bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evidence for an association between U1 RNA and interspersed repeat single-copy RNAs in the cytoplasm of sea urchin eggs†
Authors: Ruzdijic Sabera , Pederson Thoru 
Published: April 2021

ABSTRACT
Psoralen crosslinking of RNA–RNA intermolecular duplexes in sea urchin egg extracts reveals that some maternal poly(A)+ RNA molecules are complexed with U1 RNA, a cofactor in somatic nuclear pre-mRNA splicing. Reaction of egg extracts with a monoclonal antibody specific for U1 snRNP selects, in addition to Ul, RNAs that contain repeated sequences interspersed with single-copy elements. Antibodyselection experiments with nucleate and anucleate egg halves demonstrate that most of the Ul RNA–inter-spersed RNA complexes are cytoplasmic, as is the egg’s store of total Ul snRNP. These results raise the possibility that maternal interspersed RNAs include unprocessed pre-messenger RNA molecules in arrested complexes with splicing cofactors.
Gastrulation movements provide an early marker of mesoderm induction in Xenopus laevis
Authors: Symes K. , Smith J. C. 
Published: April 2021

ABSTRACT
The first inductive interaction in amphibian development is mesoderm induction, in which an equatorial mesodermal rudiment is induced from the animal hemisphere under the influence of a signal from vegetal pole blastomeres. We have recently discovered that the Xenopus XTC cell line secretes a factor which has the properties we would expect of a mesoderm-inducing factor. In this paper, we show that an early response to this factor by isolated Xenopus animal pole regions is a change in shape, involving elongation and constriction. We show by several criteria, including general appearance, timing, rate of elongation and the nonrequirement for cell division that these movements resemble the events of gastrulation. We also demonstrate that the movements provide an early, simple and reliable indicator of mesoderm induction and are of use in providing a ‘model system’ for the study of mesoderm induction and gastrulation. For example, we show that the timing of gastrulation movements does not depend upon the time of receipt of a mesoderm-induction signal, but on an intrinsic gastrulation ‘clock’ which is present even in those animal pole cells that would not normally require it.
The postimplantation development of spontaneous digynic triploid embryos in LT/Sv strain mice
Authors: Kaufman M. H. , Speirs S. 
Published: April 2021

ABSTRACT
When spontaneously ovulating LT/Sv female mice are mated with fertile males, between one third and one half of the zygotes analysed at the first cleavage mitosis are found to be triploid. This is due to the fact that LT/Sv females ovulate both primary and secondary oocytes, all of which are capable of being fertilized. Fertilization of the former group results in the production of digynic triploid conceptuses, while their diploid littermates result from the fertilization of normal secondary oocytes. The present study was therefore carried out in order to investigate the ‘spontaneous’ level of triploidy in these mice, and to provide insight into the developmental fate of the LT/Sv triploid embryos, as previous studies had indicated that in this species triploids invariably fail to develop beyond the early postimplantation period. This study revealed that when autopsies were carried out on the 7th and 8th days of gestation, it was generally difficult to distinguish between the kary-ologically normal diploids and the digynic triploid conceptuses when only morphological criteria were used. However, by the 10th day of gestation, the triploid conceptuses could usually be readily distinguished from their diploid littermates by their smaller size and (occasionally) by their disorganized or abnormal morphological appearance.
Modification of cell division by phorbol ester in preimplantation mouse embryos
Authors: Mystkowska Ewa T. , Sawicki Wojciech 
Published: April 2021

ABSTRACT
2-cell mouse embryos were treated in vitro with a 2 h pulse of phorbol myristate acetate (PMA) at 32nd, 38th and 50th h after hCG, then chased in culture for up to 46 h. Embryos were fixed at various time intervals of chasing, then stained and inspected. Some embryos were carefully inspected with a video recording system, every l·44s and the cell divisions (cytokinesis) as well as formation of large, single blastomeres, each from two smaller ones, were recorded. PMA pulse led to the suppression of cell divisions. The rate of the suppression was time dependent: with a delay of 0–1, 12 and 18 h between the PMA pulse and time of scheduled cell division about 99, 87 and 44 % of 2-cell embryos remained at this stage of development, for at least 10 h, respectively, and 90, 58 and 12 % of their blastomeres revealed binu-clearity. Since we found that PMA-mediated formation of binuclearity was not the effect of cell fusions, it was assumed that the inhibition of cytokinesis preceded by karyokinesis was reponsible for binuclearity. PMA effect on cell divisions was reversible. PMA-treated embryos revealed formation of large, single blastomeres, each from two smaller ones. If cell division appeared after PMA pulse, in about 52 % of 3-to 6-cell embryos, the large blastomere formation was recorded in the course of the subsequent 38 h. Large blastomere formation was concluded to be the result of either cell fusion or reversion of incompleted cytokinesis brought about by PMA.
Cytoskeleton and thyroglobulin expression change during transformation of thyroid epithelium to mesenchyme-like cells*
Authors: Greenburg Gary , Hay Elizabeth D. 
Published: April 2021

Abstract
In considering the mechanism of transformation of epithelium to mesenchyme in the embryo, it is generally assumed that the ability to give rise to fibroblast-like cells is lost as epithelia mature. We reported previously that a definitive embryonic epithelium, that of the anterior lens, gives rise to freely migrating mesenchyme-like cells when suspended in type I collagen matrices. Here, we show that a highly differentiated epithelium that expresses cytokeratin changes to a vimentin cytoskeleton and loses thyroglobulin during epithelial-mesenchymal transformation induced by suspension in collagen gel. Using dispase and collagenase, we isolated adult thyroid follicles devoid of basal lamina and mesenchyme, and we suspended the follicles in 3D collagen gels. Cells bordering the follicle lumen retain epithelial polarity and thyroid phenotype, but basal cell surface organization is soon modified as a result of tissue multilayering and elongation of basal cells into the collagenous matrix. Cytodifferentiation, determined by thyroglobulin immunoreactivity, is lost as the basal epithelial cells move into the matrix after 3 – 4 days in collagen. By TEM, it can be seen that the elongating cells acquire pseudopodia, filopodia and mesenchyme-like nuclei and RER. Immunofluorescence examination of intermediate filaments showed that freshly isolated follicles and follicles cultured on planar substrata react only with anticytokeratin. However, all of the inesen-chyme-like cells express vimentin and they gradually lose cytokeratin. These results suggest that vimentin may be necessary for cell functions associated with migration within a 3D matrix. The mesenchymal cells do not revert to epithelium when grown on planar substrata and the transformation of epithelium to mesenchyme-like cells does not occur within basement membrane gels. The results are relevant to our understanding of the initiation of epithelial-mesenchymal transformation in the embryo and the genetic mechanisms controlling cell shape, polarity and cytoskeletal phenotype.
The early development of the atrioventricular node and bundle of His in the embryonic chick heart. An electrophysiological and morphological study
Authors: Argüello Carlos , Alanis Jesus , Valenzuela Blanca 
Published: April 2021

Abstract
The development of the atrioventricular node and bundle of His of embryonic chick hearts was studied by electrophysiological and morphological techniques. The dorsal wall of the AV canal and the interatrial septum were explored to determine if they contribute to the formation of the AV node and bundle of His. The resting membrane and action potentials of the interatrial septum cells were systematically analysed and found to undergo progressive differentiation with development. The earliest identification of the AV node and upper bundle of His group of cells was achieved at days of development by the electrical recording of their corresponding characteristic action potentials, from a circumscribed area located in the lowest and dorsal segment of the interatrial septum.
The morphological and anatomical characterization of the cells was made following electrical recording and labelling with charcoal particles. The earlier AV node and bundle of His responses had similar characteristics to those of the adult heart. It is concluded that the AV node and upper bundle of His cells derive from the low interatrial septum. The possibility that AV canal cells contribute to this event was discarded. The functional relationship of the AV node and bundle of His with other cardiac tissues during the early development of the heart is discussed.
Spatial organization of the epithelium and the role of neural crest cells in the initiation of the mammalian tooth germ
Authors: Lumsden A. G. S. 
Published: April 2021

ABSTRACT
Teeth develop from composite organ rudiments that are formed through the interaction of oral epithelium and mesenchyme of the first branchial arch; cells of the former differentiate into enamelsecreting ameloblasts whereas those of the latter differentiate into dentinesecreting odontoblasts. Experimental analysis of odontogenic tissue interactions in mammalian embryos has focused on the late developmental stages of morphogenesis and cytodifferentiation; little is known about initial pattern-forming events, during which presumptive tooth-forming cells are specified and the sites of tooth initiation become established. It requires to be shown, for example, whether the mesenchymal cells of mammalian teeth are derived, like those of amphibians, from the cranial neural crest, and if so, whether these form a specified subpopulation in the neural folds. Alternatively, are they specified after migration into the mandibular arch, possibly by interaction with the oral epithelium?
The developmental potentials of mouse embryo premigratory cranial neural crest cells (CNC explanted from the caudal mesencephalic and rostral metencephalic neural folds) have been studied in intraocular homograft recombinations with various regions of embryonic surface ectoderm. Cartilage, bone and neural tissue developed in all combinations of CNC and epithelium. Teeth formed in combinations of CNC with mandibular arch epithelium but not in combinations of CNC with limb bud epithelium. Teeth also formed in combinations of mandibular arch epithelium with neural crest explanted from the trunk level. These results indicate that mammalian neural crest has an odontogenic potential but that this is not restricted to the crest of presumptive toothforming levels. Normal migration appears not to be a prerequisite for expression of odontogenic potential but this does require an interaction with regionspecific epithelium. It is reasonable to infer that during normal development the neural crest that enters the mandibular arch is odontogenically unspecified before or during migration and that the oral epithelium is the earliest known site of tooth pattern.
Palate development
Authors: Ferguson Mark W. J. 
Published: April 2021

ABSTRACT
In all vertebrates, the secondary palate arises as bilateral outgrowths from the maxillary processes. In birds and most reptiles, these palatal shelves grow initially horizontally, but do not fuse with each other resulting in physiological cleft palate. In crocodilians, shelf fusion occurs resulting in an intact secondary palate. Mammalian palatal shelves initially grow vertically down the side of the tongue, but elevate at a precise time to a horizontal position above the dorsum of the tongue and fuse with each other to form an intact palate. Palatal shelf-elevation is the result of an intrinsic shelf elevating force, chiefly generated by the progressive accumulation and hydration of hyaluronic acid. In all vertebrates the nasal epithelium differentiates into pseudostratified ciliated columnar cells and the oral epithelia differentiates into stratified squamous cells, but the medial edge epithelial (MEE) phenotype differs in different groups. In mammals, the MEE of opposing shelves adhere to each other to form an epithelial seam which then disrupts by cell death and cell migration into the mesenchyme accompanied by an epitheliomesenchymal transformation. In birds, the MEE keratinize resulting in cleft palate whereas, in alligators, the MEE migrate onto the nasal aspect of the palate. In all vertebrates, this regional, temporal and species-specific epithelial differentiation is specified by the underlying mesen-chyme. Signalling of this interaction is complex but involves both extracellular matrix and soluble factors e.g. minor collagen types, tenascin, EGF, TGFα, TGFβ, PDGF, FGF. These soluble growth factors have a biphasic effect: directly on the epithelia and on the mesenchyme where they stimulate or inhibit cell division and synthesis of specific extracellular matrix molecules. The extracellular matrix molecules (and bound growth factors) synthesized by the mesenchymal cells may then directly affect the epithelium. These signals cause differential gene expression via second messenger systems e.g. cAMP, cGMP, Ca2+, pH, pl etc. Molecular markers for nasal, medial and oral epithelial cell differentiation include the types of cytokeratin intermediate filaments and specific cell surface molecules recognized by monoclonal antibodies: the genes for such molecules are probably expressed in response to mesenchymal signals. Using such an approach, it is possible to go from a morphological description of palate development to a cellular analysis of the mechanisms involved and then to identification of candidate genes that may be important for screening and diagnosis of cleft palate.
Cell-adhesion and substrate-adhesion molecules: their instructive roles in neural crest cell migration
Authors: Tucker Gordon C. , Duband Jean-Loup , Dufour Sylvie , Thiery Jean Paul 
Published: April 2021

ABSTRACT
The individualization of crest cells from the neural folds and neural tube involves distinct mechanisms affecting both the tissue shape and the cell environment. Though these mechanisms are not fully understood at the molecular level, the analysis of the distribution of several molecules reported to promote intercellular contacts indicates a correlation between cell detachment from the neurepithelium and the decrease of cell adhesion molecule expression. During the following phase of migration, the mode of adhesion of crest cells switches preferentially to the cell-to-substratum type. Various experiments showed that among the major extracellular matrix components, fibronectins were decisive in promoting cell attachment, spreading and motility. Additional studies on receptors for fibronectins gave new insights on the differences between a motile and a stationary cell. These results will be discussed with particular reference to the migration at the cephalic level where most perturbation experiments were performed.
The molecular biology of fibronectins provided a finer understanding of the interactions between a cell and these molecules. The tools derived from this technique will open new areas of investigation hopefully leading to a better understanding of (i) the regulation of the cell-fibronectins interaction and (ii) the specificity of the pathways of migration followed by migrating cells, like the descendants of the neural crest.
β3 tubulin expression characterizes the differentiating mesodermal germ layer during Drosophila embryogenesis
Authors: Leiss Dagmar , Hinz Uwe , Gasch Alexander , Mertz Ronald , Renkawitz-Pohl Renate 
Published: April 2021

ABSTRACT
During embryogenesis, the β3 tubulin gene of Drosophila is transcribed predominantly in the mesoderm. We have raised antibodies specific to the C-terminal domain of the β3 tubulin and analysed by immunostaining the distribution of this tubulin isotype during Drosophila embryogenesis. The protein is first detectable in the cephalic mesoderm at maximal germband extension. Shortly afterwards, β3 tubulin is expressed in single cells at identical positions of the thoracic and abdominal segments. We suggest that these cells represent muscle pioneer cells of Drosophila. During later embryonic development the somatic musculature, visceral musculature, dorsal vessel and macrophages contain β3 tubulin. In dorsalizing mutants dorsal, snail and twist, which do not form a ventral furrow during gastrulation, β3 expression is greatly reduced but not completely abolished. Our analysis shows that β3 tubulin immunostaining characterizes the differentiation of mesodermal derivatives during embryogenesis.
Development of functional innervation in the second and third order auditory nuclei of the chick
Authors: Pettigrew A. G. , Ansselin A. D. , Bramley J. R. 
Published: April 2021

Abstract
The neurones that constitute the auditory nuclei of the brainstem in the chick (nuclei magnocellularis, NM, and laminaris, NL) are generated between days 2 and 4 of incubation. These neurones migrate towards the dorsal surface of the brainstem over the next few days and reach their final destination at about day 9 of incubation. We have examined the development of functional connections between the auditory nerve and neurones in NM and between neurones in NM and NL in embryos from stage 34 (day 8 of incubation) using electrophysiological techniques and electron and light microscopy. The earliest extracellular recordings of electrically evoked field and spike potentials were made in NM with stimulation of the ipsilateral auditory nerve and in NL with stimulation of the ipsilateral NM at stage 35 (day 9). No activity could be recorded in NL with stimulation of the auditory nerve at this stage. By stage 37 (day 11), direct stimulation of the contralateral NM evoked responses in NL and by stage 38 (day 12) stimulation of the auditory nerves evoked stable field potentials in NL. These potentials changed polarity as the electrode penetrated NL in a direction that was perpendicular to the laminar arrangement of neurone somas and parallel to the dendritic axes of these neurones. In 18 of 26 analyses of current-source density in NL of 12 preparations between stages 38 and 40 there was a sink of current associated with synaptic activity at levels both above and below the source of current (cell somas) following stimulation of the ipsilateral auditory nerve. In the remaining analyses, and in all 15 analyses from preparations older than stage 40, stimulation of the ipsilateral input evoked only a single sink of current above the level of the cell somas. In all preparations from embryos at stage 38 and older, stimulation of the contralateral auditory nerve was associated with a single sink of current below the level of the cell somas. The axon projections to the ipsilateral NL from neurones in NM were examined using HRP labelling between stages 38 and 40. The presence of terminal fields of single axons in both the dorsal and ventral dendritic regions of the ipsilateral NL at these ages was confirmed. Furthermore, dense vesicles within synaptic terminals in both the dorsal and ventral dendritic fields could be identified in preparations at stage 36 following injection of HRP into NL and stimulation of the ipsilateral NM. The observations from these experiments suggest that the ventral dendrites in NL receive a transient functional innervation from neurones in the ipsilateral NM at early stages of development before the normal segregated innervation of NL is established.
Pioneer neurones use basal lamina as a substratum for outgrowth in the embryonic grasshopper limb
Authors: Anderson Hilary , Tucker Richard P. 
Published: April 2021

Abstract
During axonogenesis, contacts made by the growth cone with its substratum are important in guiding the direction of neurone outgrowth. This study examines the contacts made by the growth cones of pioneer neurones in the embryonic grasshopper limb. Individual pioneer neurones at different stages of development were injected with horseradish peroxidase and the contacts made by the filopodia at the tip of their growth cones were examined by electron microscopy.
Filopodia made few contacts with mesodermal cells, some contacts with ectodermal cells and very frequent contacts with basal lamina underlying the ectoderm. Components of the basal lamina may therefore play a role in guiding pioneer axon outgrowth.
Experimental manipulation of sexual differentiation in wallaby pouch young treated with exogenous steroids
Authors: Shaw G. , Renfree M. B. , Short R. V. , O W.-S. 
Published: April 2021

Abstract
We have investigated the effects of androgen or oestrogen treatment of female or male tammar wallabies from the day of birth, when the gonads are histologically undifferentiated, to day 25 of pouch life, when the gonads and the Wolffian and Müllerian ducts have differentiated and the testes have migrated through the inguinal canal.
Female tammars treated with testosterone propionate (24-50 mg kg−1 day−1) orally for 25 days had enlarged Wolffian and Müllerian ducts. Mammary and pouch development, however, was indistinguishable from that of control females. The treatment had no apparent effect on ovarian development, or on ovarian position in the abdomen. The phallus of males and females was similar in size, and neither experimental treatment had a significant effect on its size at day 25.
Male tammars treated with oestradiol benzoate (l-2-2-5mgkg−1day−1) orally for 25 days had gross hypertrophy of the urogenital sinus. Testicular morphology was abnormal; many of the germ cells appeared necrotic, the seminiferous tubules were of reduced diameter, and there were few Leydig cells and increased amounts of fibrous tissue between the tubules. The cortex of these gonads contained some areas which had an ovarian appearance, lacking tubules and containing numerous germ cells. The
Müllerian ducts of control males had regressed, but this was prevented by oestrogen treatment, suggesting an inhibition of either Müllerian Inhibiting Substance (MIS) production or its action. Normal testicular migration was inhibited in treated males; the testes remained high in the abdomen, similar in position to the ovaries of control females, whilst control males all had testes in the inguinal region. The gubernaculum and processus vaginalis of control males extended into the scrotum, but in treated males they terminated outside it. Oestrogen treatment had no effect on the size of the scrotum and did not induce mammary or pouch development.
These experiments show that marsupials, like eutherians, have a dual hormonal control of Wolffian and Müllerian development. By contrast, the initial development of the mammary glands, pouch, gubernaculum and scrotum does not appear to be under hormonal control and is therefore likely to be autonomous and dependent on genotype.