bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polyembryony inDendrocoelum lacteumO. F. Müller
Authors: Kościelski Bogusław 
Published: April 2021

ABSTRACTThe development of freshwater Turbellaria has been investigated by few scientists, but the embryonic development of Dendrocoelum lacteum was described in detail by Fuliński (1914, 1916). An experimental analysis of the embryonic development of Dendrocoelum lacteum and Planaria torva has been conducted by Seilern-Aspang (1957, 1958). By placing the contents of a cocoon of Planaria torva on a cover-slide one can observe the course of early development. Certain conditions of culture give rise to deformations of the embryonic rudiments, which in turn leads to polyembryony (Seilern-Aspang, 1951b). The phenomenon of polyembryony also occurs in Procerodes lobata (Seilern-Aspang, (1957a). In our investigations normal polyembryony in Dendrocoelum lacteum has been studied in embryonic development not disturbed by experimental factors.
La compétence neurogène du feuillet externe du blastoderme de Poulet en fonction du facteur‘temps’
Authors: Gallera par J. , Ivanov I. 
Published: April 2021

ABSTRACTThe neural competence of the epiblast of the chick blastoderm as a function of timeAll the experiments were done on White Leghorn chick blastoderms, cultured in vitro by a slightly modified version of New’s technique. The anterior region of the full primitive streak (Hensen’s node and the material slightly posterior to it) was excised and implanted on blastoderms of different stages of development. The grafts were always of uniform size (0 · 6 × 0 · 4 mm.). They were implanted either in the antero-lateral region of the area pellucida or in the area opaca. Generally, the grafts gave rise to material which exceeded their presumptive fate. These grafts would normally have formed the notochord, some somites, part of the mid-brain and the hind-brain and, lastly, the roof of the foregut. Our grafts also gave rise to prechordal mesoblast, and some even gave rise to lateral plates. The differentiation of these grafts does not depend on their localization and is not influenced by the age of the host. All the grafts transplanted on blastoderms which had not yet passed the full primitive streak stage, induced the formation of brain which in many cases develops into a more or less reduced medullary anlage. During the whole period of the formation of the primitive streak, the capacity of the ectoblast to form cerebral structures decreases very slowly. However, the frequency of the medullary inductions falls off rapidly from the mid-primitive streak stage on-wards. None of the grafts, made on the blastoderms at the beginning of the regression of the Hensen’s node or later, induced neural structures. At the most, the host ectoblast in contact with the grafts sometimes presents a placode-like appearance. Even these secondary types of inductions are no longer obtained when the implantations are made in the blastoderms at early head-fold or later stages.
The wingless signalling pathway and the patterning of the wing margin in Drosophila
Authors: Couso Juan Pablo , Bishop Sarah A. , Arias Alfonso Martinez 
Published: April 2021

ABSTRACT
The margin of the wing of Drosophila is defined and patterned from a stripe of cells expressing the wingless (wg) gene that is established during the third larval instar in the developing wing blade. The expression of the genes cut and achaete in a small domain in the prospective wing margin region reflects the activity of wg and probably mediate its function. Our results indicate that, in the wing margin, the wingless signal requires the activity of at least three genes: armadillo (arm), dishevelled (dsh) and shaggy (sgg) and that the functional relationship between these genes and wg is the same as that which exist during the patterning of the larval epidermis. These observations indicate that arm, dsh and sgg encode elements of a unique ‘wingless signalling pathway’ that is used several times throughout development.
Distinct developmental expression of a new avian fibroblast growth factor receptor
Authors: Marcelle Christophe , Eichmann Anne , Halevy Orna , Bréant Christiane , Douarin Nicole M. Le 
Published: April 2021

ABSTRACT
We have cloned a new member of the fibroblast growth factor receptor family from avian embryonic RNA. The FREK (for fibroblast growth factor receptor-like embryonic kinase) primary transcript can be alternatively spliced in a tissue- and stage-specific manner to give rise to molecules containing either two or three Ig-like domains. During elongating primitive streak stages, FREK is expressed in the rostral and lateral epiblast and in the Hensen’s node. From 2.5 days of development (E 2.5) on, it is expressed in various ectoderm- and mesoderm-derived structures. Most striking is FREK expression in the skeletal muscle lineage. It is highly expressed in the early myotome and, at later stages, in all skeletal muscles of the embryo. From E9 to hatching, FREK expression in the muscles decreases dramatically but is maintained in satellite cells of adult muscles. FREK transcript is elevated upon addition of basic fibroblast growth factor to serum-starved satellite cells. From this sudy, we conclude: (1) that the structure and pattern of expression of FREK set it apart from other cloned fibroblast growth factor receptors (FGFR) and suggest that FREK is a new member of that family; (2) that FREK may play multiple roles in early avian development, including a specialized role in the early differentiation of skeletal muscle.
Ingrowth by photoreceptor axons induces transcription of a retrotransposon in the developing Drosophila brain
Authors: Mozer Brian A. , Benzer Seymour 
Published: April 2021

ABSTRACT
The development of the lamina, the first optic ganglion of the fly visual system, depends on inductive cues from the innervating photoreceptor axons. lacZ expression from a Pelement insertion, A72, occurs in the anlage of the lamina coincident with axon ingrowth from the eye imaginal disc. In eyeless mutants lacking photoreceptor axons, lacZ expression did not occur.
The P-element was found to have inserted within the 3 long terminal repeat (LTR) of a ‘17.6’ type retrotransposon. The expression pattern of 17.6 transcripts in the brain in wild-type and eyeless mutants paralleled the expression of the lacZ reporter. Analysis of 17.6 cis-regulatory sequences indicates that the lamina-specific expression is due to the combined action of an enhancer element in the LTR and a repressor element within the internal body of the retrotransposon. The regulation of the 17.6 retrotransposon provides a model for the study of innervationdependent gene expression in postsynaptic cells during neurogenesis.
The role of Pax-1 in axial skeleton development
Authors: Wallin Johan , Wilting Jörg , Koseki Haruhiko , Fritsch Rüdiger , Christ Bodo , Balling Rudi 
Published: April 2021

ABSTRACT
Previous studies have identified a single amino-acid substitution in the transcriptional regulator Pax-1 as the cause of the mouse skeletal mutant undulated (un). To evaluate the role of Pax-1 in the formation of the axial skeleton we have studied Pax-1 protein expression in early sclerotome cells and during subsequent embryonic development, and we have characterized the phenotype of three different Pax-1 mouse mutants, un, undulated-extensive (unex ) and Undulated short-tail (Uns ). In the Uns mutation the whole Pax-1 locus is deleted, resulting in the complete absence of Pax-1 protein in these mice. The other two genotypes are interpreted as hypomorphs. We conclude that Pax-1 is necessary for normal vertebral column formation along the entire axis, although the severity of the phenotype is strongest in the lumbar region and the tail. Pax-1-deficient mice lack vertebral bodies and intervertebral discs. The proximal part of the ribs and the rib homologues are also missing or severely malformed, whereas neural arches are nearly normal. Pax-1 is thus required for the development of the ventral parts of vertebrae. Embryonic analyses reveal that although sclerotomes are formed in mutant embryos, abnormalities can be detected from day 10.5 p.c onwards. The phenotypic analyses also suggest that the notochord still influences vertebral body formation some days after the sclerotomes are formed. Furthermore, the notochord diameter is larger in mutant embryos from day 12 p.c., due to increased cell proliferation. In the strongly affected genotypes the notochord persists as a rod-like structure and the nucleus pulposus is never properly formed. Since the notochord is Pax-1-negative these findings suggest a bidirectional interaction between notochord and paraxial mesoderm. The availability of these Pax-1 mutant alleles permitted us to define an early role for Pax-1 in sclerotome patterning as well as a late role in intervertebral disc development. Our observations suggest that Pax-1 function is required for essential steps in ventral sclerotome differentiation, i.e. for the transition from the mesenchymal stage to the onset of chondrogenesis.
Ectopic expression of either the Drosophila gooseberry-distal or proximal gene causes alterations of cell fate in the epidermis and central nervous system
Authors: Zhang Yu , Ungar Anne , Fresquez Catalina , Holmgren Robert 
Published: April 2021

ABSTRACT
Previous studies have shown that the segment polarity locus gooseberry, which contains two closely related transcripts gooseberry-proximal and gooseberry-distal, is required for proper development in both the epidermis and the central nervous system of Drosophila. In this study, the roles of the gooseberry proteins in the process of cell fate specification have been examined by generating two fly lines in which either gooseberry-distal or gooseberryproximal expression is under the control of an hsp70 promoter. We have found that ectopic expression of either gooseberry protein causes cell fate transformations that are reciprocal to those of a gooseberry deletion mutant. Our results suggest that the gooseberry-distal protein is required for the specification of naked cuticle in the epidermis and specific neuroblasts in the central nervous system. These roles may reflect independent functions in neuroblasts and epidermal cells or a single function in the common ectodermal precursor cells. The gooseberryproximal protein is also found in the same neuroblasts as gooseberry-distal and in the descendants of these cells.
Pseudodirected variation in the requirement of cultured plant cells for celldivision factors
Authors: Meins Frederick , Seldran Monique 
Published: April 2021

ABSTRACT
Cells cultured from explants of tobacco leaf require exogenous cell-division factors such as the cytokinin kinetin for sustained proliferation. When cytokinin-requiring (C− ) cells are cultured on medium containing 1/100 the optimum cytokinin concentration they rapidly give rise to cytokinin-autotrophic (C+ ) variants. Some of these variants result from a meiotically transmitted change at the Habituated leaf-2 locus. We measured the rate of phenotypic variation by a simple, quantitative method and found that cultured tobacco cells alternate between the C− and C+ states at extremely high rates of approx. 10−2 per cell generation, which is 102 to 103 -fold more rapid than most somatic mutations in tobacco. These changes are so rapid that the classical distinction between random and induced events is blurred. Selection of alternate phenotypes arising by rapid, reversible cellular variation results in changes that appear to be directed at the tissue level. This phenomenon, called pseudodirected variation, is of particular interest because it suggests novel stochastic mechanisms of cytokinin action and a plausible explanation for the directed, but plastic nature of development in plants.
Microtubule translocation and polymerisation during cortical rotation in Xenopus eggs
Authors: Houliston Evelyn 
Published: April 2021

ABSTRACT
The development of dorsal axial structures in frogs depends on a process of cortical rotation in which the cortex of the fertilised egg becomes displaced with respect to the cytoplasm. An array of aligned microtubules that develops between the vegetal cortex and cytoplasm is implicated in generating movement. Rhodamine-tubulin was injected into eggs to allow patterns of microtubule movement and polymerisation in the vegetal array to be examined. Time-lapse video microscopy of living eggs showed that most of these microtubules move with the vegetal cytoplasm relative to the cortex, at the same speed as cytoplasmic pigment granules. This implies that movement is generated between the microtubules of the vegetal array and the cortex. A few microtubules were also detected that appeared immobile with respect to the cortex. Rhodamine-tubulin became incorporated into vegetal microtubules when injected at any time during the period of cortical rotation. The newly formed microtubules connected the vegetal array and internal cytoplasm. This indicates that local outward-directed polymerisation continues in this region as the cortex translocates. Experiments with low doses of nocodazole showed that this continuing polymerisation does not contribute to the rotation. Concentrations of the drug that prevented tubulin polymerisation had no effect on the speed of rotation if applied after the vegetal array had formed. The same doses prevented movement if applied early enough to prevent the formation of the array. These observations support the idea that mechanochemical enzymes associated with the vegetal microtubules translocate the cortex along microtubules anchored in the subcortical cytoplasm.
Maintenance of Wnt-3 expression in Purkinje cells of the mouse cerebellum depends on interactions with granule cells
Authors: Salinas Patricia C. , Fletcher Colin , Copeland Neal G. , Jenkins Nancy A. , Nusse Roel 
Published: April 2021

ABSTRACT
Wnt genes encode secreted proteins implicated in cell fate changes during development. To define specific cell populations in which Wnt genes act, we have examined Wnt expression in the cerebellum. This part of the brain has a relatively simple structure and contains well-characterized cell populations. We found that Wnt-3 is expressed during development of the cerebellum and that expression is restricted to the Purkinje cell layer in the adult. Wnt-3 expression in Purkinje cells increases postnatally as granule cells start to make contacts with Purkinje cells. To investigate whether interactions with granule cells influence Wnt-3 expression in Purkinje cells, we examined gene expression in several mouse mutants, using the expression of En-2 to follow the fate of granule cells. In the weaver mutant, in which granule cells fail to migrate and subsequently die in the external granular layer, Wnt-3 expression was normal at postnatal day 15 (P15). At that time, some granule cells are still present in the external granular layer. At P28, however, when granule cells could no longer be detected, Wnt-3 expression was almost absent. In the meander tail mutant, in which the anterior cerebellar lobes lack granule cells, Wnt-3 expression was only detected in the normal posterior lobes. Since En genes are implicated in cell-cell interactions mediated by Wnt genes, we examined En-2/En-2 mutant mice, finding normal Wnt3 expression, indicating that the effect of granule cells on the maintenance of Wnt-3 is not mediated by En-2. Our results show that Wnt-3 expression in Purkinje cells is modulated by their presynaptic granule cells at the time of neuronal maturation.
Development of specific muscle and cutaneous sensory projections in cultured segments of spinal cord
Authors: Sharma K. , Korade Z. , Frank E. 
Published: April 2021

ABSTRACT
Development of sensory projections was studied in cultured spinal segments with attached dorsal root ganglia. In spinal segments from stage 30 (E6.5) and older chicken embryos, prelabeled muscle and cutaneous afferents established appropriate projections. Cutaneous afferents terminated solely within the dorsolateral laminae, whereas some muscle afferents (presumably Ia afferents) projected ventrally towards motoneurons. Development of appropriate projections suggests that sufficient cues are preserved in spinal segments to support the formation of modality-specific sensory projections. Further, because these projections developed in the absence of muscle or skin, these results show that the continued presence of peripheral targets is not required for the formation of specific central projections after stage 29 (E6.0).
Development of the dorsal horn in cultured spinal segments was assessed using the dorsal midline as a marker. In ovo, this midline structure appears at stage 29. Lack of midline formation in stage 28 and 29 cultured spinal segments suggests that the development of the dorsal horn is arrested in this preparation. This is consistent with earlier reports suggesting that dorsal horn development may be dependent on factors outside the spinal cord.
Because dorsal horn development is blocked in cultured spinal segments, this preparation makes it possible to study the consequences of premature ingrowth of sensory axons into the spinal cord. In chicken embryos sensory afferents reach the spinal cord at stage 25 (E4.5) but do not arborize within the gray matter until stage 30. During this period dorsal horn cells are still being generated. In spinal segments, only those segments that have developed a midline at the time of culture support the formation of specific sensory projections. The end of the waiting period therefore coincides with the formation of a dorsal midline and, interestingly, also with the development of cues in the dorsal horn that are required for the formation of specific sensory projections. Based on these results, we propose that one important function of the waiting period is to delay the ingrowth of sensory fibers until appropriate guidance cues have developed within the dorsal horn.
Proneural genes influence gliogenesis in Drosophila
Authors: Giangrande Angela 
Published: April 2021

ABSTRACT
Fly glial cells in the wing peripheral nervous system of Drosophila melanogaster originate from underlying epithelial cells. Two findings indicate that gliogenesis is closely associated with neurogenesis. First, it only occurs in regions that also give rise to sensory organs. Second, in mutants that induce the development of ectopic sensory organs glial cells develop at new positions. These findings prompted a genetic analysis to establish whether glial and sensory organ differentiation depend on the same genes. Loss of function mutations of the achaete-scute complex lead to a significant reduction of sensory bristles and glial cells. Genes within the complex affect gliogenesis with different strength and display some functional redundancy. Thus, neurogenesis and gliogenesis share the same genetic pathway. Despite these similarities, however, the mechanism of action of the achaete-scute complex seems to be different in the two processes. Neural precursors express products of the complex, therefore the role of these genes on neurogenesis is direct. However, markers specific to glial cells do not colocalize with products of the achaete-scute complex, showing that the complex affects gliogenesis indirectly. These observations lead to the hypothesis that glio-genesis is induced by the presence of sensory organ cells, either the precursor or its progeny.
The mouse Fgf8 gene encodes a family of polypeptides and is expressed in regions that direct outgrowth and patterning in the developing embryo
Authors: Crossley Philip H. , Martin Gail R. 
Published: April 2021

ABSTRACT
Evidence is accumulating that members of the FGF gene family provide signals that act locally to regulate growth and patterning in vertebrate embryos. In this report, we provide a detailed analysis of the mouse Fgf8 gene. We have mapped the Fgf8 locus to the distal region of mouse chromosome 19, and sequenced the 5′coding region of the gene. Our data identify a new coding exon, and locate multiple splice donor and splice acceptor sites that can be used to produce at least seven transcripts encoding a family of secreted FGF8 proteins with different N termini. From these results, it appears that Fgf8 is structurally the most complex member of the FGF family described to date. In the embryo, many of the regions in which Fgf8 RNA is localized are known to direct outgrowth and patterning, including the apical ectodermal ridge of the limb bud, the primitive streak and tail bud, the surface ectoderm overlying the facial primorida and the midbrain-hindbrain junction, suggesting that FGF8 may be a component of the regulatory signals that emanate from these regions.
An inductive role for the endoderm in Xenopus cardiogenesis
Authors: Nascone Nanette , Mercola Mark 
Published: April 2021

ABSTRACT
Heart induction in Xenopus has been thought to be dependent primarily on the interaction of the heart primordia with the Spemann organizer. We demonstrate, however, that signals derived from the deep dorsoanterior endoderm during early gastrulation are also essential for heart formation. The presence of deep endoderm dramatically enhances heart formation in explants of heart primordia, both in the presence and absence of organizer. Likewise, extirpation of the entire endoderm can decrease the frequency of heart formation in embryos that retain organizer activity. Finally, we show that the combined presence of both endoderm and organizer is necessary and sufficient to induce heart in ventral mesoderm explants that would not otherwise form heart tissue. Xenopus heart induction, therefore, may be a multistep process requiring separate dorsalization and cardiogenic signalling events. This is the first demonstration of a heart-inducing role for the endoderm in Xenopus, indicating that the mechanism of heart formation may be similar in most vertebrates.
Development of the mammalian ear: coordinate regulation of formation of the tympanic ring and the external acoustic meatus
Authors: Mallo Moisés , Gridley Thomas 
Published: April 2021

ABSTRACT
The tympanic membrane in mammals is a trilaminar structure formed by the apposition of two epithelial cell layers, along with an intervening layer of cells derived from pharyngeal arch mesenchyme. One epithelial layer is contributed by the external acoustic meatus, a derivative of the first pharyngeal cleft. The other epithelial layer is contributed by the tubotympanic recess, a derivative of the first pharyngeal pouch. We demonstrate here an absolute correlation between formation of the external acoustic meatus and formation of the tympanic ring, a first archderived membrane bone that anchors the tympanic membrane. Experimental loss of the tympanic ring by retinoic acid treatment, or duplication of the ring in Hoxa-2 null mutant embryos, resulted in corresponding alterations in formation of the external acoustic meatus. We suggest that the tympanic ring primordium induces formation and morphogenesis of the external acoustic meatus, and that expression of the Hoxa-2 and goosecoid genes may be involved in regulating the formation and morphogenesis of these structures.