Erk MAP kinase regulates branching morphogenesis in the developing mouse kidney

Branching morphogenesis of epithelium is a common and important feature of organogenesis; it is, for example, responsible for development of renal collecting ducts, lung airways, milk ducts of mammary glands and seminal ducts of the prostate. In each case, epithelial development is controlled by a variety of mesenchyme-derived molecules, both soluble (e.g. growth factors) and insoluble (e.g. extracellular matrix). Little is known about how these varied influences are integrated to produce a coherent morphogenetic response, but integration is likely to be achieved at least partly by cytoplasmic signal transduction networks. Work in other systems (Drosophila tracheae, MDCK models) suggests that the mitogen-activated protein (MAP) kinase pathway might be important to epithelial branching. We have investigated the role of the MAP kinase pathway in one of the best characterised mammalian examples of branching morphogenesis, the ureteric bud of the metanephric kidney. We find that Erk MAP kinase is normally active in ureteric bud, and that inhibiting Erk activation with the MAP kinase kinase inhibitor, PD98059, reversibly inhibits branching in a dose-dependent manner, while allowing tubule elongation to continue. When Erk activation is inhibited, ureteric bud tips show less cell proliferation than controls and they also produce fewer laminin-rich processes penetrating the mesenchyme and fail to show the strong concentration of apical actin filaments typical of controls; apoptosis and expression of Ret and Ros, are, however, normal. The activity of the Erk MAP kinase pathway is dependent on at least two known regulators of ureteric bud branching; the GDNF-Ret signalling system and sulphated glycosaminoglycans. MAP kinase is therefore essential for normal branching morphogenesis of the ureteric bud, and lies downstream of significant extracellular regulators of ureteric bud development.

The infrequency of transmission of herpesviruses between humans and animals; postulation of an unrecognised protective host mechanism

The infrequency of natural transmission of herpesviruses between humans and animals is surprising as there is extensive contact between humans and non-human species with unequivocal evidence that host cells from non-susceptible species will support replication of herpesviruses which do not seem to naturally infect that species. This review examines natural cross-infections between human and other species and suggests that, firstly, it is possible that humans and animals do become asymptomatically or symptomatically cross-infected from other species, but the infection is not diagnosed or not diagnosable by conventional methods; secondly, an as yet unidentified novel mechanism(s) may operate to prevent infection using chemical, electrical or as yet unidentified pathways and may even be 'switched on' by exposure to the virus.

Glycosaminoglycans in the study of mammalian organ development

Glycosaminoglycans (GAGs) are linear polymers of amino sugar uronic acid disaccharides, and are generally attached to protein cores to form proteoglycans. GAGs interact with a large number of proteins and can participate in matrix organization, cell adhesion, differentiation, growth and apoptosis. Proteoglycans are expressed in tightly regulated spatio-temporal patterns during organ development, and changes in expression frequently correlate with developmental events. Here we review the evidence that GAGs play important roles in the development of mouse kidneys, which are organs that will undergo organotypic development in simple culture conditions and that are therefore highly accessible to experimentation. Depleting kidneys of GAGs, either biochemically or genetically, blocks the development of the urinary collecting-duct system, probably because critical signalling molecules require GAGs to form stable associations with their receptors. The insensitivity of GAG-deprived organ rudiments to physiological concentrations of growth factors can be used to screen candidate signalling molecules for morphoregulatory activity; candidate growth factors are applied at supraphysiological levels to GAG-deprived kidneys and assessed for their ability to rescue normal development. This approach has assisted the identification of four collecting-duct morphogens: hepatocyte growth factor, glial cell line-derived neurotrophic factor, nerturin and persephin.

An evaluation of the efficacy of in-patient bladder retraining

This is a retrospective review of 50 consecutive patients with urinary frequency, urgency and urge incontinence, admitted in 1995 and early 1996 for bladder retraining in the form of timed voiding. At discharge 80% of the women were subjectively cured or satisfactorily improved, but this was significantly reduced to 32% of the 37 who replied to a postal survey between 12 and 29 months (mean interval 21.3 months) later. There were no significant associations between outcome and urodynamic diagnosis, reduced cystometric capacity, length of symptomatology, previous treatment or requirement for additional therapy, but this may have been in part due to small numbers. In conclusion, bladder retraining is a method of treatment for patients with both sensory urgency and detrusor instability which appears to be at least as successful as other modes of treatment for these conditions.

Synaptogenesis in the giant-fibre system of Drosophila: interaction of the giant fibre and its major motorneuronal target

The tergotrochanteral (jump) motorneuron is a major synaptic target of the Giant Fibre in Drosophila. These two neurons are major components of the fly's Giant-Fibre escape system. Our previous work has described the development of the Giant Fibre in early metamorphosis and the involvement of the shaking-B locus in the formation of its electrical synapses. In the present study, we have investigated the development of the tergotrochanteral motorneuron and its electrical synapses by transforming Drosophila with a Gal4 fusion construct containing sequences largely upstream of, but including, the shaking-B(lethal) promoter. This construct drives reporter gene expression in the tergotrochanteral motorneuron and some other neurons. Expression of green fluorescent protein in the motorneuron allows visualization of its cell body and its subsequent intracellular staining with Lucifer Yellow. These preparations provide high-resolution data on motorneuron morphogenesis during the first half of pupal development. Dye-coupling reveals onset of gap-junction formation between the tergotrochanteral motorneuron and other neurons of the Giant-Fibre System. The medial dendrite of the tergotrochanteral motorneuron becomes dye-coupled to the peripheral synapsing interneurons between 28 and 32 hours after puparium formation. Dye-coupling between tergotrochanteral motorneuron and Giant Fibre is first seen at 42 hours after puparium formation. All dye coupling is abolished in a shaking-B(neural) mutant. To investigate any interactions between the Giant Fibre and the tergotroachanteral motorneuron, we arrested the growth of the motorneuron's medial neurite by targeted expression of a constitutively active form of Dcdc42. This results in the Giant Fibre remaining stranded at the midline, unable to make its characteristic bend. We conclude that Giant Fibre morphogenesis normally relies on fasciculation with its major motorneuronal target.

Prevention of herpes genitalis by the 'Bulgarian' vaccine F.HSV-2V(PRK): preliminary clinical evidence

AIM

To examine the antigenic properties of the formalin-inactivated herpes simplex virus type 2 (HSV-2) virus-particle vaccine F. HSV-2V(PRK), which has been used therapeutically in Bulgaria for 30 years, and to make preliminary assessment of its potential protective efficacy by a follow-up of vaccinated patients with herpes genitalis.

METHODS

Properties of the vaccine were examined by standard immunological laboratory tests. Fifty-five patients at risk of herpes genitalis received 2-4 vaccinations and were monitored during a 6-year follow-up.

RESULTS

The vaccine was antigenic in laboratory tests and absorbed neutralizing antibody from hyperimmune rabbit serum against herpes simplex virus type 1 (HSV-1). In vaccinated patients, there was an overall contraction rate of herpes genitalis of 5.4%. There was no evidence of significant local or generalized adverse effects from vaccination.

CONCLUSION

Bulgarian vaccine F.HSV-2V(PRK) may have protective efficacy, which, in association with its apparent safety from our findings and from its clinical use for over 30 years in Bulgaria, suggests that it should be scrutinized by a formal clinical trial.

Hypoxia/hypoglycemia-induced amino acid release is decreased in vitro by preconditioning

The aim of this study was to investigate the effects of preconditioning on amino acid neurotransmitter release, induced by hypoxia/hypoglycaemia, from rat brain cortical slices. Tissue, perfused with artificial cerebrospinal fluid (aCSF) at 37 degrees C with zero glucose and gassed with 95% nitrogen and 5% carbon dioxide, showed a fivefold increase in glutamate release with little effect on gamma-aminobutyric acid (GABA) release. Preconditioning, with three 5-min periods of hypoxia/hypoglycaemia preceding continuous hypoxia/hypoglycaemia, significantly decreased glutamate release whilst significantly elevating GABA release. These results suggest that GABA may reduce the release of glutamate and consequently decrease the neurotoxic effects of glutamate.

A study to evaluate the field efficacy of ivermectin, fenbendazole and pyrantel pamoate, with preliminary observations on the efficacy of doramectin, as anthelmintics in horses

The efficacy of ivermectin, fenbendazole, pyrantel pamoate and doramectin was evaluated under field conditions at 2 sites in the Free State Province of South Africa. The study involved 25 horses at each site, divided into 5 groups of equal size. Ivermectin, fenbendazole and pyrantel pamoate were administered orally at doses of 0.2, 10 and 19 mg/kg respectively. Doramectin was administered by intramuscular injection at a dose of 0.2 mg/kg. Treatment efficacy was based on the mean faecal egg count reduction 14 days post treatment. At site A a faecal egg count reduction of 100% was found after treatment with ivermectin, fenbendazole and doramectin. A 96.1% reduction was found after treatment with pyrantel pamoate. At site B ivermectin and doramectin produced a 100% reduction in faecal egg counts, fenbendazole produced an 80.8% reduction and pyrantel pamoate a 94.1% reduction. Doramectin produced a 100% reduction in faecal egg counts at both sites, despite not being registered for use in horses. In addition, the results indicated reduced efficacy of fenbendazole at site B, which suggested benzimidazole resistance. Larval cultures showed that cyathostomes accounted for between 86 and 96% of pre-treatment parasite burdens at both sites. Other helminths identified in the faecal samples were Strongylus spp. and Trichostrongylus axei.

Two Drosophila innexins are expressed in overlapping domains and cooperate to form gap-junction channels

Members of the innexin protein family are structural components of invertebrate gap junctions and are analogous to vertebrate connexins. Here we investigate two Drosophila innexin genes, Dm-inx2 and Dm-inx3 and show that they are expressed in overlapping domains throughout embryogenesis, most notably in epidermal cells bordering each segment. We also explore the gap-junction-forming capabilities of the encoded proteins. In paired Xenopus oocytes, the injection of Dm-inx2 mRNA results in the formation of voltage-sensitive channels in only approximately 40% of cell pairs. In contrast, Dm-Inx3 never forms channels. Crucially, when both mRNAs are coexpressed, functional channels are formed reliably, and the electrophysiological properties of these channels distinguish them from those formed by Dm-Inx2 alone. We relate these in vitro data to in vivo studies. Ectopic expression of Dm-inx2 in vivo has limited effects on the viability of Drosophila, and animals ectopically expressing Dm-inx3 are unaffected. However, ectopic expression of both transcripts together severely reduces viability, presumably because of the formation of inappropriate gap junctions. We conclude that Dm-Inx2 and Dm-Inx3, which are expressed in overlapping domains during embryogenesis, can form oligomeric gap-junction channels.

Femtosecond time-resolved photoelectron angular distributions probed during photodissociation of NO2

Femtosecond time-resolved photoelectron angular distributions (PADs) are measured for the first time in the molecular frame of a dissociating molecule. Various stages of the dissociation process, NO2-->NO(C Pi)+O(P), are probed using ionization of the NO(C Pi) fragment to NO+(X Sigma(+)). The PADs evolve from forward-backward asymmetric with respect to the dissociation axis at short time delays ( < or =500 fs) to symmetric at long time delays (> or = 1 ps). Changes in the PADs directly reflect the time-dependent separation and reorientation of the dissociating photofragments.

Neurturin: an autocrine regulator of renal collecting duct development

Urine is produced in the kidney by excretory nephrons and is drained by a tree-like system of collecting ducts to the ureter. The collecting ducts develop by arborisation of an initially unbranched epithelial rudiment, the ureteric bud, which ramifies through the surrounding mesenchyme and induces the formation of nephrons by mesenchyme-to-epithelial transition. The question of how collecting duct morphogenesis is controlled is an important one, from the points of view of both basic developmental biology and congenital renal pathology (multi- and polycystic renal disease, and some forms of renal agenesis, arise from defective collecting duct development). We report that neurturin, a neurotrophin related to glial cell line-derived neurotrophic factor and expressed in the developing kidney, acts as a collecting duct morphogen in culture. Applied in culture medium, it promotes epithelial branching and can induced branch initiation that has otherwise been blocked by depleting cultured kidneys of their sulfated proteoglycans or by antibody treatments. Applied locally on agarose beads, neurturin induces supernumerary ureteric buds to emerge from the wolffian duct and causes nearby collecting duct branches to distend to an abnormally large diameter. Like its receptors, neurturin is expressed by the developing collecting ducts themselves, suggesting that it forms an autocrine morphoregulatory control loop. This is in marked contrast to previously identified morphogens such as glial cell line derived neurotrophic factor and hepatocyte growth factor, which act in a paracrine manner.

The Kidney Development Database

The Kidney Development Database is a bioinformatics resource dedicated to providing easily accessible information on gene expression during the development of the pro-, meso-, and metanephroi of a range of vertebrates. It also contains data on mutant phenotypes and on the effects of experimental manipulation of kidneys developing in culture. The database is searchable by gene name or by expression pattern. It is now being used as a test bed for more "advanced" search strategies that measure hypotheses of gene interactions against expression data to test for any clashes that would make the hypotheses untenable and that scan the database for potentially interesting correlations between changes in gene expression. The Kidney Development Database can be accessed free of charge via the World Wide Web at either of the following uniform resource locators (URLs); http://golgi.ana.ed.ac.uk/kidhome.html, and http://www.ana.ed.ac.uk/anatomy/database/kidbase/ kidhome.html.

Gap-Junctional communication between developing Drosophila muscles is essential for their normal development

Recent experiments have demonstrated that a family of proteins, known as the innexins, are structural components of invertebrate gap junctions. The shaking-B (shak-B) locus of Drosophila encodes two members of this emerging family, Shak-B(lethal) and Shak-B(neural). This study focuses on the role of Shak-B gap junctions in the development of embryonic and larval muscle. During embryogenesis, shak-B transcripts are expressed in a subset of the somatic muscles; expression is strong in ventral oblique muscles (VO4-6) but only weak in ventral longitudinals (VL3 and 4). Carboxyfluorescein injected into VO4 of wild-type early stage 16 embryos spreads, via gap junctions, to label adjacent muscles, including VL3 and 4. In shak-B2 embryos (in which the shak-B(neural) function is disrupted), dye injected into VO4 fails to spread into other muscles. In the first instar larva, when dye coupling between muscles is no longer present, another effect of the shak-B2 mutation is revealed by whole-cell voltage clamp. In a calcium-free saline, only two voltage-activated potassium currents are present in wild-type muscles; a fast IA and a slow IK current. In shak-B2 larvae, these two currents are significantly reduced in magnitude in VO4 and 5, but remain normal in VL3. Expression of shak-B(neural) in a shak-B2 background fully rescues both dye coupling in embryonic muscle and whole-cell currents in first instar VO4 and 5. Our observations show that Shak-B(neural) is one of a set of embryonic gap-junction proteins, and that it is required for the normal temporal development of potassium currents in some larval muscles.

Optimising the information yield from a series of cross-sectional surveys: an example from Scotland

OBJECTIVE

To optimise the information yield from a series of cross-sectional caries prevalence surveys by identifying population cohorts resampled in later surveys and thus to assess the likelihood of continued improvement in the dental health of 12-year-old children

DESIGN

A cohort perspective was applied to a series of cross-sectional caries prevalence surveys undertaken by the Scottish Health Boards' Dental Epidemiological Programme and the Office of Population Censuses and Surveys.

PARTICIPANTS

Scottish school children aged 5 to 15 years.

OUTCOME MEASURES

Assessment of continued improvement in the dental health of 12-year-old children: predictions of future levels of dental health.

RESULTS

Results allowed age effect, period effect, and cohort effect to be assessed. By taking cohort information into account, in particular that related to recent curtailment in improvement in the caries experience of 5-year-old children, it appeared that the current downward trend in caries experience at 12-years may not continue in the short term.

CONCLUSIONS

There are now sufficient national cross-sectional dental surveys of children to allow cohort analysis to be undertaken. Results indicate the likelihood of a continued deceleration in the previously observed rate of improvement in the dental health levels of Scottish 12-year-old children.

The anticonvulsant effects of the enantiomers of losigamone

1 Losigamone is a novel anticonvulsant undergoing phase III clinical trials in patients with partial and secondary generalized seizures. This study investigated the effects of the S(+)- and R(-)- enantiomers of losigamone on endogenous amino acid release from BALB/c mouse cortical slices, spontaneous depolarizations in the cortical wedge preparation of the DBA/2 mouse and audiogenic seizures in DBA/2 mice. 2 S(+)-losigamone (100 and 200 microM) significantly reduced both potassium- and veratridine-elicited release of glutamate and aspartate from cortical slices. R(-)-losigamone had no effect on release at concentrations up to 400 microM. 3 Cortical wedges exhibit spontaneous depolarizations when perfused with magnesium-free artificial cerebrospinal fluid. S(+)-losigamone significantly reduced these depolarizations at 50-200 microM whilst R(-)-losigamone had a significant effect at 200-800 microM. 4 DBA/2 mice are susceptible to audiogenic seizures and S(+)-losigamone dose-dependently (5, 10 and 20 mg kg-1, i.p.) significantly inhibited clonic/tonic convulsions with 91% of the mice protected at 20 mg kg-1. There was no protection at 20 mg kg-1 with R(-)-losigamone. 5 These results, from both in vitro and in vivo experiments, confirm that the pharmacological activity profiles of the two losigamone enantiomers are not identical and suggest further that excitatory amino acid-mediated processes are involved in the mode of action of S(+)-losigamone whereas R(-)-losigamone does not possess such properties. For the treatment of neurological conditions involving exaggerated excitatory amino acid function the use of S(+)-losigamone might therefore be more effective clinically than losigamone or its R(-)-enantiomer.

Mechanisms of epithelial development and neoplasia in the metanephric kidney

Recent studies on the mechanisms of normal epithelial development in the kidney, and on the aetiology of renal neoplasms, are converging to reveal remarkably close relationships between the phenotypes and behaviours of normally-developing and neoplastic cells. Normal renal epithelia arise from two sources; those of the collecting duct system develop by arborisation of an initially-unbranched ureteric bud, in a manner similar to the development of other glandular organs, while epithelial nephrons develop via an unusual mesenchyme-to-epithelial transition. Both types of development require controlled proliferation, cell-cell and cell-matrix interactions, protease activity etc., but of the two tissues, the development of the nephrons is arguably the more complex. It includes many defined stages, signals and checkpoints that ensure that events happen at the right time, and that processes such as proliferation, apoptosis and differentiation are properly balanced. Detailed investigation of renal neoplasms has revealed some to be caused by mutations in molecules with known roles in normal nephrogenesis (e.g. Wilms' tumour and the WT-1 gene, renal cell carcinoma and the c-met receptor tyrosine kinase gene), some to be caused by mutations in genes expressed during normal development (e.g. renal cell carcinoma and the TSC-2 gene, renal cell carcinoma of the clear cell variety and the VHL gene). Furthermore, these and other tumours of unknown aetiology re-express genes such as Pax-2 that are expressed during the normal mesenchyme-to-epithelium transition but are shut off during terminal differentiation. Their re-appearance in tumours suggests that the cells have 'regressed' in an ontogenic sense, and their biology may therefore be understood most clearly by reference to the properties of normal developing cells rather than cells of a mature kidney.

Enhancing dental attendance rates for children from deprived areas in the UK

OBJECTIVES

To compare different methods being used to determine eligibility for enhanced capitation registration payments, which were introduced in the UK in April 1998 with the intention of improving the numbers of children aged 0-5 years from deprived areas registering with General Dental Service practitioners.

DESIGN

Comparative study of the enhanced capitation registration payment schemes; data from a longitudinal study of Scottish children used to compare patient and dentist postcodes.

OUTCOME MEASURES

Published registration rates; levels of agreement between patient and dentist postcodes.

RESULTS

Quarterly registration rates for 3-5-year-olds show little improvement as yet; Scottish figures for 0-2-year-olds indicate a more substantial increase which may have been influenced by other initiatives. In Scotland, the degree of agreement between the deprivation scores of patient's and their dentist's postcode was less good among patients from deprived areas than for the sample as a whole.

CONCLUSIONS

More detailed breakdown, using the same criteria as for the enhanced payments, may eventually offer more definitive results. Patient postcodes enable better targeting than practice postcodes, but both may omit a substantial number from the target group if area measures of deprivation are used.

Reduction of severe aggressive behaviour in acquired brain injury: case studies illustrating clinical use of the OAS-MNR in the management of challenging behaviours

Challenging behaviour, especially when this takes the form of aggression, may impede or prevent progress in neurorehabilitation. Despite its prevalence, the literature on management of aggression after brain injury is not extensive. It has been suggested that the 'Overt Aggression Scale-Modified for Neurorehabilitation' (OAS-MNR) could be used to help standardize future studies of aggressive behaviour. It was also suggested that this scale has sufficient properties to be useful in clinical work. In this paper, three case studies are described which attempt to illustrate the potential value of the OAS-MNR in neurorehabilitation. The use of the scale also provides evidence relating to the continued efficacy of the neurobehavioural model. In the first study, two cases are described in which reduction in aggression occurred through participation in individualized, needs-led holistic treatment programmes, which incorporated multiple interventions. These were based on neurobehavioural principles. In the second study, a further single case was presented which illustrated how the scale may be used to generate hypotheses regarding aggressive behaviour and to drive treatment. Causation and maintenance of aggression are discussed, especially with regard to cognitive impairment. Finally, practical points relating to the use of the OAS-MNR in clinical practice are reviewed.

Collecting duct morphogenesis

The collecting duct system of the metanephric kidney develops from the ureteric bud, an outgrowth from the caudal end of the Wolffian duct. The ureteric bud is induced to form by signals emanating from a specific area of intermediate mesoderm, which it immediately invades. In response to further mesenchyme-derived signals, the ureteric bud ramifies to form a tree-like collecting duct system, which in turn signals clumps of the mesenchyme cells that surround it to differentiate into epithelial nephrons. The morphogenesis of the collecting duct system is driven by two processes--growth and branching--which are to some extent separable. Each depends on diffusible signals, a number of which have been identified in recent years; growth promoters include hepatocyte growth factor and activin, while ramogens include glial cell line-derived neurotrophic factor, neurturin and persephin. Arborisation also depends on matrix components, including proteoglycans, integrins and their ligands, and metalloproteinases, such as matrix metalloproteinase-9, that are involved in matrix remodelling. So far, little progress has been made in elucidating the intracellular pathways responsible for translating growth factor "instructions" into morphological change, but a role for some intracellular components, such as protein kinase C, formins and the cytoskeleton, is implied by recent experimental data. More information on these internal pathways of control is expected over the next few years.

Blockade of GABA uptake potentiates GABA-induced depolarizations in adult mouse cortical slices

The electrophysiological effects of GABA and the GABA uptake inhibitor, NO-711, were investigated on cortical slices prepared from adult audiogenic seizure-prone DBA/2 mice. GABA, perfused for 1 min, elicited depolarizing responses which had a mean duration of 80-100 s and were concentration-dependent (0.1-32 mM). NO-711 (25 microM), perfused for 15 min, produced depolarizations with a mean duration of 50-60 s and these persisted for 4-5 h. The responses to both compounds were blocked by the GABA(A) receptor antagonist, bicuculline. Pre-treatment of the slices with NO-711 potentiated the responses to GABA and moved the concentration-response curve to the left. The EC50 to GABA following pre-treatment with NO-711 was 111+/-24 microM from a control value of 1.17+/-0.19 mM. These results demonstrate that in cortical slices GABA has a depolarizing action rather than the conventional one of hyperpolarization and that this response is potentiated by inhibition of GABA reuptake.

Null mutation in shaking-B eliminates electrical, but not chemical, synapses in the Drosophila giant fiber system: a structural study

Mutations in the Drosophila shaking-B gene perturb synaptic transmission and dye coupling in the giant fiber escape system. The GAL4 upstream activation sequence system was used to express a neuronal-synaptobrevin-green fluorescent protein (nsyb-GFP) construct in the giant fibers (GFs); nsyb-GFP was localized where the GFs contact the peripherally synapsing interneurons (PSIs) and the tergotrochanteral motorneurons (TTMns). Antibody to Shaking-B protein stained plaquelike structures in the same regions of the GFs, although not all plaques colocalized with nsyb-GFP. Electron microscopy showed that the GF-TTMn and GF-PSI contacts contained many chemical synaptic release sites. These sites were interposed with extensive regions of close membrane apposition (3.25 nm +/- 0.12 separation), with faint cross striations and a single-layered array of 41-nm vesicles on the GF side of the apposition. These contacts appeared similar to rectifying electrical synapses in the crayfish and were eliminated in shaking-B2 mutants. At mutant GF-TTMn and GF-PSI contacts, chemical synapses and small regions of close membrane apposition, more similar to vertebrate gap junctions, were not affected. Gap junctions with more vertebratelike separation of membranes (1.41 nm +/- 0.08) were abundant between peripheral perineurial glial processes; these were unaffected in the mutants.

The role of cell adhesion molecules in craniofacial development

The last decade has seen classification and characterization of previously identified glycoproteins which have been associated with cell adhesion. More recently, it has been realized that the range of these molecules is even wider than originally thought. Cell adhesion molecules are important in early development and their role in craniofacial development is now apparent. Furthermore, the interaction of cell adhesion molecules in other developmental phenomena such as epithelial mesenchymal transformation (EMT), reinforces the suggestion that these molecules are important in the later stages of development, particularly organogenesis. This article reviews the role of cell adhesion molecules in embryogenesis, with a particular emphasis on foetal craniofacial development.

Simultaneous loss of expression of syndecan-1 and E-cadherin in the embryonic palate during epithelial-mesenchymal transformation

Epithelial-mesenchymal transformation (EMT) is the key mechanism for fusion and confluence of the rodent palate. During this process, medial edge epithelia (MEE) form a midline seam that subsequently transforms to mesenchymal cells. We studied syndecan-1 and E-cadherin, two molecules which have been shown to promote the epithelial phenotype, to determine their fate during palatal EMT. We found that both syndecan-1 and E-cadherin are expressed on basolateral surfaces of the MEE at day 14. Twelve hours later, when a midline seam has formed, syndecan-1 and E-cadherin are still present on its basal and lateral epithelial surfaces and they persist after the seam breaks up into epithelial islands. Then, expression of both molecules is lost simultaneously and abruptly when EMT occurs. On the contrary, previous in vitro studies of cell lines transfected with antisense cDNAs suggested that loss of syndecan-1 would lead to loss of E-cadherin or vice versa. We conclude that in vivo, synthesis of both E-cadherin and syndecan-1 is downregulated synchronously by the initiation of EMT, leading to an effective and correctly timed conversion of the epithelial cells to mesenchyme.