Isabelle Miletich - Academia.edu (original) (raw)

Papers by Isabelle Miletich

Frontiers of Oral Biology, 2010

Salivary glands are a group of organs secreting a watery substance that is of utmost importance f... more Salivary glands are a group of organs secreting a watery substance that is of utmost importance for several physiological functions ranging from the protection of teeth and surrounding soft tissues to the lubrication of the oral cavity, which is crucial for speech and perception of food taste. Salivary glands are complex networks of hollow tubes and secretory units that are found in specific locations of the mouth and which, although architecturally similar, exhibit individual specificities according to their location. This chapter focuses on the embryonic development of vertebrate salivary glands, which has been classically studied in the mouse model system since the 1950s. We describe here where, when and how major salivary glands develop in the lower jaw of the mouse embryo. Key mechanisms involved in this process are discussed, including reciprocal tissue interactions between epithelial and mesenchymal cells, epithelial branching morphogenesis and coordinated cell death and cell proliferation.

European Journal of Orthodontics, Aug 27, 2016

Background: Hypofunctional occlusion is known to lead to changes in the length of roots over time... more Background: Hypofunctional occlusion is known to lead to changes in the length of roots over time. The mechanisms that drive such changes, however, are poorly understood, with most studies concentrating on juvenile rats prior to the arrest of root development. In this article, we investigated the response of the upper and lower first molar roots to lack of occlusion concentrating on timepoints after the development of the roots has ceased using the mouse as a model. Mouse molar roots finish development at weaning, much earlier than rat molars, and display a similar pattern of roots in the lower and upper jaw to humans. Methods: Hypofunctional occlusion was achieved in adult mice at 5 and 9 weeks of age by flattening the cusps of the upper first molar. Mice were then sacrificed after 6 and 2 weeks, respectively, along with control littermates. microCT was used to measure root length, alveolar bone height, and the amount of tooth eruption, followed by sectioning to understand the mechanisms behind the changes at the histological level. Results: In the lower first molar, the response to hypofunctional occlusion was characterized by elongation of both the mesial root and its surrounding alveolar bone, while the distal root was unaffected. In contrast, the response of the upper first molar was characterized by over-eruption of the mesial side of the tooth without any significant change in the alveolar bone or root length. From histologic sections, it was clear that increased deposition of cellular cementum played an important role in the changes that occurred in the lower mesial root. Conclusions: In a mouse model, upper and lower molars responded differently to hypofunctional occlusion, with adult mice showing a different response to that previously reported for juvenile rats, highlighting the importance of considering age and tooth position in cases of hypofunction.

Sebaceous gland (SG) secretions are pivotal to skin and eye health. At the SG-epidermis confluenc... more Sebaceous gland (SG) secretions are pivotal to skin and eye health. At the SG-epidermis confluence is an overlooked epidermal collar we named the follicular epidermis (FE). Here, we show that the FE is similar among different SG types and contains unique Axin2+ stem cells in a niche at its basal FE-perpendicular flexure (FE-PF). Lineage tracing and ablation assays demonstrate Axin2+ cells as integral for FE homeostasis. Wnt-secretion arrest experiments resulted in FE-obstruction via hyperproliferation and inhibited differentiation inferring FE-PF Axin2+ cells are Wnt-producers maintaining FE-patency. Upon constitutive Axin2+ cell Wnt signalling, FE-PF-specific cell proliferation with early-stage signs of malignancy formed alongside a keratin-plugging FE-obstruction type. While keratin-based obstructions are recognized, inhibited differentiation obstructions are not, which suggests a one-size-fits-all therapeutic approach is not optimal. We offer a molecular identification toolkit to...

Journal of Molecular Histology, 2019

The natriuretic peptide (NP) system comprises of three ligands, the Atrial Natriuretic Peptide (A... more The natriuretic peptide (NP) system comprises of three ligands, the Atrial Natriuretic Peptide (ANP), Brain Natriuretic peptide (BNP) and C-type Natriuretic peptide (CNP), and three natriuretic peptide receptors, NPRA, NPRB and NPRC. Here we present a comprehensive study of the natriuretic peptide system in healthy murine and human submandibular salivary glands (SMGs). We show CNP is the dominant NP in mouse and human SMG and is expressed together with NP receptors in ducts, autonomic nerves and the microvasculature of the gland, suggesting CNP autocrine signalling may take place in some of these glandular structures. These data suggest the NP system may control salivary gland function during homeostasis through the regulation of electrolyte re-absorption, neural stimulation and/or blood vessel wall contraction/relaxation. We also show abnormal expression of NPRA in the stroma of a subset of human SMGs resected from patients diagnosed with oral squamous cell carcinoma (OSCC) of non-...

The European Journal of Orthodontics, 2016

Background: Hypofunctional occlusion is known to lead to changes in the length of roots over time... more Background: Hypofunctional occlusion is known to lead to changes in the length of roots over time, the mechanisms that drive such changes, however, are poorly understood, with most studies concentrating on juvenile rats prior to the arrest of root development. In this manuscript we investigated the response of the upper and lower first molar roots to lack of occlusion concentrating on time-points after the development of the roots has ceased using the mouse as a model. Mouse molar roots finish development at weaning, much earlier than rat molars, and display a similar pattern of roots in the lower and upper jaw to humans. Methods: Hypofunctional occlusion was achieved in adult mice at 5 and 9 weeks of age by flattening the upper 1 st molars cusps. Mice were then sacrificed after 6 and 2 weeks respectively along with control littermates. microCT was used to measure root length, alveolar bone height, and the amount of tooth eruption, followed by sectioning to understand the mechanisms behind the changes at the histological level. In the lower first molar the response to hypofunctional occlusion was characterized by elongation of both the mesial root and its surrounding alveolar bone, while the distal root was unaffected. In contrast, the response of the upper first molar was characterized by overeruption of the mesial side of the tooth without any significant change in the alveolar bone or root length. From histologic sections it was clear that increased deposition of cellular cementum played an important role in the changes that occurred in the lower mesial root. In a mouse model, upper and lower molars responded differently to hypofunctional occlusion, with adult mice showing a different response to that previously reported for juvenile rats, highlighting the importance of considering age and tooth position in cases of hypofunction.

Frontiers in physiology, 2016

The Eph family receptor-interacting (ephrin) ligands and erythropoietin-producing hepatocellular ... more The Eph family receptor-interacting (ephrin) ligands and erythropoietin-producing hepatocellular carcinoma (Eph) receptors constitute the largest known family of receptor tyrosine kinases. Ephrin ligands and their receptors form an important cell communication system with widespread roles in normal physiology and disease pathogenesis. In order to investigate potential roles of the ephrin-Eph system during palatogenesis and tongue development, we have characterized the cellular mRNA expression of family members EphrinA1-A3, EphA1-A8, and EphrinB2, EphB1, EphB4 during murine embryogenesis between embryonic day 13.5-16.5 using radioactive in situ hybridization. With the exception of EphA6 and ephrinA3, all genes were regionally expressed during the process of palatogenesis, with restricted and often overlapping domains. Transcripts were identified in the palate epithelium, localized at the tip of the palatal shelves, in the mesenchyme and also confined to the medial epithelium seam. Nu...

Oncogene, Jan 21, 2015

Osteosarcoma is the most common primary malignancy of the skeleton and is prevalent in children a... more Osteosarcoma is the most common primary malignancy of the skeleton and is prevalent in children and adolescents. Survival rates are poor and have remained stagnant owing to chemoresistance and the high propensity to form lung metastases. In this study, we used in vivo transgenic models of c-fos oncogene-induced osteosarcoma and chondrosarcoma in addition to c-Fos-inducible systems in vitro to investigate downstream signalling pathways that regulate osteosarcoma growth and metastasis. Fgfr1 (fibroblast growth factor receptor 1) was identified as a novel c-Fos/activator protein-1(AP-1)-regulated gene. Induction of c-Fos in vitro in osteoblasts and chondroblasts caused an increase in Fgfr1 RNA and FGFR1 protein expression levels that resulted in increased and sustained activation of mitogen-activated protein kinases (MAPKs), morphological transformation and increased anchorage-independent growth in response to FGF2 ligand treatment. High levels of FGFR1 protein and activated pFRS2α sig...

Molecular Biology Intelligence Unit

T he Sonic hedgehog (Shh) peptide belongs to a small family of signalling molecules that have a c... more T he Sonic hedgehog (Shh) peptide belongs to a small family of signalling molecules that have a complex mode of action and wide range of function during normal vertebrate development. In common with many regions of the embryo, Shh is expressed in the developing tooth in a regionally restricted manner. Specifically, Shh expression is localised to the epithelial component of the tooth germ at various stages during the odontogenic process; however, both tooth-forming epithelium and mesenchyme are responsive to the signal. A number of studies have analysed the role of Shh during tooth development, utilising both culture based and genetic systems, and it is clear that this signalling pathway is essential for normal development of the tooth. During the initiation of odontogenesis, localised signalling is important for growth and development of the tooth bud, whilst later during morphogenesis, Shh plays a role in cellular differentiation and polarization in the epithelial component of the tooth germ. These complex interactions are mediated by intra-epithelial and epithelial-mesenchymal signalling by Shh throughout these stages of tooth development.

Proceedings of the National Academy of Sciences, 2011

Timing of organ development during embryogenesis is coordinated such that at birth, organ and fet... more Timing of organ development during embryogenesis is coordinated such that at birth, organ and fetal size and maturity are appropriately proportioned. The extent to which local developmental timers are integrated with each other and with the signaling interactions that regulate morphogenesis to achieve this end is not understood. Using the absolute requirement for a signaling pathway activity (bone morphogenetic protein, BMP) during a critical stage of tooth development, we show that suboptimal levels of BMP signaling do not lead to abnormal morphogenesis, as suggested by mutants affecting BMP signaling, but to a 24-h stalling of the intrinsic developmental clock of the tooth. During this time, BMP levels accumulate to reach critical levels whereupon tooth development restarts, accelerates to catch up with development of the rest of the embryo and completes normal morphogenesis. This suggests that individual organs can autonomously control their developmental timing to adjust their s...

Journal of Dental Research, 2008

Tricho-rhino-phalangeal syndromes (TRPS) are caused by mutation or deletion of TRPS1, a gene enco... more Tricho-rhino-phalangeal syndromes (TRPS) are caused by mutation or deletion of TRPS1, a gene encoding a GATA transcription factor. These disorders are characterized by abnormalities of the hair, face, and selected bones. Rare cases of individuals with TRPS displaying supernumerary teeth have been reported, but none of these has been examined molecularly. We used two different approaches to investigate a possible role of TRPS1 during tooth development. We looked at the expression of Tprs1 during mouse tooth development and analyzed the craniofacial defects of Trps1 mutant mice. In parallel, we investigated whether a 17-year-old Thai boy with clinical features of TRPS and 5 supernumerary teeth had mutation in TRPS1. We report here that Trps1 is expressed during mouse tooth development, and that an individual with TRPS with supernumerary teeth has the amino acid substitution A919V in the GATA zinc finger of TRPS1. These results suggest a role for TRPS1 in tooth morphogenesis.

Journal of Dental Research, 2004

Teeth develop from reciprocal interactions between mesenchyme cells and epithelium, where the epi... more Teeth develop from reciprocal interactions between mesenchyme cells and epithelium, where the epithelium provides the instructive information for initiation. Based on these initial tissue interactions, we have replaced the mesenchyme cells with mesenchyme created by aggregation of cultured non-dental stem cells in mice. Recombinations between non-dental cell-derived mesenchyme and embryonic oral epithelium stimulate an odontogenic response in the stem cells. Embryonic stem cells, neural stem cells, and adult bone-marrow-derived cells all responded by expressing odontogenic genes. Transfer of recombinations into adult renal capsules resulted in the development of tooth structures and associated bone. Moreover, transfer of embryonic tooth primordia into the adult jaw resulted in development of tooth structures, showing that an embryonic primordium can develop in its adult environment. These results thus provide a significant advance toward the creation of artificial embryonic tooth pr...

Journal of Anatomy, 2005

During mouse embryonic development, the Barx1 homeobox gene is expressed in the mesenchymal cells... more During mouse embryonic development, the Barx1 homeobox gene is expressed in the mesenchymal cells of molar teeth and stomach. During early stages of molar development, Barx1 has an instructive role, directing the as yet undetermined ectomesenchymal cells in the proximal region of the jaws to follow a multicuspid tooth developmental pathway. We review here recent results showing an absence of stomach tissue in Barx1 mutant mice. The data strongly suggest that in the presumptive stomach mesenchyme Barx1 acts to attenuate Wnt signalling allowing digestive tract endoderm to differentiate into a highly specialized stomach epithelium. In the light of these new data, we discuss the possibility that evolutionary changes in the Barx1 gene could have simultaneously altered the dentition and the digestive system, therefore positioning Barx1 as a key gene in the evolution of mammals.

Developmental Cell, 2005

Stappenbeck et al., 1998), whereas the Department of Cancer Biology stomach epithelium houses 11 ... more Stappenbeck et al., 1998), whereas the Department of Cancer Biology stomach epithelium houses 11 distinct cell lineages Dana-Farber Cancer Institute that organize within deep pits and contiguous glands 2 Department of Medicine (Karam et al., 1997). In response to chronic tissue injury Brigham & Women's Hospital and in adult life, humans frequently convert gastric epithe-Harvard Medical School lium into an intestinal type. Such intestinal metaplasia, Boston, Massachusetts 02115 the precursor to nearly all cancers of the gastroesopha-3 Institute for Craniofacial Biology geal junction and a high proportion of gastric corpus Kings College tumors (Reid et al., 2000), represents stereotypic rever-London SE1 9RT sal of normal development (Silberg et al., 2002; Slack, United Kingdom 1985). Tissue grafting experiments reveal the source of mesenchyme to be an important determinant of gut en-Summary doderm differentiation (Kedinger et al., 1986; Mizuno and Yasugi, 1990), a theme that recurs in development Inductive interactions between gut endoderm and the of diverse organs like teeth and lungs (Tucker and underlying mesenchyme pattern the developing di-Sharpe, 2004; Warburton et al., 2000). Small bowel engestive tract into regions with specific morphology doderm from 6-day-old chick embryos develops and functions. The molecular mechanisms behind proventricular (glandular stomach) architecture when these interactions are largely unknown. Expression cocultured with 6-day-old proventricular mesenchyme of the conserved homeobox gene Barx1 is restricted but fails to mature fully, as reflected in the lack of pepto the stomach mesenchyme during gut organogenesinogen gene expression (Hayashi et al., 1988). In consis. Using recombinant tissue cultures, we show that trast, stomach endoderm from 14-day-old rat embryos Barx1 loss in the mesenchyme prevents stomach epidevelops features of the stomach epithelium when thelial differentiation of overlying endoderm and ingrafted in contact with intestinal mesenchyme (Duluc duces intestine-specific genes instead. Additionally, et al., 1994). These studies evaluated tissues starting Barx1 null mouse embryos show visceral homeosis, at developmental stages when epithelial character may with intestinal gene expression within a highly disoralready be specified; while they are informative regardganized gastric epithelium. Barx1 directs mesenchying requirements for cytodifferentiation, they are not mal cell expression of two secreted Wnt antagonists, necessarily so for lineage determination. In contrast, sFRP1 and sFRP2, and these factors are sufficient rethe unspecified E7 mouse endoderm receives inplacements for Barx1 function. Canonical Wnt signalstructive signals, including fibroblast growth factors, ing is prominent in the prospective gastric endoderm that determine its anteroposterior axis (Wells and Melprior to epithelial differentiation, and its inhibition by ton, 1999). Subsequently, selected foregut segments Barx1-dependent signaling permits development of respond to signals secreted from adjacent heart or nostomach-specific epithelium. These results define a tochord cells that permit liver and pancreas differentiatranscriptional and signaling pathway of inductive tion, respectively (Hebrok et al., 1998; Jung et al., 1999; cell interactions in vertebrate organogenesis. Rossi et al., 2001). These and other studies point to a window (approximately E8-E12 in the mouse) in which Introduction endoderm responds sequentially and regionally to specification signals. Developmental patterning along the cephalocaudal The effects of well-characterized ligands, including axis of the vertebrate gastrointestinal (GI) tract distinbone morphogenetic (BMP), Wnt, and hedgehog (Hh) guishes the caudally positioned intestine from a rostral proteins, on gut epithelial cytodifferentiation have been organ that serves mechanical and chemical functions investigated, for the most part, after the endoderm is in digestion. Animals have evolved a diverse array of committed to gastric or intestinal cell fate. Endodermspecialized structures to this end, including the avian derived Hh proteins influence both epithelial and musgizzard and proventriculus and the mammalian stomcle differentiation in the GI tract of chick (Roberts et al., ach. Little is known about how distinctive GI epithelia 1995; Sukegawa et al., 2000), Xenopus (Zhang et al., are specified. 2000), and mouse (Ramalho-Santos et al., 2000; van By embryonic day (E) 9 in the mouse, the primitive den Brink et al., 2001) embryos, in part by inducing gut tube is marked rostrally by a radially enlarged gas-BMP-4 (Roberts et al., 1998; Sukegawa et al., 2000). tric anlage and caudally by the elongated intestine, al-Conversely, mesenchymal cells secrete Wnt proteins in though endodermal cell morphology remains uniformly complex patterns along the intestinal crypt-villus axis; Wnt ligands produced near the crypt base restrict differentiation of neighboring epithelial progenitors (van *

Developmental Biology, 2012

Developmental Biology, 2011

Development, 2004

The signalling peptide encoded by the sonic hedgehog gene is restricted to localised thickenings ... more The signalling peptide encoded by the sonic hedgehog gene is restricted to localised thickenings of oral epithelium, which mark the first morphological evidence of tooth development, and is known to play a crucial role during the initiation of odontogenesis. We show that at these stages in the murine mandibular arch in the absence of epithelium, the Shh targets Ptc1and Gli1 are upregulated in diastema mesenchyme, an edentulous region between the sites of molar and incisor tooth formation. This ectopic expression is not associated with Shh transcription but with Shh protein, undetectable in the presence of epithelium. These findings suggest that, in diastema mesenchyme, restriction of Shh activity is dependent upon the overlying epithelium. This inhibitory activity was demonstrated by the ability of transplanted diastema epithelium to downregulate Ptc1 in tooth explants, and for isolated diastema mesenchyme to express Ptc1. A candidate inhibitor in diastema mesenchyme is the glycosyl...

Development, 2007

Homeobox genes convey positional information in embryos and their role in patterning the mammalia... more Homeobox genes convey positional information in embryos and their role in patterning the mammalian gut is a topic of considerable interest. Barx1 is expressed selectively in fetal stomach mesenchyme and directs differentiation of overlying endoderm. Recombinant tissue cultures and study of young mouse embryos previously suggested that Barx1 controls expression of secreted Wnt antagonists, which suppress endodermal Wnt signaling, to enable stomach epithelial differentiation. We overcame mid-gestational lethality of Barx1-/- mouse embryos and report here the spectrum of anomalies in a distinctive and unprecedented model of gastrointestinal homeotic transformation. Using various mouse models, we confirm the importance of attenuated Wnt signaling in stomach development and the role of Barx1 in suppressing endodermal Wnt activity. Absence of Barx1 also results in fully penetrant defects in positioning and expansion of the spleen, an organ that originates within the mesothelial lining of ...

Frontiers of Oral Biology, 2010

Salivary glands are a group of organs secreting a watery substance that is of utmost importance f... more Salivary glands are a group of organs secreting a watery substance that is of utmost importance for several physiological functions ranging from the protection of teeth and surrounding soft tissues to the lubrication of the oral cavity, which is crucial for speech and perception of food taste. Salivary glands are complex networks of hollow tubes and secretory units that are found in specific locations of the mouth and which, although architecturally similar, exhibit individual specificities according to their location. This chapter focuses on the embryonic development of vertebrate salivary glands, which has been classically studied in the mouse model system since the 1950s. We describe here where, when and how major salivary glands develop in the lower jaw of the mouse embryo. Key mechanisms involved in this process are discussed, including reciprocal tissue interactions between epithelial and mesenchymal cells, epithelial branching morphogenesis and coordinated cell death and cell proliferation.

European Journal of Orthodontics, Aug 27, 2016

Background: Hypofunctional occlusion is known to lead to changes in the length of roots over time... more Background: Hypofunctional occlusion is known to lead to changes in the length of roots over time. The mechanisms that drive such changes, however, are poorly understood, with most studies concentrating on juvenile rats prior to the arrest of root development. In this article, we investigated the response of the upper and lower first molar roots to lack of occlusion concentrating on timepoints after the development of the roots has ceased using the mouse as a model. Mouse molar roots finish development at weaning, much earlier than rat molars, and display a similar pattern of roots in the lower and upper jaw to humans. Methods: Hypofunctional occlusion was achieved in adult mice at 5 and 9 weeks of age by flattening the cusps of the upper first molar. Mice were then sacrificed after 6 and 2 weeks, respectively, along with control littermates. microCT was used to measure root length, alveolar bone height, and the amount of tooth eruption, followed by sectioning to understand the mechanisms behind the changes at the histological level. Results: In the lower first molar, the response to hypofunctional occlusion was characterized by elongation of both the mesial root and its surrounding alveolar bone, while the distal root was unaffected. In contrast, the response of the upper first molar was characterized by over-eruption of the mesial side of the tooth without any significant change in the alveolar bone or root length. From histologic sections, it was clear that increased deposition of cellular cementum played an important role in the changes that occurred in the lower mesial root. Conclusions: In a mouse model, upper and lower molars responded differently to hypofunctional occlusion, with adult mice showing a different response to that previously reported for juvenile rats, highlighting the importance of considering age and tooth position in cases of hypofunction.

Sebaceous gland (SG) secretions are pivotal to skin and eye health. At the SG-epidermis confluenc... more Sebaceous gland (SG) secretions are pivotal to skin and eye health. At the SG-epidermis confluence is an overlooked epidermal collar we named the follicular epidermis (FE). Here, we show that the FE is similar among different SG types and contains unique Axin2+ stem cells in a niche at its basal FE-perpendicular flexure (FE-PF). Lineage tracing and ablation assays demonstrate Axin2+ cells as integral for FE homeostasis. Wnt-secretion arrest experiments resulted in FE-obstruction via hyperproliferation and inhibited differentiation inferring FE-PF Axin2+ cells are Wnt-producers maintaining FE-patency. Upon constitutive Axin2+ cell Wnt signalling, FE-PF-specific cell proliferation with early-stage signs of malignancy formed alongside a keratin-plugging FE-obstruction type. While keratin-based obstructions are recognized, inhibited differentiation obstructions are not, which suggests a one-size-fits-all therapeutic approach is not optimal. We offer a molecular identification toolkit to...

Journal of Molecular Histology, 2019

The natriuretic peptide (NP) system comprises of three ligands, the Atrial Natriuretic Peptide (A... more The natriuretic peptide (NP) system comprises of three ligands, the Atrial Natriuretic Peptide (ANP), Brain Natriuretic peptide (BNP) and C-type Natriuretic peptide (CNP), and three natriuretic peptide receptors, NPRA, NPRB and NPRC. Here we present a comprehensive study of the natriuretic peptide system in healthy murine and human submandibular salivary glands (SMGs). We show CNP is the dominant NP in mouse and human SMG and is expressed together with NP receptors in ducts, autonomic nerves and the microvasculature of the gland, suggesting CNP autocrine signalling may take place in some of these glandular structures. These data suggest the NP system may control salivary gland function during homeostasis through the regulation of electrolyte re-absorption, neural stimulation and/or blood vessel wall contraction/relaxation. We also show abnormal expression of NPRA in the stroma of a subset of human SMGs resected from patients diagnosed with oral squamous cell carcinoma (OSCC) of non-...

The European Journal of Orthodontics, 2016

Background: Hypofunctional occlusion is known to lead to changes in the length of roots over time... more Background: Hypofunctional occlusion is known to lead to changes in the length of roots over time, the mechanisms that drive such changes, however, are poorly understood, with most studies concentrating on juvenile rats prior to the arrest of root development. In this manuscript we investigated the response of the upper and lower first molar roots to lack of occlusion concentrating on time-points after the development of the roots has ceased using the mouse as a model. Mouse molar roots finish development at weaning, much earlier than rat molars, and display a similar pattern of roots in the lower and upper jaw to humans. Methods: Hypofunctional occlusion was achieved in adult mice at 5 and 9 weeks of age by flattening the upper 1 st molars cusps. Mice were then sacrificed after 6 and 2 weeks respectively along with control littermates. microCT was used to measure root length, alveolar bone height, and the amount of tooth eruption, followed by sectioning to understand the mechanisms behind the changes at the histological level. In the lower first molar the response to hypofunctional occlusion was characterized by elongation of both the mesial root and its surrounding alveolar bone, while the distal root was unaffected. In contrast, the response of the upper first molar was characterized by overeruption of the mesial side of the tooth without any significant change in the alveolar bone or root length. From histologic sections it was clear that increased deposition of cellular cementum played an important role in the changes that occurred in the lower mesial root. In a mouse model, upper and lower molars responded differently to hypofunctional occlusion, with adult mice showing a different response to that previously reported for juvenile rats, highlighting the importance of considering age and tooth position in cases of hypofunction.

Frontiers in physiology, 2016

The Eph family receptor-interacting (ephrin) ligands and erythropoietin-producing hepatocellular ... more The Eph family receptor-interacting (ephrin) ligands and erythropoietin-producing hepatocellular carcinoma (Eph) receptors constitute the largest known family of receptor tyrosine kinases. Ephrin ligands and their receptors form an important cell communication system with widespread roles in normal physiology and disease pathogenesis. In order to investigate potential roles of the ephrin-Eph system during palatogenesis and tongue development, we have characterized the cellular mRNA expression of family members EphrinA1-A3, EphA1-A8, and EphrinB2, EphB1, EphB4 during murine embryogenesis between embryonic day 13.5-16.5 using radioactive in situ hybridization. With the exception of EphA6 and ephrinA3, all genes were regionally expressed during the process of palatogenesis, with restricted and often overlapping domains. Transcripts were identified in the palate epithelium, localized at the tip of the palatal shelves, in the mesenchyme and also confined to the medial epithelium seam. Nu...

Oncogene, Jan 21, 2015

Osteosarcoma is the most common primary malignancy of the skeleton and is prevalent in children a... more Osteosarcoma is the most common primary malignancy of the skeleton and is prevalent in children and adolescents. Survival rates are poor and have remained stagnant owing to chemoresistance and the high propensity to form lung metastases. In this study, we used in vivo transgenic models of c-fos oncogene-induced osteosarcoma and chondrosarcoma in addition to c-Fos-inducible systems in vitro to investigate downstream signalling pathways that regulate osteosarcoma growth and metastasis. Fgfr1 (fibroblast growth factor receptor 1) was identified as a novel c-Fos/activator protein-1(AP-1)-regulated gene. Induction of c-Fos in vitro in osteoblasts and chondroblasts caused an increase in Fgfr1 RNA and FGFR1 protein expression levels that resulted in increased and sustained activation of mitogen-activated protein kinases (MAPKs), morphological transformation and increased anchorage-independent growth in response to FGF2 ligand treatment. High levels of FGFR1 protein and activated pFRS2α sig...

Molecular Biology Intelligence Unit

T he Sonic hedgehog (Shh) peptide belongs to a small family of signalling molecules that have a c... more T he Sonic hedgehog (Shh) peptide belongs to a small family of signalling molecules that have a complex mode of action and wide range of function during normal vertebrate development. In common with many regions of the embryo, Shh is expressed in the developing tooth in a regionally restricted manner. Specifically, Shh expression is localised to the epithelial component of the tooth germ at various stages during the odontogenic process; however, both tooth-forming epithelium and mesenchyme are responsive to the signal. A number of studies have analysed the role of Shh during tooth development, utilising both culture based and genetic systems, and it is clear that this signalling pathway is essential for normal development of the tooth. During the initiation of odontogenesis, localised signalling is important for growth and development of the tooth bud, whilst later during morphogenesis, Shh plays a role in cellular differentiation and polarization in the epithelial component of the tooth germ. These complex interactions are mediated by intra-epithelial and epithelial-mesenchymal signalling by Shh throughout these stages of tooth development.

Proceedings of the National Academy of Sciences, 2011

Timing of organ development during embryogenesis is coordinated such that at birth, organ and fet... more Timing of organ development during embryogenesis is coordinated such that at birth, organ and fetal size and maturity are appropriately proportioned. The extent to which local developmental timers are integrated with each other and with the signaling interactions that regulate morphogenesis to achieve this end is not understood. Using the absolute requirement for a signaling pathway activity (bone morphogenetic protein, BMP) during a critical stage of tooth development, we show that suboptimal levels of BMP signaling do not lead to abnormal morphogenesis, as suggested by mutants affecting BMP signaling, but to a 24-h stalling of the intrinsic developmental clock of the tooth. During this time, BMP levels accumulate to reach critical levels whereupon tooth development restarts, accelerates to catch up with development of the rest of the embryo and completes normal morphogenesis. This suggests that individual organs can autonomously control their developmental timing to adjust their s...

Journal of Dental Research, 2008

Tricho-rhino-phalangeal syndromes (TRPS) are caused by mutation or deletion of TRPS1, a gene enco... more Tricho-rhino-phalangeal syndromes (TRPS) are caused by mutation or deletion of TRPS1, a gene encoding a GATA transcription factor. These disorders are characterized by abnormalities of the hair, face, and selected bones. Rare cases of individuals with TRPS displaying supernumerary teeth have been reported, but none of these has been examined molecularly. We used two different approaches to investigate a possible role of TRPS1 during tooth development. We looked at the expression of Tprs1 during mouse tooth development and analyzed the craniofacial defects of Trps1 mutant mice. In parallel, we investigated whether a 17-year-old Thai boy with clinical features of TRPS and 5 supernumerary teeth had mutation in TRPS1. We report here that Trps1 is expressed during mouse tooth development, and that an individual with TRPS with supernumerary teeth has the amino acid substitution A919V in the GATA zinc finger of TRPS1. These results suggest a role for TRPS1 in tooth morphogenesis.

Journal of Dental Research, 2004

Teeth develop from reciprocal interactions between mesenchyme cells and epithelium, where the epi... more Teeth develop from reciprocal interactions between mesenchyme cells and epithelium, where the epithelium provides the instructive information for initiation. Based on these initial tissue interactions, we have replaced the mesenchyme cells with mesenchyme created by aggregation of cultured non-dental stem cells in mice. Recombinations between non-dental cell-derived mesenchyme and embryonic oral epithelium stimulate an odontogenic response in the stem cells. Embryonic stem cells, neural stem cells, and adult bone-marrow-derived cells all responded by expressing odontogenic genes. Transfer of recombinations into adult renal capsules resulted in the development of tooth structures and associated bone. Moreover, transfer of embryonic tooth primordia into the adult jaw resulted in development of tooth structures, showing that an embryonic primordium can develop in its adult environment. These results thus provide a significant advance toward the creation of artificial embryonic tooth pr...

Journal of Anatomy, 2005

During mouse embryonic development, the Barx1 homeobox gene is expressed in the mesenchymal cells... more During mouse embryonic development, the Barx1 homeobox gene is expressed in the mesenchymal cells of molar teeth and stomach. During early stages of molar development, Barx1 has an instructive role, directing the as yet undetermined ectomesenchymal cells in the proximal region of the jaws to follow a multicuspid tooth developmental pathway. We review here recent results showing an absence of stomach tissue in Barx1 mutant mice. The data strongly suggest that in the presumptive stomach mesenchyme Barx1 acts to attenuate Wnt signalling allowing digestive tract endoderm to differentiate into a highly specialized stomach epithelium. In the light of these new data, we discuss the possibility that evolutionary changes in the Barx1 gene could have simultaneously altered the dentition and the digestive system, therefore positioning Barx1 as a key gene in the evolution of mammals.

Developmental Cell, 2005

Stappenbeck et al., 1998), whereas the Department of Cancer Biology stomach epithelium houses 11 ... more Stappenbeck et al., 1998), whereas the Department of Cancer Biology stomach epithelium houses 11 distinct cell lineages Dana-Farber Cancer Institute that organize within deep pits and contiguous glands 2 Department of Medicine (Karam et al., 1997). In response to chronic tissue injury Brigham & Women's Hospital and in adult life, humans frequently convert gastric epithe-Harvard Medical School lium into an intestinal type. Such intestinal metaplasia, Boston, Massachusetts 02115 the precursor to nearly all cancers of the gastroesopha-3 Institute for Craniofacial Biology geal junction and a high proportion of gastric corpus Kings College tumors (Reid et al., 2000), represents stereotypic rever-London SE1 9RT sal of normal development (Silberg et al., 2002; Slack, United Kingdom 1985). Tissue grafting experiments reveal the source of mesenchyme to be an important determinant of gut en-Summary doderm differentiation (Kedinger et al., 1986; Mizuno and Yasugi, 1990), a theme that recurs in development Inductive interactions between gut endoderm and the of diverse organs like teeth and lungs (Tucker and underlying mesenchyme pattern the developing di-Sharpe, 2004; Warburton et al., 2000). Small bowel engestive tract into regions with specific morphology doderm from 6-day-old chick embryos develops and functions. The molecular mechanisms behind proventricular (glandular stomach) architecture when these interactions are largely unknown. Expression cocultured with 6-day-old proventricular mesenchyme of the conserved homeobox gene Barx1 is restricted but fails to mature fully, as reflected in the lack of pepto the stomach mesenchyme during gut organogenesinogen gene expression (Hayashi et al., 1988). In consis. Using recombinant tissue cultures, we show that trast, stomach endoderm from 14-day-old rat embryos Barx1 loss in the mesenchyme prevents stomach epidevelops features of the stomach epithelium when thelial differentiation of overlying endoderm and ingrafted in contact with intestinal mesenchyme (Duluc duces intestine-specific genes instead. Additionally, et al., 1994). These studies evaluated tissues starting Barx1 null mouse embryos show visceral homeosis, at developmental stages when epithelial character may with intestinal gene expression within a highly disoralready be specified; while they are informative regardganized gastric epithelium. Barx1 directs mesenchying requirements for cytodifferentiation, they are not mal cell expression of two secreted Wnt antagonists, necessarily so for lineage determination. In contrast, sFRP1 and sFRP2, and these factors are sufficient rethe unspecified E7 mouse endoderm receives inplacements for Barx1 function. Canonical Wnt signalstructive signals, including fibroblast growth factors, ing is prominent in the prospective gastric endoderm that determine its anteroposterior axis (Wells and Melprior to epithelial differentiation, and its inhibition by ton, 1999). Subsequently, selected foregut segments Barx1-dependent signaling permits development of respond to signals secreted from adjacent heart or nostomach-specific epithelium. These results define a tochord cells that permit liver and pancreas differentiatranscriptional and signaling pathway of inductive tion, respectively (Hebrok et al., 1998; Jung et al., 1999; cell interactions in vertebrate organogenesis. Rossi et al., 2001). These and other studies point to a window (approximately E8-E12 in the mouse) in which Introduction endoderm responds sequentially and regionally to specification signals. Developmental patterning along the cephalocaudal The effects of well-characterized ligands, including axis of the vertebrate gastrointestinal (GI) tract distinbone morphogenetic (BMP), Wnt, and hedgehog (Hh) guishes the caudally positioned intestine from a rostral proteins, on gut epithelial cytodifferentiation have been organ that serves mechanical and chemical functions investigated, for the most part, after the endoderm is in digestion. Animals have evolved a diverse array of committed to gastric or intestinal cell fate. Endodermspecialized structures to this end, including the avian derived Hh proteins influence both epithelial and musgizzard and proventriculus and the mammalian stomcle differentiation in the GI tract of chick (Roberts et al., ach. Little is known about how distinctive GI epithelia 1995; Sukegawa et al., 2000), Xenopus (Zhang et al., are specified. 2000), and mouse (Ramalho-Santos et al., 2000; van By embryonic day (E) 9 in the mouse, the primitive den Brink et al., 2001) embryos, in part by inducing gut tube is marked rostrally by a radially enlarged gas-BMP-4 (Roberts et al., 1998; Sukegawa et al., 2000). tric anlage and caudally by the elongated intestine, al-Conversely, mesenchymal cells secrete Wnt proteins in though endodermal cell morphology remains uniformly complex patterns along the intestinal crypt-villus axis; Wnt ligands produced near the crypt base restrict differentiation of neighboring epithelial progenitors (van *

Developmental Biology, 2012

Developmental Biology, 2011

Development, 2004

The signalling peptide encoded by the sonic hedgehog gene is restricted to localised thickenings ... more The signalling peptide encoded by the sonic hedgehog gene is restricted to localised thickenings of oral epithelium, which mark the first morphological evidence of tooth development, and is known to play a crucial role during the initiation of odontogenesis. We show that at these stages in the murine mandibular arch in the absence of epithelium, the Shh targets Ptc1and Gli1 are upregulated in diastema mesenchyme, an edentulous region between the sites of molar and incisor tooth formation. This ectopic expression is not associated with Shh transcription but with Shh protein, undetectable in the presence of epithelium. These findings suggest that, in diastema mesenchyme, restriction of Shh activity is dependent upon the overlying epithelium. This inhibitory activity was demonstrated by the ability of transplanted diastema epithelium to downregulate Ptc1 in tooth explants, and for isolated diastema mesenchyme to express Ptc1. A candidate inhibitor in diastema mesenchyme is the glycosyl...

Development, 2007

Homeobox genes convey positional information in embryos and their role in patterning the mammalia... more Homeobox genes convey positional information in embryos and their role in patterning the mammalian gut is a topic of considerable interest. Barx1 is expressed selectively in fetal stomach mesenchyme and directs differentiation of overlying endoderm. Recombinant tissue cultures and study of young mouse embryos previously suggested that Barx1 controls expression of secreted Wnt antagonists, which suppress endodermal Wnt signaling, to enable stomach epithelial differentiation. We overcame mid-gestational lethality of Barx1-/- mouse embryos and report here the spectrum of anomalies in a distinctive and unprecedented model of gastrointestinal homeotic transformation. Using various mouse models, we confirm the importance of attenuated Wnt signaling in stomach development and the role of Barx1 in suppressing endodermal Wnt activity. Absence of Barx1 also results in fully penetrant defects in positioning and expansion of the spleen, an organ that originates within the mesothelial lining of ...