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.