bluuebunny/crossref_metadata_2025_split huggingface dataset:
Retinoic acid signaling is required during early chick limb development
Authors: Helms Jill A. , Kim Chang Hee , Eichele Gregor , Thaller Christina 
Published: April 2021

ABSTRACT
In the chick limb bud, the zone of polarizing activity controls limb patterning along the anteroposterior and proximodistal axes. Since retinoic acid can induce ectopic polarizing activity, we examined whether this molecule plays a role in the establishment of the endogenous zone of polarizing activity. Grafts of wing bud mesenchyme treated with physiologic doses of retinoic acid had weak polarizing activity but inclusion of a retinoic acid-exposed apical ectodermal ridge or of prospective wing bud ectoderm evoked strong polarizing activity. Likewise, polarizing activity of prospective wing mesenchyme was markedly enhanced by co-grafting either a retinoic acid-exposed apical ectodermal ridge or ectoderm from the wing region. This equivalence of ectoderm-mesenchyme interactions required for the establishment of polarizing activity in retinoic acid-treated wing buds and in prospective wing tissue, suggests a role of retinoic acid in the establishment of the zone of polarizing activity. We found that prospective wing bud tissue is a high-point of retinoic acid synthesis. Furthermore, retinoid receptor-specific antagonists blocked limb morphogenesis and down-regulated a polarizing signal, sonic hedgehog. Limb agenesis was reversed when antagonist-exposed wing buds were treated with retinoic acid. Our results demonstrate a role of retinoic acid in the establishment of the endogenous zone of polarizing activity.
Contrasting effects of protein synthesis inhibition and of cyclic AMP on apoptosis in the developing retina
Authors: Rehen S. K. , Varella M. H. , Freitas F. G. , Moraes M. O. , Linden R. 
Published: April 2021

ABSTRACT
The role of protein synthesis in apoptosis was investigated in the retina of developing rats. In the neonatal retina, a ganglion cell layer, containing neurons with long, centrally projecting axons, is separated from an immature neuro-blastic layer by a plexiform layer. This trilaminar pattern subsequently evolves to five alternating cell and plexiform layers that constitute the mature retina and a wave of programmed neuron death sweeps through the layers. Apoptosis due to axon damage was found in ganglion cells of retinal explants within 2 days in vitro and was prevented by inhibition of protein synthesis. Simultaneously, protein synthesis blockade induced apoptosis among the undamaged cells of the neuroblastic layer, which could be selectively prevented by an increase in intracellular cyclic AMP. Both the prevention and the induction of apoptosis among ganglion cells or neuroblastic cells, respectively, occurred after inhibition of protein synthesis in vivo. The results show the coexistence of two mechanisms of apoptosis within the organized retinal tissue. One mechanism is triggered in ganglion cells by direct damage and depends on the synthesis of proteins acting as positive modulators of apoptosis. A distinct, latent mechanism is found among immature neuroblasts and may be repressed by continuously synthesized negative modulators, or by an increase in intracellular cyclic AMP.
Drosophila nonmuscle myosin II has multiple essential roles in imaginal disc and egg chamber morphogenesis
Authors: Edwards Kevin A. , Kiehart Daniel P. 
Published: April 2021

ABSTRACT
Morphogenesis is characterized by orchestrated changes in the shape and position of individual cells. Many of these movements are thought to be powered by motor proteins. However, in metazoans, it is often difficult to match specific motors with the movements they drive. The nonmuscle myosin II heavy chain (MHC) encoded by zipper is required for cell sheet movements in Drosophila embryos. To determine if myosin II is required for other processes, we examined the phenotypes of strong and weak larval lethal mutations in spaghetti squash (sqh), which encodes the nonmuscle myosin II regulatory light chain (RLC). sqh mutants can be rescued to adulthood by daily induction of a sqh cDNA transgene driven by the hsp70 promoter. By transiently ceasing induction of the cDNA, we depleted RLC at specific times during development. When RLC is transiently depleted in larvae, the resulting adult phenotypes demonstrate that RLC is required in a stage-specific fashion for proper development of eye and leg imaginal discs. When RLC is depleted in adult females, oogenesis is reversibly disrupted. Without RLC induction, developing egg chambers display a succession of phenotypes that demonstrate roles for myosin II in morphogenesis of the interfollicular stalks, three morphologically and mechanistically distinct types of follicle cell migration, and completion of nurse cell cytoplasm transport (dumping). Finally, we show that in sqh mutant tissues, MHC is abnormally localized in punctate structures that do not contain appreciable amounts of filamentous actin or the myosin tail-binding protein p127. This suggests that sqh mutant phenotypes are chiefly caused by sequestration of myosin into inactive aggregates. These results show that myosin II is responsible for a surprisingly diverse array of cell shape changes throughout development.
Pathways for inflorescence and floral induction in Antirrhinum
Authors: Bradley Desmond , Vincent Coral , Carpenter Rosemary , Coen Enrico 
Published: April 2021

ABSTRACT
The presentation of flowers on a modified stem, the inflorescence, requires the integration of several aspects of meristem behaviour. In Antirrhinum, the inflorescence can be distinguished by its flowers, hairy stem, modified leaves, short internodes and spiral phyllotaxy. We show, by a combination of physiological, genetical and morphological analysis, that the various aspects of the inflorescence are controlled by three pathways. The first pathway, depends on expression of the floricaula gene, and is rapidly and discretely induced by exposure to long daylength. Activation of this pathway occurs in very young axillary meristems, resulting in a floral identity. In addition, the length of subtending leaves and hairiness of the stem are partially modified. The second pathway affects leaf size, internode length, and stem hairiness, but does not confer floral meristem identity. This pathway is induced by long daylength, but not as rapidly or discretely as the floricauladependent pathway. The third pathway controls the switch in phyllotaxy from decussate to spiral and is activated independently of daylength. The coordination of these three programmes ensures that apical and axillary meristem behaviour is integrated.
The mec-8 gene of C. elegans encodes a protein with two RNA recognition motifs and regulates alternative splicing of unc-52 transcripts
Authors: Lundquist Erik A. , Herman Robert K. , Rogalski Teresa M. , Mullen Gregory P. , Moerman Donald G. , Shaw Jocelyn E. 
Published: April 2021

ABSTRACT
Mutations in the mec-8 gene of Caenorhabditis elegans were previously shown to affect the functions of body wall muscle and mechanosensory and chemosensory neurons. Mutations in mec-8 also strongly enhance the mutant phenotype of specific mutations in unc-52, a gene that encodes, via alternative splicing of pre-mRNA, a set of basement membrane proteins, homologs of perlecan, that are important for body wall muscle assembly and attachment to basement membrane, hypodermis and cuticle. We have cloned mec-8 and found that it encodes a protein with two RNA recognition motifs, characteristic of RNA binding proteins. We have used reverse transcription-PCR and RNase protection experiments to show that mec-8 regulates the accumulation of a specific subset of alternatively spliced unc-52 transcripts. We have also shown with antibodies to UNC-52 that mec-8 affects the abundance of a subset of UNC-52 isoforms. We propose that mec-8 encodes a trans-acting factor that regulates the alternative splicing of the pre-mRNA of unc-52 and one or more additional genes that affect mechanosensory and chemosensory neuron function.
A functional homologue of goosecoid in Drosophila
Authors: Goriely Anne , Stella Michael , Coffinier Catherine , Kessler Daniel , Mailhos Carolina , Dessain Scott , Desplan Claude 
Published: April 2021

ABSTRACT
We have cloned a Drosophila homologue (D-gsc) of the ver- tebrate homeobox gene goosecoid (gsc). In the Gsc proteins, the pressure for conservation has been imposed on the homeodomain, the functional domain of the protein: sequence homology is limited to the homeodomain (78% identity) and to a short stretch of 7 aminoacids also found in other homeoproteins such as Engrailed. Despite this weak homology, D-gsc is able to mimic gsc function in a Xenopus assay, as shown by its ability to rescue the axis development of a UV-irradiated embryo. Moreover, our data suggest that the position of insect and vertebrate gsc homologues within a regulatory network has also been conserved: D-gsc expression is controlled by decapenta- plegic, orthodenticle, sloppy-paired and tailless whose homo- logues control gsc expression (for BMP4 and Otx-2), or are expressed at the right time and the right place (for XFKH1/Pintallavis and Tlx) to be interacting with gsc during vertebrate development. However, the pattern of D- gsc expression in ectodermal cells of the nervous system and foregut cannot easily be reconciled with that of ver- tebrate gsc mesodermal expression, suggesting that its precise developmental function might have diverged. Still, this comparison of domains of expression and functions among Gsc proteins could shed light on a common origin of gut formation and/or on basic cellular processes. The identification of gsc target genes and/or other genes involved in similar developmental processes will allow the definition of the precise phylogenetic relationship among Gsc proteins.
Alternative RNA splicing that determines agrin activity regulates binding to heparin and α-dystroglycan
Authors: Campanelli James T. , Gayer Gregory G. , Scheller Richard H. 
Published: April 2021

ABSTRACT
Agrin is a component of the extracellular matrix that regulates aspects of neuromuscular junction differentiation. Identification of agrin-binding proteins has lead to the suggestion that α-dystroglycan is a muscle cell surface proteoglycan that mediates agrin activity. To further test this hypothesis, we have compared the ability of differentially active agrin isoforms to interact with a model component of proteoglycans, heparin, as well as with the putative proteoglycan α-dystroglycan. We demonstrate that an alternately spliced exon (encoding the sequence lysine, serine, arginine, lysine: Y site) is necessary for agrin-heparin interactions. We also show that alternate splicing at another site (Z site) dramatically affects inter-action of α-dystroglycan with agrin. We propose a model in which multiple distinct domains of agrin interact with both protein and sugar moieties of α-dystroglycan. The isoform-specific binding of agrin to α-dystroglycan is con-sistent with a functional role for this interaction during synaptogenesis.
Amphiregulin in lung branching morphogenesis: interaction with heparan sulfate proteoglycan modulates cell proliferation
Authors: Schuger Lucia , Johnson Gibbes R. , Gilbride Kevin , Plowman Gregory D. , Mandel Richard 
Published: April 2021

ABSTRACT
Epithelial and mesenchymal cells isolated from mouse embryonic lungs synthesized and responded to amphiregulin (AR) in a different fashion. Mesenchymal cells produced and deposited 3- to 4-fold more AR than epithelial cells, proliferated in the presence of exogenous AR, and their spontaneous growth was blocked by up to 85% by anti-AR antibodies. In contrast, epithelial cells exhibited a broad response to this growth regulator factor depending on whether they were supplemented with extracellular matrix (ECM) and whether this ECM was of epithelial or mesenchymal origin. AR-treated epithelial cells proliferated by up to 3-fold in the presence of mesenchymal-deposited ECM, remained unchanged in the presence of epithelial-deposited ECM, and decreased in their proliferation rate below controls in the absence of ECM supplementation. This effect was abolished by treatment with the glycosaminoglycan-degrading enzymes heparinase and heparitinase suggesting the specific involvement of heparan sulfate proteoglycan (HSPG) in AR-mediated cell proliferation. In whole lung explants, branching morphogenesis was inhibited by antibodies against the AR heparan sulfate binding site and stimulated by exogenous AR. Since during development, epithelial cells are in contact with mesenchymal ECM at the tips of the growing buds and alongside the basement membrane, focal variations in the proportion of epithelial and mesenchymal HSPG will focally affect epithelial proliferation rates. Therefore, AR-HSPG interaction may underlie the process of branching morphogenesis by inducing differential cell proliferation.
An HF-1a/ HF-1b/MEF-2 combinatorial element confers cardiac ventricular specificity and establishes an anterior-posterior gradient of expression
Authors: Ross Robert S. , Navankasattusas Sutip , Harvey Richard P. , Chien Kenneth R. 
Published: April 2021

ABSTRACT
The molecular determinants that direct gene expression to the ventricles of the heart are for the most part unknown. Additionally, little data is available on how the anterior/posterior axis of the heart tube is determined and whether the left and right atrial and ventricular chambers are assigned as part of this process. Utilizing myosin light chain-2 ventricular promoter/β-galactosidase reporter transgenes, we have determined the minimal cis-acting sequences required for ventricular-specific gene expression. In multiple independent transgenic mouse lines, we found that both a 250 base pair myosin light chain-2 ventricular promoter fragment, as well as a dimerized 28 bp sub-element (HF-1) containing binding sites for HF1a and HF1b/MEF2 factors, directed ventricular-specific reporter expression from as early as the endogenous gene, at day 7.5-8.0 post coitum. While the endogenous gene is expressed uniformly throughout both ventricles, the transgenes were expressed in a right ventricular/conotruncal dominant fashion, suggesting that they contain only a subset of the elements which respond to positional information in the developing heart tube. Expression of the transgene was cell autonomous and its temporospatial characteristics not affected by mouse strain/methylation state of the genome. To determine whether ventricular-specific expression of the transgene was dependent upon regulatory genes required for correct ventricular differentiation, the 250 base pair transgene was bred into both retinoid X receptorα and Nkx2-5 null back-grounds. The transgene was expressed in both mutant backgrounds, despite the absence of endogenous myosin light chain-2 ventricular transcript in Nkx2-5 null embryos. Ventricular specification, as judged by transgene expression, appeared to occur normally in both mutants. Thus, the HF-1 element, directs chamber-specific transcription of a transgene reporter independently of retinoid X receptorα and Nkx2-5, and defines a minimal combinatorial pathway for ventricular chamber gene expression. The patterned expression of this transgene may provide a model system in which to investigate the cues that dictate anterior-posterior (right ventricle/left ventricle) gradients during mammalian heart development.
LOP1: a gene involved in auxin transport and vascular patterning in Arabidopsis
Authors: Carland Francine M. , McHale Neil A. 
Published: April 2021

ABSTRACT
We have taken a genetic approach to understanding the mechanisms that control vascular patterning in the leaves of higher plants. Here we present the identification and characterization of the lop1 mutant of Arabidopsis which is defective in basipetal transport of IAA. Mutant leaf midveins show disoriented axial growth, and bifurcation into twin veins that are frequently rotated out of the normal dorsal/ventral axis of the leaf. Mutant plants also display abnormal patterns of cell expansion in the midrib cortex and in the epidermis of the elongation zone of lateral roots. Lateral roots show abnormal curvature during initiation, sometimes encircling the primary root prior to growth in a normal downward direction. Mutant seedlings have normal levels of free IAA, and appear normal in auxin perception, suggesting that transport is the primary lesion. The abnormalities in vascular development, lateral root initiation and patterns of cell expansion observed in the lop1 mutant are consistent with a basic disruption in basipetal transport of IAA.
The Drosophila pipsqueak gene encodes a nuclear BTB-domain-containing protein required early in oogenesis
Authors: Horowitz Heidi , Berg Celeste A. 
Published: April 2021

ABSTRACT
Mutations at the pipsqueak locus affect early patterning in the Drosophila egg and embryo. We have cloned pipsqueak and found that it is a large and complex gene, encoding multiple transcripts and protein isoforms. One protein, PsqA, is absent in all of the mutants that we have examined. We show that PsqA is a nuclear protein present in the germ cells and somatically derived follicle cells throughout oogenesis and that it is required prior to stage one of oogenesis. PsqA contains a BTB (POZ) domain at its amino terminus; additionally, we have identified an evolutionarily conserved motif of unknown function present four times in tandem at the C terminus of the protein. PZ pipsqueak mutants produce a putative fusion protein containing the pipsqueak BTB domain fused to sequences resident on the PZ element (H. Horowitz and C. Berg, 1995 Genetics 139, 327-335). We demonstrate here that expression of this fusion protein in wild-type flies has a dominant effect, resulting in infertility and eggshell defects. These dominant phenotypes are discussed in light of current theories on the role of the BTB domain in protein-protein interactions.
In vitro and transgenic analysis of a human HOXD4 retinoid-responsive enhancer
Authors: Morrison Alastair , Moroni Maria Cristina , Ariza-McNaughton Linda , Krumlauf Robb , Mavilio Fulvio 
Published: April 2021

ABSTRACT
Expression of vertebrate Hox genes is regulated by retinoids in cell culture and in early embryonic development. We have identified a 185-bp retinoid-responsive transcriptional enhancer 5′ of the human HOXD4 gene, which regulates inducibility of the gene in embryonal carcinoma cells through a pattern of DNA-protein interaction on at least two distinct elements. One of these elements contains a direct repeat mediating ligand-dependent interaction with retinoic acid receptors, and is necessary though not sufficient for the enhancer function. The HOXD4 enhancer directs expression of a lacZ reporter gene in the neural tube of transgenic mouse embryos in a timeregulated and regionally restricted fashion, reproducing part of the anterior neuroectodermal expression pattern of the endogenous Hoxd-4 gene. Administration of retinoic acid to developing embryos causes alterations in the spatial restriction of the transgene expression domain, indicating that the HOXD4 enhancer is also a retinoid-responsive element in vivo. The timing of the retinoic acid response differs from that seen with more 3′ Hox genes, in that it occurs much later. This shows that the temporal window of competence in the ability to respond to retinoic acid differs between Hox genes and can be linked to specific enhancers. Mutations in the direct repeat or in a second element in the enhancer affect both retinoid response in culture and developmental regulation in embryos, suggesting that co-operative interactions between different factors mediate the enhancer activity. These data provide further support for a role of endogenous retinoids in regulation and spatial restriction of Hox gene expression in the central nervous system.
Position-effect variegation in Drosophila depends on the dose of the gene encoding the E2F transcriptional activator and cell cycle regulator
Authors: Seum Carole , Spierer Anne , Pauli Daniel , Szidonya Janos , Reuter Gunter , Spierer Pierre 
Published: April 2021

ABSTRACT
A dominant mutation due to the insertion of a P-element at 93E on the third chromosome of Drosophila melanogaster enhances position-effect variegation. The corresponding gene was cloned by transposon tagging and the sequence of the transcript revealed that it corresponds to the gene encoding the transcriptional activator and cell cycle regulator dE2F. The transposon-tagged allele is homozygous viable, and the insertion of the transposon in an intron correlates with a strong reduction in the amount of transcript. A homozygous lethal null allele was found to behave as a strong enhancer when heterozygous. Overexpression of the gene in transgenic flies has the opposite effect of suppressing variegation. A link is established here, and discussed, between the dose of a transcriptional activator, which controls the cell cycle, and epigenetic silencing of chromosomal domains in Drosophila.
Mesoderm and endoderm differentiation in animal cap explants: identification of the HNF4-binding site as an activin A responsive element in the Xenopus HNF1α promoter
Authors: Weber Heike , Holewa Beatrix , Jones Elizabeth A. , Ryffel Gerhart U. 
Published: April 2021

ABSTRACT
The gene encoding the tissue-specific transcription factor HNF1α (LFB1) is transcriptionally activated shortly after mid-blastula transition in Xenopus embryos. We have now shown that the HNF1α protein is localized in the nuclei of the liver, gall bladder, gut and pronephros of the developing larvae. In animal cap explants treated with activin A together with retinoic acid, we induced HNF1α in pronephric tubules and epithelial gut cells, i.e. in mesodermal as well as in endodermal tissues. HNF1α can also be induced by activin A, but not by retinoic acid alone. To define the promoter element responding to the activin A signal, we injected various HNF1α promoter luciferase constructs into fertilized eggs and cultured the isolated animal caps in the presence of activin A. From the activity profiles of the promoter mutants used, we identified the HNF4-binding site as an activin-A-responsive element. As HNF4 is a maternal protein in Xenopus and localized in an animal-to-vegetal gradient in the cleaving embryo, we speculate that the activin A signal emanating from the vegetal pole cooperates with the maternal transcription factor HNF4 to define the embryonic regions expressing HNF1α.