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PubMed2006

scylla and charybde, homologues of the human apoptotic gene RTP801, are required for head involution in Drosophila.

We employed robotic methods and the whole-genome sequence of Drosophila melanogaster to facilitate a large-scale expression screen for spatially restricted transcripts in Drosophila embryos. In this screen, we identified a pair of genes, scylla (scyl) and charybde (chrb), that code for dorsal transcripts in early Drosophila embryos and are homologous to the human apoptotic gene RTP801. In Drosophila, both gene products are transcriptionally regulated targets of Dpp/Zen-mediated signal transduction and appear more generally to be downstream targets of homeobox regulation. Gene disruption studies revealed the functional redundancy of scyl and chrb, as well as their requirement for embryonic head involution. From the perspective of functional genomics, our studies demonstrate that global surveys of gene expression can complement traditional genetic screening methods for the identification of genes essential for development: beginning from their spatio-temporal expression profiles and extending to their downstream placement relative to dpp and zen, our studies reveal roles for the scyl and chrb gene products as links between patterning and cell death.

Amino Acid Sequence↗
PubMed2006

Anteriorward shifting of asymmetric Xnr1 expression and contralateral communication in left-right specification in Xenopus.

Transient asymmetric Nodal signaling in the left lateral plate mesoderm (L LPM) during tailbud/early somitogenesis stages is associated in all vertebrates examined with the development of stereotypical left-right (L-R) organ asymmetry. In Xenopus, asymmetric expression of Nodal-related 1 (Xnr1) begins in the posterior L LPM shortly after the initiation of bilateral perinotochordal expression in the posterior tailbud. The L LPM expression domain rapidly shifts forward to cover much of the flank of the embryo before being progressively downregulated, also in a posterior-to-anterior direction. The mechanisms underlying the initiation and propagation of Nodal/Xnr1 expression in the L LPM, and its transient nature, are not well understood. Removing the posterior tailbud domain prevents Xnr1 expression in the L LPM, consistent with the idea that normal embryos respond to a posteriorly derived asymmetrically acting positive inductive signal. The forward propagation of asymmetric Xnr1 expression occurs LPM-autonomously via planar tissue communication. The shifting is prevented by Nodal signaling inhibitors, implicating an underlying requirement for Xnr1-to-Xnr1 induction. It is also unclear how asymmetric Nodal signals are modulated during L-R patterning. Small LPM grafts overexpressing Xnr1 placed into the R LPM of tailbud embryos induced the expression of the normally L-sided genes Xnr1, Xlefty, and XPitx2, and inverted body situs, demonstrating the late-stage plasticity of the LPM. Orthogonal Xnr1 signaling from the LPM strongly induced Xlefty expression in the midline, consistent with recent findings in the mouse and demonstrating for the first time in another species conservation in the mechanism that induces and maintains the midline barrier. Our findings suggest that there is long-range contralateral communication between L and R LPM, involving Xlefty in the midline, over a substantial period of tailbud embryogenesis, and therefore lend further insight into how, and for how long, the midline maintains a L versus R status in the LPM.

Animals↗
PubMed2000

Novel signaling from the peripodial membrane is essential for eye disc patterning in Drosophila.

The Drosophila eye disc is a sac of single layer epithelium with two opposing sides, the peripodial membrane (PM) and the disc proper (DP). Retinal morphogenesis is organized by Notch signaling at the dorsoventral (DV) boundary in the DP. Functions of the PM in coordinating growth and patterning of the DP are unknown. We show that the secreted proteins, Hedgehog, Wingless, and Decapentaplegic, are expressed in the PM, yet they control DP expression of Notch ligands, Delta and Serrate. Peripodial clones expressing Hedgehog induce Serrate in the DP while loss of peripodial Hedgehog disrupts disc growth. Furthermore, PM cells extend cellular processes to the DP. Therefore, peripodial signaling is critical for eye pattern formation and may be mediated by peripodial processes.

Animals↗
PubMed2002

Expression of the L-type calcium channel in the developing mouse visual system by use of immunocytochemistry.

Developmental refinement of the retinogeniculate and retinocollicular pathways is partially dependent upon Ca(2+) channel function [J. Comp. Neurol. 440 (2001) 177-191]. We have examined the development of the L-type voltage gated Ca(2+) channel to determine if the onset of expression matches this period of refinement. Labeling by an antibody directed against the alpha 1C subunit of this channel was examined in the superior colliculus (SC), lateral geniculate nucleus (LGN), visual cortex (CTX), hippocampus (HC) and cerebellum (CB) in mice aged P3-4, P8-9, P15, P21, P28, and adults. At P3-4, labeled cells within the SC were concentrated within a dense band in the retinorecipient zone of the superficial gray layer. More lightly labeled neurons were seen in other layers. This dense band was still seen at P15, while more labeled neurons were seen in other layers. By P21-P28, labeled neurons were fairly uniformly distributed throughout all layers of SC. Neuronal cell types appeared to be labeled at all ages examined within the LGN. Within CTX, putative layer V-VI pyramidal neurons were well labeled at P4 and later ages, and labeled layer II-III pyramids could be distinguished by P9 and later ages. The dendrites and cell bodies of pyramidal neurons within CA1-CA3 of HC, granule neurons in the dentate gyrus, and Purkinje neurons in CB were labeled at all ages examined. We conclude that the L-type Ca(2+) channel is expressed in many neurons within retinorecipient targets as well as in other brain regions during the developmental period in which pathway refinement and synaptic plasticity occurs.

Aging↗
PubMed2003

Coquillette, a sea urchin T-box gene of the Tbx2 subfamily, is expressed asymmetrically along the oral-aboral axis of the embryo and is involved in skeletogenesis.

Transcription factors of the T-domain family regulate many developmental processes. We have isolated from the sea urchin a new member of the Tbx2 subfamily: coquillette. Coquillette has a late zygotic expression whose localization is dynamic: at the blastula stage it is restricted to the aboral side of most of the presumptive ectoderm and endoderm territories and from gastrulation on, to the aboral-most primary mesenchyme cells. Perturbation of coquillette function delays gastrulation and strongly disorganizes the skeleton of the larva. Coquillette is sensitive to alteration of the oral-aboral (OA) axis and we identify goosecoid, which controls oral and aboral fates in the ectoderm, as a probable upstream regulator. Coquillette appears to be an integral part of the patterning system along the OA axis.

Amino Acid Sequence↗
PubMed1998

Conserved Spätzle/Toll signaling in dorsoventral patterning of Xenopus embryos.

The Spätzle/Toll signaling pathway controls ventral axis formation in Drosophila by generating a gradient of nuclear Dorsal protein. Dorsal controls the downstream regulators dpp and sog, whose patterning functions are conserved between insects and vertebrates. Although there is no experimental evidence that the upstream events are conserved as well, we set out to ask if a vertebrate embryo can respond to maternal components of the fly Dorsal pathway. Here we demonstrate a dorsalizing activity for the heterologous Easter, Spätzle and Toll proteins in UV-ventralized Xenopus embryos, which is inhibited by a co-injected dominant Cactus variant. We conclude that the Dorsal signaling pathway is a component of the conserved dorsoventral (d/v) patterning system in bilateria.

Animals↗
PubMed1999

Versatility in signalling: multiple responses to EGF receptor activation during Drosophila oogenesis.

The Drosophila epidermal growth factor receptor (EGFR) is active in different tissues and is involved in diverse processes such as patterning of the embryonic ectoderm, growth and differentiation of imaginal discs and cell survival. During oogenesis, the EGFR is expressed in the somatic follicle cells that surround individual oocyte-nurse cell complexes. In response to germline signals, the follicle cells differentiate in a complex pattern, which in turn leads to the establishment of the egg axes. Two recent reports have shown that the strategies used to pattern posterior follicle cells are different from those used to pattern dorsal follicle cells. In posterior follicle cells, EGFR activity is translated into an on-off response, whereas, in dorsal follicle cells, patterning mechanisms are initiated and refined by feedback that modulates receptor activity over time.

Animals↗
PubMed1996

Cyclopia and defective axial patterning in mice lacking Sonic hedgehog gene function.

Targeted gene disruption in the mouse shows that the Sonic hedgehog (Shh) gene plays a critical role in patterning of vertebrate embryonic tissues, including the brain and spinal cord, the axial skeleton and the limbs. Early defects are observed in the establishment or maintenance of midline structures, such as the notochord and the floorplate, and later defects include absence of distal limb structures, cyclopia, absence of ventral cell types within the neural tube, and absence of the spinal column and most of the ribs. Defects in all tissues extend beyond the normal sites of Shh transcription, confirming the proposed role of Shh proteins as an extracellular signal required for the tissue-organizing properties of several vertebrate patterning centres.

Animals↗
PubMed2002

Distalization of the Drosophila leg by graded EGF-receptor activity.

Arthropods and higher vertebrates both possess appendages, but these are morphologically distinct and the molecular mechanisms regulating patterning along their proximodistal axis (base to tip) are thought to be quite different. In Drosophila, gene expression along this axis is thought to be controlled primarily by a combination of transforming growth factor-beta (TGF-beta) and Wnt signalling from sources of ligands, Decapentaplegic (Dpp) and Wingless (Wg), in dorsal and ventral stripes, respectively. In vertebrates, however, proximodistal patterning is regulated by receptor tyrosine kinase (RTK) activity from a source of ligands, fibroblast growth factors (FGFs), at the tip of the limb bud. Here I revise our understanding of limb development in flies and show that the distal region is actually patterned by a distal-to-proximal gradient of RTK activity, established by a source of epidermal growth factor (EGF)-related ligands at the presumptive tip. This similarity between proximodistal patterning in vertebrates and flies supports previous suggestions of an evolutionary relationship between appendages/body-wall outgrowths in animals.

Animals↗
PubMed2002

Par-1 regulates stability of the posterior determinant Oskar by phosphorylation.

Par-1 kinase is critical for polarization of the Drosophila melanogaster oocyte and the one-cell Caenorhabditis elegans embryo. Although Par-1 localizes specifically to the posterior pole in both cells, neither its targets nor its function at the posterior pole have been elucidated. Here we show that Drosophila Par-1 phosphorylates the posterior determinant Oskar (Osk) and demonstrate genetically that Par-1 is required for accumulation of Osk protein. We show in cell-free extracts that Osk protein is intrinsically unstable and that it is stabilized after phosphorylation by Par-1. Our data indicate that posteriorly localized Par-1 regulates posterior patterning by stabilizing Osk.

3' Untranslated Regions↗
PubMed2004

Restriction of BMP4 activity domains in the developing neural tube of the mouse embryo.

Bone morphogenetic protein (BMP) signals pattern the dorsal neural tube, defining distinct neuronal progenitor cell domains along the dorsoventral axis of the developing spinal cord. These dorsally expressed BMPs appear to have a limited range of action. The mechanisms that regulate this range of action are unclear. We created a GAL4/UAS bigenic mouse system to overexpress BMP4 or a mutant form of BMP4 (mutBMP4), which lacks a subset of amino-terminal basic amino acids that limits its range of action, in the dorsal neural tube. UAS-Bmp4 and UAS-mutBmp4 responder genes were activated in the dorsal neural tube by a Wnt1-GAL4 transgene. Analysis of the spinal cords of bigenic embryos that expressed comparable levels of transgenic transcripts revealed that mutBMP4 acted more ventrally in the neural tube than BMP4. This suggests that the amino-terminal basic amino-acid motif of mature BMP4 controls long-range activity for dorsoventral patterning of the vertebrate neural tube.

Amino Acid Motifs↗
PubMed2006

Stomach development is dependent on fibroblast growth factor 10/fibroblast growth factor receptor 2b-mediated signaling.

BACKGROUND & AIMS: Fibroblast growth factors (Fgfs) and their receptors (Fgfrs) are important intercellular signaling molecules that are essential to mammalian embryonic development. The signaling pathways between endoderm-derived gastric epithelium and the surrounding mesenchyme are largely unknown; however, the developmental expression profile of the IIIb isoform of Fgfr2 (Fgfr2b) and its main ligand, Fgf10, suggest that they may be strong candidates. Mice lacking either component (Fgfr2b-/- or Fgf10-/-) were examined to determine the role of Fgfr2b-mediated signaling during gastric organogenesis. METHODS: Stomachs from embryonic day 13.5-18.5 Fgfr2b-/-, Fgf10-/-, and wild-type littermates were collected and analyzed by conventional histology, immunohistochemistry, in situ hybridization, and electron microscopy. RESULTS: Fgfr2b-/- and Fgf10-/- fetuses had stomachs smaller than wild-type, consisting of relatively proportionate forestomach but disproportionately reduced glandular stomach, the mucosa of which has low cytoarchitectural complexity with a spiral arrangement of large mucosal folds. During mid to late fetal stages (embryonic day 15.5-18.5), epithelial differentiation to mucous and chief cell lineages was rudimentary, with no expression of several early cytodifferentiation markers including GATA4, GATA6, and H+/K+-adenosine triphosphatase and abnormal expression of members of the hedgehog family of signaling molecules. CONCLUSIONS: Fgfr2b and Fgf10 are part of a signaling network with Sonic hedgehog and Indian hedgehog that are essential to anterior-posterior and radial patterning in gastric development.

Animals↗
PubMed1995

Biorhythms in infants and role of the care environment.

All physiologic functions demonstrate cyclic activity. Infant development includes maturation of biorhythms. Two basic changes in biorhythm include establishment of circadian rhythm and day-night pattern. Biorhythms are driven by internal pacemakers yet are highly susceptible to environmental influences. Sleep-wake pattern and body temperature rhythm are two examples of infant biorhythms that demonstrate significant change with development. Biorhythm is the scientific basis for interventions (such as cycled lighting, feeding schedule, and caregiving pattern) aimed at improving the fit between infant and the environment.

Circadian Rhythm↗
PubMed2003

Making headway: the roles of Hox genes and neural crest cells in craniofacial development.

Craniofacial development is an extraordinarily complex process requiring the orchestrated integration of multiple specialized tissues such as the surface ectoderm, neural crest, mesoderm, and pharyngeal endoderm in order to generate the central and peripheral nervous systems, axial skeleton, musculature, and connective tissues of the head and face. How do the characteristic facial structures develop in the appropriate locations with their correct shapes and sizes, given the widely divergent patterns of cell movements that occur during head development? The patterning information could depend upon localized interactions between the epithelial and mesenchymal tissues or alternatively, the developmental program for the characteristic facial structures could be intrinsic to each individual tissue precursor. Understanding the mechanisms that control vertebrate head development is an important issue since craniofacial anomalies constitute nearly one third of all human congenital defects. This review discusses recent advances in our understanding of neural crest cell patterning and the dynamic nature of the tissue interactions that are required for normal craniofacial development.

Animals↗
PubMed2002

A direct requirement for Hedgehog signaling for normal specification of all ventral progenitor domains in the presumptive mammalian spinal cord.

The hedgehog signaling pathway organizes the developing ventral neural tube by establishing distinct neural progenitor fates along the dorsoventral axis. Smoothened (Smo) is essential for all Hedgehog (Hh) signaling, and genetic inactivation of Smo cells autonomously blocks the ability of cells to transduce the Hh signal. Using a chimeric approach, we examined the behavior of Smo null mutant neural progenitor cells in the developing vertebrate spinal cord, and we show that direct Hh signaling is essential for the specification of all ventral progenitor populations. Further, Hh signaling extends into the dorsal half of the spinal cord including the intermediate Dbx expression domain. Surprisingly, in the absence of Sonic hedgehog (Shh), we observe the presence of a Smo-dependent Hh signaling activity operating in the ventral half of the spinal cord that most likely reflects Indian hedgehog (Ihh) signaling originating from the underlying gut endoderm. Comparative studies of Shh, Smo, and Gli3 single and compound mutants reveal that Hh signaling acts in part to specify neural cell identity by counteracting the repressive action of Gli3 on p0, p1, p2, and pMN formation. However, whereas these cell identities are restored in Gli3/Smo compound mutants, correct stratification of the rescued ventral cell types is lost. Thus, Hh signaling is essential for organizing ventral cell pattern, possibly through the control of differential cell affinities.

Animals↗
PubMed2005

The Drumstick/Lines/Bowl regulatory pathway links antagonistic Hedgehog and Wingless signaling inputs to epidermal cell differentiation.

Hedgehog and Wingless signaling in the Drosophila embryonic epidermis represents one paradigm for organizer function. In patterning this epidermis, Hedgehog and Wingless act asymmetrically, and consequently otherwise equivalent cells on either side of the organizer follow distinct developmental fates. To better understand the downstream mechanisms involved, we have investigated mutations that disrupt dorsal epidermal pattern. We have previously demonstrated that the gene lines contributes to this process. Here we show that the Lines protein interacts functionally with the zinc-finger proteins Drumstick (Drm) and Bowl. Competitive protein-protein interactions between Lines and Bowl and between Drm and Lines regulate the steady-state accumulation of Bowl, the downstream effector of this pathway. Lines binds directly to Bowl and decreases Bowl abundance. Conversely, Drm allows Bowl accumulation in drm-expressing cells by inhibiting Lines. This is accomplished both by outcompeting Bowl in binding to Lines and by redistributing Lines to the cytoplasm, thereby segregating Lines away from nuclearly localized Bowl. Hedgehog and Wingless affect these functional interactions by regulating drm expression. Hedgehog promotes Bowl protein accumulation by promoting drm expression, while Wingless inhibits Bowl accumulation by repressing drm expression anterior to the source of Hedgehog production. Thus, Drm, Lines, and Bowl are components of a molecular regulatory pathway that links antagonistic and asymmetric Hedgehog and Wingless signaling inputs to epidermal cell differentiation. Finally, we show that Drm and Lines also regulate Bowl accumulation and consequent patterning in the epithelia of the foregut, hindgut, and imaginal discs. Thus, in all these developmental contexts, including the embryonic epidermis, the novel molecular regulatory pathway defined here is deployed in order to elaborate pattern across a field of cells.

Animals↗
PubMedDate not supplied

Context and occasion setting in Drosophila visual learning.

In a permanently changing environment, it is by no means an easy task to distinguish potentially important events from negligible ones. Yet, to survive, every animal has to continuously face that challenge. How does the brain accomplish this feat? Building on previous work in Drosophila melanogaster visual learning, we have developed an experimental methodology in which combinations of visual stimuli (colors and patterns) can be arranged such that the same stimuli can either be directly predictive, indirectly predictive, or nonpredictive of punishment. Varying this relationship, we found that wild-type flies can establish different memory templates for the same contextual color cues. The colors can either leave no trace in the pattern memory template, leading to context-independent pattern memory (context generalization), or be learned as a higher-order cue indicating the nature of the pattern-heat contingency leading to context-dependent memory (occasion setting) or serve as a conditioned stimulus predicting the punishment directly (simple conditioning). In transgenic flies with compromised mushroom-body function, the sensitivity to these subtle variations is altered. Our methodology constitutes a new concept for designing learning experiments. Our findings suggest that the insect mushroom bodies stabilize visual memories against context changes and are not required for cognition-like higher-order learning.

Adaptation, Physiological↗
PubMed2004

Targeted expression of the class II phosphoinositide 3-kinase in Drosophila melanogaster reveals lipid kinase-dependent effects on patterning and interactions with receptor signaling pathways.

Phosphoinositide 3-kinases (PI3Ks) can be divided into three distinct classes (I, II, and III) on the basis of their domain structures and the lipid signals that they generate. Functions have been assigned to the class I and class III enzymes but have not been established for the class II PI3Ks. We have obtained the first evidence for a biological function for a class II PI3K by expressing this enzyme during Drosophila melanogaster development and by using deficiencies that remove the endogenous gene. Wild-type and catalytically inactive PI3K_68D transgenes have opposite effects on the number of sensory bristles and on wing venation phenotypes induced by modified epidermal growth factor (EGF) receptor signaling. These results indicate that the endogenous PI3K_68D may act antagonistically to the EGF receptor-stimulated Ras-mitogen-activated protein kinase pathway and downstream of, or parallel to, the Notch receptor. A class II polyproline motif in PI3K_68D can bind the Drk adaptor protein in vitro, primarily via the N-terminal SH3 domain of Drk. Drk may thus be important for the localization of PI3K_68D, allowing it to modify signaling pathways downstream of cell surface receptors. The phenotypes obtained are markedly distinct from those generated by expression of the Drosophila class I PI3K, which affects growth but not pattern formation.

Animals↗