bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spatially restricted patterns of expression of the homeobox-containing gene Hox 2.1. during mouse embryogenesis
Authors: Holland Peter W. H. , Hogan Brigid L. M. 
Published: April 2021

Abstract
The mouse Hox 2.1 gene contains a homeobox sequence and is therefore a candidate for a vertebrate gene involved in the control of embryonic patterning or positional specification. To investigate this possibility, we have used in situ hybridization to determine the pattern of Hox 2.1 expression during mouse embryogenesis. At 8·5 days post coitum, Hox 2.1 is expressed at a low level in the posterior neuroectoderm and mesoderm, and in the neuroectoderm of the presumptive hindbrain. At 12·5 days p.c., Hox 2.1 is expressed in an anteroposterior restricted domain extending from the hindbrain throughout the length of the spinal cord, predominantly in the dorsal region. Between 12·5 and 13·5 days p.c. the domain becomes localized to the occipital and cervical regions. We also detect Hox 2.1 RNA in the embryonic lung, stomach, mesonephros and metanephros, as well as in myenteric plexus, dorsal root ganglia and the nodose ganglion, and in mature granulocytes. The embryonic expression of Hox 2.1 in neural tissue is compared with that of Hox 3.1, which also shows anteroposterior restricted domains of gene expression. These patterns of expression are not clearly consistent with Hox 2.1 or Hox 3.1 having roles in segmental patterning. However, the data are consistent with these genes having regulatory roles in anteroposterior positional specification in the neuroectoderm and mesoderm, and suggest that Hox 2.1 may also have functions during organogenesis.
Teratocarcinomas and Embryonic Stem Cells: A Practical Approach
Authors: Robertson E. J. , Beddington Rosa 
Published: April 2021

ABSTRACT
Thirty years ago teratocarcinomas were little more than pathological oddities, of passing interest to some oncologists but quite unknown to most biologists. Their emergence from obscurity was largely due to the work of Roy Stevens and Barry Pierce who, between them, gradually impressed on their audiences the special features of these obscure tumours. At a gross level, there was something immediately fascinating in the monstrous form of some teratocarcinomas, the jumble of hair and teeth, skin and brain tissue, intestine and skeletal elements all chaotically cohabiting in a single tumour. But it was the ‘life cycle’ of teratocarcinomas that was especially intriguing, particularly in the context of the major advances in manipulating early mammalian embryos which occurred in the 1960s.
The restrictive effect of early exposure to lithium upon body pattern in Xenopus development, studied by quantitative anatomy and immunofluorescence
Authors: Cooke Jonathan , Smith Emma J. 
Published: April 2021

Abstract
We have carried out an anatomical study of Xenopus larval and gastrula stages resulting from treatment of synchronous early blastulae for brief periods with Li+. We confirm the proposal that such treatment causes a particular transformation, and partial elimination, of the normal body pattern. Coordinated restriction of pattern, without appreciable loss of cell number, is seen in all three germ layers. The distortion has been investigated by quantitative study of mesoderms at a standard stage, in relation to the normal fate map for mesoderm, and with the help of immunofluorescence on sections for somitic muscle and for blood. In the extreme syndrome, mesoderm arises from all around the blastula as usual, but is symmetrical and corresponds to that arising near the dorsal/anterior meridian of the normally specified egg or embryo with a large posterior subset of the normal pattern values thus missing. The effect is independent of any inhibition of archenteron formation or mesoderm migration (i.e. the cell mechanics of gastrulation) incurred by the treatment. It is also quite separate from a syndrome caused by more prolonged exposure to Li+ during gastrulation. A small, but distinctive, anterior pattern region is also not expressed and, anomalously in relation to their general nature, these forms differentiate considerable blood tissue. We consider the implications of some details of the pattern restriction for our understanding of interaction in the normal development and propose that the Li+ embryo is likely to be useful as a specific ‘differential screen’, in relation to the normal, during the search for those gene products that mediate initial regionalization of the body.
The cadherins: cell-cell adhesion molecules controlling animal morphogenesis
Authors: Takeichi Masatoshi 
Published: April 2021

AbstractCadherins are a family of glycoproteins involved in the Ca2+-dependent cell-cell adhesion mechanism which is detected in most kinds of tissues. Inhibition of the cadherin activity with antibodies induces dissociation of cell layers, indicating a fundamental importance of these molecules in maintaining the multicellular structure. Cadherins are divided into subclasses, including E-, N- and P-cadherins. While all subclasses are similar in molecular weight, Ca2+- and proteasesensitivity, each subclass is characterized by a unique tissue distribution pattern and immunological specificity. Analysis of amino acid sequences deduced from cDNA encoding these molecules showed that they are integral membrane proteins of 723–748 amino acids long and share common sequences; similarity in the sequences between subclasses is in a range of 50–60 % when compared within a single animal species.L cells, with very little endogenous cadherin activity, transfected with the cadherin cDNA acquired high cadherin-mediated aggregating activity. Their colony morphology was altered by the ectopic expression of cadherins from the dispersed type to the compact type, providing direct evidence for a key role of cadherins in cell-cell adhesion. It has been suggested that cadherins bind cells by their homophilic interactions at the extracellular domain and are associated with actin bundles at the cytoplasmic domain.It appears that each cadherin subclass has binding specificity and this molecular family is involved in selective cell-cell adhesion. In development, the expression of each cadherin subclass is spatiotemporally regulated and associated with a variety of morphogenetic events; e.g. the termination or initiation of expression of a cadherin subclass in a given cell collective is correlated with its segregation from or connection with other cell collectives. Antibodies to cadherins were shown to perturb the morphogenesis of some embryonic organs in vitro. These observations suggest that cadherins play a crucial role in construction of tissues and the whole animal body.
Retinoic acid coordinately proximalizes regenerate pattern and blastema differential affinity in axolotl limbs
Authors: Crawford Karen , Stocum David L. 
Published: April 2021

AbstractAn assay that detects position-related differences in affinity of axolotl regeneration blastema cells in vivo was used to test whether retinoic acid, which proximalizes regenerate pattern, simultaneously proximalizes blastema cell affinity. The assay involved autografting or homografting late bud forelimb blastemas derived from the wrist, elbow or midupper arm levels to the dorsal surface of the blastema-stump junction of an ipsilateral, medium-bud-stage hindlimb regenerating from the midthigh level. The grafted blastemas consistently displaced to their corresponding levels on the proximodistal axis of the host regenerate, indicating the existence of level-specific differences in blastema cell affinity. Retinoic acid proximalized the pattern of donor forelimb regenerates to the level of the girdle and abolished their displacement behaviour on untreated host hindlimbs. Conversely, untreated forelimb donor blastemas displaced distally to their corresponding levels on host ankle regenerates, that had been proximalized to the level of the girdle by retinoic acid. These results indicate that positional memory in regenerating limbs is directly related to blastema cell affinity, and that very similar or identical sets of level-specific affinity properties are shared by forelimb and hindlimb cells.
Carbohydrate-binding properties of boar sperm proacrosin and assessment of its role in sperm-egg recognition and adhesion during fertilization
Authors: Jones R. , Brown C. R. , Lancaster R. T. 
Published: April 2021

AbstractRecent evidence indicates that a carbohydrate recognition mechanism is involved in the early stages of sperm-egg interaction in mammals. In this communication, we describe a potential zona-ligand molecule on boar spermatozoa that has the capacity to recognize and bind to carbohydrate moieties of zona pellucida glycoproteins as well as neoglycoproteins, BSA-fucose and BSA-mannose. The molecule has broad specificity for carbohydrate binding and there is a requirement for a polysaccharide structure or for ‘clustering’ of saccharides on a protein backbone. The molecule has been identified as proacrosin, the zymogen form of the acrosomal protease acrosin. Strong similarities exist between proacrosin and ‘bindin’, the lectin-like protein that is thought to mediate sperm-egg adhesion in echinoderms. An hypothesis is proposed for spermegg interaction in mammals in which proacrosin, released during the early stages of the acrosome reaction, mediates secondary or consolidated binding of spermatozoa to the zona pellucida by virtue of its carbohydrate-binding capacity. The localized proteolytic action of active acrosin on the zona enhances this interaction in a manner analogous to the requirement for trypsinization of erythrocytes before agglutination by certain lectins. This hypothesis, which is supported by evidence from in vitro fertilization experiments, is discussed in relation to current concepts on sperm-egg recognition.
The preimplantation pig embryo: cell number and allocation to trophectoderm and inner cell mass of the blastocyst in vivo and in vitro
Authors: Papaioannou V. E. , Ebert K. M. 
Published: April 2021

Abstract
Total cell number as well as differential cell numbers representing the inner cell mass (ICM) and trophectoderm were determined by a differential staining technique for preimplantation pig embryos recovered between 5 and 8 days after the onset of oestrus. Total cell number increased rapidly over this time span and significant effects were found between embryos of the same chronological age from different females. Inner cells could be detected in some but not all embryos of 12 –16 cells. The proportion of inner cells was low in morulae but increased during differentiation of ICM and trophectoderm in early blastocysts. The proportion of ICM cells then decreased as blastocysts expanded and hatched.
Some embryos were cultured in vitro and others were transferred to the oviducts of immature mice as a surrogate in vivo environment and assessed for morphology and cell number after several days. Although total cell number did not reach in vivo levels, morphological development and cell number increase was sustained better in the immature mice than in vitro. The proportion of ICM cells in blastocysts formed in vitro was in the normal range.
Influence of chromosomal determinants on development of androgenetic and parthenogenetic cells
Authors: Surani M. Azim , Barton Sheila C. , Howlett Sarah K. , Norris Michael L. 
Published: April 2021

AbstractWe have examined the role of germline-specific chromosomal determinants of development in the mouse. Studies were carried out using aggregation chimaeras between androgenetic ↔ fertilized embryos and compared with similar parthenogenetic ↔ fertilized chimaeras. Several adult chimaeras were found with parthenogenetic cells but none were found with androgenetic cells. Analysis of chimaeras at mid-gestation showed that parthenogenetic cells were detected in the embryo and yolk sac but that androgenetic cells were found only in the trophoblast and yolk sac and not in the embryo. The contribution of parthenogenetic cells to the embryo and yolk sac was increased by aggregating 2-cell parthenogenetic and 4-cell fertilized embryos but the contribution of parthenogenetic cells in extraembryonic tissues remained negligible even after aggregation of 4-cell parthenogenetic and 2-cell fertilized embryos. Furthermore, parthenogenetic cells were primarily found in the yolk sac mesoderm and not in the yolk sac endoderm.These results suggest that maternal chromosomes in parthenogenetic cells permit their participation in the primitive ectoderm lineage but these cells are presumably eliminated by selective pressure or autonomous cell lethality from the primitive endoderm and troph-ectoderm lineages. Conversely paternal chromosomes in androgenetic cells confer opposite properties since the embryonic cells can be detected in the trophoblast and the yolk sac but not in the embryos, presumably because they are eliminated from the primitive ectoderm lineage. The spatial distribution of cells with different parental chromosomes may occur partly because of differential expression of some genes, such as proto-oncogenes, and partly due to their ability to respond to a variety of diffusible growth factors.
Evidence that the nerve controls molecular identity of progenitor cells for limb regeneration
Authors: Fekete Donna M. , Brockes Jeremy P. 
Published: April 2021

AbstractAdult urodele amphibians can regenerate their limbs after amputation by a process that requires the presence of axons at the amputation plane. Paradoxically, if the limb develops in the near absence of nerves (the ‘aneurogenic’ limb) it can subsequently regenerate in a nerve-independent fashion. The growth zone (blastema) of regenerating limbs normally contains progenitor cells whose division is nerve-dependent. A monoclonal antibody that marks these nerve-dependent cells in the normal blastema does not stain the mesenchymal cells of developing limb buds and only stains the amputated limb bud when axons have reached the plane of amputation. This report shows that the blastemal cells of the regenerating aneurogenic limb also fail to react with the antibody in situ. These data suggest that the blastemal cells arising during normal regeneration have been altered by the nerve. This regulation may occur either at the time of amputation (when the antigen is expressed) or during development (when the limb is first innervated).
Inductive effects of fibroblast growth factor and lithium ion on Xenopus blastula ectoderm
Authors: Slack J. M. W. , Isaacs H. V. , Darlington B. G. 
Published: April 2021

Abstract
We have studied the response of Xenopus blastula ectoderm to fibroblast growth factor and to lithium ion. The properties of acidic and basic FGF are very similar showing a 50 % induction level at 1–2 ng ml−1 and a progressive increase of muscle formation up to concentrations of 100–200 ng ml The elongation of explants also shows a dose-response relationship. The minimum contact requirement for induction of ectoderm explants is about 90 min and the stage range of ectodermal competence extends from midblastula to early gastrula, both these figures resembling those obtained in embryological experiments with vegetal tissue as the inducer. Lithium chloride concentrations which produce anteriorization of whole embryos have no effect on isolated ectoderms unless accompanied by FGF. Simultaneous treatment with FGF and Li lead to a marked enhancement of both elongation and muscle formation over that produced by FGF alone. By contrast, ventral marginal explants show increased elongation and muscle formation if treated with lithium alone suggesting that they have already received a low-dose FGF treatment within the embryo. It is concluded that endogenous FGF may be solely responsible for inducing the ventral mesoderm and that dorsalization of ventral mesoderm to the level of somitic muscle might be achieved either by a very high local concentration of FGF in the dorsal region, or by the action of a second, synergistic, agent in the dorsal region.
Purification, partial characterization and biological effects of the XTC mesoderm-inducing factor
Authors: Smith J. C. , Yaqoob M. , Symes K. 
Published: April 2021

Abstract
The mesoderm of Xenopus laevis is formed through an inductive interaction in which a signal from the vegetal hemisphere of the blastula acts on overlying animal pole cells. We have recently reported that the Xenopus XTC cell line secretes a mesoderm-inducing factor (MIF) which may resemble the natural signal. In this paper, we describe the purification and biological effects of XTC-MIF. XTC-MIF is a hydrophobic protein with an isoelectric point of 7·8 and an apparent relative molecular mass (Mr) of 23500. On reduction, XTC-MIF loses its biological activity and the protein dissociates into two inactive subunits with apparent Mr of about 15 000. These properties closely resemble those of transforming growth factor type β (TGF-β2), and it is interesting that TGF-)32 has recently been shown to have mesoderm-inducing activity.
The biological response to XTC-MIF is graded. After exposure to 0·2 – 1·0 ng ml−1 XTC-MIF, stage-8 animal pole explants form mesenchyme and mesothelium. At higher concentrations, up to about 5 ng ml−1, muscle is formed, occasionally with neural tissue. In response to concentrations of XTC-MIF greater than 5·10 ng ml−1, notochord and neural tissue are usually formed. The formation of notochord and neural tissue in response to XTC-MIF represents a qualitative difference between this inducing factor and the other known group of MIFs, the heparin-binding growth factors.
Cyclic AMP–phosphodiesterase induces dedifferentiation of prespore cells in Dictyostelium discoideum slugs: evidence that cyclic AMP is the morphogenetic signal for prespore differentiation
Authors: Wang Mei , Driel Roel Van , Schaap Pauline 
Published: April 2021

Abstract
We investigated whether cyclic AMP is an essential extracellular stimulus for the differentiation of prespore cells in slugs of D. discoideum. A local reduction of the extracellular cAMP level inside the slug was induced by implantation of cAMP-phosphodiesterase (cAMP-PDE)-coated spheres in intact slugs. This treatment caused the disappearance of prespore antigen in the vicinity of the sphere. A general reduction of extracellular cAMP levels in slugs, induced by submerging slugs in 0·25i.u.ml−1 cAMP-PDE, reduced the proportion of prespore cells from 66 % to 15 %, without affecting slug morphology. The cAMP-PDE-induced dedifferentiation of prespore cells was counteracted by cAMP and was not due to the production of the hydrolysis product 5′AMP, but to the reduction of extracellular cAMP levels. We conclude that extra-cellular cAMP is the major morphogenetic signal for the differentiation of prespore cells in the multicellular stages of D. discoideum development and we present a working hypothesis for the generation of the prestalk/ prespore pattern during multicellular development.
Reinitiation of chondroitin sulphate proteoglycan synthesis in regenerating skeletal muscle
Authors: Carrino David A. , Oron Uri , Pechak David G. , Caplan Arnold I. 
Published: April 2021

Abstract
Previous work from this laboratory involved the characterization of a large chondroitin sulphate proteoglycan unique to chick skeletal muscle. This proteoglycan is synthesized by embryonic skeletal muscle both in ovo and in culture but is not synthesized by adult muscle in vivo and myotubes in advanced cultures. Because regenerating skeletal muscle has been found to recapitulate synthesis of embryonic muscle protein isoforms, an analysis was performed to assess whether synthesis of chondroitin sulphate proteoglycans is reinitiated during muscle regeneration. Adult chicken pectoral and leg (gastrocnemius) muscle was injured by excision of a small piece of tissue or by cold injury; in the latter, the basement membrane has been reported to remain intact. At various times after injury, whole animals were exposed to [35S]sulphate and the proteoglycans were isolated by ion-exchange chromatography and analysed. Synthesis of only small proteoglycans, typical of normal adult skeletal muscle, is observed in the contralateral, uninjured muscle. In the regenerating muscle 4 days after injury, there is increased sulphate incorporation and abundant synthesis of chondroitin sulphate proteoglycans. This is observed in both pectoral and leg muscle irrespective of the type of injury, which suggests that the presence of basement membrane does not affect reinitiation of chondroitin sulphate proteoglycan synthesis. By 25 days after injury, synthesis of chondroitin sulphate proteoglycans is still detected but is significantly diminished. These data are consistent with the notion that skeletal muscle regeneration involves a recapitulation of embryonic events and give further credence to the hypothesis that skeletal muscle chondroitin sulphate proteoglycans play a role in some early aspect of myogenesis.
The distribution of fibronectin and tenascin along migratory pathways of the neural crest in the trunk of amphibian embryos
Authors: Epperlein Hans-Henning , Halfter Willi , Tucker Richard P. 
Published: April 2021

AbstractIt is generally assumed that in amphibian embryos neural crest cells migrate dorsally, where they form the mesenchyme of the dorsal fin, laterally (between somites and epidermis), where they give rise to pigment cells, and ventromedially (between somites and neural tube), where they form the elements of the peripheral nervous system. While there is agreement about the crest migratory routes in the axolotl (Ambystoma mexicanum), different opinions exist about the lateral pathway in Xenopus. We investigated neural crest cell migration in Xenopus (stages 23, 32, 35/36 and 41) using the X. laevis-X. borealis nuclear marker system and could not find evidence for cells migrating laterally. We have also used immunohistochemistry to study the distribution of the extracellular matrix (ECM) glycoproteins fibronectin (FN) and tenascin (TN), which have been implicated in directing neural crest cells during their migrations in avian and mammalian embryos, in the neural crest migratory pathways of Xenopus and the axolotl. In premigratory stages of the crest, both in Xenopus (stage 22) and the axolotl (stage 25), FN was found subepidermally and in extracellular spaces around the neural tube, notochord and somites. The staining was particularly intense in the dorsal part of the embryo, but it was also present along the visceral and parietal layers of the lateral plate mesoderm. TN, in contrast, was found only in the anterior trunk mesoderm in Xenopus; in the axolotl, it was absent. During neural crest cell migration in Xenopus (stages 25–33) and the axolotl (stages 28–35), anti-FN stained the ECM throughout the embryo, whereas anti-TN staining was limited to dorsal regions. There it was particularly intense medially, i.e. in the dorsal fin, around the neural tube, notochord, dorsal aorta and at the medial surface of the somites (stage 35 in both species). During post migratory stages in Xenopus (stage 40), anti-FN staining was less intense than anti-TN staining. In culture, axolotl neural crest cells spread differently on FN- and TN-coated substrata. On TN, the onset of cellular outgrowth was delayed for about 1 day, but after 3 days the extent of outgrowth was indistinguishable from cultures grown on FN. However, neural crest cells in 3-day-old cultures were much more flattened on FN than on TN. We conclude that both FN and TN are present in the ECM that lines the neural crest migratory pathways of amphibian embryos at the time when the neural crest cells are actively migrating. FN is present in the embryonic ECM before the onset of neural crest migration. In contrast, the appearance of TN is correlated with the initiation of migration. Since amphibian neural crest cells find FN, but not TN, to be adhesive migratory substrata in vitro, our results suggest that an interaction between these ECM components is important in regulating the onset and pathways of neural crest cell migration in the amphibian embryo.