bluuebunny/crossref_metadata_2025_split huggingface dataset:
A role for Pax-1 as a mediator of notochordal signals during the dorsoventral specification of vertebrae
Authors: Koseki Haruhiko , Wallin Johan , Wilting Jörg , Mizutani Yoko , Kispert Andreas , Ebensperger Cecilia , Herrmann Bernhard G. , Christ Bodo , Balling Rudi 
Published: April 2021

ABSTRACT
The notochord plays an important role in the differentiation of the paraxial mesoderm and the neural tube. We have analyzed the role of the notochord in somite differentiation and subsequent formation of the vertebral column using a mouse mutant, Danforth’s short-tail (Sd). In this mutant, the skeletal phenotype is most probably a result of degeneration and subsequent loss of the notochord. The Sd gene is known to interact with undulated (un), a sclerotome mutant. Double mutants between Sd and un alleles show an increase in the severity of the defects, mainly in the ventral parts of the vertebrae. We also show that part of the Sd phenotype is strikingly similar to that of the un alleles. As un is known to be caused by a mutation in the Pax-1 gene, we analyzed Pax-1 expression in Sd embryos. In Sd embryos, Pax-1 expression is reduced, providing a potential molecular basis for the genetic interaction observed. A complete loss of Pax-1 expression in morphologically intact mesenchyme was found in the lower thoracic-lumbar region, which is phenotypically very similar to the corresponding region in a Pax-1 null mutant, Undulated short-tail. The sclerotome developmental abnormalities in Sd coincide closely, both in time and space, with notochordal changes, as determined by whole-mount T antibody staining. These findings indicate that an intact notochord is necessary for normal Pax-1 expression in sclerotome cells, which is in turn required for the formation of the ventral parts of the vertebrae. The observed correlation among structural changes of the notochord, Pax-1 expression levels and skeletal phenotypes, suggests that Pax-1 might be an intrinsic mediator of notochordal signals during the dorsoventral specification of vertebrae.
Distinct elements of the xsna promoter are required for mesodermal and ectodermal expression
Authors: Mayor Roberto , Essex Linda J. , Bennett Michael F. , Sargent Michael G. 
Published: April 2021

ABSTRACT
Xsna, the Xenopus homologue of Drosophila snail, is expressed in both mesoderm and ectoderm. Expression occurs in all mesoderm initially but is down regulated in a tissue-specific fashion at the end of gastrulation in a way that reveals the subdivision of the mesoderm before its derivatives are overtly differentiated. Xsna is also expressed in the ectoderm of the prospective neural fold from stage 11, in a distinct band of cells surrounding the prospective neural plate, which we designate the neural plate border. The deep and superficial ectoderm compartments labelled by Xsna represent the prospective neural crest and the prospective roof of the neural tube, respectively. Xsna expression persists in neural crest cells during their subsequent migration.
The role of the Xsna promoter in creating this pattern of expression has been investigated by injecting fertilised eggs with constructs containing the 5 upstream sequence of the gene fused to a reporter. An element of 115 base pairs ( 160 to 45 relative to the transcriptional start) is sufficient to drive appropriate reporter gene expression. The promoter does not contain a TATA or CAAT box and does not have a high GC content, but RNA synthesis starts precisely at 33 bases upstream to the translational start. The start sequence can be deleted so that transcription is initiated elsewhere without affecting the expression pattern. The distribution of Xsna promoter activity within the embryo, examined using -galactosidase ( -gal) fusions, is similar to that of the endogenous mRNA seen by in situ hybridisation. The contribution of elements within the 5 sequence have been assessed by comparing the expression patterns of constructs that have deletions in this region. Sequences from 112 to 97 are required for mesodermal expression and sequences from 96 to 44 are required for ectodermal expression. The behaviour of the injected promoter constructs differ in one important respect from the endogenous gene in that expression in an animal cap assay is not inducible by mesoderm-inducing factors but is inducible by cells of the vegetal pole.
Combinatorial control of touch receptor neuron expression in Caenorhabditis elegans
Authors: Mitani Shohei , Du Hongping , Hall David H. , Driscoll Monica , Chalfie Martin 
Published: April 2021

ABSTRACT
Six touch receptor neurons with distinctive morphological features sense gentle touch in Caenorhabditis elegans. Previous studies have identified three genes (lin-32, unc-86 and mec-3) that regulate touch cell development. However, since other cell types also require these genes, we suspected that other genes help restrict the expression of touch cell characteristics to the six neurons seen in the wild type. To identify such genes, we have examined mutants defective in genes required for the development of other C. elegans cells for changes in the pattern of touch cell-specific features. Mutations in seven genes either reduce (lin-14) or increase (lin-4, egl-44, egl-46, sem-4, ced-3 and ced-4) the number of touch receptor-like cells. The combinatorial action of these genes, all of which are required for the production of many cell types, restrict the number of cells expressing touch receptor characteristics in wild-type animals by acting as positive and negative regulators and by removing cells by programmed cell death.
Formation of the shoot apical meristem in Arabidopsis thaliana: an analysis of development in the wild type and in the shoot meristemless mutant
Authors: Barton M. Kathryn , Poethig R. Scott 
Published: April 2021

ABSTRACT
The primary shoot apical meristem of Arabidopsis is initiated late in embryogenesis, after the initiation of the cotyledons. We have identified a gene, called SHOOT MERISTEMLESS, which is critical for this process. shoot meristemless mutant seedlings lack a shoot apical meristem but are otherwise healthy and viable. The anatomy of mutant embryos demonstrates that the shoot meristemless-1 mutation completely blocks the initiation of the shoot apical meristem, but has no other obvious effects on embryo development. The failure of shoot meristemless tissue to regenerate shoots in tissue culture suggests that this gene regulates adventitious shoot meristem formation, as well as embryonic shoot meristem formation.
glp-1 can substitute for lin-12 in specifying cell fate decisions in Caenorhabditis elegans
Authors: Fitzgerald Kevin , Wilkinson Hilary A. , Greenwald Iva 
Published: April 2021

ABSTRACT
Members of the lin-12/Notch gene family encode receptors for intercellular signals and are found throughout the animal kingdom. In many animals, the presence of at least two lin-12/Notch genes raises the issue of the significance of this duplication and divergence. In Caenorhabditis elegans, two lin-12/Notch genes, lin-12 and glp-1, encode proteins that are 50% identical, with different numbers of epidermal growth factor-like motifs in their extracellular domains. Many of the cell fate decisions mediated by lin-12 and glp-1 are distinct. Here, we express glp-1 protein under the control of lin12 regulatory sequences in animals lacking endogenous lin-12 activity and find that glp-1 can substitute for lin12 in mediating cell fate decisions. These results imply that the lin-12 and glp-1 proteins are biochemically interchangeable, sharing common ligand and effector proteins, and that the discrete lin-12 and glp-1 mutant phenotypes result from differential gene expression. In addition, these results suggest that the duplicate lin12/Notch genes found in vertebrates may also be biochemically interchangeable.
pipsqueak, an early acting member of the posterior group of genes, affects vasa level and germ cell-somatic cell interaction in the developing egg chamber
Authors: Siegel Vivian , Jongens Thomas A. , Jan Lily Yeh , Jan Yuh Nung 
Published: April 2021

ABSTRACT
We have identified a new member of the posterior group of genes, which we call pipsqueak. We show that pipsqueak acts after the establishment of the oskar posterior anchor but before the localization of vasa protein during oogenesis. Characterization of multiple alleles at the pipsqueak locus shows that pipsqueak, like vasa, is required for early stages of oogenesis, including but not limited to formation of the egg chamber and progression through Stage 6 of oogenesis. Genetic interaction studies suggest that pipsqueak acts at least partially through vasa; molecular studies indicate that pipsqueak affects vasa level in the ovary. We compare vasa and pipsqueak mutant phenotypes in order to determine whether pipsqueak acts solely through vasa, and present a model for the role of pipsqueak in posterior pattern formation.
Cell patterning in the Drosophila segment: engrailed and wingless antigen distributions in segment polarity mutant embryos
Authors: van de Heuvel Marcel , Klingensmith John , Perrimon Norbert , Nusse Roel 
Published: April 2021

ABSTRACT
By a complex and little understood mechanism, segment polarity genes control patterning in each segment of the Drosophila embryo. During this process, cell to cell communication plays a pivotal role and is under direct control of the products of segment polarity genes. Many of the cloned segment polarity genes have been found to be highly conserved in evolution, providing a model system for cellular interactions in other organisms. In Drosophila, two of these genes, engrailed and wingless, are expressed on either side of the parasegment border. wingless encodes a secreted molecule and engrailed a nuclear protein with a homeobox. Maintenance of engrailed expression is dependent on wingless and vice versa. To investigate the role of other segment polarity genes in the mutual control between these two genes, we have examined wingless and engrailed protein distribution in embryos mutant for each of the segment polarity genes.
In embryos mutant for armadillo, dishevelled and porcupine, the changes in engrailed expression are identical to those in wingless mutant embryos, suggesting that their gene products act in the wingless pathway. In embryos mutant for hedgehog, fused, cubitus inter- ruptus Dominant and gooseberry, expression of engrailed is affected to varying degrees. However wingless expression in the latter group decays in a similar way earlier than engrailed expression, indicating that these gene products might function in the maintenance of wingless expression. Using double mutant embryos, epistatic relationships between some segment polarity genes have been established. We present a model showing a current view of segment polarity gene interactions.
Cell fate patterning during C. elegans vulval development
Authors: Hill Russell J. , Sternberg Paul W. 
Published: April 2021

ABSTRACT
Precursor cells of the vulva of the C. elegcuis hermaphrodite choose between two vulval cell fates (1°and 2°) and a non-vulval epidermal fate (3°) in response to three intercellular signals. An inductive signal produced by the anchor cell induces the vulval precursors to assume the 1 and 2 vulval fates. This inductive signal is an EGF-like growth factor encoded by the gene lin-3. An inhibitory signal mediated by lin-/5, and which may originate from the surrounding epidermis, prevents the vulval precursors from assuming vulval fates in the absence of the inductive signal. A short range lateral signal, which acts through the gene lin-12, regulates the pattern of 1°and 2° fates assumed by the induced vulval precursors.
The combined action of the three signals precisely directs the six vulval precursors to adopt a 3° 3° 2° 1° 2° 3° pattern of fates. The amount of inductive signal produced by the anchor cell appears to determine the number of vulval precursors that assume vulval fates. The three induced vulval precursors most proximal to the anchor cell are proposed to adopt the 2° 1° 2° pattern of fates in response to a gradient of the inductive signal and also in response to lateral signalling that inhibits adjacent vulval precursor cells from both assuming the 1°fate.
Dry mass, lipid content and protein content of the intact and zona-free mouse ovum
Authors: Loewenstein Joseph E. , Cohen Adolph I. 
Published: April 2021

ABSTRACT
Intact and zona-free single-celled mouse ova were analyzed for total protein and were dried and weighed on a quartz fiber fishpole balance before and after lipid extraction. The zona pellucida was found to contribute 19 per cent, of the dry mass of the intact ovum. It was estimated to be 96 per cent, water and 4 per cent, solid matter, of which 30 per cent, was protein. No statistically significant amount of lipid was found. The cytoplasm was estimated to be 85 per cent, water and 15 per cent, solid matter, of which 12·5 per cent, was lipid and 71 per cent, protein. The lipid content was no greater than that of protoplasm from other sources, indicating the presence of only a small amount of yolk. The cytoplasm was found to be less variable in mass than the zona pellucida.
Developmental abnormalities in the head region of the talpid3 mutant of the fowl
Authors: Ede D. A. , Kelly W. A. 
Published: April 2021

ABSTRACT
The inherited abnormality talpid3 in the fowl causes embryonic death on or before the 14th day of incubation, and developmental defects have been observed to appear on the 2nd day. Abnormalities in the head region include a tendency for the eyes to be drawn together in the mid-line, and absence of the upper beak. Rathke’s pouch is abnormal or absent, and in some cases ectopic lenses are produced within the head. Multiple epiphyseal structures are produced from the roof and abnormal ventral evaginations from the floor of the diencephalon. The developmental interrelations of these abnormalities are described, and the possible nature of the basic developmental disturbance isdiscussed. The production of extraocular lens tissue is discussed in the light of information on lens induction in normal embryos.
Effect of various inhibitors on several enzymes and other biochemical substances in chick embryo explants
Authors: Newburgh R. W. , Clark Alice , Wilson Audrey , Scholz Marion 
Published: April 2021

ABSTRACT
Earlier studies in our laboratory indicated the predominance of pentose cycle activity in early embryos (Jolley, Cheldelin & Newburgh, 1959; Coffey, 1963). In addition a correlation was demonstrated between enzymes generating reduced triphosphopyridine nucleotide and lipid synthesis (Bieber, Cheldelin & Newburgh, 1962; Baker & Newburgh, 1963). Since several of the biosynthetic pathways involve this compound, it is conceivable that in a rapidly growing system such as the early chick embryo enzymes generating TPNH may play a major röle. We have chosen to use explants of chick embryos in an attempt to gain insight into the relation of changes of these enzymes with other chemical changes which may more directly relate to differentiation. These latter changes include synthesis of such macromolecules as DNA, RNA, hemoglobin, collagen and myosin. This method permits the addition of certain chemicals to the media such as substrates or inhibitors (Hayashi et al., 1959), allowing easy manipulation of the environment. Prior to studying the above macromolecules it seemed appropriate to study the effect of certain inhibitors on glucose-6-phosphate, 6-phosphogluconic acid and isocitric dehydrogenase. It was hoped that such information might be useful for purposes of establishing base lines of biochemical activity. The inhibitors chosen were fluorouracil, chloramphenicol and acetyl pyridine, and it will be shown that these had several rather specific effects on the enzymes studied. The first two inhibitors were chosen because of their relation to RNA or protein biosynthesis and the latter since it is an analogue of the pyridine moiety of TPN.
The ultrastructure of germ cells in foetal and neonatal male rats
Authors: Franchi L. L. , Mandl Anita M. 
Published: April 2021

ABSTRACT
Male germ cells of foetal and neonatal rats (14 · 5 days p.c. to 7 days p.p.) were examined with the electron microscope. Female germ cells of young specimens (14 · 5 to 16 · 5 days p.c.) were re-examined for comparison. Shortly after sex differentiation, male and female germ cells have many features in common. The endoplasmic reticulum in oögonia, however, is the more highly developed, while the outline of gonocytes becomes markedly more angular as development proceeds. Between 15-5 and 18-5 days p.c., mitochondria in the male aggregate at one pole of the cell; those of the female remain randomly distributed. The significance of mitochondrial ‘polarization’ is obscure, but it is possible that the process is in some way related to cessation of mitotic activity. From 18 · 5 days p.c. onwards, when mitochondria become re-distributed evenly, groups of specific organelles (A- and B-bodies) appear in the cytoplasm. Three types of B-bodies have been identified. Of these, one type resembles lysosomes. The incidence of B-bodies increases during late intra-uterine life and reaches its peak between birth and 2 days p.p. Thereafter, they become rarer, as do germ cells situated in the centre of the seminiferous cord. At this time, a high proportion of gonocytes grow cytoplasmic extensions establishing contact with the basement membrane; their nucleus and nucleolus change their shape, while their mitochondria contain more regularly arranged parallel cristae than do those of ‘unattached’ gonocytes. Cells showing these signs of ‘streaming’ or migration are believed to correspond to the ‘transitional’ cells identified under the light microscope, and to be the immediate precursors of the first generation of spermatogonia type-A. After 2 days p.p., B-bodies appear to persist almost only in those gonocytes that have failed to establish contact with the basement membrane. The possible significance of B-bodies in spontaneous degeneration and high radiosensitivity of gonocytes is discussed. A few isolated germ cells show degenerative changes during the first 3 days after birth. These frequently show swollen endoplasmic reticulum, abnormal mitochondria and an abundance of B-bodies. Widespread degeneration does not set in until about 5 days, and largely affects ‘unattached’ gonocytes at inter-phase; a few degenerating cells undergoing mitosis have been observed. Degeneration takes the form of lysis: the cell membrane ruptures, the cytoplasm streams out over a wide area, and the nucleus becomes distorted. The process by which lysing germ cells are eliminated from the testis has not been fully established. The ultrastructure of spermatogonia type-A is essentially similar to that of their precursors. Most of the small germ cells corresponding to spermatogonia type-A seen under the light microscope lie with their long axis parallel to the basement membrane.
Developmental abnormalities in the trunk and limbs of the talpid3 mutant of the fowl
Authors: Ede D. A. , Kelly W. A. 
Published: April 2021

ABSTRACT
Three talpid mutants have been described in the fowl, all of which are characterized by lethal embryonic abnormalities. As explained in a previous paper (Ede & Kelly, 1964), Cole’s talpid and talpid3 are similar in all essential respects and show striking abnormalities in the head region, whereas talpid2 has a relatively normal head. In all three, embryos surviving to 11 days and over show the following abnormalities in the trunk region: (1) The vertebral column is shortened. (2) The limbs are extremely short and the number of digits on each is greater than normal. (3) The viscera are ectopic, i.e. they protrude through the ventral body wall, which remains open. (4) Feather development is incomplete. (5) There is much subcutaneous oedema and haemorrhage. Instances of inherited polydactyly have always excited interest on account of the light they may throw on the origins and production of the pentadactyl limb pattern in typical vertebrate embryos. The talpid mutants are particularly interesting in this respect since the effect on limb development is much more drastic than in other cases of inherited polydactyly in the fowl, producing a totally different pattern rather than simply duplicating one of the digits as in polydactyly (Po), duplicate (Pod) and diplopodia (dp) (reviewed by Hutt, 1949). Also, unlike these other mutants in which other structures are affected only to a very minor degree, the effect of the talpid genes is extremely pleiotropic, producing widespread developmental disturbances. The unravelling of complex pleiotropic patterns of damage has long been established as a powerful technique of embryological investigation, especially by Grüneberg in many studies on mouse mutants (reviewed by Grüneberg, 1963). In these studies it is postulated that gene action is unitary, and that by establishing a ‘pedigree of causes’ the primary action of the gene, producing the primary defect from which all the others ultimately arise, is revealed. In this paper the development of the abnormalities in the trunk and limbs of talpid3 is analysed with a view to discovering the connexions between them and relating them to the abnormalities of the head region. The basic defect appears to lie in some disturbance of the mesenchyme, affecting its segregation into mesenchymal condensations, and later the formation within it of cartilage and bone. It is hoped that further work will test this hypothesis, and give more precise information about the fundamental developmental disturbances.
The rôle of tissue organization in the differentiation of embryonic chick neural retina
Authors: Peck D. 
Published: April 2021

ABSTRACT
Neural retina from chick embryos 6 to 14 day incubation was cultured either as intact fragments or as populations of dispersed cells following enzymatic dissociation into a suspension of single cells. Within 10 to 24 hr., 95 to 100 per cent, of the cells cultured as populations of dispersed cells transformed into pigmented cells reminiscent of, but not identical to, those of pigmented retina. This transformation did not occur in intact fragments of neural retina similarly cultured. The nature of the mechanism by which the transformation occurs has been experimentally investigated. The results indicate that some unstable inhibitor of tyrosinase may be responsible for the unorthodox differentiation of these cells.
The rôle of neurohumours in early embryogenesis. : I. Serotonin content of developing embryos of sea urchin and loach
Authors: Buznikov G. A. , Chudakova I. V. , Zvezdina N. D. 
Published: April 2021

ABSTRACT
Serotonin (5-hydroxytryptamine, 5-HT) is shown to be present in early embryos of Deuterostomia, in the sea urchin Strongylocentrotus dröbachiensis, and in a teleost—the loach Misgurnus fossilis. 5-HT is found in mature unfertilized eggs of S. dröbachiensis’, soon after fertilization the concentration of this substance rises sharply, while the first four cleavage divisions are accompanied by rhythmical rises in 5-HT content. In the early blastula 5-HT concentration is low, it rises somewhat in the mid- and late blastula and at the beginning of gastrulation, dropping again in the late gastrula to zero. Pluteus formation is accompanied by the resumption of 5-HT synthesis. 5-HT seems to appear in the loach eggs within the first minutes of fertilization. The first three cleavage divisions are accompanied by sharp fluctuations of 5-HT content, although no distinct synchrony could be found between the 5-HT rises and divisions in this case. Up to the stage of the late blastula no 5-HT is found. Two high 5-HT peaks are observed during gastrulation. From this and earlier work the suggestion is put forward that 5-HT is a universal participant in the processes of early embryogenesis both in Protostomia and Deuterostomia. The elucidation of the rôle of this embryonic hormone requires further investigation.