bluuebunny/crossref_metadata_2025_split huggingface dataset:
The role of secondary mesenchyme cells during sea urchin gastrulation studied by laser ablation
Authors: Hardin Jeff 
Published: April 2021

Abstract
It has long been thought that traction exerted by filopodia of secondary mesenchyme cells (SMCs) is a sufficient mechanism to account for elongation of the archenteron during sea urchin gastrulation. The filopodial traction hypothesis has been directly tested here by laser ablation of SMCs in gastrulae of the sea urchin, Lytechinus pictus. When SMCs are ablated at the onset of secondary invagination, the archenteron doubles in length at the normal rate of elongation, but advance of the tip of the archenteron stops at the gastrula stage. In contrast, when all SMCs are ablated at or following the gastrula stage, further elongation does not occur. However, if a few SMCs are allowed to remain in gastrulae, elongation continues, although more slowly than in controls. The final length of archenterons in embryos ablated at the gastrula stage is virtually identical to the final length of everted archenterons in LiCl-induced exogastrulae; since filopodial traction is not exerted in either case, an alternate, common mechanism of elongation probably operates in both cases. These results suggest that archenteron elongation involves two processes: (1) active, filopodia-independent elongation, which depends on active cell rearrangement and (2) filo-podia-dependent elongation, which depends on mechanical tension exerted by the filopodia.
Adenosine induces dormancy in starfish blastulae
Authors: Tsuchimori Noboru , Miyashiro Shigeyoshi , Shibai Hiroshiro , Ikegami Susumu 
Published: April 2021

Abstract
External application of 50 μg ml-1 adenosine inhibits development of the starfish Asterina pectinifera at the 256-cell stage when all the embryonic cells differentiate to epithelial cells. Intracellular concentration of adenosine in the adenosine-treated embryo is 2·7 times higher than those of the normal embryo whereas the contents of ATP, ADP, AMP and adenosine 3′,5′-monophosphate are the same for both embryos. Adenosine causes more than 95 % reduction in the rate of protein, DNA and RNA syntheses. By returning the embryo to normal sea water, macromolecular synthesis restarts and the embryo develops to the bipin-naria stage.
The developmental specification of the vertebrate skull
Authors: Thorogood Peter 
Published: April 2021

ABSTRACT
The initial form of the embryonic bony skull is determined in two ways; cranially, by the relative growth of the developing brain, and facially, by the chondrocranium. Both are essentially acting as structural templates around which the bony components of the skull are assembled. Assuming, therefore, that the specification of form and pattern in the facial skeleton occurs at the formation of the chondrocranium, this paper will focus on precisely how the chondrocranium forms. Any acceptable explanation of chondrocranial morphogenesis must satisfy at least two prerequisites. First, given the constancy of chondrocranial form in vertebrates, any model proposed should be equally applicable to all vertebrates. Second, it should enable us to answer questions of homology concerning the skull and, in particular, provide explanation for those instances where ‘homologous’ structures have a different (lineage) composition.
From studies limited to a small number of amphibian, avian and mammalian species, it is apparent that chondrogenesis in the vertebrate skull is largely, if not entirely, elicited by epitheliomesenchymal tissue interactions. Analysis of such interactions (and of those promoting osteogenesis) reveals that these are matrixmediated and, recently, the expression of certain ‘relevant’ matrix components has been shown to be developmentally regulated in a fashion that correlates with the location and timing of these interactions. From these, and related, observations a morphogenetic model, the so-called ‘Flypaper Model’, has been proposed to explain the specification of chondro-cranial form. A number of predictions arising from that model are currently being tested experimentally and the current status of the model is reviewed. Finally, the ability of this model to satisfy the prerequisites defined above is assessed.
Homeobox genes and the vertebrate head
Authors: Holland Peter W. H. 
Published: April 2021

ABSTRACT
Several Drosophila genes important in the control of embryonic development contain a characteristic sequence of DNA, known as the homeobox. Homeobox sequences are also present in a family of vertebrate genes, which may therefore have regulatory roles during vertebrate embryogenesis. In this article, data concerning the spatial patterns of vertebrate homeobox gene expression are discussed in relation to recent descriptive and experimental analyses of head development. It is concluded that the patterns of gene expression are consistent with homeobox genes having roles in anteroposterior positional specification within the developing brain and possibly the neural crest. The data are not clearly consistent with these genes having direct roles in controlling the patterns of cranial segmentation, although further studies may reveal whether vertebrate segments are units of developmental specification.
Localization of c-myc expression during oogenesis and embryonic development in Xenopus laevis
Authors: Hourdry Jacques , Brulfert Annie , Gusse Michel , Schoevaert Damien , Taylor Michael V. , Mechali Marcel 
Published: April 2021

Abstract
The expression of the proto-oncogene c-myc during oogenesis and embryonic development was followed by in situ hybridization using a cytological protocol adapted to amphibian embryos. The c-myc RNA was highly expressed in the cytoplasm of young oocytes and was further diluted during oocyte growth without specific localization. From the neurula stage on, new myc transcripts were detected and the whole embryo appeared positive with antisense myc RNA probes relative to control sense RNA probes. In addition, a spatial localization of high levels of the transcript was also observed in specific areas of the developing embryo, including the epidermis, gill buds, optic vesicles and lens placodes. These observations might indicate a specific role of the c-myc gene during the differentiation of these tissues. Alternatively, this high level of myc expression might prevent such tissues from entering into terminal differentiation during the growth of the embryo.
Evidence for dedifferentiation and metaplasia in amphibian limb regeneration from inheritance of DNA methylation
Authors: Casimir Colin M. , Gates Phillip B. , Patient Roger K. , Brockes Jeremy P. 
Published: April 2021

Abstract
Amphibian limb regeneration is a process in which it has been suggested that cells of one differentiated type may dedifferentiate and give rise to cells of another type in the regenerate. We have used two tissue-specific hypomethylations in the newt cardioskeletal myosin heavy chain gene as lineage markers to follow the fate of cells during limb regeneration. Analysis of genomic DNA from different muscle cell populations allowed the assignment of one marker to the muscle (Hypo A) lineage and the other, more tentatively, to the ‘connective tissue’ (Hypo B) component of muscle. The contribution to regenerated limb cartilage and limb blastemal tissue by çells carrying these markers was estimated by quantitative analysis of Southern blot hybridizations using DNA from regenerate tissues. The results are consistent with a contribution of cells from both muscle and connective tissue lineages to cartilage in regenerated limbs. In addition, removal of the humerus at the time of amputation (eliminating any contribution from pre-existing cartilage), has provided evidence for an increased representation of cells carrying the connective tissue marker in regenerate cartilage but did not affect the representation of cells carrying the muscle cell marker.
Retinoic acid proximalizes level-specific properties responsible for intercalary regeneration in axolotl limbs
Authors: Crawford Karen , Stocum David L. 
Published: April 2021

Abstract
The objective of this study was to determine whether retinoic acid (RA) coordinately proximalizes positional memory and the cellular recognition system that detects pattern discontinuity in regenerating amphibian limbs. The strategy was to test the capacity of RA-treated blastemas to evoke intercalary regeneration when grafted to an amputation level proximal to their level of origin. Control wrist and ankle, or elbow and knee blastemas treated with the retinoid solvent, dimethylsulphoxide, evoked intercalary regeneration as effectively as untreated blastemas, when grafted to the midstylopodial amputation surface of host limbs. RA-treated wrist and ankle or elbow and knee blastemas were proximalized and formed complete limbs that were at an angle to, or continuous with, the midstylopodium of the host limb. No intercalary regeneration, from either graft or host, was observed in these cases. The results indicate that the cellular mechanism that recognizes disparities between nonneighbouring cells and initiates intercalary regeneration is coordinately proximalized with positional memory. Thus the recognition mechanism and positional memory are directly related. Intercalary regeneration and corrective displacement (affinophoresis), both of which restore a pattern of normal cell neighbours by different means in regenerating axolotl limbs, appear to use the same mechanism to recognize pattern discontinuity.
Clonal analysis of the crustacean segment: the discordance between genealogical and segmental borders
Authors: Dohle Wolfgang , Scholtz Gerhard 
Published: April 2021

ABSTRACT
The post-naupliar germ bands of many higher crustaceans show a regular grid-like pattern of cells. This pattern is generated, in part but not in toto, by the proliferation of teloblasts. The exact lineage of all the cells of the post-naupliar germ band has been investigated in most of the orders belonging to the monophyletic unit Peracarida (Cumacea, Tanaidacea, Isopoda, Mysidacea, Amphipoda). The cell divisions and differentiation could be followed up to the formation of appendage buds, of ganglia and of intersegmental furrows.
The most-striking result is that the genealogical borders between cells of different clones do not correspond to the transverse intersegmental furrows. Instead, the genealogical borders divide a segment, and even the appendage buds, into anterior and posterior compartments.
There are different pathways for the formation of the cells of the post-naupliar germ band, though the subsequent differentiation may be nearly identical. It has been deduced from these findings that the fate of the cells is not determined by their origin. This supposition could be substantiated by a comparative analysis of the different orders. In Amphipoda, for instance, ectoteloblasts are not differentiated; the post-naupliar germ band is formed by an assemblage of blastoderm cells. Nevertheless, the cleavage pattern of these cells is for the most part identical to that of the other orders that possess ectoteloblasts.
The developmental expression of the heat-shock response in Xenopus laevis
Authors: Davis Robin E. , King Mary Lou 
Published: April 2021

ABSTRACT
We have investigated the Xenopus heat-shock response of somatic cells, oocytes and embryos. Xenopus defolli-culated oocytes displayed a highly variable response to heat shock depending on the culture medium. Intact follicles, however, respond to heat stress by synthesizing an invariant pattern of hsps. Although a subset of the hsp70/68 complex is expressed constitutively in the absence of heat shock in oocytes and embryos (hsc70), actual induction of hsps in response to stress does not occur until the blastula stage when transcription of the zygotic genome is first activated. By gastrulation, the hsps of somatic cells, including members of the hsp30/26 complex, were expressed coordinately in response to heat shock. We further show that Xenopus hsps have different solubilities perhaps reflecting their different subcellular locations. The 26 000-30 000Mr complex (hsp30/26) was present almost exclusively in a detergent-insoluble fraction, as was 25−50 % of the hsp70/68 complex and greater than 50 % of hsp56, suggesting that these hsps may be associated with the cytoskeleton during a heat shock. In contrast, the other Xenopus hsps (hsp86, hsp75 and hsp61) were totally solubilized in a low-salt buffer.
Expression and role of E- and P-cadherin adhesion molecules in embryonic histogenesis II. Skin morphogenesis
Authors: Hirai Yohei , Nose Akinao , Kobayashi Shigeyasu , Takeichi Masatoshi 
Published: April 2021

ABSTRACT
Expression and the role of E- and P-cadherin in the histogenesis of the surface epidermis and hair follicles were examined using the upper lip skin of the mouse. P-cadherin is expressed exclusively in the proliferating region of these tissues, that is in the germinative layer of the surface epidermis, the outer root sheath and the hair matrix. E-cadherin is coexpressed in these layers but this molecule was also detected in non-proliferating regions such as the intermediate layer of the surface epidermis and the immature regions of the inner root sheath. Neither P- nor E-cadherin was detected in fully keratinized layers such as the horny layer of the surface epidermis, the outermost layer of the outer root sheath and the mature hair fibres. These two cadherins were not detected in dermal cells. We cultured pieces of the upper lip skin in vitro in the absence or presence of a monoclonal antibody to E-cadherin (ECCD-1) or to P-cadherin (PCD-1). In control cultures, skin morphogenesis normally occurred in a pattern whereby the hair follicles grew and dermal cells were condensed to form the dermal sheath. A mixture of ECCD-1 and PCD-1, however, induced abnormal morphogenesis in the skin in several respects. (1) The cuboidal or columnar arrangement of basal epithelial cells was distorted. (2) Hair follicles were deformed. (3) Condensation of dermal cells was suppressed, causing a homogeneous distribution of these cells. These results suggest that cadherins present in epidermal cells are involved not only in maintaining the arrangement of these cells but also in inducing dermal condensation.
Pattern regulation during the development of the ventral abdomen in the flesh fly Sarcophaga agryostoma
Authors: Smith Hazel 
Published: April 2021

ABSTRACT
The adult abdominal epidermis of the flesh fly, Sarco-phaga agryostoma, arises from small nests of diploid histoblasts which grow out and replace the polytene larval epidermal cells during metamorphosis. Extirpation experiments are used to investigate the roles of interactions with neighbouring nests or larval epidermis in determining the fates of the ventral histoblast nests. The extirpation of both left and right ventral histoblast nests deletes the sternite in the corresponding adult segment, but when only one nest is extirpated the hemisternite on that side of the adult is regenerated by the remaining nest. Regenerated hemisternites are smaller and bear fewer bristles than normal hemisternites. Extirpation of the larval epidermis between the two ventral nests leads to the production of small duplicate hemisternites, which resemble the regenerated hemisternites produced by single ventral nests. These midventral extirpations were also found to delay ventral nest fusion.
The results suggest that each ventral nest has an autonomous capacity to form both hemisternites, but that interactions between the nests after fusion normally limit their development and prevent pattern duplication. The possible nature of such interactions is discussed and related to models of pattern regulation and growth control in imaginal disc development.
Genetic analysis of developmental mechanisms in hydra XIX. Stimulation of regeneration by injury in the regeneration-deficient mutant strain, reg-16
Authors: Kobatake Eucaly , Sugiyama Tsutomu 
Published: April 2021

ABSTRACT
A mutant strain of Hydra magnipapillata, reg-16, has a very low regenerative capacity. After head removal, it usually restores 10-20% of the original number of tentacles in 7 days.
A procedure was found to markedly improve tentacle regeneration in this strain. The closed wound located at the apical regenerating tip of the decapitated polyp was gently reopened using a pair of forceps. Reg-16 polyps treated in this way at 24 and 48 h after head removal restored nearly all of the original number of tentacles in 7 days.
A lateral tissue transplantation procedure was employed to examine the effect of wound reopening on the morphogenetic potential of decapitated reg-16 polyps. Wound reopening produced a significant increase in head activation level without producing a preceding decrease in head inhibition level. This and other observations suggest that the coupled activationinhibition changes that normally occur after head removal from the wild-type hydra do not occur in this strain.
Mechanisms responsible for the wound reopening effect and the absence of activation-inhibition coupling in the mutant strain reg-16 are discussed.
Molecular differences between the rostral and caudal halves of the sclerotome in the chick embryo
Authors: Norris Wendie E. , Stern Claudio D. , Keynes Roger J. 
Published: April 2021

ABSTRACT
It is known that both neural crest cell migration and motor axon outgrowth in most vertebrate embryos are segmented because of restrictions imposed upon their distribution by the neighbouring sclerotomes, each of which is divided into a rostral and a caudal half. The caudal half does not allow crest migration or axon outgrowth, while the rostral half does. In this paper, we investigate the expression of proteins and glycoproteins in the two halves of the sclerotome of the chick embryo at stages between 20 and 32 pairs of somites by two-dimensional SDS-polyacrylamide gel electrophoresis. We find that the patterns of expression are complex, and that polypeptides and glycoproteins vary both spatially and temporally: of those that are expressed differentially by the sclerotome, some differ quantitatively and others qualitatively. Some macromolecules change their spatial distribution with developmental age, and some appear or disappear as the embryos become older.
An assessment of the developmental potential of embryonic stem cells in the midgestation mouse embryo
Authors: Beddington R. S. P. , Robertson E. J. 
Published: April 2021

ABSTRACT
Embryonic stem cells (ES) cells were injected into host blastocysts either in groups of 10–15 cells or as single cells in order to test their developmental potential in the developing embryo. The analysis of midgestation chimaeras, by electrophoretic separation of glucose phosphate isomerase (GPI) isozymes, showed that ES cells were capable of colonizing trophectoderm and primitive endoderm derivatives at a low frequency, as well as producing a high rate of chimaerism in tissues of the fetus and extraembryonlc mesoderm.
The specification of heart mesoderm occurs during gastrulation in Xenopus laevis
Authors: Sater Amy K. , Jacobson Antone G. 
Published: April 2021

ABSTRACT
The establishment of heart mesoderm during Xenopus development has been examined using an assay for heart differentiation in explants and explant combinations in culture. Previous studies using urodele embryos have shown that the heart mesoderm is induced by the prospective pharyngeal endoderm during neurula and postneurula stages. In this study, we find that the specification of heart mesoderm must begin well before the end of gastrulation in Xenopus embryos. Explants of prospective heart mesoderm isolated from mid- or late neurula stages were capable of heart formation in nearly 100% of cases, indicating that the specification of heart mesoderm is complete by midneurula stages. Moreover, inclusion of pharyngeal endoderm had no statistically significant effect upon either the frequency of heart formation or the timing of the initiation of heartbeat in explants of prospective heart mesoderm isolated after the end of gastrulation. When the superficial pharyngeal endoderm was removed at the beginning of gastrulation, experimental embryos formed hearts, as did explants of prospective heart mesoderm from such embryos. These results indicate that the inductive interactions responsible for the establishment of heart mesoderm occur prior to the end of gastrulation and do not require the participation of the superficial pharyngeal endoderm.
Oligodendrocyte progenitors isolated directly from developing telencephalon at a specific phenotypic stage: myelinogenic potential in a defined environment
Authors: Gard A. L. , Pfeiffer S. E. 
Published: April 2021

Abstract
Oligodendroglia differentiate asynchronously in the developing central nervous system, passing through a series of stages identified by the sequential expression of specific differentiation antigens, culminating in the formation of the myelin sheath. In the work presented here, oligodendrocyte progenitors at a temporally narrow and well-defined phenotypic stage of development have been isolated in high purity and yield directly from postnatal rat telencephalon. This stage is identified by the expression of the O4 antigen, the earliest recognized surface marker specific for the oligodendroglial lineage, but the absence of the differentiation marker galactosylcerebroside (GalC). These O4+GalC– progenitors first appear at birth (105/telencephalon), 2–3 days before O4+GalC+ oligodendrocytes. The work presented here demonstrates that a major subpopulation of O4+GalC– progenitors (80 %), which we have termed ‘proligoden-drocytes’, is fully committed to terminal oligodendrocyte differentiation. A relatively small, maximal set of nutritional supplements are sufficient for proligodendro-cytes to carry out the myelinogenic cascade of differentiated gene expression in a temporally normal manner, in quantitatively significant amounts, in normal ratios of myelin protein isoforms, and in a regulated relationship to the inclusion of myelin-specific products into myelinlike membrane sheets. An important corollary is that this step of myelinogenesis does not require contact with other cell types, in particular neurones and astrocytes, nor does it require unknown growth factors unique to these cell types. Additionally under these conditions, there exists a developmentally quiescent subpopulation (20 %) of O4+GalC– cells that may have significance for understanding the progenitors previously described in adult brain and suggested to be instrumental in remyelination under pathological conditions.
Muscle-specific (CArG) and serum-responsive (SRE) promoter elements are functionally interchangeable inXenopusembryos and mouse fibroblasts
Authors: Taylor Michael , Treisman Richard , Garrett Nigel , Mohun Tim 
Published: April 2021

AbstractThe Xenopus cardiac actin gene contains four copies of a promoter element, the CArG box, which is conserved amongst striated muscle actin genes and is essential for tissue-specific expression in the developing Xenopus embryo. Our aim is to identify embryo and muscle proteins that interact with the CArG box as a step towards understanding the molecular basis of this developmentally regulated gene expression. The CArG box shares some sequence similarity with the Serum Response Element (SRE), which mediates the transcriptional activation by serum of genes such as c-fos and cytoskeletal actin. We show here that the most proximal cardiac actin CArG box is recognized by the same binding activity as the cytoskeletal actin SRE in nuclear extracts from both Xenopus embryos and mammalian muscle cells. This activity is indistinguishable from the previously characterized HeLa cell SRE-binding activity, Serum Response Factor (SRE). Importantly, we extend these in vitro studies to demonstrate that the CArG box and SRE are functionally interchangeable, both in Xenopus embryos and mouse fibroblasts. This implies that the CArG box and SRE can bind the same protein in vivo, as well as in vitro. Our results identify an SRF-like protein as a CArG box-binding factor and we discuss the implication that a common mechanism may be utilized in both muscle-specific gene expression and serum-responsive transcription.