Palate development: mechanisms and malformations

Is the collateral circulation pattern in the hard palate affected by cleft deformity?

OBJECTIVES

To evaluate the influence of collateral vascularization on surgical cleft palate closure and deformities.

MATERIALS AND METHODS

Corrosion casting was performed using red-colored acrylic resin in twelve fresh adult cadavers with a normal hard palate. Additionally, white-colored barium sulfate was injected into a fetus with a unilateral complete cleft palate, and layer-by-layer tissue dissection was performed. Both substances were injected into the external carotid arteries. Corrosion casting involved dissolving the soft and hard tissues of the orofacial area utilizing an enzymatic solution.

RESULTS

In normal palates, bilateral intraosseous infraorbital arteries formed a network in the premaxilla with the intraosseous nasopalatine- and greater palatine arteries (GPAs). The perforating GPAs anastomosed with the sphenopalatine artery sub-branches. Bilateral extraosseous GPA anastomoses penetrated the median palatine suture. Complex vascularization in the retrotuberal area was detected. In the cleft zone, anastomoses were omitted, whereas in the non-cleft zone, enlarged GPAs were distributed along the cleft edges and followed the anatomical course anteriorly to initiate the network with facial artery sub-branches.

CONCLUSIONS

The anatomical subunits of the palate exhibited distinct anastomosis patterns. Despite omitted anastomoses with collateral circulation in the cleft zone, arteries maintained their anatomical pattern as seen in the normal specimen in the non-cleft zone.

CLINICAL RELEVANCE

Based on the findings in normal- and cleft palates, surgeons may expect developed anastomosis patterns in the non-cleft zone. Due to the lack of microcirculation in the cleft zone, the existent anastomoses should be maintained as much as possible by the surgical technique. This applies anteriorly in the incisive canal territory, alveolar ridges, and posteriorly in the retrotuberal area.

LncRNA-NONMMUT100923.1 regulates mouse embryonic palatal shelf adhesion by sponging miR-200a-3p to modulate medial epithelial cell desmosome junction during palatogenesis

Cleft palate (CP) is a common neonatal craniofacial defect caused by the adhesion and fusion dysfunction of bilateral embryonic palatal shelf structures. Long non-coding RNA (lncRNA) is involved in CP formation with regulatory mechanism unknown. In this study, all-trans retinoic acid (ATRA) was used to induced cleft palate in embryonic mice as model group. The RNA-sequencing was performed to screen differentially expressed genes between the normal and model group on embryonic day 16.5, and the expression of LncRNA-NONMMUT100923.1 and miR-200a-3p, Cdsn was confirmed by RT-PCR and western blotting. Colony formation, CCK-8 and EDU assays were performed to measure cell proliferation and apoptosis on mouse embryonic palatal shelf (MEPS) epithelial cells in vitro. Fluorescence in situ hybridization (FISH) and dual luciferase activity assays was used to investigate the regulatory effect of LncRNA-NONMMUT100923.1 on miRNA and its target genes. Up-regulation of LncRNA-NONMMUT100923.1 and Cdsn while downregulation of miR-200a-3p was found in the model group. The sponging effects of LncRNA-NONMMUT100923 on miR-200a-3p and the target gene relations between Cdsn and miR-200a-3p was confirmed. Low expression of miR-200a-3p was related to the increased expressed levels of Cdsn and the proliferation of MEPS epithelial cells. Thus, a potential ceRNA regulatory network in which LncRNA-NONMMUT100923.1 regulates Cdsn expression by competitively binding to endogenous miR-200a-3p during palatogenesis, which may inhibit MEPS adhesion by preventing the disintegration of the desmosome junction in medial edge epithelium cells. These findings indicate the regulatory role of lncRNA and provides a potential direction for target gene therapy of CP.

LncRNA Meg3-mediated regulation of the Smad pathway in atRA-induced cleft palate

Palatal mesenchymal cell proliferation is essential to the process of palatogenesis, and the proliferation of mouse embryonic palate mesenchymal (MEPM) cells is impacted by both all-trans retinoic acid (atRA) and the TGF-β/Smad signaling pathway. The long non-coding RNA (lncRNA) MEG3 has been shown to activate TGF-β/Smad signaling and to thereby regulate cell proliferation, differentiation, and related processes. Herein, we found that atRA treatment (100 mg/kg) promoted Meg3 upregulation in MEPM cells, and that such upregulation was linked to the suppression of MEPM cell proliferation in the context of secondary palate fusion on gestational day (GD) 13 and 14. Moreover, the demethylation of specific CpG sites within the lncRNA Meg3 promoter was detected in atRA-treated MEPM cells, likely explaining the observed upregulation of this lncRNA. Smad signaling was also suppressed by atRA treatment in these cells, and RNA immunoprecipitation analyses revealed that Smad2 can directly interact with Meg3 in MEPM cells following atRA treatment. Therefore, we propose a model wherein Meg3 is involved in the suppression of MEPM cell proliferation, functioning at least in part via interacting with the Smad2 protein and thereby suppressing Smad signaling in the context of atRA-induced cleft palate.

Polarized Sonic Hedgehog Protein Localization and a Shift in the Expression of Region-Specific Molecules Is Associated With the Secondary Palate Development in the Veiled Chameleon

Secondary palate development is characterized by the formation of two palatal shelves on the maxillary prominences, which fuse in the midline in mammalian embryos. However, in reptilian species, such as turtles, crocodilians, and lizards, the palatal shelves of the secondary palate develop to a variable extent and morphology. While in most Squamates, the palate is widely open, crocodilians develop a fully closed secondary palate. Here, we analyzed developmental processes that underlie secondary palate formation in chameleons, where large palatal shelves extend horizontally toward the midline. The growth of the palatal shelves continued during post-hatching stages and closure of the secondary palate can be observed in several adult animals. The massive proliferation of a multilayered oral epithelium and mesenchymal cells in the dorsal part of the palatal shelves underlined the initiation of their horizontal outgrowth, and was decreased later in development. The polarized cellular localization of primary cilia and Sonic hedgehog protein was associated with horizontal growth of the palatal shelves. Moreover, the development of large palatal shelves, supported by the pterygoid and palatine bones, was coupled with the shift in Meox2, Msx1, and Pax9 gene expression along the rostro-caudal axis. In conclusion, our results revealed distinctive developmental processes that contribute to the expansion and closure of the secondary palate in chameleons and highlighted divergences in palate formation across amniote species.

Recent insights into the morphological diversity in the amniote primary and secondary palates

The assembly of the upper jaw is a pivotal moment in the embryonic development of amniotes. The upper jaw forms from the fusion of the maxillary, medial nasal, and lateral nasal prominences, resulting in an intact upper lip/beak and nasal cavities; together called the primary palate. This process of fusion requires a balance of proper facial prominence shape and positioning to avoid craniofacial clefting, whilst still accommodating the vast phenotypic diversity of adult amniotes. As such, variation in craniofacial ontogeny is not tolerated beyond certain bounds. For clarity, we discuss primary palatogenesis of amniotes into in two categories, according to whether the nasal and oral cavities remain connected throughout ontogeny or not. The transient separation of these cavities occurs in mammals and crocodilians, while remaining connected in birds, turtles and squamates. In the latter group, the craniofacial prominences fuse around a persistent choanal groove that connects the nasal and oral cavities. Subsequently, all lineages except for turtles, develop a secondary palate that ultimately completely or partially separates oral and nasal cavities. Here, we review the shared, early developmental events and highlight the points at which development diverges in both primary and secondary palate formation.

Tak1, Smad4 and Trim33 redundantly mediate TGF-β3 signaling during palate development

Transforming growth factor-beta3 (TGF-β3) plays a critical role in palatal epithelial cells by inducing palatal epithelial fusion, failure of which results in cleft palate, one of the most common birth defects in humans. Recent studies have shown that Smad-dependent and Smad-independent pathways work redundantly to transduce TGF-β3 signaling in palatal epithelial cells. However, detailed mechanisms by which this signaling is mediated still remain to be elucidated. Here we show that TGF-β activated kinase-1 (Tak1) and Smad4 interact genetically in palatal epithelial fusion. While simultaneous abrogation of both Tak1 and Smad4 in palatal epithelial cells resulted in characteristic defects in the anterior and posterior secondary palate, these phenotypes were less severe than those seen in the corresponding Tgfb3 mutants. Moreover, our results demonstrate that Trim33, a novel chromatin reader and regulator of TGF-β signaling, cooperates with Smad4 during palatogenesis. Unlike the epithelium-specific Smad4 mutants, epithelium-specific Tak1:Smad4- and Trim33:Smad4-double mutants display reduced expression of Mmp13 in palatal medial edge epithelial cells, suggesting that both of these redundant mechanisms are required for appropriate TGF-β signal transduction. Moreover, we show that inactivation of Tak1 in Trim33:Smad4 double conditional knockouts leads to the palatal phenotypes which are identical to those seen in epithelium-specific Tgfb3 mutants. To conclude, our data reveal added complexity in TGF-β signaling during palatogenesis and demonstrate that functionally redundant pathways involving Smad4, Tak1 and Trim33 regulate palatal epithelial fusion.

Signaling networks in palate development

Palatogenesis, the formation of the palate, is a dynamic process regulated by a complex series of context-dependent morphogenetic signaling events. Many genes involved in palatogenesis have been discovered through the use of genetically manipulated mouse models as well as from human genetic studies, but the roles of these genes and their products in signaling networks regulating palatogenesis are still poorly known. In this review, we give a brief overview on palatogenesis and introduce key signaling cascades leading to formation of the intact palate. Moreover, we review conceptual differences between pathway biology and network biology and discuss how some of the recent technological advances in conjunction with mouse genetic models have contributed to our understanding of signaling networks regulating palate growth and fusion. For further resources related to this article, please visit the WIREs website.

CONFLICT OF INTEREST

The authors have declared no conflicts of interest for this article.

Molecular signaling along the anterior-posterior axis of early palate development

Cleft palate is a common congenital birth defect in humans. In mammals, the palatal tissue can be distinguished into anterior bony hard palate and posterior muscular soft palate that have specialized functions in occlusion, speech or swallowing. Regulation of palate development appears to be the result of distinct signaling and genetic networks in the anterior and posterior regions of the palate. Development and maintenance of expression of these region-specific genes is crucial for normal palate development. Numerous transcription factors and signaling pathways are now recognized as either anterior- (e.g., Msx1, Bmp4, Bmp2, Shh, Spry2, Fgf10, Fgf7, and Shox2) or posterior-specific (e.g., Meox2, Tbx22, and Barx1). Localized expression and function clearly highlight the importance of regional patterning and differentiation within the palate at the molecular level. Here, we review how these molecular pathways and networks regulate the anterior-posterior patterning and development of secondary palate. We hypothesize that the anterior palate acts as a signaling center in setting up development of the secondary palate.

Multi-layered hypertrophied MEE formation by microtubule disruption via GEF-H1/RhoA/ROCK signaling pathway

BACKGROUND

Formation of the secondary palate is complex and disturbance during palatal fusion may result in cleft palate. The processes of adhesion, intercalation, and disappearance of medial edge epithelia (MEE) are characterized by morphological changes requiring dynamic cytoskeletal rearrangement. Microtubules are one of the cytoskeletal elements involved in maintenance of cell morphology. Microtubule-disrupting drugs have been reported to cause craniofacial malformations including cleft palate. The mechanisms underlying the failure of palatal fusion remain poorly understood. We evaluated the effect of nocodazole (NDZ), a drug that disrupts microtubules, on palatal fusion in organ culture.

RESULTS

NDZ caused failure of palatal fusion due to the induction of a multi-layered hypertrophied MEE in the mid-region of the secondary palatal shelves. Microtubule disruption increased RhoA activity and stress fiber formation. Pharmacological inhibition of the RhoA/ROCK pathway blocked multi-layered MEE formation. Partial prevention of hypertrophied MEE was observed with Y27632 and cytochalasin, but not with blebbistatin. NDZ induced re-localization of GEF-H1 into cytoplasm from cell-cell junctions.

CONCLUSIONS

The present study provided evidence that the GEF-H1/RhoA/ROCK pathway plays a pivotal role in linking microtubule disassembly to the remodeling of the actin cytoskeleton, which resulted in a multi-layered hypertrophied MEE and failure of palatal fusion.

Gene expression of Hsp70, Hsp90 and Hsp110 families in normal palate and cleft palate during mouse embryogenesis

Most previous studies focused on a small number of heat shock proteins (Hsps) and their relationships with embryogenesis, and the actual roles of these Hsps in normal and abnormal embryonic development remain unclear. It was found in the present systemic study that except for Grp170, whose expression was not detectable at GD18, all 19 Hsps of Hsp70, Hsp90 and Hsp110 families were expressed in the normal development of embryonic palate tissue in mice, but their expression patterns varied with different Hsps, presenting as a correlation with the developmental phases. In the treatment group by all-trans retinoic acid (atRA), the messenger RNA (mRNA) abundance of HspA1A, HspA1L, HspA8, HspA9, HspA12A, HspA12B, HspA13, HspA14, Hsp90AA1, Hsp90AB1, Grp94, Trap1, Hsp105, Hsp110 and Grp170 was higher in the palates at GD11 (the beginning of palate development), the mRNA abundance of HspA1A, HspA12A and HspA12B was higher at GD18 (before birth) and an mRNA expression peak of HspA1L, HspA8, HspA9, Hsp90AA1, Grp94, Hsp110 and Grp170 was observed at GD17. The mRNA abundance of most genes in atRA-induced cleft palates of the treatment group was different from that of the control group. Grp78, HspA14 and Hsp105 were closely associated with the normal palate development and cleft palate in mouse embryo, possibly as palate development-related genes. Except Grp170, the other genes may be closely associated with the development of mouse palates through participating in the stress response process and/or the antiapoptosis process.

Spatiotemporal localization of periostin and its potential role in epithelial-mesenchymal transition during palatal fusion

The medial epithelial seam (MES) between the palatal shelves degrades during palatal fusion to achieve the confluence of palatal mesenchyme. Cellular mechanisms underlying the degradation of MES have been proposed, such as apoptosis, epithelial-mesenchymal transition (EMT) and migration of medial edge epithelia (MEE). Extracellular matrix components have been shown to play an important role in EMT in many model systems. Periostin (also known as osteoblast-specific factor-2) is a secreted mesenchymal extracellular matrix component that affects the ability of cells to migrate and/or facilitates EMT during both embryonic development and pathologic conditions. In this study, we evaluated the spatiotemporal expression patterns of periostin during mouse palatal fusion by in situ hybridization and immunofluorescence. Periostin mRNA and protein were present in the palatal mesenchyme, the protein being distributed in a fine fibrillar network and in the basement membrane, but absent from the epithelium. During MES degradation, the protein was strongly expressed in the basement membrane underlying the MES and in some select MEE. Confocal microscopic analysis using an EMT marker, twist1, and an epithelial marker, cytokeratin 14, provided evidence that select MEE were undergoing EMT in association with periostin. Moreover, the major extracellular matrix molecules in basement membrane, laminin and collagen type IV were degraded earlier than periostin. The result is that select MEE establish interactions with periostin in the mesenchymal extracellular matrix, and these new cell-matrix interactions may regulate MEE transdifferentiation during palatal fusion.

Follistatin antagonizes transforming growth factor-beta3-induced epithelial-mesenchymal transition in vitro: implications for murine palatal development supported by microarray analysis

Epithelial-mesenchymal transition (EMT) is involved in normal embryonic development as well as in tumor progression and invasiveness. This process is also known to be a crucial step in palatogenesis during fusion of the bi-lateral palatal processes. Disruption of this step results in a cleft palate, which is among the most frequent birth defects in humans. A number of genes and encoded proteins have been shown to play a role in this developmental stage. The central role is attributed to the cytokine transforming growth factor-beta3 (TGF-beta3), which is expressed in the medial edge epithelium (MEE) already before the fusion process. The MEE covers the tips of the growing palatal shelves and eventually undergoes EMT or programmed cell death (apoptosis). TGF-beta3 is described to induce EMT in embryonic palates. With regard to the early expression of this molecule before the fusion process, it is not well understood which mechanisms prevent the TGF-beta3 producing epithelial cells from undergoing differentiation precociously. We used the murine palatal fusion to study the regulation of EMT. Specifically, we analyzed the MEE for the expression of known antagonists of TGF-beta molecules using in situ hybridization and detected the gene coding for Follistatin to be co-expressed with TGF-beta3. Further, we could show that Follistatin directly binds to TGF-beta3 and that it completely blocks TGF-beta3-induced EMT of the normal murine mammary gland (NMuMG) epithelial cell line in vitro. In addition, we analyzed the gene expression profile of NMuMG cells during TGF-beta3-induced EMT by microarray hybridization, detecting strong changes in the expression of apoptosis-regulating genes.

Cytokeratin expression in palatal and marginal mucosa of cleft palate patients

OBJECTIVE

The margin of a palatal cleft is a unique anatomical site since the palatal mucosa is continuous with the nasal or nasopharyngeal mucosa. The aim of this study was to compare the expression patterns of cytokeratins and basal membrane components of the mucosa in the area of the cleft.

DESIGN

Biopsies from the mucosa of the hard palate and from the cleft margin in the soft palate were obtained from five patients during the primary surgical closure of the cleft. The tissues were processed for haematoxylin-eosin staining and for immunohistochemistry. Antibodies against the cytokeratins (CK) 4, 7, 8, 10, 13, 16 and 18, and the basal membrane components heparan sulphate (HS) and collagen type IV (CIV) were used for immunostaining.

RESULTS

The nasopharyngeal epithelium was thinner than the epithelium of the soft palatal mucosa, and showed less interpapillary ridges. The nasopharyngeal epithelium was stratified but expressed the keratins of a simple epithelium (CK 7, 8 and 18). The expression pattern abruptly changed into that of a typical non-keratinized stratified epithelium (CK 4, 13) at the transition to the soft palatal epithelium. The epithelium of the hard palate was a fully differentiated, keratinized and stratified epithelium (CK 10, 16). The basal membrane was thinner in the nasopharyngeal epithelium, which might be related to the presence of abundant inflammatory cells.

CONCLUSION

The area around the palatal cleft showed three different types of epithelium. There was an abrupt transition in phenotype of the epithelium from the oral side to the nasopharyngeal side.

Transforming growth factor-beta3 restores fusion in palatal shelves exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin

The pollutant, 2,3,7,8-tetrachlorodibenzo-p-dioxin ("dioxin"), has been implicated in the etiology of a wide variety of human birth defects. In an effort to identify pharmacological blockers of dioxin-induced terata, we performed a histological and microscopic analysis of the developing murine palate that had been exposed to dioxin. In both in vivo and in vitro model systems, we observed that dioxin exposure leads to a reduction in the number of filopodial extensions at the medial epithelial edge of the developing palate. Given that this filopodial aberration is similar to the phenotype observed in Tgfbeta3 null mice, a mutant known to display a 100% incidence of cleft palate, we examined the interaction between TGFbeta3 and dioxin in palatal fusion. We found that that the addition of TGFbeta3 to an in vitro palate culture model prevented the dioxin-induced reduction in filopodial density. Moreover, TGFbeta3 exposure completely prevented the dioxin-induced block of palatal fusion in this system. Although these data do not point to a direct cellular or molecular mechanism for TGFbeta3 dioxin antagonism, these results do suggest that TGFbeta3 or stimulators of this signaling pathway hold potential as antidotes for dioxin-induced terata and that this opposing pharmacology may extend to additional toxicological endpoints.

Analysis of polymorphic TGFB1 codons 10, 25, and 263 in a German patient group with non-syndromic cleft lip, alveolus, and palate compared with healthy adults

Background

Clefts of the lip, alveolus, and palate (CLPs) rank among the most frequent and significant congenital malformations. Leu10Pro and Arg25Pro polymorphisms in the precursor region and Thr263Ile polymorphism in the prodomain of the transforming growth factor β1 (TGF-β1) gene have proved to be crucial to predisposition of several disorders.

Methods

In this study, polymorphism analysis was performed by real-time polymerase chain reaction (LightCycler) and TGF-β1 levels determined by enzyme-linked immunosorbent assay.

Results

Only 2/60 Caucasian non-syndromic patients with CLP (3.3%) carried the Arg25Pro and another 2/60 patients (3.3%) the Thr263Ile genotypes, whereas, in a control group of 60 healthy Caucasian blood donors, these heterozygous genotypes were more frequent 16.7% having Arg25Pro (10/60; p < 0.035) and 10,0% having Thr263Ile (6/60), respectively. TGF-β1 levels in platelet-poor plasma of heterozygous Arg25Pro individuals were lower than those of homozygous members (Arg25Arg) in the latter group, but this discrepancy narrowly failed to be significant. Although polymorphisms in codon 10 and 25 were associated with each other, no difference was found between patients and controls concerning the Leu10Pro polymorphism.

Conclusions

The genetic differences in codons 25 and 263 suggest that TGF-β1 could play an important role in occurrence of CLP, however, functional experiments will be required to confirm the mechanisms of disturbed development.

Association between palatal morphogenesis and Pax9 expression pattern in CL/Fr embryos with clefting during palatal development

The CL/Fr mouse strain develops cleft lip and palate (CLP) spontaneously. In this study, Pax9 mRNA expression was investigated in the palatal shelves during palatal morphogenesis to assess the correlation between secondary palatal morphogenesis and Pax9 expression of CL/Fr embryos with spontaneous cleft lip and palate. The expression of Pax9 mRNA was characterised using whole mount in situ hybridisation with a digoxygenin-labelled probe. In the control strain of C57BL/6 and CL/Fr normal embryos, Pax9 was expressed in the palate, especially along the medial edge (ME), on embryonic day 13.5 (E13.5) and E14.5 when the palatal shelves grew vertically down the side of the tongue and subsequently elevated to a horizontal position, and was down regulated on E15.5 when the palatal shelves met and began fusing. In the cleft embryo, Pax9 was expressed in the ME region but was not down regulated on E15.5. Furthermore, whole mount in situ hybridisation was performed after organ culture, using CL/Fr-N and CL/Fr-BCL palatal shelves dissected and approximated by pairs on E13.5. This showed that Pax9 was still expressed in the ME region in separated palatal shelves of CL/Fr-N and CL/Fr-BCL embryos, while Pax9 expression was down regulated in paired palatal shelves. These expression patterns of Pax9 in normal and cleft embryos during palatal fusion indicate that Pax9 expression is altered in spontaneous cleft lip and palate, and concludes that there is a direct correlation between Pax9 expression and palatal fusion.

Molecular, clinical and political approaches to the problem of cleft lip and palate

The oral facial complex in man appears to be exquisitively sensitive to genetic and environmental influences which is why clefts of the palate are the most common congenital birth anomaly. The development of the palate starts at about the 6th week of inter-uterine life and requires development of the palatal shelves from the maxillary processes of the first arch, shelf elevation, medial edge epithelial breakdown and mesenchyme flow with subsequent establishment of osteogenic and myogenic blastemata. This significant level of matrix turnover is partly regulated by the matrix metalloproteinases and potentially this could be affected by abnormalities in gene function. This may represent a common mechanism for a variety of different genes associated with clefting of the palate. The measurement of outcomes for children born with a cleft requires a wide input from a variety of specialities. The development of these outcome measures requires rigorous testing and validation, but it is now possible to use a variety of outcome measures to establish clinical standards and this has been done nationally. The impact of identifying a need for a change in organisation of service delivery was probably underestimated. It is clear that the current organisations in the National Health Service struggle to implement change, even with a detailed study and hard evidence. Reasons for this are outlined and a potential harder hitting strategy for effecting this change is outlined. The move towards primary care trusts within the latest reorganisation of the Health Service is potentially extremely damaging for specialised services for low incidence anomalies.

Rescue of an in vitro palate nonfusion model using interposed embryonic mesenchyme

The authors previously established an in vitro palate nonfusion model on the basis of a spatial separation between prefusion embryonic day 13.5 mouse palates (term gestation, 19.5 days). They found that an interpalatal separation distance of 0.48 mm or greater would consistently result in nonfusion after 4 days in organ culture. In the present study, they interposed embryonic palatal mesenchymal tissue between embryonic day 13.5 mouse palatal shelves with interpalatal separation distances greater than 0.48 mm in an attempt to "rescue" this in vitro palate nonfusion phenotype. Because no medial epithelial bilayer (i.e., medial epithelial seam) could potentially form, palatal fusion in vitro was defined as intershelf mesenchymal continuity with resolution of the medial edge epithelia bilaterally. Forty-two (n = 42) palatal shelf pairs from embryonic day 13.5 CD-1 mouse embryos were isolated and placed on cell culture inserts at precisely graded distances (0, 0.67, and 0.95 mm). Positive controls consisted of shelves placed in contact (n = 6). Negative controls consisted of shelves placed at interpalatal separation distances of 0.67 mm (n = 6) and 0.95 mm (n = 7) with no interposed mesenchyme. Experimental groups consisted of embryonic day 13.5 palatal shelves separated by 0.67 mm (n = 11) and 0.95 mm (n = 12) with interposed lateral palatal mesenchyme isolated at the time of palatal shelf harvest. Specimens were cultured for 4 days (n = 19) or 10 days (n = 23), harvested, and evaluated histologically. All positive controls at 4 and 10 days in culture showed complete histologic palatal fusion. All negative controls at 4 days and 10 days in culture remained unfused. Five of six palatal shelves separated at 0.67 mm interpalatal separation distance with interposed mesenchyme were fused at 4 days, and all five were fused at 10 days. At an interpalatal separation distance of 0.95 mm with interposed mesenchyme (n = 12), no palates (zero of four) were fused at 4 days, but seven of eight were fused at 10 days. These data suggest that nonfused palatal shelves can be "rescued" with an interposed graft of endogenous embryonic mesenchyme to induce fusion in vitro.

Prenatal and perinatal factors associated with isolated oral clefting

OBJECTIVE

To describe medical service utilization and maternal morbid conditions of women who carry offspring with oral clefts (OCs), to describe maternal and offspring complications during birth, and to evaluate postnatal characteristics of their newborns with isolated OCs.

METHODS

Two thousand four hundred thirty-seven patients with isolated OCs and 4871 unaffected matched controls meeting inclusion criteria were selected from the U.S. Natality database for 1997. Matching variables were mother's and father's race and child's race, sex, county of birth, and month of birth. Patients and controls were compared in terms of maternal demographic characteristics, gestational complications, physical characteristics of the newborns, maternal exposure to potential risk factors, and adequacy of prenatal care.

RESULTS

Although the quality of care was very good in both groups, low gestational age, low birth weight, and low 5-minute Apgar score are more frequent among newborns with OCs than in unaffected controls. Mothers of offspring with OCs are at increased risk, compared with mothers of controls, of having hydramnios or oligohydramnios, eclampsia, and abruptio placenta. Obstetric procedures, such as amniocentesis, electronic fetal monitoring, induction of labor, tocolysis, and ultrasound, and repeat cesarean deliveries are more frequent among mothers of patients than those of controls. At birth, newborns with isolated OCs are at risk of having hyaline membrane disease and of requiring assisted ventilation, independently of gestational age.

CONCLUSION

The results of this large population-based, case-control study suggest that the presence of an OC in the offspring is associated with increased risk for prenatal and perinatal complications in the mother.

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.

Immunolocalization of fibroblast growth factor receptors 1 and 2 in mouse palate development

Recent evidence has implicated mutations of fibroblast growth factor receptors (FGF-R) in the pathogenesis of craniosynostotic syndromes. Cleft palate can be a component of such syndromes. The expression of FGF-R1 and FGF-R2 has been delineated in normally developing cranium, where they seem to regulate cellular differentiation and proliferation, respectively. The specific role of fibroblast growth factor signaling in mammalian palate development is unclear. The authors investigated the patterns of expression of FGF-R1 and FGF-R2 throughout mouse palatal development in the embryo. Time-dated CD-1 mouse heads (n = 135) were harvested at embryonic ages 12.5, 13.5, 14.5, 15.5, and 16.5 days (term gestation = 19.5 days), fixed in paraformaldehyde, embedded in paraffin, and sectioned. In addition, paired palatal shelves (n = 30) were isolated by means of microdissection from embryonic day--13.5 embryos, grown on Millipore filters in serum-free medium in vitro for 24, 48, 72, or 96 hours and processed for histological analysis. Immunohistochemical analysis for FGF-R1 and FGF-R2 was performed on the in vivo and in vitro specimens. FGF-R1 and FGF-R2 were found to be specifically expressed in the epithelium of the developing palatal shelves from the time of their outgrowth from the maxillary processes through completion of fusion in vivo and in vitro. Expression of both receptors was particularly strong during the phases of medial epithelial-medial epithelial contact between the individual shelves, through the formation of the medial epithelial seam, to the ultimate dissolution of the seam. Such a pattern of expression seems to implicate fibroblast growth factor signaling in the regulation of the critical phase of fusion of the bilateral shelves. The expression of both FGF-R1 and FGF-R2 in the lateral palatal mesenchyme, where such secondary structures as tooth primordia and bone begin to appear, also suggests a role for fibroblast growth factor signaling in the induction of ongoing differentiation and maturation of the palate after fusion. These data suggest that fibroblast growth factor signaling may play a role in the epithelial-mesenchymal interactions that dictate fusion and maturation of the developing palate. Furthermore, the data are consistent with the correlation of cleft palate formation with aberrant fibroblast growth factor signaling.

Temporal and spatial expression of Hoxa-2 during murine palatogenesis

1. Mice homozygous for a targeted mutation of the Hoxa-2 gene are born with a bilateral cleft of the secondary palate associated with multiple head and cranial anomalies and these animals die within 24 hr of birth (Gendron-Maguire et al., 1993; Rijli et al., 1993; Mallo and Gridley, 1996). We have determined the spatial and temporal expression of the Hoxa-2 homeobox protein in the developing mouse palate at embryonic stages E12, E13, E13.5, E14, E14.5, and E15. 2. Hoxa-2 is expressed in the mesenchyme and epithelial cells of the palate at E12, but is progressively restricted to the tips of the growing palatal shelves at E13. 3. By the E13.5 stage of development, Hoxa-2 protein was found to be expressed throughout the palatal shelf. These observations correlate with palatal shelf orientation and Hoxa-2 protein may play a direct or indirect role in guiding the palatal shelves vertically along side the tongue, starting with the tips of the palatal shelves at E13, followed by the entire palatal shelf at E13.5. 4. As development progresses to E14, the stage at which shelf elevation occurs, Hoxa-2 protein is downregulated in the palatal mesenchyme but remains in the medial edge epithelium. Expression of Hoxa-2 continues in the medial edge epithelium until the fusion of opposing palatal shelves. 5. By the E15 stage of development, Hoxa-2 is downregulated in the palate and expression is localized in the nasal and oral epithelia. 6. In an animal model of phenytoin-induced cleft palate, we report that Hoxa-2 mRNA and protein expression were significantly decreased, implicating a possible functional role of the Hoxa-2 gene in the development of phenytoin-induced cleft palate. 7. A recent report by Barrow and Capecchi (1999), has illustrated the importance of tongue posture during palatal shelf closure in Hoxa-2 mutant mice. This along with our new findings of the expression of the Hoxa-2 protein during palatogenesis has shed some light on the putative role of this gene in palate development.

Prenatal exposure to disulfiram implicated in the cause of malformations in discordant monozygotic twins

Female monozygotic (MZ) twins were discordant for congenital structural anomalies: Twin A had a reduction defect of the right forearm; Twin B had a cleft palate. Both infants were small for gestational age. Specific prenatal exposures were identified at different times in the first trimester of pregnancy: crack cocaine, marijuana, disulfiram, heavy ethanol exposure, and cigarettes. The mother's hospitalization in a drug abuse program and incarceration allowed for identification of exposure timing. The cleft palate could have been related to either disulfiram or alcohol exposure; the limb abnormality most likely corresponded to the timing of disulfiram exposure. Discordance of anomalies in these twins may reflect differences in developmental timing, differences in susceptibility to one or more teratogens, or random events occurring within very complex developmental programs, with the thresholds for malformation affected by one or multiple teratogenic compounds.

Glucocorticoid receptor gene expression during rat embryogenesis. An in situ hybridization study

Glucocorticoids play an important role in embryonic development. The existence of sufficient amounts of their receptors during rodent embryogenesis has proved to be an absolute necessity for the physiological growth of the animal. We have analyzed the pattern of glucocorticoid receptor gene expression in the rat embryo through embryonic days 12 to 17, by using in situ hybridization histochemistry. Glucocorticoid receptor mRNA is present in the rat liver on embryonic day (E) 12, and by E13 the signal can also be detected in several other tissues, such as the lung, the heart, the mesonephros, the sclerotomes, the thymus and Rathke's pouch. Glucocorticoid receptor gene expression was quite ubiquitous in tissue derivatives of all three germ layers and appeared to vary in intensity within the same tissue during embryogenesis. These variations in the level of receptor gene expression paralleled the developmental stage of each tissue: Intense labelling was detected just prior to the final differentiation step of a structure. Upon differentiation, cell populations highly expressing glucocorticoid receptor gene in the previous stage were found to have reduced amounts of the receptor mRNA. Our results support a morphogenetic role for glucocorticoids during embryogenesis.

Maternal smoking and orofacial clefts

To investigate a possible association between maternal smoking during pregnancy and oral clefts, a study was conducted using Swedish health registries. Infants with oral clefts (N = 1834) were selected among 1,002,742 infants born between 1983 and 1992 with known smoking exposure in early pregnancy. Confounders such as maternal age and parity were controlled for by using the Mantel-Haenszel technique. A statistically significant association with maternal smoking was found. The odds ratio (OR) for any maternal smoking among cases of cleft lip with or without cleft palate [CL(P)] was 1.16 (95%Cl: 1.02-1.32). For cases of cleft palate alone (CP), the corresponding OR was 1.29 (95%Cl: 1.08-1.54). The results of the present study, based on the largest series of oral cleft cases published to date, indicate that cigarette smoking during pregnancy is associated with increased risks of CL(P) and CP.

Transforming growth factor-beta 3 is required for secondary palate fusion

Mice lacking TGF-beta 3 exhibit an incompletely penetrant failure of the palatal shelves to fuse leading to cleft palate. The defect appears to result from impaired adhesion of the apposing medial edge epithelia of the palatal shelves and subsequent elimination of the mid-line epithelial seam. No craniofacial abnormalities were observed. This result demonstrates that TGF-beta 3 affects palatal shelf fusion by an intrinsic, primary mechanism rather than by effects secondary to craniofacial defects.

Regulation of TGF beta 3 gene expression in embryonic palatal tissue

The TGF beta family of genes has been shown to play an important role in regulating various aspects of development, although the mechanisms by which TGF beta exerts its effects have not yet been clarified. Growth and differentiation of both murine embryonic palate mesenchymal (MEPM) cells and palatal epithelium can be regulated by the TGF beta s. We therefore examined the expression of mRNAs encoding TGF beta 1, TGF beta 2, and TGF beta 3 in developing embryonic palatal tissue as well as factors that modulate their levels of expression. Northern blot analysis of RNA isolated from murine embryonic palatal tissue on gestational days (GD) 12, 13, and 14 demonstrated the presence of one mRNA transcript for TGF beta 1 (2.5 kb), two transcripts for TGF beta 2 (4.4 kb, 6.0 kb), and one transcript for TGF beta 3 (3.5 kb). Although steady-state levels of TGF beta 1 mRNA showed no changes during development of the palate, TGF beta 2 mRNA levels were maximal on both GD13 and GD14 and TGF beta 3 mRNA levels transiently increased on GD 13. In addition, levels of TGF beta 3 mRNA seemed much higher than either TGF beta 1 or TGF beta 2. both TGF beta 1 and TGF beta 2 were able to increase, in a dose-related manner, the expression of TGF beta 3 mRNA in murine embryonic palate mesenchymal cells in vitro. In contrast, epidermal growth factor (EGF) down-regulated the expression of TGF beta 3 mRNA even in the presence of TGF beta 1 or TGF beta 2.(ABSTRACT TRUNCATED AT 250 WORDS)

Exclusion of candidate genes from a role in cleft lip with or without cleft palate: linkage and association studies

Candidate genes and marker loci for cleft lip/palate (CL/P) were tested using linkage analyses and association studies. Eight British families with apparent autosomal dominant inheritance of non-syndromic CL/P participated in the linkage analyses while the association analyses involved 61 unrelated British white people with CL/P and 60 controls. The report of an association between RARA (17q21) and unrelated Australian persons with CL/P (p = 0.016) was not confirmed in British CL/P persons (chi 2 = 0.954, p > 0.1). There was also no evidence of linkage between RARA and the eight CL/P families (Z = -3.211, theta = 0.001). Linkage was excluded between familial CL/P and F13A1 (map position 6p24-25) with an observed maximum lod score of Z = -2.052 at theta = 0.05. No association was found between alleles at VIM (10p13) and the British CL/P subjects (chi 2 = 0.110, p > 0.5). Multipoint analysis excluded linkage between familial CL/P and the markers D1S65 and D1S58 which flank the Van der Woude syndrome locus with a maximum lod score of Z = -4.0. This suggests that the genetic defect underlying VWS is not the same as in non-syndromic CL/P. There was no evidence of linkage between CRTL1 (5q15) and the eight CL/P families (Z = -3.466, theta = 0.05).

Linkage of Van der Woude syndrome (VWS) to REN and exclusion of the candidate gene TGFB2 from the disease locus in a large pedigree

Van der Woude syndrome (VWS) is an autosomal dominant disorder associated with one or more of the following features: clefting of the primary or secondary palate, hypodontia or lower lip pits. It has been estimated to account for 2% of all cases of cleft lip and palate. VWS is one of the rare disorders in which clefting of the primary and secondary palate may be seen to segregate as components associated with the same gene. Because of its autosomal dominant inheritance, VWS is readily accessable to linkage analysis as a preliminary step in the identification of the molecular abnormality underlying the clefting effect in the primary and secondary palate. A reported linkage between REN and VWS has promoted us to use pHRnX3.6 (REN) and several markers surrounding REN for a linkage analysis in a large Swiss family. In a second step, linkage analysis was performed to study restriction fragment length polymorphisms for the candidate gene TGFB2 and other loci recently mapped to the candidate region 1q32-1q41. Evidence for linkage (theta = 0.00, lod score = 3.01) between REN and VWS could be confirmed in this pedigree. TGFB2 demonstrated recombination with the disease locus and is unlikely to be causative in VWS. The results of a multipoint linkage analysis showed that VWS was flanked by D1S65 and TGFB2 at a maximum location score of 20.3.

No evidence of linkage between the transforming growth factor-alpha gene in families with apparently autosomal dominant inheritance of cleft lip and palate

Eight families have been identified with cleft lip, with or without cleft palate (CL/P), inherited in an apparently autosomal dominant manner. Transforming growth factor-alpha (TGFA) has been tested as a candidate gene for clefting in these families. Negative lod scores were generated in an autosomal dominant model with 80% penetrance (Z = -3.152 at theta = 0.05 and Z = -2.49 at theta = 0.05 with only affected subjects scored). After testing with a reduced penetrance of 28%, less negative lod scores were generated (Z = -0.157 at theta = 0.00), but there was still no evidence of linkage. An autosomal recessive model with a penetrance of 35% was also tested. Regardless of the model used there was little evidence of linkage between TGFA and the CL/P phenotype, which is in contrast to the previously published findings of an association between TGFA and CL/P in unrelated subjects.

The effects of epidermal growth factor, transforming growth factors alpha and beta and platelet-derived growth factor on murine palatal shelves in organ culture

Palatal shelves isolated from day-13 embryonic mice were explanted on to the surfaces of collagen gels either singly or in pairs with their medial edges in contact, and cultured submerged in a 1:1 mixture of Dulbecco's modified Eagle's medium/Ham's F12 medium. The medium was supplemented with either 10 ng/ml epidermal growth factor (EGF), 10 ng/ml transforming growth factor alpha (TGF alpha), 1 ng/ml transforming growth factor beta (TGF beta 1) or 2 ng/ml platelet-derived growth factor (PDGF) all in the presence or absence of 2.5% donor calf serum (DCS). Cultures were terminated after 0, 24, 48 or 72 h and processed for histological and immunocytochemical examination. In serum-free medium and medium supplemented with 2.5% DCS the palatal epithelia differentiated in a manner similar to that seen in vivo (oral, keratinization; nasal, pseudostratified, ciliated columnar cells and medial edge, epithelial degeneration). A similar pattern was obtained in serum-free medium supplemented with either EGF or TGF alpha. However in cultures with either EGF or TGF alpha plus 2.5% DCS present in the medium, medial-edge epithelial degeneration was inhibited and the oral epithelia were more heavily keratinized. The mesenchyme of such cultures stained more intensely for various extracellular matrix molecules. In TGF beta 1-supplemented cultures (with, but especially without, serum supplementation) the epithelia were thin, medial-edge epithelial degeneration was marked, and the fibronectin content of the mesenchyme was increased. PDGF prevented medial-edge epithelial degeneration in the presence, but not in the absence, of serum; mesenchymal extracellular molecules were not as prevalent as with the EGF treatment. These results indicate that exogenous growth factors (including those present in serum) exert effects on organ-cultured mouse palatal shelves in a fashion similar to their effects in cell culture and that controlled physiological levels of such factors may be important in mouse palatal development.

Regulation of murine embryonic epithelial cell differentiation by transforming growth factors beta

The expression of some members of the transforming growth factor beta (TGF beta) family of genes in embryonic craniofacial tissue suggests a functional role for these molecules in orofacial development. In an attempt to ascertain a role for the TGF beta s during palatal ontogeny, murine palatal shelves were excised on gestation day (GD) 12, prior to overt epithelial differentiation, grown in organ culture under serum-free conditions and exposed to TGF beta 1 and TGF beta 2 for 18 or 42 h. Shelves were labeled with [3H]-thymidine (20 microCi/ml) during the last 4 h in culture, fixed, dehydrated, embedded in paraffin and sections stained and examined by autoradiography. Treatment of GD12 palates with TGF beta 1 and TGF beta 2 resulted in precocious cessation of medial edge epithelium (MEE) DNA synthesis followed by elimination of the MEE. In addition, this response appeared to be dose-related with higher concentrations of growth factor eliciting a more marked biological response. TGF beta treatment of homologous shelves grown in apposition also resulted in precocious fusion of apposing MEE. Thus, members of the TGF beta family, known to be synthesized by palatal MEE, appear to act in an autocrine/paracrine fashion in this tissue and are capable of regulating differentiation of embryonic palatal medial edge epithelium.

Biologic basis for a risk assessment model for cleft palate

A biologic model for palatogenesis is presented, intended as a basis for risk assessment. It comprises a sequence of developmental stages: growth and migration of neural crest cells, downward growth of palatal buds, elevation of palatal shelves, and differentiation of the epithelium followed by shelf fusion. Several events representing these stages and amenable to mathematical translation may be measurable in the form of biomarkers such as DNA and protein synthesis, phospholipid metabolism, and signal transducing systems. Interrupting components of the model will result in cleft palate. Teratogens with known mechanisms of action are compared with the model. The quantitative risk of cleft palate is conceived as a sequence of mathematical probabilities that any stage of the model runs an abnormal course. Stage-specific probabilities are determined by a chemical's potency and dose, and by duration of exposure and gestational age. Species or strain sensitivity may be expressed as quantitative differences in model parameters. Although the model is designed for cleft palate, the risk model may also estimate a multiple response risk to the same exposures.

Managing the cleft lip and palate patient

We have attempted to elucidate, first through an examination of the basic science of clefting and then through a description of the roles of the various members of the cleft palate team, an understanding of the multiplicity of problems faced by this heterogeneous group of children with cleft lip or palate. With an incidence of cleft of 1 in 700 births, all practicing pediatricians will at some time be faced with a patient with a cleft. Pediatric management begins in the hospital nursery by ruling out possible associated anomalies (e.g., congenital heart disease or urinary tract) or syndromes. At the same time, cleft palate nursers may be needed to overcome feeding problems. Simultaneously, counseling for the family begins with a positive attitude toward outcome and an initial explanation of the schedule of corrective procedures, i.e., lip repair at 3 months of age and palate repair at about 1 year. The counseling should incorporate an understanding of the cause of clefting, both its genetics and teratogenetics, and then proceed to noting the actual recurrence risks of 1% for a new cleft and 16% if there is a positive family history in a first-degree relative. The recurrence risks in recognized syndromes may follow mendelian patterns. Later, the pediatrician can help the family deal with multiple ear infections and the likely need for tympanostomy tubes, anticipating the need for tubes in a way that might facilitate placement at the time of anesthesia for the lip or the palate repairs. An understanding of the speech and language difficulties that may be encountered in later infancy may relieve parental anxiety. Later, after palate repair, knowledge of velopharyngeal incompetence may avert premature hypernasal speech problems caused by adenoidectomy, which should be avoided if at all possible. The pediatrician needs to be aware of the tooth malformations that accompany clefting of the alveolus as well as the increased susceptibility to caries, so that the family may be directed to early intervention by the pediatric dentist. With support by pediatrics of the efforts of pediatric dentistry, the child is then in optimal condition for orthodontics. Continually keeping the child's emotional adjustment in mind, the pediatrician can encourage the child and family, knowing that with palatal expansion techniques plus possible bone graft surgery to the cleft alveolus at about 9 years of age, the child may be orthodontically corrected to very near normal.(ABSTRACT TRUNCATED AT 400 WORDS)

Immunolocalization of epidermal growth factor (EGF), EGF receptor and transforming growth factor alpha (TGF alpha) during murine palatogenesis in vivo and in vitro

The distribution of epidermal growth factor, the epidermal growth factor receptor and transforming growth factor alpha during murine palatogenesis was investigated immunocytochemically. On embryonic day 12 staining for transforming growth factor alpha was present throughout the palatal mesenchyme, with little in the epithelia. On embryonic day 13 staining increased in the palatal epithelia and in the mesenchyme at the tip of the palate. As the palatal shelves fused together (embryonic day 14.5) intense staining for transforming growth factor alpha was seen in the midline epithelial seam and in the subjacent mesenchyme. On embryonic day 15 there was a generalised increase in palatal epithelial staining; this was most marked in the remnants of the degenerating epithelial seam. Mesenchymal staining was, however, uniform. Whilst palatal staining for epidermal growth factor was sparse, at all stages, staining for its receptor was present throughout the palatal epithelia and mesenchyme. This was most intense in the palatal medial edge epithelia at the time of midline epithelial seam degeneration. The regional and temporal differences in staining for the epidermal growth factor receptor and transforming growth factor alpha suggested that these molecules may play an important role in normal palate development in vivo, particularly in degeneration of the midline epithelial seam.

Differential expression of genes encoding TGFs beta 1, beta 2, and beta 3 during murine palate formation

Transforming growth factor beta 1 (TGF beta 1) has been shown to have multiple effects on primary cultures of palate-derived cell types. We report the analysis, by in situ hybridization, of RNA expression for three different TGF beta isoforms (TGF beta 1, beta 2, and beta 3) during murine embryonic palate development. Differential expression of the three TGF beta genes is seen in the palatal shelves in mesenchymal and epithelial cells known to be involved in the morphogenesis of this organ. Taken together, these results suggest that the TGF beta s act as endogenous factors involved in the formation of the mammalian palate.

Influence of epithelial-mesenchymal interaction on the viability of facial mesenchyme. II: Synthesis of basement-membrane components during tissue recombination

The presence of basement-membrane components during tissue separation procedures was determined employing monoclonal antibodies to laminin and type IV collagen. In addition, the reconstitution of basement-membrane components and the formation of the basement-membrane were examined in isolated epithelium and mesenchyme and in tissue recombination. Epithelium and mesenchyme of maxillary processes of chick embryos were separated by a variety of protocols, including those employed in a prior study (Saber et al: Anat. Rec. 225:56-66, 1989). Results indicated that the protocol previously employed did not remove basement-membrane components after enzymatic tissue separation. A revised protocol in which the basement-membrane components (i.e., laminin and type IV collagen) were removed from isolated tissues prior to recombination revealed that a developmental compartment and a gradient of cell viability, comparable in size and dimensions to that observed in the study of Saber et al. (ibid.) was present in the mesenchyme of recombined explants. Type IV collagen and laminin, therefore, do not appear to be required initially during tissue recombination in order for subsequent growth-sustaining effects to be expressed. Additional studies revealed, however, that synthesis of basement-membrane components occurred not only in isolated tissues but was altered markedly by tissue recombination. Culture of isolated tissues demonstrated induction of laminin synthesis in separated epithelium by 24 hours and induction of collagen synthesis in isolated mesenchyme by 24 hours. Recombination of epithelium and mesenchyme, however, resulted in rapid induction of laminin synthesis within 1 hour. Recombination of epithelium and mesenchyme after 24 hours resulted in the presence of laminin not only in epithelium but in mesenchyme as well. Both tissues were required for basement-membrane formation which appeared to be fully reconstituted by 24 hours in culture. These observations indicate that recombination in culture alters the pattern of synthetic activity of these basement-membrane components. These can be characterized as "early" (temporal) and "late" spatial) responses by the recombined tissues.

Tenascin distribution in the normal human breast is altered during the menstrual cycle and in carcinoma

Tenascin is a novel extracellular matrix glycoprotein which appears to have a major role in tissue development. Previous studies have stated that tenascin is absent from the normal human, rat and mouse breast, its distribution being restricted to embryonic and malignant mammary tissues. No previous studies have investigated tenascin distribution as a function of the normal menstrual cycle. Therefore this study addresses the cyclical appearance of tenascin in the normal breast and associated changes in distribution in preinvasive cancer (carcinoma-in-situ) and invasive infiltrating ductal carcinoma. Tenascin is present in the normal human adult mammary gland, principally in the basement membrane, sub-basement-membrane zone and delimiting layer of fibroblasts around the ductules. Both the distribution and quantity of tenascin change during the menstrual cycle. In carcinoma-in-situ (preinvasive cancer) tenascin is present in the attenuated basement membrane/sub-basement-membrane zone around the expanded ductules and in small amounts in the stroma. In infiltrating ductal carcinoma, tenascin is absent from the remnants of the basement membrane and sub-basement-membrane zone but greatly increased in the adjacent intralobular and interlobular stroma. Therefore, if tenascin is used as a basement membrane/sub-basement-membrane marker for distinguishing carcinoma-in-situ from invasive ductal carcinoma, the time of the menstrual cycle is of importance in interpreting the biopsy appearance. This study suggests that the optimal time for biopsy is between weeks 3 and 4 of the cycle, to avoid confusion between the normal low levels of tenascin (due to hormonal status) and those due to microinvasive disease.(ABSTRACT TRUNCATED AT 250 WORDS)