bluuebunny/crossref_metadata_2025_split huggingface dataset:
Division and differentiation during normal and liguleless-1 maize leaf development
Authors: Sylvester Anne W. , Cande W. Zacheus , Freeling Michael 
Published: April 2021

Abstract
The maize leaf is composed of a blade and a sheath, which are separated at the ligular region by a ligule and an auricle. Mutants homozygous for the recessive liguleless-1 (lgl) allele exhibit loss of normal ligule and auricle. The cellular events associated with development of these structures in both normal and liguleless plants are investigated with respect to the timing of cell division and differentiation. A new method is used to assess orientation of anticlinal division planes during development and to determine a division index based on recent epidermal cross-wall deposition. A normal leaf follows three stages of development: first is a preligule stage, in which the primordium is undifferentiated and dividing throughout its length. This stage ends when a row of cells in the preligule region divides more rapidly in both transverse and longitudinal anticlinal planes. During the second stage, ligule and auricle form, blade grows more rapidly than sheath, divisions in the blade become exclusively transverse in orientation, and differentiation begins. The third stage is marked by rapid increase in sheath length. The leaf does not have a distinct basal meristem. Instead, cell divisions are gradually restricted to the base of the leaf with localized sites of increased division at the preligule region. Divisions are not localized to the base of the sheath until near the end of development. The liguleless-1 homozygote shows no altération in this overall pattern of growth, but does show distinct alteration in the anticlinal division pattern in the preligule region. Two abnormal patterns are observed: either the increase in division rate at the preligule site is absent or it exhibits loss of all longitudinal divisions so that only transverse (or cell-file producing) divisions are present. This pattern is particularly apparent in developing adult leaves on older Igl plants, in which sporadic ligule vestiges form. From these and results previously published (Becraft et al. (1990)Devl Biol. 14), we conclude that the information carried by the Lgl+ gene product acts earlier in development than formation of the ligule proper. We hypothesize that Lgl+ may be effective at the stage when the blade-sheath boundary is first determined.
The distribution of plasmodesmata and its relationship to morphogenesis in fern gametophytes
Authors: Tilney Lewis G. , Cooke Todd J. , Connelly Patricia S. , Tilney Mary S. 
Published: April 2021

Abstract
Fern (Onoclea sensibilis) gametophytes when grown in the dark form a linear file of cells (one-dimensional) called a protonema. In the light two-dimensional growth occurs which results in a heart-shaped prothallus one cell thick. The objective of this paper is to relate the most common pattern of cell division observed in developing gametophytes to the formation of the plasmodesmatal network. Since the prothalli are only two dimensional, we can easily determine from thin sections the total number and the density (number per unit surface area) of plasmodesmata at each developmental stage. As the prothallus grows the number of plasmodesmata increases 50-fold in the apical or meristematic cell. This number eventually reaches a plateau even though the density continues to increase with each new cell division. What is particularly striking is that both the number and density of plasmodesmata between adjacent cells is precisely determined. Furthermore, the pattern of plasmodesmata distribution is predictable so that (1) we can identify the apical meristematic cells by their plasmodesmata number, or density, as well as by their size, shape and location, (2) we can predict, again from plasmodesmata number, the location of a future wall of the apical cell prior to its actual formation, (3) we can show that the density of plasmodesmata in the triangular apical cell of the prothallus (14 plasmodesmata μm-2) is comparable to those reported for secretory glands which are known to have high rates of plasmodesmatal transport and (4) we can show that once the plasmodesmata have been formed during division, no subsequent change in the number of plasmodesmata occurs following cell plate formation.
An in situ assessment of the routes and extents of colonisation of the mouse embryo by embryonic stem cells and their descendants
Authors: Lallemand Yvan , Brûlet Philippe 
Published: April 2021

Abstract
An embryonic stem (ES) cell line stably expressing lacZ under the control of an endogenous promoter has been isolated and used as a marker to follow the fate of ES cells injected into blastocysts and morulae, before midgestation. The results show a multisite pattern of blastocyst colonization by ES cells deposited into the blastocoel cavity and a low degree of mingling between ES cells and ICM cells. Furthermore, analysis of dispersal of ES cell descendants in postimplantation chimaeric embryos showed that colonization can be highly variable from one region of the embryo to another. In contrast, a high and reproducible degree of chimaerism was obtained when the ES cells were injected at the morula stage prior to ICM formation.
Blocking cell division does not remove the requirement for Polycomb function in Drosophila embryogenesis
Authors: Gould Alex P. , Lai Robert Y. K. , Green Michael J. , White Robert A. H. 
Published: April 2021

Abstract
The Polycomb (Pc) gene is required from the extended germ band stage onwards, to maintain spatially restricted patterns of homeotic gene expression. It has been thought to be involved in the ‘stable inheritance of the determined state’. In this paper, we have tested the notion that the Pc gene is required specifically during or after DNA replication to enable the stable transmission of states of gene activity. We found that arresting cell division using the string mutation or blocking DNA replication with aphidicolin failed to prevent ectopic expression of the homeotic gene Ultrabithorax in Pc mutants. Thus, even in the absence of DNA replication, Pc is required to maintain spatially restricted patterns of homeotic gene expression. The role of the Pc gene product in the stable repression of homeotic gene transcription is discussed.
Neonatal seminal vesicle mesenchyme induces a new morphological and functional phenotype in the epithelia of adult ureter and ductus deferens
Authors: Cunha Gerald R. , Young Peter , Higgins Stephen J. , Cooke Paul S. 
Published: April 2021

ABSTRACT
Mesenchyme from neonatal mouse and rat seminal vesicles (SVM) was grown in association with postnatal (adult) epithelial cells from the ureter (URE) and ductus deferens (DDE) in chimeric tissue recombinants composed of mouse mesenchyme and rat epithelium or vice versa. Functional cytodifferentiation was examined in these SVM+URE and SVM+DDE tissue recombinants with antibodies against major androgen-dependent seminal-vesicle-specific secretory proteins. Adult DDE and URE were induced to express seminal cytodifferentiation and produced the complete spectrum of major seminal vesicle secretory (SVS) proteins. The SVS proteins produced were specific for the species that provided the epithelium. In the case of SVM+URE recombinants, the URE, which normally lacks androgen receptors (AR), expressed AR. These results demon strate that adult epithelial cells retain a developmental plasticity equivalent to their undifferentiated fetal counterparts and are capable of being reprogrammed to express a completely new morphological, biochemical and functional phenotype.
Microsurgically generated discontinuities provoke heritable changes in cellular handedness of a ciliate, Stylonychia mytilus
Authors: Shi Xinbai , Lu Li , Qiu Zijian , He Wei , Frankel Joseph 
Published: April 2021

Abstract
Stylonychia mytilus is a dorsoventrally flattened ciliate with compound ciliary structures arranged in a specific manner on the cell surface. In Mirror-image (MI) doublets of this ciliate, two nearly complete sets of ciliary structures are arrayed side-by-side, one in a normal or ‘right-handed’ (RH) arrangement, the other in a reversed or ‘left-handed’ (LH) arrangement. MI-doublets exist in two forms, one with the RH component on the right, the LH component on the left, and feeding structures near the center (‘buccal-adjoining MI-doublet’); the other with the RH component on the left, the LH component on the right, and feeding structures on the lateral edges (‘buccal-opposing MI-doublet’).
We describe an operation that can generate either type of MI-doublet. This operation interchanges large anterior and posterior regions of the cell, transposing the original posterior region anteriorly (P→A) and the original anterior region posteriorly (A—*P), while retaining the original anteroposterior polarity of each region. Two sets of new ciliary structures then are formed in Mirror-image arrangement, with the set in the P→A region oriented normally and the set in the A→P region undergoing a reversal of polarity along its anteroposterior axis. This sometimes creates end-to-end MI forms, but more commonly produces side-by-side MI-doublets through a folding together of the P→A and A→P regions. This folding occurs because one lateral edge of the cell had been removed during the operation; if the left edge was removed, the complex folds to the left and forms a buccal-adjoining MI-doublet, whereas if the right edge was removed, the complex folds to the right and forms a buccal-opposing MI-doublet. Both types can reorganize and later divide true-to-type, although the ‘buccal-opposing’ type is by far the more stable of the two.
The generation of Mirror-image forms is dependent on the prior abnormal juxtaposition of regions from opposite ends of the cell, and involves a coordinated respecification of large-scale organization. We interpret this response to be a consequence of intercalation of Missing intervening positional values in the zone of posterior–anterior abutment.
Expression of v-src induces aberrant development and twinning in chimaeric mice
Authors: Boulter Catherine A. , Aguzzi Adriano , Williams R. Lindsay , Wagner Erwin F. , Evans Martin J. , Beddington Rosa 
Published: April 2021

Abstract
The role of the proto-oncogene c-src in mouse development has been investigated by studying the consequences of expressing its viral homologue, v-src. Embryonic stem (ES) cell lines with differing levels of v-src tyrosine kinase activity have been used to generate chimaeric mice. Whereas a low level of v-src expression is compatible with embryogenesis, chimaeras derived from ES clones with high levels of v-src activity develop abnormally and die on the 8th–9th day of gestation. These abnormalities are characterized by the formation of twin or multiple embryos within the same Reichert’s membrane, and by the arrest of embryonic development at the late egg cylinder stage, accompanied by relative expansion of the visceral yolk sac (VYS) and hyperplasia of the VYS endoderm. These results demonstrate for the first time that deregulated expression of the src protooncogene product can induce developmental abnormalities during early embryogenesis.
Control of the expression of the bithorax complex genes abdominal-A and Abdominal-B by c/s-regulatory regions in Drosophila embryos
Authors: Sánchez-Herrero Ernesto 
Published: April 2021

Abstract
The abdominal-A (abd-A) and Abdominal-B (Abd-B) genes of the bithorax complex (BX-C) specify the identity of most of the Drosophila abdomen. Six different classes of infraabdominal (iab) mutations within the BX-C transform a subset of the parasegments affected by the lack of these two genes. It is thought that these mutations defíne parasegmental cw-regulatory regions that control the expression of abd-A and Abd-B. By staining embryos mutant for different iab mutations with anti-aiJ-A and anti-Abd-B antibodies I show here that the expression of Abd-B (and probably also abd-A) exhibit a parasegmental regulation. I have also studied the significance of the chromosomal order of parasegmental iab regulatory sequences, and the possible presence of chromosomal ‘boundaries’ between them, by looking at the expression of abd-A and Abd-B in embryos carrying the Uab1 and Mcp mutations. These data are discussed in the light of models of parasegmental-specific regulatory regions within the BX-C.
Single cell analysis of mesoderm formation in the Xenopus embryo
Authors: Godsave S. F. , Slack J. M. W. 
Published: April 2021

Abstract
We have examined the developmental specification of individual cells in the Xenopus blastula using a new in vitro culture system. Regional differences are apparent at the mid-blastula stage when animal hemisphere cells form only ectodermal cell types, while many clones from below the pigment boundary contain mesodermal cell types. A number of clones give rise to more than one differentiated cell type indicating that the initial steps of mesoderm induction are potentially reversible.
Animal hemisphere cells can be induced to form mesoderm by fibroblast growth factor (FGF). Different cell types predominate at different FGF concentrations and the neighbours in this sequence are also the pairs of cell types most usually associated in mixed clones derived from the marginal zone. We propose that the specification of individual cells depends upon both the concentration of inducing factor and on stochastic intracellular events.
Cephalic expression and molecular characterization of Xenopus En-2
Authors: Hemmati-Brivanlou Ali , Torre Jose R. de la , Holt Christine , Harland Richard M. 
Published: April 2021

ABSTRACT
We have isolated and characterized cDNAs corresponding to the Xenopus En-2 gene. Comparison of amino acid sequences between the entire Xenopus En-2 and the Drosophila engrailed proteins confirms conservation of sequences inside as well as proximal to the homeobox and reveals a region of similarity towards the N terminus. Two transcripts encode the Xenopus En-2 protein. Both transcripts are regulated temporally in an identical fashion and are likely to be transcribed from two copies of the En-2 gene.
We have also analyzed the distribution of the protein in the head tissue and in the dissected brain of tailbud stage embryos. In addition to the main band of expression at the midbrain–hindbrain boundary, we show that the protein is expressed in three novel areas: the mandibular arch, the optic tectum and the region of anterior pituitary.
The mRNAs encoding acidic FGF, basic FGF and FGF receptor are coordinately downregulated during myogenic differentiation
Authors: Moore James W. , Dionne Craig , Jaye Michael , Swain Judith L. 
Published: April 2021

ABSTRACT
Acidic and basic fibroblast growth factors (FGFs) are members of a family of proteins that exert pleiotropic effects in a range of cell types including skeletal myocytes. Previous studies demonstrate that exogenously supplied FGFs stimulate proliferation of myoblasts and inhibit their differentiation in culture, but little information is available concerning endogenous expression of FGFs by skeletal myocytes. In this study acidic and basic FGF mRNAs were found to be expressed in murine and rat skeletal muscle, and expression was demonstrated to vary with the tissue and species examined. Myogenic cell lines were then analyzed to determine if FGFs are expressed in myoblasts, and if so, whether expression is regulated during myogenic differentiation. Murine Sol 8 and rat L6 myoblasts were found to express acidic and basic FGF mRNAs, and the expression of both growth factors was downregulated at the transcriptional level during myogenic differentiation. A decrease in expression of the mouse homologue of the human FGF receptor paralleled the decrease in acidic and basic FGF mRNAs in Sol 8 cells, indicating that the decrease in FGF receptor abundance previously observed during myogenic differentiation is regulated at the mRNA level. The results of this study suggest that a coordinate decrease in endogenously produced acidic and basic FGFs and their cognate receptor may participate in the regulation of myogenic differentiation. Furthermore, the observation that expression of a myogenic determination gene, myogenin, increases as FGF transcripts decline, together with previous data demonstrating suppression of myogenin expression by FGF, suggest a mechanism whereby endogenously produced FGFs may exert their effect on differentiation.
Isolation and embryonic expression of an abdominal-A-like gene from the lepidopteran, Manduca sexta
Authors: Nagy Lisa M. , Booker Ronald , Riddiford Lynn M. 
Published: April 2021

ABSTRACT
Using sequence homology to the Drosophila Antenna-pedia gene, we isolated a homeobox-containing gene from the lepidopteran, Manduca sexta. Sequence analysis and in situ hybridizations to tissue sections suggest that the Manduca gene encodes a lepidopteran homologue of the Drosophila Bithorax complex gene abdominal-A. The predicted amino acid sequence of a 76 amino acid region that includes the homeobox and the regions immediately flanking it are identical between the Manduca and Drosophila genes. Northern blots reveal that the Manduca abd-A gene is expressed first in the early embryo and continues to be expressed throughout later embryonic and larval stages. In situ hybridizations show that the posterior half of the first abdominal segment marks the anterior border of the Manduca abdA expression. This expression pattern demonstrates the conservation of parasegments as domains of gene activity in the lepidopteran embryo. The Manduca abd-A expression extends from the posterior half of the first abdominal segment through the tenth abdominal segment, a domain that is greater than that of the Drosophila abd-A expression, and reflects the difference in visible segment number between the two insects.
Cyclic changes in amphibian egg microvilli occur during the division cycle: implication of MPF
Authors: Aimar C. 
Published: April 2021

ABSTRACT
The microvilli (MV) of Pleurodeles (amphibian) eggs were examined following fertilization and compared with those of artificially activated eggs and enucleated eggs using scanning and transmission electron microscopy. The MV pattern in fertilized eggs was found to undergo a cyclic transformation during the course of the first few division cycles. Similar changes also occurred in the MV of artificially activated eggs and enucleated eggs. The reorganization of the MV was sensitive to cycloheximide and cytochalasin B, but was unaffected by colchicine. Thus, this MV alteration requires protein synthesis and microfilaments but microtubules are not implicated in this process. In addition, the effects on the MV pattern of the maturation or mitosis promoting factor (MPF) were tested. Injection of MPF into eggs at different times during the first division cycle nearly always induced an elongation of the MV. This observation suggests that MPF could regulate either directly or indirectly, via a MPF-sensitive factor, the cyclic transformation of amphibian egg MV.
Developmental profile of glucose phosphate isomerase allozymes in parthenogenetic and tetrapioid mouse embryos
Authors: Petzoldt Ulrich 
Published: April 2021

ABSTRACT
Glucose phosphate isomerase (GPI) allozymes were compared in eggs and embryos of the mouse strains C57BL/6-JHan (GPI-1BB) and 129/Sv (GPI-1AA) under different experimental conditions. The quantitative differences in eggs of the two strains disappeared by the blastocyst stage at day 4 to 5, both in fertilized and diploid parthenogenetic embryos. The degree of degradation of oocyte-coded enzyme molecules and the activation of the embryonic genome for GPI appeared to be equivalent in parthenogenetic embryos from heterozygous females when only one or other maternal allele type remained in the egg after meiosis. Also in tetrapioid embryos, generated by electrofusion of homozygous fertilized eggs from the two strains, both genomes seemed to be activated at the same time at day 4; here, however, the GPI-1BB allozyme remained predominant up to day 6.
Morphogenesis and regulated gene activity are independent of DNA replication in Xenopus embryos
Authors: Rollins Martha B. , Andrews Matthew T. 
Published: April 2021

ABSTRACT
Xenopus embryos were transferred into media containing aphidicolin at late blastula, mid-gastrula, and early neurula stages. In each case, embryos continued to differentiate in the absence of DNA replication. When the inhibitor was added at late blastula, embryos continued to develop for about 8h. However, when aphidicolin was added at the early neurula stage, development could be seen for up to 40 h after addition. The influence of replication on embryonic gene activity was studied by RNA blot analysis. Of the genes we examined only histone gene expression was down regulated by the addition of aphidicolin. The expression of various embryo-specific genes was unaffected by the lack of DNA synthesis. Even after several hours of treatment with aphidicolin, replication-inhibited tailbud and tadpole stages showed the same levels of specific mRNAs as control embryos containing 4 –5 times more DNA. We conclude that morphogenesis and embryospecific gene activity are independent of both DNA replication and a precise amount of DNA per embryo.
Aldehyde dehydrogenase is a positional marker in the retina
Authors: McCaffery Peter , Tempst Paul , Lara Gustavo , Dräger Ursula C. 
Published: April 2021

ABSTRACT
An asymmetrically distributed protein in the embryonic mouse retina was identified as an aldehyde dehydrogenase through protein microsequencing. It was characterized as a cytosolic isoform with basic isoelectric point and preference for aliphatic substrates, features that resemble those of the isoform AHD-2 which is known to oxidize retinaldehyde to retinoic acid. Immunohistochemistry with aldehyde dehydrogenase antisera showed strong labeling of the dorsal retina from the early eye vesicle stage into adulthood. In addition, optic axons originating from the dorsal retina were transiently labeled during their outgrowth phase. Whereas in the embryo the enzyme was expressed in undifferentiated cells and in neurons, in the retina of the adult mouse the asymmetrically distributed isoform was mainly expressed in Müller glia, with the number of labeled glial cells varying with retinal position.
The regulation of the cell cycle during Drosophila embryogenesis: the transition to polyteny
Authors: Smith Albert V. , Orr-Weaver Terry L. 
Published: April 2021

ABSTRACT
The process of polytenization plays a crucial role in Drosophila development, and most of the larval tissues are polytene. By analyzing the pattern of DNA replication in embryos pulse-labeled with BrdU, we show that many larval tissues undergo a transition to begin becoming polytene late in embryogenesis. Our results demonstrate that in these larval tissues polyteny results from a modified cell cycle, the endo cell cycle, in which there is only an S (synthesis) phase and a G (gap) phase. A key regulator of the mitotic cell cycle, the product of the string gene (the Drosophila homologue of cdc25), is not required for the endo cell cycle. The developmental regulation of the endo cell cycle is striking in that tissue-specific domains undergo polytene DNA replication in a dynamic pattern at defined times in embryogenesis. During subsequent rounds of the endo cell cycle in late embryogenesis and first instar larval development, the domains are subdivided and the temporal control is not as rigid. The length of the G phase varies among different tissues. By quantifying DNA content, we show that during the early polytene S phases the genome is not fully duplicated.