Ophir D Klein

University of California, San Francisco, San Francisco, California, United States

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Publications (84)472.82 Total impact

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    ABSTRACT: The evolutionary relationships of extinct species are ascertained primarily through the analysis of morphological characters. Character inter-dependencies can have a substantial effect on evolutionary interpretations, but the developmental underpinnings of character inter-dependence remain obscure because experiments frequently do not provide detailed resolution of morphological characters. Here we show experimentally and computationally how gradual modification of development differentially affects characters in the mouse dentition. We found that intermediate phenotypes could be produced by gradually adding ectodysplasin A (EDA) protein in culture to tooth explants carrying a null mutation in the tooth-patterning gene Eda. By identifying development-based character inter-dependencies, we show how to predict morphological patterns of teeth among mammalian species. Finally, in vivo inhibition of sonic hedgehog signalling in Eda null teeth enabled us to reproduce characters deep in the rodent ancestry. Taken together, evolutionarily informative transitions can be experimentally reproduced, thereby providing development-based expectations for character-state transitions used in evolutionary studies.
    Nature 07/2014; · 42.35 Impact Factor
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    ABSTRACT: Taste buds are assemblies of elongated epithelial cells, which are innervated by gustatory nerves that transmit taste information to the brain stem. Taste cells are continuously renewed throughout life via proliferation of epithelial progenitors, but the molecular regulation of this process remains unknown. During embryogenesis, sonic hedgehog (SHH) negatively regulates taste bud patterning, such that inhibition of SHH causes the formation of more and larger taste bud primordia, including in regions of the tongue normally devoid of taste buds. Here, using a Cre-lox system to drive constitutive expression of SHH, we identify the effects of SHH on the lingual epithelium of adult mice. We show that misexpression of SHH transforms lingual epithelial cell fate, such that daughter cells of lingual epithelial progenitors form cell type-replete, onion-shaped taste buds, rather than non-taste, pseudostratified epithelium. These SHH-induced ectopic taste buds are found in regions of the adult tongue previously thought incapable of generating taste organs. The ectopic buds are composed of all taste cell types, including support cells and detectors of sweet, bitter, umami, salt and sour, and recapitulate the molecular differentiation process of endogenous taste buds. In contrast to the well-established nerve dependence of endogenous taste buds, however, ectopic taste buds form independently of both gustatory and somatosensory innervation. As innervation is required for SHH expression by endogenous taste buds, our data suggest that SHH can replace the need for innervation to drive the entire program of taste bud differentiation.
    Development 07/2014; · 6.27 Impact Factor
  • Adrien Naveau, Kerstin Seidel, Ophir D. Klein
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    ABSTRACT: The vertebrate ectoderm gives rise to organs that produce mineralized or keratinized substances, including teeth, hair, and claws. Most of these ectodermal derivatives grow continuously throughout the animal's life and have active pools of adult stem cells that generate all the necessary cell types. These organs provide powerful systems for understanding the mechanisms that enable stem cells to regenerate or renew ectodermally derived tissues, and remarkable progress in our understanding of these systems has been made in recent years using mouse models. We briefly compare what is known about stem cells and their niches in incisors, hair follicles, and claws, and we examine expression of Gli1 as a potential example of a shared stem cell marker. We summarize some of the features, structures, and functions of the stem cell niches in these ectodermal derivatives; definition of the basic elements of the stem cell niches in these organs will provide guiding principles for identification and characterization of the niche in similar systems.
    Experimental Cell Research 07/2014; · 3.37 Impact Factor
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    ABSTRACT: The transition between the proliferation and differentiation of progenitor cells is a key step in organogenesis, and alterations in this process can lead to developmental disorders. The extracellular signal-regulated kinase 1/2 (ERK) signaling pathway is one of the most intensively studied signaling mechanisms that regulates both proliferation and differentiation. How a single molecule (e.g. ERK) can regulate two opposing cellular outcomes is still a mystery. Using both chick and mouse models, we shed light on the mechanism responsible for the switch from proliferation to differentiation of head muscle progenitors and implicate ERK subcellular localization. Manipulation of the fibroblast growth factor (FGF)-ERK signaling pathway in chick embryos in vitro and in vivo demonstrated that blockage of this pathway accelerated myogenic differentiation, whereas its activation diminished it. We next examined whether the spatial subcellular localization of ERK could act as a switch between proliferation (nuclear ERK) and differentiation (cytoplasmic ERK) of muscle progenitors. A myristoylated peptide that blocks importin 7-mediated ERK nuclear translocation induced robust myogenic differentiation of muscle progenitor/stem cells in both head and trunk. In the mouse, analysis of Sprouty mutant embryos revealed that increased ERK signaling suppressed both head and trunk myogenesis. Our findings, corroborated by mathematical modeling, suggest that ERK shuttling between the nucleus and the cytoplasm provides a switch-like transition between proliferation and differentiation of muscle progenitors.
    Development 06/2014; · 6.27 Impact Factor
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    ABSTRACT: Hypohidrotic ectodermal dysplasia (HED) is the most prevalent type of ectodermal dysplasia (ED). ED is an umbrella term for a group of syndromes characterized by missing or malformed ectodermal structures, including skin, hair, sweat glands, and teeth. The X-linked recessive (XL), autosomal recessive (AR), and autosomal dominant (AD) types of HED are caused by mutations in the genes encoding ectodysplasin (EDA1), EDA receptor (EDAR), or EDAR-associated death domain (EDARADD). Patients with HED have a distinctive facial appearance, yet a quantitative analysis of the HED craniofacial phenotype using advanced three-dimensional (3D) technologies has not been reported. In this study, we characterized craniofacial morphology in subjects with X-linked hypohidrotic ectodermal dysplasia (XLHED) by use of 3D imaging and geometric morphometrics (GM), a technique that uses defined landmarks to quantify size and shape in complex craniofacial morphologies. We found that the XLHED craniofacial phenotype differed significantly from controls. Patients had a smaller and shorter face with a proportionally longer chin and midface, prominent midfacial hypoplasia, a more protrusive chin and mandible, a narrower and more pointed nose, shorter philtrum, a narrower mouth, and a fuller and more rounded lower lip. Our findings refine the phenotype of XLHED and may be useful both for clinical diagnosis of XLHED and to extend understanding of the role of EDA in craniofacial development.
    Molecular Genetics & Genomic Medicine. 05/2014;
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    ABSTRACT: Costello syndrome (CS) is a RASopathy characterized by a wide range of cardiac, musculoskeletal, dermatological, and developmental abnormalities. The RASopathies are defined as a group of syndromes caused by activated Ras/mitogen-activated protein kinase (MAPK) signaling. Specifically, CS is caused by activating mutations in HRAS. Although receptor tyrosine kinase (RTK) signaling, which is upstream of Ras/MAPK, is known to play a critical role in craniofacial and dental development, the craniofacial and dental features of CS have not been systematically defined in a large group of individuals. In order to address this gap in our understanding and fully characterize the CS phenotype, we evaluated the craniofacial and dental phenotype in a large cohort (n = 41) of CS individuals. We confirmed that the craniofacial features common in CS include macrocephaly, bitemporal narrowing, convex facial profile, full cheeks, and large mouth. Additionally, CS patients have a characteristic dental phenotype that includes malocclusion with anterior open bite and posterior crossbite, enamel hypo-mineralization, delayed tooth development and eruption, gingival hyperplasia, thickening of the alveolar ridge, and high palate. Comparison of the craniofacial and dental phenotype in CS with other RASopathies, such as cardio-facio-cutaneous syndrome (CFC), provides insight into the complexities of Ras/MAPK signaling in human craniofacial and dental development. © 2014 Wiley Periodicals, Inc.
    American Journal of Medical Genetics Part A 03/2014; · 2.30 Impact Factor
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    ABSTRACT: Objective: GPCR-mediated G-protein signaling orchestrates crucial intercellular communications during the development of multicellular organs such as mammary glands, brain, liver, and bone. Tooth development is also governed by communication between epithelial and mesenchymal cells. We aim to identify target GPCRs with greater expression in developing teeth than in vital organs such as brain/liver to enable tooth-specific pharmacologic targeting, and to modulate tooth formation through the GPCR signaling. Method: To identify the target GPCRs, we compared RNA sequencing data derived from teeth, brain and liver in E13.5 wild-type mice. To identify potential ligands, we constructed atomic models for the corresponding protein sequences, bioinformatically mapped all compounds co-crystallized with GPCRs, chemoinformatically compared them to small molecules and FDA-approved drugs, and evaluated for molecular fit. To examine if altered G-protein signals can affect tooth formation, transgenic mice were developed to express Rs1, an engineered GPCR that constitutively activates stimulatory G-protein (Gs) signaling, in dental epithelial cells using the cytokeratin-5 promoter. Jaws from the Rs1 and wild-type mice were processed for immunohistochemistry. Result: Gs protein expression in wild-type mice was greater in the developing tooth buds than in adjacent tissues. We found that increased Gs signaling in dental epithelial cells induced the development of supernumerary teeth in K5/Rs1 mice. Twenty GPCRs were highly expressed in E13.5 developing teeth with at least two-fold greater expression. Structural analysis indicates that over 100 drugs are predicted to interact with these GPCRs. The 5HTR1b protein, a GPCR similar to the Rs1, was also found to be expressed highly in odontogenic epithelial cells and at higher levels in teeth as compared to liver (3.9-fold) and brain (390-fold). Pharmacological activationof the 5HTR1b in wild-type mice resulted in supernumerary incisor formation as seen in the K5/Rs1 mice. Conclusion: Differential expression of GPCRs in developing teeth will enable pharmacological manipulation to specifically control tooth formation.
    AADR Annual Meeting & Exhibition 2014; 03/2014
  • Clinical dysmorphology 02/2014; · 0.47 Impact Factor
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    ABSTRACT: Mesenchymal stem cells (MSCs) are typically defined by their in vitro characteristics, and as a consequence the in vivo identity of MSCs and their niches are poorly understood. To address this issue, we used lineage tracing in a mouse incisor model and identified the neurovascular bundle (NVB) as an MSC niche. We found that NVB sensory nerves secrete Shh protein, which activates Gli1 expression in periarterial cells that contribute to all mesenchymal derivatives. These periarterial cells do not express classical MSC markers used to define MSCs in vitro. In contrast, NG2(+) pericytes represent an MSC subpopulation derived from Gli1+ cells; they express classical MSC markers and contribute little to homeostasis but are actively involved in injury repair. Likewise, incisor Gli1(+) cells, but not NG2(+) cells, exhibit typical MSC characteristics in vitro. Collectively, we demonstrate that MSCs originate from periarterial cells and are regulated by Shh secretion from an NVB.
    Cell stem cell 02/2014; 14(2):160-73. · 23.56 Impact Factor
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    ABSTRACT: Understanding the cellular and molecular mechanisms that underlie tooth regeneration and renewal has become a topic of great interest(1-4), and the mouse incisor provides a model for these processes. This remarkable organ grows continuously throughout the animal's life and generates all the necessary cell types from active pools of adult stem cells housed in the labial (toward the lip) and lingual (toward the tongue) cervical loop (CL) regions. Only the dental stem cells from the labial CL give rise to ameloblasts that generate enamel, the outer covering of teeth, on the labial surface. This asymmetric enamel formation allows abrasion at the incisor tip, and progenitors and stem cells in the proximal incisor ensure that the dental tissues are constantly replenished. The ability to isolate and grow these progenitor or stem cells in vitro allows their expansion and opens doors to numerous experiments not achievable in vivo, such as high throughput testing of potential stem cell regulatory factors. Here, we describe and demonstrate a reliable and consistent method to culture cells from the labial CL of the mouse incisor.
    Journal of Visualized Experiments 01/2014;
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    ABSTRACT: Development of the mammalian external genitalia is controlled by a network of signaling molecules and transcription factors. Because FGF signaling plays a central role in this complicated morphogenetic process, we investigated the role of Sprouty genes, which are important intracellular modulators of FGF signaling, during embryonic development of the external genitalia in mice. We found that Sprouty genes are expressed by the urethral epithelium during embryogenesis, and that they have a critical function during urethral canalization and fusion. Development of the genital tubercle (GT), the anlage to the prepuce and glans penis in males and glans clitoris in females, was severely affected in male embryos carrying null alleles of both Spry1 and Spry2. In Spry1(-/-);Spry2(-/-) embryos, the internal tubular urethra was absent, and urothelial morphology and organization was abnormal. These effects were due, in part, to elevated levels of epithelial cell proliferation in Spry1(-/-);Spry2(-/-) embryos. Despite changes in overall organization, terminal differentiation of the urothelium was not significantly affected. Characterization of the molecular pathways that regulate normal GT development confirmed that deletion of Sprouty genes leads to elevated FGF signaling, whereas levels of signaling in other cascades were largely preserved. Together, these results show that levels of FGF signaling must be tightly regulated during embryonic development of the external genitalia in mice, and that this regulation is mediated in part through the activity of Sprouty gene products.
    Developmental Biology 12/2013; · 3.64 Impact Factor
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    ABSTRACT: In this review, we discuss the central role of fibroblast growth factor (FGF) signaling in mammalian tooth development. The FGF family consists of 22 members, most of which bind to four different receptor tyrosine kinases, which in turn signal through a cascade of intracellular proteins. This signaling regulates a number of cellular processes, including proliferation, differentiation, cell adhesion and cell mobility. FGF signaling first becomes important in the presumptive dental epithelium at the initiation stage of tooth development, and subsequently, it controls the invagination of the dental epithelium into the underlying mesenchyme. Later, FGFs are critical in tooth shape formation and differentiation of ameloblasts and odontoblasts, as well as in the development and homeostasis of the stem cell niche that fuels the continuously growing mouse incisor. In addition, FGF signaling is critical in human teeth, as mutations in genes encoding FGF ligands or receptors result in several congenital syndromes characterized by alterations in tooth number, morphology or enamel structure. The parallel roles of FGF signaling in mouse and human tooth development demonstrate the conserved importance of FGF signaling in mammalian odontogenesis.
    Odontology 12/2013; · 1.35 Impact Factor
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    ABSTRACT: As the average lifespan of humans continues to increase, improvement in the quality of life for elderly people is important. Among the most severe problems during aging are bone loss-associated diseases such as poor fracture healing and osteoporosis. Therapy-induced bone loss such as bisphosphonate-associated osteonecrosis of the jaw also increases in incidence with age. Most of the current treatment strategies are focused on antiresorptive and bone formation pharmacological agents, but it is hard to obtain appropriate bone augmentation and there are concerns regarding their long-term safety without side effects. Therefore, a novel method for improvement of bone quality is required, and stem cells are of great interest as potential therapeutic tools for diseases that remain without clinically effective therapies. In this review, we describe the concept of stem cell-based therapy and evaluate the current progress of cell therapy for the improvement of bone quality. In addition, we report and discuss a new clinical strategy in which improved bone quality was obtained by applying bone-marrow derived MSCs with platelet rich plasma in clinical therapy.
    Histology and histopathology 12/2013; · 2.24 Impact Factor
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    ABSTRACT: The rodent incisor is one of a number of organs that grow continuously throughout the life of an animal. Continuous growth of the incisor arose as an evolutionary adaptation to compensate for abrasion at the distal end of the tooth. The sustained turnover of cells that deposit the mineralized dental tissues is made possible by epithelial and mesenchymal stem cells residing at the proximal end of the incisor. A complex network of signaling pathways and transcription factors regulates the formation, maintenance, and differentiation of these stem cells during development and throughout adulthood. Research over the past 15 years has led to significant progress in our understanding of this network, which includes FGF, BMP, Notch, and Hh signaling, as well as cell adhesion molecules and microRNAs. This review surveys key historical experiments that laid the foundation of the field and discusses more recent findings that definitively identified the stem cell population, elucidated the regulatory network, and demonstrated possible genetic mechanisms for the evolution of continuously growing teeth. © 2013 Wiley Periodicals, Inc.
    genesis 12/2013; · 2.04 Impact Factor
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    ABSTRACT: Dental anomalies are common congenital malformations that can occur either as isolated findings or as part of a syndrome. This review focuses on genetic causes of abnormal tooth development and the implications of these abnormalities for clinical care. As an introduction, we describe general insights into the genetics of tooth development obtained from mouse and zebrafish models. This is followed by a discussion of isolated as well as syndromic tooth agenesis, including Van der Woude syndrome (VWS), ectodermal dysplasias (EDs), oral-facial-digital (OFD) syndrome type I, Rieger syndrome, holoprosencephaly, and tooth anomalies associated with cleft lip and palate. Next, we review delayed formation and eruption of teeth, as well as abnormalities in tooth size, shape, and form. Finally, isolated and syndromic causes of supernumerary teeth are considered, including cleidocranial dysplasia and Gardner syndrome. © 2013 Wiley Periodicals, Inc.
    American Journal of Medical Genetics Part C Seminars in Medical Genetics 10/2013; 163(4). · 3.54 Impact Factor
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    ABSTRACT: RASopathies are syndromes caused by gain-of-function mutations in the Ras signaling pathway. One of these conditions, Costello syndrome (CS), is typically caused by an activating de novo germline mutation in HRAS and is characterized by a wide range of cardiac, musculoskeletal, dermatological, and developmental abnormalities. We report that a majority of individuals with CS have hypo-mineralization of enamel, the outer covering of teeth, and that similar defects are present in a CS mouse model. Comprehensive analysis of the mouse model revealed that ameloblasts, the cells that generate enamel, lacked polarity, and the ameloblast progenitor cells were hyperproliferative. Ras signals through two main effector cascades, the mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K) pathways. To determine through which pathway Ras affects enamel formation, inhibitors targeting either PI3K or MEK1/2, a kinase in the MAPK pathway, were utilized. MEK1/2 inhibition rescued the hypo-mineralized enamel, normalized the ameloblast polarity defect, and restored normal progenitor cell proliferation. In contrast, PI3K inhibition only corrected the progenitor cell proliferation phenotype. We demonstrate for the first time the central role of Ras signaling in enamel formation in CS individuals, and we present the mouse incisor as a model system to dissect the roles of the Ras effector pathways in vivo.
    Human Molecular Genetics 09/2013; · 6.68 Impact Factor
  • The Journal of pediatrics 09/2013; 163(3):616-617.e1. · 4.02 Impact Factor
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    American Journal of Medical Genetics Part A 08/2013; 161(12). · 2.30 Impact Factor
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    Kyle B Jones, Ophir D Klein
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    ABSTRACT: The identification and characterization of stem cells is a major focus of developmental biology and regenerative medicine. The advent of genetic inducible fate mapping techniques has made it possible to precisely label specific cell populations and to follow their progeny over time. When combined with advanced mathematical and statistical methods, stem cell division dynamics can be studied in new and exciting ways. Despite advances in a number of tissues, relatively little attention has been paid to stem cells in the oral epithelium. This review will focus on current knowledge about adult oral epithelial stem cells, paradigms in other epithelial stem cell systems that could facilitate new discoveries in this area and the potential roles of epithelial stem cells in oral disease.International Journal of Oral Science (2013) 5, doi:10.1038/ijos.2013.46; published online 26 July 2013.
    International Journal of Oral Science 07/2013; · 2.03 Impact Factor

Publication Stats

1k Citations
472.82 Total Impact Points


  • 2004–2014
    • University of California, San Francisco
      • • Institute for Human Genetics
      • • Department of Orofacial Sciences
      • • Division of Hospital Medicine
      • • Department of Pediatrics
      • • Division of Medical Genetics
      San Francisco, California, United States
  • 2013
    • Charles University in Prague
      • Katedra antropologie a genetiky člověka
      Praha, Hlavni mesto Praha, Czech Republic
  • 2010
    • Academy of Sciences of the Czech Republic
      • Ústav experimentální medicíny
      Praha, Hlavni mesto Praha, Czech Republic
  • 2007
    • Baylor College of Dentistry
      • Department of Biomedical Sciences
      Port Arthur, Texas, United States