bluuebunny/crossref_metadata_2025_split huggingface dataset:
Development of segmentation in zebrafish
Authors: Kimmel Charles B. , Sepich Diane S. , Trevarrow Bill 
Published: April 2021

ABSTRACT
Recent findings on the nature and origin of segmentation in zebrafish, Brachydanio rerio, are reviewed. Segmented peripheral tissues include the trunk and tail myotomes, that are derived from somitic mesoderm, and the pharyngeal arches that are derived from head mesoderm in addition to other sources. Two major regions of the central nervous system, the spinal cord and hindbrain, are also segmentally organized, as deduced from the distribution of identified neurones in both regions and by formation of neuromeres in the hindbrain that contain single sets of these neurones. Neural and mesodermal segments in the same body region can be related to one another by their patterns of motor innervation. This relationship is simple for the spinal/myotomal segments and complex for the hindbrain/pharyngeal arch segments. Development of the segments is also complex. Mesodermal and ectodermal progenitors have separate embryonic origins and indeterminate cell lineages, and the embryonic cells migrate extensively before reaching their definitive segmental positions. Results of heat-shock experiments suggest that development of myotomal and spinal segments are regulated coordinately in postgastrula embryos. Segmental patterning may be a relatively late feature of zebrafish embryonic development.
Regulation and putative function of the Drosophila gap gene Krüppel
Authors: Jäckle Herbert , Gaul Ulrike , Redemann Norbert 
Published: April 2021

ABSTRACT
The Drosophila segmentation gene Krüppel (Kr) is expressed in a broad band of cells that covers about four-segment primordia in the blastoderm embryo. Examination of size and position of the Kr protein domain in various mutant embryos revealed that the establishment of the domain of Kr gene expression is under the control of the maternal effect pattern organizers which act at the poles. The lack of Kr activity causes a gap in the segment pattern of the embryo which is about twice the size of the Kr expression domain and extends posterior to it. This indicates that Kr activity per se is not directly responsible for the establishment of the pattern elements which are deleted in the mutant embryo. Examination of the molecular lesions in four Kr alleles indicated that each of them is a point mutant within the coding sequence of the Kr gene and each mutation results in a different replacement of a single amino acid within the ‘finger domain’ of the Kr protein. Thus, this region of the Kr protein is essential for Kr function. Since this portion of the Kr protein shares structural homology with the DNA-binding domain of several transcription factors, we propose that Kr acts as a transcription factor on subordinate genes that process the spatial cues provided by Kr activity to establish eventually the segments in the central region of the embryo.
Expression of Schwann cell markers by mammalian neural crest cells in vitro
Authors: Smith-Thomas L. C. , Fawcett J. W. 
Published: April 2021

ABSTRACT
During embryonic development, neural crest cells differentiate into a wide variety of cell types including Schwann cells of the peripheral nervous system. In order to establish when neural crest cells first start to express a Schwann cell phenotype immunocytochemical tech niques were used to examine rat premigratory neural crest cell cultures for the presence of Schwann cell markers. Cultures were fixed for immunocytochemistry after culture periods ranging from 1 to 24 days. Neural crest cells were identified by their morphology and any neural tube cells remaining in the cultures were ident ified by their epithelial morphology and immunocyto chemically. As early as 1 to 2 days in culture, approxi mately one third of the neural crest cells stained with m217c, a monoclonal antibody that appears to recognize the same antigen as rat neural antigen-I (RAN-1). A similar proportion of cells were immunoreactive in cultures stained with 192-IgG, a monoclonal antibody that recognizes the rat nerve growth factor receptor. The number of immunoreactive cells increased with time in culture. After 16 days in culture, nests of cells, many of which had a bipolar morphology, were present in the area previously occupied by neural crest cells. The cells in the nests were often associated with neurones and were immunoreactive for m217c, 192-IgG and antibody to S-100 protein and laminin, indicating that the cells were Schwann cells. At all culture periods examined, neural crest cells did not express glial fibrillary acidic protein.
These results demonstrate that cultured premigratory neural crest cells express early Schwann cell markers and that some of these cells differentiate into Schwann cells. These observations suggest that some neural crest cells in vivo may be committed to forming Schwann cells and will do so provided that they then proceed to encounter the correct environmental cues during embry onic development.
Differential timing of nuclear lamin A/C expression in the various organs of the mouse embryo and the young animal: a developmental study
Authors: Röber Ruth-Ariane , Weber Klaus , Osborn Mary 
Published: April 2021

ABSTRACT
In mouse embryos, acquisition of the nuclear lamin polypeptides A/C varies according to developmental stage and tissue type. In order to determine the precise time points and cell types in which lamin A/C are first observed, we have used two monoclonal antibodies in immunofluorescence studies of different tissues of developing mouse embryos and of young mice. One antibody (mAB346) is specific for lamins A and C, while the other (PKB8) detects lamins A, B and C. Dividing uterine development into three phases - germ layer formation, organogenesis and tissue differentiation - our results show that lamin A/C expression in the embryo proper is not observed until the third phase of development. Lamin A/C first appears at embryonic day 12 in muscle cells of the trunk, head and the appendages. Three days iater it is also seen in cells of the epidermis where its appearance coincides with the time of stratification. In the simple epithelia of lung, liver, kidney and intestine, as well as in heart and brain, lamins A/C do not appear until well after birth. Embryonal carcinoma (EC) cells express lamin B but not lamin A/C. Lamin A/C expression is noted in some EC cells after they are induced to differentiate and in several differentiated teratocarcinoma cell lines. Our results suggest that commitment of a cell to a particular pathway of differentiation (assayed by cell-type-specific expression of intermediate filament proteins) usually occurs prior to the time that lamin A/C can be detected. Thus lamin A/C expression may serve as a limit on the plasticity of cells for further developmental events.
PDGF receptors on cells of the oligodendrocyte-type-2 astrocyte (O-2A) cell lineage
Authors: Hart Ian K. , Richardson William D. , Heldin Carl-Henrik , Westermark Bengt , Raff Martin C. 
Published: April 2021

ABSTRACT
It has been shown previously that cultures of rat optic nerve contain three types of macroglial cells - oligodendrocytes and two types of astrocytes. Type-1 astrocytes develop from their own precursor cells beginning before birth, while oligodendrocytes and type-2 astrocytes develop postnatally from a common bipotential precursor called the O-2A progenitor cell. Proliferating O-2A progenitor cells give rise to postmitotic oligodendrocytes beginning around birth, and to type-2 astrocytes beginning in the second postnatal week. Studies in vitro have suggested that platelet-derived growth factor (PDGF), secreted by type-1 astrocytes, plays an important part in timing oligodendrocyte development: PDGF seems to keep O-2A progenitor cells proliferating until an intrinsic clock in the progenitor cells initiates the process leading to oligodendrocyte differentiation. The clock apparently determines when a progenitor cell becomes unresponsive to PDGF, at which point the cell stops dividing and, as a consequence, automatically differentiates into an oligodendrocyte.
Here we have used radiolabelled PDGF to show that O-2A progenitor cells have PDGF receptors, suggesting that these cells respond directly to PDGF. The receptors resemble the type A PDGF receptor previously described on human fibroblasts and are initially retained when progenitor cells stop dividing and develop in vitro into oligodendrocytes. The latter finding indicates that receptor loss is not the reason that progenitor cells initially become mitotically unresponsive to PDGF.
Octopod, a homeotic mutation of the moth Manduca sexta, influences the fate of identifiable pattern elements within the CNS
Authors: Booker Ronald , Truman James W. 
Published: April 2021

ABSTRACT
Octopod (Octo) is a mutation of the moth Manduca sexta, which results in the homeotic transformation of the ventral surface of the first (Al) and less often the second (A2) abdominal segments in the anterior direction. The extent of the transformation ranges from a slight deformation of the ventral cuticle, up to the formation of miniature thoracic legs on Al. The extent of the transformation is always less within A2 as compared to Al. A genetic analysis revealed that Octo is an autosomal mutation which shows incomplete dominance. The effect of this mutation on the central nervous system (CNS) was assessed by examining the distribution and fate of the postembryonic neuroblasts in the segmental ganglia of Octo larvae. In each of the thoracic ganglia of wildtype larvae, there is a set of 45–47 neuroblasts; a reduced but homologous array of 24 and 10 neuroblasts are found in Al and A2, respectively. Ganglion Al of Octo larvae had 1 to 6 supernumerary neuroblasts, and 20% of the A2 ganglia showed a single ectopic neuroblast. The supernumerary neuroblasts corresponded to identifiable neuroblasts normally found in more anterior ganglia. The Octo mutation also influenced the mitotic activity of stem cells normally present in Al. In this case, the neuroblasts generated a lineage of cells that were typical of a thoracic location rather than Al. These data demonstrate that homeotic mutations can influence the fate of identifiable pattern elements within the CNS of an insect.
Inducible expression of an hsp68-lacZ hybrid gene in transgenic mice
Authors: Kothary Rashmi , Clapoff Susan , Darling Susan , Perry Marc D. , Moran Laurence A. , Rossant Janet 
Published: April 2021

ABSTRACT
Transgenic mice have been generated that express the E. coli β-galactosidase gene under the control of the promoter from the mouse heat-shock gene, hsp68. Sequences from -664 to +113 relative to the start of transcription of the hsp68 gene were sufficient to direct stress-induced expression of the β-galactosidase gene in adult tail tissue and various tissues of fetal stages of development. Expression was detected in situ by staining with the chromogenic substrate, X-gal. The hybrid gene was refractory to induction in preimplantation embryos until the blastocyst stage of development, as reported for the endogenous hsp68 gene. No constitutive expression was observed by in situ staining or Northern analysis at any stage of development, even in tissues that constitutively express the endogenous hsp68 gene. We conclude that the hsp68 promoter region included in the construct contains sufficient sequence information for heat and arsenite inducibility, but it does not contain sequences controlling tissue-specific expression during development. This tightly regulated inducible promoter may provide a useful tool for short-term inducible gene expression in transgenic mice.
Biochemical research on oogenesis. RNA accumulation in the oocytes of the newt Pleurodeles waltl
Authors: Eynde Hilde Van Den , Mazabraud André , Denis Herman 
Published: April 2021

Abstract
We have compared the accumulation of 5S RNA and tRNA in oocytes of Pleurodeles waltl with the corresponding process previously studied in Xenopus laevis. 5S RNA synthesis is regulated similarly in both species since different families of 5S RNA genes are transcribed in oocytes and in somatic cells of P. waltl, as in those of X. laevis. Previtellogenic oocytes of P. waltl contain only one prominent kind of storage particles (thesaurisomes). In contrast, X. laevis oocytes of the same size contain two major classes of thesaurisomes, sedimenting at 42S and 7S. The more abundant particles found in P. waltl oocytes are homologous to the larger thesaurisomes (42S) of X. laevis, but they have a lower sedimentation coefficient and a higher tRNA/5S RNA molar ratio than their X. laevis counterparts. Small amounts of particles which we think to be homologous to the 7S particles of X. laevis are present in previtellogenic oocytes of P. waltl. Therefore, the storage function of the 7S particle protein (TFIIIA) is only marginal in this species. In X. laevis oocytes TFIIIA has a second function. It acts as a positive transcription factor involved in the developmentally regulated expression of the 5S RNA genes. In X. laevis expression of the oocyte-type 5S RNA genes is accompanied by a massive accumulation of TFIIIA. This is not the case in P. waltl.
A study of shaggy reveals spatial domains of expression of achaete–scute alleles on the thorax of Drosophila
Authors: Simpson Pat , Carteret Cathie 
Published: April 2021

Abstract
A study of shaggy mutant clones on the notum reveals that a greater number of cells are diverted into the bristle pathway of differentiation and fewer cells remain to produce the epidermis, shaggy clones differentiate supernumerary microchaetae and macrochaetae but these are found in the correct spatial locations, e.g. clusters of macrochaetae are formed round the position of the extant macrochaetae. The shaggy mutant phenotype requires the functioning of the genes of the achaete-scute (AS–C) complex but a dosage study shows that it is unlikely that the AS–C is overexpressed in shaggy cells. Data are presented that argue, also, for a correct spatial expression of the AS–C in shaggy mutants. A study of clones doubly mutant for shaggy and different achaete and scute alleles is consistent with the hypothesis that the clusters of macrochaetae formed by shaggy represent the restricted spatial domains of expression of the AS–C. The results can be reconciled with the known role for the AS–C, in determining which bristle types differentiate where, and a role for shaggy in the cell interactions, within domains of the AS–C expression, leading to the definition of only one bristle mother cell.
Paradoxical perpendicular contact guidance displayed by mouse cerebellar granule cell neurons in vitro
Authors: Nakatsuji Norio , Nagata Isao 
Published: April 2021

ABSTRACT
In order to study migration of neurons in vitro, we cultured microexplants of the newborn mouse cerebellum outer layer, which is rich in immature granule cells, on a substratum double-coated with poly-L-lysine and laminin. The granule cells first migrated away from the explant along radially oriented parallel bundles of their neurites, thus displaying typical contact guidance. Then, in almost all explants, they changed their orientation by 90° to extend cell processes and translocate perpendicular to the radial neurites. Orientation and migration of neurons perpendicular to the aligned parallel structure is a novel type of contact-guided cell behavior, and may have interesting implications in migration of neurons in the cerebellum and other parts of the nervous system.
Prepupal differentiation in Drosophila: distinct cell types elaborate a shared structure, the pupal cuticle, but accumulate transcripts in unique patterns
Authors: Fechtel Kim , Fristrom Dianne K. , Fristrom James W. 
Published: April 2021

ABSTRACT
The components of the pupal cuticle are the main differentiation products synthesized by both the larval and adult epidermis during the prepupal period of Drosophila development. The pupal cuticle is formed in vitro by imaginal discs in response to a 6 h pulse of 20-hydroxyecdysone (20-HE). We previously described the isolation and initial characterization of four ecdysone-dependent genes (EDGs) whose expression in imaginal discs occurs only in response to a pulse of 20-HE. In this report, we demonstrate that the pattern of temporal and tissue-specific expression of these EDGs in vivo is like that expected for genes that encode pupal cuticle proteins. Transcripts of these genes are detected in prepupae only in the epidermis and only when cuticle components are synthesized and secreted. Nonetheless, their temporal and spatial patterns of accumulation differ. EDG-84A-1 transcripts accumulate only in prepupae and only in imaginal cells. EDG-78E and EDG-64CD transcripts accumulate at the same time in both larval and imaginal cells. EDG42-A transcripts appear first in prepupae in imaginal cells and then, after a 2-4 h lag, in larval cells. It is evident that some genes are not restricted in their expression to only larval or imaginal epidermis.
Biochemical differentiation in a mutant of Dictyostelium discoideum defective in cyclic AMP chemotaxis and in intercellular cohesion
Authors: Srinivas Usha K. , Henderson Ellen J. 
Published: April 2021

ABSTRACT
A temperature-sensitive mutant of Dictyostelium discoideum has been isolated based on its lack of chemotaxis toward cyclic AMP at the restrictive temperature, 27°C. The mutant develops normally at the permissive temperature, 22°C, but fails to aggregate or complete development at the restrictive temperature. The temperature-sensitive phenotype can be bypassed by allowing cultures to grow into late log phase or to starve for 60 –90 min at 22°C prior to a shift to 27°C. At 27°C, the mutant overproduces cell surface cyclic AMP receptors of both high and low affinity and is capable of spontaneous oscillations in light scattering in cell suspensions.
Despite its complete lack of morphological development, the mutant undergoes extensive biochemical differentiation. At the onset of starvation, it shows increased levels of N-acetylglucosaminidase, it expresses cyclic AMP receptors at the normal time and, although somewhat slowly, suppresses those receptors as if aggregation had been achieved. Metabolic pulse labellings with [35S]methionine revealed that the mutant at 27 °C displays the same changes in the patterns of newly synthesized proteins observed during the vegetative-to-aggregation and the aggregation-to-slug stages of normal development. The only clear difference from wild type was the failure of the culmination-stage isozyme of β-glucosidase to appear.
The mutant is defective in establishment of intercellular cohesion mechanisms, correlated with poor agglutination by concanavalin A, at the restrictive temperature. The properties of the mutant place severe constraints on models regarding the role of chemoreception and intercellular cohesion in regulation of gene expression.
The development of the Xenopus retinofugal pathway: optic fibers join a pre-existing tract
Authors: Easter S. S. , Taylor J. S. H. 
Published: April 2021

ABSTRACT
The developing optic nerve and tract have received considerable attention in recent years, but the cellular and subcellular microenvironment of the growing axons has not been described. In the belief that such a description is essential (though certainly not sufficient) for an understanding of pathway formation, we have examined the normal development of the retinofugal projection of Xenopus laevis.
Optic fibers were labeled anterogradely at the retina with horseradish peroxidase (HRP) or the carbocyanine dye, Dil, at stages 32 to postmetamorphosis. The brains were examined both as whole mounts and in sections, light- and electron-microscopically, with the emphasis on tracts associated with the route of the optic fibers.
At stage 32, two ventral commissures were present, the anterior and postoptic. They were immediately subjacent to the pia. All tracts and even isolated axons were in similarly superficial locations. The first deep pathway (separated from the pia by cell nuclei) was seen at stage 46; it was a dorsal commissure, probably the posterior.
The first retinal axons passed from the optic stalk into the ventral part of the diencephalon, where they coursed along the rostral edge of the postoptic commissure, and maintained this position, relative to the other fibers in the tract of the commissure, throughout the remainder of their contralateral trajectory. They reached the presumptive thalamic and tectal termination sites and arborized. Subsequent optic axons followed this same route, thus enlarging the optic pathway relative to the more slowly growing nonoptic part of the commissure and its tract. Electron microscopy revealed, as early as stage 35, specialized contacts between cellular processes in the neuropil. These contacts had the form of symmetric membranous thickenings; some were associated with vesicles and were presumed to be synapses.
We conclude that the early forebrain and midbrain have only two ventral commissural pathways, and most axons that grow out after these pathways have formed add to them rather than establish new tracts. The optic axons travel a stereotyped pathway alongside a preexisting tract associated with the postoptic commissure. The possibility that optic fiber outgrowth is normally influenced by pre-existing tracts is discussed in relation to recent experimental investigations of fiber growth from ectopic eyes.
Complex spatio-temporal accumulation of alternative transcripts from the neurogenic geneDeltaduringDrosophilaembryogenesis
Authors: Kopczynski Casey C. , Muskavttch Marc A. T. 
Published: April 2021

ABSTRACTDelta (Dl) function is required for proper specification of epidermal and neural lineages within the neurogenic ectoderm of Drosophila melanogaster. We have determined the spatial accumulation of five Dl transcripts that arise as the result of alternative RNA processing during embryogenesis. We find that these transcripts accumulate in all cells of the neurogenic ectoderm immediately preceding neuroblast segregation, indicating that transcription of Dl does not differ between presumptive neuroblasts and presumptive dermoblasts. Dl transcripts also accumulate transiently in mesodermal and endodermal cells, suggesting that Dl may function in developmental processes in addition to differentiation of the neurogenic ectoderm. We find that three of the Dl transcripts are localized to the base of the nucleus during cellularization. The apparent association of these three transcripts with polysomes suggests that they accumulate within the cytoplasm at the nuclear periphery and is consistent with the hypothesis that Dl encodes multiple translational products.