bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of extracellular matrix proteins on the expression of neuronal polarity
Authors: Chamak B. , Prochiantz A. 
Published: April 2021

ABSTRACT
The influence of laminin (LN) and fibronectin (FN) on the differentiation of individual neurones from the embryonic rat central nervous system was studied in vitro. In control cultures or in the presence of soluble FN, most neurones had several dendrite-like and one axon-like processes. On substratum-bound LN, multipolar and unipolar cells were present. Soluble LN and bound FN induced a very simple neuronal morphology, most neurones having only one axon-like neurite as defined by morphological and immunocytochemical characteristics. The significant reduction of neuronal adhesion and spreading in conditions leading to the growth inhibition of dendrite-like processes suggests that, contrary to that of axons, dendrite growth strongly depends on neuronal adhesion. We propose a model in which the different dependency of axonal and dendritic outgrowth towards adhesion and spreading is explained by the respective physical properties of the two types of neurites.
Temporal changes in the expression of the insulin-like growth factor II gene associated with tissue maturation in the human fetus
Authors: Brice A.L. , Cheetham J. E. , Bolton V. N. , Hill N. C. W. , Schofield P. N. 
Published: April 2021

ABSTRACTThe insulin-like growth factors are broadly distributed in the human conceptus and are thought to play a role in the growth and differentiation of tissues during development. Using in situ hybridization we have shown that a wide variety of specific cell types within tissues express the gene for insulin-like growth factor O at times of development from 18 days to 14 weeks of gestation. Examination of blastocysts produced by in vitro fertilization showed no expression, thus bracketing the time of first accumulation of IGF-II mRNA to between 5 and 18 days postfertilization. The pattern of IGF-II expression shows specific age-related differences in different tissues. In the kidney, for example, expression is found in the cells of the metanephric blastema which is dramatically reduced as the blastema differentiates. The reverse is also seen, and we have noted an increase in expression of IGF-II in the cytotrophoblast layer of the placenta with gestational age. The sites of expression do not correlate with areas of either high mitotic activity or specific types of differentiation, but the observed pattern of expression in the kidney, adrenal glands and liver suggests an explanation for the abnormally high IGF-II mRNA expression in developmental tumours such as Wilms’ tumour.
Homing behaviour of regenerating axons in the amphibian limb
Authors: Wilson Steve , Tonge D. A. , Holder Nigel 
Published: April 2021

ABSTRACT
Following peripheral nerve deviation in the limbs of urodele amphibians axons regrow distally toward their previous target muscles (Holder et al. 1984; Proc. Roy. Soc. Lond. B 222, 477-489). This study describes analysis of this axon regeneration over time following deviation of the forearm flexor nerve in Trituras cristatus and the extensor cranialis nerve in the axolotl. Using horseradish peroxidase (HRP) axonal tracing, electro-physiology and electron microscopy, we describe the sequence of events leading to reestablishment of functional innervation. HRP fills reveal axons leaving the deviated nerve via a number of possible routes and they invariably grow distally. Many axons take a path close to that of the original nerve but others fasciculate forming parallel paths. Electrophysiology and electron microscopy show that axons in the deviated region of the nerve degenerate extensively compared with cut, but undeviated, controls. The results are discussed in terms of the possible axon-growth-promoting mechanisms that result in directed growth.
J1 /tenascin-related molecules are not responsible for the segmented pattern of neural crest cells or motor axons in the chick embryo
Authors: Stern Claudio D. , Norris Wendie E. , Bronner-Fraser Marianne , Carlson Geoffrey J. , Faissner Andreas , Keynes Roger J. , Schachner Melitta 
Published: April 2021

ABSTRACT
It has been suggested that substrate adhesion molecules of the tenascin family may be responsible for the segmented outgrowth of motor axons and neural crest cells during formation of the peripheral nervous system. We have used two monoclonal antibodies (M1B4 and 578) and an antiserum [KAF9(1)] to study the expression of Jl/tenascin-related molecules within the somites of the chick embryo. Neural crest cells were identified with monoclonal antibodies HNK-1 and 20B4. Young somites are surrounded by Jl/tenascin immunoreactive material, while old sclerotomes are immunoreactive predominantly in their rostral halves, as described by other authors (Tan et al. 1987 - Proc. natn. Acad. Sci. U.S.A. 84, 7977; Mackie et al. 1988 - Development 102, 237). At intermediate stages of development, however, immunoreactivity is found mainly in the caudal half of each sclerotome. After ablation of the neural crest, the pattern of immunoreactivity is no longer localised to the rostral halves of the older, neural-crest-free sclerotomes. SDS–polyacrylamide gel electrophoresis of affinity-purified somite tissue, extracted using M1B4 antibody, shows a characteristic set of bands, including one of about 230×103, as described for cytotactin, Jl-200/220 and the monomeric form of tenascin. Affinity-purified somite material obtained from neural-crest-ablated somites reveals some of the bands seen in older control embryos, but the high molecular weight components (120-230X103) are missing. Young epithelial somites also lack the higher molecular mass components. The neural crest may therefore participate in the expression of Jl/tenascin-related molecules in the chick embryo. These results suggest that these molecules are not directly responsible for the segmented outgrowth of precursors of the peripheral nervous system.
Cell death of motoneurons in the chick embryo spinal cord: XI. Acetylcholine receptors and synaptogenesis in skeletal muscle following the reduction of motoneuron death by neuromuscular blockade
Authors: Oppenheim Ronald W. , Bursztajn Sherry , Prevette David 
Published: April 2021

ABSTRACT
Treatment of chick embryos with neuromuscular blocking agents such as curare during periods of naturally occurring motoneuron death results in a striking reduction of this normal cell loss. Inactivity-induced changes in motoneuron survival were found to be associated with increased levels of AChRs and AChR-clusters in skeletal muscle and with increased focal sites of AChE that are innervated (‘synaptic sites’). Treatment of embryos with curare after the normal cell death period (E12–E15) resulted in no change in motoneuron survival. Although AChR-clusters and focal sites of AChE were increased in these embryos on E16, many of these sites were uninnervated. Treatment of embryos with nicotine or decamethonium (E6–E10) also reduced neuromuscular activity but did not alter motoneuron survival nor did such treatment alter AChRs. The different effects of curare vs nicotine and decamethoniam on motoneuron survival and AChRs may be related to the fact that the former is a competitive blocker whereas the latter two drugs are depolarizing blockers. Finally, treatment of embryos (E6–9) with doses of curare (1 mg daily) that allow for the almost complete recovery of neuromuscular activity a few days following treatment (by E16) resulted in the gradual loss of the excess motoneurons that were present on E10, and by E16 the number of remaining AChR clusters and focal sites of AChE were also decreased to levels comparable to control values. Inactivity-induced changes in AChRs or AChR-clusters may be an important factor in the reduced motoneuron death that accompanies neuromuscular blockade during critical stages of development. These receptor changes very likely reflect increased synaptogenesis in the muscles of paralyzed embryos which in turn may act to reduce motoneuron death by providing increased access to muscle-derived neurotrophic molecules.
Development of adult sensilla on the wing and notum of Drosophila melanogaster
Authors: Hartenstein Volker , Posakony James W. 
Published: April 2021

ABSTRACT
We have investigated the temporal pattern of appearance, cell lineage, and cytodifferentiation of selected sensory organs (sensilla) of adult Drosophila. This analysis was facilitated by the discovery that the monoclonal antibody 22C10 labels not only the neuron of the developing sensillum organ, but the accessory cells as well. The precursors of the macrochaetes and the recurved (chemosensory) bristles of the wing margin divide around and shortly after puparium formation, while those of the microchaetes and the stout and slender (mechanosensory) bristles of the wing margin divide between 9h and 18 h after puparium formation (apt). The onset of sensillum differentiation follows the terminal precursor division within a few hours. Four of the cells in an individual microchaete organ are clonally related: A single first-order precursor cell divides to produce two second-order precursors; one of these divides into the neuron and thecogen cell, the other into the trichogen cell and tormogen cell. Along the anterior wing margin, two rounds of division generate the cells of the mechanosensory sensilla; here, no strict clonal relationship seems to exist between the cells of an individual sensillum. At the time of sensillum precursor division, many other, non-sensillum-producing cells within the notum and wing proliferate as well. This mitotic activity follows a spatially non-random pattern.
Genetic differences in glucose phosphate isomerase activity among mouse embryos
Authors: West John D. , Flockhart Jean H. 
Published: April 2021

ABSTRACT
We have compared mouse embryos of three heterozygous, congenic genotypes (with high, medium and low levels of oocyte-coded glucose phosphate isomerase (GPI-1) activity respectively) to test whether 1) the survival time of oocyte-coded GPI-1 activity in the early embryo is affected by its activity level in the oocyte and 2) whether embryo-coded GPI-1 is detected earlier in embryos that inherit low levels of oocyte-coded GPI-1. The oocyte-coded GPI-1 was entirely GPI-1 A allozyme in the high and medium groups but was the less stable GPI-1C allozyme in the low group. We determined total GPI-1 activity and the ratio of different GPI-1 allozymes in early embryos and calculated the activity of oocyte-coded and embryo-coded GPI-1. In all three groups, the oocyte-coded enzyme activity remained at a more or less constant level for the first days. Some oocyte-coded GPI-1 remained in day embryos from the high and medium groups but was gone by days. Very little remained in day embryos that inherited low levels of a less stable form of the enzyme (GPI-1C allozyme). Despite a 4- to 5-fold difference in initial oocyte-coded GPI-1 activity, no differences were seen among the three genotypically distinct groups of embryos in the time of activation of the embryonic Gpi-1s genes. The embryo-coded GPI-1 was first detectable in day compacted morulae in all three groups. The level of oocyte-coded GPI-1, in the high group, when embryo-coded GPI-1 was first detected was higher than the level in the low group at any stage prior to detection of embryo-coded GPI-1. These results imply that embryonic Gpi-1s genes are not activated by a mechanism that depends on oocyte-coded GPI-1 enzyme activity falling below a critical threshold. Once both embryonic Gpi-ls alleles were activated. they were usually equally expressed in Gpi-lsa/Gpi-lsb heterozygous embryos. However, the maternal: paternal expression was closer to 2:1 in 5 % (3/60) of the and day embryos. These could have been digynic triploid embryos.
Spatial control of hairy protein expression during embryogenesis
Authors: Hooper Katharine L. , Parkhurst Susan M. , Ish-Horowicz David 
Published: April 2021

ABSTRACT
We have used a polyclonal antiserum specific for the Drosophila segmentation gene, hairy (h), to analyse its expression during embryogenesis. The pattern of wildtype expression resembles that of h transcription, being expressed in stripes at the blastoderm stage, h is also expressed later in the stomodæum, proctodæum, tracheal pits and mesoderm. We demonstrate that h protein stripes show consistent phase relationships to those of the even-skipped (eve) pair-rule gene. We examine h protein patterns in embryos mutant for other segmentation genes, including h itself. We show that lack of h activity appears not to affect h striping, arguing that h expression is not under autoregulatory control. We also show that h activity is not needed for tracheal invagination. Mutations that are rearranged upstream of the h gene cause the loss of specific stripes, indicating that the h promoter includes activating elements that respond to specific spatial cues. Our observations suggest that pairrule striping may be under redundant control, and we discuss possible implications for hierarchical models of pair-rule gene action.
The maternal store of the xlgv7 mRNA in full-grown oocytes is not required for normal development in Xenopus
Authors: Kloc Malgorzata , Miller Mill , Carrasco Andres E. , Eastman Eric , Etkin Laurence 
Published: April 2021

ABSTRACT
We have attempted to analyze the function of a maternal mRNA xlgv7 which is distributed as an animal - vegetal gradient in stage 6 oocytes using a combination of antisense oligodeoxynucleotide injection into oocytes followed by in vitro maturation and fertilization. Injection of 20 ng of the antisense oligodeoxynucleotide resulted in the destruction of the xlgv7 mRNA to undetectable levels. Upon maturation and fertilization the resulting embryos develop with no specific defects suggesting that the maternal store of xlgv7 in stage 6 oocytes is not required and that the embryo can develop solely with the maternal store of the xlgv7 protein. Also, these results demonstrate the feasibility of this approach in destroying a specific maternal RNA and assaying its effect on development.
Tissue-specific regulation of junctional communication in the skin of mouse fetuses homozygous for the repeated epilation (Er) mutation
Authors: Kam Ephraim , Pitts John D. 
Published: April 2021

ABSTRACT
Mouse embryos homozygous for the repeated epilation (Er) gene have abnormally developed skin characterised by hyper-proliferation and incomplete differentiation of the epidermis. In this report, we have studied the patterns of junctional communication in the skin of these mutants to see if the loss of control of proliferation/ differentiation is associated with any altered patterns of communication. Using the dye-injection technique we have shown that, compared to normal skin, junctional communication among dermal cells of Er/Er mutants is greatly reduced and the frequency of dermal-epidermal communication is, on the other hand, increased. These results support our previously proposed model, which suggests that selective regulation of junctional communication can be a component of proliferative control in a complex tissue.
Transactivation of the adenovirus Ella promoter in the absence of adenovirus E1A protein is restricted to mouse oocytes and preimplantation embryos
Authors: Dooley Thomas P. , Miranda Miriam , Jones Nicholas C. , DePamphilis Melvin L. 
Published: April 2021

ABSTRACT
Undifferentiated mouse embryonal carcinoma (EC) cells are capable of transactivating the adenovirus Ella promoter in the absence of its normal transactivator, E1A protein, suggesting that EC cells contain an E1A-like activity. In an effort to identify where this activity appears during normal mouse development, mouse oocytes and preimplantation embryos were injected with plasmids containing the Ella promoter coupled to various reporter genes. These expression vectors were fully active in human 293 cells where E1A is present, but were inactive in differentiated fibroblast cell lines unless cotransfected with the El A gene. In mouse oocytes and preimplantation embryos, Ella promoter activity in the absence of adenovirus E1A protein was equivalent to or greater than activity of the HSV thymidine kinase promoter coupled to a strong enhancer. Coinjection of the E1A gene failed to stimulate Ella activity further, perhaps because c-myc protein, which has been reported to transactivate this promoter, was already present at high levels in mouse oocytes. Activation of the Ella promoter in the absence of E1A was unique to mouse oocytes and preimplantation embryos because gene expression from an Ella promoter introduced into transgenic mice was observed only in the adult ovary, and particularly in the oocytes. In addition, postimplantation transgenic embryos failed to express the ElA-activatable reporter gene, thereby indicating that expression from the Ella promoter is restricted to the relatively undifferentiated stages of oogenesis and preimplantation development. These data suggest that cellular promoters of the class that can be transactivated by E1A may serve uniquely to initiate transcription of genes that are needed for preimplantation development.
Mutations affecting skeletal muscle myofibril structure in the zebrafish*
Authors: Felsenfeld Adam L. , Walker Charline , Westerfield Monte , Kimmel Charles , Streisinger George 
Published: April 2021

Abstract
We describe embryonic lethal mutations in the zebrafish, Brachydanio rerio, which affect organization of skeletal muscle myofibrils. The mutations, fub-l(b45) and fub-l( b126), were independently isolated from progeny of gamma-irradiated females. Each segregates as a single recessive gene; b45 is located about 23 map units from its centromere. The b126 mutation has a similar but slightly larger apparent gene–centromere distance and a less severe phenotype. The two mutations fail to complement, suggesting that they are allelic. Homozygous b45 mutant embryos are paralyzed, and their axial skeletal muscle cells are unstriated, containing severely disorganized myofibrillar components. Gel-electrophoretic comparisons of b45 mutant and wildtype muscle proteins failed to reveal absent or altered major myofibrillar proteins. Embryos genetically mosaic for b45 were also phenotypically mosaic, suggesting that the defect is cell-autonomous. We suggest that these mutations identify a gene required for proper organization of skeletal muscle myofibrils, and that the more severe mutation may represent a null allele.
Insulin and insulin-like growth factor I (IGF I) in early mouse embryogenesis
Authors: Spaventi Radan , Antica Mariastefania , Pavelić Krešimir 
Published: April 2021

Abstract
Growth factors have an important role in the regulation of cell growth, division and differentiation. They are also involved in the regulation of embryonic growth and differentiation. Insulin and insulin-like growth factor I (IGF I) play an important part in these events in the later stages of embryogenesis, when organogenesis is completed. In this study, we are presenting evidence that insulin and IGF I are also secreted by embryonic tissues during the prepancreatic stage of mouse development. We found measurable amounts of insulin and IGF I in 8- to 12-day-old mouse embryos. We also showed that embryonic cells derived from 8-, 9- and 10-day-old mouse embryos secrete insulin, IGF I and/or related molecules. Furthermore, the same growth factors, when added to the culture of 9-day-old mouse embryonic cells, stimulate their proliferation. These results lead to the conclusion that insulin can stimulate the growth of embryonic cells during the period when pancreas is not yet formed, which is indirect evidence for a paracrine (or autocrine) type of action.
The early development of retinal ganglion cells with uncrossed axons in the mouse: retinal position and axonal course
Authors: Colello R. J. , Guillery R. W. 
Published: April 2021

Abstract
The carbocyanine dye, Dil, has been used to study the retinal origin of the uncrossed retinofugal component of the mouse and to show the course taken by these fibres through the optic nerve and chiasm during development. Optic axons first arrive at the chiasm at embryonic day 13 (E13) but do not cross the midline until E14. After this stage, fibres taking an uncrossed course can be selectively labelled by unilateral tract implants of Dil. The earliest ipsilaterally projecting ganglion cells are located in the dorsal central retina. The first sign of the adult pattern of distribution of ganglion cells with uncrossed axons located mainly in the ventrotemporal retina is seen on embryonic day 16.5, thus showing that the adult line of decussation forms early in development. A small number of labelled cells continue to be found in nasal and dorsal retina at all later stages.
At early stages (E14-15), retrogradely labelled uncrossed fibres are found in virtually all fascicles of the developing nerve, intermingling with crossed axons throughout the length of the nerve. At later stages of development (E16–17), although uncrossed fibres pass predominantly within the temporal part of the stalk, they remain intermingled with crossed axons. A significant number of uncrossed axons also lie within the nasal part of the optic stalk. The position of uncrossed fibres throughout the nerve in the later developmental stages is comparable to that seen in the adult rodent (Baker and Jeffery, 1989). The distribution of uncrossed axons thus indicates that positional cues are not sufficient to account for the choice made by axons when they reach the optic chiasm.
Calcium and cell cycle control
Authors: Whitaker Michael , Patel Rajnikant 
Published: April 2021

Abstract
The cell division cycle of the early sea urchin embryo is basic. Nonetheless, it has control points in common with the yeast and mammalian cell cycles, at START, mitosis ENTRY and mitosis EXIT.
Progression through each control point in sea urchins is triggered by transient increases in intracellular free calcium. The Cai transients control cell cycle progression by translational and post-translational regulation of the cell cycle control proteins pp34 and cyclin. The START Cai transient leads to phosphorylation of pp34 and cyclin synthesis. The mitosis ENTRY Cai transient triggers cyclin phosphorylation. The motosis EXIT transient causes destruction of phosphorylated cyclin.
We compare cell cycle regulation by calcium in sea urchin embryos to cell cycle regulation in other eggs and oocytes and in mammalian cells.
Cell movements during epiboly and gastrulation in zebrafish
Authors: Warga Rachel M. , Kimmel Charles B. 
Published: April 2021

Abstract
Beginning during the late blastula stage in zebrafish, cells located beneath a surface epithelial layer of the blastoderm undergo rearrangements that accompany major changes in shape of the embryo. We describe three distinctive kinds of cell rearrangements. (1) Radial cell intercalations during epiboly mix cells located deeply in the blastoderm among more superficial ones. These rearrangements thoroughly stir the positions of deep cells, as the blastoderm thins and spreads across the yolk cell. (2) Involution at or near the blastoderm margin occurs during gastrulation. This movement folds the blastoderm into two cellular layers, the epiblast and hypoblast, within a ring (the germ ring) around its entire circumference. Involuting cells move anteriorwards in the hypoblast relative to cells that remain in the epiblast; the movement shears the positions of cells that were neighbors before gastrulation. Involuting cells eventually form endoderm and mesoderm, in an anteriorposterior sequence according to the time of involution. The epiblast is equivalent to embryonic ectoderm. (3) Mediolateral cell intercalations in both the epiblast and hypoblast mediate convergence and extension movements towards the dorsal side of the gastrula. By this rearrangement, cells that were initially neighboring one another become dispersed along the anterior-posterior axis of the embryo. Epiboly, involution and convergent extension in zebrafish involve the same kinds of cellular rearrangements as in amphibians, and they occur during comparable stages of embryogenesis.