Localization of epidermal growth factor precursor in tooth and lung during embryonic mouse development

Regulation of alveologenesis: clinical implications of impaired growth

During its development that begins in intrauterine life, the lung is transformed from a simple epithelial lined sac that emerges from the foregut into a complex arrangement of blood vessels, airways, and alveoli that make up the mature lung structure. This remarkable transformation that continues for several years postnatally, is achieved by the influence of several genes, transcription factors, growth factors and hormones upon the cells and proteins of the lung bud. A seminal event in this process is the formation of the air-blood barrier within the alveolar wall, an evolutionary modification that permits independent air-breathing existence in mammals. Molecular biological techniques have enabled elucidation of the mechanistic pathways contributing to alveologenesis and have provided probable molecular bases for examples of impaired alveologenesis encountered by the paediatric pathologist.

Immunohistochemical detection of phosphorylated Akt, PI3K, and PTEN in ameloblastic tumors

OBJECTIVE

To evaluate roles of the Akt signaling pathway in oncogenesis and cytodifferentiation of odontogenic tumors, expression of phosphorylated Akt (pAkt), PI3K, and PTEN was analyzed in ameloblastic tumors as well as in tooth germs.

METHODS

11 tooth germs, 40 ameloblastomas, and 5 malignant ameloblastic tumors were examined immunohistochemically with antibodies against pAkt, PI3K, and PTEN.

RESULTS

Immunoreactivity for pAkt, PI3K, and PTEN was detected predominantly in odontogenic epithelial cells near the basement membrane in tooth germs and ameloblastic tumors. The levels of immunoreactivity for pAkt and PI3K were slightly higher in ameloblastic tumors than in tooth germs. Plexiform ameloblastomas showed significantly higher expression of PI3K than follicular ameloblastomas, and PI3K immunoreactivity in ameloblastomas without cellular variation was significantly higher than that in acanthomatous ameloblastomas. The level of PTEN immunoreactivity was significantly lower in ameloblastomas than in tooth germs.

CONCLUSION

Expression of pAkt, PI3K, and PTEN in tooth germs and ameloblastic tumors suggests that these signaling molecules regulate cell survival and growth in normal and neoplastic odontogenic tissues by mediating growth factor signals. Increased expression of pAkt and PI3K and decreased expression of PTEN in ameloblastic tumors may participate in oncogenesis of odontogenic epithelium by activating the Akt signaling pathway.

GD3 synthase gene found expressed in dental epithelium and shown to regulate cell proliferation

GD3 synthase is one of the key enzymes involved with ganglioside synthesis, and its activity regulates the main profile of ganglioside expression. We analyzed the expression of the GD3 synthase gene in laser-dissected teeth germs using RT-PCR. The GD3 synthase gene was found expressed in brain, thymus, and tooth germ tissues, however, not in liver or skin specimens. Further, it was highly expressed during the early stage of tooth germ development (embryonic day 14.5), especially in dental epithelia, which gradually reduced in the molar site until postnatal day 7, whereas it was not in dental mesenchyme tissues. In addition, dental epithelial cells transiently transfected with the GD3 synthase gene showed enhanced proliferation. These results indicate that the GD3 synthase gene may be involved in early tooth development, particularly in the proliferation of dental epithelium.

Effects of maternal ethanol intake on immunoexpression of epidermal growth factor in developing rat mandibular molar

OBJECTIVE

A polyclonal antibody was used to investigate the effects of ethanol ingestion before and during pregnancy, in the expression of EGF on dentinogenesis and amelogenesis of rat mandibular first molar.

DESIGN

Ethanol was administered to drinking water (treated group) starting at concentrations of 1% and increasing weekly to 5, 10, 15, 20 and 25% (v/v). During week 7, these rats were mated and continued to receive the 25% alcoholic solution, up to delivery. The control group received tap water. On postnatal days 0, 4 and 9, two offspring of each litter were killed, their hemimandibles removed and prepared for paraffin processing and immunohistochemistry.

RESULTS

At postnatal day 0 the EGF immunoreactivity of the inner enamel epithelium and presecretory ameloblasts was weak when compared to controls. At postnatal day 4 EGF immunoreactivity of the secretory ameloblasts and odontoblasts was only moderate compared to controls. At postnatal day 9 EGF staining of the ameloblasts was weak when compared to controls.

CONCLUSIONS

These results suggest that, maternal alcoholism interferes with EGF expression during initial dentinogenesis and amelogenesis and in the secretion and maturation of the dentin and enamel, therefore, which may cause a reduction of dentin and enamel formation.

Tissue transglutaminase was up-regulated by EGF-retinoid interplay in epithelial carcinoma cells

Retinoids have been shown the most powerful inducers of transglutaminase activity, a well known marker of differentiation. In this work, we tested the effects of all-trans retinoic acid and EGF, used alone or in combination, on transglutaminase activity in a squamous, epithelial carcinoma cell line, HEp-2. We demonstrated that nanomolar EGF further enhances transglutaminase activity previously induced by all-trans retinoic acid. Confocal laser scanning microscopy revealed functional changes in transglutaminase activity localisation, at first restricted to the outermost region of cytosol, then diffused both in the membrane region and extracellular space. RT-PCR showed the presence of mRNA transcripts of different transglutaminases (1, 2, 3). Transglutaminase 2 expression was increased by either all-trans retinoic acid or EGF, and further up-regulated by the simultaneous addition of both substances. These effects were confirmed by Western blotting with transglutaminase 2 specific antibody. The results obtained by combined use of retinoic acid and EGF suggest that transglutaminase activity and expression are differently regulated, and that EGF-signalling can be involved in differentiation of epithelial carcinoma cells induced by retinoids.

Regulation of mandibular growth and morphogenesis

The development of the vertebrate face is a dynamic process that starts with the formation of facial processes/prominences. Facial processes are small buds made up of mesenchymal masses enclosed by an epithelial layer that surround the primitive mouth. The 2 maxillary processes, the 2 lateral nasal processes, and the frontonasal processes form the upper jaw. The lower jaw is formed by the 2 mandibular processes. Although the question of the embryonic origin of facial structures has received considerable attention, the mechanisms that control differential growth of the facial processes and patterning of skeletal tissues within these structures have been difficult to study and still are not well-understood. This has been partially due to the lack of readily identifiable morphologically discrete regions in the developing face that regulate patterning of the face. Nonetheless, in recent years there has been significant progress in the understanding of the signaling network controlling the patterning and development of the face (for review, see Richman et al., 1991; Francis-West et al., 1998). This review focuses on current understanding of the processes and signaling molecules that are involved in the formation of the mandibular arch.

Teratogenicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in mice lacking the expression of EGF and/or TGF-alpha

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) exposure produces hydronephrosis and cleft palate in mice. These responses are correlated with disruption of expression of epidermal growth factor (EGF) receptor ligands, primarily EGF and transforming growth factor-alpha (TGF-alpha), and altered epithelial cell proliferation and differentiation. This research examined the role of these growth factors in TCDD-induced teratogenicity by using wild type (WT) and knockout (-/-) mice that do not express EGF, TGF-alpha, or both EGF and TGF-alpha. Pregnant females were weighed on GD 12 and dosed by gavage with either corn oil or TCDD at 24 microg/kg, 5 ml/kg. On GD 17.5, the maternal parameters evaluated included body weight, body weight gain, liver weight (absolute and adjusted for body weight). The number of implantations, live and dead fetuses, early or late resorptions, the proportion of males, fetal body weight, fetal absolute and relative liver weight, placenta weight, incidence of cleft palate, and the severity and incidence of hydronephrosis were recorded. TCDD did not affect maternal weight gain, fetal weight, or survival, but maternal and fetal liver weights and liver-to-body weight ratios were increased in all genotypes. The WT and TGF-alpha (-/-), but not the EGF (-/-) and EGF + TGF-alpha (-/-) fetuses, developed cleft palate after exposure to 24 microg TCDD/kg. Hydronephrosis was induced by TCDD in all genotypes, with the incidence in EGF + TGF-alpha (-/-) fetuses comparable to that of the WT. The incidence and severity of this defect was substantially increased in EGF (-/-) and TGF-alpha (-/-). In conclusion, this study demonstrated that expression of EGF influences the induction of cleft palate by TCDD. Also, EGF and TGF-alpha are not required for the induction of hydronephrosis, but when either is absent the response of the fetal urinary tract to TCDD is enhanced.

The murine amelogenin promoter: developmentally regulated expression in transgenic animals

We are interested in understanding hierarchical regulation pathways that control gene expression in developing teeth. In pursuit of the molecular basis for the regulated expression of amelogenin by developing ameloblasts during tooth formation, we isolated the murine amelogenin promoter. Analysis of this promoter will provide additional details towards the identification of signals generated through instructive-, dissimilar-germ layer interactions that are for responsible for temporal- and spatial-regulation for amelogenin gene expression. Using transgenic mice we demonstrate that a 2263 nucleotide stretch of the murine amelogenin promoter conveys appropriate temporal- and spatial-regulation for amelogenin gene expression in response to instructive-signals. These transgenic animals are useful reagents to further dissect signaling pathways responsible for regulated gene expression by terminally differentiated ameloblasts.

DNA sequence and functional characterization of the human and rat epidermal growth factor promoter: regulation by cell growth

Epidermal growth factor (EGF) regulates cell growth and differentiation through intracellular transduction networks activated by its tyrosine kinase receptor, EGFR. In this report we describe the structure and DNA sequence of transcriptional control regions from both human and Wistar-rat single copy EGF genes and their functional analysis in epithelial cell cultures. By sequence comparison we show these proximal gene regions have remained conserved in evolution to -640 (relative to the rodent mRNA initiation site), where similarity is interrupted by a rodent interspersed-repeat element (SINE). Transcript mapping reveals complexity in EGF initiation site selection: whereas a single rat liver initiation site (+1) appears 30bp 3' to the TTTAA element, an additional upstream site is detected in kidney RNA at -14. In contrast, in human RNA a single initiation is observed, which is displaced 12bp 3' to the rodent RNA terminus. Both promoters were defined in transient expression assays. Our results show the human promoter to be at least 20-fold more active than the equivalent rodent sequence, although both are activated during cell proliferation and negatively regulated in contact inhibited and quiescent cultures. The results indicate EGF gene expression and cell division are temporally linked, suggesting its promoter comprises a growth responsive regulatory domain.

Differentiation and proliferation of pulmonary neuroendocrine cells

In this review article the morphological profiles of pulmonary neuroendocrine cells (PNEC) in experimental animals and humans are described. Although the mechanisms of differentiation and proliferation of neuroendocrine cells in the airway epithelium remain to be solved, several experimental studies using explant culture and cell culture systems of fetal animal lungs have been performed to clarify fundamental phenomena associated with neuroendocrine differentiation and proliferation. Experimental animal studies using chronic hypoxia, toxic substances and carcinogens have succeeded in inducing alterations in PNEC systems, and these studies have elucidated the reactions of PNEC in cell injury and inflammation, and functional aspects of PNEC in disease conditions. Human pulmonary neuroendocrine tumors include various histological subtypes, and show divergent morphological and biological varieties. Molecular abnormalities of small cell carcinoma, the most aggressive subtype of pulmonary neuroendocrine tumors, have been extensively studied, but the mechanism of neuroendocrine differentiation of this tumor is still largely unknown. PNEC share common phenotypes with neuronal cells, and developmental studies have begun contributed evidence that similar transcriptional networks, including active and repressive basic helix-loop-helix (bHLH) factors, function in the differentiation of both PNEC and neuronal cells. Such a bHLH network may also play a central role in determining cell differentiation in lung carcinomas. Further studies of the neuronal bHLH network, its regulatory system and related signal transduction pathways, will be required for understanding the mechanisms of neuroendocrine differentiation and proliferation in normal and pathological lung conditions.

Effects of BMP-7 on mouse tooth mesenchyme and chick mandibular mesenchyme

BMP-7 is a member of the BMP family of signaling molecules that are thought to play key roles in mediating inductive events during embryogenesis. In the present study the possible roles of BMP-7 in mediating inductive events during the initiation phase of odontogenesis and mandibular morphogenesis were investigated. To do so, we have examined the effects of agarose beads soaked in recombinant BMP-7 on E11 mouse molar-forming mesenchyme and stage 23 chick mandibular mesenchyme, and analyzed the patterns of expression of Bmp-7 in developing mouse and chick first branchial arches. Beads releasing BMP-7 induced a translucent zone, cellular proliferation, and expression of Msx-1, Msx-2, and Bmp-4 in molar-forming mesenchyme after 24 hr. The effects of BMP-7 on molar-forming mesenchyme are similar to the effects of BMP-4 and are consistent with their overlapping patterns of expression in the thickened epithelium of the early developing tooth buds, which is suggestive of cooperative and/or redundant roles of BMPs in mediating the inductive interactions during the early stages of odontogenesis. Our studies in the developing chick mandible showed that Bmp-7 is expressed in the mandibular epithelium. In the absence of mandibular epithelium, BMP-7 beads maintained cell proliferation and Msx expression in the medial mandibular mesenchyme and were able to induce cell proliferation, cell death, and Msx expression in the lateral chick mandibular mesenchyme. The effects of BMP-7 on the expression of Msx genes in lateral chick mandibular mesenchyme, although different from the effects of lateral mandibular epithelium, are similar to the effects of epithelium from the medial region where multiple Bmps are expressed. We also showed that laterally placed BMP-7 beads induced ectopic expression of Msx genes and changes in the development of posterior skeletal elements in the maxillary and mandibular arches. However, despite its proliferative effects on mandibular mesenchyme, BMP-7 did not support the directional outgrowth of the mandible. These observations suggest that epithelial-mesenchymal interactions in the medial region of the mandibular arch regulating directional outgrowth of the mandibular mesenchyme are mediated by cooperative interactions between BMPs and other growth factors. Our observations also indicated that EGF, another growth factor implicated in mediating epithelial-mesenchymal interactions in the initiation phase of odontogenesis and morphogenesis of the developing mandible, induces an extensive translucent zone and cellular proliferation in the E11 mouse molar-forming mesenchyme and stage 23 chick mandibular mesenchyme. However, in contrast to BMPs, EGF did not induce Msx-1, Msx-2, and Bmp-4, but modulated the effects of BMPs on the expression of Msx-1 and Msx-2 in these mesenchymes. Our combined data suggest that BMP-7 is a component of the signaling network mediating epithelial-mesenchymal interactions during the initiation phase of odontogenesis and morphogenesis of the mandibular arch.

Nerve growth factor (NGF) supports tooth morphogenesis in mouse first branchial arch explants

Posterior midbrain and anterior hindbrain neuroectoderm trans-differentiate into cranial neural crest cells (CNCC), emigrate from the neural folds, and become crest-derived ectomesenchyme within the mandibular and maxillary processes. To investigate the growth factor requirement specific for the initiation of tooth morphogenesis, we designed studies to test whether nerve growth factor (NGF) can support odontogenesis in a first branchial arch (FBA) explant culture system. FBA explants containing neural-fold tissues before CNCC emigration and the anlagen of the FBA were microdissected from embryonic day 8 (E8) mouse embryos, and cultured for 8 days in medium supplemented with 10% fetal calf serum only, or serum-containing medium further supplemented with either NGF or epidermal growth factor (EGF) at three different concentrations: 50, 100, or 200 ng/ml. Morphological, morphometric, and total protein analyses indicated that growth and development in all groups were comparable. Meckel's cartilage and tongue formation were also observed in all groups. However, odontogenesis was only detected in explants cultured in the presence of exogenous NGF. NGF-supplemented cultures were permissive for bud stage (50 ng/ml) as well as cap stage of tooth morphogenesis (100 and 200 ng/ml). Morphometric analyses of the volume of tooth organs showed a significant dose-dependent increase in tooth volume as the concentration of NGF increased. Whole-mount in situ hybridization and semiquantitative reverse transcription-polymerase chain reaction for Pax9, a molecular marker of dental mesenchyme, further supported and confirmed the morphological data of the specificity and dose dependency of NGF on odontogenesis. We conclude that (1) E8 FBA explants contain premigratory CNCC that are capable of emigration, proliferation, and differentiation in vitro; (2) serum-supplemented medium is permissive for CNCC differentiation into tongue myoblasts and chondrocytes in FBA explants; and (3) NGF controls CNCC cell fate specification and differentiation into tooth organs.

Developmental shift in the relative percentages of lung fibroblast subsets: role of apoptosis postseptation

We have used the lipophilic, fluorescent dye Nile red and flow cytometry to identify and isolate two rat lung fibroblast subsets, lipid-containing interstitial cells (LICs) and non-LICs (NLICs) and to quantitate developmental changes in the relative percentages of these subsets. A significant decrease was observed in the percentage of LICs (from 79.0 +/- 3.8% on postnatal day 4 to 28.6 +/- 4.2% on day 30; P < 0.0001). To determine whether one or both subsets undergo apoptosis postseptation, fibroblasts from 16- to 18-day rats were treated with BODIPY-conjugated dUTP to label DNA strand breaks, which were then quantitated by flow cytometry. Apoptotic cells were judged to be predominantly LICs based on flow cytometric estimates of cell size and granularity and on light-microscopic colocalization of intracellular lipid and Hoechst-positive apoptotic bodies. Cell proliferation was compared in LICs and NLICs with both an in vitro [(3)H]thymidine incorporation assay and cell cycle analysis of propidium iodide-stained cells. Results of both assays indicated that on days 4-5, LICs proliferated more rapidly than NLICs. Tropoelastin and fibronectin mRNA expression, evaluated by RT-PCR, indicated that although tropoelastin mRNA levels did not differ, fibronectin mRNA levels were approximately ninefold greater in LICs. These results demonstrate the feasibility of a flow cytometric assay for the analysis of size, granularity, and intracellular lipid content of neonatal rat lung fibroblast subsets. Subsets differed substantially with respect to proliferative capacity, fibronectin mRNA expression, and incidence of apoptosis postseptation. Together with the observed changes in relative percentages of fibroblast subsets with age, these data suggest that the ratio of LICs to NLICs could be a critical determinant of fibroblast function during lung development.

The immunohistochemical localization of phospholipase Cgamma and the epidermal growth-factor, platelet-derived growth-factor and fibroblast growth-factor receptors in the cells of the rat molar enamel organ during early amelogenesis

Findings on the localization and possible roles of the major growth factors, epidermal (EGF), platelet-derived (PDGF) and fibroblast (FGF) in early amelogenesis are contradictory and inconclusive. This study sought to localize immunohistochemically phospholipase (PLCgamma) and the EGF, PDGF and FGF receptors in the cells of the enamel organ during the events leading directly to early enamel formation in rat molars. PLCgamma is an immediate, downstream, signal-transduction pathway effector unique to the three receptors. A whole-head, freeze-dried sectioning method was used to reduce the possibilities of false-negative staining. A modification of the avidin/biotin complex method of immunohistochemical localization was used. Anti-PLCgamma and antibodies to each of EGF, PDGF and FGF receptors colocalized in the preameloblasts of the cervical loop, adjacent to the undifferentiated mesenchymal cells of the dental pulp. This staining disappeared shortly after the beginning of dentine mineralization. Staining for all four antibodies appeared on the proximal ends of the differentiating presecretory ameloblasts at the level of the beginning of predentine matrix deposition and continued in the secretory ameloblasts. It appears that EGF, PDGF and FGF have roles in the differentiation of ameloblasts and in control of cellular functions in presecretory and secretory ameloblasts. Their roles may represent redundancy of the kind seen in highly conserved tissues.

The distribution of BrdU- and TUNEL-positive cells during odontogenesis in mouse lower first molars

This study investigated the minute distribution of both proliferating and non-proliferating cells, and cell death in the developing mouse lower first molars using 5-bromo-2'-deoxyuridine (BrdU) incorporation and the terminal deoxynucleotidyl transferase-mediated deoxyuridine-5'-triphosphate (dUTP)-biotin nick end labeling (TUNEL) double-staining technique. The distribution pattern of the TUNEL-positive cells was more notable than that of the BrdU-positive cells. TUNEL-positive cells were localized in the following six sites: (1) in the most superficial layer of the dental epithelium during the initiation stage, (2) in the dental lamina throughout the period during which tooth germs grow after bud formation, (3) in the dental epithelium in the most anterior part of the antero-posterior axis of the tooth germ after bud formation, (4) in the primary enamel knot from the late bud stage to the late cap stage, (5) in the secondary enamel knots from the late cap stage to the late bell stage, and (6) in the stellate reticulum around the tips of the prospective cusps after the early bell stage. These peculiar distributions of TUNEL-positive cells seemed to have some effect on either the determination of the exact position of the tooth germ in the mandible or on the complicated morphogenesis of the cusps. The distribution of BrdU-negative cells was closely associated with TUNEL-positive cells, which thus suggested cell arrest and the cell death to be essential for the tooth morphogenesis.

Manipulation of the angiopoietic/hemangiopoietic commitment in the avian embryo

The hypothesis that the endothelial and hemopoietic lineages have a common ontogenic origin is currently being revived. We have shown previously by means of quail/chick transplantations that two subsets of the mesoderm give rise to endothelial precursors: a dorsal one, the somite, produces pure angioblasts (angiopoietic potential), while a ventral one, the splanchnopleural mesoderm, gives rise to progenitors with a dual endothelial and hemopoietic potential (hemangiopoietic potential). To investigate the cellular and molecular controls of the angiopoietic/hemangiopoietic potential, we devised an in vivo assay based on the polarized homing of hemopoietic cell precursors to the floor of the aorta detectable in the quail/chick model. In the present work, quail mesoderm was grafted, after various pretreatments, onto the splanchnopleure of a chick host; the homing pattern and nature of graft-derived QH1(+) cells were analyzed thereafter. We report that transient contact with endoderm or ectoderm could change the behavior of cells derived from treated mesoderm, and that the effect of these germ layers could be mimicked by treatment with several growth factors VEGF, bFGF, TGFbeta1, EGF and TGF(α), known to be involved in endothelial commitment and proliferation, and/or hemopoietic processes. The endoderm induced a hemangiopoietic potential in the associated mesoderm. Indeed, the association of somatopleural mesoderm with endoderm promoted the ‘ventral homing’ and the production of hemopoietic cells from mesoderm not normally endowed with this potential. The hemangiopoietic induction by endoderm could be mimicked by VEGF, bFGF and TGFbeta1. In contrast, contact with ectoderm or EGF/TGF(α) treatments totally abrogated the hemangiopoietic capacity of the splanchnopleural mesoderm, which produced pure angioblasts with no ‘ventral homing’ behaviour. We postulate that two gradients, one positive and one negative, modulate the angiopoietic/hemangiopoietic potential of the mesoderm.

Differential effects of various growth factors and cytokines on the syntheses of DNA, type I collagen, laminin, fibronectin, osteonectin/secreted protein, acidic and rich in cysteine (SPARC), and alkaline phosphatase by human pulp cells in culture

The purpose of this study is to differentiate roles of several growth factors and cytokines in proliferation and differentiation of pulp cells during development and repair. In human pulp cell cultures, laminin and type I collagen levels per cell remained almost constant during the whole culture period (22 days). On the other hand, secreted protein, acidic and rich in cysteine (SPARC/osteonectin) and alkaline phosphatase (ALPase) levels markedly increased after the cultures reached confluence. Laminin and type I collagen, as well as fibronectin, stimulated the spreading of pulp cells within 1 h. Adding transforming growth factor-beta (TGF-beta) decreased laminin and ALPase levels, whereas it increased SPARC and fibronectin levels 3- to 10-fold. Western and Northern blots showed that TGF-beta enhanced SPARC synthesis at the protein and mRNA levels. Basic fibroblast growth factor (bFGF) decreased type I collagen, laminin, SPARC, and ALPase levels without changing the fibronectin level. Platelet-derived growth factor (PDGF) selectively decreased laminin, SPARC, and ALPase levels. Epidermal growth factor (EGF) also decreased SPARC and ALPase levels. Tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) decreased type I collagen and laminin levels, and abolished SPARC and ALPase syntheses. Of these peptides, bFGF and PDGF showed the greatest stimulation of [3H]thymidine incorporation into DNA. TGF-beta, EGF, and TNF-alpha had less effect on DNA synthesis, whereas IL-1beta inhibited DNA synthesis. These findings demonstrated that TGF-beta, bFGF, EGF, PDGF, TNF-alpha, and IL-1beta have characteristically different patterns of actions on DNA, laminin, type I collagen, fibronectin, ALPase, and SPARC syntheses by pulp cells.

Impaired lung branching morphogenesis in the absence of functional EGF receptor

The mammalian lung develops through branching morphogenesis which is controlled by growth factors, hormones, and extracellular matrix proteins. We have evaluated the role of EGF-receptor signaling in lung morphogenesis by analyzing the developmental phenotype of lungs in mice with an inactivated the EGF-receptor gene both in vivo and in organ culture. Neonatal EGF-receptor-deficient mice often show evidence of lung immaturity which can result in visible respiratory distress. The lungs of these mutant mice had impaired branching and deficient alveolization and septation, resulting in a 50% reduction in alveolar volume and, thus, a markedly reduced surface for gas exchange. The EGF-receptor inactivation also resulted in type II pneumocyte immaturity, which was apparent from their increased glycogen content and a reduced number of lamellar bodies. The defective branching was already evident at Day 12 of embryonic development. When explants of embryonic lungs from Day 12 embryos were cultured under defined conditions, the branching defect in EGF-receptor-deficient lungs was even more pronounced, with only half as many terminal buds as normal lungs. EGF treatment stimulated the expression of surfactant protein C and thyroid transcription factor-1 in cultured normal lungs, but not in EGF-receptor-deficient lungs, suggesting that EGF-receptor signaling regulates the expression of these marker genes during type II pneumocyte maturation. Taken together, our data indicate that signal transduction through the EGF receptor plays a major role in lung development and that its inactivation leads to a respiratory distress-like syndrome.

Expression of transforming growth factor alpha (TGF-alpha) gene in mouse embryonic development

PURPOSE

The expression of genes for TGF-alpha, epidermal growth factor (EGF), and the EGF receptor (EGFR) in mouse blastocysts was evaluated by the reverse transcription-polymerase chain reaction (RT-PCR). We evaluated the effects of TGF-alpha and EGF on the development of mouse embryo prior to implantation.

RESULTS

The results revealed the presence of transcripts of TGF-alpha and EGFR. However, EGF mRNA was not observed in repeated experiments. None of these growth factors influenced the rate of development from the two-cell stage to the blastocyst stage when added to the culture medium. These effects were further examined on measuring the incorporation of tritiated thymidine and leucine, providing indices of the synthesis of DNA and protein, respectively. A concentration of only 0.1 ng/ml of TGF-alpha, which shares a cell surface receptor with EGF, stimulated the synthesis of both DNA and protein. EGF at a concentration of 10 ng/ml stimulated the synthesis of DNA and protein by blastocysts. To explore autocrine effects of TGF-alpha on the rate of blastocoel expansion, TGF-alpha antisense oligodeoxynucleotides was used to reduce expression of the TGF-alpha gene. TGF-alpha at a concentration of 0.1 ng/ml stimulates the rate of blastocoel expansion in early cavitating mouse blastocysts. In contrast, TGF-alpha antisense oligonucleotides significantly reduced the rate of expansion.

CONCLUSIONS

Our present observations suggest that TGF-alpha/EGF and the EGFR may be involved in regulating embryonic development. In particular, TGF-alpha may serve as an autocrine factor in the regulation of embryonic development.

Epidermal growth factor inhibits morphogenesis of the embryonic quail uropygial gland cultured in vitro

Formation of the uropygial papilla and glandular lumena was inhibited when the uropygial rudiment of a day 8 1/3 quail embryo was cultured for 2 days in a chemically defined medium in the presence of 50 ng/mL of epidermal growth factor (EGF). The epithelium of EGF-treated explants remained at the placode stage, or underwent minor invagination into the mesenchyme and became stratified like that of a 12- or 13-day-old embryo. EGF promoted cellular proliferation in the uropygial epithelium and the epidermis adjacent to the gland and it shortened the lag phase of proliferation and markedly stimulated epithelial DNA synthesis, detected immunocytochemically by labeling explants with 5-bromodeoxyuridine (BrdU). The maximal labeling index in EGF-treated uropygial epithelium was 55% higher than in the control. Electron microscopic observation revealed that the basal lamina had become irregular in the EGF-treated explants and that epithelial cytoplasmic processes penetrated through the basal lamina toward the mesenchyme. These same phenomena are observed in vivo when the glandular buds are formed during day 12-13. Some precocious changes occurred in the uropygial epithelium when the rudiment was cultured in the presence of EGF.

Growth factor control of growth and epithelial differentiation in embryonic lungs

embryonic lung cultures were exposed to either EGF (10 ng/ml) or TGF beta 1 (2 ng/ml) for 72 h, and branching morphogenesis, cell proliferation, and epithelial differentiation (the expression of DSPC synthesis and of surfactant protein C (SP-C) mRNA) were studied. EGF treatment stimulated branching morphogenesis (measured as the number of terminal left lung buds), epithelial differentiation, and cell proliferation. Branching morphogenesis was increased compared to controls after 48 h of culture by 47% and after 72 h by 34% (P < 0.0005). Choline incorporation into DSPC was stimulated by 343% (P = 0.05). SP-C expression was increased sixfold. Thymidine incorporation was stimulated by 49% (P < 0.05). The effects of EGF on thymidine labeling were distributed among epithelial cells of the airway walls and of the branching tips, and also the mesenchyme (P < 0.01 for each area compared to controls). In contrast, TGF beta 1 did not alter the number of terminal left lung buds, inhibited choline incorporation into DSPC by 35% (P < 0.05), and had no effect on thymidine incorporation (87% of control). There was increased thymidine labeling at the branching tips (P < 0.01), while other areas were not different from controls. We conclude that both EGF and TGF beta 1 affect the development of branching morphogenesis and of epithelial differentiation in the embryonic lung.

Cell proliferation and expression of EGF, TGF-alpha, and EGF receptor in the developing primary palate

Growth factors such as epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha) play an important role in cell proliferation during embryogenesis. The purposes of the study were to characterize the expression patterns of EGF and TGF-alpha and their receptor, EGF receptor (EGF-R), and to analyze regional patterns of cell proliferation during primary palate morphogenesis when facial primordia outgrow and fuse to form the premaxillary and upper lip regions. The expression of all molecules was studied with indirect immunohistochemistry with conventional and/or confocal microscopes in normal days 10 and 11 CD1 mice. 5-Bromodeoxyuridine (BrdU) and proliferating cell nuclear antigen (PCNA) were used as markers of cell proliferation. EGF, TGF-alpha, and EGF-R were found to have similar distribution patterns at all stages examined. In the anterior region of the face, the molecules were intensely localized at the tips and peripheral regions of the medial and lateral nasal prominences. Upon fusion of the facial prominences, all three molecules were present mainly at the fusion area and the tips and peripheral areas of the maxillary and nasal prominences. BrdU and PCNA were found to have distribution patterns similar to those of EGF, TGF-alpha, and EGF-R, with intense staining at the tips and peripheral regions of the facial prominences. These results show that EGF, TGF-alpha, and their receptor were expressed more intensely in regions of the developing primary palate where cell proliferation was most pronounced, and suggest that EGF, TGF-alpha, and EGF-R may play a role in cell proliferation during morphogenesis of the primary palate.

Periodontal ligament cell population: the central role of fibroblasts in creating a unique tissue

BACKGROUND

Fibroblasts are the predominant cells of the periodontal ligament (PL) and have important roles in the development, function, and regeneration of the tooth support apparatus. Biological processes initiated during the formation of the PL contribute to the long-lasting homeostasic properties exhibited by PL fibroblast populations.

DEVELOPMENT

The formation of the PL is likely controlled by epithelial-mesenchymal and epithelial hard tissue interactions, but the actual mechanisms that contribute to the development of cellular lineages in the PL are unknown. Fibroblasts in the normally functioning PL migrate through the tissue along collagen fibres to cementum and bone and in an apico-coronal direction during tooth eruption. ADULT TISSUE: Cell kinetic experiments have shown that PL fibroblasts comprise a renewal cell system in steady-state and the progenitors can generate multiple types of more differentiated, specialized cells. Progenitor cell populations of the PL are enriched in locations adjacent to blood vessels and in contiguous endosteal spaces. In normally functioning periodontal tissues, there is a relatively modest turnover of cells in which apoptotic cell death balances proliferation. Large increases of cell formation and cell differentiation occur after application of orthodontic forces or wounding. As PL cells comprise multiple cellular phenotypes, it has been postulated that after wounding, the separate phenotypes repopulating the site will ultimately dictate the tissue form and type.

CONCLUSIONS

PL fibroblasts play an essential role in responses to mechanical force loading of the tooth by remodelling and repairing effete or damaged matrix components. In consideration of the important roles played by fibroblasts in PL homeostasis, they could be described as "the architect, builder, and caretaker" of the periodontal ligament.

Epidermal growth factor and epidermal growth factor-receptor expression in the mouse dental follicle during tooth eruption

When the role of exogenous epidermal growth factor (EGF) during tooth eruption was first demonstrated it was strongly suggested that EGF was a natural regulator of eruption. Recent immunohistochemical studies have shown that EGF and EGF-receptors are localized in the dental follicle, alveolar bone and ameloblasts before and during the prefunctional stage of eruption. Localization of mRNA for EGF has also been successfully attempted in mouse incisors and molars. The purpose now was to study the temporal expression of EGF and EGF-receptor genes in the coronal aspect of the dental follicle. First molars from 2-, 5-, 9- and 11-day-old CD-1 mouse neonates were incubated in 1% trypsin for 1.5 h at 4 degrees C. Follicles were carefully separated from the coronal aspect of the molar and processed for RNA extraction. Reverse transcriptase-polymerase chain reaction was performed on each mRNA sample. EGF expression was detected at day 2, 5 and 9 in the coronal aspect of the follicle whereas EGF-receptor expression was found at day 9 only. These findings strongly suggest that cells of the dental follicle are the target of EGF at a specific stage of their development and therefore may have a very important role during eruption.

The role of the placenta in fetal nutrition and growth

The placenta plays a key role in the nutrition of the fetus. It mediates the active transport of nutrients and metabolic wastes across the barrier separating maternal and fetal compartments, as well as modifying the composition of some nutrients through its own metabolic activity. The function of the placenta is essential to the growth of a healthy fetus; it is becoming apparent that the activities of the placenta are in turn modulated by signals originating from the fetus. Communication between placenta and fetus is especially critical in intrauterine growth retardation. The importance of the interaction of factors like insulin-like growth factor and epidermal growth factor with their receptors is becoming increasingly clear.

Expression and localization of epidermal growth factor, transforming growth factor-alpha, and localization of their common receptor in fetal human lung development

Transforming growth factor-alpha (TGF-alpha), epidermal growth factor (EGF), and their common EGF receptor have been shown to be involved in cell proliferation and lung maturation. The aim of the study was to determine the site of production of TGF-alpha and EGF mRNA and the cellular distribution of TGF-alpha/EGF proteins and EGF receptor, in fetal human lung. By using in situ hybridization with 35S-labeled cDNA probes in frozen sections from eight lungs from fetuses ranging from 12 to 33 wk of gestation, TGF-alpha and EGF mRNA transcripts appeared to be confined to the mesenchymal cells and mainly found in the dense connective tissue along the pleura, bronchi, and large vessels, but undetected in bronchial epithelial cells. The streptavidin-biotin immunoperoxidase method, applied to paraffin-embedded specimens from 39 fetuses ranging from 10 to 41 wk, showed that TGF-alpha, EGF, and EGF receptor exhibited a similar cellular distribution during the whole period of gestation. They were detected in the undifferentiated cells of the airway surface epithelium, mesothelial cells, smooth muscle, and a few mesenchymal cells, as early as 10 wk. After 12 wk, the immunoreactivity was strong in the ciliated, secretory, and basal cells, and in growing glands along the large airways, but proved lower in the distal airways. After 24 wk, the immunoreactivity remained in the airway epithelium, but was mainly localized in the apical domain of ciliated cells, in alveolar cells, and in the serous cells of the glands. The presence of TGF-alpha, EGF, and EGF receptor during the whole period of fetal lung development suggests that these factors are not only mitogenic, but can also be involved in epithelial maturation, through paracrine secretion, as most TGF-alpha and EGF mRNA transcripts are expressed in mesenchymal cells.

Apoptosis in the developing tooth: association with an embryonic signaling center and suppression by EGF and FGF-4

Apoptosis was localized in developing mouse teeth from initiation of morphogenesis to completion of cusp formation by using modified TUNEL method for serial sections and Nile Blue staining for whole mounts. Apoptosis was first detected at bud stage (E12-E13) in the central cells of the invaginating dental epithelium suggesting involvement of cell death in epithelial budding morphogenesis. During cusp development, apoptotic cells were located in the enamel knots, which are transient clusters of dental epithelial cells proposed to act as signaling centers directing the morphogenesis of tooth cusps. Apoptosis was also detected in other restricted epithelial cell populations including the dental lamina, ameloblasts, as well as stratum intermedium and stellate reticulum cells suggesting that the removal of these epithelial cells occurs by apoptosis. Apoptotic cells, presumably osteoclasts, were also located on the surfaces of the developing alveolar bone. When dissected E13 dental epithelium or mesenchyme were cultured in isolation, apoptotic cells were abundant throughout the tissues, whereas when cultured together, apoptosis was inhibited in both tissues close to their interface indicating that epithelial-mesenchymal tissue interactions prevent apoptosis. Epidermal growth factor (EGF) and fibroblast growth factor-4 (FGF-4) inhibited apoptosis in the dental mesenchyme when applied locally using agarose or heparin-coated acrylic beads, suggesting involvement of these or related growth factors in the prevention of apoptosis in dental tissues in vivo. The spatially and temporally restricted distribution patterns of apoptotic cells suggest multiple roles for programmed cell death in dental development. Of particular interest is the removal of the enamel knots by apoptosis which may terminate their tasks as regulators of the patterning of the tooth cusps. The apical ectodermal ridge (AER) of the limb bud has similar signaling characteristics as the enamel knot, and it also undergoes apoptosis. Hence, apoptosis may be a general mechanism for the silencing of embryonic signaling centers.

The expression of the gene coding for parathyroid hormone-related protein (PTHrP) during tooth development in the rat

By means of in situ hybridisation studies, it is shown that parathyroid hormone-related protein (PTHrP) mRNA is strongly expressed in the developing enamel organs of rat teeth. In particular, the cervical loop hybridises strongly with the PTHrP probe and expression is maintained at this site throughout life in the permanently erupting incisor teeth. In mature molar teeth, expression is downregulated to low levels and confined to the epithelial cell rests of Malassez and/or cementoblasts which may derive from these. The gene is also expressed at low levels in the tissue overlying the erupting molars and, thereafter, in the junctional epithelia and connective tissue cells of the epithelial attachment on all tooth surfaces. The premise that PTHrP may undergo post-translational processing and that the resultant products could act in different ways raises the possibility of its exerting multiple paracrine actions during tooth development. These could include the control of cell division and local vascular dilation during development.

EGF receptor expression in mineralized tissues: an in situ hybridization and immunocytochemical investigation in rat and human mandibles

There is extensive evidence that growth factors play a central part in the autocrine/paracrine regulation of cell growth and differentiation in mineralized tissues. In order to investigate involvement of the EGFr receptor (EGFr) in forming mineralized tissues, its expression was studied by in situ hybridization and immunocytochemistry in mandibles of growing rats, as well as in human embryos. In Hertwig's epithelial root sheath of rat molar, EGFr mRNAs appeared strongly expressed, while dental pulp and dental follicle showed weak labeling. The lingual epithelium of rat incisor showed strong labeling, which decreased after epithelial dislocation. Cells of the adjoining lingual dental pulp and dental follicle, as compared to epithelium, contained a low level of EGFr mRNAs. In contrast, a significant signal with antisense RNA probe was observed in bone. Sense RNA probes provided a regular background or no labeling. Undifferentiated cells located in the periosteum and endosteal spaces were labeled. EGFr mRNAs were also present in osteoblasts and in lesser amounts in some osteocytes. In rat and in human bone, both osteoblasts and osteocytes were positive on immunostaining. Similarly in the Hertwig's root sheath, EGFr immunostaining and in situ hybridization labeling were closely related. These data show that different patterns of EGFr expression in forming mineralized tissues are tissue- and stage-specific. However, in all these cells, the present in situ investigation supports the assumption that EGFr is involved in the early stages of cellular proliferation and differentiation. This report also suggests that EGFr may play a role in differentiated and mature cells of mineralized tissues.

Molecular biology experimental strategies for craniofacial-oral-dental dysmorphology

This paper is a minireview of molecular biology experimental strategies for problems within craniofacial-oral-dental biology. Many of these strategies have already made remarkable contributions towards understanding the complex developmental processes associated with craniofacial biology. For example, the utilization of these strategies has resulted in the successful mapping of approximately 70 genes related to craniofacial anomalies (e.g., Pax, retinoic acid receptors, cadhedrins, aggrecan, cell adhesion molecules, substrate adhesion molecules, etc.), 30 genes related to dental tissue disorders (e.g., BMPs, bone morphogenetic proteins; dentin phosphoproteins, dentin sialoglycoproteins, enamelins, amelogenins), 20 genes related to facial clefting defects (e.g., Hox genes, transforming growth factor alpha), and 3 genes related to craniosynostosis (e.g., Msx-2). This minireview highlights selected examples of scientific progress derived from the following experimental strategies: (i) molecular approaches to the organization of the mouse and human chromosomes, with the mapping of specific gene sequences linked to human diseases (e.g., amelogenesis imperfecta, Boston type craniosynostosis, Rieger's syndrome, Treacher Collins syndrome); (ii) reverse genetic approaches for studies of gene function; (iii) homologous recombinations and the advances from "knock-out" transgenic mouse models for human craniofacial-oral-dental diseases; (iv) mutational analyses of congenital craniofacial-oral-dental dysmorphogenesis; (v) structural biology studies using computer-assisted molecular modeling for protein-protein, protein-nucleic acid and protein-inorganic interactions; (vi) computer modeling of genetic paradigms; and (vii) a cluster of newer methodologies including computer-assisted morphometry, new microinjection techniques, new cell membrane and intracellular dyes, and a number of new RNA and DNA viral constructs for the delivery of genes to enhance the resolution of cell fate maps, cell lineage studies and gene therapy approaches to human diseases.

Epidermal growth factor and transforming growth factor-alpha mRNA in rat small intestine: in situ hybridization study

The expression of epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha) mRNA in the small intestine of suckling and adult rats was examined by in situ hybridization. EGF mRNA was found mainly in the intestinal crypts in adult rats. Adult rats also exhibited a considerably stronger signal for EGF mRNA in comparison to suckling rats, where the signal was very low or absent. In contrast to EGF, very strong expression of TGF-alpha mRNA was observed in the small intestine of both adult and suckling rats. These data suggest the differences between the expression of EGF and TGF-alpha in the developing small intestine.

Antisense oligodeoxynucleotides targeting PDGF-B mRNA inhibit cell proliferation during embryonic rat lung development

There is increasing evidence to suggest that platelet-derived growth factor (PDGF) or PDGF-like molecules play a role in fetal lung morphogenesis. Our previous studies demonstrated the presence of PDGF-AA and PDGF-BB homodimers in embryonic and fetal rat lung. To explore further the role for PDGF-BB in embryonic lung development, we conducted intervention studies using PDGF-B chain-specific antisense oligodeoxynucleotides in a simple embryonic rat lung explant system. Unmodified antisense PDGF-B oligodeoxynucleotides inhibited, in a concentration-dependent manner, DNA synthesis of embryonic lung. A maximal inhibition of 50% was observed. The inhibitory effect of antisense PDGF-B oligodeoxynucleotides on DNA synthesis was reversed by the addition of exogenous PDGF-BB but not PDGF-AA. Antisense treatment decreased PDGF-BB but not PDGF-AA protein content, as assessed by immunoblot analyses. Incubation of lung explants with PDGF-BB neutralizing antibodies also resulted in an inhibition of DNA synthesis. Morphometric analyses of antisense-treated cultures showed a significant reduction in lung size when compared to control cultures. The epithelial component of the embryonic lungs was specifically reduced, both in mass and DNA labelling index, by antisense treatment. The number of terminal buds of the lung explants was not significantly affected by antisense PDGF-B treatment. Scrambled PDGF-B oligodeoxynucleotides had no effect. These data suggest that PDGF-BB is involved in regulating growth, but not the degree of branching, of embryonic rat lung.

Respiratory epithelial cell expression of human transforming growth factor-alpha induces lung fibrosis in transgenic mice

Increased production of EGF or TGF-alpha by the respiratory epithelial cells has been associated with the pathogenesis of various forms of lung injury. Growth factors and cytokines are thought to act locally, via paracrine and autocrine mechanisms, to stimulate cell proliferation and matrix deposition by interstitial lung cells resulting in pulmonary fibrosis. To test whether TGF-alpha mediates pulmonary fibrotic responses, we have generated transgenic mice expressing human TGF-alpha under control of regulatory regions of the human surfactant protein C (SP-C) gene. Human TGF-alpha mRNA was expressed in pulmonary epithelial cells in the lungs of the transgenic mice. Adult mice bearing the SP-C-TGF-alpha transgene developed severe pulmonary fibrosis. Fibrotic lesions were observed in peribronchial, peribronchiolar, and perivascular regions, as well as subjacent to pleural surfaces. Lesions consisted of fibrous tissue that included groups of epithelial cells expressing endogenous SP-C mRNA, consistent with their identification as distal respiratory epithelial cells. Peripheral fibrotic regions consisted of thickened pleura associated with extensive collagen deposition. Alveolar architecture was disrupted in the transgenic mice with loss of alveoli in the lung parenchyma. Pulmonary epithelial cell expression of TGF-alpha in transgenic mice disrupts alveolar morphogenesis and produces fibrotic lesions mediated by paracrine signaling between respiratory epithelial and interstitial cells of the lung.

Epidermal growth factor secretion by submandibular glands is not perturbed in the early phase of streptozotocin-induced diabetes in mice

In rodents, diabetes mellitus is accompanied by a decreased concentration of epidermal growth factor (EGF) in plasma and urine and by a reduced number of EGF receptors on the surface of target cells. A combination of these two abnormalities may reduce the effects of EGF and could be implicated in some complications of diabetes. The aim of the present work was to investigate the possible implication of the major source of EGF in the organism, the submandibular glands, upon the reduced EGF concentration in blood and urine. Firstly, we measured the content of mice submandibular gland EGF by radioimmunoassay and by morphometric determinations of the relative volume occupied by granular convoluted tubules in the gland and by the EGF-containing granules in the cells at the light and electron microscopical levels respectively. We found no differences in the EGF content of submandibular glands of streptozotocin-treated diabetic animals compared to control ones. Secondly, we estimated stimulus-secretion coupling by EGF-secreting cells, present in an enriched preparation of granular convoluted tubules (GCT) perifused in thermoregulated chambers. Phenylephrine was the only agent tested that was capable of stimulating EGF secretion. The stimulation was dose-dependent and similar in streptozotocin-diabetic and control mice. Thus, the EGF deficiency observed in diabetic mice is related neither to a defect of EGF content in the submandibular glands nor to an abnormal EGF secretion by the glands.

A mutation in the homeodomain of the human MSX2 gene in a family affected with autosomal dominant craniosynostosis

Craniosynostosis, the premature fusion of calvarial sutures, is a common developmental anomaly that causes abnormal skull shape. The locus for one autosomal dominant form of craniosynostosis has been mapped to chromosome 5qter. The human MSX2 gene localizes to chromosome 5, and a polymorphic marker in the MSX2 intron segregates in a kindred with the disorder with no recombination. Moreover, a histidine substitutes for a highly conserved proline at position 7 of the MSX2 homeodomain exclusively in affected members. In the mouse, transcripts of the Msx2 gene are localized to calvarial sutures. These results provide compelling evidence that the mutation causes this craniosynostosis syndrome.

Rieger syndrome revisited: experimental approaches using pharmacologic and antisense strategies to abrogate EGF and TGF-alpha functions resulting in dysmorphogenesis during embryonic mouse craniofacial morphogenesis

The major manifestations of Rieger syndrome (RS), an autosomal dominant disorder, include absent maxillary incisor teeth, malformations of the anterior chamber of the eye, and umbilical anomalies [Aarskog et al., 1983: Am J Med Genet 15:29-38; Gorlin et al., 1990: "Syndromes of the Head and Neck" 3rd ed.]. Linkage of RS to human chromosome 4q markers has been identified with tight linkage to epidermal growth factor (EGF) [Murray et al., 1992: Nat Genet 2:46-48]. Mutations associated with genes of the EGF superfamily are implicated in malformations arising from abnormal development of the first branchial arch [Ardinger et al., 1989: Am J Hum Genet 45:348-353; Sassani et al., 1993: Am J Med Genet 45:565-569]. Down-regulation of EGF during early mouse development results in ablation of tooth formation [Kronmiller et al., 1991: Dev Biol 147:485-488]. Since EGF, TGF-alpha, and EGF receptor (EGFr) transcripts are expressed in the mouse first branchial arch and derivatives, experimental strategies were employed to investigate the consequences of down-regulation of EGF translation and inhibition of EGF receptor during embryonic mandibular morphogenesis. Antisense inhibition of EGF expression produces mandibular dysmorphogenesis with decreased tooth bud size; these effects are reversed by the addition of exogenous EGF to the culture medium [Shum et al., 1993: Development 118:903-917]. Tyrphostin RG 50864, which inhibits EGF receptor kinase activity, inhibits EGF or TGF-alpha stimulation of tyrosine phosphorylation in a concentration-dependent manner and severely retards mandibular development [Shum et al., 1993: Development 118:903-917].(ABSTRACT TRUNCATED AT 250 WORDS)

EGF abrogation-induced fusilli-form dysmorphogenesis of Meckel's cartilage during embryonic mouse mandibular morphogenesis in vitro

Mutations associated with genes of the EGF superfamily are implicated in facial malformations arising from abnormal development of the first branchial arch. EGF and EGF receptor (EGFr) transcripts are expressed in the mouse embryonic first branchial arch and derivatives from E9 through E15. EGF transcripts are localized to ectomesenchymal cells associated with precartilage, cartilage, bone and tooth-forming cells. EGF and EGFr proteins co-localize to the same cells suggesting an autocrine regulation. To test whether EGF effects the timing and positional information required for Meckel's cartilage (MC) and tooth development, we cultured E10 mandibular explants in serumless, chemically defined medium with either antisense or sense EGF oligodeoxynucleotides. Antisense inhibition of EGF expression produces bilaterally symmetrical Fusilli-form dysmorphogenesis of MC and decreases tooth bud size; these effects are reversed by the addition of exogenous EGF to the culture medium. Tyrphostin RG 50864, which inhibits EGF receptor kinase activity, inhibits EGF stimulation of tyrosine phosphorylation in a concentration-dependent manner and severely retards mandibular development yet increases tooth size. These findings support the hypothesis that endogenous EGF and EGF-like proteins provide signalling to regulate the size and shape both of cartilage and tooth formation during craniofacial morphogenesis.

Expression of transforming growth factor-alpha in mid-gestation human fetal lung

Transforming growth factor-alpha (TGF-alpha), a member of the epidermal growth factor (EGF) family, is a potent mitogen for several cell types. To investigate the possible role of TGF-alpha in the development of midgestation human fetal lung, we studied its distribution with immunohistochemistry and determined levels of steady-state TGF-alpha mRNA by Northern analysis of cellular RNA isolates from lung. Lung was obtained from fetuses at 10 to 22 wk of gestation (n = 14) and immunostained for TGF-alpha. TGF-alpha was localized in epithelial cells at all gestational ages examined. Immunostaining was particularly prominent in bronchiolar epithelial cells. TGF-alpha immunoreactivity was also associated with arterial smooth muscle cells, as well as with nerves. Occasional chondrocytes were also associated with TGF-alpha immunoreactivity. Total cellular RNA was isolated from lung tissue obtained from additional fetuses at gestational ages 10 to 24 wk (n = 22). TGF-alpha mRNA was present in RNA extracts of all fetal lungs studied. We conclude that TGF-alpha is probably produced in human fetal lung during mid-gestation. The prominent immunostaining of bronchiolar epithelial cells for TGF-alpha is consistent with its playing a role in distal airway formation.

Retardation of mouse odontoblast differentiation by heparin in vitro

The effect of heparin was studied histologically and immunohistochemically. Tooth germs from 15-day-old mouse embryos were cultured with or without heparin. After 6 days of culture in control medium, mesenchymal cells underlying the inner enamel epithelium had differentiated into odontoblasts and secreted predentine. In medium with heparin, mesenchymal cells were undifferentiated. In medium with other glycosaminoglycans such as chondroitin sulphate, dermatan sulphate or hyaluronate, tooth germs were similar to those in control medium, as were those in medium with heparin-Sepharose absorbed serum. After 12 days of culture in the heparin medium, mesenchymal cells in some cusps had differentiated into odontoblasts and secreted predentine but in other cusps remained undifferentiated. Immunohistochemically, exogenous heparin did not prevent the deposition of type IV collagen, laminin and fibronectin in the basement membrane and extracellular matrix. These results suggest that exogenous heparin retards differentiation of odontoblasts but not by disruption of the basement membrane nor inactivation of heparin-binding growth factors present in serum.

Expression of the genes for TGF alpha, EGF and the EGF receptor during early pig development

Expression of mRNA for transforming growth factor-alpha (TGF-alpha), epidermal growth factor (EGF) and the epidermal growth factor receptor (EGF-R) during early pig development was evaluated by reverse transcription-PCR. In the unfertilised pig oocyte, maternal transcripts for EGF, but not for TGF alpha or the EGF-R, were detected. Pig conceptuses were analysed at days 7, 8, 10, 12, 15, 17, 18 and 22 of pregnancy. EGF-R mRNA was detected at all stages of conceptus development analysed. Interestingly, TGF alpha mRNA was expressed by the developing blastocyst only at days 8, 10 and 12 of pregnancy, with the highest levels apparent at day 10. In contrast, EGF mRNA was first expressed by the post-elongation conceptus at around day 15 of pregnancy with levels continuing to increase up to day 22. In the day-18 and day-22 conceptuses, this EGF message was shown to be primarily a product of the embryo-amnion and not the placental membranes. Furthermore, EGF was immunolocalised in the day-22 embryo to the developing lung bud, gut loop and amnion. In summary, the expression pattern of TGF alpha mRNA during early pig development is coincident with the onset of blastocyst elongation and suggests a possible role for TGF alpha during this period of cellular remodelling. The temporal and spatial expression of EGF mRNA and protein suggests a possible involvement for EGF in the establishment of the early organ systems.

Granule proteins of the dental follicle and stellate reticulum inhibit tooth eruption and eyelid opening in postnatal rats

Electron-dense granules within cells of the dental follicle and stellate reticulum of rat mandibular molars can be isolated; their major components are 167 and 200 kDa proteins. Injecting these granule proteins into postnatal rats results in a delay of incisor eruption and eyelid separation. These inhibitory effects were most pronounced with the 167 kDa protein (a delay of 3 days in incisor eruption and of 2 days in eyelid opening) and were opposite to the stimulatory effects of epidermal growth factor. Thus, these granules may play an inhibitory part in tooth eruption.

Human ameloblastoma tumors express the amelogenin gene

Instructive signals are responsible for the regulation of the expression of gene products characteristic of many cell lineages during normal development and potentially during neoplasia. The odontogenic origin of ameloblastomas is based largely on the similarity in histologic appearance between the tumor and the developing tooth organ. A pathognomonic pattern for odontogenic tissue-specific gene expression in ameloblastomas has not been previously shown. In these studies, the gene expression parameters for human ameloblastomas have been characterized with the techniques of messenger RNA phenotyping in combination with Northern and in situ hybridization analysis of messenger RNA. The results of these studies confirm that amelogenin, a gene transcribed solely by differentiated ameloblasts, was expressed by epithelial cells from human ameloblastomas. This observation suggests that the instructive signals required for ameloblast differentiation are shared during normal development and tumorigenesis of odontogenic epithelium.

Current concepts of the biology of tooth eruption

Tooth eruption is defined as the movement of a tooth from its site of development within the jaws to its position of function within the oral cavity. We present a critical review of evidence for the mechanisms and regulation of the intraosseous and supraosseous phases of eruption, with an emphasis upon the canine premolar model studied by the authors. Analyses at different stages of premolar eruption indicate that selective fragmentation of dental follicle protein DF-95 correlates with the presence of elevated levels of follicular collagenase and stromelysin, and with the onset of premolar movement. A dramatic decrease in these metalloproteinases followed initiation of movement. A biochemical and cell biological model for regulation of tooth eruption is proposed based upon these new and existing data.

Epidermal growth factor transcription, translation, and signal transduction by rat type II pneumocytes in culture

Epidermal growth factor (EGF) is known to induce fetal lung maturation and its receptor is present in the lungs of several species. Recently, EGF has been immunolocalized in type II pneumocytes in rat lung. We postulated that EGF is synthesized in type II pneumocytes and that, because of its position-restricted distribution within the alveolus, EGF might act as an autocrine regulator of type II pneumocyte function. Herein, we have tested the hypothesis using adult rat type II pneumocytes in primary culture. In situ hybridization, using an oligonucleotide probe corresponding to amino acid residues 1070 to 1081 of mouse EGF precursor, demonstrated the presence of EGF precursor mRNA. Upon S-200 Sephacryl gel chromatography of type II pneumocyte extracts, EGF-reactive protein eluted as a high-molecular-weight form (greater than 100 kD). EGF immunoreactivity was localized within type II pneumocytes in the periphery of groups of 10 to 15 cells in culture. The type II pneumocytes bound [125I]EGF in a specific manner, indicating the presence of EGF receptors. Scatchard plots gave an apparent affinity constant (Ka) of 1 x 10(9) liters/mol, and the number of receptors was estimated to be 4.8 x 10(11) mg protein (50 per cell). EGF receptor binding specificity was confirmed by the absence of an autoradiographic signal for cells incubated in the presence of a 100-fold excess concentration of transforming growth factor-alpha. Binding of [125I]EGF could also be downregulated 95% by incubation with 0.2 nM transforming growth factor-alpha.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunohistochemical localization of nerve growth factor (NGF) and NGF receptor (NGF-R) in the developing first molar tooth of the rat

Nerve growth factor (NGF) is a well established target-derived trophic factor supporting sympathetic and sensory innervation in the peripheral tissues as well as cholinergic innervation in the brain. Despite its name, NGF may have broader biological functions early in development in a wide range of non-neuronal differentiating cells. The many effects of NGF are directly dependent on initial binding of NGF to specific plasma membrane receptors on target cells. Here we use immunohistochemical methods to show that NGF and its receptor (NGF-R) are localized in a variety of embryonic epithelial and mesenchymal cells in the rat developing molar tooth. Dental cells known to play important roles in morphogenesis and inductive tissue interactions show NGF-like reactivity. Thus, labelling is seen in epithelial preameloblasts and mesenchymal odontoblasts. We also show a transient expression of NGF-R in restricted parts of the dental epithelium (inner dental epithelium) and dental mesenchyme differentiating cells (post-mitotic, polarizing odontoblasts). The expression patterns of NGF are different to those of NGF-R during embryogenesis and this is illustrated in detail in the developing tooth. The histochemical findings reported here support the notion that NGF may have multiple roles during morphogenetic and cytodifferentiation events in the tooth.

Epigenetic role of epidermal growth factor expression and signalling in embryonic mouse lung morphogenesis

A major unsolved problem in developmental biology is to determine when and how time- and position-restricted instructions are signaled and received during secondary embryonic inductions such as branching morphogenesis. The mouse embryonic lung rudiment was used to test the hypothesis that endogenous peptide growth factors, specifically epidermal growth factor (EGF), serve as instructive epigenetic signals for morphogenesis. The presence of EGF precursor mRNA transcripts was detected using the reverse-transcriptase-coupled polymerase chain reaction both in E11-E17-day mouse embryo lung tissues in vivo and in E11-day lung cultured for up to 7 days in vitro under chemically defined, serum-free conditions. Immunolocalization identified a position-restricted distribution of EGF in and around the primitive airways both during in vivo lung morphogenesis and in culture. EGF receptors (EGFR) coimmunolocalized with EGF in the primitive airways. Addition of exogenous EGF to lungs in culture resulted in significant concentration-dependent stimulation of branching morphogenesis, DNA, RNA, and protein content, and in [3H]thymidine incorporation into DNA. Conversely, the addition of tyrphostin (specific EGF receptor kinase antagonist) to lungs in culture resulted in concentration-dependent inhibition of branching morphogenesis, DNA, RNA, and protein content, and in [3H]thymidine incorporation into DNA without apparent cytotoxicity. The inhibition of the EGF signal by tyrphostin was confirmed by immunoprecipitation of tyrosine phosphoproteins. We conclude that early mouse embryo lungs express EGF transcripts and corresponding EGF peptides in a specific position-restricted distribution which coimmunolocalizes with EGFR in the primitive airways, while stimulatory and inhibitory studies indicate a functional role for the transduced EGF signal in the epigenetic regulation of lung branching morphogenesis. We speculate that the peptide growth factor EGF serves a function in secondary embryonic morphogenetic inductions, which may be modulated by interaction with other growth factors.