bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pattern formation during gastrulation in the sea urchin embryo
Authors: McClay David R. , Armstrong Norris A. , Hardin Jeff 
Published: April 2021

ABSTRACT
The sea urchin embryo follows a relatively simple cell behavioral sequence in its gastrulation movements. To form the mesoderm, primary mesenchyme cells ingress from the vegetal plate and then migrate along the basal lamina lining the blastocoel. The presumptive secondary mesenchyme and endoderm then invaginate from the vegetal pole of the embryo. The archenteron elongates and extends across the blastocoel until the tip of the archenteron touches and attaches to the opposite side of the blastocoel. Secondary mesenchyme cells, originally at the tip of the archenteron, differentiate to form a variety of structures including coelomic pouches, esophageal muscles, pigment cells and other cell types. After migration of the secondary mesenchyme cells from their original position at the tip of the archenteron, the endoderm fuses with an invagination of the ventral ectoderm (the stomodaem), to form the mouth and complete the process of gastrulation. A larval skeleton is made by primary mesenchyme cells during the time of archenteron and mouth formation.
A number of experiments have established that these morphogenetic movements involve a number of cell autonomous behaviors plus a series of cell interactions that provide spatial, temporal and scalar information to cells of the mesoderm and endoderm. The cell autonomous behaviors can be demonstrated by the ability of micromeres or endoderm to perform their morphogenetic functions if either is isolated and grown in culture. The requirement for cell interactions has been demonstrated by manipulative experiments where it has been shown that axial information, temporal information, spatial information and scalar information is obtained by mesoderm and endoderm from other embryonic cells. This information governs the cell autonomous behavior and places the cells in the correct embryonic context
The midblastula transition, the YSL transition and the onset of gastrulation in Fundulus
Authors: Trinkaus J. P. 
Published: April 2021

ABSTRACT
The first signs of cell motility appear in Fundulus toward the end of cleavage, after cleavages 11 and 12. When blastomeres cease cleaving, their surfaces undulate and form blebs. At first, these blebbing cells remain in place. Gradually thereafter they begin movement, with blebs and filolamellipodia serving as organs of locomotion. Non-motile cleaving blastomeres have thus differentiated into motile blastula cells. This transformation corresponds to the midblastula transition of amphibian embryos.
Gastrulation in Fundulus begins with vegetalward contraction of the external yolk syncytial layer. This causes narrowing of the E-YSL and initiates the epibolic expansion of the blastoderm. Convergent movements of deep cells within the blastoderm begin toward the end of this contraction. The YSL forms as a result of invasion of the yolk cell cytoplasm by nuclei from open marginal blastomeres during cleavage. These YSL nuclei then undergo five metachronous divisions. After this, they divide no more. YSL contraction begins approximately 1.5 hours after cessation of these divisions (21-22°C). This cessation of nuclear divisions is preceded by a gradual decrease in rate. (1) The duration of each succeeding mitosis increases steadily and often some nuclei do not divide at mitosis V. (2) The duration of interphases between succeeding mitoses also increases, but to a much greater degree, and the longest interphase by far is the last one, I-IV, between mitoses IV and V. (3) The mitotic waves responsible for mitosis V move much more slowly than those for the first four mitoses and invariably decelerate. This gradual cessation of YSL nuclear divisions clearly sets the stage for the contraction of YSL cytoplasm and thus the beginning of gastrulation. We call this the YSL transition. It is not to be confused with the midblastula transition, which occurs 3-4 hours earlier. The MBT commences cytodifferentiation; the YSL transition commences morphogenesis.
NCAM and its polysialic acid moiety: a mechanism for pull/push regulation of cell interactions during development?
Authors: Rutishauser U. 
Published: April 2021

ABSTRACT
Many cell adhesion molecules have a distinct pattern of expression and well-defined role in cell-cell recognition. In contrast, NCAM is broadly expressed and perturbations of its function affect many diverse aspects of embryonic development Evidence has been obtained suggesting that the molecule and its polysialic acid moiety serve not only to contribute to specific interactions, but also to regulate overall cell-cell apposition. In this latter mode, the molecule can have both a positive and a negative effect on a wide variety of contact-dependent cellular events.
Rhombomere transplantation repatterns the segmental organization of cranial nerves and reveals cell-autonomous expression of a homeodomain protein
Authors: Kuratani Shigeru C. , Eichele Gregor 
Published: April 2021

ABSTRACT
The developing vertebrate hindbrain consists of segmental units known as rhombomeres. Hindbrain neuroectoderm expresses 3 Hox 1 and 2 cluster genes in characteristic patterns whose anterior limit of expression coincides with rhombomere boundaries. One particular Hox gene, referred to as Ghox 2.9, is initially expressed throughout the hindbrain up to the anterior border of rhombomere 4 (r4). Later, Ghox 2.9 is strongly upregulated in r4 and Ghox 2.9 protein is found in all neuroectodermal cells of r4 and in the hyoid crest cell population derived from this rhombomere. Using a polyclonal antibody, Ghox 2.9 was immunolocalized after transplanting r4 within the hindbrain. Wherever r4 was transplanted, Ghox 2.9 expression was cell-autonomous, both in the neuroectoderm of the graft and in the hyoid crest cell population originating from the graft.
In all vertebrates, rhombomeres and cranial nerves (nerves V, VII+VIII, IX, X) exhibit a stereotypic relationship: nerve V arises at the level of r2, nerve VII+VIII at r4 and nerves IX-X extend caudal to r6. To examine how rhombomere transplantation affects this pattern, operated embryos were stained with monoclonal antibodies E/C8 (for visualization of the PNS and of even-numbered rhombomeres) and HNK-1 (to detect crest cells and odd-numbered rhombomeres). Upon transplantation, rhombomeres did not change E/C8 or HNK-1 expression or their ability to produce crest cells. For example, transplanted r4 generated a lateral stream of crest cells irrespective of the site into which it was grafted. Moreover, later in development, ectopic r4 formed an additional cranial nerve root. In contrast, transplantation of r3 (lacks crest cells) into the region of r7 led to inhibition of nerve root formation in the host.
These findings emphasize that in contrast to spinal nerve segmentation, which entirely depends on the pattern of somites, cranial nerve patterning is brought about by factors intrinsic to rhombomeres and to the attached neural crest cell populations. The patterns of the neuroectoderm and of the PNS are specified early in hindbrain development and cannot be influenced by tissue transplantation. The observed cell-autonomous expression of Ghox 2.9 (and possibly also of other Hox genes) provides further evidence for the view that Hox gene expression underlies, at least in part, the segmental specification within the hindbrain neuroectoderm.
Mouse Cdx-1 expression during gastrulation
Authors: Meyer Barbara I. , Gruss Peter 
Published: April 2021

ABSTRACT
We describe the expression pattern of the mouse Cdx-1 gene during early development, examined by both RNA and protein analyses. Cdx-1 expression began with the onset of the head process formation (day 7.5) in ectodermal and mesodermal cells of the primitive streak. Expression extended initially to the middle of the prospective hindbrain and subsequently regressed caudad to the spinal cord level by day 9.5. The mesoderm-specific expression was detected in the first somites and could be followed during their differentiation to the myotome of the dorsal somitic edge by day 12. The developing limb buds and the mesonephros exhibited expression up to day 12. No signal could be detected in notochordal cells and cells of the definitive endoderm. Thus, Cdx-1 is expressed during gastrulation when anterior-posterior positional values are established along the embryonic axes. Furthermore, the expression correlates with the formation of segmented tissue in the posterior hindbrain, the spinal cord and structures like the mesonephros.
Induction of floor plate differentiation by contact-dependent, homeogenetic signals
Authors: Placzek Marysia , Jessell Thomas M. , Dodd Jane 
Published: April 2021

ABSTRACT
The floor plate is located at the ventral midline of the neural tube and has been implicated in neural cell patterning and axon guidance. To address the cellular mechanisms involved in floor plate differentiation, we have used an assay that monitors the expression of floorplate-specific antigens in neural plate explants cultured in the presence of inducing tissues. Contact-mediated signals from both the notochord and the floor plate act directly on neural plate cells to induce floor plate differentiation. Floor plate induction is initiated medially by a signal from the notochord, but appears to be propagated to more lateral cells by homeogenetic signals that derive from medial floor plate cells. The response of neural plate cells to inductive signals declines with embryonic age, suggesting that the mediolateral extent of the floor plate is limited by a loss of competence of neural cells. The rostral boundary of the floor plate at the midbrain-forebrain junction appears to result from the lack of inducing activity in prechordal mesoderm and the inability of rostral neural plate cells to respond to inductive signals.
Genetic analysis of the Drosophila cdc2 homolog
Authors: Stern Bodo , Ried Gabriele , Clegg Nigel J. , Grigliatti Thomas A. , Lehner Christian F. 
Published: April 2021

ABSTRACT
We have identified mutations in the Drosophila cdc2 gene. The recessive lethality of these mutant alleles was rescued after P-element-mediated transformation with a genomic cdc2 fragment. Sequence analysis of amorphic alleles revealed non-conservative exchanges in evolutionary conserved positions. These alleles caused lethality at the larval-pupal interphase due to the absence of imaginal tissues. Embryonic lethality resulted when the maternal Dm cdc2 contribution was reduced through the use of a temperature-sensitive allele. Dm cdc2 function, therefore, is essential for cell proliferation throughout development. Dm cdc2 function is clearly required for mitosis, but no evidence for a requirement in S-phase was obtained. The reversible block of the mitotic proliferation which was observed in the PNS of mutant embryos occurred exclusively in the G2-phase. Moreover, while the mitotic proliferation of imaginal cells was blocked in the amorphic mutant larvae, non-imaginal larval cells continued to grow and endoreplicate their DNA. The Dm cdc2 mutant phenotype could neither be rescued with Dm cdc2c (encoding a cdc2-like kinase) nor enhanced by a reduction of the Dm cdc2c gene dose. These results indicate that the Dm cdc2- and Dm cdc2c-kinases control different processes.
Properties of the dorsalizing signal in gastrulae of Xenopus laevis
Authors: Lettice Laura A. , Slack Jonathan M. W. 
Published: April 2021

ABSTRACT
According to the ‘three signal model’, the regional specification of tissue type within the mesoderm of Xenopus laevis occurs in a process called ‘dorsalization’. We have studied the timing and transmission characteristics of this signal, and assessed the dorsalizing activity of the lithium ion and a panel of cytokines.
The marginal zone has been fate mapped during gastrulation by colloidal gold labelling and it is shown that the ventral tissue undergoes substantial circumferential expansion. The fate map information is used to provide tissues of constant cellular composition for experiments conducted at different stages.
The stage at which dorsalization can occur has been investigated by means of heterochronic dorsal-ventral combinations. The results indicate that the interaction occurs during gastrulation, with a decline in both signal strength and competence of the ventral marginal zone to respond as gastrulation proceeds.
The signal is capable of passing through arrangements of membranes that exclude the possibility of cytoplasmic contact, implying that it can be carried by a diffusible morphogen.
The effect on the ventral marginal zone of lithium and a number of cytokines has also been studied. While none appears to function as a dorsalizing signal, lithium acts during blastula stages to alter the response to the mesoderm-inducing signal such that the inductions are of a more dorsal character.
These data confirm that the dorsalizing signal is independent of and operates later than the signal(s) from the vegetal hemisphere that induce mesoderm during the blastula stages.
Mesonephric contribution to testis differentiation in the fetal mouse
Authors: Buehr Mia , Gu Subin , McLaren Anne 
Published: April 2021

ABSTRACT
Testes from 11.5-day-old mouse embryos, with and without attached mesonephroi, were cultured for 7 days. Isolated testes failed to develop well-differentiated testis cords: however, when cultured attached to a mesonephros from either a male or a female donor embryo, testes developed cords that were normal in appearance. Testes cultured next to a mesonephric region but separated from it by a permeable filter, did not develop normal cords, nor did testes grafted to fragments of embryonic limb or heart. When testes were grafted to mesonephric regions from mice carrying a transgenic marker, the marker was found in some of the peritubular myoid cells and other interstitial cells of the testis, but not in the Sertoli cells or the germ cells. We conclude that after 11.5 days post coitum, cells can migrate from the mesonephric region into the differentiating testis and can contribute to the interstitial cell population, and that this contribution is necessary for the establishment of normal cord structure. The germ cells in all cultured testes, whether or not differentiated cords were present, were T1 prospermatogonia: no meiotic germ cells were seen.
Programmed cell death during Drosophila embryogenesis
Authors: Abrams John M. , White Kristin , Fessler Liselotte I. , Steller Hermann 
Published: April 2021

ABSTRACT
The deliberate and orderly removal of cells by programmed cell death is a common phenomenon during the development of metazoan animals. We have examined the distribution and ultrastructural appearance of cell deaths that occur during embryogenesis in Drosophila melanogaster. A large number of cells die during embryonic development in Drosophila. These cells display ultrastructural features that resemble apoptosis observed in vertebrate systems, including nuclear condensation, fragmentation and engulfment by macrophages. Programmed cell deaths can be rapidly and reliably visualized in living wild-type and mutant Drosophila embryos using the vital dyes acridine orange or nile blue. Acridine orange appears to selectively stain apoptotic forms of death in these preparations, since cells undergoing necrotic deaths were not significantly labelled. Likewise, toluidine blue staining of fixed tissues resulted in highly specific labelling of apoptotic cells, indicating that apoptosis leads to specific biochemical changes responsible for the selective affinity to these dyes. Cell death begins at stage 11 (∼7 hours) of embryogenesis and thereafter becomes widespread, affecting many different tissues and regions of the embryo. Although the distribution of dying cells changes drastically over time, the overall pattern of cell death is highly reproducible for any given developmental stage. Detailed analysis of cell death in the central nervous system of stage 16 embryos (13-16 hours) revealed asymmetries in the exact number and position of dying cells on either side of the midline, suggesting that the decision to die may not be strictly predetermined at this stage. This work provides the basis for further molecular genetic studies on the control and execution of programmed cell death in Drosophila.
Cellular patterning of fast and slow fibres in the intermandibularis muscle of chick embryos
Authors: Robson L. G. 
Published: April 2021

ABSTRACT
The way in which the pattern of cell types arises during development of individual muscles was explored. The pattern of cellular differentiation resulting from the synthesis of particular fast and slow myosin heavy chains (MyHC) was investigated in the intermandibularis muscle in the lower jaw of chick embryos. The intermandibularis muscle has a proximodistal pattern of fibre type distribution. The distal region of the muscle contains a ratio of 1.5:1 fast to slow muscle fibres, which increases to &gt;2.5:1 in the proximal region. The intermandibularis muscle is assembled in a proximodistal sequence, with both fast and slow muscle cells differentiating within the earliest muscle and then establishing the specific pattern of cell types. This pattern is not dependent on a specific innervation source, as normal lower jaw muscles develop and the intermandibularis has the same graded cellular pattern when the mandibular primordium is grafted to the limb bud stump. Micromass cultures were used to explore the pool of potentially myogenic cells that are available to construct the muscles. Even before the muscle differentiates in vivo, both fast and slow cells are present in the primordia. These potentially myogenic cells are already distributed within the primordium in a proximodistal fashion that mimics the cellular pattern found in the muscle that develops.
Repression of Drosophila pair-rule segmentation genes by ectopic expression of tramtrack
Authors: Brown J. Lesley , Wu Carl 
Published: April 2021

ABSTRACT
The tramtrack (ttk) protein has been proposed as a maternally provided repressor of the fushi tarazu (ftz) gene in Drosophila embryos at the preblastoderm stage. Consistent with this hypothesis, we have detected by immunohistochemistry the presence of ttk protein in preblastoderm embryos. This is followed by a complete decay upon formation of the cellular blastoderm when ftz striped expression is at its peak. In addition, the highly complex pattern of zygotic ttk expression suggests specific functions for ttk late in development that are separate from the regulation of ftz. We have produced ttk protein ectopically in blastoderm-stage embryos transformed with a heat shock-ttk construct. Ectopic ttk caused complete or near-complete repression of the endogenous ftz gene, as well as significant repression of the pair-rule genes even skipped, odd skipped, hairy and runt. These findings suggest that specific repression by ttk (or by undiscovered repressors) may be more than an isolated phenomenon during the rapid cleavage divi-sions, a period when the need for genetic repression has not been generally anticipated.
Allocation of the thoracic imaginal primordia in the Drosophila embryo
Authors: Cohen Barbara , Simcox Amanda A. , Cohen Stephen M. 
Published: April 2021

ABSTRACT
The primordia of the thoracic imaginal discs of the Drosophila embryo originate as groups of cells spanning the parasegment boundary. We present evidence that the thoracic imaginal primordia are allocated in response to signals from the wingless (wg) and decapen - taplegic (dpp) gene products. Rows of cells that express wg intersect rows of cells that express dpp to form a ladder-like pattern in the ectoderm of the germ band extended embryo. The imaginal primordia originate as groups of cells which lie near these intersection points. We have used a molecular probe derived from the Distal-less (Dll) gene to show that this population contains progenitor cells for both the dorsal (i.e. wing) and ventral (i.e. leg) discs. Although we show that Dll function is not required for allocation of imaginal cells, acti-vation of an early Dll enhancer may serve as a molecular marker for allocation. A group of cells, which includes the imaginal progenitors, activate this enhancer in response to intercellular signals from wg and perhaps from dpp. We have used a conditional allele of wg to show that wg function is transiently required for both allocation of the imaginal primordia and for initiation of Dll expression in these cells during the brief interval when wg and dpp form the ladder-like pattern. Allocation of the imaginal primordium and activation of Dll expression appear to be parallel responses to a single set of positional cues.
Germline chimeric chickens from dispersed donor blastodermal cells and compromised recipient embryos
Authors: Carsience R. Stuart , Clark Mary Ellen , Verrinder Gibbins Ann M. , Etches Robert J. 
Published: April 2021

ABSTRACT
Stage-X blastoderms, within intact eggs from White Leghorn hens, were exposed to 500-700 rads of radiation from a 60Co source prior to injection, into the subgerminal cavity, of approximately 100 or 200-400 dispersed cells from stage-X blastoderms isolated from eggs laid by Barred Plymouth Rock hens. Embryos developing past day 14 of incubation and hatched chicks were assessed for donor and recipient cell contribution to the melanocyte population through examination of black and yellow down pigmentation, respectively (Barred Plymouth Rocks have a recessive allele at the I locus while the White Leghorns have a dominant allele at the I locus). Of the 809 embryos injected with approximately 100 cells, 192 developed past day 14 and black pigmentation, indicating somatic chimerism, was observed on 118 of the 192 (58%) embryos and chicks. Of the 296 embryos injected with 200-400 donor cells, 86 developed past day 14 of incubation. Somatic chimerism was observed on 55 of the 86 (64%) embryos and chicks. To test for germline chimerism, birds surviving to maturity were mated to Barred Plymouth Rocks. Five somatically chimeric females were produced when approximately 100 cells were injected, and one was a germline chimera. Six somatic female chimeras were produced following the injection of 200-400 cells, three of which proved to be germline chimeras by the presence of Barred Rock chicks among their offspring. Two of the nine males produced by injecting approximately 100 cells were germline chimeras. Five of 6 somatic male chimeras, produced by injection of 200-400 cells, have sired black chicks; furthermore, one of the roosters produced by the injection of 200-400 cells has sired only donor-derived chicks. These data indicate that irradiation of the recipient embryo, prior to injection of the donor cells, consistently yields somatic and germline chimeric chickens. The ability to insert donor cells into the germline provides a powerful new tool that will facilitate molecular and cellular manipulation of the developing chick embryo.