[Ontogeny of the jaw]

Four pairs of branchial arch appear apparently in the neck region of human embryo about 32 days after fertilization. Maxillary prominence of the first branchial arch gives rise to the maxilla and zygomatic bone etc., and mandibular prominence forms the mandible and so on. Muscles for mastication are also derived from 1st branchial arch, into which fifth cranial nerves grow from the brain. Thus, human embryo improves the 1st branchial arches into the upper and lower jaws, and forms digestive organs needed for intake, mastication, and swallowing of foods. Finally they develop the brain for integral treatment of sensory information from eyes, tongue, nose, and ears.

Live view of gonadotropin-releasing hormone containing neuron migration

Neurons that synthesize GnRH control the reproductive axis and migrate over long distances and through different environments during development. Prior studies provided strong clues for the types of molecules encountered and movements expected along the migratory route. However, our studies provide the first real-time views of the behavior of GnRH neurons in the context of an in vitro preparation that maintains conditions comparable to those in vivo. The live views provide direct evidence of the changing behavior of GnRH neurons in their different environments, showing that GnRH neurons move with greater frequency and with more changes in direction after they enter the brain. Perturbations of guiding fibers distal to moving GnRH neurons in the nasal compartment influenced movement without detectable changes in the fibers in the immediate vicinity of moving GnRH neurons. This suggests that the use of fibers by GnRH neurons for guidance may entail selective signaling in addition to mechanical guidance. These studies establish a model to evaluate the influences of specific molecules that are important for their migration.

Early development of the nose in human embryos: a stereomicroscopic and histologic analysis

OBJECTIVES/HYPOTHESIS

To analyze the morphologic features of the nose in the human embryo from the 4th to 8th developmental week according to Carnegie stage.

STUDY DESIGN

Stereomicroscopic and histologic analysis of the morphology of the human embryo.

METHODS

A total of 27 cases of embryos, ranging from Carnegie stage 13 to 23, were analyzed. The external morphology was observed with a stereomicroscope, photographed, and analyzed. The histologic features were observed with a light microscope in the horizontally transected specimens stained with hematoxylin-eosin.

RESULTS

The nasal placode was observed in stage 13, and it became flat or even concave in stage 14. In stage 15, the nasal pit was formed. In stage 16, the nasal sac and nasal fin were observed. In stage 17, the oronasal membrane was formed by thinning of the nasal fin. In stage 18, the primitive choana was established by a rupture of the oronasal membrane. In stage 19, the lateral palatine process projected vertically below the level of the tongue. The cartilaginous nasal capsule was formed in stage 20. In stage 21, the olfactory area was localized to the upper portion of the lateral nasal wall and the nasal septum. In stage 22, the lateral palatine process developed in a somewhat horizontal orientation. In stage 23, the premaxilla and primitive choana were formed.

CONCLUSIONS

The development of the nose is most active from Carnegie stage 13 to 19, which corresponds to the end of the fourth embryonic week to the end of the seventh week. Thus, this period is considered to be the most important period in human nasal embryonic development.

Functional matrix cleft repair: principles and techniques

As an application of developmental anatomy, functional matrix cleft repair has scientific value. It tests out many aspects of periosteal physiology, and it is based squarely on concepts central to orthodontics. The "molecular revolution" has melded together developmental anatomy and genetics to create a new and clinically relevant model of facial development. This article outlines the scientific rationale for cleft repair based on this model.

Nasal capsular cartilage is required for rat transpalatal suture morphogenesis

In the cranial vault, suture morphogenesis occurs when the growing cranial bones approximate and overlap or abut one another. Patency of developing sutures is regulated by the underlying dura mater. Once cranial sutures form, bone growth proceeds from the sutures in response to growth signals from the rapidly expanding neurocranium. Facial sutures do not develop in contact with the dura mater. It was therefore hypothesized that facial suture morphogenesis and bone growth from facial sutures are regulated by tissues with an equivalent role to the dura mater. The present study was designed to test this hypothesis by characterizing the morphology and growth factor expression in developing transpalatal (TP) sutures and their surrounding tissues, and then assessing the role of the overlying nasal capsular (NC) cartilages in maintaining suture patency. TP sutures develop as overlapping sutures, similar to cranial coronal sutures, and expression of Tgf-betas in TP sutures was similar to their distribution in cranial coronal sutures. To establish whether NC cartilages play a role in regulating TP suture morphogenesis, fetal rat TP sutures were cultured with associated attached NC cartilages or with NC cartilages removed. Sutures cultured for upward of 5 days with intact NC cartilages remained patent and maintained their cellular and fibrous components. However, in the absence of NC cartilages, the cellular nature of the sutures was not maintained and they became progressively acellular, with bony bridging across the suture. This finding is similar to that for cranial vault sutures cultured in the absence of dura mater, indicating that NC cartilages play an equivalent role to dura mater in maintaining the patency of developing sutures. These studies indicate that tissue interactions likely regulate morphogenesis of all cranial and facial sutures.

Proboscis lateralis: a report of two cases

Proboscis Lateralis (PL) is one of the congenital anomalies of the nose which presents as obvious deformity. This is a report of two cases of the rare anomaly PL. One presented with right PL and the second presented with left PL. In this rare anomaly, the nasal cavity on one side is completely normal while on the affected side, the nasal cavity is replaced by a tube of skin and soft tissue attached to the inner canthus of the eye. This anomaly occurs sporadic as an isolated defect or in association with other anomalies. It is usually associated with failure of the paranasal sinuses and the nasolacrimal duct development. Embryologically, this anomaly is a result of imperfect fusion of the lateral nasal wall and maxillary processes (Int. J. Pediatr. Otorhinolaryngol. 23 (1992) 275).

Congenital nasal anomalies: a classification scheme

The purpose of this work was to develop a simple yet comprehensive classification scheme dedicated to congenital nasal anomalies. To date, no such classification system has been proposed and widely used. A 22-year retrospective review was performed. Two hundred sixty-one patients with congenital nasal anomalies were identified. From this extensive database, a systematic morphogenic classification system was devised. Congenital nasal deformities were classified into four categories. Type I, hypoplasia and atrophy, represents paucity, atrophy, or underdevelopments of skin, subcutaneous tissue, muscle, cartilage, and/or bone. Type II, hyperplasia and duplications, representing anomalies of excess tissue, ranging from duplications of parts to complete multiples, are categorized here. In the type III category, clefts, the comprehensive and widely utilized Tessier classification of craniofacial clefts is applied. Type IV deformities consist of neoplasms and vascular anomalies. Both benign and malignant neoplasms are found in this category.

Six1controls patterning of the mouse otic vesicle

Six1 is a member of the Six family homeobox genes, which function as components of the Pax-Six-Eya-Dach gene network to control organ development. Six1 is expressed in otic vesicles, nasal epithelia,branchial arches/pouches, nephrogenic cords, somites and a limited set of ganglia. In this study, we established Six1-deficient mice and found that development of the inner ear, nose, thymus, kidney and skeletal muscle was severely affected. Six1-deficient embryos were devoid of inner ear structures, including cochlea and vestibule, while their endolymphatic sac was enlarged. The inner ear anomaly began at around E10.5 and Six1was expressed in the ventral region of the otic vesicle in the wild-type embryos at this stage. In the otic vesicle of Six1-deficient embryos,expressions of Otx1, Otx2, Lfng and Fgf3,which were expressed ventrally in the wild-type otic vesicles, were abolished,while the expression domains of Dlx5, Hmx3, Dach1and Dach2, which were expressed dorsally in the wild-type otic vesicles, expanded ventrally. Our results indicate that Six1functions as a key regulator of otic vesicle patterning at early embryogenesis and controls the expression domains of downstream otic genes responsible for respective inner ear structures. In addition, cell proliferation was reduced and apoptotic cell death was enhanced in the ventral region of the otic vesicle, suggesting the involvement of Six1 in cell proliferation and survival. In spite of the similarity of otic phenotypes of Six1- and Shh-deficient mice, expressions of Six1 and Shhwere mutually independent.

The prenatal development of the human cerebellar field in Down syndrome

OBJECTIVES

To describe the development of the osseous field enclosing the cerebellum and part of the brain stem (the neuro-osteological cerebellar field) in Down syndrome, and compare the development with normal developmental standard of the field.

DESIGN

Radiographic, cephalometric and histologic examination of 58 legally or spontaneously aborted Down syndrome prenatal human fetuses; crown-rump length of 80-255 mm and approximate gestational age from 13 to 26 weeks.

RESULTS

The growth of the Down syndrome cerebellar field is smaller in the sagittal and vertical directions than in normal fetuses.

CONCLUSION

In the present study the pathological development of the cerebellar field was described in a genotypic sample. In combining normal and pathological development of neural and osseous tissues a better understanding of the genotype/phenotype interactions is attainable and fields of common gene expression maybe defined.

Developmental distribution of coxsackie virus and adenovirus receptor localized in the nervous system

Mouse coxsackie virus and adenovirus receptor (mCAR), which was isolated from the nerve growth cone-enriched fraction of newborn mouse brains, is a member of immunoglobulin-super family, and functions as a homophilic adhesion molecule. We observed the expression of mCAR in embryos to adult tissues by means of immunohistochemical analysis with a peptide antibody. mCAR expression was first detected in the embryonic ectoderm in the uterus on embryonic day 6.5 (E6.5). Then it was strongly expressed in the neuroepithelium of the neural tube, the developing brain and the spinal cord from E8.5 to postnatal day 7 (P7), in the cranial motor nerves from E9.5 to E11.5, and in the optic nerve from E13.5 to P7, which agrees with periods of their respective morphogenetic peaks. This expression of mCAR decreased postnatally and was absent in adult tissues. We found that mCAR occurred in a few proliferating cells of the hippocampal dentate gyrus, the subventricular zone (SVZ) of the lateral ventricles, and the rostral migratory stream (RMS) over P21. These observations demonstrate that mCAR was expressed characteristically in the immature neuroepithelium including progenitor cells or radial cells derived from the neural tube and in immature cells in a selected germinal zone of the mature brain. Based on our findings, we propose that mCAR is involved in migration and fasciculation during a restricted period as an adhesion molecule.

Ultrastructural characterization of the mesenchyme of the facial processes during development of the rat intermaxillary segment

This study quantifies ultrastructural changes within the mesenchyme of the maxillary and medial/lateral nasal processes before and after formation of the intermaxillary segment. At both day 11 and day 13 of development, 4 fetal rat heads were fixed with 3% glutaraldehyde and processed for electron microscopy. Differences between cells within the facial processes were discerned at day 11 of gestation. Significantly more rough endoplasmic reticulum was present in the cells of the maxillary processes than in the lateral nasal processes (p < .05), and a greater number of cell projections was found in the maxillary processes than in the medial nasal processes (p < .05). At day 13, no significant differences were found in the facial processes. Of particular note, a consistent increase in the number of cell projections within all the facial processes was found on day 13 when compared with day 11 (p < .05). This change may be related to intercellular signaling between the mesenchymal cells at the time of onset of major histogenic changes.

Functional analysis of chicken Sox2 enhancers highlights an array of diverse regulatory elements that are conserved in mammals

Sox2 expression marks neural and sensory primordia at various stages of development. A 50 kb genomic region of chicken Sox2 was isolated and scanned for enhancer activity utilizing embryo electroporation, resulting in identification of a battery of enhancers. Although Sox2 expression in the early embryonic CNS appears uniform, it is actually pieced together by five separate enhancers with distinct spatio-temporal specificities, including the one activated by the neural induction signals emanating from Hensen's node. Enhancers for Sox2 expression in the lens and nasal/otic placodes and in the neural crest were also determined. These functionally identified Sox2 enhancers exactly correspond to the extragenic sequence blocks conspicuously conserved between chicken and mammals, which are not discernible by sequence comparison among mammals.

Frontonasal dysplasia in 3H1 Br/Br mice

The adult Brachyrrhine (3H1 Br/+) mouse displays severe midfacial retrognathia, with a "pugnose" external appearance, but information concerning craniofacial morphology of the homozygote (3H1 Br/Br) mutant is lacking. This study characterized craniofacial phenotype and genotypic features of the homozygous condition. Segregation analysis was performed by phenotypic scoring of offspring from 3H1 Br/+ reciprocal matings. Whole-mount staining was undertaken to determine the presence or absence of cranial base structures in newborn and adult mice, while features of cranial base chondrification were examined using light microscopy and type II collagen immunohistochemistry. Karyotype analysis was performed to determine whether gross chromosomal aberrations were present. Finally, microsatellite mapping analysis was undertaken to provide further resolution of the Br locus. Results showed that Br was inherited as an autosomal semidominant feature. 3H1 Br/Br mice consistently lacked a presphenoid (with its lateral projections, including a preoptic root, postoptic root, and lesser wing). Karyotyping did not reveal major gross aberrations; however, microsatellite analysis localized Br to distal mouse chromosome 17 in the vicinity of D17Mit155. These results indicated that 3H1 Br/Br mice show characteristic features of frontonasal dysplasia, including median facial clefting and bifid cranium, as well sphenoidal malformations. Furthermore, this mutant should serve as a useful model for examining mechanisms of frontonasal dysplasia.

Recent developments in orofacial cleft genetics

Nonsyndromic cleft of the lip and/or palate (CLP or orofacial cleft) derives from an embryopathy with consequent failure of the nasal process and/or palatal shelves fusion. This severe birth defect is one of the most common malformations among live births. Nonsyndromic CLP is composed of two separate entities: cleft lip and palate (CL+/-P) and cleft palate only (CPO). Both have a genetic background, and environmental factors probably disclose these malformations. In CL+/-P, several loci have been identified, and, in one case, a specific gene has also been found. In CPO, one gene has been identified, but many more are probably involved. Because of the complexity of the genetics of nonsyndromic CLP as a result of the difference between CL+/-P and CPO, heterogeneity of each group caused by the number of involved genes, type of inheritance, and interaction with environmental factors, we discuss the more sound results obtained with different approaches: epidemiological studies, animal models, human genetic studies, and in vitro studies.

Chondrogenic differentiation during midfacial development in the mouse: in vivo and in vitro studies

Because the mouse is now the main model for developmental research of all types, it is important to understand the basic developmental pattern of various organs. The first aim of the present study was to establish normal prenatal developmental standards of the cartilaginous nasal capsule during embryonic development of the mouse. For this purpose we have performed sagittal and coronal sections ranging from E12.5 to E18.5 in gestation age. The primordia of the nasal septal cartilage is recognizable around the 14th embryonic day as demonstrated by the metachromatic toluidine blue staining and by immunostaining of type II collagen. Northern blot analysis of the transcription factors Cart-1 and Sox-9 indicated maximum mRNA levels at E12.5 then a decreased expression during the following days of gestation. Type II collagen and aggrecan mRNA levels are constant during the embryonic period. In the second part of this study, we have established a primary culture system where chondrocytes were isolated from E.18 mouse embryo nasal septum. The purpose of this second part was to assess if chondrocytes could further differentiate in vitro until the hypertrophic phase and matrix mineralization. After the condensation phase, the cells synthesize an extracellular matrix including type II collagen and aggrecan. Progressively, typical cartilaginous nodules composed of clusters of round cells are visible, then increase in size and finally mineralize at day 12 of culture. Cart-1 and Sox-9 mRNA levels remain constant throughout the cultures, whereas type II collagen and aggrecan gradually decrease. Ultrastructural observations of the nodules show typical chondrocytes embedded in a dense network of fibers with matrix vesicles and mineralized foci. Other ultrathin sections revealed the presence of chondrons, typical of hyaline cartilage. Results from this study provide useful tools to further investigate morphogenesis and differentiation of the cartilaginous nasal capsule, and could in the future serve as a basic developmental standard.

Microvascularization of the mucocutaneous junctions of the head in fetuses and neonates

The mucocutaneous junctions of the head (oral, nasal and palpebral) are transitional zones between the integuments and the mucosa. Their microvascularization is studied in the heads of fetuses and neonates by injection of agarized China ink into the vascular system. These zones are situated deep with respect to the free edge of the oral or nasal cavity or relative to the free margin of the eyelid. They present cutaneous-type microvascularization with a papillary network and reticular networks. Long capillary loops connected to the deep reticular network are their main feature. In the lips and eyelids, the morphology of the networks and their relationship with the orbicular muscles are suggestive of a functional structure.

Repair of the unilateral cleft lip/nose deformity

Successful surgical repair of the unilateral cleft lip and nose deformity, defined as normal orbicularis oris function and near-perfect symmetry of the repaired lip and nose, demands that the surgeon possess complete understanding of the embryology and anatomy of the midfacial defects. The surgical approach to repair of the unilateral cleft lip/nose should place great emphasis on achieving symmetry, not only with the lip segments but also perhaps even more importantly with the nasal tip. The reconstruction should recreate an intact fully functional orbicularis oris muscle across the cleft and camouflage the scar optimally. We have found that modification of the Millard rotation-advancement flap technique, with particular attention to the primary nasal repair, provides the best outcomes. In patients who have undergone primary repair of the lip and/or nose deformity, secondary rhinoplasty is generally required, regardless of the technique used at the primary repair. The degree of nasal deformity, however, is less severe following primary repair of the asymmetric nasal tip. We have found that the sliding flap cheliorhinoplasty, Wang's modification of the Vissarionov technique, provides excellent results for most secondary cleft rhinoplasties.

Development of the basement membrane and formation of collagen fibrils below the placodes in the head of anuran larvae

The development of the basement membrane and collagen fibrils below placodes, including the corneal region of the ectoderm, lens epithelium, nasal plate, and auditory vesicle in anuran larvae was observed by transmission electron microscopy and compared with that in nonplacodal regions such as the epidermis, neural tube, and optic vesicle. In the corneal region the lamina densa becomes thick concomitantly with the development of the connecting apparatuses such as hemidesmosomes and anchoring fibrils. The collagen fibrils increase in number and form a multilayered structure, showing similar morphology to the connective tissues below the epidermis. These two areas, i.e., the corneal region and epidermis, possess much collagenous connective tissue below them. On the other hand, the neural tube and ophthalmic vesicle that originated from the neural tube each have a thin lamina densa and a small number of underlying collagen fibrils. The lamina densa does not thicken and the number of collagen fibrils do not significantly increase during development. These two areas possess little extracellular matrix. The nasal plate and auditory vesicle show intermediate characteristics between the epidermis-type and the neural tube-type areas. In these areas, the lamina densa becomes thick and hemidesmosomes and anchoring fibrils develop. The number of collagen fibrils increases during development, but does not show an orderly arrangement; rather, they are randomly distributed. It is thought that the difference in the arrangement of collagen fibrils in different tissues is due to differences in the extracellular matrix around the collagen fibrils. Placodal epithelia have the same origin as epidermis, but during development their morphological characteristics differ and they are not associated with the pattern of extracellular matrix with characteristics of epidermal and corneal multilayered collagen fibril areas.

The cellular and molecular origins of beak morphology

Cellular and molecular mechanisms underlying differences in beak morphology likely involve interactions among multiple embryonic populations. We exchanged neural crest cells destined to participate in beak morphogenesis between two anatomically distinct species. Quail neural crest cells produced quail beaks in duck hosts and duck neural crest produced duck bills in quail hosts. These transformations involved morphological changes to non-neural crest host beak tissues. To achieve these changes, donor neural crest cells executed autonomous molecular programs and regulated gene expression in adjacent host tissues. Thus, neural crest cells are a source of molecular information that generates interspecific variation in beak morphology.

Staging criteria for embryos of the spiny softshell turtle, Apalone spinifera (Testudines: Trionychidae)

Previous work describing the embryonic stages of turtle development has not included members of the highly derived trionychid turtles. Staging criteria are described for the spiny softshell turtle (Apalone spinifera) to facilitate comparisons between phylogenetically distant taxa of turtles. Embryonic development in A. spinifera is placed in the context of the widely used sequence of Yntema stages. Novel features are included in the descriptions of staging criteria for Stages 13-26. Comparisons of the development of specific features are made between A. spinifera and other taxa of turtles. Data on the duration of developmental stages at different temperatures and embryo dimensions support the conclusion that morphology-based staging criteria are superior to developmental rate temperature coefficients.

In situ GABAergic modulation of synchronous gonadotropin releasing hormone-1 neuronal activity

Evidence indicates that gonadotropin releasing hormone-1 [GnRH-1, also known as luteinizing hormone releasing hormone (LHRH)] neurons can exhibit synchronized neuroendocrine secretory activity before entrance into the CNS. In this study, we used calcium imaging to evaluate patterns of activity in individual, embryonic, GnRH-1 neurons as well as population dynamics of GnRH-1 neurons in mouse nasal explants maintained for 1 versus 3 weeks. Independent of age, GnRH-1 neurons displayed significant calcium peaks that synchronized at an interval of approximately 20 min across multiple GnRH-1 cells within an explant. Acute tetrodotoxin treatment decreased the amplitude of calcium peaks in individual GnRH-1 neurons and the duration but not the frequency of synchronized activity in the population of GnRH-1 neurons. Acute GABA(B) receptor antagonism increased the frequency of synchronized neuronal activity at both ages, whereas acute GABA(A) receptor antagonism decreased calcium oscillations in individual GNRH-1 cells as well as synchronization of the calcium pulses within the GnRH-1 population at the 1 week time point to background non-GNRH-1 cell levels. These results indicate that developing GnRH-1 neurons rely heavily on GABAergic signaling to initiate synchronized bouts of activity but thereafter, possess an innate capacity for synchronized activity patterns that are modulated by, but not completely dependent on GABAergic signaling.

FGF signaling regulates expression of Tbx2, Erm, Pea3, and Pax3 in the early nasal region

Fgf8 is required for normal development of the nasal region. Here, we have used a candidate approach to identify genes that are induced in chick nasal mesenchyme in response to FGF signaling. Using an explant culture system, we show that expression of the transcription factors Tbx2, Erm, Pea3, and Pax3, but not Pax7, in nasal mesenchyme is regulated by ectodermal signals in a stage-dependent manner. Using beads soaked in recombinant FGF protein and an FGF receptor antagonist, we furthermore demonstrate that FGF signaling is necessary and sufficient for expression of Tbx2, Erm, Pea3, and Pax3, but has no effect on Pax7 expression. We also show that, within the nasal mesenchyme, competence to respond to FGF signaling is initially widespread and uniform but becomes restricted to regions normally exposed to FGF at later stages of development, coincident with changes in FGF receptor expression. Finally, we provide evidence that FGF8 also regulates Erm and Pea3 expression in the nasal placodes. Together, these results identify Tbx2, Erm, Pea3, and Pax3 as downstream targets of FGF signaling in the facial area and suggest that these genes may mediate some of the effects of FGF8 during development of the nasal region.

[Fetal ventilation and craniomaxillary development]

Data acquired by means of color Doppler ultrasound very explicitly suggest what the role of the fetal ventilation and nasal capsules in the morphogenesis of the maxillary prognathism, turbinates, nasal valves and nasopharynx could be. Furthermore, the dysmorphologies observed in Apert or Crouzon craniosynostosis, achondroplasia or unilateral cleft lip would also testify that the influence of the fetal ventilatory dynamics goes beyond the limits of the face and extends to the cranial base and the cranium. The wealth of raised hypothesis thanks to the contribution of this imaging system could question the validity of some conceptions of the fetal craniomaxillary morphogenesis.