Developmental mechanisms in normal and abnormal palate formation with particular reference to the aetiology, pathogenesis and prevention of cleft palate

Prenatal growth patterns of the upper jaw complex with implications for laryngeal echolocation in bats

Craniofacial morphology is extremely diversified within bat phylogeny, however growth and development of the palate in bats remains unstudied. The formation of both midline and bilateral orofacial clefts in laryngeally echolocating bats, morphologically similar to the syndromic and non-syndromic cleft palate in humans, are not well understood. Developmental series of prenatal samples (n = 128) and adults (n = 10) of eight bat species (two pteropodids, four rhinolophoids, and two yangochiropterans), and two non-bat mammals (Mus musculus and Erinaceus amurensis), were CT-scanned and cranial bones forming the upper jaw complex were three-dimensionally visualised to assess whether differences in palate development can be observed across bat phylogeny. Volumetric data of bones composing the upper jaw complex were measured to quantify palate growth. The premaxilla is relatively reduced in bats compared to other mammals and its shape is heterogeneous depending on the presence and type of orofacial cleft across bat phylogeny. The palatine process of premaxillary bones is lacking in pteropodids and yangochiropterans, whereas the premaxilla is a mobile structure which is only in contact caudally with the maxilla by a fibrous membrane or suture in rhinolophoids. In all bats, maxillary bones progressively extend caudally and palatine bones, in some cases split into three branches, extend caudally so that they are completely fused to another one medially prior to the birth. Ossification of the vomer and fusion of the maxillary and palatine bones occur earlier in rhinolophoids than in pteropodids and yangochiropterans. The vomer ossifies bilaterally from two different ossification centres in yangochiropterans, which is uncommon in other bats and non-bat mammals. Analysis of ontogenetic allometric trajectories of the upper jaw complex revealed faster development of maxillary, vomer, and palatine bones in yangochiropterans compared to other bats, especially rhinolophoids. Ancestral state reconstruction revealed that yangochiropterans have a higher magnitude of change in ossification rate compared to other bats and E. amurensis a lower magnitude compared to M. musculus and bats. This study provides new evidence of heterochronic shifts in craniofacial development and growth across bat phylogeny that can improve understanding of the developmental differences characterising nasal and oral emission strategies.

A Rare Case of Cleft Palate Associated With Tongue Hamartoma: A Case Report and Systematic Review

INTRODUCTION

Palate development involves a genetic regulation through a complex molecular mechanism that may be disrupted by environmental factors, resulting in impaired fusion and cleft palate formation. An encounter with a case of cleft palate due to dorsal tongue hamartoma prompted us to perform this systematic review.

OBJECTIVE

To review the clinical profile and management approach for a case with cleft palate and tongue hamartoma.

DESIGN

A systematic literature search was conducted using keywords related to cleft palate and tongue hamartoma in PubMed, Scopus, MEDLINE, and Scielo databases through December 2021, with no time or language restrictions.

PATIENTS, PARTICIPANTS

Studies reporting patients with cleft palate and tongue hamartoma were included.

MAIN OUTCOME MEASURE(S)

Information related to clinical profile, diagnostic tests, histopathology, management, and outcomes were extracted.

Fourteen relevant publications were identified with 16 cases reported so far. Among them, thirteen patients were females (81.25%), and 3 were males (18.75%). The age of presentation varied from birth to 19 years. Oral-facial-digital syndrome (type II) was the most commonly associated syndrome.

Congenital tongue hamartoma with cleft palate is a rare presentation, which can present as an isolated entity or part of a syndrome. Genetic evaluation is warranted, particularly for multiple hamartomatous lesions. The preferred treatment is immediate excision of hamartoma while following a standard timeline for palatoplasty.

Premaxilla: up to which age it remains separated from the maxilla by a suture, how often it occurs in children and adults, and possible clinical and therapeutic implications: Study of 1,138 human skulls

Objective:

To evaluate topographic and temporal aspects of premaxillary bone and premaxillary-maxillary suture, since they are fundamental anatomical elements little explored clinically.

Methods:

1,138 human dry skulls were evaluated, of which 116 (10.19%) of the specimens were children, and 1,022 (89.81%) were adults. The skulls were photographed and the percentage of premaxillary-maxillary suture opening was determined. Subsequently the data were tabulated and submitted to statistical analysis, adopting a level of significance of 5%.

Results:

The progression of premaxillary suture closure from birth to 12 years of age was 3.72% per year. In 100% of the skulls up to 12 years, the premaxillary-maxillary suture open in the palatal region was observed, while 6.16% of adults presented different degrees of opening.

Conclusions:

The premaxilla exists in an independent way within the maxillary complex and the presence of the premaxilla-maxillary suture justifies the success of anteroposterior expansions to stimulate the growth of the middle third of the face, solving anatomical and functional problems.

MicroCT Imaging on Living Alligator Teeth Reveals Natural Tooth Cycling

To study tooth cycling in polyphyodont animals, we chose to work on alligators. Alligators have teeth in three phases of development at each tooth location. This assembly of three teeth is called a tooth family unit. As part of the study, in order to study tooth cycling in alligators, we wanted to know the configuration of the tooth family unit in every tooth position. From the surface of the mouth, this is difficult to assess. Therefore, we decided to use MicroCT which can image X-ray dense materials providing a three-dimensional view. MicroCT provided us with valuable information for this study. The method described below can be applied to study tooth cycling in other vertebrate species.

Nonproliferative and Proliferative Lesions of the Gastrointestinal Tract, Pancreas and Salivary Glands of the Rat and Mouse

The INHAND (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions in Rats and Mice) project is a joint initiative of the Societies of Toxicologic Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP), and North America (STP) to develop an internationally accepted nomenclature and diagnostic criteria for nonproliferative and proliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature and diagnostic criteria for classifying lesions in the digestive system including the salivary glands and the exocrine pancreas of laboratory rats and mice. Most lesions are illustrated by color photomicrographs. The standardized nomenclature, the diagnostic criteria, and the photomicrographs are also available electronically on the Internet (http://www.goreni.org/). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous and age related lesions as well as lesions induced by exposure to test items. Relevant infectious and parasitic lesions are included as well. A widely accepted and utilized international harmonization of nomenclature and diagnostic criteria for the digestive system will decrease misunderstandings among regulatory and scientific research organizations in different countries and provide a common language to increase and enrich international exchanges of information among toxicologists and pathologists.

Specialized stem cell niche enables repetitive renewal of alligator teeth

Reptiles and fish have robust regenerative powers for tooth renewal. However, extant mammals can either renew their teeth one time (diphyodont dentition) or not at all (monophyodont dentition). Humans replace their milk teeth with permanent teeth and then lose their ability for tooth renewal. Here, we study tooth renewal in a crocodilian model, the American alligator, which has well-organized teeth similar to mammals but can still undergo life-long renewal. Each alligator tooth is a complex family unit composed of the functional tooth, successional tooth, and dental lamina. Using multiple mitotic labeling, we map putative stem cells to the distal enlarged bulge of the dental lamina that contains quiescent odontogenic progenitors that can be activated during physiological exfoliation or artificial extraction. Tooth cycle initiation correlates with β-catenin activation and soluble frizzled-related protein 1 disappearance in the bulge. The dermal niche adjacent to the dermal lamina dynamically expresses neural cell adhesion molecule, tenascin-C, and other molecules. Furthermore, in development, asymmetric β-catenin localization leads to the formation of a heterochronous and complex tooth family unit configuration. Understanding how these signaling molecules interact in tooth development in this model may help us to learn how to stimulate growth of adult teeth in mammals.

Strategies to improve regeneration of the soft palate muscles after cleft palate repair

Children with a cleft in the soft palate have difficulties with speech, swallowing, and sucking. These patients are unable to separate the nasal from the oral cavity leading to air loss during speech. Although surgical repair ameliorates soft palate function by joining the clefted muscles of the soft palate, optimal function is often not achieved. The regeneration of muscles in the soft palate after surgery is hampered because of (1) their low intrinsic regenerative capacity, (2) the muscle properties related to clefting, and (3) the development of fibrosis. Adjuvant strategies based on tissue engineering may improve the outcome after surgery by approaching these specific issues. Therefore, this review will discuss myogenesis in the noncleft and cleft palate, the characteristics of soft palate muscles, and the process of muscle regeneration. Finally, novel therapeutic strategies based on tissue engineering to improve soft palate function after surgical repair are presented.

Coordinated events: FGF signaling and other related pathways in palatogenesis

Cleft palate is a common craniofacial anomaly that is costly to both patients and the health care system. Investigation of each stage of palate development enhances understanding of this anomaly. Although the exact molecular signaling mechanisms that contribute to palatogenesis remain elusive, multiple pathways, such as fibroblast growth factor (FGF) signaling, have been recognized as important contributors. Alterations in FGF signaling have previously been implicated in palatal clefting. The current review discusses FGF signaling and the major signaling mediators affecting FGF signaling during each stage of palatogenesis.

In vitro investigation of the secondary palate development in two strains of mice

The pathogenesis of cleft lip and palate (CL/P) is studied in animal experiments. This study revealed significant differences in foetal secondary palate development in two strains of mice (NMRI, A/WySnJ) using a palatal organ model. Palatal shelves of 114 NMRI embryos, resistant to cleft occurrence, and 93 A/WySnJ embryos, a strain with a high spontaneous CL/P rate, were micro-dissected at 14.25 GD (gestational day), before palatal fusion takes place. After cultivation in serum-free medium, palatal development was investigated microscopically and scored in a six-step system. At death (14.25 GD) the palatal shelves of the NMRI embryos (mean 3.5) were significant more developed than those of A/WySnJ (mean 2.7; p=0.05). After incubation, 53% (60/114) NMRI and 14% (13/93) A/WySnJ cultures had over two-thirds fusion to stage V-VI, therefore in 17% NMRI (19/114) and 1% A/WySnJ cultures (1/93) fusion was macroscopically complete. 62% of the A/WySnJ cultures showed no significant development in vitro (mean 2.84; p=0.094). There is a significant palatal development difference between normally developed NMRI (mean 4.45, p=0.05) and CL/P appearance in A/WySnJ mice (mean 2.84). Palatal development of both strains was significantly delayed in organ culture (p=0.05). The A/WySnJ strain was more susceptible to manipulation and vulnerable.

The etiology of cleft palate: a 50-year search for mechanistic and molecular understanding

Dates of special, historical significance, such as the 50th anniversary of the founding of the Teratology Society, prompt a desire to pause and look back and contemplate where we began, how far we have come, and consider the future for our scientific endeavors. The study of the etiology of cleft palate extends many years into the past and was a subject of interest to many of the founding members of the Teratology Society. This research area was intensively pursued and spawned a vast portfolio of published research. This article will look back at the state of the science around the time of the founding of the Teratology Society, in the 1950s and 1960s, and track the emergence and pursuit of an interest in an etiology for cleft palate involving failure of palatal fusion. Studies of medial epithelial cell fate and induction of cleft palate by interference with adhesion or fusion span the period from the 1960s to the present time. Teratology Society members have been and continue to be key players in cleft palate research. In this retrospective article, seminal research published by Teratology Society members will serve as a platform to launch the discussion of the emergence of our current understanding of medial epithelial cell differentiation and fate and the potential for these processes to be targets of teratogenic action.

[Genes, forces and forms: mechanical aspects of prenatal craniofacial development]

Current knowledge of molecular signaling during craniofacial development is advancing rapidly. We know that cells can respond to mechanical stimuli by biochemical signaling. Thus, the link between mechanical stimuli and gene expression has become a new and important area of the morphological sciences. This field of research seems to be a revival of the old approach of developmental mechanics, which goes back to the embryologists His [36], Carey [13, 14], and Blechschmidt [5]. These researchers argued that forces play a fundamental role in tissue differentiation and morphogenesis. They understood morphogenesis as a closed system with living cells as the active part and biological, chemical, and physical laws as the rules. This review reports on linking mechanical aspects of developmental biology with the contemporary knowledge of tissue differentiation. We focus on the formation of cartilage (in relation to pressure), bone (in relation to shearing forces), and muscles (in relation to dilation forces). The cascade of molecules may be triggered by forces, which arise during physical cell and tissue interaction. Detailed morphological knowledge is mandatory to elucidate the exact location and timing of the regions where forces are exerted. Because this finding also holds true for the exact timing and location of signals, more 3D images of the developmental processes are required. Further research is also required to create methods for measuring forces within a tissue. The molecules whose presence and indispensability we are investigating appear to be mediators rather than creators of form.

Calcium and morphogenetic fields

Experiments on polarizing fucoid eggs indicate that they drive a steady calcium ion current through themselves as they establish a developmental axis. Moreover, the experiments strongly suggest that this current establishes a pCa gradient within the egg which is part of the mechanism which establishes this axis. It is suggested that Child's 'metabolic gradients' (as well as Bünning's unequal plant cell divisions) likewise include pCa gradients with Child's 'high' ends and Bünning's antimeristemoid ends being regions of low pCa. Evidence for other developmental calcium currents (obtained with a vibrating extracellular voltage electrode) is reviewed, and the development of a vibrating extracellular pCa electrode is proposed. Finally, progress towards direct observations of intracellular pCa gradients is reviewed. This includes visualization of an apparent steady high calcium cap at the vegetal (and perhaps, too, the animal) pole of medaka fish eggs with the aid of aequorin.

Genes, forces, and forms: mechanical aspects of prenatal craniofacial development

Current knowledge of molecular signaling during craniofacial development is advancing rapidly. We know that cells can respond to mechanical stimuli by biochemical signaling. Thus, the link between mechanical stimuli and gene expression has become a new and important area of the morphological sciences. This field of research seems to be a revival of the old approach of developmental mechanics, which goes back to the embryologists His (1874), Carey (1920), and Blechschmidt (1948). These researchers argued that forces play a fundamental role in tissue differentiation and morphogenesis. They understood morphogenesis as a closed system with living cells as the active part and biological, chemical, and physical laws as the rules. This review reports on linking mechanical aspects of developmental biology with the contemporary knowledge of tissue differentiation. We focus on the formation of cartilage (in relation to pressure), bone (in relation to shearing forces), and muscles (in relation to dilation forces). The cascade of molecules may be triggered by forces, which arise during physical cell and tissue interaction. Detailed morphological knowledge is mandatory to elucidate the exact location and timing of the regions where forces are exerted. Because this finding also holds true for the exact timing and location of signals, more 3D images of the developmental processes are required. Further research is also required to create methods for measuring forces within a tissue. The molecules whose presence and indispensability we are investigating appear to be mediators rather than creators of form.

Initial innervation of the palatal gustatory epithelium in the rat as revealed by growth-associated protein-43 (GAP-43) immunohistochemistry

We studied the earliest stages of the palate in rat embryos using scanning electron microscopy and immunohistochemistry of growth-associated protein-43 (GAP-43) to investigate the role of nerves in the development of the palatal taste buds. Chronological sequences of the palatal gustatory structures revealed characteristic several stages: 1) At embryonic day 13.5 (E13.5), the palatal shelves were widely separated, and no nerves could be observed in the vicinity of their epithelium which was formed of an undifferentiated single cell layer. 2) At E14, intraepithelial GAP-43-immunoreactive fine nerves were first observed along the medial border of the palatal shelves which became several layers thick but still separate along their entire length. 3) At E15, the fusion process resulted in the formation of cranial parts of the soft palate, the epithelium of which was heavily innervated and revealed small fungiform-like papillae devoid of nerves. 4) As the fusion process continued more caudally at E15, there was a substantial increase in palatal innervation and number of fungiform-like papillae. Primordial stages of taste buds were first distinguished in the papillae where they coincided with sparsely distributed GAP-43-immunoreactive nerve fibers. 5) At E16, the whole soft palate was eventually differentiated and attained its definitive morphology. Different stages of taste buds (i.e. pored and non-pored) were recognized, and an extensive subgemmal plexus characteristic for the adult palatal taste buds was observed. 6) Mature taste buds with alpha-gustducin-immunopositive cells were observed at E18, and their numbers increased gradually with age. The present study reveals that the gustatory nerves preceded the development of taste buds in the palate of rats, and therefore may have some roles in the initial induction of taste buds as proposed in lingual taste buds.

Initial findings on teratological and developmental relationships and differences between neural tube defects and facial clefting. First experimental results

Unless genetically caused, the occurrence of neural tube defects and clefts of the lip, alveolus and palate are not associated. These malformations do, however, share some common causes, one of which is folic acid deficiency. Nevertheless, it is not known why a neural tube defect resulting from folic acid deficiency does not occur in combination with facial clefts. Based on animal experiments and a review of the literature, it is assumed that other factors--such as vitamin B6 deficiency--though clinically not diagnosed, can more often cause malformations.

Reduction of procarbazine-induced cleft palates by prenatal folic acid supplementation in rats

We investigated the effects of prenatal folic acid supplementation on procarbazine (PCZ)-induced intra-uterine growth retardation (IUGR), cleft palates, and microgenia. Three groups of gravid rats were treated with 200 mg/kg body weight (BW) PCZ on day 13.5 of gestation (GD13.5). Two groups of them were additionally supplemented with 1 and 2.5 mg/kg folic acid, respectively, from GD13.5 through GD16.5. On GD19.5, all fetuses were delivered by caesarian sections and sexed subsequently. Numbers of live and dead fetuses as well as resorptions were counted. Data on fetal BW, crown-rump length, tail length, placental weight, and diameter were collected. Fetal heads were histologically scrutinized for the occurrence of cleft palates and microgenia. Folic acid at 2.5 mg/kg diminished PCZ-induced IUGR. In male fetuses, both folic acid doses significantly reduced the incidence of cleft palates and microgenia, while in females, only the high folic acid dose was capable of lowering the occurrence frequency of cleft palates. We conclude that folic acid supplementation at the used doses confers a substantial protection against PCZ-induced IUGR and incidence of cleft palates and microgenia. However, these effects are gender-related and dose-dependent.

The time of palatal fusion in mice: a factor of strain susceptibility to teratogens

Induction of facial clefts in an animal model is often performed in experimental teratology. The susceptibility to teratogens of different strains of mice is genetically determined and seems to depend on the time of palatal fusion during embryogenesis. In order to elucidate the mode of action of preventive measures, we determined the exact time of palatal fusion in different strains of mice used for experiments in our laboratory. Fusion of the secondary palate is finished in the Halle: NMRI-mice at day 15, 0 h of gestation, in Halle: DBA and in A/WySnJ mice at day 15, 6 h and in the Halle: Jena AB-mice at day 15, 12 h. This sequence is at variance with spontaneous cleft rates and susceptibility to teratogens.

Deformations of the midfacial complex in twins with orofacial clefts

OBJECTIVE

To investigate the craniofacial morphology in twins with cleft lip and/or palate (OFC) and localize differences, compared with noncleft (NC) twins.

DESIGN

Retrospective study.

SETTING

School of Dentistry, University of Michigan.

SAMPLE

Posteroanterior cephalographs of 32 pairs of dizygotic, concordant, like-sexed twins. The NC group consisted of 20 pairs of noncleft twins. The cleft twin (CT) group consisted of 12 pairs of concordant twins (both exhibited OFC).

MAIN OUTCOME MEASURES

Changes in linear distances, differences in form difference matrices, and visualization of deformations of thin-plate spline (TPS) transformation grids.

RESULTS

Linear analysis indicated significant reductions in interorbital distance ( approximately 12%; p <.01) and reduced maxillary heights ( approximately 27%; p <.001) in CTs. Euclidean distance matrix analysis strongly supported these findings, confirmed that the form matrices were significantly different (p <.05), and indicated relative decreases in internasal width ( approximately 12%) and maxillary base width ( approximately 10%). The TPS analysis produced a transformation grid that showed superoinferior compression, suggesting that OFC is associated with a downward displacement of the nasomaxillary complex as well as distortion in the region of the maxillary base.

CONCLUSIONS

Twins with orofacial clefts differ from their unaffected counterparts by a midfacial skeletal morphology characterized by decreases in interorbital and internasal widths and relatively shorter maxillary basal heights and widths. Although most of these differences appear to be due to compression and regionalized deformation, the resultant inferior displacement of the medial region of the midface concomitant with horizontal widening in the presumptive palatal region may be a development model associated with OFC.

An in vitro mouse model of cleft palate: defining a critical intershelf distance necessary for palatal clefting

It is unclear whether cleft palate formation is attributable to intrinsic biomolecular defects in the embryonic elevating palatal shelves or to an inability of the shelves to overcome a mechanical obstruction (such as the tongue in Pierre Robin sequence) to normal fusion. Regardless of the specific mechanism, presumably embryonic palatal shelves are ultimately unable to bridge a critical distance and remain unapproximated, resulting in a clefting defect at birth. We propose to use a palate organ culture system to determine the critical distance beyond which embryonic palatal shelves fail to fuse (i.e., the minimal critical intershelf distance). In doing so, we hope to establish an in vitro cleft palate model that could then be used to investigate the contributions of various signaling pathways to cleft formation and to study novel in utero treatment strategies. Palatal shelves from CD-1 mouse embryos were microdissected on day 13.5 of gestation (E13.5; term = 19.5 days), before fusion. Using a standardized microscope ocular grid, paired palatal shelves were placed on a filter insert at precisely graded distances ranging from 0 (in contact) to 1.9 mm (0, 0.095, 0.19, 0.26, 0.38, 0.48, 0.57, 0.76, 0.95, and 1.9 mm). A total of 68 paired palatal shelves were placed in serum-free organ culture for 96 hours (n = 68). Sample sizes of 10 were used for each intershelf distance up to and including 0.48 mm (n = 60). For intershelf distances of 0.57 mm and greater, two-paired palatal shelves were cultured (n = 8). All specimens were assessed grossly and histologically for palatal fusion. Palatal fusion occurred in our model only when intershelf distances were 0.38 mm or less. At 0.38 mm, eight of 10 palates appeared grossly adherent, whereas six of 10 demonstrated clear fusion histologically with resolution of the medial epithelial seam and continuity of the palatal mesenchyme. None of the 18 palates fused when placed at intershelf distances of 0.48 mm or greater. Using our selected intershelf distances as a guideline, we have established an approximate minimal critical intershelf distance (0.48 mm) at which we can reliably expect no palatal fusion. Culturing palatal shelves at intershelf distances of 0.48 mm or greater results in nonfusion or clefting in vitro. This model will allow us to study biomolecular characteristics of unfused or cleft palatal shelves in comparison with fused shelves. Furthermore, we plan to study the efficacy of grafting with exogenous embryonic mesenchyme or candidate factors to overcome clefting in vitro as a first step toward future in utero treatment strategies.

Double tongue, intraoral anomalies, and cleft palate--case reports and a discussion of developmental pathology

OBJECTIVE

Isolated cleft palate is the most common presentation of the nonsyndromic cleft lip/palate combinations and is multifactorial in etiology. We report two cases of children with clefts of the secondary palate coexistent with double tongue and in either case mandibular epulis or superiorly displaced salivary gland.

RESULTS AND DISCUSSION

In each case, the palatal cleft correlated anatomically with the intraoral space-occupying lesion. The ratio of tongue volume to intraoral volume during palatogenesis is discussed with reference to the pathogenesis of cleft palate. These clinical cases propose the model of a unifying sequence of developmental events whereby deformation of palatal shelf elevation results in secondary palatal clefting.

Effect of X irradiation on secondary palate development in mice

The mechanisms whereby X irradiation induces palatal clefting were investigated in vivo and in an in vitro organ culture system. When pregnant mice at day 12.5 of gestation were exposed to a 4-Gy dose of whole-body X radiation, the incidence of palatal clefting in their offspring was 91%. The volume of the irradiated palatal shelves was too low for them to make contact with each other. On gestational day 13.5 after labeling, bromodeoxyuridine-positive cells were sparse and apoptotic cells were abundant in the irradiated shelves. To prevent secondary effects of irradiation from the injured maternal body, fetal palatal explants were immediately transferred to an organ culture system after X irradiation in utero. The incidence of palatal clefting was 24%, much lower than the incidence in vivo. The addition of 10(-4) M of dexamethasone to the culture medium increased the incidence of palatal clefting to 56%. These findings indicated that X irradiation inhibited cell proliferation and induced apoptosis, resulting in small-volume palatal shelves that could not fuse with each other. The organ culture data also indicated that 4 Gy of irradiation appears to produce its effects both by a direct action on the fetus and indirectly by affecting the metabolism of the pregnant dam.

Effects of vitamin B6 on beta-aminoproprionitrile-induced palatal cleft formation in the rat

OBJECTIVE

This study was conducted to evaluate the effects of beta-aminoproprionitrile and vitamin B6 on palatal clefting.

METHOD

In four groups of pregnant Sprague-Dawley rats, beta-aminoproprionitrile (BAPN; 600 mg/kg b.w.) was given by gavage on embryonal day 15, 7 hours to induce palatal clefts. Vitamin B6 (10 mg/kg b.w., IM) was given twice on embryonal day 14, 7 hours and on day 15, 7 hours. The possibility that the food's content of vitamin B6 affected the results was also tested. Palatal cleft formation was divided into four different grades, ranging from no cleft formation to total cleft formation.

RESULTS/CONCLUSION

It was found that BAPN induces cleft palate in rat fetuses and that this defect can be prevented both in number and severity by administration of vitamin B6 before and simultaneously with BAPN.

Mesenchymal cell activity during 5-fluoro-2-deoxyuridine-induced cleft palate formation in the rat

Biosynthetic activity of the mesenchymal cells within the palatal shelves was determined during cleft palate formation induced by 5-fluoro-2-deoxyuridine (FUDR). The palatal shelves of 30 fetal rat heads with palatal clefts were surveyed at stages corresponding to normal palatogenesis, nucleolar organizer region (NOR) staining being employed to determine cell activity. Comparing cellular activity during normal and cleft palatogenesis, significantly lower counts were recorded for most stages of cleft formation. When anterior or posterior regions were compared, significant changes in NOR counts cell were found at a time corresponding to the pre-elevation stage of normal palatogenesis. At a time equivalent to normal fusion, the shelves in the anterior region showed signs of recovery, but posteriorly significantly lower activity occurred throughout all stages of palate dysmorphogenesis. The depressed level of cellular activity found after treatment with FUDR may be directly or indirectly related to the abolition of an intrinsic shelf-elevation force and, subsequently, cleft palate formation.

Histomorphologic analysis of the soft palate musculature in prenatal cleft and noncleft A/Jax mice

The two specific aims of this study were as follows: to evaluate the appropriateness of the A/Jax mouse model in the investigation of the key cellular stages in prenatal soft palate morphogenesis and myogenesis; and to describe structural differences in the histomorphology of the soft palate anatomy from cleft and noncleft mice prior to, during, and after palatogenesis. Cleft-induced and control groups of A/Jax mouse embryos from timed pregnancies were harvested sequentially on gestational days 15 to 19. Embryos were weighed and staged for external body morphology. The heads were removed and fixed for light microscopy, sectioned serially in the frontal plane at 10 microns and stained with hematoxylin-eosin to characterize and compare the soft palate musculature. All observations were made at the head depth of the trigeminal ganglion in both age- and stage-matched embryos. The following findings were made: (1) the A/Jax mouse is a suitable animal model for the study of soft palate myogenesis; (2) there were no discernible morphologic differences between the soft palate muscles in cleft and noncleft A/Jax mice when viewed under light microscopy; (3) the soft palate and related muscles were identifiable as muscle fields, in both the cleft and noncleft fetuses, as early as gestational day 15 and as specific muscles at gestational day 18; (4) in both the cleft and noncleft A/Jax fetuses, the soft palate muscles appeared in a sequential anatomic fashion (the palatine aponeurosis appeared first, next the tensor palatini, and then the levator palatini muscles); and (5) in the cleft palate fetuses, both pterygoid plates were angulated and displaced laterally.

Pathogenesis of bromodeoxyuridine-induced cleft palate in mice

This study was designed to examine the pathogenesis of bromodeoxyuridine-induced (BrdU) clefts of the secondary palate in mice. Intraperitoneal injections of BrdU (500 mg/kg body weight) were given on days 11 and 12 to some pregnant mice and on days 12 and 13, and days 11, 12 and 13 to others. Evaluation of craniofacial relations and palate development in BrdU-treated mice revealed inhibition of vertical development of the palatal shelves, mandibular hypoplasia which led to failure of downward displacement of the tongue and the creation of an obstacle to reorientation of the palatal shelves. The results of this study demonstrate a strong correlation between induction of cleft palate and the presence of structural alterations in the mandible, and the mechanism of BrdU-induced cleft palate resembles the defect in the Pierre Robin anomaly.

Changes in the composition of glycosaminoglycans during normal palatogenesis in the rat

The synthesis and hydration of glycosaminoglycans (GAG) has been implicated in the generation of a palatal shelf-elevating force in mammals. This study quantifies the GAG composition in the palatal shelves of Wistar rat fetuses at various stages of palatogenesis. Hyaluronan, heparin sulphate and chondroitin-4-sulphate were detected but not dermatan sulphate or chondroitin-6-sulphate. The distribution of the GAG differed in the anterior and posterior regions (i.e. the presumptive hard and soft palates) and with the stage of development. At the time of palatal-shelf reorientation, there were no significant differences for either the total amount of GAG or for the percentages of specific GAG types between anterior and posterior regions. Indeed, the most marked differences were detected at the stages of histogenesis after shelf elevation. Nevertheless, the results support the view that hyaluronan is involved in palatal-shelf reorientation, its percentage being initially high and decreasing after shelf elevation. No changes were detected for the other (sulphated) GAG during the time of elevation. The findings point to the need to correlate the events during histogenesis with changes in the ground substance of palatal-shelf mesenchyme and indicate that there are different developmental mechanisms within the presumptive hard and soft palates.

Effects of 5-fluorouracil on embryonic rat palate in vitro: fusion in the absence of proliferation

5-Fluorouracil (5-FU) inhibits the enzyme thymidylate synthetase (TS) which results in inhibition of DNA synthesis. 5-FU is teratogenic in many species, inducing cleft palate, limb, and tail defects. In the present study, gestation day (GD) 14 embryonic rat craniofacial explants were exposed to 5-FU in organ culture with increasing concentrations and durations of exposure. Palates exposed to 5-FU were morphologically abnormal and craniofacial shape, size, and palatal fusion pattern were affected with the severity of effects dependent on concentration and duration of exposure. Cleft palate was induced in vitro as opposing palates overlapped in a narrowed oral cavity. Palates exposed to higher levels of 5-FU were growth inhibited, but fused even though proliferation ceased and few cells were available to participate in elevation and fusion. This was demonstrated as a biphasic concentration-response profile for palatal fusion in which 0.05 to 0.15 micrograms 5-FU/ml produced decreasing rates of palatal fusion, while exposure to 0.15 to 3.0 micrograms/ml resulted in progressively increasing rates of fusion. The effects of 5-FU were detected biochemically as a reduction in TS activity which was concentration and time dependent during the first 12 hours, with a return to control levels by 24 hours. During the first day, 5-FU did not alter protein levels, but DNA levels significantly decreased at the high concentration, 2.0 micrograms/ml. After 5 days in culture, both DNA and protein decreased with increasing 5-FU concentration and duration of exposure. Also by the end of the culture period, 3H-TdR incorporation had decreased in a concentration dependent manner. It is concluded that progressive inhibition of proliferation and growth in organ culture results in two different morphological outcomes: cleft palate resulting from a narrowed oral cavity and increased incidence of anterior palatal fusion under conditions of strong growth reduction. This study demonstrates that elevation and fusion can occur in the absence of growth and proliferation. Based on these observations, severe inhibition of growth or proliferation would not necessarily be sufficient to induce cleft palate.

Morphogenesis of the secondary palate in mouse embryos with special reference to the development of rugae

Morphological studies of secondary palate formation, with special reference to the development of rugae, were carried out on Jcl:ICR mouse embryos. Three rugae were observed on the anterior part of the future oral surface of the vertically developing palatal shelves in 13-day embryos. Rugae increased in number as the development of the palatal shelves proceeded, and five to six prominent rugae were observed in 14-day embryos just prior to shelf elevation. The folding of these five to six rugae progressed in conjunction with the formation of a sharp, valley-like groove at the base of the anterior two-fifths of the vertical palatal shelves. As palatal shelves elevated, the groove disappeared gradually, and, accordingly, the folding of rugae loosened. In the groove region, the superficial epithelial cells were roundish, while the basal ones were elongated. Such characteristic features were no longer observed when the disappearance of the groove was completed. Eight rugae were observed on the future hard palate of 14-day embryos with already completed palatal fusion. An additional ruga was frequently found in 15-day embryos, and the pattern then was almost the same as that of an adult. Epithelial thickening and condensation at the rugae region, as well as mesenchymal condensation under the epithelium of the rugae, were confirmed in embryos both before and after elevation of the palatal shelves. There is a possibility that these structural characteristics observed in the epithelial and mesenchymal cells of the rugae and groove regions may be related to palatal shelf elevation.

Medial edge epithelium transforms to mesenchyme after embryonic palatal shelves fuse

The disappearance of palatal medial edge epithelium (MEE) after fusion of secondary palatal shelves is often cited as a classical example of embryonic remodeling by programmed cell death. We reinvestigated this phenomenon in 16-day rat embryos, using light and electron microscopy. We confirm reports that the periderm of the two-layered MEE begins to slough after shelves assume horizontal positions. In vitro, peridermal cells are not able to slough and are trapped during the adhesion process. In vivo, however, surface cells shed before the shelves in the anterior palate adhere, allowing junctions to form between opposing basal epithelial cells. Midline seams so formed consist of two layers of basal cells, all of which appear healthy. Even though its cells are dividing, growth of the seam fails to keep pace with palatal growth and it thins to one layer of cells, and then breaks up into small islands. The basal lamina disappears and elongating MEE cells extend filopodia into adjacent connective tissue. Electron micrographs reveal transitional steps in loss of epithelial characteristics and gain of fibroblast-like features by transforming MEE cells. One such feature, observed with the aid of immunofluorescence, is the turn of the mesenchymal cytoskeletal protein, vimentin. No cell death or macrophages are observed after adhesion and thinning over most of the palate. These data indicate that MEE is an ectoderm that retains the ability to transform into mesenchymal cells. Epithelial-mesenchymal transformation may be expressed in other embryonic remodelings (R.L. Trelstad, A. Hayashi, K. Hayashi, and P.K. Donahue, 1982, Dev. Biol. 92, 27), resulting in heretofore unsuspected conservation of embryonic cell populations.

Relaxin as an aetiological factor in diabetic embryopathy

Relaxin, an insulin homologue, has effects on collagen resembling those of certain teratogenic agents. It is suggested that diabetic embryopathy could be due to disturbances of relaxin secretion during fetal organogenesis.

The development of mast cells in facial skin, palate and tongue of the mouse

This was examined in connective tissues of facial skin, palatal mucosa and tongue in fetal and adult mice. Mast cells were first observed in skin at 15 days of fetal age, but until 17 days in palate and tongue. With increasing age they increased in size and granularity. At birth they were 6-7 times more numerous per unit volume of tissue in skin compared with palate or tongue but, in the adult, numbers were similar in each region. Either mast cells enter developing tissues at different times or they differentiate and proliferate in some regions before they do so in others.

The cell surface coat in neurulating mouse and rat embryos, studied with lectins

Carbohydrates in the surface coat of cells are thought to have a function in cell adhesion. The surface coat of cells, located in the fusion zone of the neural walls is investigated during neural tube closure in mammalian embryos. The presence of alpha-D-mannose, alpha-D-glucose and N-acetyl-D-glucosamine is quantified with the help of the lectins concanavalin A and wheat germ agglutinin in absence or after enzymic treatment. A two-step incubation is used, in which the second step consists of a protein-gold conjugate. A high incidence of these sugar residues was found in the fusion zone, indicating a relation to the specific capacity of these cells in establishing cell contacts.

Embryonic head posture and palatal shelf elevation

During embryonic and fetal stages of human development, elongation and straightening of the neck occurs. Authors have suggested that the resulting change in head posture lifts the lower border of the mandible from the pericardial region, so allowing jaw movements to assist the withdrawal of the tongue from between the palatal shelves. This aids elevation of the palatal processes prior to fusion. This paper reports on histological sections of 28 mm twin embryos which demonstrate that palatal elevation can take place in the absence of elongation and straightening of the neck, demonstrated by observation of existence of cephalic, pontine and cervical neural flexure of the brain.

Cell degeneration and mitosis in the buccopharyngeal and branchial membranes in the mouse embryo

The frequencies of cell degeneration and mitosis were investigated in the rupturing buccopharyngeal membrane (BPM) and in the persistent first branchial membrane (BM). In the BPM, cell degeneration starts many hours before rupture is visible, but mitotic figures are absent. In the BM this situation is reversed: mitotic figures are regularly observed, but a degenerating cell only occasionally. It is concluded that the ratio between the numbers of degenerating and dividing cells regulates the fate of both the BPM and the BM.

Craniofacial development: the possible mechanisms for some malformations

Normal craniofacial development is reviewed and some mechanisms in the fusion of mammalian facial 'processes' are discussed. The manipulation of environmental factors and effects of teratogens are related to genetic susceptibility of animal models, and extrapolated to craniofacial malformations in man.

Experimental induction of an incomplete hard-palate cleft in the rat

Incomplete clefts of the hard palate with soft-palate integrity are among the rarest malformations found in human beings. They appear as oval-shaped openings in the midline of the hard palate and do not extend along its whole length. The amniotic-sac-puncture technique was used to induce such clefts in 10 percent of a group of rat fetuses at day 15.3 of pregnancy. The upper jaws of such fetuses, either 17.3 or 21.3 days old, were examined in the scanning electron microscope and in serial Epon sections. At day 17.3 incomplete clefts of the hard palate were extending toward the soft palate, with the anterior portion of palatal shelves still in the vertical position and with the soft palate already fused. At day 21.3, the incomplete hard-palate clefts were smaller in both extension and width. These observations support the idea that fusion of the soft palate can occur independently of fusion in the hard-palate region.