bluuebunny/crossref_metadata_2025_split huggingface dataset:
Migration and proliferation of cultured neural crest cells in W mutant neural crest chimeras
Authors: Huszar D. , Sharpe A. , Jaenisch R. 
Published: April 2021

ABSTRACT
Chimeric mice, generated by aggregating preimplantation embryos, have been instrumental in the study of the development of coat color patterns in mammals. This approach, however, does not allow for direct experimental manipulation of the neural crest cells, which are the precursors of melanoblasts. We have devised a system that allows assessment of the developmental potential and migration of neural crest cells in vivo following their experimental manipulation in vitro. Cultured C57B1/6 neural crest cells were microinjected in utero into neurulating Balb/c or W embryos and shown to contribute efficiently to pigmentation in the host animal. The resulting neural crest chimeras showed, however, different coat pigmentation patterns depending on the genotype of the host embryo. Whereas Balb/c neural crest chimeras showed very limited donor cell pigment contribution, restricted largely to the head, W mutant chimeras displayed extensive pigmentation throughout, often exceeding 50 % of the coat. In contrast to Balb/c chimeras, where the donor melanoblasts appeared to have migrated primarily in the characteristic dorsoventral direction, in W mutants the injected cells appeared to migrate in the longitudinal as well as the dorsoventral direction, as if the cells were spreading through an empty space. This is consistent with the absence of a functional endogenous melanoblast population in W mutants, in contrast to Balb/c mice, which contain a full complement of melanocytes. Our results suggest that the IV mutation disturbs migration and/or proliferation of endogenous melanoblasts. In order to obtain information on clonal size and extent of intermingling of donor cells, two genetically marked neural crest cell populations were mixed and coinjected into W embryos. In half of the tricolored chimeras, no co-localization of donor crest cells was observed, while, in the other half, a fine intermingling of donor-derived colors had occurred. These results are consistent with the hypothesis that pigmented areas in the chimeras can be derived from extensive proliferation of a few donor clones, which were able to colonize large territories in the host embryo. We have also analyzed the development of pigmentation in neural crest cultures in vitro, and found that neural tubes explanted from embryos carrying wt or weak IV alleles produced pigmented melanocytes while more severe W genotypes were associated with deficient pigment formation in vitro.
The ability of hamster oolemma to fuse with spermatozoa: Its acquisition during oogenesis and loss after fertilization
Authors: Zuccotti Maurizio , Yanagimachi Ryuzo , Yanagimachi Hiroko 
Published: April 2021

ABSTRACTTo determine when the growing hamster oocyte gains the ability to fuse with the spermatozoon, oocytes at various stages of development were collected from ovaries, and zona-pellucida-free oocytes were inseminated in vitro with acrosome-reacted spermatozoa. Very small primary oocytes were unable to fuse with spermatozoa. Oocytes first became competent to fuse with spermatozoa when they had grown to about 20 μm in diameter. The acquisition of fusibility coincided with the first appearance of zona pellucida material and oolemma microvilli. The fusibility of the oolemma increased as the oocyte grew, reaching a maximum when the oocyte reached the metaphase of the second meiosis. The fusibility of the oolemma was reduced drastically after fertilization, and was lost completely by the 8-cell stage. The appearance and subsequent disappearance of a putative fusion-mediating molecule in the oolemma is proposed. Since this molecule is fairly resistant to proteinase digestion, at least in the hamster, it could be a cryptic protein or a glycolipid.
Formation and regeneration of rhombomere boundaries in the developing chick hindbrain
Authors: Guthrie Sarah , Lumsden Andrewc 
Published: April 2021

ABSTRACT
Development in the chick hindbrain is founded on a segmented pattern. Groups of cells are allocated to particular segmental levels early in development, the cells of each segment (rhombomere) mixing freely with each other, but not with those of adjacent segments. After rhombomere formation, cells in the boundary regions become increasingly specialised. Rhombomeres are thus separate territories that will ultimately pursue different developmental fates. We are investigating the mechanisms that establish and maintain the pattern of rhombomeres and their boundaries. Donor-to-host transplantation experiments were used to confront tissue from different axial levels within the hindbrain. The frequency of boundary regeneration and patterning in the hindbrain was then assessed, based on gross morphology, arrangement of motor neurons and immunohistochemistry. We found that when rhombomeres from adjacent positions or positions three rhombomeres distant from one another were confronted, a normal boundary was invariably reconstructed. Juxtaposition of rhombomere 5 with 7 also yielded a new boundary. By contrast, donor and host tissue of the same positional origin combined without forming a boundary. The same result was obtained in combinations of rhombomeres 3 and 5. Confrontation of tissue from even-numbered rhombomeres 4 with 6 or 2 with 4 also failed to regenerate a boundary in the majority of cases. These results suggest that cell surface properties vary according to rhombomeric level in the hindbrain, and may support the idea of a two-segment periodicity.
Separate elements cause lineage restriction and specify boundaries of Hox-1·1 expression
Authors: Puschel Andreas W. , Balling Rudi , Gruss Peter 
Published: April 2021

ABSTRACT
The Hox genes are a class of putative developmental control genes that are thought to be involved in the specification of positional identity along the anteroposterior axis of the vertebrate embryo. It is apparent from their expression pattern that their regulation is dependent upon positional information. In a previous analysis of the Hox-1·1 promoter in transgenic mice, we identified sequences that were sufficient to establish transgene expression in a specific region of the embryo. The construct used, however, did not contain enough regulatory sequences to reproduce all aspects of Hox-1·1 expression. In particular, neither a posterior boundary nor a restriction of expression to prevertebrae was achieved. Here we show correct regulation by Hox-1·1 sequences in transgenic mice and identify the elements responsible for different levels of control. Concomitant with the subdivision of mesodermal cells into different lineages during gastrulation and organogenesis, Hox-1·1 expression is restricted to successively smaller sets of cells. Distinct elements are required at different stages of development to execute this developmental programme. One position-responsive element (130 bp nontranslated leader) was shown to be crucial for the restriction of expression not only along the anteroposterior axis of the embryo, setting the posterior border, but also along the dorsoventral axis of the neural tube and to the lineage giving rise to the prevertebrae. Thus, Hox-1 ·1 expression is established in a specific region of the embryo and in a specific lineage of the mesoderm by restricting the activity of the promoter by the combined effect of several regulatory elements.
Cell rearrangement during gastrulation ofXenopus:direct observation of cultured explants
Authors: Wilson Paul , Keller Ray 
Published: April 2021

ABSTRACTWe have analyzed cell behavior in the organizer region of the Xenopus laevis gastrula by making high resolution time-lapse recordings of cultured expiants. The dorsal marginal zone, comprising among other tissues prospective notochord and somitic mesoderm, was cut from early gastrulae and cultured in a way that permits high resolution microscopy of the deep mesodermal cells, whose organized intercalation produces the dramatic movements of convergent extension. At first, the expiants extend without much convergence. This initial expansion results from rapid radial intercalation, or exchange of cells between layers. During the second half of gastrulation, the expiants begin to converge strongly toward the midline while continuing to extend vigorously. This second phase of extension is driven by mediolateral cell intercalation, the rearrangement of cells within each layer to lengthen and narrow the array. Toward the end of gastrulation, fissures separate the central notochord from the somitic mesoderm on each side, and cells in both tissues elongate mediolaterally as they intercalate. A detailed analysis of the spatial and temporal pattern of these behaviors shows that both radial and mediolateral intercalation begin first in anterior tissue, demonstrating that the anteriorposterior timing gradient so evident in the mesoderm of the neurula is already forming in the gastrula. Finally, time-lapse recordings of intact embryos reveal that radial intercalation takes places primarily before involution, while mediolateral intercalation begins as the mesoderm goes around the lip. We discuss the significance of these findings to our understanding of both the mechanics of gastrulation and the patterning of the dorsal axis.
Developmental expression of the axonal glycoprotein TAG-1: differential regulation by central and peripheral neurons in vitro
Authors: Karagogeos D. , Morton S. B. , Casano F. , Dodd J. , Jessell T. M. 
Published: April 2021

ABSTRACT
TAG-1 is a 135000 Mr axonal glycoprotein of the immunoglobulin superfamily that promotes axon extension in vitro. One distinguishing feature of TAG-1 is its transient expression on subsets of axons in the developing nervous system. To examine the mechanisms that regulate TAG-1, we have monitored the expression of this protein by developing central and peripheral neurons in vitro. TAG-1 was detected on the surface of a subset of Ell to E13 spinal cord neurons in vitro and was also released by these neurons. Expression of TAG-1 on the cell surface was transient but it was possible to detect a released form of TAG-1 at all times in vitro. Spinal cord neurons isolated from older embryos did not express surface TAG-1 when they regenerated axons in vitro. Changes in the environment of spinal cord neurons did not alter the time course of TAG-1 expression, suggesting that regulation of the protein is cell autonomous. In contrast to these results with spinal cord neurons, surface expression of TAG-1 by DRG neurons persisted in vitro and adult DRG neurons re-expressed TAG-1 when grown in vitro. The cell surface and released forms of TAG-1 therefore appear to be regulated differently by central and peripheral neurons.
Interactions between fused, a segment-polarity gene in Drosophila, and other segmentation genes
Authors: Limbourg-Bouchon Bernadette , Busson Denise , Lamour-Isnard Claudie 
Published: April 2021

ABSTRACT
Fused (fu) is a segment polarity gene whose product is maternally required in the posterior part of each segment. To define further the role of fused and determine how it interacts with other segmentation genes, we examined the phenotypes obtained by combining fused with mutations of pair rule, homeotic and other segment polarity loci. When it was possible, we also looked at the distribution of corresponding proteins in fused mutant embryos. We observed that fused;naked (fu;nkd) double mutant embryos display a phenotypic suppression of simple mutant phenotypes: both naked cuticle and denticle belts, which would normally have been deleted by one of the two mutants alone, were restored. In fused, mutant embryos, engrailed (en) and wingless (wg) expression was normal until germ band extension, but partially and completely disappeared respectively during germ band retraction. In the fu;nkd double mutant embryo, en was expressed as in nkd mutant at germ band extension, but later this expression was restricted and became normal at germ band retraction. On the contrary, wg expression disappeared as in fu simple mutant embryos. We conclude that the requirements for fused, naked and wingless activities for normal segmental patterning are not absolute, and propose mechanisms by which these genes interact to specify anterior and posterior cell fates.
Dye-coupling and the formation and fate of the hypoblast in the teleost fish embryo, Barbus conchonius
Authors: Gevers Petra , Timmermans Lucy P. M. 
Published: April 2021

ABSTRACT
The present report describes Lucifer Yellow (LY) transfer between the syncytial layer of the yolk cell (YSL) and blastodermal cells during epiboly in the teleost fish Barbus conchonius. The fate of a group of labeled cells is described until germ layer formation.
At the onset of epiboly, LY seems to be transferred from the YSL to all blastodermal cells. Between 10 % and 40 % epiboly, dye-coupling appears to be restricted to the marginal region. Within 60 min individually labeled cells are distributed among unlabeled cells within the blastoderm. Between 40 % and 60 % epiboly, we observed a ring-shaped group of labeled cells, which probably have involuted during early gastrulation. Consequently, this cell group may correlate with the leading edge of the hypoblast layer within the germ ring. At 60 % epiboly and later, the blastodermal cells are dye-uncoupled from the YSL.
A gradual translocation of the ring-shaped hypoblast towards a dorsally located bar-like structure is observed between 50 % and 100 % epiboly. At 100 % epiboly, fluorescent cells were located in contact with the YSL within the embryo proper, with the brightest fluorescence in the future head region. The translocation is due to dorsalwards convergent cell movements during the gastrulation process. The appearance of the hypoblast as a dye-coupled cell layer may correlate with some restriction in cell fate since the hypoblast differs in fate from the epiblast.
Hypoxanthine phosphoribosyl transferase deficiency, haematopoiesis and fertility in the mouse
Authors: Ansell J. D. , Samuel K. , Whittingham D. G. , Patek C. E. , Hardy K. , Handyside A. H. , Jones K. W. , Muggleton-HARRIS A. L. , Taylor A. H. , Hooper M. L. 
Published: April 2021

ABSTRACT
We have looked for effects of deficiency in hypoxanthine phosphoribosyl transferase (HPRT) in the mouse comparable to non-behavioural consequences of HPRT-deficiency in humans. HPRT-deficient humans show abnormalities in haematopoiesis and, in heterozygotes, there is strong selection in haematopoietic tissues against HPRT-deficient cells arising as a result of X-chromosome inactivation. We have examined two situations in mice in which HPRT- and HPRT+ cells occur in the same individual. First, in chimaeras resulting from the injection of HPRT- embryonal stem cells into HPRT+ blastocysts the fate of HPRT- and HPRT+ cell populations was monitored by their expression of different isozymes of glucose phosphate isomerase and also, in those chimaeras that resulted from injecting the male ES cells into female blastocysts, by in situ hybridisation using a Y-chromosome-specific repetitive DNA probe. There was a small statistically significant selection against the HPRT- population in haematopoietic tissues in both XX↔-&gt;XY and XY&lt;-*XY chimaeras. Second, in female mice doubly heterozygous for HPRT-deficiency and for an electrophoretic variant of the X-linked enzyme phosphoglycerate kinase, there was a similar small statistically significant selection against the HPRT- population in haematopoietic tissues. While further work is required to establish whether this selection is a consequence of the HPRT mutation, it is clear that any selection against cells in the haematopoietic system as a consequence of HPRT-deficiency is at most small compared with the effect seen in humans.
In HPRT-deficient human males surviving beyond the normal age of puberty, there is testicular atrophy. However, we find no effect of HPRT-deficiency on the fertility of either male or female mice.
Thus, as with effects on behaviour, the consequences of HPRT-deficiency for haematopoiesis and testis development in the mouse are at most small compared with those in the human. We conclude that the reason for the difference in effects between the two species lies in a difference in purine-related intermediary metabolism per se, rather than in its interaction with brain amine biochemistry.
Ghox 4.7: a chick homeobox gene expressed primarily in limb buds with limb-type differences in expression
Authors: Mackem Susan , Mahon Kathleen A. 
Published: April 2021

ABSTRACT
Homeobox genes play a key role in specifying the segmented body plan of Drosophila, and recent work suggests that at least several homeobox genes may play a regulatory role during vertebrate limb morphogenesis. We have used degenerate oligonucleotide primers from highly conserved domains in the homeobox motif to amplify homeobox gene segments from chick embryo limb bud cDNAs using the polymerase chain reaction. Expression of a large number of homeobox genes (at least 17) is detected using this approach. One of these genes contains a novel homeobox loosely related to the Drosophila Abdominal B class, and was further analyzed by determining its complete coding sequence and evaluating its expression during embryogenesis by in situ hybridization. Based on sequence and expression patterns, we have designated this gene as Ghox 4.7 and believe that it is the chick homologue of the murine Hox 4.7 gene (formerly Hox 5.6). Ghox 4.7 is expressed primarily in limb buds during development and shows a striking spatial restriction to the posterior zone of the limb bud, suggesting a role in specifying anterior-posterior pattern formation. In chick, this gene also displays differences in expression between wing and leg buds, raising the possibility that it may participate in specifying limb-type identity.
A regulatory region from the mouse Hox-2.2 promoter directs gene expression into developing limbs
Authors: Schughart Klaus , Bieberich Charles J. , Eid Roland , Ruddle Frank H. 
Published: April 2021

ABSTRACT
To characterize cis-acting regulatory elements of the murine homeobox gene, Hox-2.2, transgenic mouse lines were generated that contained the LacZ reporter gene under the control of different fragments from the presumptive Hox-2.2 promoter. A promoter region of 3600 base pairs (bp) was identified, which reproducibly directed reporter gene expression into specific regions of developing mouse embryos. At 8.5 days postcoitum (p.c.) reporter gene activity was detected in posterior regions of the lateral mesoderm and, in subsequent developmental stages, expression of the LacZ gene was restricted to specific regions of the developing limb buds and the mesenchyme of the ventrolateral body region. This pattern of Hox-2.2-LacZ expression was found in all transgenic embryos that have been generated with the 3.6 kb promoter fragment (two founder embryos and embryos from five transgenic lines). In addition, embryos from two transgenic mouse lines expressed the reporter gene at low levels in the developing central nervous system (CNS). Our results are consistent with the idea that in addition to their presumptive role in CNS and vertebrae development, Hox-2.2 gene products are involved in controlling pattern formation in developing limbs.
A 3 kb sequence from the mouse cellular retinoic-acid-binding protein gene upstream region mediates spatial and temporal LacZ expression in transgenic mouse embryos
Authors: Wei Li-Na , Chen Gee-Jang , Chu Ya-Shu , Tsao Jen-Lan , Nguyen-Huu M. Chi 
Published: April 2021

ABSTRACT
A 3233 base pair (bp) sequence of the 5′-flanking region of the mouse cellular retinoic-acid-binding protein (CRABP) gene is determined. From this region, a 3 kb fragment located 150 bp upstream from the transcriptional initiation site is isolated and fused to a LacZ reporter sequence. Transgenic mouse embryos of this fusion gene show spatially and temporally specific expression of LacZ protein and the expression of this fusion gene at the RNA level is confirmed by RNAase protection assays, which detect specific fusion transcripts in RNA samples from tissues of transgenic mouse embryos. In contrast, transgenic mouse embryos of a shorter fusion gene containing only 583 bp from the same upstream region of the mouse CRABP gene fused to the same reporter sequence show no LacZ activities. Thus, it is concluded that the 3 kb sequence, but not the 583 bp sequence, of the mouse CRABP gene contains information for its temporally and spatially specific expression in mouse embryos.
The switch from larval to adult globin gene expression in Xenopus laevis is mediated by erythroid cells from distinct compartments
Authors: Weber Rudolf , Blum Beat , Müller Peter Rudolf 
Published: April 2021

ABSTRACT
The transition of hemoglobins during metamorphosis of Xenopus laevis involves replacement of the larval erythrocytes by adult ones, suggesting that the developmental control of this event depends upon the growth characteristics of the precursor cells. To identify the erythroid precursor cells and to investigate their developmental fate, we analyzed the distribution of stage-specific globin mRNAs by northern blotting in dorsal and ventral fragments of stage 32 embryos after in vitro culture as well as presumptive erythropoietic tissues of tadpoles during metamorphosis.
The histological analysis shows that erythrocytes differentiate only in ventral fragments, suggesting that the ventral blood islands and most likely also the dorsolateral mesoderm are the primary sites of erythropoiesis. We also demonstrate that the first generations of erythrocytes, already express the predominating larval specific a-globin mRNAs. The globin mRNA patterns obtained from presumptive erythropoietic tissues suggest an important role of circulating precursor cells in larval erythropoiesis, whereas the liver appears to be the main site of formation and maturation of the adult erythrocytes.
Tentatively we propose that anuran erythropoiesis is dependent upon a self-perpetuating stem-cell line and that the larval and the adult erythrocytes are derived from successive generations of erythroid precursors, whose commitment may be imposed by the erythropoietic sites.
The expression of tenascin by neural crest cells and glia
Authors: Tucker Richard P. , Mckay Sharen E. 
Published: April 2021

ABSTRACT
The extracellular matrix glycoprotein tenascin is concentrated in both the embryo and adult in regions where cell motility is taking place. For example, during avian neural crest morphogenesis tenascin is concentrated in the rostral half of the sclerotome, precisely where the neural crest cells themselves are found. Previous in vitro studies indicated that somite cells were the source of this tenascin, implying a role for tenascin in directing the ventral migration of neural crest cells and thus the establishment of the periodic arrangement of the PNS. In this study, we have used a cDNA probe to identify the source of tenascin found along the pathways of the neural crest using in situ hybridization. In tissue sections, individual cells found along the neural crest migratory pathways, both before entering the somites and within the somites, are strongly labelled by the tenascin cDNA. In vitro neural crest cells are more strongly labelled with the tenascin probe than somite cells. Finally, western blotting has been used to identify tenascin in culture medium conditioned by neural crest cells. This indicates that neural crest cells themselves are the source of much of the tenascin found lining their migratory pathways, and that interactions with somite cells may not be needed to induce the expression of tenascin. We have also studied the distribution of tenascin mRNA in the developing spinal cord and spinal ganglia. At embryonic days 7 and 10, tenascin cDNA hybridizes within cells that appear to be migrating from the ependymal layer to the white matter, as well as within cells in the dorsal roots. The hybridization is transient, as tenascin mRNA is no longer detected at E18. Thus, the role of tenascin in neural crest and CNS morphogenesis is not related to defining routes of migration, but perhaps to generating a local environment that supports motility.