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PubMed2001

Drosophila Tsc1 functions with Tsc2 to antagonize insulin signaling in regulating cell growth, cell proliferation, and organ size.

Tuberous sclerosis complex is a dominant disorder that leads to the development of benign tumors in multiple organs. We have isolated a mutation in the Drosophila homolog of TSC1 (Tsc1). Cells mutant for Tsc1 are dramatically increased in size yet differentiate normally. Organ size is also increased in tissues that contain a majority of mutant cells. Clones of Tsc1 mutant cells in the imaginal discs undergo additional divisions but retain normal ploidy. We also show that the Tsc1 protein binds to Drosophila Tsc2 in vitro. Overexpression of Tsc1 or Tsc2 alone in the wing and eye has no effect, but co-overexpression leads to a decrease in cell size, cell number, and organ size. Genetic epistasis data are consistent with a model that Tsc1 and Tsc2 function together in the insulin signaling pathway.

Animals↗

PubMed2002

Control of actin reorganization by Slingshot, a family of phosphatases that dephosphorylate ADF/cofilin.

The ADF (actin-depolymerizing factor)/cofilin family is a stimulus-responsive mediator of actin dynamics. In contrast to the mechanisms of inactivation of ADF/cofilin by kinases such as LIM-kinase 1 (LIMK1), much less is known about its reactivation through dephosphorylation. Here we report Slingshot (SSH), a family of phosphatases that have the property of F actin binding. In Drosophila, loss of ssh function dramatically increased levels of both F actin and phospho-cofilin (P cofilin) and disorganized epidermal cell morphogenesis. In mammalian cells, human SSH homologs (hSSHs) suppressed LIMK1-induced actin reorganization. Furthermore, SSH and the hSSHs dephosphorylated P cofilin in cultured cells and in cell-free assays. Our results strongly suggest that the SSH family plays a pivotal role in actin dynamics by reactivating ADF/cofilin in vivo.

Actin Depolymerizing Factors↗

PubMed1997

Toxaphene congeners differ from toxaphene mixtures in their dysmorphogenic effects on cultured rat embryos.

The presence of persistent organic pollutants, including the pesticide toxaphene has been reported even in remote regions such as the Arctic and is becoming a health concern. The technical mixture of toxaphene contains over 800 different congeners. The numbers of prevalent congeners, however, decrease along the food chain. About 20 major congeners are found in fish, eight in marine mammals and only two major ones in human, 2-exo,3-endo,5-exo,6-endo,8,8,10,10-octachlorobornane (T2) and 2-exo,3-endo,5-exo,6-endo,8,8,9,10,10-nonachlorobornane (T12). Embryotoxicity of these individual congeners is not known, as previous studies focused on the toxaphene technical mixture. We studied the relative dysmorphogenic activity of toxaphene technical mixture and individual congeners (T2 and T12) using rat embryo culture. Explanted embryos (0-2 somites) were treated for 48 h with concentrations of 0 (DMSO 0.01%), 100, 1000 and 5000 ng/ml of either (a) toxaphene technical mixture; (b) T2; (c) T12; or (d) a 50:50 mixture of T2 and T12. The treatment period corresponds to gestational days (GD) 10-12, a period within the critical time of morphogenesis and organogenesis. Both the technical mixture and the two individual congeners had a significant adverse effects on the total morphological score, somite number, head and crown rump length and the central nervous system scores of embryos. All treatments caused a high incidence of central nervous system defects. The T2 and T12 congeners differed in their spectrum of abnormalities as exposure to T2 caused limb and flexion defects which were not observed with the T12 congener. Differences were also observed in the type of toxicity and the target sites between the technical mixture and the congeners. T2 showed a more potent adverse effect on the morphological score as compared to the technical mixture. Both T2 and T12 were less inhibitory on growth than the technical mixture as indicated by crown-rump length but they showed a stronger inhibitory effect on otic system development. The mixture of T2 + T12 showed a synergistic effect on decreasing crown-rump and head length. Conversely, the combination of T2 and T12 inhibited the strong adverse effect of the individual congeners on otic development. The results suggest environmentally predominant toxaphene congeners can have organ specific embryotoxic effects not predicted by the toxaphene technical mixture.

Animals↗

PubMedDate not supplied

[Cystic diseases of the liver. From embryology to malformations].

Cystic diseases of the liver which are in most cases hereditary, are related to an embryonic disorder know as ductal plate malformation. These diseases correspond to partial or total arrest of remodeling of the ductal plate, leading to more or less complete persistence of the excess of embryonic biliary structures. The ductal plate malformation may concern different segments of the intrahepatic biliary tree (segmental bile ducts, interlobular bile ducts and the smallest bile duct ramifications) leading to various pathoclinical entities. Caroli's disease is characterized by persistent dilated large intrahepatic bile ducts and appears to be the result of a factor acting during the early period of bile duct embryogenesis. Congenital hepatic fibrosis is characterized by ductal plate malformations of more distal, interlobular, bile ducts, and could be due to a factor that acts later on during bile duct development. This disorder may be isolated or associated with malformations of large, segmental, intrahepatic bile ducts. Von Meyenburg complexes and autosomal dominant polycystic liver disease are related to ductal plate malformation of more peripheral interlobular bile ducts and caused by a factor intervening in the later phase of bile duct embryogenesis. The genetic or non genetic factors leading to these ductal plate malformations are unknown.

Bile Ducts, Intrahepatic↗

PubMed1999

Delta-mediated specification of midline cell fates in zebrafish embryos.

BACKGROUND: Fate mapping studies have shown that progenitor cells of three vertebrate embryonic midline structures - the floorplate in the ventral neural tube, the notochord and the dorsal endoderm - occupy a common region prior to gastrulation. This common region of origin raises the possibility that interactions between midline progenitor cells are important for their specification prior to germ layer formation. RESULTS: One of four known zebrafish homologues of the Drosophila melanogaster cell-cell signaling gene Delta, deltaA (dlA), is expressed in the developing midline, where progenitor cells of the ectodermal floorplate, mesodermal notochord and dorsal endoderm lie close together before they occupy different germ layers. We used a reverse genetic strategy to isolate a missense mutation of dlA, dlAdx2, which coordinately disrupts the development of floorplate, notochord and dorsal endoderm. The dlAdx2 mutant embryos had reduced numbers of floorplate and hypochord cells; these cells lie above and beneath the notochord, respectively. In addition, mutant embryos had excess notochord cells. Expression of a dominant-negative form of Delta protein driven by mRNA microinjection produced a similar effect. In contrast, overexpression of dlA had the opposite effect: fewer trunk notochord cells and excess floorplate and hypochord cells. CONCLUSION: Our results indicate that Delta signaling is important for the specification of midline cells. The results are most consistent with the hypothesis that developmentally equivalent midline progenitor cells require Delta-mediated signaling prior to germ layer formation in order to be specified as floorplate, notochord or hypochord.

Animals↗

PubMed2003

Hedgehog signal transduction via Smoothened association with a cytoplasmic complex scaffolded by the atypical kinesin, Costal-2.

The seven-transmembrane protein Smoothened (Smo) transduces extracellular activation of the Hedgehog (Hh) pathway by an unknown mechanism to increase transcriptional activity of the latent cytoplasmic transcription factor Ci (Cubitus interruptus). Here, we present evidence that Smo associates directly with a Ci-containing complex that is scaffolded and stabilized by the atypical kinesin, Costal-2 (Cos2). This complex constitutively suppresses pathway activity, but Hh signaling reverses its regulatory effect to promote Ci-mediated transcription. In response to Hh activation of Smo, Cos2 mediates accumulation and phosphorylation of Smo at the membrane as well as phosphorylation of the cytoplasmic components Fu and Su(fu). Positive response of Cos2 to Hh stimulation requires a portion of the Smo cytoplasmic tail and the Cos2 cargo domain, which interacts directly with Smo.

Amino Acid Sequence↗

PubMed2001

Drosophila neuralized is a ubiquitin ligase that promotes the internalization and degradation of delta.

The Drosophila gene neuralized (neur) has long been recognized to be essential for the proper execution of a wide variety of processes mediated by the Notch (N) pathway, but its role in the pathway has been elusive. In this report, we present genetic and biochemical evidence that Neur is a RING-type, E3 ubiquitin ligase. Next, we show that neur is required for proper internalization of Dl in the developing eye. Finally, we demonstrate that ectopic Neur targets Dl for internalization and degradation in a RING finger-dependent manner, and that the two exist in a physical complex. Collectively, our data indicate that Neur is a ubiquitin ligase that positively regulates the N pathway by promoting the endocytosis and degradation of Dl.

Animals↗

PubMed2001

neuralized Encodes a peripheral membrane protein involved in delta signaling and endocytosis.

Activation of the Notch (N) receptor involves an intracellular proteolytic step triggered by shedding of the extracellular N domain (N-EC) upon ligand interaction. The ligand Dl has been proposed to effect this N-EC shedding by transendocytosing the latter into the signal-emitting cell. We find that Dl endocytosis and N signaling are greatly stimulated by expression of neuralized (neur). neur inactivation suppresses Dl endocytosis, while its overexpression enhances Dl endocytosis and Notch-dependent signaling. We show that neur encodes an intracellular peripheral membrane protein. Its C-terminal RING domain is necessary for Dl accumulation in endosomes, but may be dispensable for Dl signaling. The potent modulatory effect of Neur on Dl activity makes Neur a candidate for establishing signaling asymmetries within cellular equivalence groups.

Animals↗

PubMed1999

The expression of tenascin-X in developing and adult rat and human eye.

Tenascin-X has been studied in developing and adult rat eye and in foetal and adult human eyes, using immunohistochemistry and frozen sections. The data were compared with the distribution of tenascin-C. The immunoreactivity for tenascin-X was seen in a basement membrane-like feature in different structures of embryonic (E) day 16-17 rat eyes. Postnatal (P) day 2 and older rat eyes showed immunoreactivity for tenascin-X in different connective tissues. In the epithelial basement membrane zone of the cornea, immunostaining was positive in P5 eyes, negative in P10 and P15 eyes and again positive in P30 and adult eyes. In the 20-week-old human foetus, immunoreactivity for the tenascin was seen in the posterior parts of the conjunctival stroma adjacent to the sclera and in a basement membrane-like fashion in anterior conjunctiva. In the adult human eye, immunoreactivity for tenascin-X was seen in the anterior one-third stroma of cornea as thin fibrils, in the stroma of the limbus and conjunctiva, and in blood vessels. Immunostaining for tenascin-C was seen in the posterior aspect of the further cornea, and in mesenchyme adjacent to cornea in E1617 rat eyes. Corneal keratocytes and Descemet's membrane showed immunoreactivity for tenascin-C in P2-P15 rat eyes. Sclera and the junction of the cornea, and sclera expressed tenascin-C in P2 and older rat eyes. In human foetal eyes, immunostaining for tenascin-C was seen in the anterior parts of the corneal stroma, in the basement membrane zone and Bowman's membrane of the corneal epithelium, in the posterior one-fifth of the corneal stroma and the sclera starting from the junction of the cornea and sclera. In normal human adult eyes, immunostaining for tenascin-X was seen in the anterior one-third stroma of cornea, in the stroma of limbus and conjunctiva, and in blood vessels. The association of tenascin-X and basement membranes in early development evokes a question of its potential function in the development of the basement membrane. The results also suggest the association of tenascin-X with connective tissue development as well as the association of tenascin-C with the migration of keratocytes during the development of the corneal stroma.

Adult↗

PubMed2003

The Salvador partner Hippo promotes apoptosis and cell-cycle exit in Drosophila.

Tissue growth during animal development is tightly controlled so that the organism can develop harmoniously. The salvador (sav) gene, which encodes a scaffold protein, has been shown to restrict cell number by coordinating cell-cycle exit and apoptosis during Drosophila development. Here we identify Hippo (Hpo), the Drosophila orthologue of the mammalian MST1 and MST2 serine/threonine kinases, as a partner of Sav. Loss of hpo function leads to sav-like phenotypes, whereas gain of hpo function results in the opposite phenotype. Whereas Sav and Hpo normally restrict cellular quantities of the Drosophila inhibitor of apoptosis protein DIAP1, overexpression of Hpo destabilizes DIAP1 in cell culture. We show that DIAP1 is phosphorylated in a Hpo-dependent manner in S2 cells and that Hpo can phosphorylate DIAP1 in vitro. Thus, Hpo may promote apoptosis by reducing cellular amounts of DIAP1. In addition, we show that Sav is an unstable protein that is stabilized by Hpo. We propose that Hpo and Sav function together to restrict tissue growth in vivo.

Animals↗

PubMed2003

Stability and association of Smoothened, Costal2 and Fused with Cubitus interruptus are regulated by Hedgehog.

The mechanisms involved in transduction of the Hedgehog (Hh) signal are of considerable interest to developmental and cancer biologists. Stabilization of the integral membrane protein Smoothened (Smo) at the plasma membrane is a crucial step in Hh signalling but the molecular events immediately downstream of Smo remain to be elucidated. We have shown previously that the transcriptional mediator Cubitus interruptus (Ci) is associated in a protein complex with at least two other proteins, the kinesin-like Costal2 (Cos2) and the serine-threonine kinase Fused (Fu). This protein complex governs the access of Ci to the nucleus. Here we show that, consequent on the stabilization of Smo, Cos2 and Fu are destabilized. Moreover, we find that the Cos2-Fu-Ci protein complex is associated with Smo in membrane fractions both in vitro and in vivo. We also show that Cos2 binding on Smo is necessary for the Hh-dependent dissociation of Ci from this complex. We propose that the association of the Cos2 protein complex with Smo at the plasma membrane controls the stability of the complex and allows Ci activation, eliciting its nuclear translocation.

Active Transport, Cell Nucleus↗

PubMed2003

A defective response to Hedgehog signaling in disorders of cholesterol biosynthesis.

Smith-Lemli-Opitz syndrome (SLOS), desmosterolosis and lathosterolosis are human syndromes caused by defects in the final stages of cholesterol biosynthesis. Many of the developmental malformations in these syndromes occur in tissues and structures whose embryonic patterning depends on signaling by the Hedgehog (Hh) family of secreted proteins. Here we report that response to the Hh signal is compromised in mutant cells from mouse models of SLOS and lathosterolosis and in normal cells pharmacologically depleted of sterols. We show that decreasing levels of cellular sterols correlate with diminishing responsiveness to the Hh signal. This diminished response occurs at sterol levels sufficient for normal autoprocessing of Hh protein, which requires cholesterol as cofactor and covalent adduct. We further find that sterol depletion affects the activity of Smoothened (Smo), an essential component of the Hh signal transduction apparatus.

3T3 Cells↗

PubMed1998

Somatic cell cloned transgenic bovine neurons for transplantation in parkinsonian rats.

Parkinson's disease symptoms can be improved by transplanting fetal dopamine cells into the putamen of parkinsonian patients. Because the supply of human donor tissue is limited and variable, an alternative and genetically modifiable non-human source of tissue would be valuable. We have generated cloned transgenic bovine embryos, 42% of which developed beyond 40 days. Dopamine cells collected from the ventral mesencephalon of the cloned fetuses 42 to 50 days post-conception survived transplantation into immunosuppressed parkinsonian rats and cells from cloned and wild-type embryos improved motor performance. Somatic cell cloning can efficiently produce transgenic animal tissue for treating parkinsonism.

Animals↗

PubMed1999

Expression of tissue transglutaminase in the developing chicken limb is associated both with apoptosis and endochondral ossification.

The cross-linking enzyme tissue transglutaminase (tTG) participates in a variety of cellular functions. To assess its contribution to extracellular and intracellular processes during development we cloned the cDNA for chicken heart tissue transglutaminase and localized the sites of transglutaminase expression by in situ hybridization and immunohistochemistry. Compared with the chicken red blood cell transglutaminase cDNA, the heart cDNA encodes a transglutaminase with an amino-terminal truncation. The truncated enzyme retains full catalytic activity and is GTP-inhibitable. Tissue transglutaminase expression was observed in developmentally transient structures in embryonic chicken limb at day 7.5 of incubation suggesting that its expression is dynamically regulated during limb morphogenesis. The major morphogenetic events of the limb associated with transglutaminase expression were cartilage maturation during skeletal development, interdigital apoptosis, and differentiation of skeletal muscle. Maturation of the cartilage during endochondral ossification was characterized by intra- and extracellular transglutaminase accumulation in the zone of hypertrophic chondrocytes. Only intracellular enzyme could be detected in mesenchymal cells of the prospective joints, in apoptotic cells of the interdigital web, and in skeletal muscle myoblasts. An apparently constitutive expression of tissue transglutaminase was found in vascular endothelial cells corresponding to the adult expression pattern. The dynamic pattern of transglutaminase expression during morphogenesis suggests that tissue remodeling is a major trigger for transglutaminase induction.

Animals↗

PubMed2006

Displacement of D1, HP1 and topoisomerase II from satellite heterochromatin by a specific polyamide.

The functions of DNA satellites of centric heterochromatin are difficult to assess with classical molecular biology tools. Using a chemical approach, we demonstrate that synthetic polyamides that specifically target AT-rich satellite repeats of Drosophila melanogaster can be used to study the function of these sequences. The P9 polyamide, which binds the X-chromosome 1.688 g/cm3 satellite III (SAT III), displaces the D1 protein. This displacement in turn results in a selective loss of HP1 and topoisomerase II from SAT III, while these proteins remain bound to the adjacent rDNA repeats and to other regions not targeted by P9. Conversely, targeting of (AAGAG)n satellite V repeats by the P31 polyamide results in the displacement of HP1 from these sequences, indicating that HP1 interactions with chromatin are sensitive to DNA-binding ligands. P9 fed to larvae suppresses the position-effect variegation phenotype of white-mottled adult flies. We propose that this effect is due to displacement of the heterochromatin proteins D1, HP1 and topoisomerase II from SAT III, hence resulting in stochastic chromatin opening and desilencing of the nearby white gene.

AT Rich Sequence↗

PubMed2006

Self-refinement of Notch activity through the transmembrane protein Crumbs: modulation of gamma-secretase activity.

Cell interactions mediated by Notch family receptors have been implicated in the specification of tissue boundaries. Tightly localized activation of Notch is crucial for the formation of sharp boundaries. In the Drosophila wing imaginal disc, the Notch receptor is expressed in all cells. However, Notch activity is limited to a narrow stripe of cells along the dorsal-ventral compartment boundary, where it induces the expression of target genes. How a widely expressed protein becomes tightly regulated at the dorsal-ventral boundary in the Drosophila wing is not completely understood. Here, we show that the transmembrane protein Crumbs is involved in a feedback mechanism used by Notch to refine its own activation domain at the Drosophila wing margin. Crumbs reduces the activity of the gamma-Secretase complex, which mediates the proteolytic intracellular processing of Notch. These results indicate a novel molecular mechanism of the regulation of Notch signal, and also that defects in Crumbs might be involved in similar abnormal gamma-Secretase complex activity observed in Alzheimer's disease.

Amyloid Precursor Protein Secretases↗

PubMed2005

Generation of embryos directly from embryonic stem cells by tetraploid embryo complementation reveals a role for GATA factors in organogenesis.

Gene targeting in ES (embryonic stem) cells has been used extensively to study the role of proteins during embryonic development. In the traditional procedure, this requires the generation of chimaeric mice by introducing ES cells into blastocysts and allowing them to develop to term. Once chimaeric mice are produced, they are bred into a recipient mouse strain to establish germline transmission of the allele of interest. Although this approach has been used very successfully, the breeding cycles involved are time consuming. In addition, genes that are essential for organogenesis often have roles in the formation of extra-embryonic tissues that are essential for early stages of post-implantation development. For example, mice lacking the GATA transcription factors, GATA4 or GATA6, arrest during gastrulation due to an essential role for these factors in differentiation of extra-embryonic endoderm. This lethality has frustrated the study of these factors during the development of organs such as the liver and heart. Extraembryonic defects can, however, be circumvented by generating clonal mouse embryos directly from ES cells by tetraploid complementation. Here, we describe the usefulness and efficacy of this approach using GATA factors as an example.

Animals↗

PubMed2001

Prenatal diagnosis of fetal tail and postabortum anatomical description.

Fetal ultrasound examination at 13 weeks of gestation demonstrated a homogeneously echogenic protrusion, or tail, 7 mm in length, in the sacral region. At 15 weeks, the ultrasound appearance was consistent with a regression of the tail and by 21 weeks it had completely disappeared. Severe intrauterine growth restriction with reduced uterine blood flow was diagnosed at 21 weeks and intrauterine death occurred at 24 weeks of gestation. Postmortem examination revealed a 4-mm caudal appendage which contained no vertebrae on radiography. The appendage was located under and behind the last sacral vertebra suggesting a true vestigial tail with a delayed process of regression.

Adult↗