bluuebunny/crossref_metadata_2025_split huggingface dataset:
Expression of the Drosophila gonadal gene: alternative promoters control the germ-line expression of monocistronic and bicistronic gene transcripts
Authors: Schulz Robert A. , Miksch Jennifer L. , Xie Xiaoling , Cornish Judith A. , Galewsky Samuel 
Published: April 2021

Abstract
The Drosophila gonadal (gdl) gene is differentially expressed in the male and female germ lines. In males, expression in the gdl™ mode results in a 1200-/1500-nucleotide RNA pair, whereas in females, expression in the gdlF mode results in a 1000-/1300-nucleotide RNA pair. Since the two expression modes are a result of alternative promoter usage, the sex-specific transcripts differ at their 5’ ends. These sequence differences affect the coding capacity of the gene. A common open reading frame (ORF) of 193 codons (ORF193) is present in all four gdl transcripts; a consequence of the additional sequences at the 5’ end of the gdlM transcripts is the presence of an additional ORF of 39 codons (ORF39). Translation of gdlF and gdlM cRNAs in a reticulocyte lysate reveals that these transcripts can serve as mono-cistronic and bicistronic mRNAs in vitro. An analysis of germ-line transformants harboring gdl-lacZ gene fusions provides information on gdl gene expression during gametogenesis. The fusion genes are transcribed and translated in the germ line; β-galactosidase activity is detected in premeiotic and postmeiotic spermatogenic stages in males, and in nurse cells and oocytes of developing egg chambers in females. Both gdl™ ORFs are used because transformant lines expressing the lacZ gene, fused in frame with either ORF39 or ORF193, are positive for β-galactosidase activity in the testes. These studies also reveal that separable transcription control elements are responsible for gdl expression in the male and female germ lines.
Topographical control of cell behaviour: II. multiple grooved substrata
Authors: Clark P. , Connolly P. , Curtis A. S. G. , Dow J. A. T. , Wilkinson C. D. W. 
Published: April 2021

ABSTRACT
Electronics miniaturisation techniques have been used to fabricate substrata to study contact guidance of cells. Topographical guidance of three cell types (BHK, MDCK and chick embryo cerebral neurones) was examined on grooved substrata of varying dimensions (4-24 μm repeat, 0.2-1.9 μm depth). Alignment to within 10° of groove direction was used as our criterion for guidance. It was found that repeat spacing had a small effect (alignment is inversely proportional to spacing) but that groove depth proved to be much more important in determining cell alignment, which increased with depth. Measurements of cell alignment and examination by scanning electron microscopy showed that BHK cells and MDCK cells interacted differently with grooved substrata, and also that the response of MDCK cells depended on whether or not the cells were isolated or part of an epithelial cell island. Guidance by a multiple topographical cue is greater than could be predicted from cells’ reactions to a single cue (Clark et al. Development 99: 439-448, 1987). Substratum topography is considered to be an important cue in many developmental processes. Cellular properties such as cytoskeletal organisation, cell adhesion and the interaction with other cells are discussed as being factors determining a cells susceptibility to topography.
The Xenopus MyoD gene: an unlocalised maternal mRNA predates lineage- restricted expression in the early embryo
Authors: Harvey Richard P. 
Published: April 2021

Abstract
Expression of the mouse MyoD gene appears to represent a critical point in the commitment of cultured cells to muscle. In Xenopus, myogenic commitment begins during mesoderm induction which is initiated early in development by endogenous growth factors. To study MyoD gene expression during induction, a Xenopus MyoD gene and homologous cDNAs were selected from Xenopus libraries and analysed. Two different cDNAs have been sequenced. They code for proteins closely related to each other and to mouse MyoD and are likely to be expressed from duplicated Xenopus MyoD genes. Surprisingly, MyoD mRNA is first detected during oogenesis and the maternal species is not localized exclusively to the region of the blastula fated to muscle. Zygotic MyoD mRNA accumulates slowly above maternal levels beginning at the MBT and new transcripts are localized to the somitic mesoderm. Expression outside of somites has been detected in developing heads of tailbud embryos and can be induced in blastula animal pole expiants treated with mesoderm-inducing factors. The early expression of MyoD in Xenopus development suggests that it may play a part in the induction of muscle mesoderm and generally strengthens the evidence that MyoD is determinative in muscle commitment. In addition, the initiation of MyoD transcription at the MBT and its stimulation by mesoderm-inducing factors implies that MyoD gene expression is an immediate early response to mesoderm induction.
Identification of early developing axon projections from spinal interneurons in the chick embryo with a neuron specific β-tubulin antibody: evidence for a new ‘pioneer’ pathway in the spinal cord
Authors: Yaginuma Hiroyuki , Shiga Takashi , Homma Shunsaku , Ishihara Rieko , Oppenheim Ronald W. 
Published: April 2021

Abstract
The early development of interneurons in the chick embryo spinal cord was studied using a monoclonal antibody against a neuron-specific β-tubulin isoform. Early developing interneurons were divided into two cell groups on the basis of their location and the pattern of growth of their axons. One group is composed of cells that establish a primitive longitudinal pathway (PL-cells), whereas the other group contains cells constituting a circumferential pathway (C-cells). The onset of axonal development in both cell groups occurs at stage (st.) 15 (embryonic day, (E), 2) in the brachial segments, which is prior to axonogenesis of motoneurons. PL-cells develop in the region between the floor plate and the motoneuron nucleus. Their axons are the first neuronal processes (‘pioneer axons’) to arrive in the ventrolateral marginal zone and they project both rostrally and caudally to establish a primitive longitudinal association pathway at the ventrolateral surface of the neural tube. This pathway is formed before axons of C-cells arrive in the ventrolateral region. The first C-cells are initially located in the most dorsal portion of the neural tube, whereas later appearing C-cells are also located in both intermediate and ventral regions of the neural tube. The axons of C-cells project ventrally, without fasciculating, along the lateral border of the neural tube. Some of their axons enter the ipsilateral ventrolateral longitudinal pathway at st. 17. We often observed apparent contacts and interactions between preexisting axons of PL-cells and newly arriving axons of C-cells. The axons of commissural C-cells first enter the floor plate at st. 17 and cross the midline at st. 18. Axons of C cells begin to join the contralateral ventrolateral longitudinal pathway at st. 18+ to st. 19. In the floor plate region, contacts between growth cones and axons were often observed. However, axons in the floor plate at these stages were not fasciculated.
These observations establish the timing and pattern of growth of axons from two specific populations of early developing interneurons in the chick spinal cord. Additionally, we have identified an early and apparently previously undescribed ‘pioneer’ pathway that constitutes the first longitudinal pathway in the chick spinal cord.
Heterochromatization and euchromatization of whole genomes in scale insects (Coccoidea: Homoptera)
Authors: Nur Uzi 
Published: April 2021

ABSTRACT
In several families of scale insects (coccids), the sex of an embryo is determined by the number of genetically active genomes present (one=males, two=females). In mealybugs (Pseudococcidae), both males and females develop from fertilized eggs but, in the embryos that develop into males, the set of chromosomes (genome) of paternal origin (PG) becomes heterochromatic (H) and genetically inactive and is not transmitted to the offspring. The mechanism that reduces the number of active genomes in male embryos may vary between families and even between congeneric species. Thus, in male embryos of most armored scale species (Diaspididae), the PG is eliminated, while in a few species it becomes H. In two genera of soft scales (Coccidae), males develop from unfertilized eggs when one of two identical genomes of maternal origin becomes H. In most male tissues, one genome remains H. However, in several tissues that become polyploid by endoreduplication, the PG becomes E and genetically active. The tissues in which the PG becomes E often vary between species and the analysis of hybrid males demonstrated that whether the PG becomes H or remains E is determined by the genome of maternal origin. The euchromatization of the PG in the haploid sector of mosaic male embryos and the presence of spermatocytes with two E genomes (instead of one E and one H), following the irradiation of young mealybug males, strongly suggest that the maintenance of the H state requires the presence of a genetically active genome.
The development of handedness in left/right asymmetry
Authors: Brown Nigel A. , Wolpert Lewis 
Published: April 2021

ABSTRACT
The development of handed asymmetry requires a special mechanism for consistently specifying a difference between left and right sides. This is to be distinguished from both random asymmetry, and from those left/right differences that are mirror symmetrical. We propose a model for the development of handedness in bilateral animals, comprising three components. (I) A process termed conversion, in which a molecular handedness is converted into handedness at the cellular level. A specific model for this process is put forward, based on cell polarity and transport of cellular constituents by a handed molecule. (Ii) A mechanism for random generation of asymmetry, which could involve a reaction-diffusion process, so that the concentration of a molecule is higher on one side than the other. The handedness generated by conversion could consistently bias this mechanism to one side. (iii) A tissue-specific interpretation process which responds to the difference between the two sides, and results in the development of different structures on the left and right. There could be direct genetic control of the direction of handedness in this model, most probably through the conversion process. Experimental evidence for the model is considered, particularly the iv mutation in the mouse, which appears to result in loss-of-function in biasing, and so asymmetry is random. The model can explain the abnormal development of handedness observed in bisected embryos of some mammalian, amphibian and sub-vertebrate species. Spiral asymmetry, as seen in spiral cleavage and in ciliates, involves only conversion of molecular asymmetry to the cellular and multicellular level, with no separate interpretation step.
The Xenopus XIHbox 6 homeo protein, a marker of posterior neural induction, is expressed in proliferating neurons
Authors: Wright Christopher V. E. , Morita Elaine A. , Wilkin Douglas J. , Robertis Eddy M. De 
Published: April 2021

ABSTRACT
XIHbox 6 is an early spatially restricted marker for molecular studies of neural induction. The sequence of the full-length XIHbox 6 protein is reported. An antibody raised against a β-galactosidase/XIHbox 6 fusion protein was used to analyze the expression of XIHbox 6 proteins during frog embryogenesis. The anterior border of XIHbox 6 expression lies just posterior of the hindbrain/spinal cord junction. Immunostalnlng extends the entire length of the spinal cord. A much weaker transient expression with a similar anterior border is observed in mesoderm. Almost all nuclei in the newly closed spinal cord contain XIHbox 6. The number of positive nuclei decreases over the next stages of development, until in later embryos XIHbox 6 is restricted to nuclei of the dividing neuroepithelium, and not the mantle or marginal zones of the spinal cord. When the limb buds begin to grow, there is a second burst of XIHbox 6 expression in proliferating neurons of the cervical and lumbar enlargements, where nerves arise that supply the limbs. The data suggest that XIHbox 6 expression is spatially and temporally restricted to immature neurons of the spinal cord, before their differentiation into mature neurons.
Permissiveness to murine leukemia virus expression during preimplantation and early postimplantation mouse development
Authors: Savatier P. , Morgenstern J. , Beddington R. S. P. 
Published: April 2021

ABSTRACT
Permissiveness to Moloney Murine Leukemia Virus (MoMuLV) expression was examined during preimplan tation and early postimplantation development of the mouse embryo. Blastocysts and 8th, 9th and 10th day postimplantation embryos were infected in vitro with a MoMuLV-based retroviral vector expressing the lacZ gene driven off an internal rat beta-actin promoter. Beta-galactosidase-positive cells were identified in all embryonic tissues including inner cell mass, epiblast, mesoderm, endoderm and definitive ectoderm. In con trast, embryos infected with a MoMuLV-based vector expressing the lacZ gene driven off the viral LTR showed beta-galactosidase-positive cells only in mesoderm and definitive ectoderm. We conclude that permissiveness to transcriptional activity of the LTR is acquired immedi ately upon differentiation of epiblast during gastrulation of the mouse embryo.
Morphological and Functional Development of the Ovary of the Mouse: I. Morphology and Histochemistry of the Developing Ovary in Normal Conditions and after FSH Treatment
Authors: Ben-Or Sarah 
Published: April 2021

ABSTRACT
Maturation and maintenance of ovarian function are under the control of the pituitary gonadotrophins. The capacity of the ovary to respond to FSH stimulation develops gradually with age, and is most pronounced when the animal approaches sexual maturity. In very young animals reactivity to gonadotrophins is found to be lacking, and up to a certain age, which is characteristic for each species, sexual maturity cannot be accelerated by exogenous gonadotrophic stimulation (for references see Price & Ortize, 1944). However, in transplantation experiments of young ovarian tissue into adult spayed hosts, the grafted ovary reaches maturity much earlier than in its normal surroundings (Goodman, 1934; Dunham, Watts & Adair, 1941).
Immunological Attack by Adult Cells in the Developing Chick Embryo: Influence of the Vascularity of the Host Spleen and of Homograft Rejection by the Embryo on Splenomegaly
Authors: Solomon J. B. , Tucker D. F. 
Published: April 2021

ABSTRACT
Adult chicken spleen was implanted on to the chorio-allantoic membrane of chick embryos at 8,9,11,13 and 15 days of incubation. The initial manifestation of graft against the host attack by these adult cells was an increase of host spleen weight (splenomegaly). No splenomegaly appeared in the embryonic hosts before 15 days of incubation. The appearance of splenomegaly roughly coincided with the appearance of reticulum cell foci in the chimaeric spleens. Varying latent periods between the time of introduction of donor cells and the first appearance of increased spleen weights necessitated comparison of the host spleen weights 3 days after the onset of splenomegaly. This showed that implantation at 13 days produced the greatest splenomegaly. Only very slight splenomegaly was obtained after implantation of spleen at 15 days. A possible homograft rejection by the host and poor ‘take’ of the splenic implant on the chorio-allantoic membrane are both thought to be responsible. Intravenous injection of adult chicken spleen cells into embryos at 6, 8, 11 and 13 days of incubation again produced no splenomegaly before 15 days of incubation. Comparison of the host spleen weights 3 days after onset of splenomegaly showed that injection at 13–15 days gave the greatest splenomegaly. Injection before this time gave very slight splenomegaly and injections after 13 days produced a decreasing degree of splenomegaly with increasing age of embryo injected. Increasing the number of adult spleen cells at 15 days or giving large doses of blood at 8, 9, 11, 15 and 17 days of incubation and in the 1-and 2-day-old chick failed to increase the splenomegaly greatly or markedly to alter the above pattern. When 1-day-old chicks were injected with allogenic blood only slight splenomegaly occurred and when 2-day-old chicks were injected there was no splenomegaly 6 days later. The suitability of the chick embryo as an environment for the proliferation of immunologically competent cells is discussed. The reduction in splenomegaly when embryos older than 13-15 days are injected is discussed in relation to the appearance from this time of a weak homograft response by the embryo and to the greater difficulty of induction of both splenomegaly and tolerance to skin grafts soon after hatching. It is proposed that very small numbers of immunologically competent cells appear in the embryo soon after 15 days and progressively increase from this time until onset of competence of the host at 10 days post-hatching. Possible effects of such cell growth on the degree of induction of tolerance are discussed.
The Culture of Small Aggregates of Amphibian Embryonic Cells in vitro
Authors: Jones K. W. , Elsdale T. R. 
Published: April 2021

ABSTRACT
Methods are described for the short term culture of disaggregated amphibian embryonic cells in a medium consisting of about 0·1 per cent protein in Steinberg’s physiological salt solution. In a medium containing whole serum or serum protein cells differentiate according to their presumptive fate in the embryo. The use of a particle-free extract of mouse bone marrow causes ectoderm cells to develop as mesoderm. Gastrula ectoderm cells will differentiate ciliated epidermis providing they are permitted to reaggregate into balls of about thirty cells and upwards. Gastrula mesoderm cells and induced ectoderm cells likewise do not differentiate unless aggregated, but the majority of aggregates fail to differentiate. This seems to be because these cells have exacting requirements for precise concentrations of the protein component in the medium. There is some variation between species in this respect, and requirements vary between ovulations in the case of Rana pipiens and Xenopus laevis. Ciliated epidermal cells differentiate in cohesive balls that detach from the glass. All other cell types differentiate as thin outgrowths of cells attached to the glass by cytoplasmic fringes or pseudopodia. The first visible event in the differentiation of non-epidermal cells is their attachment to the glass by pseudopodia or cytoplasmic fringes, and the rapid expansion of these contributes to the deformation of the cell from the spherical embryonic form to that approximating to the form of the differentiated cell. This rapid change in form and activity is termed germination. It appears to be a necessary preliminary for cytodifferentiation, the rapid utilization of yolk and the build up of large mitochondrial populations. Germination precedes the formation of striated muscle fibres, vacuoles in chordal cells and other indications of cytodifferentiation by a time interval that is characteristic for each cell type within a species. The time and order in which cells differentiate in culture is related to the behaviour of comparable cells in the embryo. It is concluded that, by the neurula stage, the control of the time of germination is vested in the individual cells. It is concluded that the development of neural and mesodermal cells involves two necessary periods of decisive change, one at the end of gastrulation unconnected with any gross morphological changes in the cells, the second, closely following neural closure and involving the in vivo counterpart of germination in culture, by which the potentialities of the cells are mobilized in the interests of cytodifferentiation. Both these important epigenetic events coincide with changes in the adhesive properties of cells.
The Effects of β-Mercaptoethanol on the Morphogenetic Movements of Amphibian Embryos
Authors: Malpoix P. , Quertier J. , Brachet J. 
Published: April 2021

ABSTRACT
Explant systems and vital staining have been used to study the specific effects of various concentrations of β-mercaptoethanol on the morphogenetic movements of amphibians. Three different types of effect were observed. (a) rapid but reversible inhibition of neurulation, becoming irreversible after prolonged treatments; (b) slow, progressive inhibition of epiboly, convergent stretching and ingression; (c) very slight inhibition of invagination, occurring only at high concentrations or after prolonged treatments. The significance of these results is discussed.
The Preparation and Teratogenic Properties of Pure Trypan Blue and its Common Contaminants
Authors: Beck F. , Lloyd J. B. 
Published: April 2021

ABSTRACT
Starting with impure commercial samples of the dye, methods for the preparation of pure trypan blue and each of its chief contaminants are presented. The teratogenic component of the commercial mixture is shown to be the blue fraction, which is presumably trypan blue itself. The impurities are not active teratogens and do not modify qualitatively the teratogenic activity of the blue fraction.
Studies on Hydroid Differentiation, II. Colony Growth and the Initiation of Sexuality
Authors: Braverman Maxwell H. 
Published: April 2021

ABSTRACT
When grown on microscope slides under controlled conditions, the marine hydroid Podocoryne carnea provides excellent material for the investigation of the origin of difference, regulation and the control of pattern during development. The growth of both stolons and hydranths is exponential and the ratio of hydranths to stolons is constant. Qualitative analysis of colony growth during a 5-month period delimits five discrete states that arise in the center and spread peripherally in the radially organized system during the first 3 months. When colony expansion stops, the centrifugal pattern of differentiation is replaced by an apparently random one and the number and proportion of zooids in the colony change. Extirpation and isolation experiments indicate that sexuality is not transmitted from sexual to asexual portions of the colony, and that it is associated with the dense stolon matte. A theory accounting for the origin of sexuality in terms of decreased permeability of the stolon to substances that necessitate sexual differentiation is suggested.
Groupes Sulfhydriles et Morphogénèse: IV. Effets du β-Mercaptoéthanol et de l’Acide-α-Lipoïque sur le Métabolisme des Acides Nucléiques chez les Embryons de Batracien et de Poulet
Authors: Pohl par V. , Quertier J. 
Published: April 2021

ABSTRACT
A study has been made of the incorporation of nucleic acid precursors (thymidine, uridine, cytidine) in two embryonic materials: Pleurodeles and Chicken, in the presence of two substances known to have a morphostatic effect on the closure of the neural plate: β-mercaptoethanol and lipoic acid. The results reveal a marked similarity of action. Thymidine incorporation into DNA is stimulated by mercaptoethanol and lipoic acid. Both substances also stimulate the incorporation of cytidine and uridine into RNA. But there is a difference in the case of DNA : mercaptoethanol has a slight stimulatory effect on the incorporation of the two nucleosides, whereas lipoic acid is definitely inhibitory. All the evidence suggests a specific effect of lipoic acid on the reduction of ribonucleosides to deoxyribonucleosides. The results have been discussed.