Elevated blood pressure and craniofacial abnormalities in mice deficient in endothelin-1

Phylogeny, taxonomy, and evolution of the endothelin receptor gene family

A gene phylogeny provides the natural historical order to classify genes and to understand their functional, structural, and genomic diversity. The gene family of endothelin receptors (EDNR) is responsible for many key physiological and developmental processes of tetrapods and teleosts. This study provides a well-defined gene phylogeny for the EDNR family, which is used to classify its members and to assess their evolution. The EDNR phylogeny supports the recognition of the EDNRA, EDNRB, and EDNRC subfamilies, as well as more lineage-specific duplicates of teleosts and the African clawed frog. The duplications for these nominal genes are related to the various whole-genome amplifications of vertebrates, jawed vertebrates, fishes, and frog. The EDNR phylogeny also identifies several gene losses, including that of EDNRC from placental and marsupial (therian) mammals. When coupled with structural and biochemical information, site-specific analyses of evolutionary rate shifts reveal two distinct patterns of potential functional changes at the sequence level between therian versus non-therian EDNRA and EDNRB (i.e., between groups without and with EDNRC). An analysis of linkage maps and tetrapod synteny further suggests that the loss of therian EDNRC may be related to a chromosomal deletion in its common ancestor.

Pathophysiology of the endothelin system - lessons from genetically manipulated animal models

Shortly after discovery of ET-1 in 1988, the entire endothelin system was characterized. The endothelin system consists of the three peptides ET-1, ET-2 and ET-3, their G-protein-coupled receptors endothelin receptor A and B (ETRA and ETRB) and the two endothelin-converting enzymes (ECE-1 and ECE-2). Genetically modified animal models are an important tool in biomedical research. Here we describe the key findings obtained from genetically modified animal models either over-expressing compounds of the ET system or lacking these compounds (knockout mice). Results from the different transgenic and knockout models disclose that the ET system plays a major role in embryonic development. Two ET system-dependent neural crest-driven developmental pathways become obvious: one of them being an ET-1/ETAR axis, responsible for cardio-renal function and development as well as cranial development; the other seems to be an ET-3/ETBR mediated signalling pathway. Mutations within this axis are associated with disruptions in epidermal melanocytes and enteric neurons. These findings led to the discovery of similar findings in humans with Hirschsprung disease. In adult life the ET system is most important in the cardiovascular system and plays a role in fibrotic remodelling of the heart, lung and kidney as well as in the regulation of water and salt excretion.

Quantitative trait loci for biomechanical performance and femoral geometry in an intercross of recombinant congenic mice: restriction of the Bmd7 candidate interval

Despite steady progress in identifying quantitative trait loci (QTLs) for bone phenotypes, relatively little progress has been made in moving from QTLs to identifying the relevant gene. We exploited the genetic structure of recombinant congenic mouse strains by performing a reciprocal intercross of the strains HcB-8 and HcB-23, phenotyped for body size, femoral biomechanical performance, and femoral diaphyseal geometry and mapped with R/qtl and QTL Cartographer. Significant QTLs are present on chromosomes 1, 2, 3, 4, 6, and 10. We found significant sex x QTL and cross-direction x QTL interactions. The chromosome 4 QTL affects multiple femoral anatomic features and biomechanical properties. The known segregating segment of chromosome 4 contains only 18 genes, among which Ece1, encoding endothelin-converting enzyme 1, stands out as a candidate. Endothelin signaling has been shown to promote the growth of osteoblastic metastases and to potentiate signaling via the Wnt pathway. The colocalizing chromosome 4 QTL Bmd7 (for bone mineral density 7) increases responsiveness to mechanical loading. By exploiting the short informative segment of chromosome 4 and the known biology, we propose that Ece1 is the gene responsible for Bmd7 and that it acts by increasing responsiveness to mechanical loading through modulation of Wnt signaling.

Signaling pathways regulating the expression of Prx1 and Prx2 in the chick mandibular mesenchyme

Prx1 and Prx2 are members of the aristaless-related homeobox genes shown to play redundant but essential roles in morphogenesis of the mandibular processes. To gain insight into the signaling pathways that regulate expression of Prx genes in the mandibular mesenchyme, we used the chick as a model system. We examined the patterns of gene expression in the face and the roles of signals derived from the epithelium on the expression of Prx genes in the mandibular mesenchyme. Our results demonstrated stage-dependent roles of mandibular epithelium on the expression of Prx in the mandibular mesenchyme and provide evidence for positive roles of members of the fibroblast and hedgehog families derived from mandibular epithelium on the expression of Prx genes in the mandibular mesenchyme. Our studies suggest that endothelin-1 signaling derived from the mesenchyme is involved in restricting the expression of Prx2 to the medial mandibular mesenchyme.

Elucidating timing and function of endothelin-A receptor signaling during craniofacial development using neural crest cell-specific gene deletion and receptor antagonism

Cranial neural crest cells (NCCs) play an intimate role in craniofacial development. Multiple signaling cascades participate in patterning cranial NCCs, some of which are regulated by endothelin-A receptor (Ednra) signaling. Ednra(-/-) embryos die at birth from severe craniofacial defects resulting from disruption of neural crest cell patterning and differentiation. These defects include homeotic transformation of lower jaw structures into upper jaw-like structures, suggesting that some cephalic NCCs alter their "identity" in the absence of Ednra signaling. To elucidate the temporal necessity for Ednra signaling in vivo, we undertook two strategies. We first used a conditional knockout strategy in which mice containing a conditionally targeted Ednra allele (Ednra(fl)) were bred with mice from the Hand2-Cre and Wnt1-Cre transgenic mouse strains, two strains in which Cre expression occurs at different time periods within cranial NCCs. In our second approach, we used an Ednra-specific antagonist to treat wild type pregnant mice between embryonic days E8.0 and E10.0, a time frame encompassing the early migration and proliferation of cranial NCCs. The combined results suggest that Ednra function is crucial for NCC development between E8.25 and E9.0, a time period encompassing the arrival of NCCs in the arches and/or early post-migratory patterning. After this time period, Ednra signaling is dispensable. Interestingly, middle ear structures are enlarged and malformed in a majority of Ednra(fl/fl);Wnt1-Cre embryos, instead resembling structures found in extinct predecessors of mammals. These observations suggest that the advent of Ednra signaling in cranial NCCs may have been a crucial event in the evolution of the mammalian middle ear ossicles.

Paracrine regulation of the resumption of oocyte meiosis by endothelin-1

Mammalian oocytes remain dormant in the diplotene stage of prophase I until the resumption of meiosis characterized by germinal vesicle breakdown (GVBD) following the preovulatory gonadotropin stimulation. Based on genome-wide analysis of peri-ovulatory DNA microarray to identify paracrine hormone-receptor pairs, we found increases in ovarian transcripts for endothelin-1 and endothelin receptor type A (EDNRA) in response to the preovulatory luteinizing hormone (LH)/human chorionic gonadotropin (hCG) stimulation. Immunohistochemical analyses demonstrated localization of EDNRA in granulosa and cumulus cells. In cultured preovulatory follicles, treatment with endothelin-1 promoted oocyte GVBD. The stimulatory effect of endothelin-1 was blocked by cotreatment with antagonists for the type A, but not related type B, receptor. The stimulatory effect of hCG on GVBD was partially blocked by the same antagonist. The endothelin-1 promotion of GVBD was found to be mediated by the MAPK/ERK pathway but not by the inhibitory G protein. Studies using cumulus-oocyte complexes and denuded oocytes demonstrated that the endothelin-1 actions are mediated by cumulus cells. Furthermore, intrabursal administration with endothelin-1 induced oocyte GVBD in preovulatory follicles. Our findings demonstrate a paracrine role of endothelin-1 in the induction of the resumption of meiosis and provide further understanding on the molecular mechanisms underlying the nuclear maturation of oocytes induced by the preovulatory LH surge.

Identification of multiple quantitative trait loci affecting the size and shape of the mandible in mice

A quantitative trait locus (QTL) analysis was performed on the size and shape of the mandible in F(2) mice between KK-A ( y ) and C57BL/6 J strains and the effect of the A ( y ) allele on the morphology of the mandible was analyzed. A total of 13 measurements were taken on each right mandible. By means of discriminant and canonical discriminant analyses, KK-A ( y ) males and KK males were exactly discriminated from each other. In contrast to its known effects on body weight, the A ( y ) allele reduced the overall size of the mandible. QTL analysis of the 13 measurements and on three principal components extracted from these measurements identified multiple QTLs. When F(2) a/a and F(2) A ( y )/a were analyzed separately, 11 significant main-effect QTLs were identified in F(2) a/a, whereas only two QTLs were identified in F(2) A ( y )/a. Although four significant interactions were identified, all were in F(2) a/a. The A ( y ) allele thus made the difference in the size and shape of the mandible between strains obscure. Among mandible QTLs, those on Chrs 5 (Mssq6 and Mssq7) and 15 (Mssq14) were important. Mssq6 had an effect on the height of the posterior mandible. Mssq7 had an effect on mandible length. Mssq14 had an effect on the height of the anterior and posterior mandible. Mssq7 and Mssq14 also had an effect on the overall size. Thus, mandible QTLs have distinct and characteristic sites of action. Therefore, mandible morphology will be determined largely by the combination of these QTLs.

An endothelin-1 switch specifies maxillomandibular identity

Articulated jaws are highly conserved structures characteristic of gnathostome evolution. Epithelial-mesenchymal interactions within the first pharyngeal arch (PA1) instruct cephalic neural crest cells (CNCCs) to form the different skeletal elements of the jaws. The endothelin-1 (Edn1)/endothelin receptor type-A (Ednra)-->Dlx5/6-->Hand2 signaling pathway is necessary for lower jaw formation. Here, we show that the Edn1 signaling is sufficient for the conversion of the maxillary arch to mandibular identity. Constitutive activation of Ednra induced the transformation of upper jaw, maxillary, structures into lower jaw, mandibular, structures with duplicated Meckel's cartilage and dermatocranial jaws constituted by 4 dentary bones. Misexpression of Hand2 in the Ednra domain caused a similar transformation. Skeletal transformations are accompanied by neuromuscular remodeling. Ednra is expressed by most CNCCs, but its constitutive activation affects predominantly PA1. We conclude that after migration CNCCs are not all equivalent, suggesting that their specification occurs in sequential steps. Also, we show that, within PA1, CNCCs are competent to form both mandibular and maxillary structures and that an Edn1 switch is responsible for the choice of either morphogenetic program.

Loss of protein kinase Cϵ results in impaired cutaneous wound closure and myofibroblast function

Cutaneous wound repair requires the de novo induction of a specialized form of fibroblast, the α-smooth muscle actin (α-SMA)-expressing myofibroblast, which migrates into the wound where it adheres to and contracts extracellular matrix (ECM), resulting in wound closure. Persistence of the myofibroblast results in scarring and fibrotic disease. In this report, we show that, compared with wild-type littermates, PKCϵ-/- mice display delayed impaired cutaneous wound closure and a reduction in myofibroblasts. Moreover, both in the presence and absence of TGFβ, dermal fibroblasts from PKCϵ-/- mice cultured on fibronectin show impaired abilities to form `supermature' focal adhesions and α-SMA stress fibers, and reduced pro-fibrotic gene expression. Smad3 phosphorylation in response to TGFβ1 was impaired in PKCϵ-/- fibroblasts. PKCϵ-/- fibroblasts show reduced FAK and Rac activation, and adhesive, contractile and migratory abilities. Overexpressing constitutively active Rac1 rescues the defective FAK phosphorylation, cell migration, adhesion and stress fiber formation of these PKCϵ-/- fibroblasts, indicating that Rac1 operates downstream of PKCϵ, yet upstream of FAK. These results suggest that loss of PKCϵ severely impairs myofibroblast formation and function, and that targeting PKCϵ may be beneficial in selectively modulating wound healing and fibrotic responses in vivo.

Aryl hydrocarbon receptor-mediated down-regulation of sox9b causes jaw malformation in zebrafish embryos

Exposure to environmental contaminants can disrupt normal development of the early vertebrate skeleton. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) impairs craniofacial skeletal development across many vertebrate species, and its effects are especially prominent in early life stages of fish. TCDD activates the aryl hydrocarbon receptor, a transcription factor that mediates most if not all TCDD responses. We investigated the transcriptional response in the developing zebrafish jaw after TCDD exposure using DNA microarrays. Zebrafish larvae were exposed to TCDD at 96 h after fertilization, and jaw cartilage tissue was harvested for microarray analysis at 1, 2, 4, and 12 h after exposure. Numerous chondrogenic transcripts were misregulated by TCDD in the jaw. Comparison of transcripts altered by TCDD in jaw with transcripts altered in embryonic heart showed that the transcriptional responses in the jaw and the heart were strikingly different. Sox9b, a critical chondrogenic transcription factor, was the most significantly reduced transcript in the jaw. We hypothesized that the TCDD reduction of sox9b expression plays an integral role in affecting the formation of the embryonic jaw. Morpholino knockdown of sox9b expression demonstrated that partial reduction of sox9b expression alone was sufficient to produce a TCDD-like jaw phenotype. Loss of a single copy of the sox9b gene in sox9b(+/-) heterozygotes increased sensitivity to jaw malformation by TCDD. Finally, embryos injected with sox9b mRNA and then exposed to TCDD blocked TCDD-induced jaw toxicity in approximately 14% of sox9b-injected embryos. These results suggest that reduced sox9b expression in TCDD-exposed zebrafish embryos contributes to jaw malformation.

Sex-specific hippocampus-dependent cognitive deficits and increased neuronal autophagy in DEspR haploinsufficiency in mice

Aside from abnormal angiogenesis, dual endothelin-1/VEGF signal peptide-activated receptor deficiency (DEspR(-/-)) results in aberrant neuroepithelium and neural tube differentiation, thus elucidating DEspR's role in neurogenesis. With the emerging importance of neurogenesis in adulthood, we tested the hypothesis that nonembryonic-lethal DEspR haploinsufficiency (DEspR(+/-)) perturbs neuronal homeostasis, thereby facilitating aging-associated neurodegeneration. Here we show that, in male mice only, DEspR-haploinsufficiency impaired hippocampus-dependent visuospatial and associative learning and induced noninflammatory spongiform changes, neuronal vacuolation, and loss in the hippocampus, cerebral cortex, and subcortical regions, consistent with autophagic cell death. In contrast, DEspR(+/-) females exhibited better cognitive performance than wild-type females and showed absence of neuropathological changes. Signaling pathway analysis revealed DEspR-mediated phosphorylation of activators of autophagy inhibitor mammalian target of rapamycin (mTOR) and dephosphorylation of known autophagy inducers. Altogether, the data demonstrate DEspR-mediated diametrical, sex-specific modulation of cognitive performance and autophagy, highlight cerebral neuronal vulnerability to autophagic dysregulation, and causally link DEspR haploinsufficiency with increased neuronal autophagy, spongiosis, and cognitive decline in mice.

Cardiac expression patterns of endothelin-converting enzyme (ECE): implications for conduction system development

The spatiotemporal distribution of the endothelin-converting enzyme (ECE) protein in the embryonic chick heart and the association of this polypeptide with the developing cardiac conduction system is described here for the first time. Further, we show how cardiac hemodynamic load directly affects ECE level and distribution. Endothelin (ET) is a cytokine involved in the inductive recruitment of Purkinje fibers. ET is produced by proteolytic cleavage of Big-ET by ECE. We generated an antibody against chick ECE recognizing a single band at approximately 70 kD to correlate the cardiac expression of this protein with that reported previously for its mRNA. ECE protein expression was more widespread compared to its mRNA, being present in endothelial cells, mesenchymal cells, and myocytes, and particularly enriched in the trabeculae and nascent ventricular conduction system. The myocardial expression was significantly modified under experimentally altered hemodynamic loading. In vivo, ET receptor blockade with bosentan delayed activation sequence maturation. These data support a role for ECE in avian cardiac conduction system differentiation and maturation.

Transcriptional regulation during development of the ductus arteriosus

The ductus arteriosus is a specialized blood vessel containing highly differentiated and contractile vascular smooth muscle, derived largely from neural crest cells, that is essential for fetal life but typically closes after birth. Impaired development of the ductus arteriosus or disruption of signaling pathways that initiate postnatal closure can result in persistent patency of the ductus arteriosus, the third most common congenital heart defect. We found that Tfap2beta, a transcription factor associated with patent ductus arteriosus in humans, was uniquely expressed in mouse ductal smooth muscle. Endothelin-1 and the hypoxia-induced transcription factor, Hif2alpha were also highly enriched in ductal smooth muscle at embryonic day 13.5 and were dependent on Tfap2beta for their expression in this domain. Hif2alpha functioned as a negative regulator of Tfap2beta-induced transcription by disrupting protein-DNA interactions, suggesting a negative feedback loop regulating Tfap2beta activity. Our data indicate that Tfap2beta, Et-1, and Hif2alpha act in a transcriptional network during ductal smooth muscle development and that disruption of this pathway may contribute to patent ductus arteriosus by affecting the development of smooth muscle within the ductus arteriosus.

Efficacy and safety of darusentan: a novel endothelin receptor antagonist

OBJECTIVE

To summarize the role of the endothelin system (ETS) in cardiovascular disease (CVD) and evaluate the potential usefulness of darusentan, a selective endothelin type A (ET(A)) receptor antagonist, in the treatment of hypertension and chronic heart failure (CHF).

DATA SOURCES

A literature search was conducted in MEDLINE (1966-February 2008), International Pharmaceutical Abstracts (1970-February 2008), and EMBASE (1990-February 2008) using the search terms endothelin, darusentan, LU 135252, hypertension, and heart failure.

STUDY SELECTION AND DATA EXTRACTION

Studies evaluating the role of the ETS in CVD and the pharmacology, pharmacokinetics, safety, and efficacy of darusentan for the treatment of hypertension and CHF were included.

DATA SYNTHESIS

Darusentan represents a novel treatment strategy for patients with resistant hypertension. Its safety and efficacy have been evaluated in the treatment of hypertension and CHF. Darusentan selectively blocks the ET(A) receptor, promoting vasodilatation and preventing several proliferative and inflammatory processes, while promoting the actions of the ET(B) receptor. Studies in patients with stage 2 or resistant hypertension concluded that darusentan safely and effectively lowers blood pressure. Darusentan's unique mechanism of action, dose-dependent blood pressure-lowering profile, once-daily dosing regimen, and sustained 24-hour blood pressure-lowering effect are valuable features. Darusentan is well tolerated, with only peripheral edema, headache, and nasal symptoms being reported more frequently than with placebo. Endothelin receptor antagonists, including darusentan, have been associated with a decrease in hemoglobin and hematocrit and are teratogens. Darusentan does not appear to cause hepatotoxicity. Additional studies in CHF are warranted to assess the safety and efficacy of darusentan, especially given its association with peripheral edema and decreased red blood cell count.

CONCLUSIONS

Given the important role of the ETS in hypertension and available data with darusentan, selective antagonism of the ET(A) receptor represents a promising approach to managing resistant hypertension. Darusentan's role will be more clearly elucidated by ongoing Phase 3 studies.

Enzymatic activity of lysosomal carboxypeptidase (cathepsin) A is required for proper elastic fiber formation and inactivation of endothelin-1

BACKGROUND

Lysosomal carboxypeptidase, cathepsin A (protective protein, CathA), is a component of the lysosomal multienzyme complex along with beta-galactosidase (GAL) and sialidase Neu1, where it activates Neu1 and protects GAL and Neu1 against the rapid proteolytic degradation. On the cell surface, CathA, Neu1, and the enzymatically inactive splice variant of GAL form the elastin-binding protein complex. In humans, genetic defects of CathA cause galactosialidosis, a metabolic disease characterized by combined deficiency of CathA, GAL, and Neu1 and a lysosomal storage of sialylated glycoconjugates. However, several phenotypic features of galactosialidosis patients, including hypertension and cardiomyopathies, cannot be explained by the lysosomal storage. These observations suggest that CathA may be involved in hemodynamic functions that go beyond its protective activity in the lysosome.

METHODS AND RESULTS

We generated a gene-targeted mouse in which the active CathA was replaced with a mutant enzyme carrying a Ser190Ala substitution in the active site. These animals expressed physiological amounts of catalytically inactive CathA protein, capable of forming lysosomal multienzyme complex, and did not develop secondary deficiency of Neu1 and GAL. Conversely, the mice showed a reduced degradation rate of the vasoconstrictor peptide, endothelin-1, and significantly increased arterial blood pressure. CathA-deficient mice also displayed scarcity of elastic fibers in lungs, aortic adventitia, and skin.

CONCLUSIONS

Our results provide the first evidence that CathA acts in vivo as an endothelin-1-inactivating enzyme and strongly confirm a crucial role of this enzyme in effective elastic fiber formation.

Loss of unc45a precipitates arteriovenous shunting in the aortic arches

Aortic arch malformations are common congenital disorders that are frequently of unknown etiology. To gain insight into the factors that guide branchial aortic arch development, we examined the process by which these vessels assemble in wild type zebrafish embryos and in kurzschluss(tr12) (kus(tr12)) mutants. In wild type embryos, each branchial aortic arch first appears as an island of angioblasts in the lateral pharyngeal mesoderm, then elaborates by angiogenesis to connect to the lateral dorsal aorta and ventral aorta. In kus(tr12) mutants, angioblast formation and initial sprouting are normal, but aortic arches 5 and 6 fail to form a lumenized connection to the lateral dorsal aorta. Blood enters these blind-ending vessels from the ventral aorta, distending the arteries and precipitating fusion with an adjacent vein. This arteriovenous malformation (AVM), which shunts nearly all blood directly back to the heart, is not exclusively genetically programmed, as its formation correlates with blood flow and aortic arch enlargement. By positional cloning, we have identified a nonsense mutation in unc45a in kus(tr12) mutants. Our results are the first to ascribe a role for Unc45a, a putative myosin chaperone, in vertebrate development, and identify a novel mechanism by which an AVM can form.

Genetic analysis of craniofacial traits in the medaka

Family and twin studies suggest that a substantial genetic component underlies individual differences in craniofacial morphology. In the current study, we quantified 444 craniofacial traits in 100 individuals from two inbred medaka (Oryzias latipes) strains, HNI and Hd-rR. Relative distances between defined landmarks were measured in digital images of the medaka head region. A total of 379 traits differed significantly between the two strains, indicating that many craniofacial traits are controlled by genetic factors. Of these, 89 traits were analyzed via interval mapping of 184 F(2) progeny from an intercross between HNI and Hd-rR. We identified quantitative trait loci for 66 craniofacial traits. The highest logarithm of the odds score was 6.2 for linkage group (LG) 9 and 11. Trait L33, which corresponds to the ratio of head length to head height at eye level, mapped to LG9; trait V15, which corresponds to the ratio of snout length to head width measured behind the eyes, mapped to LG11. Our initial results confirm the potential of the medaka as a model system for the genetic analysis of complex traits such as craniofacial morphology.

The role of shear stress on ET-1, KLF2, and NOS-3 expression in the developing cardiovascular system of chicken embryos in a venous ligation model

In this review, the role of wall shear stress in the chicken embryonic heart is analyzed to determine its effect on cardiac development through regulating gene expression. Therefore, background information is provided for fluid dynamics, normal chicken and human heart development, cardiac malformations, cardiac and vitelline blood flow, and a chicken model to induce cardiovascular anomalies. A set of endothelial shear stress-responsive genes coding for endothelin-1 (ET-1), lung Krüppel-like factor (LKLF/KLF2), and endothelial nitric oxide synthase (eNOS/NOS-3) are active in development and are specifically addressed.

Recombinase-mediated cassette exchange reveals the selective use of Gq/G11-dependent and -independent endothelin 1/endothelin type A receptor signaling in pharyngeal arch development

The endothelin (Edn) system comprises three ligands (Edn1, Edn2 and Edn3) and their G-protein-coupled type A (Ednra) and type B (Ednrb) receptors. During embryogenesis, the Edn1/Ednra signaling is thought to regulate the dorsoventral axis patterning of pharyngeal arches via Dlx5/Dlx6 upregulation. To further clarify the underlying mechanism, we have established mice in which gene cassettes can be efficiently knocked-in into the Ednra locus using recombinase-mediated cassette exchange (RMCE) based on the Cre-lox system. The first homologous recombination introducing mutant lox-flanked Neo resulted in homeotic transformation of the lower jaw to an upper jaw, as expected. Subsequent RMCE-mediated knock-in of lacZ targeted its expression to the cranial/cardiac neural crest derivatives as well as in mesoderm-derived head mesenchyme. Knock-in of Ednra cDNA resulted in a complete rescue of craniofacial defects of Ednra-null mutants. By contrast, Ednrb cDNA could not rescue them except for the most distal pharyngeal structures. At early stages, the expression of Dlx5, Dlx6 and their downstream genes was downregulated and apoptotic cells distributed distally in the mandible of Ednrb-knock-in embryos. These results, together with similarity in craniofacial defects between Ednrb-knock-in mice and neural-crest-specific Galpha(q)/Galpha(11)-deficient mice, indicate that the dorsoventral axis patterning of pharyngeal arches is regulated by the Ednra-selective, G(q)/G(11)-dependent signaling, while the formation of the distal pharyngeal region is under the control of a G(q)/G(11)-independent signaling, which can be substituted by Ednrb. This RMCE-mediated knock-in system can serve as a useful tool for studies on gene functions in craniofacial development.

Endothelin and endothelin converting enzyme-1 in the fish gill:evolutionary and physiological perspectives

In euryhaline fishes like the killifish (Fundulus heteroclitus)that experience daily fluctuations in environmental salinity, endothelin 1(EDN1) may be an important regulator molecule necessary to maintain ion homeostasis. The purpose of this study was to determine if EDN1 and the endothelin converting enzyme (ECE1; the enzyme necessary for cleaving the precursor proendothelin-1 to EDN1) are present in the killifish, to determine if environmental salinity regulates their expression, and to examine the phylogenetic relationships among the EDNs and among the ECEs. We sequenced killifish gill cDNA for two EDN1 orthologues, EDN1A and EDN1B, and also sequenced a portion of ECE1 cDNA. EDN1A and ECE1 mRNA are expressed ubiquitously in the killifish while EDN1B mRNA has little expression in the killifish opercular epithelium or gill. Using in situ hybridization and immunohistochemistry, EDN1 was localized to large round cells adjacent to the mitochondrion-rich cells of the killifish gill, and to lamellar pillar cells. In the gill, EDN1A and EDN1B mRNA levels did not differ with acute (<24 h) or chronic (30 days) acclimation to seawater (SW); however, EDN1B levels increased threefold post SW to freshwater (FW) transfer,and ECE1 mRNA levels significantly increased twofold over this period. ECE1 mRNA levels also increased sixfold over 24 h post FW to SW transfer. Chronic exposure to SW or FW had little effect on ECE1mRNA levels. Based upon our cellular localization studies, we modeled EDN1 expression in the fish gill and conclude that it is positioned to act as a paracrine regulator of gill functions in euryhaline fishes. It also may function as an autocrine on pillar cells, where it is hypothesized to regulate local blood flow in the lamellae. From our phylogenetic analyses, ECE is predicted to have an ancient origin and may be a generalist endoprotease in non-vertebrate organisms, while EDNs are vertebrate-specific peptides and may be key characters in vertebrate evolution.

The endothelin system as a therapeutic target in cardiovascular disease: great expectations or bleak house?

There is considerable evidence that the potent vasoconstrictor endothelin-1 (ET-1) contributes to the pathogenesis of a variety of cardiovascular diseases. As such, pharmacological manipulation of the ET system might represent a promising therapeutic goal. Many clinical trials have assessed the potential of ET receptor antagonists in cardiovascular disease, the most positive of which have resulted in the licensing of the mixed ET receptor antagonist bosentan, and the selective ET(A) receptor antagonists, sitaxsentan and ambrisentan, for the treatment of pulmonary arterial hypertension (PAH). In contrast, despite encouraging data from in vitro and animal studies, outcomes in human heart failure have been disappointing, perhaps illustrating the risk of extrapolating preclinical work to man. Many further potential applications of these compounds, including resistant hypertension, chronic kidney disease, connective tissue disease and sub-arachnoid haemorrhage are currently being investigated in the clinic. Furthermore, experience from previous studies should enable improved trial design and scope remains for development of improved compounds and alternative therapeutic strategies. Although ET-converting enzyme inhibitors may represent one such alternative, there have been relatively few suitable compounds developed, and consequently, clinical experience with these agents remains extremely limited. Recent advances, together with an increased understanding of the biology of the ET system provided by improved experimental tools (including cell-specific transgenic deletion of ET receptors), should allow further targeting of clinical trials to diseases in which ET is involved and allow the therapeutic potential for targeting the ET system in cardiovascular disease to be fully realized.

MEF2: a central regulator of diverse developmental programs

The myocyte enhancer factor 2 (MEF2) transcription factor acts as a lynchpin in the transcriptional circuits that control cell differentiation and organogenesis. The spectrum of genes activated by MEF2 in different cell types depends on extracellular signaling and on co-factor interactions that modulate MEF2 activity. Recent studies have revealed MEF2 to form an intimate partnership with class IIa histone deacetylases, which together function as a point of convergence of multiple epigenetic regulatory mechanisms. We review the myriad roles of MEF2 in development and the mechanisms through which it couples developmental, physiological and pathological signals with programs of cell-specific transcription.

Cranial neural crest and development of the head skeleton

The skeletal derivatives of the cranial neural crest (CNC) are patterned through a combination of intrinsic differences between crest cells and extrinsic signals from adjacent tissues, including endoderm and ectoderm. In this chapter, we focus on how CNC cells positionally interpret these cues to generate such highly specialized structures as the jaw and ear ossicles. We highlight recent genetic studies of craniofacial development in zebrafish that have revealed new tissue interactions and show that the process of CNC development is highly conserved across the vertebrates.

Fate of cranial neural crest cells during craniofacial development in endothelin-A receptor-deficient mice

Most of the bone, cartilage and connective tissue of the lower jaw is derived from cranial neural crest cells (NCCs) arising from the posterior midbrain and hindbrain. Multiple factors direct the patterning of these NCCs, including endothelin-1-mediated endothelin A receptor (Edn1/Ednra) signaling. Loss of Ednra signaling results in multiple defects in lower jaw and neck structures, including homeotic transformation of lower jaw structures into upper jaw-like structures. However, since the Ednra gene is expressed by both migrating and post-migrating NCCs, the actual function of Ednra in cranial NCC development is not clear. Ednra signaling could be required for normal migration or guidance of NCCs to the pharyngeal arches or in subsequent events in post-migratory NCCs, including proliferation and survival. To address this question, we performed a fate analysis of cranial NCCs in Ednra-/- embryos using the R26R;Wnt1-Cre reporter system, in which Cre expression within NCCs results in permanent beta-galactosidase activity in NCCs and their derivatives. We find that loss of Ednra does not detectably alter either migration of most cranial NCCs into the mandibular first arch and second arch or their subsequent proliferation. However, mesenchymal cell apoptosis is increased two fold in both E9.5 and E10.5 Ednra-/- embryos, with apoptotic cells being present in and just proximal to the pharyngeal arches. Based on these studies, Ednra signaling appears to be required by most cranial NCCs after they reach the pharyngeal arches. However, a subset of NCCs appear to require Ednra signaling earlier, with loss of Ednra signaling likely leading to premature cessation of migration into or within the arches and subsequent cell death.

Molecular dynamics of retinoic acid-induced craniofacial malformations: implications for the origin of gnathostome jaws

Background

Intake of retinoic acid (RA) or of its precursor, vitamin A, during early pregnancy is associated with increased incidence of craniofacial lesions. The origin of these teratogenic effects remains enigmatic as in cranial neural crest cells (CNCCs), which largely contribute to craniofacial structures, the RA-transduction pathway is not active. Recent results suggest that RA could act on the endoderm of the first pharyngeal arch (1stPA), through a RARß-dependent mechanism.

Methodology/Principal Findings

Here we show that RA provokes dramatically different craniofacial malformations when administered at slightly different developmental times within a narrow temporal interval corresponding to the colonization of the 1^st PA by CNCCs. We provide evidence showing that RA acts on the signalling epithelium of the 1^st PA, gradually reducing the expression of endothelin-1 and Fgf8. These two molecular signals are instrumental in activating Dlx genes in incoming CNCCs, thereby triggering the morphogenetic programs, which specify different jaw elements.

Conclusions/Significance

The anatomical series induced by RA-treatments at different developmental times parallels, at least in some instances, the supposed origin of modern jaws (e.g., the fate of the incus). Our results might provide a conceptual framework for the rise of jaw morphotypes characteristic of gnathostomes.

mef2ca is required in cranial neural crest to effect Endothelin1 signaling in zebrafish

Mef2 genes encode highly conserved transcription factors involved in somitic and cardiac mesoderm development in diverse bilaterians. Vertebrates have multiple mef2 genes. In mice, mef2c is required for heart and vascular development. We show that a zebrafish mef2c gene (mef2ca) is required in cranial neural crest (CNC) for proper head skeletal patterning. mef2ca mutants have head skeletal phenotypes resembling those seen upon partial loss-of-function of endothelin1 (edn1). Furthermore, mef2ca interacts genetically with edn1, arguing that mef2ca functions within the edn1 pathway. mef2ca is expressed in CNC and this expression does not require edn1 signaling. Mosaic analyses reveal that mef2ca is required in CNC for pharyngeal skeletal morphogenesis. Proper expression of many edn1-dependent target genes including hand2, bapx1, and gsc, depends upon mef2ca function. mef2ca plays a critical role in establishing the proper nested expression patterns of dlx genes. dlx5a and dlx6a, known Edn1 targets, are downregulated in mef2ca mutant pharyngeal arch CNC. Surprisingly, dlx4b and dlx3b are oppositely affected in mef2ca mutants. dlx4b expression is abolished while the edn1-dependent dlx3b is ectopically expressed in more dorsal CNC. Together our results support a model in which CNC cells require mef2ca downstream of edn1 signaling for proper craniofacial development.

Heredity of Endothelin Secretion

Background— Endothelial dysfunction predisposes to vascular injury in association with hypertension. Endothelin (ET-1) is a potent vasoactive peptide that is synthesized and released by the vascular endothelium and is a marker of endothelial function. Chromogranin A (CHGA) regulates the storage and release of catecholamines and may have direct actions on the microvasculature. CHGA , a candidate gene for intermediate phenotypes that contribute to hypertension, shows a pattern of single nucleotide polymorphism variations that alter the expression and function of this gene both in vivo and in vitro.

Methods and Results— In a study of twins (n=238 pairs), plasma ET-1 was 58±5% ( P <0.0001) heritable. Plasma ET-1 was both correlated and associated with chromogranin fragment levels, and the 2 were influenced by shared genetic determination (pleiotropy [ρ G ]; for the CHGA precursor, ρ G =0.318±0.105; P =0.0032). We therefore hypothesized that variation in the CHGA gene may influence ET-1 secretion. Carriers of the CHGA promoter −988G, −462A, and −89A minor alleles showed significantly higher mean plasma ET-1 than their major allele homozygote counterparts ( P =0.02, P =0.006, P =0.03, respectively). Analysis of a linkage disequilibrium block that spans these 3 single nucleotide polymorphisms showed a significant association between the GATACA haplotype and plasma ET-1 ( P =0.0075). In cultured human umbilical vein endothelial cells, CHGA caused dose-dependent secretion of ET-1 over a brief (<1 hour) time course at relatively low concentrations of CHGA (10 to 100 nmol/L) with a threshold concentration (10 nmol/L) in the range found circulating in humans in vivo.

Conclusions— These results suggest that common, heritable variation in expression of the human CHGA gene influences endothelial ET-1 secretion in vivo, explained by a CHGA stimulus/ET-1 secretion coupling in endothelial cells in vitro. The findings document a previously unsuspected interaction between the sympathochromaffin system and the endothelium and suggest novel genetic and cell biological approaches to the prediction, diagnosis, and mechanism of endothelial dysfunction in human disease.

phospholipase C, beta 3 is required for Endothelin1 regulation of pharyngeal arch patterning in zebrafish

Genetic and pharmacological studies demonstrate that Endothelin1 (Edn1) is a key signaling molecule for patterning the facial skeleton in fish, chicks, and mice. When Edn1 function is reduced early in development the ventral lower jaw and supporting structures are reduced in size and often fused to their dorsal upper jaw counterparts. We show that schmerle (she) encodes a zebrafish ortholog of Phospholipase C, beta 3 (Plcbeta3) required in cranial neural crest cells for Edn1 regulation of pharyngeal arch patterning. Sequencing and co-segregation demonstrates that two independent she (plcbeta3) alleles have missense mutations in conserved residues within the catalytic domains of Plcbeta3. Homozygous plcbeta3 mutants are phenotypically similar to edn1 mutants and exhibit a strong arch expression defect in Edn1-dependent Distalless (Dlx) genes as well as expression defects in several Edn1-dependent intermediate and ventral arch domain transcription factors. plcbeta3 also genetically interacts with edn1, supporting a model in which Edn1 signals through a G protein-coupled receptor to activate Plcbeta3. Mild skeletal defects occur in plcbeta3 heterozygotes, showing the plcbeta3 mutations are partially dominant. Through a morpholino-mediated deletion in the N-terminal PH domain of Plcbeta3, we observe a partial rescue of facial skeletal defects in homozygous plcbeta3 mutants, supporting a hypothesis that an intact PH domain is necessary for the partial dominance we observe. In addition, through mosaic analyses, we show that wild-type neural crest cells can efficiently rescue facial skeletal defects in homozygous plcbeta3 mutants, demonstrating that Plcbeta3 function is required in neural crest cells and not other cell types to pattern the facial skeleton.

The transcription factor MEF2C is required for craniofacial development

MEF2 transcription factors are well-established regulators of muscle development. We have discovered an unanticipated role for MEF2C in the neural crest, where tissue-specific inactivation results in neonatal lethality due to severe craniofacial defects. We show that MEF2C is required for expression of the Dlx5, Dlx6, and Hand2 transcription factor genes in the branchial arches, and we identify a branchial arch-specific enhancer in the Dlx5/6 locus, which is activated synergistically by MEF2C and Dlx5, demonstrating that these factors interact to induce transcription. Mef2c and Dlx5/6 also interact genetically. Mice heterozygous for either Dlx5/6 or Mef2c are normal at birth and survive to weaning. By contrast, heterozygosity for both Mef2c and Dlx5/6 results in defective palate development and neonatal lethality. Taken together, the studies presented here define a feed-forward transcriptional circuit between the MADS-box transcription factor MEF2C and the homeodomain transcription factors Dlx5 and Dlx6 in craniofacial development.

Cell-type specific interaction of endothelin and the nitric oxide system: pattern of prepro-ET-1 expression in kidneys of L-NAME treated prepro-ET-1 promoter-lacZ-transgenic mice

Nitric oxide (NO) and endothelin-1 (ET-1) are known to play a major role in renal and vascular pathophysiology and exhibit a close interaction with ET-1, stimulating NO production; NO in turn inhibits ET-1 expression. Our objectives were (1) to establish a novel transgenic mouse model facilitating ET-1 expression assessment in vivo, (2) to validate this model by assessing prepro-ET-1 promoter activity in mice embryos by means of our novel model and comparing expression sites to well-established data on ET-1 in fetal development and (3) to investigate renal ET-NO interaction by assessing prepro-ET-1 promoter activity in different structures of the renal cortex in the setting of blocked NO synthases via L-NAME administration. We established transgenic mice carrying a lacZ reporter gene under control of the human prepro-ET-1 gene promoter sequence (8 kb of 5' sequences). Bluo-Gal staining of tissue sections revealed intracellular blue particles as indicators of prepro-ET-1 promoter activity. In mouse embryos, we detected high prepro-ET-1 promoter activity in the craniofacial region, as well as in bone and cartilage consistent with the literature. In order to investigate the interaction of ET-1 and NO in the kidney in vivo, transgenic mice at the age of 3-4 months were treated with a single dose of the NO synthase inhibitor L-NAME (25 mg (kg bw)(-1) i.p.) 12 h before kidney removal. Bluo-Gal staining of kidney sections revealed intracellular blue particles as indicators of prepro-ET-1 promoter activity in tubular and vascular endothelium and glomerular cells. Particle count was closely correlated to kidney tissue ET-1 content (R=0.918, P<0.001). Comparison of counts revealed an increase by 135+/-53% in L-NAME treated (n=12) compared to non-treated mice (n=10, P=0.001). Cell-type specific evaluation revealed an increase of 136+/-51% in tubular (P=0.001) and 105+/-41% in glomerular cells (P=0.046), but no significant increase in vascular endothelium. In conclusion, our study revealed a close interaction of renal endothelin and the NO system in a cell-type specific manner. Our new transgenic model provides a unique opportunity to analyse regulation of the ET system on a cellular level in vivo.

Endothelin-1 gene and endothelial nitric oxide synthase gene polymorphisms in adolescents with juvenile and obesity-associated hypertension

Hypertension is an increasing public health problem all over the world. Essential hypertension accounts for more than 90% of cases of hypertension. It is a complex genetic, environmental and demographic trait. New method in molecular biology has been proposed a number of candidate genes, but the linkage or association with hypertension has been problematic (lack of gene-gene and gene-environment interaction). It is well known that genetic influences are more important in younger hypertensives, because children are relatively free from the common environmental factors contributing to essential hypertension. The association studies compare genotype ferquencies of the candidate gene between patient groups and the controls, in pathways known to be involved in blood pressure regulation. This study examined three polymorphisms of these factors encoding genes (ET-1 G+5665T (Lys198Asn), endothelial nitric oxide synthase (eNOS) T-786C promoter polymorphism and 27-bp repeat polymorphism in intron 4) in adolescents with juvenile essential and obesity-associated hypertension. Significant differences were found in the G/T genotype of the ET-1 polymorphism in the hypertensive and obese+hypertensive patients (body mass index (BMI) > 30). A strong association was detected between the BMI and the polymorphism of the ET-1 gene. It seems that ET-1 gene polymorphism plays a role in the development of juvenile hypertension associated with obesity. Although no significant differences were seen in the case of the eNOS promoter polymorphism and the eNOS 4th intron 27-bp repeat polymorphism. It seems that eNOS may play a role, but this is not the main factor in the control of blood pressure; it is rather a fine regulator in this process. This study with adolescents facilitates an understanding of the genetic factors promoting juvenile hypertension and obesity.

[Known gene interactions as implicated in craniofacial development]

Many genes intervening in development, morphogenesis and craniofacial growth have been identified, primarily by the use of mice mutants. We can distinguish two families: the signalling factors and the transcription factors. The latter interact with DNA to activate or to inhibit the expression of other genes. Some of the transcription factors are called homeogenes because they interact with DNA by a sequence of amino acids known as homeobox that has been carefully conserved throughout the course of evolution. Those factors interact, and signalling cascades have been described. Current research projects seek to discern the exact role of each of these genes in craniofacial growth and to develop a better understanding of the interactions between them.

Endothelin receptors and endothelin-1 in developing rat teeth

INTRODUCTION

The endothelins are a family of small peptides with multiple roles in a variety of tissues. Signaling is mediated through two receptor subtypes, the endothelin A receptor (ET(A)) specific for Et-1 and the non-specific endothelin B receptor (ET(B)).

OBJECTIVE

Our goal was to determine the location of immunoreactivity (IR) for ET(A) and ET(B) in developing and mature rat teeth as indicators of endothelin (Et) regulatory sites and to compare this to the Et-1 (ligand)-IR expression patterns.

DESIGN

We used immunohistochemistry to study developing and mature rat molars and continuously developing incisors.

RESULTS

We demonstrate ET(A), ET(B), and Et-1 expression patterns in teeth, for the first time. ET(A) was found in developing molar root pulp, pulpal vasculature, and preodontoblasts, and then persisted in odontoblasts or cellular cementocytes at the root apices of mature teeth. ET(B) was found at the molar (Hertwig's) root sheath during root formation and in molar ameloblasts, nerve fibers and odontoblasts of immature and mature teeth. In incisors, ET(B)-IR was associated with ameloblasts and the stem cell niche of the cervical loop while ET(A) was located in the substratum layer. Et-1 was found throughout the dental and periodontal tissues with higher concentrations associated with odontoblasts, nerves and incisor layers that expressed ET(B).

CONCLUSION

The patterns of ET(A) and ET(B) in teeth differ from each other and from those of adjacent tissues suggesting multiple tooth-specific functions for endothelin during development and mature dental function.

Dickkopf homolog 1 mediates endothelin-1-stimulated new bone formation

Tumor-produced endothelin-1 (ET-1) stimulates osteoblasts to form new bone and is an important mediator of osteoblastic bone metastasis. The anabolic actions of ET-1 in osteoblasts were investigated by gene microarray analyses of murine neonatal calvarial organ cultures. Targets of ET-1 action were validated by real-time RT-PCR in murine primary osteoblast cultures. IL-6, IL-11, the CCN (CYR61, CTGF, NOV) family members cysteine-rich protein 61 and connective tissue growth factor, inhibin beta-A, serum/glucocorticoid regulated kinase, receptor activator of nuclear factor kappaB ligand, snail homolog 1, tissue inhibitor of metalloproteinase 3, and TG-interacting factor transcripts were increased by ET-1. ET-1 decreased the transcript for the Wnt signaling pathway inhibitor, dickkopf homolog 1 (Dkk1). Calvarial organ cultures treated with ET-1 had lower concentrations of DKK1 protein in conditioned media than control cultures. High DKK1 concentrations in bone marrow suppress bone formation in multiple myeloma. We hypothesized that the converse occurs in osteoblastic bone metastasis, where ET-1 stimulates osteoblast activity by reducing autocrine production of DKK1. Recombinant DKK1 blocked ET-1-mediated osteoblast proliferation and new bone formation in calvarial organ cultures, whereas a DKK1-neutralizing antibody increased osteoblast numbers and new bone formation. ET-1 directed nuclear translocation of beta-catenin in osteoblasts, indicating activation of the Wnt signaling pathway. The data suggest that ET-1 increases osteoblast proliferation and new bone formation by activating the Wnt signaling pathway through suppression of the Wnt pathway inhibitor DKK1.

Bosentan for the treatment of systemic sclerosis-associated pulmonary arterial hypertension, pulmonary fibrosis and digital ulcers

Systemic sclerosis (SSc) is a devastating multisytemic autoimmune disease associated with widespread vascular damage. Pulmonary arterial hypertension (PAH) occurs in a significant proportion of patients and contributes to the morbidity and mortality that occurs in this disease. The recent development of specific therapies for the treatment of PAH mandates the early recognition, appropriate evaluation and judicious management of PAH in patients with SSc. Because endothelin (ET)-1 plays an important role in the development of PAH in SSc, and may also contribute to the vascular damage and fibrosis that occur in multiple organs in patients with the disease, inhibiting the production and activity of ET-1 is an appealing strategy for the treatment of SSc. This article reviews the pathophysiology of SSc and its vascular complications, and critically evaluates the current knowledge regarding the potential role of the ET-1 receptor blocker bosentan in the management of patients with SSc.

Requirements for Endothelin type-A receptors and Endothelin-1 signaling in the facial ectoderm for the patterning of skeletogenic neural crest cells in zebrafish

Genetic studies in mice and zebrafish have revealed conserved requirements for Endothelin 1 (Edn1) signaling in craniofacial development. Edn1 acts through its cognate type-A receptor (Ednra) to promote ventral skeletal fates and lower-jaw formation. Here, we describe the isolation and characterization of two zebrafish ednra genes - ednra1 and ednra2 -both of which are expressed in skeletal progenitors in the embryonic neural crest. We show that they play partially redundant roles in lower-jaw formation and development of the jaw joint. Knockdown of Ednra1 leads to fusions between upper- and lower-jaw cartilages, whereas the combined loss of Ednra1 and Ednra2 eliminates the lower jaw, similar to edn1-/-mutants. edn1 is expressed in pharyngeal arch ectoderm, mesoderm and endoderm. Tissue-mosaic studies indicate that, among these tissues, a crucial source of Edn1 is the surface ectoderm. This ectoderm also expresses ednrA1 in an edn1-dependent manner, suggesting that edn1 autoregulates its own expression. Collectively, our results indicate that Edn1 from the pharyngeal ectoderm signals through Ednra proteins to direct early dorsoventral patterning of the skeletogenic neural crest.

Calpain 6 is involved in microtubule stabilization and cytoskeletal organization

The calpains are a family of Ca(2+)-dependent cysteine proteases implicated in various biological processes. In this family, calpain 6 (Capn6) is unique in that it lacks the active-site cysteine residues requisite for protease activity. During the search for genes downstream of the endothelin 1 (ET-1) signaling in pharyngeal-arch development, we identified Capn6. After confirming that the expression of Capn6 in pharyngeal arches is downregulated in ET-1-null embryos by in situ hybridization, we investigated its function. In Capn6-transfected cells, cytokinesis was retarded and was often aborted to yield multinucleated cells. Capn6 overexpression also caused the formation of microtubule bundles rich in acetylated alpha-tubulin and resistant to the depolymerizing activity of nocodazole. Green fluorescent protein-Capn6 overexpression, immunostaining for endogenous Capn6, and biochemical analysis demonstrated interaction between Capn6 and microtubules, which appeared to be mainly mediated by domain III. Furthermore, RNA interference-mediated Capn6 inactivation caused microtubule instability with a loss of acetylated alpha-tubulin and induced actin reorganization, resulting in lamellipodium formation with membrane ruffling. Taken together, these results indicate that Capn6 is a microtubule-stabilizing protein expressed in embryonic tissues that may be involved in the regulation of microtubule dynamics and cytoskeletal organization.

Endothelin B receptor blockade accelerates disease progression in a murine model of autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is the most common genetic disease that causes kidney failure and accounts for 10% of all patients who are on renal replacement therapy. However, the marked phenotypic variation between patients who carry the same PKD1 or PKD2 mutation suggests that nonallelic factors may have a greater influence on the cystic phenotype. Endothelin-1 (ET-1) transgenic mice have been reported to develop profound renal cystic disease and interstitial fibrosis without hypertension. The hypothesis that ET-1 acts as a modifying factor for cystic disease progression was tested in an orthologous mouse model of ADPKD (Pkd2(WS25/-)). Four experimental groups (n = 8 to 11) were treated from 5 to 16 wk of age with the highly selective orally active receptor antagonists ABT-627 (ETA) and A-192621 (ETB) singly or in combination. Unexpected, ETB blockade led to accelerated cystic kidney disease. Of significance, this was associated with a reduction in urine volume and sodium excretion and increases in urine osmolarity and renal cAMP and ET-1 concentrations. The deleterious effect of chronic ETB blockade was neutralized by simultaneous ETA blockade. ETA blockade alone resulted in a significant increase in tubular cell proliferation but did not alter the cystic phenotype. It is concluded that the balance between ETA and ETB signaling is critical for maintaining tubular structure and function in the cystic kidney. These results implicate ET, acting via vasopressin-dependent and independent pathways, as a major modifying factor for cystic disease progression in human ADPKD.

Morphing the hyomandibular skeleton in development and evolution

How might changes in developmental regulatory pathways underlie evolutionary changes in morphology? Here we focus on a particular pathway regulated by a secreted, signaling peptide, Endothelin1 (Edn1). Developmental genetic analyses show the Edn1-pathway to be crucial for hyomandibular patterning, and we discuss our work with zebrafish suggesting how the signal may function in regulating numbers of skeletal elements, their sizes and their shapes. We then review a broader collection of comparative studies that examine morphological evolution of a subset of the same skeletal elements-the opercular-branchiostegal series of bones of the hyoid arch. We find that phenotypic changes in zebrafish mutants copy evolutionary changes that recur along many actinopterygian lineages. Hence the developmental genetic studies are informative for providing candidate pathways for macroevolution of facial morphology, as well as for our understanding of how these pathways work.

Conditional mutagenesis of G-protein coupled receptors and G-proteins

The G-protein-coupled receptor signaling system, consisting of a huge variety of receptors as well as of many G-proteins and effectors, operates in every cell and is involved in many physiological and pathological processes. The versatility of this system and the involvement of specific components makes G-protein-coupled receptors and their signaling pathways ideal targets for pharmacological interventions. Classical mouse knockout models have often provided important preliminary insights into the biological roles of individual receptors and signaling pathways and they are routinely used in the process of target validation. The recent development of efficient conditional mutagenesis techniques now allows a much more detailed analysis of G-protein-mediated signaling transduction processes. This review summarizes some of the areas in which progress has recently been made by applying conditional mutagenesis of genes coding for G-proteins and G-protein-coupled receptors.

Endothelin

In humans, the endothelins (ETs) comprise a family of three 21-amino-acid peptides, ET-1, ET-2 and ET-3. ET-1 is synthesised from a biologically inactive precursor, Big ET-1, by an unusual hydrolysis of the Trp21 -Val22 bond by the endothelin converting enzyme (ECE-1). In humans, there are four isoforms (ECE-1a-d) derived from a single gene by the action of alternative promoters. Structurally, they differ only in the amino acid sequence of the extreme N-terminus. A second enzyme, ECE-2, also exists as four isoforms and differs from ECE-1 in requiring an acidic pH for optimal activity. Human chymase can also cleave Big ET-1 to ET-1, which is cleaved, in turn, to the mature peptide as an alternative pathway. ET-1 is the principal isoform in the human cardiovascular system and remains one of the most potent constrictors of human vessels discovered. ET-1 is unusual in being released from a dual secretory pathway. The peptide is continuously released from vascular endothelial cells by the constitutive pathway, producing intense constriction of the underlying smooth muscle and contributing to the maintenance of endogenous vascular tone. ET-1 is also released from endothelial cell-specific storage granules (Weibel-Palade bodies) in response to external stimuli. ETs mediate their action by activating two G protein-coupled receptor sub-types, ETA and ET(B). Two therapeutic strategies have emerged to oppose the actions of ET-1, namely inhibition of the synthetic enzyme by combined ECE/neutral endopeptidase inhibitors such as SLV306, and receptor antagonists such as bosentan. The ET system is up-regulated in atherosclerosis, and ET antagonists may be of benefit in reducing blood pressure in essential hypertension. Bosentan, the first ET antagonist approved for clinical use, represents a significant new therapeutic strategy in the treatment of pulmonary arterial hypertension (PAH).

21st century neontology and the comparative development of the vertebrate skull

Classic neontology (comparative embryology and anatomy), through the application of the concept of homology, has demonstrated that the development of the gnathostome (jawed vertebrate) skull is characterized both by a fidelity to the gnathostome bauplan and the exquisite elaboration of final structural design. Just as homology is an old concept amended for modern purposes, so are many of the questions regarding the development of the skull. With due deference to Geoffroy-St. Hilaire, Cuvier, Owen, Lankester et al., we are still asking: How are bauplan fidelity and elaboration of design maintained, coordinated, and modified to generate the amazing diversity seen in cranial morphologies? What establishes and maintains pattern in the skull? Are there universal developmental mechanisms underlying gnathostome autapomorphic structural traits? Can we detect and identify the etiologies of heterotopic (change in the topology of a developmental event), heterochronic (change in the timing of a developmental event), and heterofacient (change in the active capacetence, or the elaboration of capacity, of a developmental event) changes in craniofacial development within and between taxa? To address whether jaws are all made in a like manner (and if not, then how not), one needs a starting point for the sake of comparison. To this end, we present here a "hinge and caps" model that places the articulation, and subsequently the polarity and modularity, of the upper and lower jaws in the context of cranial neural crest competence to respond to positionally located epithelial signals. This model expands on an evolving model of polarity within the mandibular arch and seeks to explain a developmental patterning system that apparently keeps gnathostome jaws in functional registration yet tractable to potential changes in functional demands over time. It relies upon a system for the establishment of positional information where pattern and placement of the "hinge" is driven by factors common to the junction of the maxillary and mandibular branches of the first arch and of the "caps" by the signals emanating from the distal-most first arch midline and the lamboidal junction (where the maxillary branch meets the frontonasal processes). In this particular model, the functional registration of jaws is achieved by the integration of "hinge" and "caps" signaling, with the "caps" sharing at some critical level a developmental history that potentiates their own coordination. We examine the evidential foundation for this model in mice, examine the robustness with which it can be applied to other taxa, and examine potential proximate sources of the signaling centers. Lastly, as developmental biologists have long held that the anterior-most mesendoderm (anterior archenteron roof or prechordal plate) is in some way integral to the normal formation of the head, including the cranial skeletal midlines, we review evidence that the seminal patterning influences on the early anterior ectoderm extend well beyond the neural plate and are just as important to establishing pattern within the cephalic ectoderm, in particular for the "caps" that will yield medial signaling centers known to coordinate jaw development.