Cell Dissociation from the Tongue Epithelium and Mesenchyme/Connective Tissue of Embryonic-Day 12.5 and 8-Week-Old Mice

Cell dissociation has been an essential procedure for studies at the individual-cell level and/or at a cell-population level (e.g., single cell RNA sequencing and primary cell culture). Yielding viable, healthy cells in large quantities is critical, and the optimal conditions to do so are tissue dependent. Cell populations in the tongue epithelium and underlying mesenchyme/connective tissue are heterogeneous and tissue structures vary in different regions and at different developmental stages. We have tested protocols for isolating cells from the mouse tongue epithelium and mesenchyme/connective tissue in the early developmental [embryonic day 12.5 (E12.5)] and young adult (8-week) stages. A clean separation between the epithelium and underlying mesenchyme/connective tissue was easy to accomplish. However, to further process and isolate cells, yielding viable healthy cells in large quantities, and careful selection of enzymatic digestion buffer, incubation time, and centrifugation speed and time are critical. Incubation of separated epithelium or underlying mesenchyme/connective tissue in 0.25% Trypsin-EDTA for 30 min at 37 °C, followed by centrifugation at 200 x g for 8 min resulted in a high yield of cells at a high viability rate (>90%) regardless of the mouse stages and tongue regions. Moreover, we found that both dissociated epithelial and mesenchymal/connective tissue cells from embryonic and adult tongues could survive in the cell culture-based medium for at least 3 h without a significant decrease of cell viability. The protocols will be useful for studies that require the preparation of isolated cells from mouse tongues at early developmental (E12.5) and young adult (8-week) stages requiring cell dissociation from different tissue compartments.

Fetal tongue posture associated with micrognathia: An ultrasound marker of cleft secondary palate?

Cleft lip and cleft palate (CP) are the most common facial malformations. Two-dimensional (2D) ultrasound (US) is the first-line examination in the prenatal diagnosis of CP. Three-dimensional, four-dimensional US and MRI provide a better detection of facial clefts. We present two fetuses with micrognathia and suspected secondary CP on 2D US: fetal tongue appeared in an unusual position (low tip and high dorsum position) and showed uncoordinated movements. MRI did not confirm the US suspicion, but at birth the two fetuses were affected by Pierre Robin sequence.

Embryonic development of parakeratinized epithelium of the tongue in the domestic duck (Anas platyrhynchos f. domestica): LM, SEM, and TEM observations

The parakeratinized epithelium is a common and widespread type of keratinized epithelium in the oral cavity in adult birds. In contrast to orthokeratinized epithelium, which mostly covers mechanical papillae and the lingual nail, parakeratinized epithelium covers almost the entire dorsal surface of the tongue in birds. The characteristic feature of parakeratinized epithelium is the presence of nuclei in the keratinized layer. The present study aimed to investigate for the first time the micro- and ultrastructural changes of parakeratinized epithelium during embryonic development and to assess the readiness of the epithelium to serve protective functions during food transport to the esophagus. Three developmental stages were distinguished: embryonic, transformation, and pre-hatching stages. The embryonic stage lasts from the 9th to the 14th day of incubation and the epithelium is composed of undifferentiated epithelial cells. The transformation stage lasts from the 15th to the 22nd day of incubation and the epithelium undergoes transformation into stratified epithelium consisting of basal, intermediate, and superficial layers. The characteristic feature of this stage is formation of the periderm with osmophilic granules. The pre-hatching stage starts on the 23rd day, and the epithelium with a fully developed keratinized layer resembles that of the epithelium in adult animals. No periderm was observed on the epithelial surface. It was confirmed that at the time of hatching the parakeratinized epithelium is fully differentiated and ready to fulfill its function during food transport. The presence of periderm is a common feature characteristic for para- and orthokeratinized epithelium in the oral cavity of birds. However, the formation of the keratinized/cornified layer is different for these two types of keratinized epithelia.

Pathogenesis of Cleft Palate in Robin Sequence: Observations From Prenatal Magnetic Resonance Imaging

PURPOSE

The etiology of the palatal cleft in Robin sequence (RS) is unknown. The purpose of this study was to assess the position of the fetal tongue at prenatal magnetic resonance imaging (MRI) and to suggest a potential relation between tongue position and development of the cleft palate seen in most patients with RS.

MATERIALS AND METHODS

This is a retrospective case-and-control study including fetuses with prenatal MRIs performed in the authors' center from 2002 to 2017. Inclusion criteria were 1) prenatal MRI of adequate quality, 2) liveborn infant, and 3) postnatal diagnosis of RS (Robin group) or cleft lip and palate (CLP group). Patients with postnatal RS without a palatal cleft were excluded. A control group with normal facial morphology was matched by gestational age. The outcome variable was tongue position at fetal MRI, described as within the cleft, along the floor of the mouth (normal), other, or indeterminate.

RESULTS

One hundred twenty-two patients with mean gestational age at MRI of 25.8 ± 4.9 weeks were included (Robin, n = 21 [17%]; CLP, n = 47 [39%]; control, n = 54 [44%]). The tongue was visualized within the palatal cleft in 76.2% of the Robin group and 4.3% of the CLP group. The tongue was found along the floor of the mouth (normal) in the remainder of the Robin and CLP groups and in 100% of the control group.

CONCLUSION

These findings suggest a relation between in utero tongue position and the development of cleft palate in RS.

Systems biology of facial development: contributions of ectoderm and mesenchyme

The rapid increase in gene-centric biological knowledge coupled with analytic approaches for genomewide data integration provides an opportunity to develop systems-level understanding of facial development. Experimental analyses have demonstrated the importance of signaling between the surface ectoderm and the underlying mesenchyme are coordinating facial patterning. However, current transcriptome data from the developing vertebrate face is dominated by the mesenchymal component, and the contributions of the ectoderm are not easily identified. We have generated transcriptome datasets from critical periods of mouse face formation that enable gene expression to be analyzed with respect to time, prominence, and tissue layer. Notably, by separating the ectoderm and mesenchyme we considerably improved the sensitivity compared to data obtained from whole prominences, with more genes detected over a wider dynamic range. From these data we generated a detailed description of ectoderm-specific developmental programs, including pan-ectodermal programs, prominence- specific programs and their temporal dynamics. The genes and pathways represented in these programs provide mechanistic insights into several aspects of ectodermal development. We also used these data to identify co-expression modules specific to facial development. We then used 14 co-expression modules enriched for genes involved in orofacial clefts to make specific mechanistic predictions about genes involved in tongue specification, in nasal process patterning and in jaw development. Our multidimensional gene expression dataset is a unique resource for systems analysis of the developing face; our co-expression modules are a resource for predicting functions of poorly annotated genes, or for predicting roles for genes that have yet to be studied in the context of facial development; and our analytic approaches provide a paradigm for analysis of other complex developmental programs.

Retinoid acid-induced microRNA-31-5p suppresses myogenic proliferation and differentiation by targeting CamkIIδ

BACKGROUND

We previously reported that Wnt5a/CaMKIIδ (calcium/calmodulin-dependent protein kinase II delta) pathway was involved in the embryonic tongue deformity induced by excess retinoic acid (RA). Our latest study found that the expression of miR-31-5p, which was predicted to target the 3'UTR of CamkIIδ, was raised in the RA-treated embryonic tongue. Thus, we hypothesized that the excess RA regulated Wnt5a/CaMKIIδ pathway through miR-31-5p in embryonic tongue.

METHODS

C2C12 myoblast line was employed as an in vitro model to examine the suppression of miR-31-5p on CamkIIδ expression, through which RA impaired the myoblast proliferation and differentiation in embryonic tongue.

RESULTS

RA stimulated the expression of miR-31-5p in both embryonic tongue and C2C12 myoblasts. Luciferase reporter assay confirmed that the 3'UTR of CamkIIδ was a target of miR-31-5p. MiR-31-5p mimics disrupted CamkIIδ expression, C2C12 proliferation and differentiation as excess RA did, while miR-31-5p inhibitor partially rescued these defects in the presence of RA.

CONCLUSIONS

Excess RA can stimulate miR-31-5p expression to suppress CamkIIδ, which represses the proliferation and differentiation of tongue myoblasts.

Development of mechanical papillae of the tongue in the domestic goose (Anser anser f. domestica) during the embryonic period

Three types of mechanical papillae, i.e., conical, filiform, and hair-like papillae, are present on the tongue in the domestic goose. Within conical papillae, we distinguish three categories: large and small conical papillae on the body and conical papillae on the lingual prominence. The arrangement of mechanical papillae on the tongue in Anseriformes is connected functionally with different feeding mechanisms such as grazing and filter-feeding. The present work aims to determine whether morphology of three types of mechanical papillae in goose at the time of hatching is the same as in an adult bird and if the tongue is prepared to fulfill feeding function. Our results revealed that the primordia of the large conical papillae start to develop during the differentiation stage. The primordia of the small conical papillae and conical papillae of the lingual papillae start to develop during the growth stage. At the end of the growth stage, only large conical papillae, three pairs of small conical papillae, and conical papillae of the lingual prominence have similar arrangement as in an adult bird. The shape and arrangement of the remaining small conical papillae probably will be changed after hatching. During embryonic period, the filiform papillae and hair-like papillae are not formed. The embryonic epithelium that covered the mechanical papillae undergoes transformation leading to the formation of multilayered epithelium. During prehatching stage, epithelium becomes orthokeratinized epithelium. In conclusion, the tongue of the domestic goose after hatching is well prepared only for grazing. The filtration of food from water is limited due to the lack of filiform papillae.

The Human KROX-26/ZNF22 Gene is Expressed at Sites of Tooth Formation and Maps to the Locus for Permanent Tooth Agenesis (He-Zhao Deficiency)

Tooth development is mediated by sequential and reciprocal interactions between dental epithelium and mesenchyme under the molecular control of secreted growth factors and responsive transcription factors. We have previously identified the transcription factor Krox-26 as a potential regulator of tooth formation in mice. The purpose of this study was to investigate a potentially similar role for the human KROX-26 orthologue. We cloned the KROX-26 gene and found its single mRNA transcript (2.4 kb) to be expressed in multiple adult tissues. During fetal development, KROX-26 is expressed in the epithelial component of the developing tooth organ during early bud and cap stages as well as in osteoblasts of craniofacial bone and the developing tongue. The KROX-26 gene was mapped to chromosome 10q11.21, a locus that has been associated with permanent tooth agenesis (He-Zhao deficiency). These results indicate a potential function for KROX-26 in the molecular regulation of tooth formation in humans.

Progress of Cell Proliferation in Striated Muscle Tissues during Development of the Mouse Tongue

The developmental stages of and places for the proliferation of tongue muscle cells have not yet been determined. To determine the stages of and places for proliferation between embryonic day (E) 9 and birth, we analyzed the expression of cyclin D1 mRNA and the immunolocalization for proliferating cell nuclear antigen (PCNA). The ratio of PCNA-positive nuclei to total nuclei (PCNA-labeling index) was obtained in the anterior, middle, and posterior regions. Cyclin D1 mRNA was highly expressed between E11 and E13, but decreased thereafter until birth. The distribution of PCNA-positive cell nuclei was consistent with that of myogenic cells in the occipital somites at E9. The PCNA-labeling index was highest at E11, then decreased until birth without a significant difference among the 3 regions. These findings suggest that some tongue muscle progenitor cells begin proliferation in the occipital somites at E9, and that the proliferation in the whole tongue region occurred most actively between E11 and E13, then decreased until birth without regional differences.

[Expressions of microtubule-associated protein 2 and nestin in the development of human embryo and fetal tongue muscles]

OBJECTIVE

To explore the role of microtubule-associated protein 2 (MAP-2) and nestin in the development of tongue muscles of human embryos and fetuses.

METHODS

PV immunohistochemistry was used to detect the expressions of MAP-2 and nestin proteins in the tongue tissues of human embryos and fetuses at the second, third and fourth months of gestation.

RESULTS

MAP-2 and nestin positivity was detected in the tongue muscles of human embryos at 2 to 4 months of gestation. In the embryos at the second month of gestation, no obvious MAP-2 positive cells were found in the tongue muscles; at 3 and 4 months, the number of MAP-2-positive cells in the tongue muscles was 24.14∓8.28 and 15.86∓3.89, with the expression intensity of 109.42∓11.62 and 124.27∓8.73, respectively. At 2, 3 and 4 months of gestation, the number of nestin-positive cells in the tongue muscles was 12.50∓3.17, 19.00∓7.63, and 22.80∓6.91, with expression intensity of 119.99∓24.02, 102.20∓11.76, and 98.24∓10.66, respectively. As the gestational age increased, the number of MAP-2-positive cell number continued to decline following a transient increase but the expression intensity kept increasing; nestin-positive cells increased continuously but the expression intensity kept decreasing in the embryonic or fetal tongue muscles.

CONCLUSION

MAP-2 and nestin proteins are involved in the regulation of the development of tongue muscles in human embryos and fetuses.

[Early morphogenesis of ciliated cells in human oral cavity]

Ciliated cells were found in the epithelium of the oral cavity of human embryos and fetuses starting from the seventh week of prenatal development. At the early stages of prenatal development (until the 13th week), cells with cilia cover most of the dorsal surface of the tongue and the soft palate, whereas they are found only near the gland ducts in the circumvallate and foliate lingual papillae after 17 weeks of development. The ultrastructure of the axoneme of cilia corresponds to the structure of motile cilia and is represented by nine microtubule doublets that surround the central pair of microtubule singlets. An immunohistochemical study performed on weeks 10-12 of development identified nerve endings associated with the ciliated cells. Until the 14th week of development, the cytoplasm of ciliated cells is immunopositive for NSE. The spatial distribution of ciliated cells in the tongue epithelium until the 13th week of development is not related to the morphogenesis of lingual papillae, and their role in the human oral cavity during the first trimester of pregnancy is unclear and requires further study.

[Expression of PCNA, C-fos and Bax proteins in human embryonic tongue tissues]

OBJECTIVE

To investigate of proliferating cell nuclear antigen (PCNA), C-fos and Bax proteins in human embryonic tongue tissue of different developmental stages.

METHODS

Immunohistochemistry was used to detect the expressions of PCNA, C-fos and Bax proteins in embryonic tongue tissues of fetuses with 2, 3 and 4 month gestational age (n=16). One-way ANOVA and LSD-t test were employed to compare the number of positive expression cells in tongue tissues of fetuses with different gestational age.

RESULTS

In the fetuses at 2, 3 and 4 months of gestation, the numbers of PCNA-positive cells in tongue epithelial tissues were 20.20 ± 7.13, 39.10 ± 13.44 and 26.00 ± 9.02, respectively; those in tongue muscle and fiber tissues were 17.20 ± 8.99, 22.30 ± 6.57 and 32.40 ± 14.72, respectively. In fetuses at 2 month of gestation, no C-fos-positive cells were found in tongue tissues; while at 3 and 4 months of gestation, the numbers of C-fos-positive cells in the tongue epithelial layers were 25.10 ± 7.91, 17.40 ± 2.80; those in tongue muscle and fiber tissues were 24.50 ± 4.67 and 28.00 ± 7.75, respectively. Only weak positive expression of Bax protein was observed in the third month of gestation in embryonic tongue tissues. A significant difference was noted in PCNA expression in tongue epithelial layers, the muscle and fiber tissues (P<0.01 and P<0.05) among 3 embryonic periods. A significant difference was found in C-fos expression in tongue epithelial layers (P<0.01), but not in tongue muscle and fiber tissues (P>0.05) among 3 periods.

CONCLUSION

Dynamic changes were seen in PCNA and C-fos expressions in embryonic tongue tissues in different gestational ages of fetus, indicating these two proteins may participate in regulation of the development and differentiation of tongue tissues in human embryos and fetuses.

Cell-autonomous and non-cell-autonomous roles for IRF6 during development of the tongue

Interferon regulatory factor 6 (IRF6) encodes a highly conserved helix-turn-helix DNA binding protein and is a member of the interferon regulatory family of DNA transcription factors. Mutations in IRF6 lead to isolated and syndromic forms of cleft lip and palate, most notably Van der Woude syndrome (VWS) and Popliteal Ptyerigium Syndrome (PPS). Mice lacking both copies of Irf6 have severe limb, skin, palatal and esophageal abnormalities, due to significantly altered and delayed epithelial development. However, a recent report showed that MCS9.7, an enhancer near Irf6, is active in the tongue, suggesting that Irf6 may also be expressed in the tongue. Indeed, we detected Irf6 staining in the mesoderm-derived muscle during development of the tongue. Dual labeling experiments demonstrated that Irf6 was expressed only in the Myf5+ cell lineage, which originates from the segmental paraxial mesoderm and gives rise to the muscles of the tongue. Fate mapping of the segmental paraxial mesoderm cells revealed a cell-autonomous Irf6 function with reduced and poorly organized Myf5+ cell lineage in the tongue. Molecular analyses showed that the Irf6−/− embryos had aberrant cytoskeletal formation of the segmental paraxial mesoderm in the tongue. Fate mapping of the cranial neural crest cells revealed non-cell-autonomous Irf6 function with the loss of the inter-molar eminence. Loss of Irf6 function altered Bmp2, Bmp4, Shh, and Fgf10 signaling suggesting that these genes are involved in Irf6 signaling. Based on these data, Irf6 plays important cell-autonomous and non-cell-autonomous roles in muscular differentiation and cytoskeletal formation in the tongue.

[Expressions of microtubule-associated protein 2 and nestin in the development of human embryo and fetal tongue muscles]

OBJECTIVE

To explore the role of microtubule-associated protein 2 (MAP-2) and nestin in the development of tongue muscles of human embryos and fetuses.

METHODS

PV immunohistochemistry was used to detect the expressions of MAP-2 and nestin proteins in the tongue tissues of human embryos and fetuses at the second, third and fourth months of gestation.

RESULTS

MAP-2 and nestin positivity was detected in the tongue muscles of human embryos at 2 to 4 months of gestation. In the embryos at the second month of gestation, no obvious MAP-2 positive cells were found in the tongue muscles; at 3 and 4 months, the number of MAP-2-positive cells in the tongue muscles was 24.14∓8.28 and 15.86∓3.89, with the expression intensity of 109.42∓11.62 and 124.27∓8.73, respectively. At 2, 3 and 4 months of gestation, the number of nestin-positive cells in the tongue muscles was 12.50∓3.17, 19.00∓7.63, and 22.80∓6.91, with expression intensity of 119.99∓24.02, 102.20∓11.76, and 98.24∓10.66, respectively. As the gestational age increased, the number of MAP-2-positive cell number continued to decline following a transient increase but the expression intensity kept increasing; nestin-positive cells increased continuously but the expression intensity kept decreasing in the embryonic or fetal tongue muscles.

CONCLUSION

MAP-2 and nestin proteins are involved in the regulation of the development of tongue muscles in human embryos and fetuses.

Bmp signalling in filiform tongue papillae development

OBJECTIVE

Tongue papillae are critical organs in mastication. There are four different types of tongue papillae; fungiform, circumvallate, foliate, and filiform papillae. Unlike the other three taste papillae, non-gustatory papillae, filiform papillae cover the entire dorsal surface of the tongue and are important structures for the mechanical stress of sucking. Filiform papillae are further classified into two subtypes with different morphologies, depending on their location on the dorsum of the tongue. The filiform papillae at the intermolar eminence have pointed tips, whereas filiform papillae with rounded tips are found in other regions (anterior tongue). It remains unknown how the shape of each type of filiform papillae are determined during their development. Bmp signalling pathway has been known to regulate mechanisms that determine the shapes of many ectodermal organs. The aim of this study was to investigate the role of Bmp signalling in filiform papillae development.

DESIGN

Comparative in situ hybridization analysis of six Bmps (Bmp2-Bmp7) and two Bmpr genes (Bmpr1a and Bmpr1b) were carried out in filiform papillae development. We further examined tongue papillae in mice over-expressing Noggin under the keratin14 promoter (K14-Noggin).

RESULTS

We identified a dynamic temporo-spatial expression of Bmps in filiform papillae development. The K14-Noggin mice showed pointed filiform papillae in regions of the tongue normally occupied by the rounded type.

CONCLUSIONS

Bmp signalling thus regulates the shape of filiform papillae.

Myosin heavy chain composition of the human genioglossus muscle

BACKGROUND

The human tongue muscle genioglossus (GG) is active in speech, swallowing, respiration, and oral transport, behaviors encompassing a wide range of tongue shapes and movement speeds. Studies demonstrate substantial diversity in patterns of human GG motor unit activation, but whether this is accompanied by complex expression of muscle contractile proteins is not known.

PURPOSE

The authors tested for conventional myosin heavy chain (MHC) MHCI, MHCIIA, MHCIIX, developmental MHCembryonic and MHCneonatal and unconventional MHCαcardiac, MHCextraocular, and MHCslow tonic in antero-superior (GG-A) and posterior (GG-P) adult human GG.

METHOD

SDS-PAGE, Western blot, and immunohistochemistry were used to describe MHC composition of GG-A and GG-P and the prevalence of muscle fiber MHC phenotypes in GG-A.

RESULTS

By SDS-PAGE, only conventional MHC are present with ranking from most to least prevalent MHCIIA > MHCI > MHCIIX in GG-A and MHCI > MHCIIA > MHCIIX in GG-P. By immunohistochemistry, many muscle fibers contain MHCI, MHCIIA, and MHCIIX, but few contain developmental or unconventional MHC. GG-A is composed of 5 phenotypes (MHCIIA > MHCI-IIX > MHCI > MHCI-IIA > MHCIIX). Phenotypes MHCI, MHCIIA, and MHCI-IIX account for 96% of muscle fibers.

CONCLUSIONS

Despite activation of GG during kinematically diverse behaviors and complex patterns of GG motor unit activity, the human GG is composed of conventional MHC isoforms and 3 primary MHC phenotypes.

Expression patterns of ubiquitin conjugating enzyme UbcM2 during mouse embryonic development

Ubiquitin conjugating enzyme UbcM2 (Ubiquitin-conjugating enzymes from Mice, the number reveals the identification order) has been implicated in many critical processes, such like growth-inhibiting, mediating cell proliferation and regulation of some transcription factor, but the expression profile during mouse embryo development remains unclear. Hereby, during mid-later embryonic stage, the expression patterns of UbcM2 were examined using in situ hybridization and quantitative real-time PCR (qRT-PCR). The signals were significantly intense in central nervous system and skeletal system, weak in tongue, heart, lung, liver, and kidney. In the central nervous system, UbcM2 was principally expressed in thalamus, external germinal layer of cerebellum (EGL), mitral cell layer of olfactory bulb, hippocampus, marginal zone and ventricular zone of cerebral cortex, and spinal cord. In the skeletal system, UbcM2 was primarily expressed in proliferating cartilage. Furthermore, qRT-PCR analysis displayed that the expression of UbcM2 was ubiquitous at E15.5, most prominent in brain, weaker in lung liver and kidney, accompanied by the lowest level in tongue and heart. During brain development, the expression level of UbcM2 first ascended and then decreased from E12.5 to E18.5, the peak of which sustained starting at E14.5 until E16.5. Together, these results suggest that UbcM2 may play potential roles in the development of mouse diverse tissues and organs, particularly in the development of brain and skeleton.

Separate and distinctive roles for Wnt5a in tongue, lingual tissue and taste papilla development

Although canonical Wnt signaling is known to regulate taste papilla induction and numbers, roles for noncanonical Wnt pathways in tongue and taste papilla development have not been explored. With mutant mice and whole tongue organ cultures we demonstrate that Wnt5a protein and message are within anterior tongue mesenchyme across embryo stages from the initiation of tongue formation, through papilla placode appearance and taste papilla development. The Wnt5a mutant tongue is severely shortened, with an ankyloglossia, and lingual mesenchyme is disorganized. However, fungiform papilla morphology, number and innervation are preserved, as is expression of the papilla marker, Shh. These data demonstrate that the genetic regulation for tongue size and shape can be separated from that directing lingual papilla development. Preserved number of papillae in a shortened tongue results in an increased density of fungiform papillae in the mutant tongues. In tongue organ cultures, exogenous Wnt5a profoundly suppresses papilla formation and simultaneously decreases canonical Wnt signaling as measured by the TOPGAL reporter. These findings suggest that Wnt5a antagonizes canonical Wnt signaling to dictate papilla number and spacing. In all, distinctive roles for Wnt5a in tongue size, fungiform papilla patterning and development are shown and a necessary balance between non-canonical and canonical Wnt paths in regulating tongue growth and fungiform papillae is proposed in a model, through the Ror2 receptor.

The inductive role of Wnt-β-Catenin signaling in the formation of oral apparatus

Proper patterning and growth of oral structures including teeth, tongue, and palate rely on epithelial-mesenchymal interactions involving coordinated regulation of signal transduction. Understanding molecular mechanisms underpinning oral-facial development will provide novel insights into the etiology of common congenital defects such as cleft palate. In this study, we report that ablating Wnt signaling in the oral epithelium blocks the formation of palatal rugae, which are a set of specialized ectodermal appendages serving as Shh signaling centers during development and niches for sensory cells and possibly neural crest related stem cells in adults. Lack of rugae is also associated with retarded anteroposterior extension of the hard palate and precocious mid-line fusion. These data implicate an obligatory role for canonical Wnt signaling in rugae development. Based on this complex phenotype, we propose that the sequential addition of rugae and its morphogen Shh, is intrinsically coupled to the elongation of the hard palate, and is critical for modulating the growth orientation of palatal shelves. In addition, we observe a unique cleft palate phenotype at the anterior end of the secondary palate, which is likely caused by the severely underdeveloped primary palate in these mutants. Last but not least, we also discover that both Wnt and Shh signalings are essential for tongue development. We provide genetic evidence that disruption of either signaling pathway results in severe microglossia. Altogether, we demonstrate a dynamic role for Wnt-β-Catenin signaling in the development of the oral apparatus.

Localization of keratins 13 and 14 in the lingual mucosa of rats during the morphogenesis of circumvallate papillae

We used fluorescence immunohistochemistry, analysis of differential interference contrast (DIC) images and confocal laser-scanning microscopy in the transmission mode, after staining specimens with toluidine blue, to examine the localization of keratin 13 (K13) and keratin 14 (K14) in the lingual epithelium of fetal and juvenile Sprague-Dawley rats during the prenatal and postnatal morphogenesis of circumvallate papillae. No immunoreactivity specific for K13 and K14 was detected in the lingual epithelium of fetuses on day 15 after conception (E15), at which time the primitive rudiment of the circumvallate papillae was detectable by the thickening of several layers of cuboidal epithelial cells. On E17 and E19, the developing circumvallate papillae were clearly recognizable, consisting of a central papilla and the surrounding sulcus. No immunoreactivity specific for K13 and K14 was evident in the lingual epithelium around these structures at this time. K14-specific immunoreactivity was first detected in the basal layer of the epithelium of the circumvallate papillae on postnatal day 0 (P0) and K13-specific immunoreactivity was detected on P7. Morphogenesis of the circumvallate papillae progressed significantly from P0 to P14, and immunoreactivity specific for K13 and K14 was clearly recognizable after P7. The respective patterns of K13-specific and K14-specific immunoreactivity differed during the development of the circumvallate papillae: K13-specific immunoreactivity was generally evident in cells of the intermediate layer of the epithelium, while K14-specific immunoreactivity was detected in cells of the basal and suprabasal layers. The present results are discussed in the context of the previously determined localization of K13 and K14 in the dorsal epithelium of the anterior part of the rat tongue during its morphogenesis.

ΔNp63 is an ectodermal gatekeeper of epidermal morphogenesis

p63, a member of p53 family, has a significant role in the development and maintenance of stratified epithelia. However, a persistent dispute remained over the last decade concerning the interpretation of the severe failure of p63-null embryos to develop stratified epithelia. In this study, by investigating both p63-deficient strains, we demonstrated that p63-deficient epithelia failed to develop beyond ectodermal stage as they remained a monolayer of non-proliferating cells expressing K8/K18. Importantly, in the absence of p63, corneal-epithelial commitment (which occurs at embryonic day 12.5 of mouse embryogenesis) was hampered 3 weeks before corneal stem cell renewal (that begins at P14). Taken together, these data illustrate the significant role of p63 in epithelial embryogenesis, before and independently of other functions of p63 in adult stem cells regulation. Transcriptome analysis of laser captured-embryonic tissues confirmed the latter hypothesis, demonstrating that a battery of epidermal genes that were activated in wild-type epidermis remained silent in p63-null tissues. Furthermore, we defined a subset of novel bona fide p63-induced genes orchestrating first epidermal stratification and a subset of p63-repressed mesodermal-specific genes. These data highlight the earliest recognized action of ΔNp63 in the induction epidermal morphogenesis at E11.5. In the absence of p63, a mesodermal program is activated while epidermal morphogenesis does not initiate.

Developmental expression of Bdnf, Ntf4/5, and TrkB in the mouse peripheral taste system

Brain-derived neurotrophic factor (BDNF), neurotrophin-4 (NT4), and their TrkB receptor regulate taste system development. To determine where and when gustatory neurons come in contact with these important factors, temporospatial expression patterns of Bdnf, Ntf4/5, and TrkB in the peripheral taste system were examined using RT-PCR. In the lingual epithelium, Ntf4/5 mRNA expression was higher than that of Bdnf at embryonic day 12.5 (E12.5), and the expression of both factors decreased afterwards. However, Ntf4/5 expression decreased at an earlier age than Bdnf. Bdnf and Ntf4/5 are expressed in equal amounts at E12.5 in geniculate ganglion, but Bdnf expression increased from E14.5 to birth, whereas Ntf4/5 expression decreased. These findings indicate that NT4 functions at early embryonic stages and is derived from different sources than Bdnf. TrkB expression in the geniculate ganglion is robust throughout development and is not a limiting factor for neurotrophin function in this system.

Differential Shh, Bmp and Wnt gene expressions during craniofacial development in mice

In this study, Bmp-4, Wnt-5a and Shh gene expressions were compared during early craniofacial development in mice by comparative non-isotopic in situ hybridization. Wild-type C57BL/6J mice were studied at various stages of embryonic development (from 8.5- to 13.5-day-old embryos--E8.5-13.5). During early odontogenesis, transcripts for Bmp-4, Shh and Wnt-5a were co-localised at the tooth initiation stage. At E8.5, Shh mRNA expression was restricted to diencephalon and pharyngeal endoderm. Before maxillae and mandible ossification, Bmp-4 and Wnt-5a signals were detected in the mesenchymal cells and around Meckel's cartilage. During palatogenesis, Shh was expressed only in the epithelium and Wnt-5a only in the mesenchyme of the elevating palatal shelves. During tongue development, Shh expression was found in mesenchyme, probably contributing to tongue miogenesis, while Wnt-5a signal was in the epithelium, possibly during placode development and papillae formation. Taken together, these findings suggest that Bmp-4, Shh and Wnt-5a gene expressions may act together on the epithelial-mesenchymal interactions occurring in several aspects of the early mouse craniofacial development, such as odontogenesis, neuronal development, maxillae and mandible ossification, palatogenesis and tongue formation.

[Bone morphogenetic protein-4 regulates embryonic tongue morphogenesis]

OBJECTIVE

To analyze the effect of Bone morphogenesis 4 and its antagonist Noggin on morphogenesis of tongue.

METHODS

Dissected rats to get embryonic day 13 (E13) tongues; fed E13 tongues in standard medium, BMP4 (0.03 mg/L, 0.3 mg/L, 1 mg/L), and the antgonist Noggin(1 mg/L, 3 mg/L, 10 mg/L) medium; cultured for 3 days; fixed samples, observed tongues with scanning electronic microscope (SEM); measured the whole tongue length, anterior 1/8, 1/4 width and middle width of cultured tongues and analyzed data with SPSS 10.0. To further study the effects of BMP4 on epithelial and mesenchymal cell proliferation, Affi-gel blue gel beads were applied. Beads were soaked in PBS and BMP4 (667 mg/L), and implanted in the E13 embryonic tongues; then after cultured in standard medium for 3 days, tongues were embedded in O.C.T. and cut into 12 microm series sections. Ki67 was detected by immunohistochemical method.

RESULTS

(1)Whole length of tongues changed greatly (P<0.05), the length was shortened in BMP4 groups (0.03 mg/L group 877.3+/-67.6 microm, 0.3 mg/L group 838.5+/-88.9 microm, 1 mg/L group 718.7+/-38.6 microm) compared with standard medium (1 037.8+/-126.2 microm), Noggin groups had no obvious change; the anterior 1/8 width of tongues changed significantly(P<0.05), the anterior 1/8 width was narrower in BMP4 groups (0.03 mg/L group 332.1+/-80.9 microm, 0.3 mg/L group 305.1+/-51.3 microm, 1 mg/L group 276.9+/-45.9 microm) compared with standard group(639.1+/-106.2 microm), except 10 mg/L group, Noggin groups were wider (1 mg/L group 815.5+/-90.3 microm, 3 mg/L group 857.6+/-87.1 microm, 10 mg/L group 807.1+/-113.8 microm); the anterior 1/4 width of tongue changed magnificently, also(P<0.05), BMP4 groups were narrower (0.03 mg/L group 421.3+/-43.8 microm, 0.3 mg/L group 407.3+/-15.6 microm, 1 mg/L group 363.7+/-24.7 microm) compared with standard group (653.7+/-101.6 microm), whereas, Noggin groups were wider greatly (1 mg/L group 838.0+/-130.5 microm, 3 mg/L group 947.2+/-34.9 microm, 10 mg/L group 889.4+/-74.6 microm); the middle width of tongue changed significantly(P<0.05), width of BMP4 groups were narrower (0.03 mg/L group 567.3+/-35.8 microm, 0.3 mg/L group 548.4+/-30.5 microm, 1 mg/L group 457.4+/-48.0 microm) compared with standard medium (683.1+/-79.8 microm), and Noggin groups had widening tendency, difference in 3 mg/L group is magnificent (1 mg/L group 776.2+/-134.1 microm, 3 mg/L group 964.3+/-44.3 microm, 10 mg/L group 777.2+/-46.7 microm). (2) The expression of Ki67 in both epithelium and mesenchym adjacent to BMP4 beads reduced greatly.

CONCLUSION

BMP4 could effect morphological development of embryonic tongue, which could change spatula-shape tongue into short, narrow and tip-point one, the antagonist Noggin tongue was wider and longer; BMP4 inhibit cell proliferation in embryonic tongues.

Skeletal units of the human embryonic mandible

The development of the mandible was traced on serial sections of 20 human embryos aged 5-8 weeks (developmental stages 13-23). Special consideration was given to the differentiation of skeletal units proposed by Sperber. The first skeletal units, namely the mandibular body, the alveolar unit and the condylar unit, may be distinguished in the 7(th) week. The primordia of all units are identified by the end of the embryonic period (8 weeks).

Structural diversification of the gustatory organs during metamorphosis in the alpine newt Triturus alpestris

Gustatory organs of the taste bud type occur in the epithelial lining of the oropharyngeal cavity of alpine newt larvae. They resemble the taste buds of bony fish, both in appearance (as revealed by scanning electron microscopy) and in detailed internal structure (seen on transmission electron micropscopy). During metamorphosis, at stage 55 of development, the secondary tongue (i.e. the soft tongue) is well formed and the anlages of taste discs are clearly apparent. Somewhat later, taste discs also appear in the epithelial lining outside the tongue, paralleling the disappearance of the taste buds. Well-developed taste discs of the newt differ from taste buds mainly by their structurally diversified set of 'associate cells' (mucous, wing and glial cells), which have no synaptic contact with nerve fibres. These cells accompany the neurosensory cellular components of the taste disc, i.e. the taste receptor cells and basal cells. This indicates that gustatory organs in metamorphosed newts, regardless of their small dimensions, fulfil the criteria established for taste discs previously defined in other Caudata and Anura species. Therefore, in the development of the newt there are two subsequent types of gustatory organs and two generations of the tongue: primary, in the larvae, and secondary, in metamorphosed animals.

Expression of keratin 14 in the basal cells of the lingual epithelium of mice during the morphogenesis of filiform papillae: visualization by fluorescent immunostaining and confocal laser-scanning microscopy in the transmission mode

We examined the expression of keratin 14 (K14) on the lingual epithelium by immunofluorescent staining while monitoring morphological changes in the filiform papillae of mice by confocal laser-scanning microscopy in the transmission mode of the same sections to define both the histology and the morphology of cells. It is difficult to visualize histological details of the fetal lingual epithelium of the mouse on semi-ultrathin sections by light microscopy after immunohistochemical staining because the histological structures in such sections cannot be distinguished by standard counterstaining. To solve this problem and to visualize the immunoreactivity specific for K14, we analyzed the results of immunofluorescent staining of semi-ultrathin sections in combination with an examination of the corresponding images by laser-scanning microscopy in the transmission mode after staining of specimens with toluidine blue. No immunoreactivity specific for K14 was detected on the lingual epithelium of fetuses on embryonic day 15 (E15), but immunoreactivity was distinct at all postnatal stages from postnatal day 0 (P0) to P21.

Mek1/2 MAPK kinases are essential for Mammalian development, homeostasis, and Raf-induced hyperplasia

The p42/p44 mitogen-activated protein kinase (MAPK) cascade includes Ras, Raf, Mek, and Erk MAPK. To determine the effect of a full knockout at a single level of this signaling pathway in mammals, and to investigate functional redundancy between Mek1 and Mek2, we disrupted these genes in murine and human epidermis. Loss of either protein alone produced no phenotype, whereas combined Mek1/2 deletion in development or adulthood abolished Erk1/2 phosphorylation and led to hypoproliferation, apoptosis, skin barrier defects, and death. Conversely, a single copy of either allele was sufficient for normal development. Combined Mek1/2 loss also abolished Raf-induced hyperproliferation. Human tissue deficient in either Mek isoform was normal, whereas loss of both proteins led to hypoplasia, which was rescued by active Erk2 expression. These data indicate that Mek1/2 are functionally redundant in the epidermis, where they act as a linear relay in the MAPK pathway to mediate development and homeostasis.

BMP2, BMP4, and their receptors are expressed in the differentiating muscle tissues of mouse embryonic tongue

To investigate the role of bone morphogenetic proteins (BMPs) in the differentiation process of skeletal muscle, we analyzed the in vivo expression of BMP2 and BMP4, of BMP receptors (BMPR) IA, IB, and II, and of activin receptors (ActR) IA, II, and IIB in mouse tongue muscle between embryonic day 11 (E11) and E17. The mRNA expression levels for BMP2 were 5-fold to 11-fold greater than those for BMP4 between E13 and E17 (P < 0.05-0.01). Expression of the BMP2, BMPRIB, ActRIA, ActRII, and ActRIIB proteins was first observed at E13. Expression of BMP2 and BMPRIB was detected in the whole area of the differentiating muscle tissues identified by immunostaining for fast myosin heavy chain (fMHC), but that of ActRIA, ActRII, and ActRIIB was detected only in the peripheral area of the differentiating muscle tissues. In the E15 tongue, all of the BMPs, BMPRs, and ActRs studied herein were expressed in the whole area of the differentiating muscle tissues identified by immunostaining for fMHC. These results suggest that BMPs play a role in the differentiation of tongue muscle tissues at E15 but have little or no effect at E13.

Development of fungiform papillae: patterned lingual gustatory organs

The fungiform papilla is a gustatory organ that provides a specific tissue residence for taste buds on the anterior tongue. Thus, during development there must be a progressive differentiation to acquire papilla epithelium, then taste cell progenitor epithelium, and finally taste cells within the papilla apex. Arranged in rows, the patterned distribution of fungiform papillae requires molecular regulation not only to induce papillae, but also to suppress papilla formation in the between-papilla tissue. Intact sensory innervation is not required to initiate papilla development or pattern. However, members of several molecular families have now been identified with specific localization in developing papillae. These may participate in papilla development and pattern formation, and subsequently in taste progenitor and taste cell differentiation. This review focuses on development of fungiform papillae in embryonic rat and mouse. Basic morphology, cell biology and molecular phenotypes of developing papillae are reviewed. Regulatory roles for molecules in several families are presented, and a broad schema is proposed for progressive epithelial differentiation to form taste cell progenitors in parallel with the temporal course, and participation of lingual sensory innervation.

Aglossia: a case report

A female child of 4 years with congenital absence of tongue has been described. This anomaly is usually associated with other congenital defects particularly limb and other cranio-facial defects. But in this case, the child enjoys the normal life, the unusual absence of tongue; she used to go to school play around with her friends and had a comparable I.Q.

Functional redundancy of NSCL-1 and NeuroD during development of the petrosal and vestibulocochlear ganglia

To study the role of different members of the bHLH gene family for sensory organ development we have generated NSCL-1 and NeuroD compound-mutant mice. Double homozygous animals were characterized by a more severe reduction of the petrosal and vestibulocochlear ganglia than NeuroD-knockout mice. The more severe reduction of the petrosal and vestibulocochlear ganglia in double-knockout mice indicates overlapping functions of the two genes during neuronal development. Interestingly, we also found that the two genes are jointly regulated by thyroid hormone during sensory hair cell development. We further present a detailed expression analysis of NSCL-1 and NSCL-2 during sensory neuron development. NSCL-1 expression was detected in all developing cranial ganglia including the petrosal and vestibulocochlear ganglion, in inner and outer hair cells of the organ of Corti and in hair cells of the vestibular system. Expression domains in other sensory structures include the retina, Merkel cells of the developing skin and sensory cells of the tongue. The expression of NSCL-2 was restricted to developing cranial ganglia, the retina and the vestibular nerve. Both NSCL-1 and NSCL-2 genes are active only in postmitotic neurons, indicating a role for neuronal cell migration and/or differentiation within the sensory system.

Sox2 is required for development of taste bud sensory cells

Sox2 is expressed in basal epithelial cells of the tongue, with high levels in taste bud placodes, fungiform papillae, and mature taste cells, and low levels in filiform papillae. High Sox2 expression appears to lie downstream from canonical Wnt signaling. In hypomorphic Sox2(EGFP/LP) embryos, placodes form but no mature taste buds develop. In contrast, transgenic overexpression of Sox2 in the basal cells inhibits differentiation of filiform keratinocytes. Together, our loss-of-function and gain-of-function studies suggest that Sox2 functions in a dose-dependent manner to regulate the differentiation of endodermal progenitor cells of the tongue into taste bud sensory cells versus keratinocytes.

Immunohistochemical detection of epidermal growth factor and epidermal growth factor receptor in the lingual mucosa of rats during the morphogenesis of filiform papillae

We examined the immunofluorescence labelling epidermal growth factor (EGF) and epidermal growth factor receptor (EGFR), as well as differential interference contrast (DIC) images, during the morphogenesis of filiform papillae and the keratinization of the lingual epithelium of rats on semi-ultrathin sections of epoxy resin-embedded samples using laser-scanning microscopy. We also examined semi-ultrathin sections of epoxy resin-embedded, toluidine blue-stained samples by light microscopy to obtain details of cell histology and morphology. No immunoreactivity specific for EGF and EGFR was detected on the lingual epithelium of fetuses on days 12 and 16 after conception (E12 and E16), during which time the number of layers of cuboidal cells in the lingual epithelium increased from one to several. Immunoreactivity specific for EGF and EGFR was first detected on the lingual epithelium of fetuses at birth or on postnatal day 0 (P0). Immunoreactivity specific both for EGF and EGFR appeared in the connective tissue and the basal cells of the papillary and interpapillary cell columns. The lingual epithelium was composed of stratified squamous cells. The rudiments of filiform papillae were compactly arranged and interpapillary cell columns were very narrow. Immunoreactivity specific for EGF and EGFR was distinct on the cell membrane of basal cells of the papillary cell column and weakly positive on the cell membrane of basal cells of the interpapillary cell column on postnatal day 21 (P21). Thus, the patterns of immunoreactivity of EGF and EGFR differed as the filiform papillae developed. Filiform papillae developed gradually from P0 to P21. The width of interpapillary spaces also increased during this period. These observations indicate a possibility that EGF might affect the expression of keratins in the lingual epithelium via epithelium-mesenchymal interactions.

Refinement of innervation accuracy following initial targeting of peripheral gustatory fibers

During development, axons of the chorda tympani nerve navigate to fungiform papillae where they penetrate the lingual epithelium, forming a neural bud. It is not known whether or not all chorda tympani axons initially innervate fungiform papillae correctly or if mistakes are made. Using a novel approach, we quantified the accuracy with which gustatory fibers successfully innervate fungiform papillae. Immediately following initial targeting (E14.5), innervation was found to be incredibly accurate: specifically, 94% of the fungiform papillae on the tongue are innervated. A mean of five papillae per tongue were uninnervated at E14.5, and the lingual tongue surface was innervated in 17 places that lack fungiform papillae. To determine if these initial errors in papillae innervation were later refined, innervation accuracy was quantified at E16.5 and E18.5. By E16.5 only two papillae per tongue remained uninnervated. Innervation to inappropriate regions was also removed, but not until later, between E16.5 and E18.5 of development. Therefore, even though gustatory fibers initially innervate fungiform papillae accurately, some errors in targeting do occur that are then refined during later embryonic periods. It is likely that trophic interactions between gustatory neurons and developing taste epithelium allow appropriate connections to be maintained and inappropriate ones to be eliminated.

Anatomic study of tongue architecture based on fetal histological sections

Tongue muscles are difficult to study by dissection and imaging methods because of the intermeshing of the muscular fibers. The study of the architecture of the tongue was based on 853 tongue sections of a fetus aged 32 weeks after conception. The analysis of the sections allowed demonstration of the different intrinsic and extrinsic muscles of the tongue, to determine their situation from the palatoglossus arch to the apex of the tongue. The tongue muscles are organized in different layers from cranial to caudal and from lateral to medial, one medial for the genioglossus muscle, one paramedial for the hyoglossus, the styloglossus and the inferior longitudinal muscles. In the anterior third of the tongue, the muscles presented a concentric organization.

Jag2-Notch1 signaling regulates oral epithelial differentiation and palate development

During mammalian palatogenesis, palatal shelves initially grow vertically from the medial sides of the paired maxillary processes flanking the developing tongue and subsequently elevate and fuse with each other above the tongue to form the intact secondary palate. Pathological palate-mandible or palate-tongue fusions have been reported in humans and other mammals, but the molecular and cellular mechanisms that prevent such aberrant adhesions during normal palate development are unknown. We previously reported that mice deficient in Jag2, which encodes a cell surface ligand for the Notch family receptors, have cleft palate associated with palate-tongue fusions. In this report, we show that Jag2 is expressed throughout the oral epithelium and is required for Notch1 activation during oral epithelial differentiation. We show that Notch1 is normally highly activated in the differentiating oral periderm cells covering the developing tongue and the lateral oral surfaces of the mandibular and maxillary processes during palate development. Oral periderm activation of Notch1 is significantly attenuated during palate development in the Jag2 mutants. Further molecular and ultrastructural analyses indicate that oral epithelial organization and periderm differentiation are disrupted in the Jag2 mutants. Moreover, we show that the Jag2 mutant tongue fused to wild-type palatal shelves in recombinant explant cultures. These data indicate that Jag2-Notch1 signaling is spatiotemporally regulated in the oral epithelia during palate development to prevent premature palatal shelf adhesion to other oral tissues and to facilitate normal adhesion between the elevated palatal shelves.

Expression of keratin 18 in the periderm cells of the lingual epithelium of fetal rats: visualization by fluorescence immunohistochemistry and differential interference contrast microscopy

We examined the expression of keratin 18 (K18), by immunofluorescence staining, while monitoring morphological changes in the periderm on the lingual epithelium of rats by laser-scanning microscopy of epoxy resin-embedded, semi-ultrathin sections. We also examined differential interference contrast (DIC) images of the same sections to define the histology and morphology of the cells. It is difficult to visualize histological details of the fetal lingual epithelium of the rat on semi-ultrathin sections by light microscopy after immunohistochemical staining, because the histological structures in such sections cannot be distinguished by standard counterstaining. To solve this problem and to visualize keratin 18 (K18), we used a combination of immunofluorescence staining of semi-ultrathin sections and corresponding differential contrast (DIC) images, obtained by laser-scanning microscopy.

Origin of the styloglossus muscle in the human fetus

The origin of the styloglossus muscle was histologically studied bilaterally in nine human fetuses (18 sides). In all cases, the muscle originated in Reichert's cartilage, which gives rise to the temporal styloid process. We identified three types of variation: type A, an accessory muscle fascicle originating from the mandibular angle, found in 7 cases (12 sides); type B, where the styloglossus muscle was attached to the mandibular angle by fibrous tracts, found in three cases (4 sides); and type C, where an accessory muscle fascicle arose from the fibrous tract connecting Reichert's cartilage to the mandibular angle; found in one case. In all cases (2 sides), the styloglossus muscle was innervated by the hypoglossal nerve. Relationships between the styloglossus muscle and vasculonervous elements of the prestyloid and retrostyloid spaces were analysed.

Sex differences in prenatal oral-motor function and development

The aim of this study was to investigate sex-related differences in the prenatal development of early oral, lingual, pharyngeal, and laryngeal motor activities. Sonographic images of oral-upper airway regions were observed in 85 healthy fetuses (43 males, 42 females; mean gestational age 24wks 3d [SD 0.69]; range 15-38wks). Biometric data on morphologic development and associated motor patterns were compared across second and third trimesters. Results showed that while males and females demonstrated statistically similar patterns of general physical growth (p>0.05), significant differences in development of specific lingual and pharyngeal structures were present (p<0.05). Significant differences were found for laryngeal and pharyngeal motor activity, and oral-lingual movements (p<0.05). Complex oral-motor and upper airway skills emerged earlier in females, suggesting a sex-specific trajectory of motor development. It was concluded that differential patterns of prenatal motor development may be important in defining sex-specific indices of oral skill maturation.

Bone morphogenetic proteins and noggin: inhibiting and inducing fungiform taste papilla development

Fungiform papillae are epithelial specializations that develop in a linear pattern on the anterior mammalian tongue and differentiate to eventually contain taste buds. Little is known about morphogenetic and pattern regulation of these crucial taste organs. We used embryonic rat tongue, organ cultures to test roles for bone morphogenetic proteins, BMP2, 4 and 7, and antagonists noggin and follistatin, in development of papillae from a stage before morphological initiation (E13) or from a stage after the pre-papilla placodes have formed (E14). BMPs and noggin proteins become progressively restricted to papilla locations during tongue development. In E13 cultures, exogenous BMPs or noggin induce increased numbers of fungiform papillae, in a concentration-dependent manner, compared to standard tongue cultures; BMPs, but not noggin, lead to a decreased tongue size at this stage. In E14 cultures, however, exogenous BMP2, 4 or 7 each inhibits papilla formation so that there is a decrease in papilla number. Noggin substantially increases number of papillae in E14 cultures. Using beads for a highly localized protein delivery, papillae are inhibited in the surround of BMP-soaked beads and induced in large clusters around noggin-soaked beads. Follistatin, presented in culture medium or by bead, does not alter papilla formation or number. In all fungiform papillae that form under various culture conditions, the molecular marker, sonic hedgehog, is within each papilla. However, the BMP inhibitory effect on papillae is not prevented by disrupting sonic hedgehog signaling through addition of cyclopamine to cultures. BMPs and noggin alter cell proliferation in tongue epithelium in opposite ways, demonstrated with Ki67 immunostaining. We propose that the BMPs and noggin, colocalized within papilla placodes and the fungiform papillae per se, have opposing inhibitory and activating or inducing roles in papilla development in linear patterns. We present a model for these effects.

Sox9 mRNA expression in the developing palate and craniofacial muscles and skeletons

BACKGROUND

SOX9 is a critical transcription factor for chondrogenesis and sex determination. Haploinsufficiency mutations of Sox9 in humans lead to campomelic dysplasia. Inactivation of Sox9 in the craniofacial region of mice results in an absence of endochondral bones and in malformation of other structures. This suggests that Sox9 plays multiple roles in craniofacial development and these remain to be elucidated. In order to study the functions of Sox9 in craniofacial development, a preliminary expression examination was performed.

MATERIAL AND METHODS

To detect the expression of Sox9 mRNA, antisense riboprobe was synthesized by in vitro transcription. Radioactive in situ hybridization was performed on sagittal and coronal sections of mice head from organogenesis to the early postnatal stage.

RESULTS

It was found that Sox9 was expressed in multiple stages and distinct processes. Besides the expression in cartilage, it was seen in the fusing stage of palatogenesis. Sox9 was also present during differentiation and maturation of craniofacial muscles. In addition, it was observed in intramembranous skeletal elements at restricted sites and stage.

CONCLUSIONS

The expression pattern suggests that Sox9 serves broad roles in craniofacial development.

Association of Shh and Ptc with keratin localization in the initiation of the formation of circumvallate papilla and von Ebner's gland

The development of gustatory papillae in mammalian embryos requires the coordination of a series of morphological events, such as proliferation, differentiation and innervation. In mice, the circumvallate papilla (CVP) is a specialized structure that develops in a characteristic spatial and temporal pattern in the posterior region of the tongue dorsal surface. The distinct expression patterns of Shh and Ptc, which play important roles in the development of other epithelial appendages, have been localized in the trench wall that gives rise to von Ebner's gland (VEG). To define the cellular mechanisms responsible for morphogenesis and differentiation during early development of CVP and VEG, the localization patterns of keratins (cytokeratins) K7, K8, K18, K19, K14 and connexin-43, which are dependent on Shh expression in other developmental systems, have been examined in detail. The distinct localization of keratins K7, K8, K18, K19, K14 and connexin-43 in the epithelium giving rise to the CVP and VEG suggests that cytodifferentiation is established prior to morphological changes. Interestingly, the localization of proliferating cell nuclear antigen, a marker for cell proliferation, is similar to that of Shh. An understanding of the regulatory roles of cell-cell interactions and signalling molecules in orchestrating a mutual network will bring us nearer to defining the molecular and cellular mechanisms underlying morphogenesis in mammalian taste bud development.

Epithelial overexpression of BDNF and NT4 produces distinct gustatory axon morphologies that disrupt initial targeting

Most fungiform taste buds fail to become innervated when BDNF or NT4 is overexpressed in the basal layer of tongue epithelium. Here, we examined when and how overexpression of BDNF and NT4 disrupt innervation to fungiform papillae. Overexpression of either factor disrupted chorda tympani innervation patterns either before or during the initial innervation of fungiform papillae. NT4 and BDNF overexpression each disrupted initial innervation by producing different gustatory axon morphologies that emerge at distinct times (E12.5 and E14.5, respectively). Chorda tympani nerve branching was reduced in NT4 overexpressing mice, and neuronal fibers in these mice were fasciculated and remained below the epithelial surface, as if repelled by NT4 overexpression. In contrast, many chorda tympani nerve branches were observed near the epithelial surface in mice overexpressing BDNF, and most were attracted to and invaded non-taste filiform papillae instead of gustatory papillae. These results suggest that BDNF, but not NT4, normally functions as a chemoattractant that allows chorda tympani fibers to distinguish their fungiform papillae targets from non-gustatory epithelium. Since BDNF and NT4 both signal through the p75 and TrkB receptors, trophin-specific activation of different internal signaling pathways must regulate the development of the distinct gustatory axon morphologies in neurotrophin-overexpressing mice.

Immunohistochemical expression of keratins 13 and 14 in the lingual epithelium of rats during the morphogenesis of filiform papillae

We examined the immunofluorescence of keratins 13 (K13) and 14 (K14) and differential interference contrast (DIC) images during the morphogenesis of filiform papillae and the keratinization of the lingual epithelium of rats on semi-ultrathin sections of epoxy resin-embedded samples by laser-scanning microscopy. We also examined semi-ultrathin sections of epoxy resin embedded, toluidine blue stained samples by light microscopy to obtain details of cell histology and morphology. No immunoreactivity specific for K13 and K14 was detected on the lingual epithelium of foetuses on days 13, 15 and 17 after conception (E13, E15 and E17), during which time the number of layers of cuboidal cells in the lingual epithelium increased from one to several. Immunoreactivity specific for K13 and K14 was first detected on the lingual epithelium of foetuses on E19. The immunoreactivity specific for K13 appeared in the suprabasal cells of the papillary and interpapillary cell columns and immunoreactivity specific for K14 was detected in the basal and suprabasal cells of the papillary and interpapillary cell columns. The lingual epithelium was composed of stratified squamous cells. The rudiments of filiform papillae were compactly arranged and interpapillary cell columns were very narrow. Filiform papillae developed gradually from postnatal day 0 (PO) to 21 (P21). The width of interpapillary spaces also increased during this period. Immunoreactivity specific for K13 and K14 was distinct at all postnatal stages examined. Thus, the patterns of immunoreactivity of K13 and K14 differed as the filiform papillae developed.