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P Kettunen

Publications and source records attributed to P Kettunen.

At least 19 recordsLinked to original sources
PubMed2006

FGF signalling in craniofacial development and developmental disorders.

The Fgf signalling pathway is highly conserved in evolution and plays crucial roles in development. In the craniofacial region, it is involved in almost all structure development from early patterning to growth regulation. In craniofacial skeletogenesis, the Fgf signal pathway plays important roles in suture and synchondrosis regulation. Mutations of FGF receptors relate to syndromatic and non-syndromatic craniosynostosis. The Fgf10/Fgfr2b signal loop is critical for palatogenesis and submandibular gland formation. Perturbation of the Fgf signal is a possible mechanism of palatal cleft. Fgf10 haploinsufficiency has been identified as the cause of autosomal dominant aplasia of lacrimal and salivary glands. The Fgf signal is also a key regulator of tooth formation: in the absence of Fgfr2b tooth development is arrested at the bud stage. Fgfr4 has recently been identified as the key signal mediator in myogenesis. In this review, these aspects are discussed in detail with a focus on the most recent advances.

Cleft Palate↗
PubMed2001

Expression of class 3 semaphorins and neuropilin receptors in the developing mouse tooth.

The semaphorins are a large family of secreted or cell-bound signals needed for the development of the nervous system. We compared mRNA expression of class 3 semaphorins (Sema3A, 3B, 3C and 3F) and their two receptors (Neuropilin-1 and -2) in the embryonic mouse first molar tooth germ (E10-18) by radioactive in situ hybridization. All genes showed distinct developmentally regulated expression patterns during tooth organogenesis. Interestingly, Sema3A and 3C were first detected in the early dental epithelium, and later both genes were present in the epithelial primary enamel knot, a putative signaling center of the embryonic tooth regulating tooth morphogenesis. Prior to birth, Sema3A was also observed in tooth-specific cells, preodontoblasts, which later differentiate into odontoblasts secreting dentin, and in the mesenchymal dental follicle cells surrounding the tooth germ. Sema3B appeared transiently in the dental mesenchyme in the bud and cap stage tooth while Sema3F was expressed in both epithelial and mesenchymal components of the tooth. Of note, Npn-1 expression pattern was largely complementary to that of Sema3A, and transcripts were restricted to the dental mesenchymal cells. Npn-1 expression was first seen in the developing dental follicle, and later transcripts also appeared in the dental papilla mesenchyme. In contrast, Npn-2 signal was seen in both epithelial and mesenchymal tissues such as in the primary enamel knot and preodontoblasts.

Animals↗
PubMed2001

Slit1 is specifically expressed in the primary and secondary enamel knots during molar tooth cusp formation.

The shape and diversity of the mammalian molar teeth is suggested to be regulated by the primary and secondary enamel knots, which are putative epithelial signaling centers of the tooth. In search of novel molecules involved in tooth morphogenesis, we analyzed mRNA expression of Slit1, -2 and -3, earlier characterized as secreted signals needed for axonal pathfinding and their two receptors Robo1 and -2 (Roundabout1 and -2) in the developing mouse first molar. In situ hybridization analysis showed that Slit1 mRNAs were expressed in the primary enamel knot of the bud and cap stage tooth germ and later the expression continued in the secondary enamel knots of the late cap and bell stage tooth. In contrast, expression of Slit2 and -3 as well Robo1, and -2 was largely restricted to mesenchymal tissue components of the tooth until the bell stage. At the late bud stage, however, Robo1 transcripts were evident in the primary enamel knot, and at the cap stage a pronounced expression was noted in the middle of the tooth germ covering the primary enamel knot and dental papilla mesenchyme. During the bell stage, Robo1 and Slit2 expression became restricted to the dental epithelia, while Slit3 continued in the dental mesenchyme. Prior to birth, Robo1 and -2 were co-localized in the predontoblasts. These results indicate that Slits and Robos display distinct, developmentally regulated expression patterns during tooth morphogenesis. In addition, our results show that Slit1 is the second known gene specifically located in the primary and secondary enamel knots.

Animals↗
PubMed2000

FGF/FGFR-2(IIIb) signaling is essential for inner ear morphogenesis.

Interactions between FGF10 and the IIIb isoform of FGFR-2 appear to be crucial for the induction and growth of several organs, particularly those that involve budding morphogenesis. We determined their expression patterns in the inner ear and analyzed the inner ear phenotype of mice specifically deleted for the IIIb isoform of FGFR-2. FGF10 and FGFR-2(IIIb) mRNAs showed distinct, largely nonoverlapping expression patterns in the undifferentiated otic epithelium. Subsequently, FGF10 mRNA became confined to the presumptive cochlear and vestibular sensory epithelia and to the neuronal precursors and neurons. FGFR-2(IIIb) mRNA was expressed in the nonsensory epithelium of the otocyst that gives rise to structures such as the endolymphatic and semicircular ducts. These data suggest that in contrast to mesenchymal-epithelial-based FGF10 signaling demonstrated for other organs, the inner ear seems to depend on paracrine signals that operate within the epithelium. Expression of FGF10 mRNA partly overlapped with FGF3 mRNA in the sensory regions, suggesting that they may form parallel signaling pathways within the otic epithelium. In addition, hindbrain-derived FGF3 might regulate otocyst morphogenesis through FGFR-2(IIIb). Targeted deletion of FGFR-2(IIIb) resulted in severe dysgenesis of the cochleovestibular membraneous labyrinth, caused by a failure in morphogenesis at the otocyst stage. In addition to the nonsensory epithelium, sensory patches and the cochleovestibular ganglion remained at a rudimentary stage. Our findings provide genetic evidence that signaling by FGFR-2(IIIb) is critical for the morphological development of the inner ear.

Animals↗
PubMed2000

Interaction between metabotropic and ionotropic glutamate receptors regulates neuronal network activity.

Experimental and computational techniques have been used to investigate the group I metabotropic glutamate receptor (mGluR)-mediated increase in the frequency of spinal cord network activity underlying locomotion in the lamprey. Group I mGluR activation potentiated the amplitude of NMDA-induced currents in identified motoneurons and crossed caudally projecting network interneurons. Group I mGluRs also potentiated NMDA-induced calcium responses. This effect was blocked by a group I mGluR-specific antagonist, but not by blockers of protein kinase A, C, or G. The effect of group I mGluRs activation was also tested on NMDA-induced oscillations known to occur during fictive locomotion. Activation of these receptors increased the duration of the plateau phase and decreased the duration of the hyperpolarizing phase. These effects were blocked by a group I mGluR antagonist. To determine its role in the modulation of NMDA-induced oscillations and the locomotor burst frequency, the potentiation of NMDA receptors by mGluRs was simulated using computational techniques. Simulating the interaction between these receptors reproduced the modulation of the plateau and hyperpolarized phases of NMDA-induced oscillations, and the increase in the frequency of the locomotor rhythm. Our results thus show a postsynaptic interaction between group I mGluRs and NMDA receptors in lamprey spinal cord neurons, which can account for the regulation of the locomotor network output by mGluRs.

Animals↗
PubMed2000

Associations of FGF-3 and FGF-10 with signaling networks regulating tooth morphogenesis.

The morphogenesis and cell differentiation in developing teeth is governed by interactions between the oral epithelium and neural crest-derived ectomesenchyme. The fibroblast growth factors FGF-4, -8, and -9 have been implicated as epithelial signals regulating mesenchymal gene expression and cell proliferation during tooth initiation and later during epithelial folding morphogenesis and the establishment of tooth shape. To further evaluate the roles of FGFs in tooth development, we analyzed the roles of FGF-3, FGF-7, and FGF-10 in developing mouse teeth. In situ hybridization analysis showed developmentally regulated expression during tooth formation for Fgf-3 and Fgf-10 that was mainly restricted to the dental papilla mesenchymal cells. Fgf-7 transcripts were restricted to the developing bone surrounding the developing tooth germ. Fgf-10 expression was observed in the presumptive dental epithelium and mesenchyme during tooth initiation, whereas Fgf-3 expression appeared in the dental mesenchyme at the late bud stage. During the cap and bell stage, both Fgf-3 and Fgf-10 were intensely expressed in the dental papilla mesenchymal cells both in incisors and molars. It is of interest that Fgf-3 expression was also observed in the primary enamel knot, a putative signaling center of the tooth, whereas no transcripts were seen in the secondary enamel knots that appear in the tips of future cusps of the bell stage tooth germs. Down-regulation of Fgf-3 and Fgf-10 expression in postmitotic odontoblasts correlated with the terminal differentiation of the odontoblasts and the neighboring ameloblasts. In the incisors, mesenchymal cells of the cervical loop area showed partially overlapping expression patterns for all studied Fgfs. In vitro analyses showed that expression of Fgf-3 and Fgf-10 in the dental mesenchyme was dependent on dental epithelium and that epithelially expressed FGFs, FGF-4 and -8 induced Fgf-3 but not Fgf-10 expression in the isolated dental mesenchyme. Beads soaked in Shh, BMP-2, and TGF-beta 1 protein did not induce either Fgf-3 or Fgf-10 expression. Cells expressing Wnt-6 did not induce Fgf-10 expression. Furthermore, FGF-10 protein stimulated cell proliferation in the dental epithelium but not in the mesenchyme. These results suggest that FGF-3 and FGF-10 have redundant functions as mesenchymal signals regulating epithelial morphogenesis of the tooth and that their expressions appear to be differentially regulated. In addition, FGF-3 may participate in signaling functions of the primary enamel knot. The dynamic expression patterns of different Fgfs in dental epithelium and mesenchyme and their interactions suggest existence of regulatory signaling cascades between epithelial and mesenchymal FGFs during tooth development.

3T3 Cells↗
PubMed2000

Sequelae of moderate finger frostbite as assessed by subjective sensations, clinical signs, and thermophysiological responses.

The aim of the study was to investigate prevalence and qualities of sequelae following moderate finger frostbite. The study material comprised 30 subjects, who had suffered second-degree frostbite (73% contact frostbite) 4-11 years before this study. In clinical tests 66% of the subjects had an elevated tendency for vasospasm, yet only 20% suffered from white fingers. However, no marked traces of frostbite-related alterations were observed in systemic cardiovascular reflex tests or in X-ray examinations of the frostbite area. Subjective assessments revealed a high prevalence of sequelae (63%), although the primary frostbite was moderate and local. The sequelae in the frostbite area included hypersensitivity to cold (53%), numbness of fingers (40%), and declined sensitivity of touch (33%). Also working ability was lowered due to frostbite sequelae (13%). In cold air provocation tests, the skin temperature of the frostbitten areas decreased more quickly and reached lower values than in healthy control subjects. In conclusion the suffered frostbite was associated with an increased tendency for vasospasm. Subjective sensations of the frostbitten area were associated with thermophysiological changes. The sequelae were reported to worsen in the cold environment thus emphasizing the probable occupational limitations of even moderate cold injury.

Adult↗
PubMed2000

Dependence of cold-related coronary and respiratory symptoms on age and exposure to cold.

Cold causes cardiopulmonary stress often perceived as shortness of breath or chest pain, and causes exacerbation of these symptoms in persons suffering heart or lung disease. We investigated the prevalence of these symptoms and their association with sex, age and cold exposure in a population-based sample of 1,785 persons who lived in three areas of Finland. The exposure to cold was measured by the annual number cold days (mean daily temperature below 0 degree C) in the resident locality and weekly hours spent in the cold in winter. Shortness of breath was 25% and chest pain 52% more common in females than in males, and their prevalence increased by 24% and 77%, respectively, for every 10 years of age. The prevalence of shortness of breath increased by 5% and chest pain by 6% for every 10 cold days in the resident locality, and by 6% and 7% for every 10 hours spent in the cold, respectively. We suggest that environmental cold, measured by the number of cold days throughout the year and weekly hours spent in the cold, may provoke cardiopulmonary symptoms independent of sex and age.

Adult↗
PubMed1999

Cusp patterning defect in Tabby mouse teeth and its partial rescue by FGF.

Tabby is a mouse mutant characterized by deficient development of the ectodermal organs: teeth, hair, and a subset of glands. Ectodysplasin, the protein encoded by the Tabby gene, was recently identified as a novel TNF-like transmembrane protein but little is known about its function. We have examined the Tabby tooth phenotype in detail by analysis of the adult and embryonic teeth. Tabby first molars had an obvious defect in cusp patterning as the number of cusps was reduced and the buccal and lingual cusps were joined. The disturbance in development was first visible morphologically in the bud stage molar. The primary enamel knot in a cap stage Tabby tooth expressed all enamel knot markers analyzed but was smaller than wild type and the first pair of developing secondary enamel knots was fused. We propose that the Tabby tooth phenotype is due to growth retardation during early stages of development which leads to reduced signaling from the primary enamel knot, followed by deficient growth of the dental epithelium and lack of formation of the last developing secondary enamel knots. The ectodysplasin transcripts were expressed in the outer enamel epithelium and dental lamina. When cultured in vitro Tabby bud/cap stage molars formed fewer cusps than wild-type controls. This phenotype was not rescued by exogenously added EGF despite the previously proposed link between Tabby and EGF. Instead FGF-10 partially restored morphogenesis and stimulated the development of additional tooth cusps in cultured Tabby molars.

Animals↗
PubMed1999

Localization of putative stem cells in dental epithelium and their association with Notch and FGF signaling.

The continuously growing mouse incisor is an excellent model to analyze the mechanisms for stem cell lineage. We designed an organ culture method for the apical end of the incisor and analyzed the epithelial cell lineage by 5-bromo-2'-deoxyuridine and DiI labeling. Our results indicate that stem cells reside in the cervical loop epithelium consisting of a central core of stellate reticulum cells surrounded by a layer of basal epithelial cells, and that they give rise to transit-amplifying progeny differentiating into enamel forming ameloblasts. We identified slowly dividing cells among the Notch1-expressing stellate reticulum cells in specific locations near the basal epithelial cells expressing lunatic fringe, a secretory molecule modulating Notch signaling. It is known from tissue recombination studies that in the mouse incisor the mesenchyme regulates the continuous growth of epithelium. Expression of Fgf-3 and Fgf-10 were restricted to the mesenchyme underlying the basal epithelial cells and the transit-amplifying cells expressing their receptors Fgfr1b and Fgfr2b. When FGF-10 protein was applied with beads on the cultured cervical loop epithelium it stimulated cell proliferation as well as expression of lunatic fringe. We present a model in which FGF signaling from the mesenchyme regulates the Notch pathway in dental epithelial stem cells via stimulation of lunatic fringe expression and, thereby, has a central role in coupling the mitogenesis and fate decision of stem cells.

Ameloblasts↗
PubMed1999

Gene expression patterns associated with suppression of odontogenesis in mouse and vole diastema regions.

Rodents have a toothless diastema region between the incisor and molar teeth which may contain rudimentary tooth germs. We found in upper diastema region of the mouse (Mus musculus) three small tooth germs which developed into early bud stage before their apoptotic removal, while the sibling vole (Microtus rossiaemeridionalis) had only a single but larger tooth germ in this region, and this developed into late bud stage before regressing apoptotically. To analyze the genetic mechanisms of the developmental arrest of the rudimentary tooth germs we compared the expression patterns of several developmental regulatory genes (Bmp2, Bmp4, Fgf4, Fgf8, Lef1, Msx1, Msx2, p21, Pitx2, Pax9 and Shh) between molars and diastema buds of mice and voles. In diastema tooth buds the expression of all the genes differed from that of molars. The gene expression patterns suggest that the odontogenic program consists of partially independent signaling cascades which define the exact location of the tooth germ, initiate epithelial budding, and transfer the odontogenic potential from the epithelium to the underlying mesenchyma. Although the diastema regions of the two species differed, in both species the earliest difference that we found was weaker expression of mesenchymal Pax9 in the diastema region than in molar and incisor regions at the dental lamina stage. However, based on earlier tissue recombination experiments it is conceivable that the developmental arrest is determined by the early oral epithelium.

Animals↗
PubMed1999

Spontaneous spiral formation in two-dimensional oscillatory media.

Computational studies of pattern formation in a modified Oregonator model of the Belousov-Zhabotinsky reaction is described. Initially inactive two-dimensional reaction media with an immobilized catalyst is connected to a reservoir of fresh reactants through a set of discrete points distributed randomly over the interphase surface. It is shown that the diffusion of reactants combined with oscillatory reaction kinetics can give rise to spontaneous spiral formation and phase waves.

Journal Article↗
PubMed1998

Expression and function of FGFs-4, -8, and -9 suggest functional redundancy and repetitive use as epithelial signals during tooth morphogenesis.

To elucidate the roles of fibroblast growth factors (FGF) in the regulation of tooth morphogenesis we have analyzed the expression patterns of Fgf-4, -8, and -9 in the developing mouse molar and incisor tooth germs from initiation to completion of morphogenesis by in situ hybridization analysis. The expression of these Fgfs was confined to dental epithelial cells at stages when epithelial-mesenchymal signaling regulates critical steps of tooth morphogenesis. Fgf-8 and Fgf-9 mRNAs were present in the oral epithelium of the first branchial arch at E10 and 1 day later expression became more restricted to the area of presumptive dental epithelium and persisted there until the start of epithelial budding. Fgf-8 mRNAs were not detected later in the developing tooth. Fgf-4 and Fgf-9 expression was upregulated in the primary enamel knot, which is a putative signaling center regulating tooth shape. Subsequently, Fgf-4 and Fgf-9 were expressed in the secondary enamel knots at the sites of tooth cusps. Fgf-9 expression spread from the primary enamel knot within the inner enamel epithelium where it remained until E18. In the continuously growing incisors Fgf-9 expression persisted in the epithelium of the cervical loops. The effects of FGFs were analyzed on the expression of the homeobox-containing transcription factors Msx-1 and Msx-2, which are associated with tissue interactions and regulated by the dental epithelium. Locally applied FGF-4, -8, and -9 stimulated intensely the expression of Msx-1 but not Msx-2 in the isolated dental mesenchyme. We suggest that the three FGFs act as epithelial signals mediating inductive interactions between dental epithelium and mesenchyme during several successive stages of tooth formation. This data suggest roles for FGF-8 and FGF-9 during initiation of tooth development, and for FGF-4 and FGF-9 during regulation of tooth shape. FGF-9 may also be involved in differentiation of odontoblasts. The coexpression of Fgfs with other signaling molecules including Shh and several Bmps and their partly similar effects suggest that the FGFs participate in the signaling networks during odontogenesis.

Animals↗
PubMed1998

Responsiveness of developing dental tissues to fibroblast growth factors: expression of splicing alternatives of FGFR1, -2, -3, and of FGFR4; and stimulation of cell proliferation by FGF-2, -4, -8, and -9.

To elucidate the roles of fibroblast growth factors (FGF) in tooth development, we have analyzed the expression patterns of fibroblast growth factor receptors (FGFR) in mouse teeth by in situ hybridization and studied the effects of FGF-2, -4, -8, and -9 on cell proliferation in vitro by local application with beads on isolated dental mesenchymes. mRNAs of FGFR-1, -2, and -3 were localized by probes specific for the alternative splice variants IIIb and IIIc. The expression patterns of FGFR1 -2, and -3 were completely different, and the two splicing variants of FGFR1 and 2 exhibited different expression domains. FGFR4 was not expressed in the developing teeth. The IIIb splice forms of FGFR1 and -2 were expressed in the dental epithelium during morphogenesis. The IIIc splice form of FGFR1 was expressed both in epithelium and mesenchyme whereas FGFR2 IIIc was confined to the mesenchymal cells of the dental follicle. Both splice forms of FGFR3 were expressed in dental papilla mesenchyme. None of the FGF-receptors was detected in the primary enamel knot, the putative signaling center regulating tooth morphogenesis. This may explain the fact that enamel knot cells do not proliferate, although they express intensely mitogenic FGFs. Beads releasing FGF-2, -4, -8, or -9 proteins stimulated cell proliferation in cultured dental mesenchymes. These data, together with our earlier data on FGF expression [Kettunen and Thesleff (1998): Dev Dyn 211:256-268] suggest that FGF-8 and -9 mediate epithelial-mesenchymal interactions during tooth initiation. During advancing morphogenesis FGF-3, -4, and -9 may act both on mesenchyme and epithelium. Finally, the intense expression of FGFR1 in odontoblasts and ameloblasts and FGFR2 IIIb in ameloblasts suggests that FGFs participate in regulation of their differentiation and/or secretory functions.

Alternative Splicing↗
PubMed1998

Association of developmental regulatory genes with the development of different molar tooth shapes in two species of rodents.

While the evolutionary history of mammalian tooth shapes is well documented in the fossil record, the developmental basis of their tooth shape evolution is unknown. We investigated the expression patterns of eight developmental regulatory genes in two species of rodents with different molar morphologies (mouse, Mus musculus and sibling vole, Microtus rossiaemeridionalis). The genes Bmp-2, Bmp-4, Fgf-4 and Shh encode signal molecules, Lef-1, Msx-1 and Msx-2, are transcription factors and p21CIP1/WAF1 participates in the regulation of cell cycle. These genes are all known to be associated with developmental regulation in mouse molars. In this paper we show that the antisense mRNA probes made from mouse cDNA cross-hybridized with vole tissue. The comparisons of gene expression patterns and morphologies suggest that similar molecular cascades are used in the early budding of tooth germs, in the initiation of tooth crown base formation, and in the initiation of each cusp's development. Furthermore, the co-localization of several genes indicate that epithelial signalling centres function at the three stages of morphogenesis. The earliest signalling centre in the early budding epithelium has not been reported before, but the latter signalling centres, the primary and the secondary enamel knots, have been studied in mouse. The appearance of species-specific tooth shapes was manifested by the regulatory molecules expressed in the secondary enamel knots at the areas of future cusp tips, whilst the mesenchymal gene expression patterns had a buccal bias without similar species-specific associations.

Animals↗
PubMed1998

The life history of an embryonic signaling center: BMP-4 induces p21 and is associated with apoptosis in the mouse tooth enamel knot.

The enamel knot, a transient epithelial structure, appears at the onset of mammalian tooth shape development. Until now, the morphological, cellular and molecular events leading to the formation and disappearance of the enamel knot have not been described. Here we report that the cessation of cell proliferation in the enamel knot in mouse molar teeth is linked with the expression of the cyclin-dependent kinase inhibitor p21. We show that p21 expression is induced by bone morphogenetic protein 4 (BMP-4) in isolated dental epithelia. As Bmp-4 is expressed only in the underlying dental mesenchyme at the onset of the enamel knot formation, these results support the role of the cyclin-dependent kinase inhibitors as inducible cell differentiation factors in epithelial-mesenchymal interactions. Furthermore, we show that the expression of p21 in the enamel knot is followed by Bmp-4 expression, and subsequently by apoptosis of the differentiated enamel knot cells. Three-dimensional reconstructions of serial sections after in situ hybridization and Tunel-staining indicated an exact codistribution of Bmp-4 transcripts and apoptotic cells. Apoptosis was stimulated by BMP-4 in isolated dental epithelia, but only in one third of the explants. We conclude that Bmp-4 may be involved both in the induction of the epithelial enamel knot, as a mesenchymal inducer of epithelial cyclin-dependent kinase inhibitors, and later in the termination of the enamel knot signaling functions by participating in the regulation of programmed cell death. These results show that the life history of the enamel knot is intimately linked to the initiation of tooth shape development and support the role of the enamel knot as an embryonic signaling center.

Animals↗
PubMed1995

Epithelial-mesenchymal signaling during tooth development.

Classic studies on experimental embryology have shown that organ development in an embryo is largely regulated by so called inductive tissue interactions which mostly take place between epithelial and mesenchymal tissues. Also in the developing tooth, both morphogenesis and cell differentiation are governed by such interactions. Characteristic features of epithelial-mesenchymal interactions are that they are sequential and reciprocal, i.e. "induction" appears to consist of a chain of signaling events between the tissues. During the last decade, the expression patterns of numerous molecules have been studied in developing organs by in situ hybridization and immunohistology. Many of them have been associated with epithelial-mesenchymal interactions, and it is apparent that same molecules participate in regulation of morphogenesis in a number of different organs. Transcription factors such as Msx-1, Msx-2 and Egr-1, growth factors, including TGF beta's, BMPs, and FGFs, and structural proteins such as syndecan and tenascin are expressed in transient, time and space-specific patterns in many organ rudiments, including the tooth. We have shown by tissue recombination studies that the expression of certain molecules is indeed regulated by epithelial-mesenchymal interactions in the early tooth germ. In particular, during the early stages of morphogenesis, when the dental epithelium induces the condensation of mesenchymal cells around the epithelial bud, the expression of many genes is upregulated in the condensed mesenchyme. Previous experimental tissue recombination studies have indicated that at the same time the capacity to instruct tooth morphogenesis shifts from the dental epithelium to the dental mesenchyme.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗