Many Aspects Of Animal Development Research Articles

DTcf/Pangolin suppresses growth and tumor formation in Drosophila

Wnt/Wingless (Wg) signaling controls many aspects of animal development and is deregulated in different human cancers. The transcription factor dTcf/Pangolin (Pan) is the final effector of the Wg pathway in Drosophila and has a dual role in regulating the expression of Wg target genes. In the presence of Wg, dTcf/Pan interacts with β-catenin/Armadillo (Arm) and induces the transcription of Wg targets. In absence of Wg, dTcf/Pan partners with the transcriptional corepressor TLE/Groucho (Gro) and inhibits gene expression. Here, we use the wing imaginal disk of Drosophila as a model to examine the functions that dTcf/Pan plays in a proliferating epithelium. We report a function of dTcf/Pan in growth control and tumorigenesis. Our results show that dTcf/Pan can limit tissue growth in normal development and suppresses tumorigenesis in the context of oncogene up-regulation. We identify the conserved transcription factors Sox box protein 15 (Sox15) and Ftz transcription factor 1 (Ftz-f1) as genes controlled by dTcf/Pan involved in tumor development. In conclusion, this study reports a role for dTcf/Pan as a repressor of normal and oncogenic growth and identifies the genes inducing tumorigenesis downstream of dTcf/Pan.

Loss of Wnt8b has no overt effect on hippocampus development but leads to altered Wnt gene expression levels in dorsomedial telencephalon.

Wnt signalling proteins regulate many aspects of animal development. We have investigated the function of mouse Wnt8b during forebrain development. Wnt8b is expressed in a highly restricted pattern including the prospective hippocampus and hypothalamus. Mutant mice lacking Wnt8b are viable and healthy. The size and morphology of the hippocampus appeared normal in mutant embryos and adults, and we found no evidence of hypothalamic defects in mutants. Wnt8b is also expressed in the neurogenic region of the adult dentate gyrus, however, cell proliferation was unchanged in Wnt8b(-/-) mutants. Mutant embryos did, however, display altered levels of expression of other Wnt genes normally expressed in forebrain. The spatial expression patterns of other Wnt genes and the overall level of canonical Wnt activity were indistinguishable from wild-types. Thus, loss of Wnt8b does not give rise to an overt morphological phenotype, but does affect expression levels of other Wnts in developing forebrain.

Systematic analysis of dynamic miRNA-target interactions during C. elegans development.

Although microRNA (miRNA)-mediated functions have been implicated in many aspects of animal development, the majority of miRNA::mRNA regulatory interactions remain to be characterized experimentally. We used an AIN/GW182 protein immunoprecipitation approach to systematically analyze miRNA::mRNA interactions during C. elegans development. We characterized the composition of miRNAs in functional miRNA-induced silencing complexes (miRISCs) at each developmental stage and identified three sets of miRNAs with distinct stage-specificity of function. We then identified thousands of miRNA targets in each developmental stage, including a significant portion that is subject to differential miRNA regulation during development. By identifying thousands of miRNA family-mRNA pairs with temporally correlated patterns of AIN-2 association, we gained valuable information on the principles of physiological miRNA::target recognition and predicted 1589 high-confidence miRNA family::mRNA interactions. Our data support the idea that miRNAs preferentially target genes involved in signaling processes and avoid genes with housekeeping functions, and that miRNAs orchestrate temporal developmental programs by coordinately targeting or avoiding genes involved in particular biological functions.

Expression Profiles ofWntGenes during Neural Differentiation of Mouse Embryonic Stem Cells

The Wnt family of secreted signaling proteins regulates many aspects of animal development and the behavior of several types of stem cells, including embryonic stem (ES) cells. Activation of canonical Wnt signaling has been shown to either inhibit or promote the differentiation of ES cells into neurons, depending on the stage of differentiation. Here, we describe the expression of all 19 mouse Wnt genes during this process. Using the well-established retinoic acid induction protocol we found that all Wnt genes except Wnt8b are expressed as ES cells differentiate into neurons, many of them in dynamic patterns. The expression pattern of 12 Wnt genes was analyzed quantitatively at 2-day intervals throughout neural differentiation, showing that multiple Wnt genes are expressed at each stage. A large proportion of these, including both canonical and noncanonical Wnts, are expressed at highest levels during later stages of differentiation. The complexity of the patterns observed indicates that disentangling specific roles for individual Wnt genes in the differentiation process will be a significant challenge.

Calcium dynamics integrated into signalling pathways that influence vertebrate axial patterning.

Many aspects of animal development including fertilization as well as organ formation and function are dependent upon the dynamic release of calcium (Ca(2+)) ions. Although the controlled release and/or accumulation of Ca(2+) ions has been extensively studied, how the release dynamics produce a specific biological output in embryonic development is less clear. We will briefly summarize Ca(2+) sources, highlight data on endogenous Ca(2+) release in vertebrate embryos relevant to body plan formation and cell movement, and integrate pharmacological and molecular-genetic studies to lend insight into the signalling pathways involved. Finally, based on in vivo imaging in zebrafish genetic mutants, we will put forward the model that distinct Ca(2+) release dynamics lead to antagonism of the developmentally important Wnt/beta-catenin signalling pathway, while sustained Ca(2+) release modulates cell polarization or directed migration.

Identification of Two Binding Regions for the Suppressor of Hairless Protein within the Intracellular Domain of Drosophila Notch

Notch is a phylogenetically conserved transmembrane receptor that is required for many aspects of animal development. Upon ligand stimulation, a fragment of Notch is released proteolytically and enters the nucleus to form a complex with the DNA-binding protein CSL (CBF1/Suppressor of Hairless/Lag1) and activate transcription of Notch-CSL target genes. The physical structure of the Notch-CSL complex remains unclear, however, clouding the interpretation of previous efforts to correlate Notch structure and function. We have, therefore, characterized the binding of Drosophila CSL (called Suppressor of Hairless, or Su(H)) to the intracellular domain of Drosophila Notch both in vitro and in vivo. We report the identification of two Su(H) binding regions in Notch. The first is in the juxtamembrane region (the "RAM" domain). The second is just C-terminal to the Notch ankyrin repeats, overlapping or identical to two previously proposed nuclear localization sequences, in a domain we term PPD (potential phosphorylated domain). The ankyrin repeats themselves do not bind to Su(H); however, they substantially enhance binding of Su(H) to the more C-terminal region. Consistent with this picture, removal of either the Ram or PPD binding sites, separately, modestly reduces Notch activity in vivo, whereas removal of both renders Notch severely defective. These results clarify the relationship between Notch and CSL, help to explain the importance of the ankyrin repeats in Notch signaling, and reconcile many apparently contradictory results from previous Notch structure/function studies. Moreover, they suggest a second function for the Notch nuclear localization sequence elements.

Fibroblast growth factor signalling in mouse mammary gland development.

Fibroblast growth factors (Fgfs) and their receptors are important intercellular signalling molecules involved in many aspects of animal development. The aberrant expression of the Fgfs or the inappropriate activation of their cell surface receptors have been implicated in tumorigenesis. Here, we describe the evidence that as well as playing a critical role in the formation of the mammary primordia during embryogenesis, signalling by Fgfs is necessary for optimal lobuloalveolar development of the mouse mammary gland during pregnancy.

Studying TGF-β superfamily signaling by knockouts and knockins

The transforming growth factor β (TGF-β) superfamily has profound effects on many aspects of animal development. In the last decade, our laboratory and others have performed in vivo functional studies on multiple components of the TGF-β superfamily signal transduction pathway, including upstream ligands, transmembrane receptors, receptor-associated proteins and downstream Smad proteins. We have taken gene knockout approaches to generate null alleles of the genes of interest, as well as a gene knockin approach to replace the mature region of one TGF-β superfamily ligand with another. We found that activin βB, expressed in the spatiotemporal pattern of activin βA, can function as a hypomorphic allele of activin βA and rescue the craniofacial defects and neonatal lethal phenotype of activin βA-deficient mice. With the knockout approach, we have shown that the expression pattern of a component in the TGF-β superfamily signal transduction cascade does not necessarily predict its in vivo function. Two liver-specific activins, activin βC and activin βE are dispensable for liver development, regeneration and function, whereas ubiquitously expressed Smad5 has specific roles in the development of multiple embryonic and extraembryonic tissues.

Protein kinase A antagonizes Hedgehog signaling by regulating both the activator and repressor forms of Cubitus interruptus.

The Hedgehog (Hh) family of secreted proteins controls many aspects of animal development. In Drosophila, Hh transduces its signal via Cubitus interruptus (Ci), a transcription factor present in two forms: a full-length activator and a carboxy-terminally truncated repressor that is derived from the full-length form by proteolytic processing. The proteolytic processing of Ci is promoted by the activities of protein kinase A (PKA) and Slimb, whereas it is inhibited by Hh. Here we show that PKA inhibits the activity of the full-length Ci in addition to its role in regulating Ci proteolysis. Whereas Ci processing is blocked in both PKA and slimb mutant cells, the accumulated full-length Ci becomes activated only in PKA but not in slimb mutant cells. Moreover, PKA inhibits an uncleavable activator form of Ci. These observations suggest that PKA regulates the activity of the full-length Ci independent of its proteolytic processing. We also provide evidence that PKA regulates both the proteolytic processing and transcriptional activity of Ci by directly phosphorylating Ci. We propose that phosphorylation of Ci by PKA has two separable roles: (1) It blocks the transcription activity of the full-length activator form of Ci, and (2) it targets Ci for Slimb-mediated proteolytic processing to generate the truncated form that functions as a repressor.

Pangolin encodes a Lef-1 homologue that acts downstream of Armadillo to transduce the Wingless signal in Drosophila.

Members of the Wnt/Wingless (Wg) family of signalling proteins organize many aspects of animal development by regulating the expression of particular target genes in responding cells. Recent biochemical studies indicate that the vertebrate HMG-domain proteins Lef-1 and XTcf-3 can physically interact with beta-catenin, a homologue of Drosophila Armadillo (Arm), the most downstream component known in the Wnt signal transduction pathway. However, these studies do not address whether the endogenous Lef/Tcf family members are required in vivo to transduce Wnt signals. Using genetic methods in Drosophila, we define a new segment polarity gene, pangolin (pan), and show that its product is required in vivo for Wg signal transduction in embryos and in developing adult tissues. In addition, we show that pan encodes a Lef/Tcf homologue and provide evidence that its protein product binds to the beta-catenin homologue Armadillo in vivo. Finally, we demonstrate that Pan functions downstream of Arm to transduce the Wg signal. Thus, our results indicate that Pan is an essential component of the Wg transduction pathway and suggest that it acts directly to regulate gene transcription in response to Wg signalling.

Genes involved in two Caenorhabditis elegans cell-signaling pathways.

Cell interactions are responsible for many aspects of animal development (see, e.g., Gurdon 1992). What are the signals, receptors, and signal transduction molecules that function as cells communicate with each other during development? Answers to this question are only beginning to emerge from studies in developmental biology (see, e.g., Greenwald and Rubin 1992; Hynes and Lander 1992; Jessell and Melton 1992). To what extent are particular intercellular signaling molecules shared among different sets of interacting cells? Are the same signaling molecules and pathways used in different cell types, at different locations, and at different times during development? Or does each group of interacting cells use a unique signaling pathway? Answers to these questions would provide fundamental insights into the molecular basis of animal development.