bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of retinoid metabolism in the developing chick limb bud
Authors: Thaller Christina , Eichele Gregor 
Published: April 2021

Abstract
Retinoids (vitamin A derivatives) have been shown to have striking effects on developing and regenerating vertebrate limbs. In the developing chick limb, retinoic acid is a candidate morphogen that may coordinate the pattern of cellular differentiation along the anteroposterior limb axis. We describe a series of investigations of the metabolic pathway of retinoids in the chick limb bud system. To study retinoid metabolism in the bud, all-trans-[3H]retinol, all-trans-[3H]retinal and all-trans-[3H]retinoic acid were released into the posterior region of the limb anlage, the area that contains the zone of polarizing activity, a tissue possibly involved in limb pattern formation. We found that the locally applied [3H]retinol is primarily converted to [3H]retinal, [3H]retinoic acid and a yet unidentified metabolite. When [3H]retinal is locally applied, it is either oxidized to [3H]retinoic acid or reduced to [3H]retinol. In contrast, local delivery of retinoic acid to the bud yields neither retinal norretinol nor the unknown metabolite. This flow of metabolites agrees with the biochemical pathway of retinoids that has previously been elucidated in a number of other animal systems. To find out whether metabolism takes place directly in the treated limb bud, we have compared the amount of [3H]retinoid present in each of the four limb anlagen following local treatment of the right wing bud. The data suggest that retinoid metabolism takes place mostly in the treated limb bud. This local metabolism could provide a simple mechanism to generate in a controlled fashion the biologically active all-trans-retinoic acid from its abundant biosynthetic precursor retinol. In addition, local metabolism supports the hypothesis that retinoids are local chemical mediators involved in pattern formation.
The control of DNA replication in a cell-free extract that recapitulates a basic cell cycle in vitro
Authors: Hutchison Christopher J. , Cox Richard , Ford Christopher C. 
Published: April 2021

Abstract
Cell-free extracts prepared from Xenopus eggs support chromosome decondensation and pronuclear formation on demembranated sperm heads. 32P-dCTP pulse-labelling studies demonstrate that DNA synthesis occurs in multiple bursts of 30–40 min in extracts containing pronuclei, each burst being followed by a period of 20–50 min during which no synthesis occurs. Density substitution with bromodeoxyuridine indicates that the synthesis in each burst is semiconservative and results from new initiations, and that, following multiple bursts of synthesis, reinitiation events can occur. Changes in nuclear morphology have been characterized in the extract by phase-contrast microscopy and by fluorescence microscopy following pulse labelling with biotin-11-dUTP and staining with anti-lamin antibodies. Lamin accumulation occurs as DNA decondenses and parallels the acquisition of membrane structures. Biotin-11-dUTP incorporation is first observed in small nuclei having decondensed DNA and an extensive lamina. While DNA synthesis is occurring nuclei remain relatively small, but rapid swelling accompanied by chromosome condensation occurs when biotin incorporation ceases. Nuclear swelling and chromatin condensation is followed by nuclear membrane breakdown, lamin dispersal and chromosome formation. Mitosis lasts for approximately 20 min. Nuclear reassembly is recognized by the appearance of membrane vesicles around small pieces of decondensed DNA, which parallels the appearance of lamin islands within a chromatin mass. These ‘islands’ incorporate biotin, indicating that DNA synthesis is occurring, and apparently fuse as larger S-phase nuclei are formed. Extensive protein synthesis occurs for at least 4h in most extracts. This synthesis is required for the initiation of mitotic events and the reinitiation of DNA synthesis.
Behaviour of microtubules and actin filaments in livingDrosophilaembryos
Authors: Kellogg Douglas R. , Mitchison Tim J. , Alberts Bruce M. 
Published: April 2021

AbstractWe describe the preparation of novel fluorescent derivatives of rabbit muscle actin and bovine tubulin, and the use of these derivatives to study the behaviour of actin filaments and microtubules in living Drosophila embryos, in which the nuclei divide at intervals of 8 to 21 min. The fluorescently labelled proteins appear to function normally in vitro and in vivo, and they allow continuous observation of the cytoskeleton in living embryos without perturbing development. By coinjecting labelled actin and tubulin into the early syncytial embryo, the spatial relationships between the distinct filament networks that they form can be followed second by second. The dynamic rearrangements of actin filaments and microtubules observed confirms and extends results obtained from previous studies, in which fixation techniques and specific staining were used to visualize the cytoskeleton in the Drosophila embryo. However, no tested fixation method produces an exact representation of the in vivo microtubule distribution.
DNA methylation in the developing marsupial embryo
Authors: Stevens Mary E. , Maidens Peta M. , Robinson Edward S. , Vandeberg John L. , Pedersen Roger A. , Monk Marilyn 
Published: April 2021

Abstract
Marsupial development differs from early development of placental mammals in that the blastocyst is unilaminar, so that both embryonic and extraembryonic cells are derived from a single layer of cells (protoderm) which faces the blastocyst cavity. Also, all cells in female marsupial conceptuses so far examined show preferential paternal X-inactivation. To test for a possible correlation between cell position, paternal X-inactivation and DNA hypomethylation, marsupial DNA preparations from three regions, embryo, vascular yolk sac and avascular yolk sac, were digested with methyl-specific restriction endonucleases, separated on agarose gels and end-labelled with 32P-dCTP. The size distribution of the fragments obtained indicated three levels of methylation: high methylation of embryonic DNA, intermediate levels of methylation of vascular yolk sac DNA and hypomethylation of avascular yolk sac DNA. The degree of methylation of repeat sequences, observed as discrete bands in end-labelled HpaII digests, was correlated with the overall methylation of tissue DNA. Thus, the difference in methylation in embryonic and extraembryonic DNA was similar to that described for the mouse conceptus, and the outside cell position of marsupial fetal precursor cells did not correlate with hypomethylation. HpaII tiny fragments, which indicate the presence of CpG-rich islands of DNA, were evident in the marsupial digests. In the mouse DNA, these islands are associated with gene transcription and provide one route to cloning of unique gene sequences.
Development of the pattern of cell renewal in the crypt-villus unit of chimaeric mouse small intestine
Authors: Schmidt Günter H. , Winton Douglas J. , Ponder Bruce A. J. 
Published: April 2021

Abstract
We have previously shown that the epithelium of each adult intestinal crypt in chimaeric mice is derived from a single progenitor cell. Whether the crypts are monoclonal from the outset - that is, are formed by the proliferation of a single cell - or whether their formation is initiated by several cells was not known. Here we report that many crypts contain cells of both chimaeric genotypes in the neonatal period indicating a polyclonal origin at this stage of morphogenesis. The cellular organization of the early neonatal crypt is therefore different from that of the adult crypt, which includes a zone of ‘anchored’ stem cells above the crypt base. Within 2 weeks, however, the crypt progenitor cell and its descendants displace all other cells from the crypt and the crypt attains monocle-nality. The distribution of enterocytes on chimaeric villi in the neonate shows a mottled pattern of mosaicism which is progressively replaced by coherent sheets of cells from the crypts, and within two weeks the orderly adult clonal pattern is established.
Stalk cell formation in monolayers from isolated prestalk and prespore cells of Dictyostelium discoideum: evidence for two populations of prestalk cells
Authors: Kwong Linda , Sobolewski André , Atkinson Leone , Weeks Gerald 
Published: April 2021

ABSTRACT
Cells from the pseudoplasmodial stage of Dictyostelium discoideum differentiation were dispersed and separated on Percoll gradients into prestalk and prespore cells. The requirements for stalk cell formation in low-density monolayers from the two cell types were determined. The isolated prespore cells required both the Differentiation Inducing Factor (DIF) and cyclic AMP for stalk cell formation. In contrast, only part of the isolated prestalk cell population required both cyclic AMP and DIF, the remainder requiring DIF alone, suggesting the possibility that there were two populations of prestalk cells, one independent of cyclic AMP and one dependent on cyclic AMP for stalk cell formation. The finding that part of the prestalk cell population required only a brief incubation in the presence of DIF to induce stalk cell formation, whilst the remainder required a considerably longer incubation in the presence of both DIF and cyclic AMP was consistent with this idea. In addition, stalk cell formation from cyclic-AMP-dependent prestalk cells was relatively more sensitive to caffeine inhibition than stalk cell formation from cyclic-AMPindependent prestalk cells. The latter cells were enriched in the most anterior portion of the migrating pseudoplasmodium, indicating that there is spatial segregation of the two prestalk cell populations.
The conversion of prespore cells to stalk cells took longer and was more sensitive to caffeine when compared to stalk cell formation from cyclic-AMP-dependent prestalk cells.
Two maternally derived X chromosomes contribute to parthenogenetic inviability
Authors: Mann Jeff R. , Lovell-Badge Robin H. 
Published: April 2021

ABSTRACT
In certain extraembryonic tissues of normal female mouse conceptuses, X-chromosome-dosage compensation is achieved by preferential inactivation of the paternally derived X. Diploid parthenogenones have two maternally derived X chromosomes, hence this mechanism cannot operate. To examine whether this contributes to the inviability of parthenogenones, XO and XX parthenogenetic eggs were constructed by pronuclear transplantation and their development assessed after transfer to pseudopregnant recipients. In one series of experiments, the frequency of post implantation development of XO parthenogenones was much higher than that of their XX counterparts. This result is consistent with the possibility that two maternally derived X chromosomes can contribute to parthenogenetic inviability at or very soon after implantation. However, both XO and XX parthenogenones showed similar developmental abnormalities at the postimplantation stage, demonstrating that parthenogenetic inviability is ultimately determined by the possession of two sets of maternally derived autosomes.
Requirements for X-linked zygotic gene activity during cellularization of early Drosophila embryos
Authors: Wieschaus Eric , Sweeton Dari 
Published: April 2021

ABSTRACT
To examine the requirements for X-chromosomal transcription during precellular stages of Drosophila embryogenesis, attached X-chromosomes and XY translocations were used to generate embryos deficient for large cytologically defined regions of that chromosome. Embryos that lack all X-chromosome material (‘nullo-X embryos’) develop normally to the cycle-14 syncytial blastoderm stage, but fail to partition their nuclei to single cells during cellularization. The cellularization defects can first be detected in the abnormal distribution of cortical actin and nuclei during early cycle 14. The same defects are produced by deletions of only a single region on the X-chromosome, between 6F and 7A. Nullo-X embryos carrying a duplication of this region cellularize and develop normally to the onset of gastrulation.
The localization of an inductive response
Authors: Gurdon J. B. 
Published: April 2021

Abstract
Combinations of tissues from Xenopus blastulae have been used to identify several mechanisms that limit the number of animal cells forming muscle after induction by vegetal cells. The results disagree with a model in which direct physical contact or very close proximity between animal and vegetal cells restricts the number of cells that receive the inductive signal. Rather it seems that a diffusible inducer is released by vegetal cells, and spreads through 4–8 animal cell diameters, equivalent to a distance of 80 μm, from the nearest vegetal cells. Several factors seem to cooperate to prevent the further spread of the mesoderm-forming induction. These include the slow diffusion and/or instability of the inducer, the time of loss of competence of animal cells to respond to induction, and the amount of vegetal tissue that releases inducer for a limited time. The combination of these, and perhaps other, processes seems to ensure that a consistent minority of animal cells are induced to form muscle, thereby leaving other animal cells available to form the nervous system and epidermis.
Blastocyst implantation precedes induction of insulin-like growth factor II gene expression in human trophoblasts
Authors: Ohlsson Rolf , Larsson Erik , Nilsson Ove , Wahlström Torsten , Sundström Per 
Published: April 2021

ABSTRACT
The cytotrophoblast cell population of the human embryonic conceptus proliferates rapidly during the first month following blastocyst implantation. Since the trophectoderm lineage is established in preimplantation morula/blastocysts, the scenario underlying initiation and maintenance of the rapid proliferative phenotype of cytotrophoblasts is a central issue. The insulin-like growth factor II (IGF-II) gene is highly expressed in proliferative cytotrophoblasts of first trimester placenta and performs as a placenta growth factor. To establish a temporal correlation between IGF-II expression and initiation of highly proliferative trophoblasts in human development, we employed in situ hybridization analysis of the expression of the IGF-II and human chorionic gonadotropin β-subunit (β-HCG) genes in human pre- and postimplantation development. The data show that the appearance of high steady-state levels of IGF-II transcripts in trophoblasts is a postimplantation event, whereas β-HCG transcripts can already be detected in preimplantation development. This observation makes a role for endogenously produced IGF-II in the normal development of preimplantation embryos unlikely, but suggests that endogenously produced IGF-II participates in the formation and subsequent expansion of the rapid proliferative phenotype of the trophoblastic shell, following implantation.
Complex regulation of TGFβ expression by retinoic acid in the vitamin A-deficient rat
Authors: Glick Adam B. , Mccune Bryan K. , Abdulkarem Nariman , Flanders Kathleen C. , Lumadue Jeanne A. , Smith Joseph M. , Sporn Michael B. 
Published: April 2021

ABSTRACT
We report the results of a histochemical study, using polyclonal antipeptide antibodies to the different TGFβ isoforms, which demonstrates that retinoic acid regulates the expression of TGFβ in the vitamin A-deficient rat. Basal expression of TGFβ diminished under conditions of vitamin A deficiency. Treatment with retinoic acid caused a rapid and transient induction of TGFβ2 and TGFβ3 in the epidermis, tracheobronchial and alveolar epithelium, and intestinal mucosa. Induction of TGFβ1 expression was also observed in the epidermis. In contrast to these epithelia, expression of the three TGFβ isoforms increased in vaginal epithelium during vitamin A deficiency, and decreased following systemic administration of retinoic acid. Our results show for the first time the widespread regulation of TGFβ expression by retinoic acid in vivo, and suggest a possible mechanism by which retinoids regulate the functions of both normal and pre-neoplastic epithelia.
Interaction of zona pellucida glycoproteins, sulphated carbohydrates and synthetic polymers with proacrosin, the putative egg-binding protein from mammalian spermatozoa
Authors: Jones Roy 
Published: April 2021

ABSTRACT
Fertilization in mammals is a unique cell-cell recognition event that involves specific receptors on the surface of each gamete. Previous work has shown that proacrosin, a protein found within the acrosome of mammalian spermatozoa, binds non-enzymatically to zona pellucida glycoproteins (ZPGPs) that surround the egg and that this binding can be inhibited by sulphated polysaccharides such as fucoidan. The mechanism of this interaction has been investigated using 125I-ZPGPs and 125I-fucoidan as probes. Results show that it involves poly(sulphate) groups on zona glycoproteins that bind with high affinity (Kd=1.2 to 5.0×10−8M) to complementary ‘docking’ sites on proacrosin. The spatial orientation of these sulphates, together with the tertiary structure of the target protein, determines the selectivity of polymer binding. Thus, dextran sulphate and poly(vinyl sulphate) are strong inhibitors of the above probes whereas dextran, chondroitin sulphates A and C and poly(vinyl phosphate) are ineffective. Proacrosin, therefore, has properties analogous to those described for ‘bindin’, the egg adhesion protein found within the acrosomal vesicle of sea urchin spermatozoa.
Localization of TIMP in cycling mouse hair
Authors: Kawabe Thomas T. , Rea Thomas J. , Flenniken Ann M. , Williams B. R. G. , E. Groppi Vincent , Buhl Allen E. 
Published: April 2021

ABSTRACT
TIMP (tissue inhibitor of metalloproteinase) is a glycoprotein inhibitor of metalloproteinases that we hypothesize to be involved in the tissue remodeling that occurs during each hair growth cycle. We examined this hypothesis by studying the expression of TIMP at selected times during a single hair cycle using T1MP– lacZ transgenic mice to localize TIMP gene activity in the hair follicle. TIMP gene induction was visualized by staining mouse back skin for β-galactosidase (β-gal) activity. Paraffin sections were analyzed for the localization of TIMP expression. TIMP gene activation appears in hair follicles only during the mid-anagen (the growing stage of the hair cycle) primarily in Henle’s layer of the inner root sheath. Some expression of TIMP is also seen in a few connective tissue cells, in the sebaceous gland and in cells at the proximity of the dermal papilla cells in catagen (regressing) and telogen (resting) follicles. These results are consistent with a role for TIMP in cyclic remodeling of connective tissue in hair follicles.
The restricted spatial and temporal expression of a nervous-system-specific antigen involved in axon outgrowth during development of the grasshopper
Authors: Seaver Elaine C. , Karlstrom Rolf O. , Bastiani Michael J. 
Published: April 2021

ABSTRACT
To identify molecules important for pathfinding by growing axons, monoclonal antibodies (mAb) have been generated against embryonic grasshopper tissue. One mAb, 2B2, shows labeling exclusively in the nervous system. It recognizes a surface epitope on neuronal growth cones, filopodia and axons in the central nervous system (CNS). Initially, the antigen is expressed on all processes of the CNS; after 70% of embryonic development, localization of the 2B2 mAb is restricted to a small subset of axon tracts within the ganglia. Immunoprecipitation from embryonic membrane extracts with the 2B2 mAb reveals a unique band of 160×103Mr. Functional studies with the 2B2 mAb demonstrate that the antigen is important in growth cone-axon interactions during process outgrowth. Growth cones that extend along axonal substrata are either blocked in growth or grow along an aberrant pathway when embryos are cultured in the presence of the 2B2 mAb. However, pioneer neurons that extend processes on non-neuronal substrata grow normally.
Control of cell fate in the tail region of C. elegans by the gene egl-5
Authors: Chisholm Andrew 
Published: April 2021

ABSTRACT
The tail region of C. elegans contains a number of blast cell and neuron types that either are found only in the tail, or are different from more anterior homologues. In egl-5 mutants, the fates of many of these tail cells are abnormal or transformed to those of anterior homologues. The affected cells are related only by position and not by ancestry, egl-5 is also required for normal development of the somatic gonad and sex muscles in males. The function of egl-5 in all these tissues is cell autonomous. By genetic mapping, egl-5 lies very close to mab-5, a gene with an analogous role in the immediately anterior body region, egl-5 and mab-5 may constitute a ‘mini-cluster’ of regional determination genes, similar to those described in other animal phyla.
Spatial mechanisms of gene regulation in metazoan embryos
Authors: Davidson Eric H. 
Published: April 2021

ABSTRACT
The basic characteristics of embryonic process throughout Metazoa are considered with focus on those aspects that provide insight into how cell specification occurs in the initial stages of development. There appear to be three major types of embryogenesis: Type 1, a general form characteristic of most invertebrate taxa of today, in which lineage plays an important role in the spatial organization of the early embryo, and cell specification occurs in situ, by both autonomous and conditional mechanisms; Type 2, the vertebrate form of embryogenesis, which proceeds by mechanisms that are essentially independent of cell lineage, in which diffusible morphogens and extensive early cell migration are particularly important; Type 3, the form exemplified by long germ band insects in which several different regulatory mechanisms are used to generate precise patterns of nuclear gene expression prior to cellularization. Evolutionary implications of the phylogenetic distribution of these types of embryogenesis are considered. Regionally expressed homeodomain regulators are utilized in all three types of embryo, in similar ways in later and postembryonic development, but in different ways in early embryonic development. A specific downstream molecular function for this class of regulator is proposed, based on evidence obtained in vertebrate systems. This provides a route by which to approach the comparative regulatory strategies underlying the three major types of embryogenesis.