Biomedical subjects

Thomas Gridley

Publications and source records attributed to Thomas Gridley.

At least 37 records · Page 2Linked to original sources

PubMed2004

Role of the Notch signalling pathway in tooth morphogenesis.

Notch receptors are involved in cell fate decisions through the process of lateral inhibition or inductive signalling. Jagged2 belongs to the family of transmembrane proteins that serve as the ligands for Notch receptors. We have analysed the expression of the Jagged2 gene in developing mouse teeth. Jagged2 expression is restricted in inner enamel epithelial cells that give rise to the ameloblasts. We have also examined the role of Jagged2 in tooth development using mutant mice that lack the domain of the Jagged2 protein required for interaction with the Notch receptors (DSL domain). Homozygous mutant mice die after birth, exhibit abnormal tooth morphology and fusions between the palatal and mandibular shelves. These results demonstrate that Notch signalling plays an essential role in tooth development.

Ameloblasts↗

PubMed2004

Notch3 is required for arterial identity and maturation of vascular smooth muscle cells.

Formation of a fully functional artery proceeds through a multistep process. Here we show that Notch3 is required to generate functional arteries in mice by regulating arterial differentiation and maturation of vascular smooth muscle cells (vSMC). In adult Notch3-/- mice distal arteries exhibit structural defects and arterial myogenic responses are defective. The postnatal maturation stage of vSMC is deficient in Notch3-/- mice. We further show that Notch3 is required for arterial specification of vSMC but not of endothelial cells. Our data reveal Notch3 to be the first cell-autonomous regulator of arterial differentiation and maturation of vSMC.

Actins↗

PubMed2004

Haploinsufficient lethality and formation of arteriovenous malformations in Notch pathway mutants.

The Notch signaling pathway is essential for embryonic vascular development in vertebrates. Here we show that mouse embryos heterozygous for a targeted mutation in the gene encoding the DLL4 ligand exhibit haploinsufficient lethality because of defects in vascular remodeling. We also describe vascular defects in embryos homozygous for a mutation in the Rbpsuh gene, which encodes the primary transcriptional mediator of Notch signaling. Conditional inactivation of Rpbsuh function demonstrates that Notch activation is essential in the endothelial cell lineage. Notch pathway mutant embryos exhibit defects in arterial specification of nascent blood vessels and develop arteriovenous malformations. These results demonstrate that vascular remodeling in the mouse embryo is sensitive to Dll4 gene dosage and that Notch activation in endothelial cells is essential for embryonic vascular remodeling.

Animals↗

PubMed2004

A requirement for Notch1 distinguishes 2 phases of definitive hematopoiesis during development.

Notch1 is known to play a critical role in regulating fates in numerous cell types, including those of the hematopoietic lineage. Multiple defects exhibited by Notch1-deficient embryos confound the determination of Notch1 function in early hematopoietic development in vivo. To overcome this limitation, we examined the developmental potential of Notch1(-/-) embryonic stem (ES) cells by in vitro differentiation and by in vivo chimera analysis. Notch1 was found to affect primitive erythropoiesis differentially during ES cell differentiation and in vivo, and this result reflected an important difference in the regulation of Notch1 expression during ES cell differentiation relative to the developing mouse embryo. Notch1 was dispensable for the onset of definitive hematopoiesis both in vitro and in vivo in that Notch1(-/-) definitive progenitors could be detected in differentiating ES cells as well as in the yolk sac and early fetal liver of chimeric mice. Despite the fact that Notch1(-/-) cells can give rise to multiple types of definitive progenitors in early development, Notch1(-/-) cells failed to contribute to long-term definitive hematopoiesis past the early fetal liver stage in the context of a wild-type environment in chimeric mice. Thus, Notch1 is required, in a cell-autonomous manner, for the establishment of long-term, definitive hematopoietic stem cells (HSCs).

Animals↗

PubMed2004

Kick it up a Notch: NOTCH1 activation in T-ALL.

While the human NOTCH1 gene initially was cloned as part of a translocation breakpoint in T cell acute lymphoblastic leukemia (T-ALL) tumors, this translocation is present in only a small percentage of T-ALL patients. A recent paper by Weng et al. (2004) demonstrates that novel types of activating mutations in the NOTCH1 gene occur in more than half of all T-ALL cases, implicating NOTCH1 as a major player in the etiology of T-ALL.

Gene Expression Regulation, Neoplastic↗

PubMed2004

gamma-secretase functions through Notch signaling to maintain skin appendages but is not required for their patterning or initial morphogenesis.

The role of Notch signaling during skin development was analyzed using Msx2-Cre to create mosaic loss-of-function alleles with precise temporal and spatial resolution. We find that gamma-secretase is not involved in skin patterning or cell fate acquisition within the hair follicle. In its absence, however, inner root sheath cells fail to maintain their fates and by the end of the first growth phase, the epidermal differentiation program is activated in outer root sheath cells. This results in complete conversion of hair follicles to epidermal cysts that bears a striking resemblance to Nevus Comedonicus. Sebaceous glands also fail to form in gamma-secretase-deficient mice. Importantly, mice with compound loss of Notch genes in their skin phenocopy loss of gamma-secretase in all three lineages, demonstrating that Notch proteolysis accounts for the major signaling function of this enzyme in this organ and that both autonomous and nonautonomous Notch-dependent signals are involved.

Amyloid Precursor Protein Secretases↗

PubMed2004

The developmental transcription factor slug is widely expressed in tissues of adult mice.

The Slug transcription factor plays an important role in epithelial-mesenchymal transformation during embryogenesis and is expressed in adult tissues during carcinogenesis. By detecting expression of a Slug-beta-galactosidase fusion protein, we have now demonstrated that Slug is also re-expressed in a variety of normal tissues in the adult mouse. Slug is expressed at relatively high levels in patchy stretches of basal cells in stratified and pseudostratified epithelium, including skin, oral mucosa, esophagus, stomach, rectum, cervix, and trachea. Slug is also found at variable levels in fibroblasts and stromal smooth muscle cells in many tissues. Sites of more intense Slug expression in mesenchymal tissues include cartilage, kidney glomeruli, lung, ovary, and uterus. Therefore, Slug expression is not restricted to the period of embryonic development or to pathological processes. The pattern of localization to basal cells in various epithelia suggests that Slug may play a role in the cell migration that occurs during continual renewal of these tissues.

Animals↗

PubMed2003

TCF and Groucho-related genes influence pituitary growth and development.

Mutations in the prophet of PIT1 gene (PROP1) are the most common cause of multiple pituitary hormone deficiency in humans; however, the mechanism of PROP1 action is not well understood. We report that Prop1 is essential for dorsally restricted expression of a Groucho-related gene, transducin-like enhancer of split 3 (Tle3), which encodes a transcriptional corepressor. Deficiency of a related gene, amino terminal enhancer of split (Aes), causes pituitary anomalies and growth insufficiency. TLE3 and AES have been shown to interact with TCF/LEF (transcripiton factors of the T cell-specific and lymphoid enhancer specific group) family members in cell culture systems. In the absence of TCF4 (Tcf7L2), Prop1 levels are elevated, pituitary hyperplasia ensues and palate closure is abnormal. Thus, we demonstrate that Tcf4 and Aes influence pituitary growth and development, and place Tcf4 and Tle3 in the genetic hierarchy with Prop1.

Animals↗

PubMed2003

Notch signaling regulates left-right asymmetry determination by inducing Nodal expression.

Generation of left-right asymmetry is an integral part of the establishment of the vertebrate body plan. Here we show that the Notch signaling pathway plays a primary role in the establishment of left-right asymmetry in mice by directly regulating expression of the Nodal gene. Embryos mutant for the Notch ligand Dll1 or doubly mutant for the Notch1 and Notch2 receptors exhibit multiple defects in left-right asymmetry. Analysis of the enhancer regulating node-specific Nodal expression revealed the presence of binding sites for the RBP-J protein, the primary transcriptional mediator of Notch signaling. Mutation of these sites destroyed the ability of this enhancer to direct node-specific gene expression in transgenic mice. Our results demonstrate that Dll1-mediated Notch signaling is essential for generation of left-right asymmetry, and that the Notch pathway acts upstream of Nodal expression during left-right asymmetry determination in mice.

Animals↗

PubMed2003

Notch signaling and inherited disease syndromes.

The Notch signaling pathway is an evolutionarily conserved, intercellular signaling mechanism essential for proper embryonic development in organisms as diverse as insects, nematodes, echinoderms and mammals. Disruptions in conserved developmental pathways frequently result in inherited congenital anomalies in humans. Mutations in genes encoding Notch pathway components underlie three inherited human diseases: Alagille syndrome, spondylocostal dysostosis, and cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy. Mouse models for these three diseases have been developed, and are leading to novel insights into the pathology of these diseases in humans.

Alagille Syndrome↗

PubMed2003

Slug expression during organogenesis in mice.

The vertebrate Slug gene encodes a zinc finger-containing transcriptional repressor. Here we report expression of the mouse Slug gene during organogenesis and late fetal development using histochemical detection of beta-galactosidase expressed from a targeted Slug(lacZ) knock-in allele. The Slug gene is highly expressed in the mesenchymal or stromal component of numerous organs. It is also highly expressed in craniofacial mesenchyme, in bone of both mesodermal and neural crest origin, and in the outflow tract and the endocardial cushions of the heart.

Animals↗

PubMed2003

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.

Animals↗

PubMed2002

Craniosynostosis in Twist heterozygous mice: a model for Saethre-Chotzen syndrome.

Saethre-Chotzen syndrome is a common autosomal dominant form of craniosynostosis, the premature fusion of the sutures of the calvarial bones of the skull. Most Saethre-Chotzen syndrome cases are caused by haploinsufficiency for the TWIST gene. Mice heterozygous for a null mutation of the Twist gene replicate certain features of Saethre-Chotzen syndrome, but have not been reported to exhibit craniosynostosis. We demonstrate that Twist heterozygous mice exhibit fusions of the coronal suture and other cranial suture abnormalities, indicating that Twist heterozygous mice constitute a better animal model for Saethre-Chotzen syndrome than was previously appreciated.

Acrocephalosyndactylia↗

PubMed2002

Lunatic fringe, FGF, and BMP regulate the Notch pathway during epithelial morphogenesis of teeth.

Teeth develop as epithelial appendages, and their morphogenesis is regulated by epithelial-mesenchymal interactions and conserved signaling pathways common to many developmental processes. A key event during tooth morphogenesis is the transition from bud to cap stage when the epithelial bud is divided into specific compartments distinguished by morphology as well as gene expression patterns. The enamel knot, a signaling center, forms and regulates the shape and size of the tooth. Mesenchymal signals are necessary for epithelial patterning and for the formation and maintenance of the epithelial compartments. We studied the expression of Notch pathway molecules during the bud-to-cap stage transition of the developing mouse tooth. Lunatic fringe expression was restricted to the epithelium, where it formed a boundary flanking the enamel knot. The Lunatic fringe expression domains overlapped only partly with the expression of Notch1 and Notch2, which were coexpressed with Hes1. We examined the regulation of Lunatic fringe and Hes1 in cultured explants of dental epithelium. The expression of Lunatic fringe and Hes1 depended on mesenchymal signals and both were positively regulated by FGF-10. BMP-4 antagonized the stimulatory effect of FGF-10 on Lunatic fringe expression but had a synergistic effect with FGF-10 on Hes1 expression. Recombinant Lunatic fringe protein induced Hes1 expression in the dental epithelium, suggesting that Lunatic fringe can act also extracellularly. Lunatic fringe mutant mice did not reveal tooth abnormalities, and no changes were observed in the expression patterns of other Fringe genes. We conclude that Lunatic fringe may play a role in boundary formation of the enamel knot and that Notch-signaling in the dental epithelium is regulated by mesenchymal FGFs and BMP.

Animals↗

PubMed2002

Slug is a novel downstream target of MyoD. Temporal profiling in muscle regeneration.

Temporal expression profiling was utilized to define transcriptional regulatory pathways in vivo in a mouse muscle regeneration model. Potential downstream targets of MyoD were identified by temporal expression, promoter data base mining, and gel shift assays; Slug and calpain 6 were identified as novel MyoD targets. Slug, a member of the snail/slug family of zinc finger transcriptional repressors critical for mesoderm/ectoderm development, was further shown to be a downstream target by using promoter/reporter constructs and demonstration of defective muscle regeneration in Slug null mice.

Animals↗

PubMed2002

Growth defect in Grg5 null mice is associated with reduced Ihh signaling in growth plates.

Gene-targeted disruption of Grg5, a mouse homologue of Drosophila groucho (gro), results in postnatal growth retardation in mice. The growth defect, most striking in approximately half of the Grg5 null mice, occurs during the first 4-5 weeks of age, but most mice recover retarded growth later. We used the nonlinear mixed-effects model to fit the growth data of wild-type, heterozygous, and Grg5 null mice. On the basis of preliminary evidence suggesting an interaction between Grg5 and the transcription factor Cbfa1/Runx2, critical for skeletal development, we further investigated the skeleton in the mice. A long bone growth plate defect was identified, which included shorter zones of proliferative and hypertrophic chondrocytes and decreased trabecular bone formation. This decreased trabecular bone formation is likely caused by a reduced recruitment of osteoblasts into the growth plate region of Grg5 null mice. Like the growth defect, the growth plate and trabecular bone abnormality improved as the mice grew older. The growth plate defect was associated with reduced Indian hedgehog expression and signaling. We suggest that Grg5, a transcriptional coregulator, modulates the activities of transcription factors, such as Cbfa1/Runx2 in vivo to affect Ihh expression and the function of long bone growth plates.

Animals↗

PubMed2002

Segmentation defects of Notch pathway mutants and absence of a synergistic phenotype in lunatic fringe/radical fringe double mutant mice.

The Notch signaling pathway is important in regulating formation and anterior-posterior patterning of somites in vertebrate embryos. Here we show that distinct segmentation defects are displayed in embryos mutant for the Notch pathway genes Notch1, Lunatic fringe (Lfng), Delta-like 1 (Dll1), and Delta-like 3 (Dll3). Lfng-deficient mice and Dll3-deficient mice exhibit very similar defects, and marker analysis suggests that progression of the segmentation clock is disrupted in Dll3 mutants. We also show that Radical fringe (Rfng)-deficient mice exhibit no obvious phenotypic defects. To assess whether the absence of a phenotype in Rfng-deficient mice was the result of functional redundancy with the Lfng gene, we generated Lfng/Rfng double homozygous mutant mice. These mice exhibit the skeletal defects normally observed in Lfng-deficient mice, but we detected no obvious synergistic or additive effects in the double mutant animals.

Animals↗

PubMed2002

Cell movements during gastrulation: snail dependent and independent pathways.

The morphogenetic process of gastrulation requires multiple inputs and intricate coordination. Genetic analyses demonstrate critical roles of vertebrate and invertebrate Snail proteins in this process. Together with other regulatory molecules including Wnt and BMP, the Snail pathways specify cell fate and reorganize cellular machineries to coordinate morphological changes and cell movements during gastrulation.

Adherens Junctions↗