Interestingly, clustering with either limiting or excess antibody led to ligand binding in the absence of Notch signaling, indicating that ligand binding is necessary but not sufficient for activation of Notch signaling. Moreover, such antibody clustering conditions blocked Notch1 signaling induced by membrane-bound DSL ligands. We propose that multimerization influences whether ligand binding to Notch results in activation or inhibition of downstream signaling and suggest that differences in ligand presentation might account for why secreted forms of DSL ligands have been reported to function as agonists and antagonists of Notch signal transduction.

Functional diversity among Notch1, Notch2, and Notch3 receptors

To clarify functional diversities among the Notch receptors, we generated truncated forms of Notch1, Notch2, and Notch3 comprising the intracellular domain (aN1, aN2, and aN3) and investigated their transcriptional activities for HES1 and HES5 promoters driving the luciferase reporter gene (HES1-Luc and HES5-Luc). The reporter assays demonstrated that the transcriptional activities of aNs were markedly different from each other and dependent on the promoters examined. Furthermore, relative activities between some aN and another for each promoter were altered by the expression level of RBP-J kappa. We also found that the activities of aN1 and aN3 were reduced by coexpression of aN2. These observations suggest that each Notch receptor has a diverse role in the downstream gene expression and that the levels of HES1 and HES5 gene expression are complexly determined by various factors, such as the type and combination of the Notch receptors which confer the downstream signals and the expression level of RBP-J kappa.

Molecular regulation of urothelial renewal and host defenses during infection with uropathogenic Escherichia coli

Uropathogenic Escherichia coli (UPEC), the principal cause of urinary tract infection in women, attaches to the superficial facet cell layer of the bladder epithelium (urothelium) via its FimH adhesin. Attachment triggers exfoliation of bacteria-laden superficial facet cells, followed by rapid reconstitution of the urothelium through differentiation of underlying basal and intermediate cells. We have used DNA microarrays to define the molecular regulators of urothelial renewal and host defense expressed in adult C57Bl/6 female mice during the early phases of infection with isogenic virulent (FimH+) or avirulent (FimH-) UPEC strains. The temporal evolution and cellular origins of selected responses were then characterized by real time quantitative reverse transcriptase-PCR, in situ hybridization, and immunohistochemical analyses. Well before exfoliation is evident, FimH-mediated attachment suppresses transforming growth factor-beta (Bmp4) and Wnt5a/Ca(2+) signaling to promote subsequent differentiation of basal/intermediate cells. The early transcriptional responses to attachment also include induction of regulators of proliferation (e.g. epidermal growth factor family members), induction of the ETS transcription factor Elf3, which transactivates genes involved in epithelial differentiation and host defense (inducible nitric-oxide synthase), induction of modulators, and mediators of pro-inflammatory responses (e.g. Socs3, Cebp/delta, Bcl3, and CC/CXC chemokines), induction of modulators of apoptotic responses (A20), and induction of intermediate cell tight junction components (claudin-4). Both early and late phases of the host response exhibit remarkable specificity for the FimH+ strain and provide new insights about the molecular cascade mobilized to combat UPEC-associated urinary tract infection.

Distinct and regulated expression of Notch receptors in hematopoietic lineages and during myeloid differentiation

Hematopoietic development is a delicate balance of cell fate decisions in multipotent cells between self-renewal and differentiation. In multiple developmental systems, the Notch receptors are important factors regulating these processes. Hematopoietic progenitor cells have been shown to express Notch1, and studies with an activated intracellular form has revealed a functional role. To assess the function of other Notch members in hematopoiesis, we investigated the expression pattern of Notch1, Notch2, and Notch3 in hematopoietic lineages at the level of RNA and protein. We demonstrate that Notch1 and Notch2 are expressed in multiple lineages, and that Notch1 in particular appears to be regulated during myeloid differentiation. Notch1 was up-regulated and expressed at high levels in adherent macrophages. Mast cells expressed only low levels of Notch1 mRNA whereas Notch2 mRNA was highly expressed. In addition we could detect Notch3 mRNA and protein in cell lines representing mast cell progenitors. These expression patterns imply that the different Notch genes may have very distinct functions during hematopoiesis, and that Notch3 could be a specific regulator of mast cell development. The finding that Notch1 was up-regulated in the adherent cells developing from a multipotent progenitor cell line suggests that this protein may posses dual functions in hematopoiesis, i.e. at the stage of cell fate decision, and at the maturation stage of monocytes when adhesion to the specific microenvironment is accomplished.

Soluble Jagged 1 represses the function of its transmembrane form to induce the formation of the Src-dependent chord-like phenotype

We have previously demonstrated that the expression of the soluble extracellular domain of the transmembrane ligand for Notch receptors, Jagged 1 (sJ1), in NIH 3T3 cells results in the formation of a matrix-dependent chord-like phenotype, the loss of contact inhibition of growth, and an inhibition of pro-alpha 1(I) collagen expression. In an effort to define the mechanism by which sJ1 induces this phenotype, we report that sJ1 transfectants display biochemical and cytoskeletal alterations consistent with the activation of Src. Indeed, cotransfection of sJ1 transfectants with a dominant-negative mutant of Src resulted in the loss of matrix-dependent chord formation and correlated with the restoration of type I collagen expression and contact inhibition of growth. We also report that the sJ1-mediated induction of Src activity and related phenotypes, including chord formation, may result from the inhibition of endogenous Jagged 1-mediated Notch signaling since it was not possible to detect an sJ1-dependent induction of CSL-dependent transcription in these cells. Interestingly, NIH 3T3 cells transfected with dominant-negative (but not constitutively active) mutants of either Notch 1 or Notch 2 displayed a similar Src-related phenotype as the sJ1 transfectants. These data suggest that the ability of sJ1 to mediate chord formation is Src-dependent and requires the repression of endogenous Jagged 1-mediated Notch signaling, which is tolerant to the destabilization of the actin cytoskeleton, a mediator of cell migration.