bluuebunny/crossref_metadata_2025 huggingface dataset:
TheDrosophilacytokine receptor Domeless controls border cell migration and epithelial polarization during oogenesis
Authors: Ghiglione Christian , Devergne Olivier , Georgenthum Emmanuelle , Carballès Fabrice , Médioni Caroline , Cerezo Delphine , Noselli Stéphane
Published: December 2002

In mammals, the JAK/STAT (Janus Kinase/Signal Transducer and Activator of Transcription) signaling pathway is activated in response to cytokines and growth factors to control blood cell development, proliferation and cell determination. In Drosophila, a conserved JAK/STAT signaling pathway controls segmentation in embryos, as well as blood cell development and other processes in larvae and adults. During embryogenesis, transduction of the Unpaired [Upd; also known as Outstretched (Os)] ligand through the JAK/STAT pathway requires Domeless, a putative membrane protein with distant homology to vertebrate type I cytokine receptors. We have isolated domeless(dome) in a screen to identify genes essential in epithelial morphogenesis during oogenesis. The level of dome activity is critical for proper border cell migration and is controlled in part through a negative feedback loop. In addition to its essential role in border cells, we show that dome is required in the germarium for the polarization of follicle cells during encapsulation of germline cells. In this process,dome controls the expression of the apical determinant Crumbs. In contrast to the ligand Upd, whose expression is limited to a pair of polar cells at both ends of the egg chamber, dome is expressed in all germline and follicle cells. However, the Dome protein is specifically localized at apicolateral membranes and undergoes ligand-dependent internalization in the follicle cells. dome mutations interact genetically with JAK/STAT pathway genes in border cell migration and abolish the nuclear translocation of Stat92E in vivo. We also show that domefunctions downstream of upd and that both the extracellular and intracellular domains of Dome are required for JAK/STAT signaling. Altogether,our data indicate that Dome is an essential receptor molecule for Upd and JAK/STAT signaling during oogenesis.
Establishing the trochlear motor axon trajectory: role of the isthmic organiser and Fgf8
Authors: Irving Carol , Malhas Amar , Guthrie Sarah , Mason Ivor
Published: December 2002

Formation of the trochlear nerve within the anterior hindbrain provides a model system to study a simple axonal projection within the vertebrate central nervous system. We show that trochlear motor neurons are born within the isthmic organiser and also immediately posterior to it in anterior rhombomere 1. Axons of the most anterior cells follow a dorsal projection, which circumnavigates the isthmus, while those of more posterior trochlear neurons project anterodorsally to enter the isthmus. Once within the isthmus, axons form large fascicles that extend to a dorsal exit point. We investigated the possibility that the projection of trochlear axons towards the isthmus and their subsequent growth within that tissue might depend upon chemoattraction. We demonstrate that both isthmic tissue and Fgf8 protein are attractants for trochlear axons in vitro, while ectopic Fgf8 causes turning of these axons away from their normal routes in vivo. Both inhibition of FGF receptor activation and inhibition of Fgf8 function in vitro affect formation of the trochlear projection within explants in a manner consistent with a guidance function of Fgf8 during trochlear axon navigation.
Influence of cell fate mechanisms upon retinal mosaic formation: a modelling study
Authors: Eglen Stephen J. , Willshaw David J.
Published: December 2002

Many types of retinal neurone are arranged in a spatially regular manner so that the visual scene is uniformly sampled. Several mechanisms are thought to be involved in the development of regular cellular positioning. One early-acting mechanism is the lateral inhibition of neighbouring cells from acquiring the same fate, mediated by Delta-Notch signalling. We have used computer modelling to test whether lateral inhibition might transform an initial population of undifferentiated cells into more regular populations of two types of differentiated cells. Initial undifferentiated cells were positioned randomly, subject only to a minimal distance constraint. Each undifferentiated cell then acquired either primary or secondary fate using one of several lateral inhibition mechanisms. Mosaic regularity was assessed using the regularity index and the packing factor. We found that for irregular undifferentiated mosaics, the arrangement of resulting primary (but not secondary) fate cells was more regular than in the initial undifferentiated population. However, for regular undifferentiated mosaics, no further increases in the regularity of the primary fate mosaics were observed. We have used this model to test the specific hypothesis that on- and off-centre retinal ganglion cells emerge from an initial, irregular undifferentiated population of ganglion cells. Lateral inhibition can subdivide an initially irregular population into two types of cell that are mildly regular. However,lateral inhibition alone is insufficient to produce mosaics of the same regularity as observed experimentally. Likewise, and in contrast to earlier reports, cell death alone is insufficient to match the regularity of experimental mosaics. We conclude that lateral inhibition can transform irregular distributions into regular mosaics, upon which subsequent processes(such as lateral cell movement or cell death) can further refine mosaic regularity.
Kinesin light chain-independent function of theKinesin heavy chainin cytoplasmic streaming and posterior localisation in theDrosophilaoocyte
Authors: Palacios Isabel M. , Johnston Daniel St
Published: December 2002

Microtubules and the Kinesin heavy chain, the force-generating component of the plus end-directed microtubule motor Kinesin I are required for the localisation of oskar mRNA to the posterior pole of theDrosophila oocyte, an essential step in the determination of the anteroposterior axis. We show that the Kinesin heavy chain is also required for the posterior localisation of Dynein, and for all cytoplasmic movements within the oocyte. Furthermore, the KHC localises transiently to the posterior pole in an oskar mRNA-independent manner. Surprisingly, cytoplasmic streaming still occurs in kinesin light chain null mutants, and bothoskar mRNA and Dynein localise to the posterior pole. Thus, the Kinesin heavy chain can function independently of the light chain in the oocyte, indicating that it associates with its cargoes by a novel mechanism.
The divergentC. elegansephrin EFN-4 functions inembryonic morphogenesis in a pathway independent of the VAB-1 Eph receptor
Authors: Chin-Sang Ian D. , Moseley Sarah L. , Ding Mei , Harrington Robert J. , George Sean E. , Chisholm Andrew D.
Published: December 2002

The C. elegans genome encodes a single Eph receptor tyrosine kinase, VAB-1, which functions in neurons to control epidermal morphogenesis. Four members of the ephrin family of ligands for Eph receptors have been identified in C. elegans. Three ephrins (EFN-1/VAB-2, EFN-2 and EFN-3) have been previously shown to function in VAB-1 signaling. We show that mutations in the gene mab-26 affect the fourth C. elegansephrin, EFN-4. We show that efn-4 also functions in embryonic morphogenesis, and that it is expressed in the developing nervous system. Interestingly, efn-4 mutations display synergistic interactions with mutations in the VAB-1 receptor and in the EFN-1 ephrin, indicating that EFN-4 may function independently of the VAB-1 Eph receptor in morphogenesis. Mutations in the LAR-like receptor tyrosine phosphatase PTP-3 and in the Semaphorin-2A homolog MAB-20 disrupt embryonic neural morphogenesis.efn-4 mutations synergize with ptp-3 mutations, but not withmab-20 mutations, suggesting that EFN-4 and Semaphorin signaling could function in a common pathway or in opposing pathways in C. elegans embryogenesis.
Neural tube closure requires Dishevelled-dependent convergent extension of the midline
Authors: Wallingford John B. , Harland Richard M.
Published: December 2002

In Xenopus, Dishevelled (Xdsh) signaling is required for both neural tube closure and neural convergent extension, but the connection between these two morphogenetic processes remains unclear. Indeed normal neurulation requires several different cell polarity decisions, any of which may require Xdsh signaling. In this paper we address two issues: (1) which aspects of normal neurulation require Xdsh function; and (2) what role convergent extension plays in the closure of the neural tube. We show that Xdsh signaling is not required for neural fold elevation, medial movement or fusion. Disruption of Xdsh signaling therefore provides a specific tool for uncoupling convergent extension from other processes of neurulation. Using disruption of Xdsh signaling, we demonstrate that convergent extension is crucial to tube closure. Targeted injection revealed that Xdsh function was required specifically in the midline for normal neural tube closure. We suggest that the inherent movement of the neural folds can accomplish only a finite amount of medial progress and that convergent extension of the midline is necessary to reduce the distance between the nascent neural folds, allowing them to meet and fuse. Similar results with Xenopus strabismus implicate the planar cell polarity (PCP) signaling cascade in neural convergent extension and tube closure. Together, these data demonstrate that PCP-mediated convergent extension movements are crucial to proper vertebrate neurulation.
DrosophilaRegulatory factor X is necessary for ciliated sensory neuron differentiation
Authors: Dubruille Raphaelle , Laurençon Anne , Vandaele Camille , Shishido Emiko , Coulon-Bublex Madeleine , Swoboda Peter , Couble Pierre , Kernan Maurice , Durand Bénédicte
Published: December 2002

Ciliated neurons play an important role in sensory perception in many animals. Modified cilia at dendrite endings serve as sites of sensory signal capture and transduction. We describe Drosophila mutations that affect the transcription factor RFX and genetic rescue experiments that demonstrate its central role in sensory cilium differentiation. Rfxmutant flies show defects in chemosensory and mechanosensory behaviors but have normal phototaxis, consistent with Rfx expression in ciliated sensory neurons and neuronal precursors but not in photoreceptors. The mutant behavioral phenotypes are correlated with abnormal function and structure of neuronal cilia, as shown by the loss of sensory transduction and by defects in ciliary morphology and ultrastructure. These results identify Rfx as an essential regulator of ciliated sensory neuron differentiation inDrosophila.
Lineage analysis of the hemangioblast as defined by FLK1 and SCL expression
Authors: Chung Yun Shin , Zhang Wen Jie , Arentson Elizabeth , Kingsley Paul D. , Palis James , Choi Kyunghee
Published: December 2002

Accumulating studies support the idea that a common progenitor, termed the hemangioblast, generates both hematopoietic and endothelial cell lineages. To better define the relationship between these cell lineages, we have generated knock-in embryonic stem (ES) cells carrying a non-functional human CD4 at theScl locus. By using in vitro differentiatedScl+/CD4 ES cells, we demonstrate that FLK1 and SCL are molecular determinants of the hemangioblast. Furthermore, our studies demonstrate that hematopoietic and endothelial cells develop via distinct,sequential generation of FLK1 and SCL-expressing cells. FLK1+CD4- cells first arise in developing embryoid bodies. The Scl gene is turned on within FLK1+CD4- cells to give rise to FLK1+CD4+ cells. Alternatively, a subpopulation of the initial FLK1+CD4- cells remains as SCL negative. Within the FLK1+CD4+ cells, FLK1 is down regulated to generate FILK1-CD4+ cells. Replating studies demonstrate that hematopoietic progenitors are enriched within FLK1+CD4+and FLK1-CD4+ cells, while endothelial cells develop from FLK1+CD4+ and FLK1+CD4- cell populations.
β-Catenin/Tcf-regulated transcription prior to the midblastula transition
Authors: Yang Jing , Tan Change , Darken Rachel S. , Wilson Paul A. , Klein Peter S.
Published: December 2002

Following fertilization, the zygotic genome in many organisms is quiescent until the midblastula transition (MBT), when large-scale transcription begins. In Xenopus embryos, for example, transcription is believed to be repressed until the twelfth cell division. Thus, although dorsal-ventral patterning begins during the first cell cycle, little attention has been given to transcriptional regulation in pre-MBT development. We present evidence that regulated transcription begins during early cleavage stages and that theβ-catenin—Tcf complex is required for the transcription of theXenopus nodal genes Xnr5 and Xnr6 as early as the 256-cell stage. Moreover, inhibition of β-catenin/Tcf function can block dorsal development, but only if the inhibition begins early and is maintained throughout pre-MBT stages. Dorsal development can be rescued in ventralized embryos if Tcf-dependent transcription is activated prior to MBT, but activation of Tcf after MBT cannot rescue ventralized embryos, suggesting thatβ-catenin/Tcf-dependent transcription is required prior to MBT for dorsal-ventral patterning in Xenopus.
Evolutionary conserved sequences are required for the insulation of the vertebrateHoxdcomplex in neural cells
Authors: Kmita Marie , Tarchini Basile , Duboule Denis , Hérault Yann
Published: December 2002

Transcriptional regulation of vertebrate Hox genes involves enhancer sequences located either inside or outside the gene clusters. In the mouseHoxd complex, for example, series of contiguous genes are coordinately controlled by regulatory sequences located at remote distances. However, in different cellular contexts, Hox genes may have to be insulated from undesirable external regulatory influences to prevent ectopic gene activation, a situation that would likely be detrimental to the developing embryo. We show the presence of an insulator activity, at one extremity of theHoxd complex, that is composed of at least two distinct DNA elements,one of which is conserved throughout vertebrate species. However, deletion of this element on its own did not detectably affect Hoxd gene expression, unless another DNA fragment located nearby was removed incis. These results suggest that insulation of this important gene cluster relies, at least in part, upon a sequence-specific mechanism that displays some redundancy.
Cellularisation in the endosperm ofArabidopsis thalianais coupled to mitosis and shares multiple components with cytokinesis
Authors: Sørensen Mikael Blom , Mayer Ulrike , Lukowitz Wolfgang , Robert Hélène , Chambrier Pierre , Jürgens Gerd , Somerville Chris , Lepiniec Loic , Berger Frédéric
Published: December 2002

Distinct forms of cytokinesis characterise specific phases of development in plants. In Arabidopsis, as in many other species, the endosperm that nurtures the embryo in the seed initially develops as a syncytium. This syncytial phase ends with simultaneous partitioning of the multinucleate cytoplasm into individual cells, a process referred to as cellularisation. Our in vivo observations show that, as in cytokinesis, cellularisation of theArabidopsis endosperm is coupled to nuclear division. A genetic analysis reveals that most Arabidopsis mutations affecting cytokinesis in the embryo also impair endosperm cellularisation. These results imply that cellularisation and cytokinesis share multiple components of the same basic machinery. We further report the identification of mutations in a novel gene, SPÄTZLE, that specifically interfere with cellularisation of the endosperm, but not with cytokinesis in the embryo. The analysis of this mutant might identify a specific checkpoint for the onset of cellularisation.
hephaestusencodes a polypyrimidine tract binding protein that regulates Notch signalling during wing development inDrosophila melanogaster
Authors: Dansereau David A. , Lunke Martine D. , Finkielsztein Ariel , Russell Michael A. , Brook William J.
Published: December 2002

We describe the role of the Drosophila melanogaster hephaestusgene in wing development. We have identified several hephaestusmutations that map to a gene encoding a predicted RNA-binding protein highly related to human polypyrimidine tract binding protein and Xenopus laevis 60 kDa Vg1 mRNA-binding protein. Polypyrimidine tract binding proteins play diverse roles in RNA processing including the subcellular localization of mRNAs, translational control, internal ribosome entry site use, and the regulation of alternate exon selection. The analysis of gene expression in imaginal discs and adult cuticle of genetic mosaic animals supports a role for hephaestus in Notch signalling. Somatic clones lacking hephaestus express the Notch target geneswingless and cut, induce ectopic wing margin in adjacent wild-type tissue, inhibit wing-vein formation and have increased levels of Notch intracellular domain immunoreactivity. Clones mutant for bothDelta and hephaestus have the characteristic loss-of-function thick vein phenotype of Delta. These results lead to the hypothesis that hephaestus is required to attenuateNotch activity following its activation by Delta. This is the first genetic analysis of polypyrimidine tract binding protein function in any organism and the first evidence that such proteins may be involved in theNotch signalling pathway.
Kremen proteins interact with Dickkopf1 to regulate anteroposterior CNS patterning
Authors: Davidson Gary , Mao Bingyu , del Barco Barrantes Ivan , Niehrs Christof
Published: December 2002

A gradient of Wnt/β-catenin signalling formed by posteriorising Wnts and anteriorising Wnt antagonists regulates anteroposterior (AP) patterning of the central nervous system (CNS) during Xenopus gastrulation. In this process, the secreted Wnt antagonist Dkk1 functions in the Spemann organiser and its anterior derivatives by blocking Wnt receptors of the lipoprotein receptor-related protein (LRP) 5 and 6 class. In addition to LRP6, Dkk1 interacts with another recently identified receptor class, the transmembrane proteins Kremen1 (Krm1) and Kremen2 (Krm2) to synergistically inhibit LRP6. We have investigated the role of Krm1 and Krm2 during early Xenopusembryogenesis. Consistent with a role in zygotic Wnt inhibition, overexpressed Krm anteriorises embryos and rescues embryos posteriorised by Wnt8. Antisense morpholino oligonucleotide (Mo) knockdown of Krm1 and Krm2 leads to deficiency of anterior neural development. In this process, Krm proteins functionally interact with Dkk1: (1) in axis duplication assays krm2 synergises with dkk1 in inhibiting Wnt/LRP6 signalling; (2) krm2rescues microcephalic embryos induced by injection of inhibitory anti-Dkk1 antibodies; and (3) injection of krm1/2 antisense Mo enhances microcephaly induced by inhibitory anti-Dkk1 antibodies. The results indicate that Krm proteins function in a Wnt inhibition pathway regulating early AP patterning of the CNS.
Cell lineage analysis of the amphipod crustaceanParhyale hawaiensisreveals an early restriction of cell fates
Authors: Gerberding Matthias , Browne William E. , Patel Nipam H.
Published: December 2002

In the amphipod crustacean, Parhyale hawaiensis, the first few embryonic cleavages are total and generate a stereotypical arrangement of cells. In particular, at the eight-cell stage there are four macromeres and four micromeres, and each of these cells is uniquely identifiable. We describe our studies of the cell fate pattern of these eight blastomeres, and find that the eight clones resulting from these cells set up distinct cell lineages that differ in terms of proliferation, migration and cell fate. Remarkably, the cell fate of each blastomere is restricted to a single germ layer. The ectoderm originates from three of the macromeres, while the remaining macromere generates the visceral mesoderm. Two of the micromeres generate the somatic mesoderm, a third micromere generates the endoderm and the fourth micromere generates the germline. These findings demonstrate for the first time a total cleavage pattern in an arthropod which results in an invariant cell fate of the blastomeres, but notably, the cell lineage pattern ofParhyale reported shows no clear resemblance to those found in spiralians, nematodes or deuterostomes. Finally, the techniques we have developed for the analysis of Parhyale development suggest that this arthropod may be particularly useful for future functional analyses of crustacean development.
HrzicN, a newZicfamily gene of ascidians, plays essential roles in the neural tube and notochord development
Authors: Wada Shuichi , Saiga Hidetoshi
Published: December 2002

Two axial structures, a neural tube and a notochord, are key structures in the chordate body plan and in understanding the origin of chordates. To expand our knowledge on mechanisms of development of the neural tube in lower chordates, we have undertaken isolation and characterization ofHrzicN, a new member of the Zic family gene of the ascidian,Halocynthia roretzi. HrzicN expression was detected by whole-mount in situ hybridization in all neural tube precursors, all notochord precursors,anterior mesenchyme precursors and a part of the primary muscle precursors. Expression of HrzicN in a- and b-line neural tube precursors was detected from early gastrula stage to the neural plate stage, while expression in other lineages was observed between the 32-cell and the 110-cell stages.HrzicN function was investigated by disturbing translation using a morpholino antisense oligonucleotide. Embryos injected with HrzicNmorpholino (`HrzicN knockdown embryos') exhibited failure of neurulation and tail elongation, and developed into larvae without a neural tube and notochord. Analysis of neural marker gene expression inHrzicN knockdown embryos revealed that HrzicN plays critical roles in distinct steps of neural tube formation in the a-line- and A-line precursors. In particular HrzicN is required for early specification of the neural tube fate in A-line precursors. Involvement of HrzicNin the neural tube development was also suggested by an overexpression experiment. However, analysis of mesodermal marker gene expression inHrzicN knockdown embryos revealed unexpected roles of this gene in the development of mesodermal tissues. HrzicN knockdown led to loss of HrBra (Halocynthia roretzi Brachyury) expression in all of the notochord precursors, which may be the cause for notochord deficiency.Hrsna (Halocynthia roretzi snail) expression was also lost from all the notochord and anterior mesenchyme precurosrs. By contrast,expression of Hrsna and the actin gene was unchanged in the primary muscle precursors. These results suggest that HrzicN is responsible for specification of the notochord and anterior mesenchyme. Finally,regulation of HrzicN expression by FGF-like signaling was investigated, which has been shown to be involved in induction of the a- and b-line neural tube, the notochord and the mesenchyme cells inHalocynthia embryos. Using an inhibitor of FGF-like signaling, we showed that HrzicN expression in the a- and b-line neural tube, but not in the A-line lineage and mesodermal lineage, depends on FGF-like signaling. Based on these data, we discussed roles of HrzicN as a key gene in the development of the neural tube and the notochord.
TheDrosophila Pox neurogene: control of male courtship behavior and fertility as revealed by a complete dissection of all enhancers
Authors: Boll Werner , Noll Markus
Published: December 2002

We have dissected the entire cis-regulatory region of theDrosophila Pox neuro gene with regard to its enhancers, and have analyzed their functions by the selective addition to Pox neuro null mutant flies of one or several functions, each regulated by a complete or partial enhancer. We have identified at least 15 enhancers with an astounding complexity in arrangement and substructure that regulate Pox neurofunctions required for the development of the peripheral and central nervous system and of most appendages. Many of these functions are essential for normal male courtship behavior and fertility. Two enhancers regulate the development of the penis, claspers and posterior lobes of male genitalia. Three enhancers, two of which overlap, control the development of chemosensory bristles in the labellum, legs and wings, some or all of which are required for the transmission of gustatory signals elicited by female pheromones. An additional enhancer regulates in the developing brain the connectivity of two specific neuronal clusters entrusted with processing olfactory pheromone signals from the antennal nerve. Finally, functions crucial for the ability of the male to copulate depend on an enhancer that activates Pox neuroexpression in the embryonic ventral cord. In addition to these male courtship and fertility functions of Pox neuro, we have identified enhancers that regulate: (1) proper segmentation of tarsal segments in the leg disc and in homologous segments of the antennal disc; and (2) proper development of the wing hinge and hence the ability of the fly to fly.
Mutations inspaltcause a severe but reversible neurodegenerative phenotype in the embryonic central nervous system ofDrosophila melanogaster
Authors: Cantera Rafael , Lüer Karin , Rusten Tor Erik , Barrio Rosa , Kafatos Fotis C. , Technau Gerhard M.
Published: December 2002

The gene spalt is expressed in the embryonic central nervous system of Drosophila melanogaster but its function in this tissue is still unknown. To investigate this question, we used a combination of techniques to analyse spalt mutant embryos. Electron microscopy showed that in the absence of Spalt, the central nervous system cells are separated by enlarged extracellular spaces populated by membranous material at 60% of embryonic development. Surprisingly, the central nervous system from slightly older embryos (80% of development) exhibited almost wild-type morphology. An extensive survey by laser confocal microscopy revealed that thespalt mutant central nervous system has abnormal levels of particular cell adhesion and cytoskeletal proteins. Time-lapse analysis of neuronal differentiation in vitro, lineage analysis and transplantation experiments confirmed that the mutation causes cytoskeletal and adhesion defects. The data indicate that in the central nervous system, spalt operates within a regulatory pathway which influences the expression of the β-catenin Armadillo, its ligand N-Cadherin, Notch, and the cell adhesion molecules Neuroglian, Fasciclin 2 and Fasciclin 3. Effects on the expression of these genes are persistent but many morphological aspects of the phenotype are transient, leading to the concept of sequential redundancy for stable organisation of the central nervous system.
The ubiquitin ligase Hyperplastic discs negatively regulateshedgehoganddecapentaplegicexpression by independent mechanisms
Authors: Lee Jeffrey D. , Amanai Kazuhito , Shearn Allen , Treisman Jessica E.
Published: December 2002

Photoreceptor differentiation in the Drosophila eye disc progresses from posterior to anterior in a wave driven by the Hedgehog and Decapentaplegic signals. Cells mutant for the hyperplastic discs gene misexpress both of these signaling molecules in anterior regions of the disc,leading to premature photoreceptor differentiation and overgrowth of surrounding tissue. The two genes are independently regulated byhyperplastic discs; decapentaplegic can still be misexpressed in cells mutant for both hyperplastic discs and hedgehog, and a repressor form of the transcription factor Cubitus interruptus can blockdecapentaplegic misexpression but not hedgehogmisexpression. Loss of hyperplastic discs causes the accumulation of full-length Cubitus interruptus protein, but not of Smoothened, in both the eye and wing discs. hyperplastic discs encodes a HECT domain E3 ubiquitin ligase that is likely to act by targeting Cubitus interruptus and an unknown activator of hedgehog expression for proteolysis.
A homolog of FBP2/KSRP binds to localized mRNAs inXenopusoocytes
Authors: Kroll Todd T. , Zhao Wei-meng , Jiang Can , Huber Paul W.
Published: December 2002

A Xenopus oocyte expression library was screened for proteins that bind to the 340-nucleotide localization element of Vg1 mRNA. Four different isolates encoded a Xenopus homolog of the human transcription factor,FUSE-binding protein 2 (FBP2). This protein has been independently identified as the splicing regulatory factor KSRP. The only significant difference between the Xenopus protein, designated VgRBP71, and KSRP is the absence of a 58 amino acid segment near the N-terminal of the former. In vivo binding assays show that VgRBP71 is associated with mRNAs localized to either the vegetal or animal hemispheres, but was not found with control mRNAs. Unlike other factors that bind to the localization element of Vg1 mRNA,VgRBP71 does not accumulate at the vegetal cortex with the mRNA; rather, it is present in the nucleus and throughout the cytoplasm at all stages of oogenesis. Cytoplasmic VgRBP71 appears to be most concentrated at the cell cortex. VgRBP71 interacts with Prrp, another protein that binds to the Vg1 localization element; this association does not require the presence of Vg1 mRNA.
Regulation of Easter activity is required for shaping the Dorsal gradient in theDrosophilaembryo
Authors: Chang Andy J. , Morisato Donald
Published: December 2002

Dorsoventral polarity of the Drosophila embryo requires maternalspätzle-Toll signaling to establish a nuclear gradient of Dorsal protein. The shape of this gradient is altered in embryos produced by females carrying dominant alleles of easter (eaD). Theeaster gene encodes a serine protease that generates processed Spätzle, which is proposed to act as the Toll ligand. By examining the expression domains of the zygotic genes zen, sog, rho andtwist, which are targets of nuclear Dorsal, we show that the slope of the Dorsal gradient is progressively flattened in strongereaD alleles. In the wild-type embryo, activated Easter is found in a high Mr complex called Ea-X, which is hypothesized to contain a protease inhibitor. In eaDembryo extracts, we detect an Easter form corresponding to the free catalytic domain, which is never observed in wild type. These mutanteaD proteins retain protease activity, as determined by the production of processed Spätzle both in the embryo and in culturedDrosophila cells. These experiments suggest that theeaD mutations interfere with inactivation of catalytic Easter, and imply that this negative regulation is essential for generating the wild-type shape of the Dorsal gradient.
Domain-specific olivocerebellar projection regulated by the EphA-ephrin-A interaction
Authors: Nishida Kazuhiko , Flanagan John G. , Nakamoto Masaru
Published: December 2002

Neural maps in the vertebrate central nervous system often show discontinuously segregated, domain-to-domain patterns. However, the molecular mechanism that establishes such maps is not well understood. Here we show that in the chicken olivocerebellar system, EphA receptors and ephrin-As are expressed with distinct levels and combinations in mapping domains. When ephrin-A2 is retrovirally overexpressed in the cerebellum, the olivocerebellar map is disrupted, excluding axons with high receptor activity from ectopic expression domains. Conversely, overexpression of a truncated EphA3 receptor in the cerebellum reduces endogenous ligand activity to undetectable levels and causes aberrant mapping, with high receptor axons invading high ligand domains. In vitro, ephrin-A2 inhibits outgrowth of inferior olive axons in a region-specific manner. These results suggest that Eph receptors and ephrins constitute domain-specific positional information, and the spatially accurate receptor-ligand interaction is essential to guide inferior olive axons to their correct target domains.
Dishevelled 2 is essential for cardiac outflow tract development, somite segmentation and neural tube closure
Authors: Hamblet Natasha S. , Lijam Nardos , Ruiz-Lozano Pilar , Wang Jianbo , Yang Yasheng , Luo Zhenge , Mei Lin , Chien Kenneth R. , Sussman Daniel J. , Wynshaw-Boris Anthony
Published: December 2002

The murine dishevelled 2 (Dvl2) gene is an ortholog of theDrosophila segment polarity gene Dishevelled, a member of the highly conserved Wingless/Wnt developmental pathway.Dvl2-deficient mice were produced to determine the role ofDvl2 in mammalian development. Mice containing null mutations inDvl2 present with 50% lethality in both inbred 129S6 and in a hybrid 129S6-NIH Black Swiss background because of severe cardiovascular outflow tract defects, including double outlet right ventricle, transposition of the great arteries and persistent truncus arteriosis. The majority of the surviving Dvl2-/- mice were female, suggesting that penetrance was influenced by sex. Expression of Pitx2 and plexin A2 was attenuated in Dvl2 null mutants, suggesting a defect in cardiac neural crest development during outflow tract formation. In addition, ∼90%of Dvl2-/- mice have vertebral and rib malformations that affect the proximal as well as the distal parts of the ribs. These skeletal abnormalities were more pronounced in mice deficient for both Dvl1and Dvl2. Somite differentiation markers used to analyzeDvl2-/- and Dvl1-/-;Dvl2-/-mutant embryos revealed mildly aberrant expression of Uncx4.1, delta 1 and myogenin, suggesting defects in somite segmentation. Finally, 2-3% ofDvl2-/- embryos displayed thoracic spina bifida, while virtually all Dvl1/2 double mutant embryos displayed craniorachishisis, a completely open neural tube from the midbrain to the tail. Thus, Dvl2 is essential for normal cardiac morphogenesis,somite segmentation and neural tube closure, and there is functional redundancy between Dvl1 and Dvl2 in some phenotypes.
Molecular control of ciliary neuron development: BMPs and downstream transcriptional control in the parasympathetic lineage
Authors: Müller Frank , Rohrer Hermann
Published: December 2002

The generation of noradrenergic sympathetic neurons is controlled by BMPs and the downstream transcription factors Mash1, Phox2b, Phox2a and dHand. We examined the role of these signals in developing cholinergic parasympathetic neurons. The expression of Mash1 (Cash1), Phox2band Phox2a in the chick ciliary ganglion is followed by the sequential expression of panneuronal, noradrenergic and cholinergic marker genes. BMPs are expressed at the site where ciliary ganglia form and are essential and sufficient for ciliary neuron development. Unlike sympathetic neurons, ciliary neurons do not express dHand; noradrenergic gene expression is eventually lost but can be maintained by ectopic dHand expression. Together, these results demonstrate a common BMP dependence of sympathetic neurons and parasympathetic ciliary neurons and implicate dHand in the maintenance of noradrenergic gene expression in the autonomic nervous system.
The early topography of thalamocortical projections is shifted inEbf1andDlx1/2mutant mice
Authors: Garel Sonia , Yun Kyuson , Grosschedl Rudolf , Rubenstein John L. R.
Published: December 2002

The prevailing model to explain the formation of topographic projections in the nervous system stipulates that this process is governed by information located within the projecting and targeted structures. In mammals, different thalamic nuclei establish highly ordered projections with specific neocortical domains and the mechanisms controlling the initial topography of these projections remain to be characterized. To address this issue, we examinedEbf1-/- embryos in which a subset of thalamic axons does not reach the neocortex. We show that the projections that do form between thalamic nuclei and neocortical domains have a shifted topography, in the absence of regionalization defects in the thalamus or neocortex. This shift is first detected inside the basal ganglia, a structure on the path of thalamic axons, and which develops abnormally in Ebf1-/- embryos. A similar shift in the topography of thalamocortical axons inside the basal ganglia and neocortex was observed in Dlx1/2-/- embryos,which also have an abnormal basal ganglia development. Furthermore,Dlx1 and Dlx2 are not expressed in the dorsal thalamus or in cortical projections neurons. Thus, our study shows that: (1) different thalamic nuclei do not establish projections independently of each other; (2)a shift in thalamocortical topography can occur in the absence of major regionalization defects in the dorsal thalamus and neocortex; and (3) the basal ganglia may contain decision points for thalamic axons' pathfinding and topographic organization. These observations suggest that the topography of thalamocortical projections is not strictly determined by cues located within the neocortex and may be regulated by the relative positioning of thalamic axons inside the basal ganglia.
The Schmidtea mediterranea database as a molecular resource for studying platyhelminthes, stem cells and regeneration
Authors: Alvarado Alejandro Sánchez , Newmark Phillip A. , Robb Sofia M. C. , Juste Réjeanne
Published: December 2002

Platyhelminthes are excellent models for the study of stem cell biology,regeneration and the regulation of scale and proportion. In addition,parasitic forms infect millions of people worldwide. Therefore, it is puzzling that they remain relatively unexplored at the molecular level. We present the characterization of ∼3000 non-redundant cDNAs from a clonal line of the planarian Schmidtea mediterranea. The obtained cDNA sequences,homology comparisons and high-throughput whole-mount in situ hybridization data form part of the S. mediterranea database (SmedDb;http://planaria.neuro.utah.edu). Sixty-nine percent of the cDNAs analyzed share similarities with sequences deposited in GenBank and dbEST. The remaining gene transcripts failed to match sequences in other organisms, even though a large number of these (∼80%)contained putative open reading frames. Taken together, the molecular resources presented in this study, along with the ability of abrogating gene expression in planarians using RNA interference technology, pave the way for a systematic study of the remarkable biological properties displayed by Platyhelminthes.
Shar-pei mediates cell proliferation arrest during imaginal disc growth inDrosophila
Authors: Kango-Singh Madhuri , Nolo Riitta , Tao Chunyao , Verstreken Patrik , Hiesinger P. Robin , Bellen Hugo J. , Halder Georg
Published: December 2002

During animal development, organ size is determined primarily by the amount of cell proliferation, which must be tightly regulated to ensure the generation of properly proportioned organs. However, little is known about the molecular pathways that direct cells to stop proliferating when an organ has attained its proper size. We have identified mutations in a novel gene,shar-pei, that is required for proper termination of cell proliferation during Drosophila imaginal disc development. Clones ofshar-pei mutant cells in imaginal discs produce enlarged tissues containing more cells of normal size. We show that this phenotype is the result of both increased cell proliferation and reduced apoptosis. Hence,shar-pei restricts cell proliferation and promotes apoptosis. By contrast, shar-pei is not required for cell differentiation and pattern formation of adult tissue. Shar-pei is also not required for cell cycle exit during terminal differentiation, indicating that the mechanisms directing cell proliferation arrest during organ growth are distinct from those directing cell cycle exit during terminal differentiation.shar-pei encodes a WW-domain-containing protein that has homologs in worms, mice and humans, suggesting that mechanisms of organ growth control are evolutionarily conserved.
Adult and embryonic blood and endothelium derive from distinct precursor populations which are differentially programmed by BMP inXenopus
Authors: Walmsley Maggie , Ciau-Uitz Aldo , Patient Roger
Published: December 2002

Blood and blood vessels develop in close association in vertebrate embryos and loss-of-function mutations suggest common genetic regulation. By the criteria of co-expression of blood and endothelial genes, and lineage tracing of progeny, we locate two distinct populations of progenitors for blood and endothelial cells in developing Xenopus embryos. The first population is located immediately posterior to the cement gland during neurula stages and gives rise to embryonic blood and vitelline veins in the anterior ventral blood island (aVBI), and to the endocardium of the heart. The second population resides in the dorsal lateral plate mesoderm, and contains precursors of adult blood stem cells and the major vessels. Both populations differentiate into endothelial cells in situ but migrate to new locations to differentiate into blood, suggesting that their micro-environments are unsuitable for haematopoietic differentiation. Both require BMP for their formation, even the Spemann organiser-derived aVBI, but individual genes are affected differentially. Thus, in the embryonic population, expression of the blood genes, SCL and GATA2, depend on BMP signalling while expression of the endothelial gene, Xfli1, does not. By contrast, Xfli1 expression in the adult,DLP population does require BMP. These results indicate that both adult and the anterior component of embryonic blood in Xenopus embryos derive from populations of progenitors that also give rise to endothelial cells. However, the two populations give rise to distinct regions of the vasculature and are programmed differentially by BMP.
Early patterning of the mouse embryo — contributions of sperm and egg
Authors: Piotrowska Karolina , Zernicka-Goetz Magdalena
Published: December 2002

The first cleavage of the fertilised mouse egg divides the zygote into two cells that have a tendency to follow distinguishable fates. One divides first and contributes its progeny predominantly to the embryonic part of the blastocyst, while the other, later dividing cell, contributes mainly to the abembryonic part. We have previously observed that both the plane of this first cleavage and the subsequent order of blastomere division tend to correlate with the position of the fertilisation cone that forms after sperm entry. But does sperm entry contribute to assigning the distinguishable fates to the first two blastomeres or is their fate an intrinsic property of the egg itself? To answer this question we examined the distribution of the progeny of early blastomeres in embryos never penetrated by sperm — parthenogenetic embryos. In contrast to fertilised eggs, we found there is no tendency for the first two parthenogenetic blastomeres to follow different fates. This outcome is independent of whether parthenogenetic eggs are haploid or diploid. Also unlike fertilised eggs, the first 2-cell blastomere to divide in parthenogenetic embryo does not necessarily contribute more cells to the blastocyst. However, even when descendants of the first dividing blastomere do predominate, they show no strong predisposition to occupy the embryonic part. Thus blastomere fate does not appear to be decided by differential cell division alone. Finally, when the cortical cytoplasm at the site of sperm entry is removed, the first cleavage plane no longer tends to divide the embryo into embryonic and abembryonic parts. Together these results indicate that in normal development fertilisation contributes to setting up embryonic patterning, alongside the role of the egg.
Gene expression profiles of mouse submandibular gland development: FGFR1 regulates branching morphogenesis in vitro through BMP- and FGF-dependent mechanisms
Authors: Hoffman Matthew P. , Kidder Benjamin L. , Steinberg Zachary L. , Lakhani Saba , Ho Susan , Kleinman Hynda K. , Larsen Melinda
Published: December 2002

Analyses of gene expression profiles at five different stages of mouse submandibular salivary gland development provide insight into gland organogenesis and identify genes that may be critical at different stages. Genes with similar expression profiles were clustered, and RT-PCR was used to confirm the developmental changes. We focused on fibroblast growth factor receptor 1 (FGFR1), as its expression is highest early in gland development. We extended our array results and analyzed the developmental expression patterns of other FGFR and FGF isoforms. The functional significance of FGFR1 was confirmed by submandibular gland organ culture. Antisense oligonucleotides decreased expression of FGFR1 and reduced branching morphogenesis of the glands. Inhibiting FGFR1 signaling with SU5402, a FGFR1 tyrosine kinase inhibitor, reduced branching morphogenesis. SU5402 treatment decreased cell proliferation but did not increase apoptosis. Fgfr, Fgf andBmp gene expression was localized to either the mesenchyme or the epithelium by PCR, and then measured over time by real time PCR after SU5402 treatment. FGFR1 signaling regulates Fgfr1, Fgf1, Fgf3 andBmp7 expression and indirectly regulates Fgf7, Fgf10 andBmp4. Exogenous FGFs and BMPs added to glands in culture reveal distinct effects on gland morphology. Glands cultured with SU5402 were then rescued with exogenous BMP7, FGF7 or FGF10. Taken together, our results suggest specific FGFs and BMPs play reciprocal roles in regulating branching morphogenesis and FGFR1 signaling plays a central role by regulating both FGF and BMP expression.
A defect in a novel Nek-family kinase causes cystic kidney disease in the mouse and in zebrafish
Authors: Liu Shanming , Lu Weining , Obara Tomoko , Kuida Shiei , Lehoczky Jennifer , Dewar Ken , Drummond Iain A. , Beier David R.
Published: December 2002

The murine autosomal recessive juvenile cystic kidney (jck)mutation results in polycystic kidney disease. We have identified injck mice a mutation in Nek8, a novel and highly conserved member of the Nek kinase family. In vitro expression of mutated Nek8results in enlarged, multinucleated cells with an abnormal actin cytoskeleton. To confirm that a defect in the Nek8 gene can cause cystic disease,we performed a cross-species analysis: injection of zebrafish embryos with a morpholino anti-sense oligonucleotide corresponding to the ortholog ofNek8 resulted in the formation of pronephric cysts. These results demonstrate that comparative analysis of gene function in different model systems represents a powerful means to annotate gene function.
Genomic analysis of neural crest induction
Authors: Gammill Laura S. , Bronner-Fraser Marianne
Published: December 2002

The vertebrate neural crest is a migratory stem cell population that arises within the central nervous system. Here, we combine embryological techniques with array technology to describe 83 genes that provide the first gene expression profile of a newly induced neural crest cell. This profile contains numerous novel markers of neural crest precursors and reveals previously unrecognized similarities between neural crest cells and endothelial cells,another migratory cell population. We have performed a secondary screen using in situ hybridization that allows us to extract temporal information and reconstruct the progression of neural crest gene expression as these cells become different from their neighbors and migrate. Our results reveal a sequential `migration activation' process that reflects stages in the transition to a migratory neural crest cell and suggests that migratory potential is established in a pool of cells from which a subset are activated to migrate.