bluuebunny/crossref_metadata_2025_split huggingface dataset:
Platelet derived growth factor (PDGF) stimulates development of bovine embryos during the fourth cell cycle
Authors: Larson R. C. , Ignotz G. G. , Currie W. B. 
Published: April 2021

ABSTRACT
In vitro produced, 2-cell bovine embryos were cultured in serum-free medium supplemented with various combinations of growth factors to test the hypothesis that these polypeptide factors are able to signal preimplantation development. The developmental arrest that occurs during the 8-cell stage with typical culture methods might be relieved by a growth factor-dependent mechanism that would stimulate expression of the embryonic genome, thereby mimicking events that occur in vivo in the oviduct during the fourth cell cycle (8-to 16-cell stage). Subsequently, other growth factors might promote compaction and blastulation, processes which normally occur in the uterus.
The effects of growth factors on early embryos were evaluated using phase contrast microscopy to monitor progression to the 8-cell stage, completion and duration of the fourth cell cycle, and blastocyst formation.
Platelet derived growth factor (PDGF) promoted development beyond the 16-cell stage in 39.1% of the 2-cell embryos examined in all experiments. The duration of the fourth cell cycle among these embryos was approximately 26 hours. During development after the 16-cell stage, PDGF reduced the proportion of embryos bastulating from 12.7% to 5.8%; in contrast, transforming growth factor (TGF ), acting during the same developmental time period, increased the proportion of embryos blastulating from 8.6% to 40.6%.
These results, using serum-free medium, indicated that PDGF signalled completion of the fourth cell cycle. TGF and perhaps basic fibroblast growth factor (bFGF), promoted blastulation of 16-cell embryos during subsequent culture.
Nuclear rotation and lineage specification in Pelvetia embryos
Authors: Allen Victoria W. , Kropf Darryl L. 
Published: April 2021

ABSTRACT
The first division of Pelvetia zygotes is an unequal division which produces two cells with distinct developmental fates. The smaller rhizoid cell gives rise to the holdfast of the mature plant, and the larger thallus cell is the progenitor of the stipe and fronds. We have investigated the role of the cytoskeleton in determining the orientation of this invariant division. Prior to mitosis, microtubuleorganizing centers (MtOCs) associated with the nuclear envelope undergo a precise realignment from transverse to axial with respect to the rhizoid/thallus axis. This is accomplished by a 90° rotation of the entire nuclear/MtOC complex. After rotation, each MtOC serves as a spindle pole during mitosis, and subsequently cytokinesis bisects the spindle. Both nocodazole and cytochalasin D cause incorrect alignment of MtOCs, indicating that both microtubules and microfilaments are required for nuclear/MtOC rotation. These inhibitors also result in aberrant orientation of the first division plane. Microtubules visualized by confocal microscopy connect the rotating nucleus to the apical cortex and may provide the force for rotation.
Platelet-derived growth factor-A and its receptor are expressed in separate, but adjacent cell layers of the mouse embryo
Authors: Orr-Urtreger Avi , Lonai Peter 
Published: April 2021

ABSTRACT
The localized developmental expression of murine platelet-derived growth factor A (PDGF-A) was compared to that of itsreceptor (Pdgfra). Our in situ hybridization study included germ layers of primitive streak embryos, early axial structures (dermatome, myotome, sclerotome, floor plate), the skin and some of its derivatives (hair and mammary gland), the developing fore-limb, the branchial arches and various sense organs (otic vesicle, olfactory epithelium and the eye). We report that PDGF-A and Pdgfra are expressed in separate, but adjacent cell layers in these structures and that in most, the ligand is expressed in the epithelium, whereas the receptor in the mesenchyme. This localization corresponds to classical experimental evidence for develop-mental interactions across cell layers. We suggest that the spatio-temporal regulation of PDGF-A and Pdgfra, and other related systems, represents one model for the spatial regulation of receptor-ligand interactions.
The developmental switch in embryonic ρ-globin expression is correlated with erythroid lineage-specific differences in transcription factor levels
Authors: Minie Mark E. , Kimura Takeshi , Felsenfeld Gary 
Published: April 2021

ABSTRACT
During chicken embryogenesis, the ρ--globin gene is expressed only in the early developmental stages. We have examined the mechanisms that are responsible for this behavior. The transcription of the ρ--globin gene is strongly correlated with the presence during development of primitive erythroid lineage cells, consistent with the idea that the expression of the ρ--globin gene is restricted to that lineage. The “switching off” of ρ--globin during development thus reflects the change from primitive to definitive cell lineages which occurs during erythropoiesis in chicken. We use transient expression assays in primary erythroid and other cells to show that the information for lineage- and tissue-specific expression of the ρ--globin gene is contained in a 456 bp region upstream of the gene’s translational start site. DNA-binding studies, coupled with analysis of the effect on expression of deletions and binding site mutations, were used to identify important control elements within this 456 bp region. We find that binding sites for the ubiquitous transcription factor Sp1, and the specific hematopoietic factor GATA-1, are crucial for expression of the gene in primitive erythroid cells. Quantitative analysis shows that nuclei of the primitive erythroid lineage contain 10-fold more of these factors than do the nuclei of definitive cells. We show that in principle these differences in factor concentration are sufficient to explain the lineage-specific behavior that we observe in our assays. We suggest that this may be an important part of the mechanism for lineage-restricted ρ--globin expression during chicken erythroid development. Similar mechanisms may be involved in regulation of other (but not all) members of the globin family.
The involvement of the Notch locus in Drosophila oogenesis
Authors: Xu Tian , A. Caron Laurent , G. Fehon Richard , Artavanis-Tsakonas Spyros 
Published: April 2021

ABSTRACT
The Notch gene in Drosophila encodes a transmembrane protein with homology to EGF that, in a variety of tissues, appears to mediate cell interactions necessary for cell fate choices. Here we demonstrate that oogenesis and spermatogenesis depend on Notch. We examine the phenotypes of the temperature-sensitive Notch allele, Nts1, and, using a monoclonal antibody, determine the cellular and subcellular distribution of Notch protein during oogenesis. We show that Nts1 is associated with a missense mutation in the extracellular, EGF homologous region of Notch and that at non-permissive temperatures oogenesis is blocked and the subcellular distribution of the protein is altered. In wild-type ovaries, Notch protein is found on the apical surface of somatically derived follicle cells, while in the germline-derived cells the protein is not polarized. These findings are discussed in view of the hypothesis that Notch acts as a multifunctional receptor to mediate developmentally important cell interactions.
Relationship between Wnt-1 and En-2 expression domains during early development of normal and ectopic met-mesencephalon
Authors: Bally-Cuif Laure , Alvarado-Mallart Rosa-Magda , Darnell Diana K. , Wassef Marion 
Published: April 2021

ABSTRACT
Grafting a met-mesencephalic portion of neural tube from a 9.5-day mouse embryo into the prosencephalon of a 2-day chick embryo results in the induction of chick En-2 (ChickEn) expression in cells in contact with the graft (Martinez et al., 1991). In this paper we investigate the possibility of Wnt-1 being one of the factors involved in En-2 induction. Since Wnt-1 and En-2 expression patterns have been described as diverging during development of the met-mesencephalic region, we first compared Wnt-1 and En-2 expression in this domain by in situ hybridization in mouse embryos after embryonic day 8.5. A ring of Wnt-1-expressing cells is detected encircling the neural tube in the met-mesencephalic region at least until day 12.5. This ring consistently overlapped with the En-2 expression domain, and corresponds to the position of this latter gene’s maximal expression. We subsequently studied ChickEn ectopic induction in chick embryos grafted with various portions of met-mesencephalon. When the graft originated from the level of the Wnt-1-positive ring, ChickEn induction was observed in 71% of embryos, and in these cases correlated with Wnt-1 expression in the grafted tissue. In contrast, this percentage dropped significantly when the graft was taken from more rostral or caudal parts of the mesencephalic vesicle. Taken together, these results are compatible with a prolonged role of Wnt-1 in the specification and/or development of the met-mesencephalic region, and show that Wnt-1 could be directly or indirectly involved in the regulation of En-2 expression around the Wnt-1-positive ring during this time. We also provide data on the position of the Wnt-1-positive ring relative to anatomical boundaries in the neural tube, which suggest a more general role for the Wnt-1 protein as a positional signal involved in organizing the met-mesencephalic domain.
Synergistic principles of development: overlapping patterning systems in Xenopus mesoderm induction
Authors: Kimelman David , Christian Jan L. , Moon Randall T. 
Published: April 2021

ABSTRACT
The first inductive event in Xenopus development establishes the mesoderm at the equator of the developing embryo. As part of this process, the dorsal-ventral and anterior-posterior axes of the embryo are initially established. A number of signalling molecules which may play a role in mesodermal induction and patterning have been identified in the last several years, including members of the FGF, TGFand Wnt gene families. A variety of experiments, using either purified factors or injection of RNA encoding these factors, have added to the wealth of classical embryogical experimental data collected over the last century.
We have synthesized some recent results with the classical data to provide a framework for examining the process of mesoderm induction, and to formulate putative roles for some of the different factors. We incorporate these ideas into a working model of mesoderm induction that provides a basis for future experimental directions. Finally, we suggest that mesoderm induction may not be a discrete set of well separated events, but instead may be a process involving partially overlapping signals that produce the same pattern.
Cleavage and gastrulation in the shrimp Sicyonia ingentis: invagination is accompanied by oriented cell division
Authors: Hertzler Philip L. , Clark Wallis H. 
Published: April 2021

ABSTRACT
Embryos of the penaeoidean shrimp Sicyonia ingentis were examined at intervals during cleavage and gastrulation using antibodies to β-tubulin and DNA and laser scanning confocal microscopy. Cleavage occurred in a regular pattern within four domains corresponding to the 4-cell-stage blastomeres and resulted in two interlocking bands of cells, each with similar spindle orientations, around a central blastocoel. Right-left asymmetry was evident at the 32-cell-stage, and mirror-image embryos occurred in a 50:50 ratio. Gastrulation was initiated by invagination into the blastocoel at the 62-cellstage of two mesendoderm cells, which arrested at the 32-cell-stage. Further invagination and expansion of the archenteron during gastrulation was accompanied by rapid and oriented cell division. The archenteron was composed of presumptive naupliar mesoderm and the blastopore was located at the site of the future anus of the nauplius larva. In order to trace cell lineages and determine axial relationships, single 2and 4-cell-stage blastomeres were microinjected with rhodamine-dextran. The results showed that the mesendoderm cells which initiated gastrulation were derived from the vegetal 2-cell-stage blastomere, which could be distinguished by its slightly larger size and the location of the polar bodies. The mesendoderm cells descended from a single vegetal blastomere of the 4-cell-stage. This investigation provides the first evidence for oriented cell division during gastrulation in a simple invertebrate system. Oriented cell division has previously been discounted as a potential morphogenetic force, and may be a common mechanism of invagination in embryos that begin gastrulation with a relatively small number of cells.
Drosophila PS2 integrin mediates RGD-dependent cell-matrix interactions
Authors: Bunch Thomas A. , Brower Danny L. 
Published: April 2021

ABSTRACT
Integrins are a family of transmembrane glycoproteins that mediate cell-matrix and cell-cell interactions. We have transfected cultured Drosophila cells with genes that express the Drosophila PS2 integrin. We demonstrate that this integrin is expressed on the surface of the cells and can mediate cell spreading on an undefined component of fetal calf serum or on the purified vertebrate matrix molecules vitronectin and fibronectin. Additionally, PS2 integrin can cause cell spreading on RGD peptide. The spreading on matrix components or RGD peptide can be inhibited by soluble RGD peptide and is dependent on divalent cations.
goosecoid and the organizer
Authors: De Robertis Eddy M. , Blum Martin , Niehrs Christof , Steinbeisser Herbert 
Published: April 2021

ABSTRACT
The molecular nature of Spemann’s organizer phenomenon has long attracted the attention of embryologists. goosecoid is a homeobox gene with a DNA-binding specificity similar to that of Drosophila bicoid. Xenopus goosecoid is expressed on the dorsal side of the embryo before the dorsal lip is formed. Cells expressing goosecoid are fated to become pharyngeal endoderm, head mesoderm and notochord. Transplantation of goosecoid mRNA to the ventral side of Xenopus embryos by microinjection mimics the properties of Spemann’s organizer, leading to the formation of twinned body axes, goosecoid is activated by dorsal inducers and not affected by ventral inducers. In the mouse, goosecoid is expressed in the anterior tip of the primitive streak. The availability of two early markers, goosecoid and Brachyury, opens the way for the comparative analysis of the vertebrate gastrula. The results suggest that the goosecoid homeodomain protein is an integral component of the biochemical pathway leading to Spemann’s organizer phenomenon.
Cell movements and cell fate during zebrafish gastrulation
Authors: Ho Robert K. 
Published: April 2021

ABSTRACT
The early lineages of the zebrafish are indeterminate and a single cell labeled before the late blastula period will contribute progeny to a variety of tissues. Therefore, early cell lineages in the zebrafish do not establish future cell fates and early blastomeres must necessarily remain pluripotent. Eventually, after a period of random cell mixing, individual cells do become tissue restricted according to their later position within the blastoderm. The elucidation of a fate map for the zebrafish gastrula (Kimmel et al., 1990), has made it possible to study the processes by which cellular identity is conferred and maintained in the zebrafish. In this chapter, I describe single cell transplantation experiments designed to test for the irreversible restriction or ‘commitment’ of embryonic blastomeres in the zebrafish embryo. These experiments support the hypothesis that cell fate in the vertebrate embryo is determined by cell position. Work on the spadetail mutation will also be reviewed; this mutation causes a subset of mesodermal precursors to mismigrate during gastrulation thereby leading to a change in their eventual cell identity.
Interaction between splotch (Sp) and curly tail (ct) mouse mutants in the embryonic development of neural tube defects
Authors: Estibeiro J. Peter , Brook Frances A. , Copp Andrew J. 
Published: April 2021

ABSTRACT
The mouse mutations splotch (Sp) and curly tail (ct) both produce spinal neural tube defects with closely similar morphology, but achieve this by different embryonic mechanisms. To determine whether the mutants may interact during development, we constructed mice carrying both mutations. Double heterozygotes exhibited tail defects in 10% of cases, although the single het-erozygotes do not express this phenotype. Backcrosses of double heterozygotes to ct/ct produced offspring with an elevated incidence of neural tube defects, both spina bifida and tail defects, compared with a control backcross in which Sp was not involved. Use of the deletion allele Sp2H permitted embryos carrying a splotch mutation to be recognised by polymerase chain reaction assay. This experiment showed that only embryos carrying Sp2H develop spina bifida in the backcross with ct/ct, suggesting that the genotype Sp2H/+, ct/ct is usually lethal around the time of birth as a result of severe disturbance of neurulation. The interaction between Sp and ct was investigated further by examining embryos in the backcross for developmental markers of the Sp/Sp and ct/ct genotypes. Sp/Sp embryos characteristically lack neural crest derivatives, such as dorsal root ganglia, and die on day 13 of gestation. Double mutant embryos from the backcross did not exhibit either of these characteristics suggesting that homozygosity for ct does not cause Sp/+ embryos to develop as if they were of genotype Sp/Sp. The angle of ventral curvature of the posterior neuropore region is enhanced in affected ct/ct embryos whereas it was found to be reduced in Sp/Sp embryos compared with their normal littermates. Double mutant embryos from the backcross had an angle of curvature that resembled the ct/ct pattern but was less exaggerated. We conclude that the non-allelic mutations Sp and ct interact to promote the development of neural tube defects in a manner that does not involve exacerbation of the specific developmental effects of either gene. The presence of enhanced curvature of the caudal region, which is responsible for neurulation disturbance in ct/ct embryos, summates with the reduced neurulation potential of the neuroepithelium in the Sp/+ genotype leading to the development of severe spina bifida. This study demonstrates that the finding of a significant interaction between genes in double mutant mice cannot be assumed to indicate that the genes operate in the same genetic pathway.
Induction of terminal differentiation of Dictyostelium by cAMP-dependent protein kinase and opposing effects of intracellular and extracellular cAMP on stalk cell differentiation
Authors: Hopper Neil A. , Anjard Christophe , Reymond Christophe D. , Williams Jeffrey G. 
Published: April 2021

ABSTRACT
Expression of the catalytic (C) subunit of the cAMP-dependent protein kinase (PKA) of Dictyostelium under the control of heterologous, cell-type-specific promoters causes ectopic terminal differentiation. When expressed under the control of a prespore-specific promoter, development is accelerated, to yield highly aberrant fruiting bodies that contain a basal mass of spore cells surrounding a central stalk-like structure. When expressed under the control of a prestalk-specific promoter, development arrests much earlier, at the tight mound stage. Prestalk cells move to the apices of these mounds, apparently normally, but no tip is formed. Most of the prestalk cells remain arrested in their development but there are a few isolated stalk cells scattered within such mounds.
We show that extracellular cAMP represses stalk cell specific gene expression in cells where the kinase is con stitutively active, suggesting that inhibition of stalk cell differentiation by cAMP in normal cells (Berks and Kay, 1988) occurs because of an effect of extracellular cAMP on an intracellular signalling pathway independent of PKA. We propose a scheme whereby two separate events, a rise in intracellular cAMP levels and a fall in extracellular cAMP concentration, are required to induce stalk cell differentiation.
FGF-4 maintains polarizing activity of posterior limb bud cells in vivo and in vitro
Authors: Vogel Astrid , Tickle Cheryll 
Published: April 2021

ABSTRACT
The polarizing region is a major signalling tissue involved in patterning the tissues of the vertebrate limb. The polarizing region is located at the posterior margin of the limb bud and can be recognized by its ability to induce additional digits when grafted to the anterior margin of a chick limb bud. The signal from the polarizing region operates at the tip of the bud in the progress zone, a zone of undifferentiated mesenchymal cells, maintained by interactions with the apical ectodermal ridge. A number of observations have pointed to a link between the apical ectodermal ridge and signalling by the polarizing region. To test this possibility, we removed the posterior apical ectodermal ridge of chick wing buds and assayed posterior mesenchyme for polarizing activity. When the apical ectodermal ridge is removed, there is a marked decrease in polarizing activity of posterior cells. The posterior apical ectodermal ridge is known to express FGF-4 and we show that the decrease in polarizing activity of posterior cells of wing buds that normally follows ridge removal can be prevented by implanting a FGF-4-soaked bead. Furthermore, we show that both ectoderm and FGF-4 maintain polarizing activity of limb bud cells in culture.
Heterotopic transplantation of presumptive placodal ectoderm changes the fate of sensory neuron precursors
Authors: Vogel Kristine S. , Davies Alun M. 
Published: April 2021

ABSTRACT
The placode-derived cranial sensory neurons of the vestibular and nodose ganglia in avian embryos exhibit differences in neurite growth rate and the duration of neurotrophin-independent survival in vitro that arise prior to gangliogenesis and target contact (Davies, A. M. (1989) Nature 337, 553-555; Vogel, K. S. and Davies, A. M. (1991) Neuron 7, 819-830). To ascertain the state of commitment of presumptive placodal ectoderm to dif-ferentiate into neurons of the vestibular or nodose type, we performed heterotopic transplantation of labelled presumptive placodal ectoderm at E1.5 in the chicken embryo. We then assayed transplant-derived neurons for hindbrain innervation patterns, neurite growth and survival at E3.5. We show that presumptive placodal ectoderm is not determined to give rise to neurons of the vestibular or nodose phenotype at E1.5. Explantation of presumptive placodal ectoderm at E1.5 showed that this ectoderm is also not specified to differentiate into neurons at this stage. In addition, we demonstrate that non-neurogenic ectoderm from the trunk can give rise to nodose-type neurons when transplanted heterotopically to the nodose region.