bluuebunny/crossref_metadata_2025_split huggingface dataset:
Establishing neuroblast-specific gene expression in the Drosophila CNS: huckebein is activated by Wingless and Hedgehog and repressed by Engrailed and Gooseberry
Authors: McDonald Jocelyn A. , Doe Chris Q. 
Published: April 2021

ABSTRACT
The Drosophila ventral neuroectoderm produces a stereo-typed array of central nervous system precursors, called neuroblasts. Each neuroblast has a unique identity based on its position, pattern of gene expression and cell lineage. To understand how neuronal diversity is generated, we need to learn how neuroblast-specific gene expression is established, and how these genes control cell fate within neuroblast lineages. Here we address the first question: how is neuroblast-specific gene expression established? We focus on the huckebein gene, because it is expressed in a subset of neuroblasts and is required for aspects of neuronal and glial determination. We show that Huckebein is a nuclear protein first detected in small clusters of neuroectodermal cells and then in a subset of neuroblasts. The secreted Wingless and Hedgehog proteins activate huckebein expression in distinct but overlapping clusters of neuroectodermal cells and neuroblasts, whereas the nuclear Engrailed and Gooseberry proteins repress huckebein expression in specific regions of neuroectoderm or neuroblasts. Integration of these activation and repression inputs is required to establish the precise neuroectodermal pattern of huckebein, which is subsequently required for the development of specific neuroblast cell lineages.
Evidence that FGF8 signalling from the midbrain-hindbrain junction regulates growth and polarity in the developing midbrain
Authors: Lee Scott M. K. , Danielian Paul S. , Fritzsch Bernd , McMahon Andrew P. 
Published: April 2021

ABSTRACT
The developing vertebrate mesencephalon shows a rostrocaudal gradient in the expression of a number of molecular markers and in the cytoarchitectonic differentiation of the tectum, where cells cease proliferating and differentiate in a rostral to caudal progression. Tissue grafting experiments have implicated cell signalling by the mesencephalicmetencephalic (mid-hindbrain) junction (or isthmus) in orchestrating these events. We have explored the role of Wnt-1 and FGF8 signalling in the regulation of mesencephalic polarity. Wnt-1 is expressed in the caudal mesencephalon and Fgf8 in the most rostral metencephalon. Wnt-1 regulates Fgf8 expression in the adjacent metencephalon, most likely via a secondary mesencephalic signal. Ectopic expression of Fgf8 in the mesencephalon is sufficient to activate expression of Engrailed-2 (En-2) and ELF-1, two genes normally expressed in a decreasing caudal to rostral gradient in the posterior mesencephalon. Ectopic expression of Engrailed-1 (En-1), a functionally equivalent homologue of En-2 is sufficient to activate ELF-1 expression by itself. These results indicate the existence of a molecular hierarchy in which FGF8 signalling establishes the graded expression of En-2 within the tectum. This in turn may act to specify other aspects of A-P polarity such as graded ELF-1 expression. Our studies also reveal that FGF8 is a potent mitogen within the mesencephalon: when ectopically expressed, neural precursors continue to proliferate and neurogenesis is prevented. Taken together our results suggest that FGF8 signalling from the isthmus has a key role in coordinately regulating growth and polarity in the developing mesencephalon.
Postmitotic neurons migrate tangentially in the cortical ventricular zone
Authors: O’Rourke Nancy A. , Chenn Anjen , McConnell Susan K. 
Published: April 2021

ABSTRACT
Patterns of cell movement play a key role in the establishment of the brain’s functional architecture during development. The migration of neuronal progenitor cells has been hypothesized to disperse clonally related cells among different areas of the developing cerebral cortex. To test this model, we explored the migratory patterns of cells in the proliferative zone of the intact cortex of the ferret. After focal injections of DiI, labeled cells migrated in all directions and over long distances within the ventricular and subventricular zones. These cells expressed the neuron-specific marker TuJ1 and did not incorporate BrdU after cumulative labeling. Our results reveal an extensive tangential dispersion of cortical cells mediated predominantly or exclusively by the non-radial migration of postmitotic neurons.
Role of BMP-2 and OP-1 (BMP-7) in programmed cell death and skeletogenesis during chick limb development
Authors: Macias D. , Gañan Y. , Sampath T. K. , Piedra M. E. , Ros M. A. , Hurle J. M. 
Published: April 2021

ABSTRACT
Bone Morphogenetic Protein 2 (BMP-2) and Osteogenic Protein 1 (OP-1, also termed BMP-7) are members of the transforming growth factor β superfamily. In the present study, we have analyzed the effects of administering them locally at different stages and locations of the chick limb bud using heparin beads as carriers. Our results show that these BMPs are potent apoptotic signals for the undiffer-entiated limb mesoderm but not for the ectoderm or the differentiating chondrogenic cells. In addition, they promote intense radial growth of the differentiating cartilages and disturb the formation of joints accompanied by alterations in the pattern of Indian hedgehog and ck-erg expression. Interestingly, the effects of these two BMPs on joint formation were found to be different. While the pre-dominant effect of BMP-2 is alteration in joint shape, OP-1 is a potent inhibitory factor for joint formation. In situ hybridizations to check whether this finding was indicative of specific roles for these BMPs in the formation of joints revealed a distinct and complementary pattern of expression of these genes during the formation of the skeleton of the digits. While Op-1 exhibited an intense expression in the perichondrium of the developing cartilages with characteristic interruptions in the zones of joint formation, Bmp-2 expression was a positive marker for the articular interspaces. These data suggest that, in addition to the proposed role for BMP-2 and OP-1 in the establishment of the anteroposterior axis of the limb, they may also play direct roles in limb morphogenesis: (i) in regulating the amount and spatial distribution of the undifferentiated prechondrogenic mesenchyme and (ii) in controlling the location of the joints and the diaphyses of the cartilaginous primordia of the long bones once the chondrogenic aggregates are established.
Developmental basis of homeosis in precociously germinating Brassica napus embryos: phase change at the shoot apex
Authors: Fernandez Donna E. 
Published: April 2021

ABSTRACT
Precociously germinating Brassica napus (oilseed rape) embryos produce extra cotyledons or chimeric organs with sectors of cotyledon and leaf tissue, rather than leaves, at the shoot apex. To investigate this phenomenon in more detail, scanning electron microscopy was used to examine the development of organ primordia at the shoot apex. In situ hybridizations with molecular markers of the embryonic phase were used to assess the status of individ- ual cells in the shoot apex with regard to the transition between embryonic and vegetative phases. The results indicate that, under conditions that support precocious germination, primordia develop at the shoot apex in the mode characteristic of postgerminative growth, i.e. they arise sequentially in a spiral phyllotaxy. Cells in the rest of the embryo, however, can continue to express molecular markers of the embryonic phase for several weeks after the start of culture. When patterns of gene expression and the fate of individual primordia were compared, a strong correlation was found between organ identity and the status of cells in the vicinity of the meristem with regard to phase. Primordia that develop in situations where neighboring cells are in the embryonic phase always produce organs with cotyledon morphology. Primordia that develop in situations where neighboring cells have exited the embryonic phase produce leaves. Based on an examination of situations where chimeric organs are produced, I propose that short range interactions or signalling are likely to be involved in communicating information about phase to developing primordia.
VP16-activation of the C. elegans neural specification transcription factor UNC-86 suppresses mutations in downstream genes and causes defects in neural migration and axon outgrowth
Authors: Sze Ji Ying , Liu Yanxia , Ruvkun Gary 
Published: April 2021

ABSTRACT
The POU homeobox gene unc-86 specifies many neuroblast and neural fates in the developing C. elegans nervous system. Genes regulated by unc-86 are mostly unknown. Here we describe a genetic strategy for the identification of downstream pathways regulated by unc-86. We activate UNC-86 transcription activity by inserting the VP16 activation domain into an unc-86 genomic clone that bears all regulatory sequences necessary for normal expression in C. elegans. unc-86/VP16 complements unc-86 mutations in the specification of neuroblast and neural cell fates, but displays novel genetic activities: it can suppress non-null mutations in the downstream genes mec-3 and mec-7 that are necessary for mechanosensory neuron differentiation and function. These data suggest that UNC-86/VP16 increases the expression of mec-3 and mec-7 to compensate Nfor the decreased activities of mutant MEC-3 or MEC-7 proteins. The suppression of mutations in downstream genes by an activated upstream transcription factor should be a general strategy for the identification of genes in transcriptional cascades. unc-86/VP16 also causes neural migration and pathfinding defects and novel behavioral defects. Thus, increased or unregulated expression of genes downstream of unc-86 can confer novel neural phenotypes suggestive of roles for unc-86-regulated genes in neural pathfinding and function. Genetic suppression of these unc-86/VP16 phenotypes may identify the unc-86 downstream genes that mediate these events in neurogenesis.
Preventing the loss of competence for neural induction: HGF/SF, L5 and Sox-2
Authors: Streit Andrea , Sockanathan Shanthini , Pérez Lidia , Rex Maria , Scotting Paul J. , Sharpe Paul T. , Lovell-Badge Robin , Stern Claudio D. 
Published: April 2021

ABSTRACT
The response to neural induction depends on the presence of inducing signals and on the state of competence of the responding tissue. The epiblast of the chick embryo loses its ability to respond to neural induction by the organizer (Hensen’s node) between stages 4 and 4+. We find that the pattern of expression of the L5220 antigen closely mirrors the changes in competence of the epiblast in time and in space. For the first time, we describe an experiment that can extend the period of neural competence: when L5220 expression is maintained beyond its normal time by implanting HGF/SF secreting cells, the competence to respond to Hensen’s node grafts is retained. The host epiblast forms a non-regionalized neural tube, which expresses the pan-neural marker SOX-2 (a Sry-related transcription factor) but not any region-specific markers for the forebrain, hindbrain or spinal cord. Although HGF/SF secreting cells can mimic signals from Hensen’s node that maintain L5 expression, they cannot rescue the ability of the node to induce anterior structures (which is normally lost after stage 4). The ectoderm may acquire stable neural characteristics during neural induction by going through a hierarchy of states: competence, neuralization and regionalization. Our findings allow us to start to define these different states at a molecular level, and show that the competence to respond to neural induction is not entirely autonomous to the responding cells, but can be regulated by extracellular signalling molecules.
Bax promotes neuronal cell death and is downregulated during the development of the nervous system
Authors: Vekrellis Konstantinos , McCarthy Mary Jane , Watson Andrea , Whitfield Jonathan , Rubin Lee L. , Ham Jonathan 
Published: April 2021

ABSTRACT
The Bcl-2 and Bcl-x proteins suppress programmed cell death, whereas Bax promotes apoptosis. We investigated the pattern of expression of Bcl-2, Bax and Bcl-x during neuronal differentiation and development. All three proteins were widely expressed in neonatal rats but, in the adult, Bax levels were 20-to 140-fold lower in the cerebral cortex, cerebellum and heart muscle, whereas Bcl-x was not downregulated in any of the tissues examined. In the cerebral cortex and cerebellum, the decrease in Bax levels occurred after the period of developmental cell death. Further, microinjection of a Bax expression vector into cultured sympathetic neurons, which depend on nerve growth factor for survival, induced apoptosis in the presence of survival factor and increased the rate of cell death after nerve growth factor withdrawal. This effect could be blocked by co-injection of an expression vector for Bcl-xL or for the baculovirus p35 protein, an inhibitor of caspases (ICE-like proteases). These results suggest that, during development, the sensitivity of neurons to signals that induce apoptosis may be regulated by modulating Bax levels and that Bax-induced death requires caspase activity.
Protease nexin-1 is expressed at the mouse met-/mesencephalic junction and FGF signaling regulates its promoter activity in primary met-/mesencephalic cells
Authors: Küry Patrick , Schaeren-Wiemers Nicole , Monard Denis 
Published: April 2021

ABSTRACT
The expression pattern of the serine protease inhibitor gene Protease nexin-1 (PN-1) has been analyzed by in situ hybridization during embryonic nervous system develop-ment. PN-1 was found to be specifically expressed at the junction between the mes-and metencephalon (mid-and hindbrain). Transgenic embryos expressing the bacterial lacZ gene under the control of different fragments of the PN-1 upstream regulatory region were used to demarcate an enhancer sufficient for expression at this putative segmental border. Primary cell cultures derived from the embryonic neural tube at the level of the met-/mesen-cephalic junction were used to demonstrate a specific effect on transcriptional activity by basic fibroblast growth factor and Engrailed transcription factors, providing evidence that PN-1 is a target gene of these factors. The results of this study place PN-1 into the signaling cascade(s) consid-ered to be important for the development of this junction and suggest a role for PN-1 in the establishment or main-tenance of the differences between these adjacent neu-romeres.
Genetic control of flower shape in Antirrhinum majus
Authors: Almeida Jorge , Rocheta Margarida , Galego Lisete 
Published: April 2021

ABSTRACT
The asymmetric shape of the Antirrhinum corolla is determined by genes acting differentially along the dorsoventral axis of the flower. Genes so far identified determine asymmetry by acting in dorsal regions. We describe a gene, divaricata, which in contrast to previously identified genes acts in ventral regions of the flower. We show by the analysis of mutant combinations that the divaricata gene is negatively regulated by the dorsal genes cycloidea and dichotoma. In addition, we show by the analysis of chromosomal duplications that the divaricata gene acts in a dosage-dependent manner, suggesting that the level of its product is critical for determining ventral identities.
Examination of the function of two kelch proteins generated by stop codon suppression
Authors: Robinson Douglas N. , Cooley Lynn 
Published: April 2021

ABSTRACT
The Drosophila kelch gene produces a single transcript with a UGA stop codon separating two open reading frames (ORF1 and ORF2). From the transcript, 76 kDa ORF1 and 160 kDa full-length (ORF1 + ORF2) proteins are made. The expression of these two proteins is regulated in a tissue-specific manner causing the ratio of full-length to ORF1 protein to vary in different tissues. The only detected defect for kelch mutants is female sterility, and kelch protein is localized to the ovarian ring canals. kelch mutant ring canals are disorganized and have partly occluded lumens, causing a failure to transport cytoplasm. ORF1 and full-length kelch proteins co-sediment with ring canals suggesting that both proteins are found in the ring canals. Transgenetic analysis reveals that ORF1 kelch protein is sufficient to rescue ring canal morphology and fertility. In addition, we have mutated the UGA stop codon to a UAA stop codon and to three sense codons that allow constitutive readthrough. Analysis of these mutants reveals that a full-length kelch protein can partially compensate for the loss of endogenous kelch, but the residue included at the stop codon is critical for function. Finally, these studies suggest that the mechanism of stop codon suppression of kelch is by tRNA suppression.
Rescue of Drosophila engrailed mutants with a highly divergent mosquito engrailed cDNA using a homing, enhancer-trapping transposon
Authors: Whiteley Mary , Kassis Judith A. 
Published: April 2021

ABSTRACT
Specific fragments of Drosophila regulatory DNA can alter the insertional specificity of transposable elements causing them to ‘home’ to their parent gene. We used this property to insert a transposon-encoded functional coding region near a defective one and rescue a null mutation. This approach differs from homologous recombination in that the endogenous defective coding region is left in place and the genomic DNA is altered by the addition of the therapeutic transposon. We constructed a P-element-based transposon in which an engrailed cDNA from Anopheles gambiae (a mosquito) is expressed from a Drosophila engrailed minimal promoter. The promoter fragment used includes 2.6 kb of regulatory DNA that causes transposons to home to the endogenous Drosophila engrailed gene at high frequencies. We inserted this transposon onto a Drosophila chromosome that produces no functional engrailed proteins. When this transposon integrated near the engrailed promoter, adult viability was restored to engrailed mutant flies showing that the highly divergent mosquito engrailed protein can replace the Drosophila engrailed protein at all stages of development. Insertion of this transposon into the adjacent invected gene, which is transcribed in a pattern similar to engrailed, led to only embryonic rescue, suggesting an important difference in the regulation of these two genes.
The roles of maternal α-catenin and plakoglobin in the early Xenopus embryo
Authors: Kofron M. , Spagnuolo A. , Klymkowsky M. , Wylie C. , Heasman J. 
Published: April 2021

ABSTRACT
Catenins (α-, β- and γ- or plakoglobin) are cytoplasmic cadherin-associated proteins. Studies on cultured cells have suggested that both α-catenin and plakoglobin are important for the adhesive function of cadherins. α-catenin binds to both β-catenin and plakoglobin and may link the cadherin/catenin complex to actin filaments. Separate domains of plakoglobin bind to cadherin and α-catenin, suggesting it may act as a bridge between these molecules. However, plakoglobin may have other activities: it is expressed in both desmosomal junctions in association with desmogleins and the cytoplasm in conjunction with APC, and previous work suggests it may act in a dorsal signalling pathway when overexpressed in Xenopus embryos. Here, we have studied the roles of α-catenin and plakoglobin directly, by depleting the maternal mRNAs coding for each of them in developing Xenopus embryos. We find that depletion of maternal α-catenin causes the loss of intercellular adhesion at the blastula stage, similar to that reported previously for EP cadherin. Depletion of plakoglobin results in a partial loss of adhesion, and a loss of embryonic shape, but does not affect dorsal signalling.
Toll, a muscle cell surface molecule, locally inhibits synaptic initiation of the RP3 motoneuron growth cone in Drosophila
Authors: Rose Demian , Zhu Xiaomao , Kose Hiroyuki , Hoang Bao , Cho John , Chiba Akira 
Published: April 2021

ABSTRACT
Toll, a transmembrane molecule with extracellular leucine-rich repeats, is dynamically expressed by the Drosophila embryonic musculature. Growth cones of RP3 and other motoneurons normally grow past Toll-positive muscle cells and innervate more distal muscle cells, which have down- regulated their Toll expression. In this study, we show that reciprocal genetic manipulations of Toll proteins can produce reciprocal RP3 phenotypes. In Toll null mutants, the RP3 growth cone sometimes innervates incorrect muscle cells, including those that are normally Toll- positive. In contrast, heterochronic misexpression of Toll in the musculature leads to the same growth cone reaching its correct target region but delaying synaptic initiation. We propose that Toll acts locally to inhibit synaptogenesis of specific motoneuron growth cones and that both temporal and spatial control of Toll expression is crucial for its role in development.
The SAR1 gene of Arabidopsis acts downstream of the AXR1 gene in auxin response
Authors: Cernac A. , Lincoln C. , Lammer D. , Estelle M. 
Published: April 2021

ABSTRACT
A screen for suppressors of the auxin resistant mutant axr1 in Arabidopsis thaliana has identified at least three second site suppressor loci called Suppressor of Auxin Resistance (SAR). In this study we focus on the SAR1 gene. Previous studies have documented the effects of the axr1 mutations on auxin-inhibition of root growth, auxin-induced gene expression, seedling morphology and aerial morphology. In this study, we show that the axr1 mutations also affect root hair development and epidermal cell length. The sar1-1 mutation suppresses at least partially, every aspect of the axr1 phenotype. Genetic experiments indicate that this sup- pression is gene specific. When crossed with the auxin- resistant mutant aux1-7, the suppressor has little affect on auxin response. However, the morphology of sar1-1 aux1-7 inflorescences is different from either of the single mutants indicating that both genes play a role in auxin mediated development of the inflorescence. The sar1-1 mutation also affects morphology in an AXR1 background. sar1-1 plants are shorter than wild-type, have altered leaf morphology, flower earlier than wild-type plants and appear to have reduced cell division in the primary root. In most respects sar1-1 axr1 and sar1 AXR1 plants are indistinguishable, indicating that sar1 both suppresses and is epistatic to axr1. Based on these results, we propose that SAR1 acts after AXR1 and that a major function of AXR1 is to relieve SAR1 mediated repression of auxin response.