bluuebunny/crossref_metadata_2025_split huggingface dataset:
Developmental and evolutionary implications of labial, Deformed and engrailed expression in the Drosophila head
Authors: Diederich Robert J. , Pattatucci Angela M. , Kaufman Thomas C. 
Published: April 2021

Abstract
Prior developmental genetic analyses have shown that labial (lab) and Deformed (Dfd) are homeotic genes that function in the development of the embryonic (larval) and adult head. Using antibody probes to reveal the spatial distribution of the lab and Dfd proteins in embryonic and imaginai tissues, we have assessed the respective roles of these genes through an analysis of the correspondence of their expression patterns with their mutant phenotypes. With regard to imaginai develop-ment, lab and Dfd occupy adjacent non-overlapping expression domains in the peripodial cell layer of the eye-antennal disc, in patterns that are consistent with their adult mutant phenotypes and published fate maps. During embryogenesis, lab and Dfd exhibit limited overlapping expression in areas that are of no obvious significance to the development of larval head struc-tures, but also in areas that may have consequences for imaginai development. The head of Drosophila and other cyclorrhaphous Dipterans is characterized by an ex-treme morphological difference between the larval and adult stages. Given this unique ontogenetic and phylo-genetic history and the observation that homeotic transformations produced by the lab, Dfd, and proboscis pedia (pb) loci are manifested only in the adult, we suggest that distinct regulatory paradigms evolved for homeotic gene function in the development of the larval versus adult head. Finally, a detailed examination of the engrailed (en) expression pattern in the embryonic head strengthens the view of insect morphologists that the clypeolabrum evolved from the fusion of paired labral appendages.
Astrotactin provides a receptor system for CNS neuronal migration
Authors: Fishell Gord , Hatten Mary E. 
Published: April 2021

ABSTRACT
CNS neuronal migration is a specialized form of cell motility that sets forth the laminar structure of cortical regions of brain. To define the neuronal receptor systems in glial-guided neuronal migration, an in vitro assay was developed for mouse cerebellar granule neurons, which provides simultaneous tracking of hundreds of migrating neurons. Three general classes of receptor systems were analyzed, the neuron-glial adhesion ligand astrotactin, the neural cell adhesion molecules of the IgG superfamily, N-CAM, LI and TAG-1, and the αsubunit of the integrin family. In the absence of immune activities, migrating cerebellar granule neurons had an average in vitro migration rate of 12 μm h-1, with individual neurons exhibiting migration rates over a range between 0 to 70 μm h-1. The addition of anti-astrotactin antibodies (or Fabs) significantly reduced the mean rate of neuronal migration by sixty-one percent, resulting in eighty percent of the neurons having migration rates below 8 μm h-1. By contrast, blocking antibodies (or Fabs) against LI, N-CAM, TAG-1 or β 1 integrin, individually or in combination, did not reduce the rate of neuronal migration.
By video-enhanced contrast differential interference contrast microscopy the effects of anti-astrotactin antibodies were seen to be rapid. Within fifteen minutes of antibody application, streaming of cytoplasmic organelles into the leading process arrested, the nucleus shifted from a caudal to a central position, and the extension of filopodia and lamellopodia along the leading process ceased. Correlated video and electron microscopy suggested that the mechanism of arrest by antiastrotactin antibodies involved the failure to form new adhesion sites along the leading process and the disorganization of cytoskeletal components. These results suggest astrotactin acts as a neuronal receptor for granule neuron migration along astroglial fibers.
Axon repulsion during peripheral nerve segmentation
Authors: Keynes Roger J. , Jaques Karen F. , Cook Geoffrey M. W. 
Published: April 2021

Abstract
The guidance of axons during embryonic development is likely to involve both adhesive and repulsive interactions between growth cones and their environment. We are characterising the role and mechanism of repulsion during the segmental outgrowth of motor and sensory axons in the somite mesoderm of chick embryos. Axons are confined to the anterior half of each somite by the expression in the posterior half of a glycoconjugate system (48×103Mr and 55×103Mr) that causes the collapse of dorsal root ganglion growth cones when applied in vitro. Enzymatic cleavage of this fraction with specific combinations of endo- and exoglycosidases removes collapse activity, suggesting that carbohydrate residues are involved in the execution of collapse. A similar activity is also detectable in normal adult grey matter, suggesting roles for repulsion beyond the development of spinal nerve segmentation.
Cell lineage in the cerebral cortex
Authors: Price Jack , Williams Brenda , Grove Elizabeth 
Published: April 2021

Abstract
We have studied cell lineage in the rat cerebral cortex using retroviral mediated gene transfer. By this method, a marker gene is inserted into dividing precursor cells such that their fate can be followed. We have applied this technique to two types of experiment. First, virus was used to label precursor cells of the cerebral cortex in situ during the period of neurogenesis. Second, cortical precursor cells were grown in dissociated cell culture, and virus was used to follow their development over the culture period. These experiments showed that the majority of precursor cells generate a single cell type - neurones, astrocytes, or oligodendrocytes. Moreover, this is true both in vivo and in dissociated cell culture. The only exception is a bipotential cell, which can generate both neurones and oligodendrocytes. These data suggest that the ventricular zone - the germinal layer of the embryonic cortex - is a mosaic of precursor cells of different restricted potentials.
Although precursor cells are restricted in terms of the cell types they generate, they seem not to be restricted in either the cortical laminae or cytoarchitectonie areas to which they can contribute. Both neuronal and grey matter astrocyte precursors contribute cells to multiple layers of both infra- and supragranular laminae. Moreover, in the hippocampal formation, neuronal precursors can contribute cells to more than one hippocampal field.
Genetic control of primary neuronal development in zebrafish
Authors: Kimmel Charles B. , Hatta Kohei , Eisen Judith S. 
Published: April 2021

Abstract
During the first day of embryogenesis in the zebrafish, a precise and relatively simple network of neurons develops, pioneering axonal pathways and apparently functioning to mediate reflexive motor responses to touch stimuli. We have begun to use zygotic lethal mutations to analyze the assembly of this ‘primary’ embryonic nervous system. Here we focus on spinal primary motoneurons, their inputs from hindbrain Mauthner neurons, and their outputs to segmental body wall muscle. The mutation nic-1 blocks synaptic transmission between nerve and muscle, yet embryonic primary motoneurons appear normal, suggesting that functional interactions with their targets are not involved in regulating their development. The mutation spt-1 directly disrupts development of this muscle, and the mutation cyc-1 appears to directly block specification of the floor plate. Both spt-1 and cyc-1 affect aspects of primary neuronal development, and they probably do so indirectly. The nonautonomous actions of these mutations are local and they produce variable neuronal phenotypes. The observations can be interpreted to mean that some cellular interactions that specify the neurons and their axonal paths occur at close range and involve multiple, possibly combinatorial, transmitterindependent pathways.
Dissection of the faint little ball (fib) phenotype: determination of the development of the Drosophila central nervous system by early interactions in the ectoderm
Authors: Raz Erez , Shilo Ben-Zion 
Published: April 2021

ABSTRACT
The complex embryonic phenotype of mutations in the faint little ball (flb) locus, encoding the Drosophila EGF receptor homolog (DER), was dissected by temperature shifts of a temperature-sensitive allele. We show that the phenotype can be resolved into at least five components, which are temporally and spatially distinct. Most notably, the central nervous system (CNS) phenotype is determined at two separate phases. A severe collapse results from early defects in the DER-expressing ectodermal cells from which neuroblasts and midline glial cells delaminate. We thus suggest that DER activity is crucial for interactions that occur in the ectoderm at an early stage, and determine the fate of neuronal and glial cell lineages. This finding explains how a severe CNS phenotype is generated in fib embryos, in spite of the absence of expression of the protein in neuronal cells. In a second phase, during germ band retraction, the fib function is required specifically in the three pairs of midline glial cells (MG). In the absence of a functional DER protein, these cells die or fail to differentiate correctly, resulting in a fused commissure phenotype.
In vitro control of neuronal polarity by glycosaminoglycans
Authors: Lafont F. , Rouget M. , Triller A. , Prochiantz A. , Rousselet A. 
Published: April 2021

ABSTRACT
We have studied the effects of proteoglycans (PGs) and glycosaminoglycans (GAGs) on the growth and morphology of neurons in culture. PGs from glial cells or Engelbreth-Hohn-Swarm tumor cells (EUS), pure bovine kidney heparan sulfate (HS), shark cartilage type C chondroïtin sulfate (CSc) and bovine mucosa dermatan sulfate (DS) added to embryonic rat neurons strongly enhanced total neurite growth after 48 h in vitro. No trophic effects were seen when PGs treated with a mixture of glycanases were used. PGs, CSc and HS not only enhanced neurite growth but induced the appearance of a majority of neurons with a single long axon whereas, in contrast, DS increased dendrite growth. GAGs bound to the cell surface and were rapidly internalized, a feature that correlated well with the absence of neurotrophicity of GAGs previously immobilized on the culture substratum. Although the mechanisms involved in GAGs neurotrophic effects and in the separate regulation of neuronal polarity by HS and DS were not elucidated, we found that, as opposed to HS, DS was able to enhance neuronal adhesion and spreading and to maintain a high level of expression of microtubule-associated protein 2 (MAP2), a specific dendritic marker. This finding confirms and extends our previous observations on the role of adhesion in the regulation of dendrite growth.
Commitment of mesoderm cells in Hensen’s node of the chick embryo to notochord and somite
Authors: Selleck Mark A. J. , Stern Claudio D. 
Published: April 2021

ABSTRACT
Hensen’s node in the chick embryo contains prospective notochord cells in a ▿-shaped midline region of the mesoderm, and prospective medial half somite cells in the lateral portions of the node mesoderm, whilst lateral somite cells are derived from the rostral part of the primitive streak (Selleck and Stern, Development 112, 615-626, 1991). In the present study, we have investigated the commitment of these mesoderm cells to their fates by grafting between these regions of the node and primitive streak. By challenging the cells in this way, we have attempted to discover whether prospective notochord and somite cells can change their fates.
We find that the mesoderm cells In the midline ▿-shaped portion of Hensen’s node, when grafted into a different region, continue to integrate into the notochord, or form a separate notochord-like structure. By contrast, the prospective somitic cells do not appear to be committed to a somitic fate.
Basic fibroblast growth factor stimulates the sustained proliferation of mouse epidermal melanoblasts in a serum-free medium in the presence of dibutyryl cyclic AMP and keratinocytes
Authors: Hirobe Tomohisa 
Published: April 2021

ABSTRACTBasic fibroblast growth factor (bFGF) stimulated the sustained proliferation of mouse epidermal melanoblasts derived from epidermal cell suspensions in a serum-free medium supplemented with dibutyryl adenosine 3′,5′-cyclic monophosphate (DBcAMP). The melanoblasts could be subcultured in the serum-free medium supplemented with the two factors in the presence of keratinocytes, but not in the absence of keratinocytes. In these conditions, some melanoblasts proliferated without differentiating for more than 20 days including a subculture. This is the first report of a successful culture of melanoblasts from mammalian skin. This culture system is expected to clarify further markers for melanoblasts and requirements for their proliferation and differentiation.
Identification and characterization of Drosophila female germ line transcriptional control elements
Authors: Frank Lawrence H. , Cheung Hung-Kam , Cohen Robert S. 
Published: April 2021

ABSTRACT
The highly organized structure of the Drosophila ovary makes it an ideal system for studying mechanisms of differential gene expression. Here we report the identification of a 171 bp sequence from the 5′ end of the hsp26 gene that functions as a female germ-line-specific transcriptional regulator when linked in two copies to a basal promoter. The regulator is active only in nondividing cells of the germ line, i.e., only in nurse cells and oocytes. It is not active in any examined tissue or cell type outside of the female germ line. Copper nuclease footprinting studies show that the germ line regulator contains two binding sites for each of two different ovarian nuclear factors. Point mutations in the DNA target sites of either nuclear factor abolish in vitro binding and in vivo transcriptional activity, indicating that each factor is a positive activator of nurse cell/oocyte transcription. The two factors may represent different classes of activator proteins, since an increase in the copy number of one factor’s DNA target site cannot compensate for a decrease in the copy number of the other factor’s target site.
Ten different Polycomb group genes are required for spatial control of the abdA and AbdB homeotic products
Authors: Simon Jeffrey , Chiang Anne , Bender Welcome 
Published: April 2021

ABSTRACT
Mutations in genes of the Polycomb (Pc) group cause abnormal segmental development due to ectopic expression of the homeotic products of the Antennapedia and bithorax complexes. Here the requirements for Pc group genes in controlling the abdA and AbdB products of the bithorax complex are described. Embryos containing mutations in the genes Polycomb (Pc), extra sex combs (esc), Enhancer of zeste [E(z)], polyhomeotic (ph), Sex comb on midleg (Scm), Polycomb-like (Pcl), Sex comb extra (See), Additional sex combs (Asx), Posterior sex combs (Psc) and pleiohomeotic (pho) were examined. In every case, both abdA and AbdB are expressed outside of their normal domains along the anterior-posterior (A–P) axis, consistent with these Pc group products acting in a single pathway or molecular complex. The earliest detectable ectopic expression is highest in the parasegments immediately adjacent to the normal expression boundary. Surprisingly, in the most severe Pc group mutants, the earliest ectopic AbdB is distributed in a pair-rule pattern. At all stages, ectopic abdA in the epidermis is highest along the anterior edges of the parasegments, in a pattern that mimics the normal abdA cell-specific pattern. These examples of highly patterned mis-expression show that Pc group mutations do not cause indiscriminate activation of homeotic products. We suggest that the ectopic expression patterns result from factors that normally activate abdA and AbdB only in certain parasegments, but that in Pc group mutants these factors gain access to regulatory DNA in all parasegments.
Spatial restriction of AChR gene expression to subsynaptic nuclei
Authors: Simon Alexander M. , Hoppe Peter , Burden Steven J. 
Published: April 2021

ABSTRACT
Acetylcholine receptors (AChRs) and the mRNAs encoding the four AChR subunits are highly concentrated in the synaptic region of skeletal myofibers. The initial localization of AChRs to synaptic sites is triggered by the nerve and is caused, in part, by post-translational mechanisms that involve a redistribution of AChR protein in the myotube membrane. We have used transgenic mice that harbor a gene fusion between the murine AChR delta subunit gene and the human growth hormone gene to show that innervation also activates two independent transcriptional pathways that are important for establishing and maintaining this non uniform distribution of AChR mRNA and protein. One pathway is triggered by signal(s) that are associated with myofiber depolarization, and these signals act to repress delta subunit gene expression in nuclei throughout the myofiber. Denervation of muscle removes this repression and causes activation of delta subunit gene expression in nuclei in non-synaptic regions of the myofiber. A second pathway is triggered by an unknown signal that is associated with the synaptic site, and this signal acts locally to activate delta subunit gene expression only in nuclei within the synaptic region. Synapse-specific expression, however, does not depend upon the continuous presence of the nerve, since transcriptional activation of the delta subunit gene in subsynaptic nuclei persists after denervation. Thus, the nuclei in the synaptic region of multinucleated skeletal myofibers are transcriptionally distinct from nuclei elsewhere in the myofiber, and this spatially restricted transcription pattern is presumably imposed initially by the nerve.
Wound closure in foetal rat skin
Authors: Ihara Setsunosuke , Motobayashi Yumiko 
Published: April 2021

ABSTRACTFoetal rat skin rapidly closes an open wound in organ culture and in vivo, this possibly being unique to organs still in the morphogenetic stage. In the present study, examination was made of morphological changes in foetal rat skin during closure of open wounds inflicted at day 16 of gestation. Phase-contrast microscopy of open-wounded skin cultured in vitro indicated inward spreading of the peripheral skin to be responsible for wound closure. Wound closure in vitro was inhibited by cytochalasin B (10 μg/ml), not by hydroxyurea (2 mM), indicating prenatal wound closure to be mediated by regulation of the microfilament system rather than cell proliferation. During wound closure in vitro and in vivo, light and scanning electron microscopy of the peripheral skin showed cells in the periderm, the outermost layer of the foetal epidermis, to elongate centripetally and en masse, whereas the shape of underlying epidermal cells not to change. Numerous spindle-shaped cells and fibrous matrices in the mesenchyme were redistributed, becoming oriented along the wound edge. Following isolation of the mesenchyme and epidermis by treatment with Dispase and separate culturing, the capacity for wound closure in vitro was found to be retained only by the mesenchyme. Cellular activity within the mesenchyme, rather than in the epidermis, would thus appear essential to wound closure in foetal rat.
Intracellular free Ca2+ changes during physiological polyspermy in amphibian eggs
Authors: Grandin Nathalie , Charbonneau Michel 
Published: April 2021

ABSTRACT
We have made the first measurements of intracellular free calcium activity ([Ca2+]i) in urodele eggs during physiological polyspermic fertilization. Jellied eggs of the urodele amphibian Pleurodeles waltlii were impaled with intracellular Ca2+-selective microelectrodes and inseminated under various conditions of sperm:egg ratio to obtain various degrees of polyspermy. In 17 out of 45 cases the egg [Ca2+]i level (0.41 μM) showed no variation following fertilization. In 28 other cases, however, the egg displayed a slow increase in [Ca2+]i of 0.15 μM, starting around 15 minutes after fertilization and reaching a plateau level around 10 minutes later. The amplitude of the fertilization-associated increase in [Ca2+]i was found to be independent of the number of sperm interacting with the egg surface. Measurements with two Ca2+-microelectrodes impaled in single eggs showed that the increase in [Ca2+]i did not simultaneously occur at distinct places within the egg cortex and, in some cases, could be detected by only one of the two microelectrodes. This latter observation, as well as the absence of [Ca2+]i change at fertilization in some experiments, strongly suggested that each sperm interacting with the egg might, at various places, trigger a localized, non-propagating change in [Ca2+]i. Experiments in which eggs were locally inseminated, using a micropipette directed towards the site of impalement of one of the two Ca2+-microelectrodes, clearly established that [Ca2+]i changes, although incapable of propagating over the entire egg cortex, might nevertheless travel very slowly over short distances, their amplitude vanishing rapidly as they propagate from around the sites of sperm entry. The physiologically polyspermic egg of urodele amphibians appears to represent an exception to the universality of a fertilization-induced Ca2+ wave.
Compensatory synaptic growth in the rod terminals as a sequel to partial photoreceptor cell loss in the retina of chimaeric mice
Authors: Sanyal S. , Hawkins R. K. , Jansen H. G. , Zeilmaker G. H. 
Published: April 2021

ABSTRACTIn the retina of chimaeric mice of rd and wild-type genotypic combination, selective loss of rd/rd photoreceptor cells, after initial development, leads to a mosaic retina with variable amounts of normal photoreceptor cells present over the retinal surface. In some of the rod terminals of these retinas the synaptic complexes with the second order retinal neurons are seen to contain multiple synaptic ribbons and an increased number of profiles of the postsynaptic elements. These changes are observed only in the rod terminals and not in the cone pedicles. Computer aided three-dimensional reconstruction of the altered synapses shows that these changes result from an increase in the number of synaptic sites, characterized by multiplication of the synaptic ribbons and enlargement of the second order neuronal processes. A quantitative analysis of such synapses, based on serial electron micrographs, shows that these are most frequently located in the retinal regions of the chimaeric individuals that have suffered maximum photoreceptor cell loss. Thus synaptic growth appears to take place as a reaction to the reduction of afferent input to the postsynaptic components. These findings demonstrate persistent synaptic plasticity in the rod terminals of mammalian retina during the maturational phase of late postnatal development. Compensatory synaptic growth in the rod terminals, as recorded here, can have important implications for the maintenance of visual sensitivity in the diseased or ageing retina.