bluuebunny/crossref_metadata_2025_split huggingface dataset:
The origin of reactive oxygen species in mouse embryos cultured in vitro
Authors: Nasr-Esfahani M. Mohammad , Johnson Martin H. 
Published: April 2021

ABSTRACT
The increase in production of reactive oxygen species such as H2O2 at the G2/M phase of the second cell cycle may be related to the in vitro block to development of mouse 2-cell embryos. The occurrence of the H2O2 rise is independent of the activation of the embryonic genome and of passage through the S, G2 and M phases of the first cell cycle and G1 and M phases of the second cell cycle, but does require the activation of the unfertilized oocyte. The H2O2 is produced via dismutation of superoxide by the enzyme superoxide dismutase. Production of superoxide via mitochondrial, NADPH-oxidase and xanthine/xanthine oxidase systems has been investigated. The evidence suggests that superoxide, and thereby H2O2, is produced by the xanthine/xanthine oxidase system, but an involvement of the other superoxide generating systems has not been excluded. The relation between H2O2 and development in vitro is discussed.
Hox-7 expression during murine craniofacial development
Authors: Mackenzie Alasdair , Ferguson Mark W. J. , Sharpe Paul T. 
Published: April 2021

ABSTRACT
We have used in situ hybridisation to establish the temporal and spatial expression patterns of the mouse homeobox-containing gene; Hox-7, in the developing embryonic cranium and nervous system of the mouse between embryonic days 9.5 (E9.5) and E15.5. Hox-7 has previously been associated with areas of mesenchymal – epithelial interaction and cell migration especially in neural crest ectomesenchymal cells. Aside from the expression patterns seen in the facial anlage at E9.5, Hox-7 transcripts were also detected in the neuroepithelium including cells of the dorsal midline of the neural tube. This expression pattern persisted throughout the embryonic time span studied. At E11.5, expression of Hox-7 became obvious in the neuroepithelium of the forming tela choroida and the telencephelii in areas destined to form the choroid plexus before any atrophy of the neuroepithelium took place. High expression of Hox-7 was also present in the mesenchyme cells invading the pouch formed by the involuting choroid plexus neuroepithelium. A second major site where Hox-7 was expressed was the anlage of the anterior pituitary; the Rathke’s pouch. Expression became obvious at E10.5 throughout the pouch but by E12.5 became more regionalised in areas of the pouch destined to form the pars distalis. Hox-7 was also expressed in the forming meninges and skull bone precursors from E10.5 onwards. Expression of the Hox-7 gene is also seen in the external ear, the forming eye, the nasal pits and forming Jacobson’s organs.
When these expression patterns are considered together with characterised human and mouse retinoic acid embryopathies and the congenital malformations seen in human children associated with deletion of chromosome 4pl6.1 (Wolf-Hirschhorn syndrome), Hox-7 may be a good candidate as one of the genes involved in the initiation of the choroid plexus phenotype and its subsequent formation, the formation of the outer ear, formation of the dentition and the differentiation of the cell types of the anterior pituitary. The expression pattern of Hox-7 in the dorsal midline of the neural tube further suggests that it may also be involved in the specification of the dorsal-ventral axis of the developing nervous system.
Perturbation of neuronal differentiation and axon guidance in the spinal cord of mouse embryos lacking a floor plate: analysis of Danforth’s shorttail mutation
Authors: Bovolenta Paola , Dodd Jane 
Published: April 2021

ABSTRACT
The floor plate of the vertebrate nervous system has been implicated in the guidance of commissural axons at the ventral midline. Experiments in chick have also suggested that at earlier stages of development the floor plate induces the differentiation of motor neurons and other neurons of the ventral spinal cord. Here we have examined the development of the spinal cord in a mouse mutant, Danforth’s short-tail, in which the floor plate is absent from caudal regions of the neuraxis. In affected regions of the spinal cord, commissural axons exhibited aberrant projection patterns as they reached and crossed the ventral midline. In addition, motor neurons were absent or markedly reduced in number in regions of the spinal cord lacking a floor plate. Our results suggest that the floor plate is indeed an intermediate target in the projection of commissural axons and support the idea that several different mechanisms operate in concert in the guidance of axons to their cellular targets in the developing nervous system. In addition, these experiments suggest that the mechanisms that govern the differentiation of the floor plate and other ventral cell types in the neural tube are common to mammals and lower vertebrates.
Early ablation of target muscles modulates the arborisation pattern of an identified embryonic Drosophila motor axon
Authors: Sink Helen , Whitington Paul M. 
Published: April 2021

ABSTRACT
The Drosophila RP3 motor axon establishes a stereotypic arborisation along the adjoining edges of muscles 6 and 7 by the end of embryogenesis. The present study has examined the role of the target muscles in determining this axonal arborisation pattern. Target muscles were surgically ablated prior to the arrival of the RP3 axon. Following further development of the embryo in culture medium, the morphology of target-deprived RP3 motor axons was assayed by intracellular injection with the dye Lucifer Yellow. Axonal arborisations were formed on a variety of non-target muscles when muscles 6 and 7 were removed and these contacts were maintained into stage 16. The pattern of axonal arborisations over non-target muscles varied between preparations in terms of the number of muscles contacted, and the distribution of arborisations on individual muscles. Following removal of muscle 6, the RP3 motor axon frequently contacted muscle 7, and axonal arborisations were present along the distal edge of the muscle. In the absence of muscle 7, the RP3 axon often did not contact muscle 6 and when muscle 6 was contacted, the arborisation of RP3 was poorly developed. Axonal processes were retained on non-target muscles when only one target muscle was present. Therefore, the establishment of a stereotypic arborisation by the RP3 motor axon is apparently dependent on growth cone contact with both target muscles.
Control of expression of the homeotic labial (lab) locus of Drosophila melanogaster. evidence for both positive and negative autogenous regulation
Authors: Chouinard Scott , Kaufman Thomas C. 
Published: April 2021

ABSTRACT
The homeotic gene labial (lab) is required for proper development of the embryonic and adult head in Drosophila melanogaster. The lab gene product accumulates in a complex pattern in both embryonic and imaginal tissue. During embryogenesis, lab is expressed in the endodermally derived cells of the midgut, in ectodermally derived cells of the procephalon and dorsal ridge, and in a small subset of progenitor sensory cells. imaginal expression is restricted to a narrow region of the peripodial membrane of the eye-antennal disc. As part of our continuing effort to understand the role of lab in development, we have begun a dissection of the regulatory elements of the lab transcription unit and used germ line transformation experiments to determine which aspects of the observed expression pattern are essential for proper head development and viability. Transgenic embryos harboring an abridged lab gene are able to overcome the embryonic lethality associated with the loss of lab function and survive to adulthood. Interestingly, in these transgenic lines the lab protein accumulates only in a subset of those embryonic cells that normally express the gene, namely the procephalon and the anterior midgut. We also find that, once initiated, lab expression is maintained by positive autoregulation. Although lab minigene activity is sufficient to rescue the embryonic lethality of lab mutations, the transgenes fail to rescue defects in the adult head capsule. However, the defects observed in this study encompass a broader domain than those seen using somatic recombination to generate lab−1 clonal tissue. The failed rescue and observed cuticular defects are, at least in part, explained by the observation that the transgenes, rather than failing to be expressed, are associated with ectopic accumulation of lab protein in the peripodial membrane of the antennal disc. Moreover, this aberrant expression pattern is correlated with the abnormal expression of two other homeotic genes, Deformed (Dfd) and Sex combs reduced (Scr) in the eye-antennal disc. These results are only observed when the transgene is resident in a lab− genotype and ectopic expression of lab and misregulation of Dfd and Scr are not seen in a lab+ background. This result suggests that the wild-type lab gene product is necessary for the normal regulation of the locus in the imaginal discs, but unlike the case in the embryo, the event is negative. We discuss the biological implications of these results in relation to the role of lab in development.
Hensen’s node induces neural tissue in Xenopus ectoderm. Implications for the action of the organizer in neural induction
Authors: Kintner C. R. , Dodd J. 
Published: April 2021

ABSTRACT
The development of the vertebrate nervous system is initiated in amphibia by inductive interactions between ectoderm and a region of the embryo called the organizer. The organizer tissue in the dorsal lip of the blastopore of Xenopus and Hensen’s node in chick embryos have similar neural inducing properties when transplanted into ectopic sites in their respective embryos. To begin to determine the nature of the inducing signals of the organizer and whether they are conserved across species we have examined the ability of Hensen’s node to induce neural tissue in Xenopus ectoderm. We show that Hensen’s node induces large amounts of neural tissue in Xenopus ectoderm. Neural induction proceeds in the absence of mesodermal differentiation and is accompanied by tissue movements which may reflect notoplate induction. The competence of the ectoderm to respond to Hensen’s node extends much later in development than that to activin-A or to induction by vegetal cells, and parallels the extended competence to neural induction by axial mesoderm. The actions of activin-A and Hensen’s node are further distinguished by their effects on lithium-treated ectoderm. These results suggest that neural induction can occur efficiently in response to inducing signals from organizer tissue arrested at a stage prior to gastrulation, and that such early interactions in the blastula may be an important component of neural induction in vertebrate embryos.
Determination of the embryonic axes of Drosophila*
Authors: Nüsslein-Volhard Christiane 
Published: April 2021

Abstract
The principles of embryonic pattern formation have been studied extensively in many systems using classical experimental approaches. In Drosophila, a powerful combination of genetics and transplantation experiments, as well as molecular biology, have helped to elucidate the mechanisms that operate during oogenesis and early embryogenesis to establish a set of positional cues required for axis determination in the early embryo.
In systematic searches for maternal effect mutations a small number of about 30 genes have been identified that specifically affect the process of determination of the embryonic axes. These ‘coordinate’ genes define four systems that determine the anteroposterior (AP) axis (three systems) and the dorsoventral (DV) axis (one system) independently. In the anteroposterior axis, the anterior system determines the segmented region of head and thorax, the posterior system determines the segmented abdominal region, and the terminal system is responsible for the formation of the nonsegmented termini at the anterior and posterior egg tips, the acron and telson. In contrast, pattern along the dorsoventral axis is determined by one system only. Although all four systems use different biochemical mechanisms, they share several properties. (1) The product of one gene in each system is localized in a specific region of the freshly laid egg and functions as a spatial signal. (2) In each system, this spatial information finally results in the asymmetrical distribution of one gene product that functions as a transcription factor. (3) This transcription factor is distributed in a concentration gradient that defines the spatial limits of expression of one or more zygotic target genes.
The combined action of these three anteroposterior systems as well as the dorsoventral system defines the expression of zygotic target genes in at least seven distinct regions along the anteroposterior and at least three in the dorsoventral axis. These longitudinal and transverse domains provide a coarse spatial prepattern which is then further refined by the action and interaction of zygotic pattern genes.
A genetic and molecular model for flower development in Arabidopsis thaliana
Authors: Meyerowitz Elliot M. , Bowman John L. , Brockman Laura L. , Drews Gary N. , Jack Thomas , Sieburth Leslie E. , Weigel Detlef 
Published: April 2021

Abstract
Cells in developing organisms do not only differentiate, they differentiate in defined patterns. A striking example is the differentiation of flowers, which in most plant families consist of four types of organs: sepals, petals, stamens and carpels, each composed of characteristic cell types. In the families of flowering plants in which these organs occur, they are patterned with the sepals in the outermost whorl or whorls of the flower, with the petals next closest to the center, the stamens even closer to the center, and the carpels central. in each species of flowering plant the disposition and number (or range of numbers) of these organs is also specified, and the floral ‘formula’ is repeated in each of the flowers on each individual plant of the species. We do not know how cells in developing plants determine their position, and in response to this determination differentiate to the cell types appropriate for that position. While there have been a number of speculative proposals for the mechanism of organ specification in flowers (Goethe, 1790; Goebel, 1900; Heslop-Harrison, 1964; Green,1988), recent genetic evidence is inconsistent with all of them, at least in the forms in which they were originally presented (Bowman et al. 1989; Meyerowitz et al. 1989). We describe here a preliminary model, based on experiments with Arabidopsis thaliana. The model is by and large consistent with existing evidence, and has predicted the results of a number of genetic and molecular experiments that have been recently performed.
How does the cytoskeleton read the laws of geometry in aligning the division plane of plant cells?
Authors: Lloyd Clive W. 
Published: April 2021

Abstract
Since Robert Hooke observed the froth-like texture of sectioned plant tissue, there have been numerous attempts to describe the geometrical properties of cells and to account for the patterns they form. Some aspects of biological patterning can be mimicked by compressed spheres and by liquid foams, implying that compression or surface tension are physical bases of patterning.
The 14-sided semi-regular tetrakaidecahedron encloses a given volume most efficiently and packs to fill space. However, observations of real plant tissue (and of soap bubbles) in the first half of this century established that plant cells only rarely form this mathematically ideal figure composed predominantly of 6-sided polygons. Instead, they tend to form a topologically transformed variant having mainly pentagonal faces although there is variability in the number of sides and the angles formed. But the one irreducible component of normal cell and tissue geometry is that only three edges meet at a point in a plane. In solid space, this gives rise to tetrahedral junctions and it is from this that certain limitations on sidedness flow. For three edges to meet at a point means that there must be an avoidance mechanism which prevents a new cell plate from aligning with an existing 3-way junction. Sinnott and Bloch (1940) saw that the cytoplasmic strands which precede the cell plate, predicted its alignment and also avoided 3-way junctions in unwounded tissues. Recently, F-actin and microtubules have been detected in these pre-mitotic, transvacuolar strands. The question considered here is why those cytoskeletal elements avoid aligning with the vertex where a neighbouring cross wall has already joined the mother wall. An hypothesis is discussed in which tensile strands - against a background of cortical re-organization during pre-mitosis - tend to seek the minimal path between nucleus and cortex. In this way, it is suggested that unstable strands are gradually drawn into a transvacuolar baffle (the phragmosome) within which cell division occurs. Vertices are avoided by the strands because they constitute unfavoured longer paths. The demonstrable tendency of tensile strands to contact mother walls perpendicularly would seem to account for Hofmeister’s and Sachs’ rules involving right-angled junctions. As others have discussed, such right-angled junctions give way to co-equal 120°angles between the three walls during subsequent cell growth. It is this asynchrony of cell division - where attachment of a cell plate causes the neighbouring wall to buckle - that forms a vertex to be avoided by subsequent pre-mitotic strands in that neighbouring cell. In this way, successive division planes would not co-align. It is therefore suggested that the exceptional formation of 4-way junctions in wounded tissue results from the fact that adjacent cells divide simultaneously; the lack of prebuckling of a common wall under these circumstances means that there is no vertex to be avoided by the minimal path mechanism.
Cell polarity and tissue patterning in plants
Authors: Sachs Tsvi 
Published: April 2021

Abstract
Cell polarization is the specialization of developmental events along one orientation or one direction. Such polarization must be an early, essential stage of tissue patterning. The specification of orientation could not occur only at the level of the genetic system and it must express a coordination of events in many cells. There is a positive feedback relation between cell polarization and the transport of the known hormone auxin: polarity determines oriented auxin transport while transport itself induces both new and continued polarization. Since cell polarization increases gradually, this feedback leads to the canalization of transport - and of the associated cell differentiation - along defined strands of specialized cells. Recent work has shown that the same canalized flow can also be an important determinant of cell shape. In primordial, embryonic regions cell growth is oriented along the flow of auxin from the shoot towards the root. In later developmental stages the cells respond to the same flow by growing in girth, presumably adjusting the capacity of the tissues to the flow of signals. Finally, disrupted flow near wounds results in the development of relatively unorganized callus. Continued callus development appears to require the participation of the cells, as sources and sinks of auxin and other signals. The overall picture to emerge suggests that cell patterning can result from competition between cells acting as preferred channels, sources and sinks for developmental signals.
Development of the spatial pattern of retinoic acid receptor-β transcripts in embryonic chick facial primordia
Authors: Rowe Annie , Richman Joy M. , Brickell Paul M. 
Published: April 2021

ABSTRACT
Retinoic acid causes a range of embryonic defects, including craniofacial abnormalities, in both birds and mammals and is believed to have a number of roles in normal development. We have previously shown that the distribution of retinoic acid receptor-β (RAR-β transcripts is spatially restricted within the neural-crestderived upper beak primordia of the chick embryo. We have now used in situ hybridisation to trace the distribution of RAR-β transcripts during the migration of cranial neural crest cells and during formation of these primordia.
RAR-β transcripts were present in a subset of migrating neural-crest-derived cells in the head of the stage 10 embryo. These cells were situated in pathways followed by cells that migrate from the neural crest overlying the posterior prosencephalic/anterior mesencephalic region of the developing brain. Cells containing RAR-β transcripts accumulated around the developing eyes and in the regions of the ventral head from which the upper beak primordia later develop. We mapped the distribution of RAR-β transcripts as the facial primordia were forming, with particular reference to the development of the maxillary primordia. We found that these form in a region of the ventral head that includes the boundary between regions of high and low levels of RAR-β transcripts. The boundary between these two groups of cells persisted as the maxillary primordia developed.
The restriction of RAR-β transcripts to a subset of migrating neural crest cells which arise from a specific region of the neural crest, and which give rise to precisely distributed populations of cells, provides further evidence that there is some form of prepatterning in the neural crest from which the facial primordia originate.
c-ros: the vertebrate homolog of the sevenless tyrosine kinase receptor is tightly regulated during organogenesis in mouse embryonic development*
Authors: Tessarollo Lino , Nagarajan Lalitha , Parada Luis F. 
Published: April 2021

Abstract
The c-ros proto-oncogene is the vertebrate homologue of the Drosophila sevenless tyrosine kinase receptor. Examination of c-ros mRNA transcripts in the mouse embryo reveals a stringent pattern of expression. Only kidney, intestine and lung exhibit ros-specific RNA using sensitive techniques such as RNAse protection and in situ hybridization. The temporal and spatial arrangement of c-ros transcripts is coincident with the phenotypic induction and proliferation of epithelium during organogenesis of the kidney and intestine. The data provide evidence for a role of c-ros in the obligate cell-cell interactions that characterize the morphogenic induction and proliferation of epithelial cells in the kidney, intestine and lung. The c-ros tyrosine kinase receptor may provide a signal transduction pathway for epithelial-mesenchymal interactions.
The prion protein gene: a role in mouse embryogenesis?
Authors: Manson J. , West J. D. , Thomson V. , Mcbride P. , Kaufman M. H. , Hope J. 
Published: April 2021

Abstract
The neural membrane glycoprotein PrP (prion protein) has a key role in the development of scrapie and related neurodegenerative diseases. During pathogenesis, PrP accumulates in and around cells of the brain from which it can be isolated in a disease-specific, protease-resistant form. Although the involvement of PrP in the pathology of these diseases has long been known, the normal function of PrP remains unknown. Previous studies have shown that the PrP gene is expressed tissue specifically in adult animals, the highest levels in the brain, with intermediate levels in heart and lung and low levels in spleen. Prenatally, PrP mRNA has been detected in the brain of rat and hamster just prior to birth. In this study we have examined the expression of the PrP gene during mouse embryonic development by in situ hybridization and observed dramatic regional and temporal gene expression in the embryo. Transcripts were detected in developing brain and spinal cord by 13.5 days. In addition, PrP gene expression was detected in the peripheral nervous system, in ganglia and nerve trunks of the sympathetic nervous system and neural cell populations of sensory organs. Expression of the PrP gene was not limited to neuronal cells, but was also detected in specific non-neuronal cell populations of the 13.5 and 16.5 day embryos and in extra-embryonic tissues from 6.5 days. This cell-specific expression suggests a pleiotropic role for PrP during development.