Elinten kehityksen geneettinen säätely

Se, miten eläinalkioiden kehitys tapahtuu, on aina kiinnostanut ihmisiä. Jo Aristoteles pohti tätä ja kysyi: Syntyvätkö kaikki alkion osat yhtäaikaa vaiko peräjälkeen? Onko kaikki jo alusta alkaen valmiiksi muodostunut vai onko kehitys verrattavissa kalastajan verkon kutomiseen? Aristoteles kallistui jälkimmäisen vaihtoehdon puolelle ja kutsui tällä tavalla tapahtuvaa kehitystä epigeneettiseksi. Kesti kuitenkin reilusti yli kaksituhatta vuotta ennen kuin teoria hyväksyttiin ja todistettiin oikeaksi

Abnormalities in Tooth Formation after Early Bisphosphonate Treatment in Children with Osteogenesis Imperfecta

Treatment with intravenous bisphosphonate (BP) in children and adolescents with osteogenesis imperfecta (OI) started in Sweden in 1991. No human studies on the role of BP therapy in development of disturbances in tooth mineralization or tooth morphology have been published. The study cohort comprised 219 individuals who were divided into four groups: group 1, BP treatment onset before 2 years of age (n = 22); group 2, BP treatment onset between 2 and 6 years of age (n = 20); group 3, BP treatment onset between 6 and 10 years of age (n = 13); and a control group of patients with OI who had not received BP therapy (n = 164). The chi-square test was used in between-group comparisons of the prevalence of tooth agenesis. The prevalence of tooth agenesis was significantly higher in children who began BP treatment before the age of 2 years (group 1; 59%,) compared to the controls (10%; p < 0.001) and to children who had begun BP therapy between ages 2 and 6 years (group 2; 10%; p = 0.009) or between ages 6 and 10 years (group 3; 8%; p = 0.003). Different types of disturbances in the enamel formation were seen in 52 premolars, where 51 were seen in those who began BP treatment before the age of 2 years. To conclude, starting BP treatment before the age of 2 years increases the risk of abnormalities in tooth formation manifesting as morphological aberrations, tooth agenesis, and enamel defects.Peer reviewe

Lunatic Fringe, FGF, and BMP Regulate the Notch Pathway during Epithelial Morphogenesis of Teeth

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

Novel strategies for expansion of tooth epithelial stem cells and ameloblast generation

Enamel is secreted by ameloblasts derived from tooth epithelial stem cells (SCs). Humans cannot repair or regenerate enamel, due to early loss of tooth epithelial SCs. Contrarily in the mouse incisors, epithelial SCs are maintained throughout life and endlessly generate ameloblasts, and thus enamel. Here we isolated Sox2-GFP+ tooth epithelial SCs which generated highly cellular spheres following a novel in vitro strategy. This system enabled analysis of SC regulation by various signaling molecules, and supported the stimulatory and inhibitory roles of Shh and Bmp, respectively; providing better insight into the heterogeneity of the SCs. Further, we generated a novel mouse reporter, Enamelin-tdTomato for identification of ameloblasts in live tissues and cells, and used it to demonstrate presence of ameloblasts in the new 3D co-culture system of dental SCs. Collectively, our results provide means of generating 3D tooth epithelium from adult SCs which can be utilized toward future generation of enamel.Peer reviewe

An integrated gene regulatory network controls stem cell proliferation in teeth.

Epithelial stem cells reside in specific niches that regulate their self-renewal and differentiation, and are responsible for the continuous regeneration of tissues such as hair, skin, and gut. Although the regenerative potential of mammalian teeth is limited, mouse incisors grow continuously throughout life and contain stem cells at their proximal ends in the cervical loops. In the labial cervical loop, the epithelial stem cells proliferate and migrate along the labial surface, differentiating into enamel-forming ameloblasts. In contrast, the lingual cervical loop contains fewer proliferating stem cells, and the lingual incisor surface lacks ameloblasts and enamel. Here we have used a combination of mouse mutant analyses, organ culture experiments, and expression studies to identify the key signaling molecules that regulate stem cell proliferation in the rodent incisor stem cell niche, and to elucidate their role in the generation of the intrinsic asymmetry of the incisors. We show that epithelial stem cell proliferation in the cervical loops is controlled by an integrated gene regulatory network consisting of Activin, bone morphogenetic protein (BMP), fibroblast growth factor (FGF), and Follistatin within the incisor stem cell niche. Mesenchymal FGF3 stimulates epithelial stem cell proliferation, and BMP4 represses Fgf3 expression. In turn, Activin, which is strongly expressed in labial mesenchyme, inhibits the repressive effect of BMP4 and restricts Fgf3 expression to labial dental mesenchyme, resulting in increased stem cell proliferation and a large, labial stem cell niche. Follistatin limits the number of lingual stem cells, further contributing to the characteristic asymmetry of mouse incisors, and on the basis of our findings, we suggest a model in which Follistatin antagonizes the activity of Activin. These results show how the spatially restricted and balanced effects of specific components of a signaling network can regulate stem cell proliferation in the niche and account for asymmetric organogenesis. Subtle variations in this or related regulatory networks may explain the different regenerative capacities of various organs and animal species

Pivotal Role of Tenascin-W (-N) in Postnatal Incisor Growth and Periodontal Ligament Remodeling

The continuously growing mouse incisor provides a fascinating model for studying stem cell regulation and organ renewal. In the incisor, epithelial and mesenchymal stem cells assure lifelong tooth growth. The epithelial stem cells reside in a niche known as the cervical loop. Mesenchymal stem cells are located in the nearby apical neurovascular bundle and in the neural plexus. So far, little is known about extracellular cues that are controlling incisor stem cell renewal and guidance. The extracellular matrix protein tenascin-W, also known as tenascin-N (TNN), is expressed in the mesenchyme of the pulp and of the periodontal ligament of the incisor, and is closely associated with collagen 3 fibers. Here, we report for the first time the phenotype of tenascin-W/TNN deficient mice, which in a C57BL/6N background exhibit a reduced body weight and lifespan. We found major defects in the alveolar bone and periodontal ligament of the growing rodent incisors, whereas molars were not affected. The alveolar bone around the incisor was replaced by a dense scar-like connective tissue, enriched with newly formed nerve fibers likely leading to periodontal pain, less food intake and reduced body weight. Using soft food to reduce mechanical load on the incisor partially rescued the phenotype. In situ hybridization and Gli1 reporter mouse experiments revealed decreased hedgehog signaling in the incisor mesenchymal stem cell compartment, which coordinates the development of mesenchymal stem cell niche. These results indicate that TNN deficiency in mice affects periodontal remodeling and increases nerve fiber branching. Through periodontal pain the food intake is reduced and the incisor renewal and the neurovascular sonic hedgehog secretion rate are reduced. In conclusion, tenascin-W/TNN seems to have a primary function in rapid periodontal tissue remodeling and a secondary function in mechanosensation.Peer reviewe

An Integrated Gene Regulatory Network Controls Stem Cell Proliferation in Teeth

Epithelial stem cells reside in specific niches that regulate their self-renewal and differentiation, and are responsible for the continuous regeneration of tissues such as hair, skin, and gut. Although the regenerative potential of mammalian teeth is limited, mouse incisors grow continuously throughout life and contain stem cells at their proximal ends in the cervical loops. In the labial cervical loop, the epithelial stem cells proliferate and migrate along the labial surface, differentiating into enamel-forming ameloblasts. In contrast, the lingual cervical loop contains fewer proliferating stem cells, and the lingual incisor surface lacks ameloblasts and enamel. Here we have used a combination of mouse mutant analyses, organ culture experiments, and expression studies to identify the key signaling molecules that regulate stem cell proliferation in the rodent incisor stem cell niche, and to elucidate their role in the generation of the intrinsic asymmetry of the incisors. We show that epithelial stem cell proliferation in the cervical loops is controlled by an integrated gene regulatory network consisting of Activin, bone morphogenetic protein (BMP), fibroblast growth factor (FGF), and Follistatin within the incisor stem cell niche. Mesenchymal FGF3 stimulates epithelial stem cell proliferation, and BMP4 represses Fgf3 expression. In turn, Activin, which is strongly expressed in labial mesenchyme, inhibits the repressive effect of BMP4 and restricts Fgf3 expression to labial dental mesenchyme, resulting in increased stem cell proliferation and a large, labial stem cell niche. Follistatin limits the number of lingual stem cells, further contributing to the characteristic asymmetry of mouse incisors, and on the basis of our findings, we suggest a model in which Follistatin antagonizes the activity of Activin. These results show how the spatially restricted and balanced effects of specific components of a signaling network can regulate stem cell proliferation in the niche and account for asymmetric organogenesis. Subtle variations in this or related regulatory networks may explain the different regenerative capacities of various organs and animal species

Sox21 Regulates Anapc10 Expression and Determines the Fate of Ectodermal Organ

The transcription factor Sox21 is expressed in the epithelium of developing teeth. The present study aimed to determine the role of Sox21 in tooth development. We found that disruption of Sox21 caused severe enamel hypoplasia, regional osteoporosis, and ectopic hair formation in the gingiva in Sox21 knockout incisors. Differentiation markers were lost in ameloblasts, which formed hair follicles expressing hair keratins. Molecular analysis and chromatin immunoprecipitation sequencing indicated that Sox21 regulated Anapc10, which recognizes substrates for ubiquitination-mediated degradation, and determined dental-epithelial versus hair follicle cell fate. Disruption of either Sox21 or Anapc10 induced Smad3 expression, accelerated TGF-beta 1-induced promotion of epithelial-to-mesenchymal transition (EMT), and resulted in E-cadherin degradation via Skp2. We conclude that Sox21 disruption in the dental epithelium leads to the formation of a unique microenvironment promoting hair formation and that Sox21 controls dental epithelial differentiation and enamel formation by inhibiting EMT via Anapc10.Peer reviewe