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<pubmed limit=5>Tongue Embryology</pubmed>
<pubmed limit=5>Tongue Development</pubmed>
SOX2 regulation by hedgehog signaling controls adult lingual epithelium homeostasis
Development. 2018 Jul 17;145(14). pii: dev164889. doi: 10.1242/dev.164889.
Castillo-Azofeifa D1,2,3, Seidel K4, Gross L1, Golden EJ1, Jacquez B1,5, Klein OD4,6,7, Barlow LA8,2,3,5.
Adult tongue epithelium is continuously renewed from epithelial progenitor cells, a process that requires hedgehog (HH) signaling. In mice, pharmacological inhibition of the HH pathway causes taste bud loss within a few weeks. Previously, we demonstrated that sonic hedgehog (SHH) overexpression in lingual progenitors induces ectopic taste buds with locally increased SOX2 expression, suggesting that taste bud differentiation depends on SOX2 downstream of HH. To test this, we inhibited HH signaling in mice and observed a rapid decline in Sox2 and SOX2-GFP expression in taste epithelium. Upon conditional deletion of Sox2, differentiation of both taste and non-taste epithelial cells was blocked, and progenitor cell number increased. In contrast to basally restricted proliferation in controls, dividing cells were overabundant and spread to suprabasal epithelial layers in mutants. SOX2 loss in progenitors also led non-cell-autonomously to taste cell apoptosis, dramatically shortening taste cell lifespans. Finally, in tongues with conditional Sox2 deletion and SHH overexpression, ectopic and endogenous taste buds were not detectable; instead, progenitor hyperproliferation expanded throughout the lingual epithelium. In summary, we show that SOX2 functions downstream of HH signaling to regulate lingual epithelium homeostasis. KEYWORDS:
Cell differentiation; Mouse; Progenitor proliferation; Smoothened antagonist; Taste bud
PMID: 29945863 DOI: 10.1242/dev.164889
How to make a tongue: Cellular and molecular regulation of muscle and connective tissue formation during mammalian tongue development
Semin Cell Dev Biol. 2018 May 18. pii: S1084-9521(17)30147-7. doi: 10.1016/j.semcdb.2018.04.016. [Epub ahead of print]
Cobourne MT1, Iseki S2, Birjandi AA3, Adel Al-Lami H4, Thauvin-Robinet C5, Xavier GM6, Liu KJ3.
The vertebrate tongue is a complex muscular organ situated in the oral cavity and involved in multiple functions including mastication, taste sensation, articulation and the maintenance of oral health. Although the gross embryological contributions to tongue formation have been known for many years, it is only relatively recently that the molecular pathways regulating these processes have begun to be discovered. In particular, there is now evidence that the Hedgehog, TGF-Beta, Wnt and Notch signaling pathways all play an important role in mediating appropriate signaling interactions between the epithelial, cranial neural crest and mesodermal cell populations that are required to form the tongue. In humans, a number of congenital abnormalities that affect gross morphology of the tongue have also been described, occurring in isolation or as part of a developmental syndrome, which can greatly impact on the health and well-being of affected individuals. These anomalies can range from an absence of tongue formation (aglossia) through to diminutive (microglossia), enlarged (macroglossia) or bifid tongue. Here, we present an overview of the gross anatomy and embryology of mammalian tongue development, focusing on the molecular processes underlying formation of the musculature and connective tissues within this organ. We also survey the clinical presentation of tongue anomalies seen in human populations, whilst considering their developmental and genetic etiology. KEYWORDS: Cranial neural crest; Hedgehog signaling; Mesoderm; Myogenesis; TGF-beta; Wnt PMID: 29784581 DOI: 10.1016/j.semcdb.2018.04.016
A Wnt/Notch/Pax7 signaling network supports tissue integrity in tongue development
J Biol Chem. 2017 Jun 2;292(22):9409-9419. doi: 10.1074/jbc.M117.789438. Epub 2017 Apr 24.
Zhu XJ1, Yuan X1, Wang M1, Fang Y1, Liu Y1, Zhang X1, Yang X1, Li Y1, Li J1, Li F1, Dai ZM1, Qiu M1, Zhang Z2, Zhang Z3.
The tongue is one of the major structures involved in human food intake and speech. Tongue malformations such as aglossia, microglossia, and ankyloglossia are congenital birth defects, greatly affecting individuals' quality of life. However, the molecular basis of the tissue-tissue interactions that ensure tissue morphogenesis to form a functional tongue remains largely unknown. Here we show that ShhCre -mediated epithelial deletion of Wntless (Wls), the key regulator for intracellular Wnt trafficking, leads to lingual hypoplasia in mice. Disruption of epithelial Wnt production by Wls deletion in epithelial cells led to a failure in lingual epidermal stratification and loss of the lamina propria and the underlying superior longitudinal muscle in developing mouse tongues. These defective phenotypes resulted from a reduction in epithelial basal cells positive for the basal epidermal marker protein p63 and from impaired proliferation and differentiation in connective tissue and paired box 3 (Pax3)- and Pax7-positive muscle progenitor cells. We also found that epithelial Wnt production is required for activation of the Notch signaling pathway, which promotes proliferation of myogenic progenitor cells. Notch signaling in turn negatively regulated Wnt signaling during tongue morphogenesis. We further show that Pax7 is a direct Notch target gene in the embryonic tongue. In summary, our findings demonstrate a key role for the lingual epithelial signals in supporting the integrity of the lamina propria and muscular tissue during tongue development and that a Wnt/Notch/Pax7 genetic hierarchy is involved in this development. KEYWORDS: Wnt signaling; connective tissue; craniofacial development; mouse; muscle progenitor cells; myogenesis PMID: 28438836 PMCID: PMC5454119 DOI: 10.1074/jbc.M117.789438
Fetal tendinous connection between the tensor tympani and tensor veli palatini muscles: A single digastric muscle acting for morphogenesis of the cranial base
Anat Rec (Hoboken). 2016 Jan 6. doi: 10.1002/ar.23310. [Epub ahead of print]
Rodríguez-Vázquez JF1, Sakiyama K2, Abe H3, Amano O2, Murakami G4.
Some researchers contend that in adults the tensor tympani muscle (TT) connects with the tensor veli palatini muscle (TVP) by an intermediate tendon, in disagreement with the other researchers. To resolve this controversy, we examined serial sections of 50 human embryos and fetuses at 6-17 weeks of development. At 6 weeks, in the first pharyngeal arch, a mesenchymal connection was found first to divide a single anlage into the TT and TVP. At and after 7 weeks, the TT was connected continuously with the TVP by a definite tendinous tissue mediolaterally crossing the pharyngotympanic tube. At 11 weeks another fascia was visible covering the cranial and lateral sides of the tube. This "gonial fascia" had two thickened borders: the superior one corresponded to a part of the connecting tendon between the TT and TVP; the inferior one was a fibrous band ending at the os goniale near the lateral end of the TVP. In association with the gonial fascia, the fetal TT and TVP seemed to provide a functional complex. The TT-TVP complex might first help elevate the palatal shelves in association with the developing tongue. Next, the tubal passage, maintained by contraction of the muscle complex, seems to facilitate the removal of loose mesenchymal tissues from the tympanic cavity. Third, the muscle complex most likely determined the final morphology of the pterygoid process. Consequently, despite the controversial morphologies in adults, the TT and TVP seemed to make a single digastric muscle acting for the morphogenesis of the cranial base. This article is protected by copyright. All rights reserved. © 2016 Wiley Periodicals, Inc. KEYWORDS: middle ear; palatal shelves; pharyngotympanic tube; tensor tympani muscle; tensor veli palatini muscle
Proc Natl Acad Sci U S A. 2013 Nov 12;110(46):18555-60. doi: 10.1073/pnas.1306495110. Epub 2013 Oct 28.
Liu H, Lan Y, Xu J, Chang CF, Brugmann SA, Jiang R. Author information
Abstract The tongue is a critical element of the feeding system in tetrapod animals for their successful adaptation to terrestrial life. Whereas the oral part of the mammalian tongue contains soft tissues only, the avian tongue has an internal skeleton extending to the anterior tip. The mechanisms underlying the evolutionary divergence in tongue skeleton formation are completely unknown. We show here that the odd-skipped related-1 (Osr1) transcription factor is expressed throughout the neural crest-derived tongue mesenchyme in mouse, but not in chick, embryos during early tongue morphogenesis. Neural crest-specific inactivation of Osr1 resulted in formation of an ectopic cartilage in the mouse tongue, reminiscent in shape and developmental ontogeny of the anterior tongue cartilage in chick. SRY-box containing gene-9 (Sox9), the master regulator of chondrogenesis, is widely expressed in the nascent tongue mesenchyme at the onset of tongue morphogenesis but its expression is dramatically down-regulated concomitant with activation of Osr1 expression in the developing mouse tongue. In Osr1 mutant mouse embryos, expression of Sox9 persisted in the developing tongue mesenchyme where chondrogenesis is subsequently activated to form the ectopic cartilage. Furthermore, we show that Osr1 binds to the Sox9 gene promoter and that overexpression of Osr1 suppressed expression of endogenous Sox9 mRNAs and Sox9 promoter-driven reporter. These data indicate that Osr1 normally prevents chondrogenesis in the mammalian tongue through repression of Sox9 expression and suggest that changes in regulation of Osr1 expression in the neural crest-derived tongue mesenchyme underlie the evolutionary divergence of birds from other vertebrates in tongue morphogenesis. KEYWORDS: cell fate, craniofacial, differentiation, tongue-tie
Morphological variations of the vallate papillae in some mammalian species
Anat Sci Int. 2013 Nov 16. [Epub ahead of print]
El Sharaby AA, El-Gendy SA, Alsafy MA, Nomir AG, Wakisaka S. Author information
Abstract The morpho-structural characteristics of the vallate papillae of the tongue of rat, dog, donkey and buffalo were investigated by macroscopy and their microstructure by light and scanning electron microscopy (SEM). The numbers of vallate papillae varied among the different species. In rat, a single vallate papilla surrounded by incomplete groove and an annular fold was observed. Taste buds were detected along the entire length of the medial and lateral groove epithelium, but not in the papillary dome. In dog, some papillae lacking the annular pad had irregular ridges and grooves toward the center of the papillary surface, while other papillae had small secondary papillary grooves arising from the center of the papilla. Taste buds were located in the medial and lateral epithelium of both primary and secondary grooves as well as in the dome epithelium. In donkey, two papillae were frequently observed around the midline of the tongue root, and an additional papilla was found occasionally in the middle and associated with secondary papilla. In buffalo, several papillae were relatively small and variable in shape. With SEM, small ridges and grooves were found in the papillae of donkey and buffalo. In both species, taste buds were constantly observed along the medial wall epithelium, but no taste buds were found in the lateral wall. We conclude that the vallate papillae exhibited peculiar characteristics, which are species specific and might have a correlation with the variable feeding habits among these animals.
Noncanonical transforming growth factor β (TGFβ) signaling in cranial neural crest cells causes tongue muscle developmental defects
J Biol Chem. 2013 Oct 11;288(41):29760-70. doi: 10.1074/jbc.M113.493551. Epub 2013 Aug 15.
Iwata J, Suzuki A, Pelikan RC, Ho TV, Chai Y. Author information
Microglossia is a congenital birth defect in humans and adversely impacts quality of life. In vertebrates, tongue muscle derives from the cranial mesoderm, whereas tendons and connective tissues in the craniofacial region originate from cranial neural crest (CNC) cells. Loss of transforming growth factor β (TGFβ) type II receptor in CNC cells in mice (Tgfbr2(fl/fl);Wnt1-Cre) causes microglossia due to a failure of cell-cell communication between cranial mesoderm and CNC cells during tongue development. However, it is still unclear how TGFβ signaling in CNC cells regulates the fate of mesoderm-derived myoblasts during tongue development. Here we show that activation of the cytoplasmic and nuclear tyrosine kinase 1 (ABL1) cascade in Tgfbr2(fl/fl);Wnt1-Cre mice results in a failure of CNC-derived cell differentiation followed by a disruption of TGFβ-mediated induction of growth factors and reduction of myogenic cell proliferation and differentiation activities. Among the affected growth factors, the addition of fibroblast growth factor 4 (FGF4) and neutralizing antibody for follistatin (FST; an antagonist of bone morphogenetic protein (BMP)) could most efficiently restore cell proliferation, differentiation, and organization of muscle cells in the tongue of Tgfbr2(fl/fl);Wnt1-Cre mice. Thus, our data indicate that CNC-derived fibroblasts regulate the fate of mesoderm-derived myoblasts through TGFβ-mediated regulation of FGF and BMP signaling during tongue development. KEYWORDS: Craniofacial Development, Development, Mouse, Muscle, Tone, Transforming Growth Factor beta (TGFbeta)
Mice with Tak1 deficiency in neural crest lineage exhibit cleft palate associated with abnormal tongue development
J Biol Chem. 2013 Apr 12;288(15):10440-50. doi: 10.1074/jbc.M112.432286. Epub 2013 Mar 4.
Song Z, Liu C, Iwata J, Gu S, Suzuki A, Sun C, He W, Shu R, Li L, Chai Y, Chen Y. Author information
Cleft palate represents one of the most common congenital birth defects in humans. TGFβ signaling, which is mediated by Smad-dependent and Smad-independent pathways, plays a crucial role in regulating craniofacial development and patterning, particularly in palate development. However, it remains largely unknown whether the Smad-independent pathway contributes to TGFβ signaling function during palatogenesis. In this study, we investigated the function of TGFβ activated kinase 1 (Tak1), a key regulator of Smad-independent TGFβ signaling in palate development. We show that Tak1 protein is expressed in both the epithelium and mesenchyme of the developing palatal shelves. Whereas deletion of Tak1 in the palatal epithelium or mesenchyme did not give rise to a cleft palate defect, inactivation of Tak1 in the neural crest lineage using the Wnt1-Cre transgenic allele resulted in failed palate elevation and subsequently the cleft palate formation. The failure in palate elevation in Wnt1-Cre;Tak1(F/F) mice results from a malformed tongue and micrognathia, resembling human Pierre Robin sequence cleft of the secondary palate. We found that the abnormal tongue development is associated with Fgf10 overexpression in the neural crest-derived tongue tissue. The failed palate elevation and cleft palate were recapitulated in an Fgf10-overexpressing mouse model. The repressive effect of the Tak1-mediated noncanonical TGFβ signaling on Fgf10 expression was further confirmed by inhibition of p38, a downstream kinase of Tak1, in the primary cell culture of developing tongue. Tak1 thus functions to regulate tongue development by controlling Fgf10 expression and could represent a candidate gene for mutation in human PRS clefting. PMID 23460641
Morphological variations of the vallate papillae in some mammalian species
Anat Sci Int. 2013 Nov 16. [Epub ahead of print]
El Sharaby AA, El-Gendy SA, Alsafy MA, Nomir AG, Wakisaka S. Source Department of Anatomy and Embryology, Faculty of Veterinary Medicine, Damanhour University, Damanhour, Egypt, firstname.lastname@example.org.
The morpho-structural characteristics of the vallate papillae of the tongue of rat, dog, donkey and buffalo were investigated by macroscopy and their microstructure by light and scanning electron microscopy (SEM). The numbers of vallate papillae varied among the different species. In rat, a single vallate papilla surrounded by incomplete groove and an annular fold was observed. Taste buds were detected along the entire length of the medial and lateral groove epithelium, but not in the papillary dome. In dog, some papillae lacking the annular pad had irregular ridges and grooves toward the center of the papillary surface, while other papillae had small secondary papillary grooves arising from the center of the papilla. Taste buds were located in the medial and lateral epithelium of both primary and secondary grooves as well as in the dome epithelium. In donkey, two papillae were frequently observed around the midline of the tongue root, and an additional papilla was found occasionally in the middle and associated with secondary papilla. In buffalo, several papillae were relatively small and variable in shape. With SEM, small ridges and grooves were found in the papillae of donkey and buffalo. In both species, taste buds were constantly observed along the medial wall epithelium, but no taste buds were found in the lateral wall. We conclude that the vallate papillae exhibited peculiar characteristics, which are species specific and might have a correlation with the variable feeding habits among these animals. PMID 24242871
Bone morphogenetic protein-2 functions as a negative regulator in the differentiation of myoblasts, but not as an inducer for the formations of cartilage and bone in mouse embryonic tongue
BMC Dev Biol. 2011 Jul 7;11(1):44. [Epub ahead of print]
Aoyama K, Yamane A, Suga T, Suzuki E, Fukui T, Nakamura Y.
Abstract ABSTRACT: BACKGROUND: In vitro studies using the myogenic cell line C2C12 demonstrate that bone morphogenetic protein-2 (BMP-2) converts the developmental pathway of C2C12 from a myogenic cell lineage to an osteoblastic cell lineage. Further, in vivo studies using null mutation mice demonstrate that BMPs inhibit the specification of the developmental fate of myogenic progenitor cells. However, the roles of BMPs in the phases of differentiation and maturation in skeletal muscles have yet to be determined. The present study attempts to define the function of BMP-2 in the final stage of differentiation of mouse tongue myoblast. RESULTS: Recombinant BMP-2 inhibited the expressions of markers for the differentiation of skeletal muscle cells, such as myogenin, muscle creatine kinase (MCK), and fast myosin heavy chain (fMyHC), whereas BMP-2 siRNA stimulated such markers. Neither the recombinant BMP-2 nor BMP-2 siRNA altered the expressions of markers for the formation of cartilage and bone, such as osteocalcin, alkaline phosphatase (ALP), collagen II, and collagen X. Further, no formation of cartilage and bone was observed in the recombinant BMP-2-treated tongues based on Alizarin red and Alcian blue stainings. Neither recombinant BMP-2 nor BMP-2 siRNA affected the expression of inhibitor of DNA binding /differentiation 1 (Id1). The ratios of chondrogenic and osteogenic markers relative to glyceraldehyde-3-phosphate dehydrogenase (GAPDH, a house keeping gene) were approximately 1000-fold lower than those of myogenic markers in the cultured tongue. CONCLUSIONS: BMP-2 functions as a negative regulator for the final differentiation of tongue myoblasts, but not as an inducer for the formation of cartilage and bone in cultured tongue, probably because the genes related to myogenesis are in an activation mode, while the genes related to chondrogenesis and osteogenesis are in a silencing mode.
Relationship between neural crest cells and cranial mesoderm during head muscle development
Grenier J, Teillet MA, Grifone R, Kelly RG, Duprez D. PLoS One. 2009;4(2):e4381. Epub 2009 Feb 9. PMID: 19198652
In vertebrates, the skeletal elements of the jaw, together with the connective tissues and tendons, originate from neural crest cells, while the associated muscles derive mainly from cranial mesoderm. Previous studies have shown that neural crest cells migrate in close association with cranial mesoderm and then circumscribe but do not penetrate the core of muscle precursor cells of the branchial arches at early stages of development, thus defining a sharp boundary between neural crest cells and mesodermal muscle progenitor cells. Tendons constitute one of the neural crest derivatives likely to interact with muscle formation. However, head tendon formation has not been studied, nor have tendon and muscle interactions in the head.
This results show that neural crest cells and muscle progenitor cells are more extensively mixed than previously believed during arch development. In addition, our results show that interactions between muscles and tendons during craniofacial development are similar to those observed in the limb, despite the distinct embryological origin of these cell types in the head.
Development of the fetal tongue between 14 and 26 weeks of gestation: in utero ultrasonographic measurements
Ultrasound Obstet Gynecol. 1997 Jan;9(1):39-41.
Achiron R1, Ben Arie A, Gabbay U, Mashiach S, Rotstein Z, Lipitz S.
Our objective was to establish nomograms for fetal tongue measurements from 14 weeks until mid-gestation by using transvaginal and transabdominal high-resolution ultrasound techniques. A prospective, cross-sectional study was performed on 120 normal singleton pregnancies between 14 and 26 weeks of gestation. Tongue circumference was measured by transvaginal ultrasonography between 14 and 17 weeks, and by abdominal ultrasound between 18 and 26 weeks of gestation. Fetal tongue circumference, as a function of gestational age, was expressed by the regression equation: tongue circumference (mm) = -23.9 + 3.75 x gestational age (weeks). The correlation, r2 = 0.95, was found to be highly statistically significant (p < 0.0001). The normal mean of tongue circumference per week and the 95% prediction limits were defined. During the study period we evaluated two cases with tongue circumference outside these 95% confidence limits: one had microglossia, the other macroglossia, and both were found to be associated with abnormal fetal karyotype. The presented normative data may be helpful in the prenatal diagnosis of suspected congenital syndromes that include, among their manifestations, tongue growth disturbances.
|Tongue circumference was measured by transvaginal ultrasonography between 14 and 17 weeks, and by abdominal ultrasound between 18 and 26 weeks of gestation.|