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Stem cells integrate inputs from multiple sources. Stem cell niches provide signals that promote stem cell maintenance (1, 2), while differentiated daughter cells are known to provide feedback signals to regulate stem cell replication and differentiation (3-6). Recently, stem cells have been shown to regulate themselves using an autocrine mechanism (7). The existence of a 'stem cell niche' was first postulated by Schofield in 1978 to define local environments necessary for the maintenance of haematopoietic stem cells (1). Since then, an increasing body of work has focused on defining stem cell niches (1-6). Yet little is known about how progenitor cell and differentiated cell numbers and proportions are maintained. In the airway epithelium, basal cells function as stem/progenitor cells that can both self-renew and produce differentiated secretory cells and ciliated cells (8, 9). Secretory cells also act as transit-amplifying cells that eventually differentiate into post-mitotic ciliated cells (9, 10). Here we describe a mode of cell regulation in which adult mammalian stem/progenitor cells relay a forward signal to their own progeny. Surprisingly, this forward signal is shown to be necessary for daughter cell maintenance. Using a combination of cell ablation, lineage tracing and signalling pathway modulation, we show that airway basal stem/progenitor cells continuously supply a Notch ligand to their daughter secretory cells. Without these forward signals, the secretory progenitor cell pool fails to be maintained and secretory cells execute a terminal differentiation program and convert into ciliated cells. Thus, a parent stem/progenitor cell can serve as a functional daughter cell niche., To establish whether post-mitotic ciliated cells send a conventional feedback signal to regulate the replication of their parent stem and progenitor cells, we genetically ablated ciliated cells using FOXJ1-creER; LSL-DTA [...]

Graft-versus-host disease (GVHD) is the main complication of allogeneic bone marrow transplantation. Current strategies to control GVHD rely on global immunosuppression. These strategies are incompletely effective and decrease the anticancer [...]

HSCs either self-renew or differentiate to give rise to multipotent cells whose progeny provide blood cell precursors. However, surprisingly little is known about the factors that regulate this choice of self-renewal versus differentiation. One candidate is the Notch signaling pathway, with ex vivo studies suggesting that Notch regulates HSC differentiation, although a functional role for Notch in HSC self-renewal in vivo remains controversial. Here, we have shown that Notch2, and not Notch1, inhibits myeloid differentiation and enhances generation of primitive [Sca-1.sup.+]c-[kit.sup.+] progenitors following in vitro culture of enriched HSCs with purified Notch ligands. In mice, Notch2 enhanced the rate of formation of short-term repopulating multipotential progenitor cells (MPPs) as well as long-term repopulating HSCs, while delaying myeloid differentiation in BM following injury. However, consistent with previous reports, once homeostasis was achieved, neither Notch1 nor Notch2 affected repopulating cell self-renewal. These data indicate a Notch2-dependent role in assuring orderly repopulation by HSCs, MPPs, myeloid cells, and lymphoid cells during BM regeneration., Introduction HSCs either self-renew or give rise to multipotent cells whose progeny provide precursors committed to the lymphoid and myeloid lineages. Recent studies have identified factors that maintain HSCs in [...]

Am J Physiol Lung Cell Mol Physiol 298: L45-L56, 2010. First published November 6, 2009; doi: 10.1152/ajplung.90550.2008.--Distal lung development occurs through coordinated induction of myofibroblasts, epithelial cells, and capillaries. Lunatic Fringe (Lfng) is a [[beta].sub.1-3] N-acetylglucosamine transferase that modifies Notch receptors to facilitate their activation by Delta-like (D111/4) ligands. Lfng is expressed in the distal lung during saccular development, and deletion of this gene impairs myofibroblast differentiation and alveogenesis in this context. A similar defect was observed in [Notch2.sup.[beta]geo/+] [Notch3.sup.[beta]-geo/[beta]-geo] compound mutant mice but not in [Notch2.sup.[beta]geo/+] or [Notch3.sup.[beta]-geo/[beta]-geo] single mutants. Finally, to directly test for the role of Notch signaling in myofibroblast differentiation in vivo, we used ROSA26-[rtTA.sup./+];[tetO-CRE.sup./+];RBPJ[[kappa].sup.flox/flox] inducible mutant mice to show that disruption of canonical Notch signaling during late embryonic development prevents induction of smooth muscle actin in mesenchymal cells of the distal lung. In sum, these results demonstrate that Lfng functions to enhance Notch signaling in myofibroblast precursor cells and thereby to coordinate differentiation and mobilization of myofibroblasts required for alveolar septation. alveolar development

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2007.10.056 Byline: Steve Rodriguez (a), Heather M. Sickles (a), Chris DeLeonardis (a), Ana Alcaraz (a), Thomas Gridley (b), David M. Lin (a) Keywords: Notch; Glia; Olfactory; Sustentacular; Neurodegeneration; Hes1; Hey1; Six1; Notch2; GST Abstract: Notch receptors are expressed in neurons and glia in the adult nervous system, but why this expression persists is not well-understood. Here we examine the role of the Notch pathway in the postnatal mouse main olfactory system, and show evidence consistent with a model where Notch2 is required for maintaining sustentacular cell function. In the absence of Notch2, the laminar nature of these glial-like cells is disrupted. Hes1, Hey1, and Six1, which are downstream effectors of the Notch pathway, are down-regulated, and cytochrome P450 and Glutathione S-transferase (GST) expression by sustentacular cells is reduced. Functional levels of GST activity are also reduced. These disruptions are associated with increased olfactory sensory neuron degeneration. Surprisingly, expression of Notch3 is also down-regulated. This suggests the existence of a feedback loop where expression of Notch3 is initially independent of Notch2, but requires Notch2 for maintained expression. While the Notch pathway has previously been shown to be important for promoting gliogenesis during development, this is the first demonstration that the persistent expression of Notch receptors is required for maintaining glial function in adult. Author Affiliation: (a) Department of Biomedical Sciences, Cornell University, Ithaca, NY 14853, USA (b) The Jackson Laboratory, 600 Main Street, Bar Harbor, ME 04609, USA Article History: Received 17 May 2007; Revised 25 October 2007; Accepted 26 October 2007

Mice heterozygous for missense mutations of the Notch ligand Jagged1 (Jag1) exhibit head-shaking behavior indicative of an inner ear vestibular defect. In contrast, mice heterozygous for a targeted deletion of the Jag1 gene ([Jag1.sup.del1]) do not demonstrate obvious head-shaking behavior. To determine whether the differences in inner ear phenotypes were due to the types of Jag1 mutations or to differences in genetic background, we crossed [Jag1.sup.del1] heterozygous mice onto the same genetic background as the missense mutants. This analysis revealed that variation of the Jag1 mutant inner ear phenotype is caused by genetic background differences and is not due to the type of Jag1 mutation. Genome scans of N2 backcross mice identified a significant modifier locus on chromosome 7, as well as a suggestive locus on chromosome 14. We also analyzed modifiers of an eye defect in [Jag1.sup.del1] heterozygous mice from this same cross.

L5Jcs1 is a perinatal lethal mutation uncovered in a screen for ENU-induced mutations on mouse chromosome 5. L5Jcs1 homozygotes exhibit posterior-to-anterior transformations of the vertebral column midsection, similar to mice deficient for Hoxc8 and Hoxc9. Positional cloning efforts identified a mutation in a novel, evolutionarily conserved, and ubiquitously expressed gene dubbed Tapt1 (Transmembrane anterior posterior transformation 1). TAPT1 is predicted to contain several transmembrane domains, and part of the gene is orthologous to an unusual alternatively spliced human transcript encoding the cytomegalovirus gH receptor. We speculate that TAPT1 is a downstream effector of HOXC8 that may act by transducing or transmitting extracellular information required for axial skeletal patterning during development.

In Drosophila, mutations in the Twist gene interact with mutations in the Snail gene. We show that the mouse Twist1 mutation interacts with Snail and Snai2 mutations to enhance aberrant cranial suture fusion, demonstrating that genetic interactions between genes of the Twist and Snail families have been conserved during evolution.

Radial glia functions as neural progenitors and as scaffolding supporting neuronal migration during CNS development. A study identifies brain lipid-binding protein as the first predominantly CNS-specific Notch target gene and mediates some aspects of Notch signaling in radial glia.

The mouse embryos heterozygous for a targeted mutation in the gene encoding the DLL4 ligand exhibit happloinsufficient lethality because of defects in vascular remodeling is reported. Notch pathway mutant embryos exhibit defects in arterial specification of nascent blood vessels and develop arteriovenous malformations.

Byline: Rulang Jiang, Yu Lan, Christine R. Norton, John P. Sundberg, Thomas Gridley Abstract: The Slug gene encodes a zinc finger protein, homologous to the product of the Drosophila Snail gene, that is implicated in the generation and migration of both mesoderm and neural crest cells in several vertebrate species. We describe here the cloning and genetic analysis of the mouse Slug (Slugh) gene. Slugh encodes a 269-amino-acid protein that shares 92% amino acid identity with the product of the chicken Slug gene. We have characterized Slugh gene expression during early mouse embryogenesis by whole mount in situ hybridization of Slugh mRNA and through detection of [beta]-galactosidase expression from an in-frame Slugh.sup.lacZ allele generated through homologous recombination. Slugh expression is first detected in extraembryonic mesoderm and is later detected in many mesodermal subsets, although it is not detected in the primitive streak. In contrast to many other vertebrates, the mouse Slug gene is not expressed in premigratory neural crest cells but is expressed in migratory neural crest cells. Analysis of a targeted null mutation that deleted all Slugh coding sequences revealed that Slugh is not required for mesoderm formation or for neural crest generation, migration, or development in mice. These results indicate that neither the expression pattern nor the biological function of the Slug gene is conserved among all vertebrates. These data also raise interesting questions about the regulation of neural crest generation, which is one of the distinguishing characteristics of the vertebrate subphylum. Author Affiliation: The Jackson Laboratory, 600 Main Street, Bar Harbor, Maine 04609

Abstract Background Members of the Snail gene family, which encode zinc finger proteins that function as transcriptional repressors, play essential roles during embryonic development in vertebrates. Mouse embryos with conditional deletion of the Snail1 (Snai1) gene in the epiblast, but not in most extraembryonic membranes, exhibit defects in left-right asymmetry specification and migration of mesoderm cells through the posterior primitive streak. Here we describe phenotypic defects that result in death of the mutant embryos by 9.5 days of gestation. Findings Endothelial cells differentiated in epiblast-specific Snai1-deficient embryos, but formation of an interconnected vascular network was abnormal. To determine whether the observed vascular defects were dependent on disruption of blood flow, we analyzed vascular remodeling in cultured allantois explants from the mutant embryos. Similar vascular defects were observed in the mutant allantois explants. Conclusion These studies demonstrate that lethality in the Snai1-conditional mutant embryos is caused by multiple defects in the cardiovascular system.

Notch3 is required to generate functional arteries in mice by regulating arterial differentiation and maturation of vascular smooth muscle cells (vSMC) and that Notch3 is required for arterial specification of vSMC but not of endothelial cells. The data from observation on Notch3 mice reveal Notch3 to be first cell-autonomous regulator of arterial differentiation and maturation of vSMC.

Research has been conducted on left-right asymmetry generation in the vertebrate body. The authors demonstrate that Notch signaling is important for the asymmetry establishment in mice carrying it out via Nodal gene expression regulation.

Inhibiting Notch signaling induces adipose browning, improves systemic glucose tolerance and insulin sensitivity, and suppresses weight gain in mice. A fundamental concept of obesity is the lack of balance between [...]

Snail family members regulate epithelial-to-mesenchymal transition ( EMT) during invasion of intestinal tumours, but their role in normal intestinal homeostasis is unknown. Studies in breast and skin epithelia indicate that Snail proteins promote an undifferentiated state. Here, we demonstrate that conditional knockout of Snai1 in the intestinal epithelium results in apoptotic loss of crypt base columnar stem cells and bias towards differentiation of secretory lineages. In vitro organoid cultures derived from Snai1 conditional knockout mice also undergo apoptosis when Snai1 is deleted. Conversely, ectopic expression of Snai1 in the intestinal epithelium in vivo results in the expansion of the crypt base columnar cell pool and a decrease in secretory enteroendocrine and Paneth cells. Following conditional deletion of Snai1, the intestinal epithelium fails to produce a proliferative response following radiation-induced damage indicating a fundamental requirement for Snai1 in epithelial regeneration. These results demonstrate that Snai1 is required for regulation of lineage choice, maintenance of CBC stem cells and regeneration of the intestinal epithelium following damage. [ABSTRACT FROM AUTHOR]

The Snail transcription factor regulates diverse aspects of stem cell biology in organisms ranging from Drosophila to mammals. Here we have asked whether it regulates the biology of neural precursor cells (NPCs) in the forebrain of postnatal and adult mice, taking advantage of a mouse containing a floxed Snail allele (Snailfl/fl mice). We show that when Snail is inducibly ablated in the embryonic cortex, this has long-term consequences for cortical organization. In particular, when Snailfl/fl mice are crossed to Nestin-cre mice that express Cre recombinase in embryonic neural precursors, this causes inducible ablation of Snail expression throughout the postnatal cortex. This loss of Snail causes a decrease in proliferation of neonatal cortical neural precursors and mislocalization and misspecification of cortical neurons. Moreover, these precursor phenotypes persist into adulthood. Adult neural precursor cell proliferation is decreased in the forebrain subventricular zone and in the hippocampal dentate gyrus, and this is coincident with a decrease in the number of adult-born olfactory and hippocampal neurons. Thus, Snail is a key regulator of the numbers of neural precursors and newborn neurons throughout life. [ABSTRACT FROM AUTHOR]

Highlights: [•] The Snai1 and Snai2 genes are important for cartilage development. [•] These genes function redundantly in mice in vivo. [•] The SNAI1 and SNAI2 proteins bind both their own and each other’s promoter. [•] These results help provide an explanation for this genetic redundancy. [ABSTRACT FROM AUTHOR]

The Snail gene family encodes zinc finger-containing transcriptional repressor proteins. Three members of the Snail gene family have been described in mammals, encoded by the Snai1, Snai2, and Snai3 genes. The function of the Snai1 and Snai2 genes have been studied extensively during both vertebrate embryogenesis and tumor progression and metastasis, and play critically important roles during these processes. However, little is known about the function of the Snai3 gene and protein. We describe here generation and analysis of Snai3 conditional and null mutant mice. We also generated an EYFP-tagged Snai3 null allele that accurately reflects endogenous Snai3 gene expression, with the highest levels of expression detected in thymus and skeletal muscle. Snai3 null mutant homozygous mice are viable and fertile, and exhibit no obvious phenotypic defects. These results demonstrate that Snai3 gene function is not essential for embryogenesis in mice. [ABSTRACT FROM AUTHOR]

ABSTRACT Endochondral bone formation is a multistep process during which a cartilage primordium is replaced by mineralized bone. Several genes involved in cartilage and bone development have been identified as target genes for the Snail family of zinc finger transcriptional repressors, and a gain-of-function study has demonstrated that upregulation of Snai1 activity in mouse long bones caused a reduction in bone length. However, no in vivo loss-of-function studies have been performed to establish whether Snail family genes have an essential, physiological role during normal bone development. We demonstrate here that the Snai1 and Snai2 genes function redundantly during embryonic long bone development in mice. Deletion of the Snai2 gene, or limb bud-specific conditional deletion of the Snai1 gene, did not result in obvious defects in the skeleton. However, limb bud-specific Snai1 deletion on a Snai2 null genetic background resulted in substantial defects in the long bones of the limbs. Long bones of the Snai1/Snai2 double mutants exhibited defects in chondrocyte morphology and organization, inhibited trabecular bone formation, and delayed ossification. Chondrocyte proliferation was markedly reduced, and transcript levels of genes encoding cell cycle regulators, such as p21Waf1/Cip1, were strikingly upregulated in the Snai1/Snai2 double mutants, suggesting that during chondrogenesis Snail family proteins act to control cell proliferation by mediating expression of cell-cycle regulators. Snai2 transcript levels were increased in Snai1 mutant femurs, whereas Snai1 transcript levels were increased in Snai2 mutant femurs. In addition, in the mutant femurs the Snai1 and Snai2 genes compensated for each other's loss not only quantitatively, but also by expanding their expression into the other genes' normal expression domains. These results demonstrate that the Snai1 and Snai2 genes transcriptionally compensate temporally, spatially, and quantitatively for each other's loss, and demonstrate an essential role for Snail family genes during chondrogenesis in mice. [ABSTRACT FROM AUTHOR]

Conclusion: Jagged1-mediated Notch signaling regulates hair cell (HC) production in a distinct way rather than lateral inhibition mediated by Hes1 and Hes5. Jagged1 may interact with Notch3, probably via candidate downstream mediators Hesr1 and Hesr2, regulating the prosensory formation in the early stage. Objectives: To explore the function of the Jagged1-mediated Notch signaling pathway in mammalian inner ear development and its possible mechanism. Methods: Using conditional gene targeting, a novel Jagged1 conditional knockout (Jag1-cko), Pax8cre/+; Jag1flox/flox, was established. The auditory brainstem response and swim ability test were utilized to identify functional disability. The expression of Jagged1, Notch3, Hes1, Hesr1, and Hesr2 was detected by immunofluorescence and immunohistochemistry. Results: Our Jag1-cko model was established and survived well. It presented hearing impairment and balance disturbance with 'waltzing' behavior. Cochleae and vestibular apparatus were all found in our Jag1-cko model. Patch deficiency of outer hair cells (OHCs) was found on the apical and middle turns of the auditory epithelium. OHCs were totally missing on the basal turn. The stereociliary bundles were disorientated on the cristae. Unlike Hes1, no expression of Notch3, Hesr1, and Hesr2 was found on embryonic day 13.5 of the Jag1-cko model. [ABSTRACT FROM AUTHOR]

Background: In the mouse ovary, oocytes initially develop in clusters termed germ-cell nests. Shortly after birth, these germ-cell nests break apart, and the oocytes individually become surrounded by somatic granulosa cells to form primordial follicles. Notch signaling plays essential roles during oogenesis in Drosophila, and recent studies have suggested that Notch signaling also plays an essential role during oogenesis and ovary development in mammals. However, no in vivo loss-of-function studies have been performed to establish whether Notch family receptors have an essential physiological role during normal ovarian development in mutant mice Results: Female mice with conditional deletion of the Notch2 gene in somatic granulosa cells of the ovary exhibited reduced fertility, accompanied by the formation of multi-oocyte follicles, which became hemorrhagic by 7 weeks of age. Formation of multi-oocyte follicles resulted from defects in breakdown of the primordial germ-cell nests. The ovaries of the Notch2 conditional mutant mice had increased numbers of oocytes, but decreased numbers of primordial follicles. Oocyte numbers in the Notch2 conditional mutants were increased not by excess or extended cellular proliferation, but as a result of decreased oocyte apoptosis. Conclusions: Our work demonstrates that Notch2-mediated signaling in the somatic-cell lineage of the mouse ovary regulates oocyte apoptosis non-cell autonomously, and is essential for regulating breakdown of germ-cell nests and formation of primordial follicles. This model provides a new resource for studying the developmental and physiological roles of Notch signaling during mammalian reproductive biology. [ABSTRACT FROM AUTHOR]

The Notch signaling pathway is an evolutionarily conserved intercellular signaling mechanism that is required for embryonic development, cell fate specification, and stem cell maintenance. Discovered and studied initially in Drosophila melanogaster, the Notch pathway is conserved and functionally active throughout the animal kingdom. In this paper, we summarize the biochemical mechanisms of Notch signaling and describe its role in regulating one particular developmental pathway, oogenesis in Drosophila [ABSTRACT FROM AUTHOR]