bluuebunny/crossref_metadata_2025_split huggingface dataset:
A model for anteroposterior patterning of the vertebrate limb based on sequential long- and short-range Shh signalling and Bmp signalling
Authors: Drossopoulou G. , Lewis K. E. , Sanz-Ezquerro J. J. , Nikbakht N. , McMahon A. P. , Hofmann C. , Tickle C. 
Published: April 2021

ABSTRACT
It has been proposed that digit identity in chick limb bud is specified in a dose-dependent fashion by a long-range morphogen, produced by the polarising region. One candidate is Sonic hedgehog (Shh) protein, but it is not clear whether Shh acts long or short range or via Bmps. Here we dissect the relationship between Shh and Bmp signalling. We show that Shh is necessary not only for initiating bmp2 expression but also for sustaining its expression during the period when additional digits are being specified. We also show that we can reproduce much of the effect of Shh during this period by applying only Bmp2. We further demonstrate that it is Bmps that are responsible for digit specification by transiently adding Noggin or Bmp antibodies to limbs treated with Shh. In such limbs, multiple additional digits still form but they all have the same identity. We also explored time dependency and range of Shh signalling by examining ptc expression. We show that high-level ptc expression is induced rapidly when either Shh beads or polarising regions are grafted to a host limb. Furthermore, we find that high-level ptc expression is first widespread but later more restricted. All these data lead us to propose a new model for digit patterning. We suggest that Shh initially acts long range to prime the region of the limb competent to form digits and thus control digit number. Then later, Shh acts short range to induce expression of Bmps, whose morphogenetic action specifies digit identity.
A developmentally regulated GAGA box-binding factor and Sp1 are required for transcription of the hsp70.1 gene at the onset of mouse zygotic genome activation
Authors: Bevilacqua Arturo , Fiorenza Maria Teresa , Mangia Franco 
Published: April 2021

ABSTRACT
We have investigated the onset of zygotic genome transcription in early two-cell mouse embryos by analyzing the regulation of hsp70.1, one of the first genes expressed after fertilization. The transcriptional activation of both an episomic hsp70 promoter and the endogenous hsp70.1 gene requires the contiguity of the GC box proximal to the TATA box with a GAGA box and involves GC box- and GAGA box-binding factors. In vivo transcription factor titrations with double-stranded oligodeoxyribonucleotides and antibodies pinpoint these factors as Sp1 and a novel murine GAGA box-binding factor, which is structurally related to the Drosophila GAGA factor and acts as transcriptional coactivator/potentiator of Sp1. Mouse unfertilized eggs and one-cell and two-cell embryos display a GAGA box-binding activity of maternal origin that disappears at the four-cell stage and is also abundant in the gonads, but is barely detectable in other adult tissues. In light of the well-established nucleosome-disruption role of the Drosophila GAGA factor, these findings suggest a novel mechanism of enhancer-independent gene derepression in early mouse embryos.
Retinoid signaling is essential for patterning the endoderm of the third and fourth pharyngeal arches
Authors: Wendling Olivia , Dennefeld Christine , and Pierre Chambon , Mark Manuel 
Published: April 2021

ABSTRACTThe requirement of retinoic acid (RA) in the initial formation of the pharyngeal arches was investigated by treating headfold-stage mouse embryos with a pan-RAR antagonist in vitro and in vivo. This results in a complete absence of mesenchyme, arteries, nerves and epibranchial placodes of the 3rd and 4th pharyngeal arches, complete agenesis of the 3rd and 4th pouches and consistent lack of the 6th arch artery. Mesodermally derived endothelial cells are absent from the 3rd and 4th pharyngeal arch region and the distribution domain of EphA2 transcripts in mesodermal cells is shifted caudally. In situ hybridization with CRABPI, kreisler and EphA4 probes and the pattern of expression of a Wnt1-lacZ transgene show that neural crest cells (NCC) normally destined to the 3rd and 4th arches migrate ectopically. Most interestingly, the appearance of the 3rd and 4th arches is prevented by the antagonist only during a very narrow window of time, which does not correspond to the period of post-otic NCC migration. Both the timing of appearance and the nature of the defects in RAR antagonist-treated embryos indicate that migrating NCC and mesodermal cells destined to the caudal pharyngeal arches do not represent primary targets of RA action. Alterations in the endodermal expression pattern of Hoxa1, Hoxb1, Pax1, Pax9, Fgf3 and Fgf8 in response to the antagonist-induced block in RA signal transduction demonstrate for the first time that RA signaling is indispensable for the specification of the pharyngeal endoderm and suggest that this signaling is necessary to provide a permissive environment locally for the migration of NCC and mesodermal cells. Our study also indicates that the formation of the 2nd pharyngeal arch and that of the 3rd and 4th pharyngeal arches probably involve distinct RA-dependent developmental processes.
A S/M DNA replication checkpoint prevents nuclear and cytoplasmic events of cell division including centrosomal axis alignment and inhibits activation of cyclin-dependent kinase-like proteins in fucoid zygotes
Authors: Corellou Florence , Bisgrove Sherryl R. , Kropf Darryl L. , Meijer Laurent , Kloareg Bernard , Bouget François-Yves 
Published: April 2021

ABSTRACT
S/M checkpoints prevent various aspects of cell division when DNA has not been replicated. Such checkpoints are stringent in yeast and animal somatic cells but are usually partial or not present in animal embryos. Because little is known about S/M checkpoints in plant cells and embryos, we have investigated the effect of aphidicolin, a specific inhibitor of DNA polymerases α and δ, on cell division and morphogenesis in Fucus and Pelvetia zygotes. Both DNA replication and cell division were inhibited by aphidicolin, indicating the presence, in fucoid zygotes, of a S/M checkpoint. This checkpoint prevents chromatin condensation, spindle formation, centrosomal alignment with the growth axis and cytokinesis but has no effect on germination or rhizoid elongation. This S/M checkpoint also prevents tyrosine dephosphorylation of cyclin-dependent kinase-like proteins at the onset of mitosis. The kinase activity is restored in extracts upon incubation with cdc25A phosphatase. When added in S phase, olomoucine, a specific inhibitor of cyclin-dependent kinases, has similar effects as aphidicolin on cell division although alignment of the centrosomal axis still occurs. We propose a model involving the inactivation of CDK-like proteins to account for the S/M DNA replication checkpoint in fucoid zygotes and embryos.
POLTERGEIST functions to regulate meristem development downstream of the CLAVATA loci
Authors: Yu Lita P. , Simon Ephraim J. , Trotochaud Amy E. , Clark Steven E. 
Published: April 2021

ABSTRACT
Mutations at the CLAVATA loci (CLV1, CLV2 and CLV3) result in the accumulation of undifferentiated cells at the shoot and floral meristems. We have isolated three mutant alleles of a novel locus, POLTERGEIST (POL), as suppressors of clv1, clv2 and clv3 phenotypes. All pol mutants were nearly indistinguishable from wild-type plants; however, pol mutations provided recessive, partial suppression of meristem defects in strong clv1 and clv3 mutants, and nearly complete suppression of weak clv1 mutants. pol mutations partially suppressed clv2 floral and pedicel defects in a dominant fashion, and almost completely suppressed clv2 phenotypes in a recessive manner. These observations, along with dominant interactions observed between the pol and wuschel (wus) mutations, indicate that POL functions as a critical regulator of meristem development downstream of the CLV loci and redundantly with WUS. Consistent with this, pol mutations do not suppress clv3 phenotypes by altering CLV1 receptor activation.
The regulation of proliferation and differentiation in oligodendrocyte progenitor cells by αv integrins
Authors: Blaschuk K. L. , Frost E. E. , ffrench-Constant C. 
Published: April 2021

ABSTRACT
We have previously shown that oligodendrocyte progenitor cells exhibit developmental switching between αv-associated β integrin subunits to sequentially express αvβ1, αvβ3 and αvβ5 integrins during differentiation in vitro. To understand the role that αvβ3 integrin may play in regulating oligodendrocyte progenitor cell behaviour, cells of the rat cell line, CG-4, were genetically engineered to constitutively express αvβ3 integrin by transfection with full-length human β3 integrin subunit cDNA. Time-lapse videomicroscopy showed no effect of β3 expression on cell migration but revealed enhanced proliferation on vitronectin substrata. Comparison of mitotic indices, as measured by 5-bromo-2′-deoxyuridine incorporation, confirmed that human β3 integrin-expressing cells exhibited enhanced proliferation, as compared to both vector-only transfected, and wild-type CG-4 cells when switched to differentiation medium from growth medium, but only in cultures grown on vitronectin and not on poly-D-lysine. The effects on proliferation were inhibited by a function-blocking antibody specifically directed against the human β3 integrin subunit. Human β3 integrin-expressing cells also exhibited reduced differentiation. This differentiation could be reduced still further by a function-blocking monoclonal antibody against αvβ5 integrin, as could differentiation in the wild-type CG-4 cells. Taken together, these results suggest that αvβ3 integrin may regulate oligodendroglial cell proliferation and that both downregulation of αvβ3 integrin expression and signalling through αvβ5 integrin may be critical to continued differentiation in vitro.
The Arabidopsis floral homeotic gene APETALA3 differentially regulates intercellular signaling required for petal and stamen development
Authors: Jenik Pablo D. , Irish Vivian F. 
Published: April 2021

ABSTRACT
Cell-cell signaling is crucial for the coordination of cell division and differentiation during plant organogenesis. We have developed a novel mosaic analysis method for Arabidopsis, based on the maize Ac/Ds transposable element system, to assess the requirements of individual genes in intercellular signaling. Using this strategy, we have shown that the floral homeotic APETALA3 (AP3) gene has distinct roles in regulating intercellular signaling in different tissues. In petals, AP3 acts primarily in a cell-autonomous fashion to regulate cell type differentiation, but its function is also required in a non-cell-autonomous fashion to regulate organ shape. In contrast, AP3-regulated intercellular interactions are required for conferring both cell type identity and organ shape and size in the stamens. Using antibodies raised against AP3, we have shown that the AP3 protein does not traffic between cells. These observations imply that AP3 acts by differentially regulating the production of intercellular signals in a whorl-specific manner.
mosaic eyes: a zebrafish gene required in pigmented epithelium for apical localization of retinal cell division and lamination
Authors: Jensen Abbie M. , Walker Charline , Westerfield Monte 
Published: April 2021

ABSTRACT
For proper function of the retina, the correct proportions of retinal cell types must be generated, they must be organized into cell-specific laminae, and appropriate synaptic connections must be made. To understand the genetic regulation of retinal development, we have analyzed mutations in the mosaic eyes gene that disrupt retinal lamination, the localization of retinal cell divisions to the retinal pigmented epithelial surface and retinal pigmented epithelial development. Although retinal organization is severely disrupted in mosaic eyes mutants, surprisingly, retinal cell differentiation occurs. The positions of dividing cells and neurons in the brain appear normal in mosaic eyes mutants, suggesting that wild-type mosaic eyes function is specifically required for normal retinal development. We demonstrate that mosaic eyes function is required within the retinal pigmented epithelium, rather than in dividing retinal cells. This analysis reveals an interaction between the retinal pigmented epithelium and the retina that is required for retinal patterning. We suggest that wild-type mosaic eyes function is required for the retinal pigmented epithelium to signal properly to the retina.
Monofocal origin of telencephalic oligodendrocytes in the anterior entopeduncular area of the chick embryo
Authors: Olivier Christelle , Cobos Immaculada , Villegas Eva Maria Perez , Spassky Nathalie , Zalc Bernard , Martinez Salvador , Thomas Jean-Léon 
Published: April 2021

ABSTRACT
Oligodendrocytes are the myelin-forming cells in the central nervous system. In the brain, oligodendrocyte precursors arise in multiple restricted foci, distributed along the caudorostral axis of the ventricular neuroepithelium. In chick embryonic hind-, mid- and caudal forebrain, oligodendrocytes have a basoventral origin, while in the rostral fore-brain oligodendrocytes emerge from alar territories (Perez Villegas, E. M., Olivier, C., Spassky, N., Poncet, C., Cochard, P., Zalc, B., Thomas, J. L. and Martinez, S. (1999) Dev. Biol. 216, 98-113). To investigate the respective territories colonized by oligodendrocyte progenitor cells that originate from either the basoventral or alar foci, we have created a series of quail-chick chimeras. Homotopic chimeras demonstrate clearly that, during embryonic development, oligodendrocyte progenitors that emerge from the alar anterior entopeduncular area migrate tangentially to invade the entire telencephalon, whereas those from the basal rhombomeric foci show a restricted rostrocaudal distribution and colonize only their rhombomere of origin. Heterotopic chimeras indicate that differences in the migratory properties of oligodendroglial cells do not depend on their basoventral or alar ventricular origin. Irrespective of their origin (basal or alar), oligodendrocytes migrate only short distances in the hindbrain and long distances in the prosencephalon. Furthermore, we provide evidence that, in the developing chick brain, all telencephalic oligodendrocytes originate from the anterior entopeduncular area and that the prominent role of anterior entopeduncular area in telencephalic oligodendrogenesis is conserved between birds and mammals.
Genetic dissection ofnodalfunction in patterning the mouse embryo
Authors: Lowe Linda A. , Yamada Satoru , Kuehn Michael R. 
Published: April 2021

ABSTRACTLoss-of-function analysis has shown that the transforming growth factor-like signaling molecule nodal is essential for mouse mesoderm development. However, definitive proof of nodal function in other developmental processes in the mouse embryo has been lacking because the null mutation blocks gastrulation. We describe the generation and analysis of a hypomorphic nodal allele. Mouse embryos heterozygous for the hypomorphic allele and a null allele undergo gastrulation but then display abnormalities that fall into three distinct mutant phenotypic classes, which may result from expression levels falling below critical thresholds in one or more domains of nodal expression. Our analysis of each of these classes provides conclusive evidence for nodal-mediated regulation of several developmental processes in the mouse embryo, beyond its role in mesoderm formation. We find that nodal signaling is required for correct positioning of the anteroposterior axis, normal anterior and midline patterning, and the left- right asymmetric development of the heart, vasculature, lungs and stomach.
Centrosome migration into the Drosophila oocyte is independent of BicD and egl, and of the organisation of the microtubule cytoskeleton
Authors: Bolívar Jorge , Huynh ean-René , López-Schier Hernán , González Cayetano , Johnston Daniel St , González-Reyes Acaimo 
Published: April 2021

ABSTRACT
During early Drosophila oogenesis, one cell from a cyst of 16 germ cells is selected to become the oocyte, and accumulates oocyte-specific proteins and the centrosomes from the other 15 cells. Here we show that the microtubule cytoskeleton and the centrosomes follow the same stepwise restriction to one cell as other oocyte markers. Surprisingly, the centrosomes still localise to one cell after colcemid treatment, and in BicD and egl mutants, which abolish the localisation of all other oocyte markers and the polarisation of the microtubule cytoskeleton. In contrast, the centrosomes fail to migrate in cysts mutant for Dynein heavy chain 64C, which disrupts the fusome. Thus, centrosome migration is independent of the organisation of the microtubule cytoskeleton, and seems to depend instead on the polarity of the fusome.
even skippedis required to produce atrans-acting signal for larval neuroblast proliferation that can be mimicked by ecdysone
Authors: Park Youngji , Fujioka Miki , Kobayashi Masatomo , Jaynes James B. , Datta Sumana 
Published: April 2021

ABSTRACTDevelopment of a multicellular organism requires precise coordination of cell division and cell type determination. The selector homeoprotein Even skipped (Eve) plays a very specific role in determining cell identity in the Drosophila embryo, both during segmentation and in neuronal development. However, studies of gene expression in eve mutant embryos suggest that eve regulates the embryonic expression of the vast majority of genes. We present here genetic interaction and phenotypic analysis showing that eve functions in the trol pathway to regulate the onset of neuroblast division in the larval CNS. Surprisingly, Eve is not detected in the regulated neuroblasts, and culture experiments reveal that Eve is required in the body, not the CNS. Furthermore, the effect of an eve mutation can be rescued both in vivo and in culture by the hormone ecdysone. These results suggest that eve is required to produce a trans-acting factor that stimulates cell division in the larval brain.
Overexpression of Snail family members highlights their ability to promote chick neural crest formation
Authors: del Barrio Marta G. , Nieto M. Angela 
Published: April 2021

The Snail gene family of transcription factors plays crucial roles in different morphogenetic processes during the development of vertebrate and invertebrate embryos. In previous studies of function interference for one of the family members, Slug, we showed its involvement and neural crest formation in the chick embryo. Now we have carried out a series of gain-of-function experiments in which we show that Slug overexpression in the neural tube of the chick embryo induces an increase in neural crest production. The analysis of electroporated embryos shows that Slug can induce the expression of rhoB and an increase in the number of HNK-1-positive migratory cells, indicating that it lies upstream of them in the genetic cascade of neural crest development. The increase in neural crest production after Slug overexpression was confined to the cranial region, indicating that the mechanisms of crest induction somehow differ between head and trunk.The expression of the two vertebrate family members, Slug and Snail, is peculiar with respect to the neural crest. Slug is not expressed in the premigratory crest in the mouse, whereas it is expressed in this cell population in the chick and the opposite is true for Snail(Sefton, M., Sánchez, S. and Nieto M. A. (1998) Development125, 3111-3121). This raises the question of whether they can be functionally equivalent. To test this hypothesis both intra- and interspecies, we have performed a series of ectopic expression experiments by electroporating chick and mouse Snail in the chick embryo hindbrain. We observe that both genes elicit the same responses in the neural tube. Our results indicate that they can be functionally equivalent, although the embryos show a higher response to the endogenous gene, chick Slug.
Expression of CD41 on hematopoietic progenitors derived from embryonic hematopoietic cells
Authors: Mitjavila-Garcia Maria Teresa , Cailleret Michel , Godin Isabelle , Nogueira Maria Manuela , Cohen-Solal Karine , Schiavon Valérie , Lecluse Yann , Le Pesteur Françoise , Lagrue Anne Hélène , Vainchenker William 
Published: April 2021

In this study, we have characterized the early steps of hematopoiesis during embryonic stem cell differentiation. The immunophenotype of hematopoietic progenitor cells derived from murine embryonic stem cells was determined using a panel of monoclonal antibodies specific for hematopoietic differentiation antigens. Surprisingly, the CD41 antigen (αIIb integrin, platelet GPIIb), essentially considered to be restricted to megakaryocytes, was found on a large proportion of cells within embryoid bodies although very few megakaryocytes were detected. In clonogenic assays, more than 80% of all progenitors (megakaryocytic, granulo-macrophagic, erythroid and pluripotent) derived from embryoid bodies expressed the CD41 antigen. CD41 was the most reliable marker of early steps of hematopoiesis. However, CD41 remained a differentiation marker because some CD41– cells from embryoid bodies converted to CD41+ hematopoietic progenitors, whereas the inverse switch was not observed. Immunoprecipitation and western blot analysis confirmed that CD41 was present in cells from embryoid bodies associated with CD61 (β3 integrin, platelet GPIIIa) in a complex. Analysis of CD41 expression during ontogeny revealed that most yolk sac and aorta-gonad-mesonephros hematopoietic progenitor cells were also CD41+, whereas only a minority of bone marrow and fetal liver hematopoietic progenitors expressed this antigen. Differences in CD34 expression were also observed: hematopoietic progenitor cells from embryoid bodies, yolk sac and aorta-gonad-mesonephros displayed variable levels of CD34, whereas more than 90% of fetal liver and bone marrow progenitor cells were CD34+.Thus, these results demonstrate that expression of CD41 is associated with early stages of hematopoiesis and is highly regulated during hematopoietic development. Further studies concerning the adhesive properties of hematopoietic cells are required to assess the biological significance of these developmental changes.
The reopening process of the esophagus in the normal chick and the crooked neck dwarf mutant
Authors: Allenspach Allan L. 
Published: April 2021

ABSTRACTThe development of the esophagus in the crooked neck dwarf was studied between and 12 days of incubation (stages 26 –38). Esophageal histogenesis in the crooked neck dwarf resembles normal development up to stage 33. Vésiculation alone does not cause the reopening of the esophagus, which depends on the participation of epithelial degeneration to complete the process. Studies of epithelial degeneration in the mutant esophagus emphasize its caudo-cephalic gradient in the reopening process. The appearance of clefts in the intervesicular epithelium suggests that tension plays a role in the reopening process. The occluded segments and persisting epithelial strands of the 18-day mutant embryonic esophagus result from critical developmental failures at 8 days of incubation (stage 34). The crooked neck dwarf mutant has a histogenetic marker in the form of ‘degenerate mesenchyme cells’ as early as stage 30.
Oligosyndactylism, an early embryonic lethal in the mouse
Authors: Valen Phebe Van 
Published: April 2021

ABSTRACT
In heterozygous condition, the gene for oligosyndactylism (Os) in the mouse (Mus musculus) causes syndactylism on all four feet and sometimes suppression of digit 2. Os/Os homozygotes are inviable and die before the 12th day of gestation (Grüneberg, 1956, 1961). The present study was initiated to identify the Os/Os homozygote and to establish the circumstances of its death.