bluuebunny/crossref_metadata_2025_split huggingface dataset:
Internal Factors Influencing Normal and Compensatory Growth of the Axolotl Pronephros
Authors: Fox H. 
Published: April 2021

ABSTRACTThe purpose of the experiments described in this paper was to distinguish between mechanical (hydrostatic) and chemical influences upon normal or compensatory growth of the pronephros in the larval axolotl (Harrison stages 24–26). Measurements were made on pronephroi and pronephric grafts from the following groups: (a) control specimens with undisturbed pronephroi; (b) specimens with paired undisturbed pronephroi and grafts; (c) specimens unilaterally pronephrectomized; (d) specimens unilaterally pronephrectomized and containing grafts. Analysis of the measurements shows that hydrostatic pressure within pronephric tubules is the main factor responsible for maintaining size and shape in both normal and compensatory growth.
Exogenous glycosaminoglycans (GAG) are able to modulate avian skin differentiation (epithelial keratinization and feather formation)
Authors: Becchetti E. , Stabellini G. , Caruso A. , Carinci P. 
Published: April 2021

ABSTRACT
Several reports have suggested that mesenchymal glycosaminoglycans (GAG) may be involved in the regulatory role of epithelial differentiation. Some researchers have pointed out that exogenous GAG affects extracellular GAG accumulation.
We have therefore examined the effect of added GAG on two typical processes of avian skin differentiation: keratinization and feather formation. Glycosaminoglycans, either obtained from fibroblasts cultures (conditioned media) or purified commercially available GAG were administered to 5/6-day chick embryo back skin explants. Control cultures were supported with 199 synthetic medium, chick embryo extract or calf serum. Explants have been examined by histological and histochemical procedures.
Skin explants maintained in vitro for 7 days exhibited an epithelial differentiation and a dermal histochemical reactivity which were related to the composition of the culture medium. In conditioned media from dermal fibroblasts, but not from heart or lung fibroblasts, explants always exhibited keratinization. In purified-GAG-containing media, keratinization was observed with condroitinsulphates and not with hyaluronic acid. Keratinization was always related to prevalent accumulation of hyaluronic acid in the underlying mesenchyme whereas feather formation was in relation to deposits of condroitinsulphates in dermis pulp.
The above findings demonstrate that exogenous GAG is able to modulate avian skin differentiation and that this regulation is linked to an influence on the mesenchymal GAG pattern.
Level of histone H4 mRNA in Xenopus laevis embryonic cells cultured in the absence of cell adhesion
Authors: Atsuchi Yasuo , Tashiro Kosuke , Yamana K. , Shiokawa Koichiro 
Published: April 2021

ABSTRACT
The amount of histone H4 mRNA per embryo was followed during early development of Xenopus laevis by Northern blot analyses using a cloned histone H4 cDNA as the probe. The H4 mRNA content was nearly constant until the blastula stage, increased greatly at the gastrula stage and then decreased at the neurula stage. Experiments with actinomycin D suggested that most H4 mRNA molecules detected at the late gastrula and neurula stages were maintained depending on new transcription of H4 genes during these stages. To see if the H4 mRNA level is affected by cell adhesion, we prepared dissociated cells and measured H4 mRNA content under conditions that inhibit cellular reaggregation. It was found that the amount of H4 mRNA per embryo in dissociated and reaggregation-inhibited cells was nearly equal to that of the control embryo at the neurula stage. Therefore, we conclude that the synthetic activity of histone H4 mRNA is not dependent on the cellular adhesion during development.
Analysis of cranial neural crest cell migration and early fates in postimplantation rat chimaeras
Authors: Tan S. S. , Morriss-Kay G. M. 
Published: April 2021

ABSTRACTRat embryos were grown in vitro during the period of cranial neural crest cell migration. In order to study the pathways and positional fates of cells from different regions of the neural crest, labelled premigratory crest cells from donor embryos were microinjected orthotopically into host embryos of the same developmental stage except for area 1 (forebrain) grafts which were, for technical reasons, injected into area 2. After various periods of time in whole embryo culture, the embryos were examined by immunohistochemical staining in order to determine the new positions of the labelled cells, and a map of their migration pathways was constructed. The observed patterns of migration were consistent with predictions from morphological studies in mammals and with extrapolations from transplantation studies in birds. However, crest cell migratory behaviour in rat and chick embryos was not identical; possible reasons for this are discussed.
The effects ofStreptomyceshyaluronidase on tissue organization and cell cycle time in rat embryos
Authors: Morriss-Kay Gillian M. , Tuckett Fiona , Solursh Michael 
Published: April 2021

ABSTRACTDay 9 rat embryos (late presomite stage with cranial neural plate or very early neural folds) were cultured for various periods of time from 6–48 h in medium containing 20TRUml-1Streptomyces hyaluronidase. Exposure to the enzyme resulted in considerable reduction of mesenchymal extracellular matrix. Access of the enzyme to the embryo was confirmed by alcian blue staining which indicated considerable reduction of extracellular and cell surface hyaluronate. Cranial neurulation was retarded, but not inhibited, and migration of both neural crest and primary mesenchyme cells occurred. In general, morphology was normal at 48 h.The major effect was on growth: embryos were smaller, with slightly reduced neuroepithelial cell number and greatly reduced mesenchymal cell number. Neuroepithelial cell cycle time was slightly prolonged, and that of the mesenchyme more than doubled. This differential effect on the growth rates of these two tissues reflects the normal distribution of hyaluronate, which is particularly abundant in the mesenchymal extracellular matrix.
The effect of retinoic acid pretreatment on the ability of murine embryonal carcinoma and inner cell mass cells to participate in chimaera development
Authors: Waters B. K. , Rossant J. 
Published: April 2021

ABSTRACT
Certain embryonal carcinoma (EC) cell lines can colonize the embryo following blastocyst injection or embryo aggregation, giving rise to EC-embryo chimaeras. However, such chimaeras often develop abnormally. For example, diploid P19 cells colonize the embryo readily but resulting chimaeras are usually abnormal, with persistence of tumour cells. Retinoic acid (RA) induces differentiation of EC cells to a variety of cell types in vitro but, in this study, it was shown that pretreatment of P19 cells with RA did not result in more normal development of P19-embryo chimaeras. The only significant effect of RA was to reduce the ability of P19 cells to participate in embryonic development at all after blastocyst injection. RA did not have a direct toxic or teratogenic effect on preimplantation mouse embryos and did not affect the ability of pluripotent embryo cells to colonize chimaeras. Therefore, RA may not be the normal inducer of differentiation in early embryogenesis.
Embryonic induction - molecular prospects
Authors: Gurdon J. B. 
Published: April 2021

ABSTRACTEmbryonic induction is an interaction between one (inducing) tissue and another (responding) tissue, as a result of which the responding tissue undergoes a change in its direction of differentiation. This is probably the single most important mechanism in vertebrate development leading to differences between cells and to the organization of cells into tissues and organs.
Expression ofXenopusN-CAM RNA in ectoderm is an early response to neural induction
Authors: Kintner C. R. , Melton D. A. 
Published: April 2021

ABSTRACTWe have isolated Xenopus laevis N-CAM cDNA clones and used these to study the expression of N-CAM RNA during neural induction. The results show that the first marked increase in N-CAM RNA levels occurs during gastrulation when mesoderm comes in contact with ectoderm and induces neural development. In situ hybridization results show that the early expression of N-CAM RNA is localized to the neural plate and its later expression is confined to the neural tube. Induction experiments with explanted germ layers show that N-CAM RNA is not expressed in ectoderm unless there is contact with inducing tissue. Together these results suggest an approach to studying how ectoderm is committed to form neural rather than epidermal tissue. Specifically, the data suggest that neural commitment is marked and perhaps mediated by the transcriptional activation of genes, like N-CAM, in the neural ectoderm.
Epithelial–mesenchymal interactions in the development of chick facial primordia and the target of retinoid action
Authors: Wedden S. E. 
Published: April 2021

ABSTRACT
The development of the chick face involves outgrowth of buds of tissue, accompanied by the differentiation of cartilage and bone in spatially defined patterns. To investigate the role of epithelial-mesenchymal interactions in facial morphogenesis, small fragments of facial tissue have been grafted to host chick wing buds to continue their development in isolation. Fragments of the frontonasal mass give rise to typical upper-beaklike structures: a long central rod of cartilage, the prenasal cartilage and an egg tooth. Meckel’s cartilage, characteristic of the lower beak, develops from fragments of the mandible. Removal of the ectoderm prior to grafting leads to truncated development. In fragments of frontonasal mass mesenchyme only a small spur of cartilage differentiates and there is no outgrowth. The mandible is less affected; a rod of cartilage still forms but the amount of outgrowth is reduced.
Retinoid treatment of chick embryos specifically affects the development of the upper beak and outgrowth and cartilage differentiation in the frontonasal mass are inhibited. The mandibles, however, are unaffected and develop normally. In order to investigate whether the epithelium or the mesenchyme of the frontonasal mass is the target of retinoid action, recombinations of retinoid-treated and untreated facial tissue have been grafted to host wing buds. Recombinations of retinoid-treated frontonasal mass ectoderm with untreated mesenchyme develop normally whereas recombinations of untreated ectoderm with retinoid-treated mesenchyme lead to truncations. The amount of outgrowth in fragments of mandibular tissue is slightly reduced when either the ectoderm or the mesenchyme has been treated with retinoids. These recombination experiments demonstrate that the mesenchyme of the frontonasal mass is the target of retinoid action. This suggests that retinoids interfere with the reciprocal epithelial-mesenchymal interactions necessary for outgrowth and normal upper beak development.
Fibre organization and reorganization in the retinotectal projection of Xenopus
Authors: Taylor J. S. H. 
Published: April 2021

ABSTRACT
This study concerns the retinotopic organization of the ganglion cell fibres in the visual system of the frog Xenopus laevis. HRP was used to trace the pathways taken by fibres from discrete retinal positions as they pass from the retina, along the optic nerve and into the chiasma. The ganglion cell fibres in the retina are arranged in fascicles which correspond with their circumferential positions of origin. Within the fascicles the fibres show little age-related layering and do not have a strict radial organization. As the fascicles of fibres pass into the optic nerve head there is some exchange of position resulting in some loss of the retinal circumferential organization. The poor radial organization of the fibres in the retinal fascicles persists as the fibres pass through the intraocular part of the nerve. At a position just behind the eye there is a major fibre reorganization in which fibres arising from cells of increasingly peripheral retinal locations are found to have passed into increasingly peripheral positions in the nerve. Thus, fibres from peripheralmost retina are located at the nerve perimeter, whilst fibres from central retina are located in the nerve core. It is at this point that the radial, chronotopic, ordering of the ganglion cell axons, found throughout the rest of the optic pathway, is established. This annular organization persists along the length of the nerve until a position just before the nerve enters the brain. Here, fibres from each annulus move to form layers as they pass into the optic chiasma. This change in the radial organization appears to be related to the pathway followed by all newly growing fibres, in the most superficial part of the optic tract, adjacent to the pia.
Just behind the eye, where fibres become radially ordered, the circumferential organization of the projection is largely lost. Fibres from every circumferential retinal position, which are of similar radial position, are distributed within the same annulus of the nerve. At the nerve-chiasma junction where each annulus forms a single layer as it enters the optic tract, there is a further mixing of fibres from all circumferential positions. However, as the fibres pass through the chiasma some active pathway selection occurs, generating the circumferential organization of the fibres in the optic tract. Additional observations of the organization of fibres in the optic nerve of Rana pipiens confirm previous reports of a dual representation of fibres within the nerve. The difference in the organization of fibres in the optic nerve of Xenopus and Rana pipiens is discussed.
The effect of the nucleocytoplasmic ratio on protein synthesis and expression of a stage-specific antigen in early cleaving mouse embryos
Authors: Petzoldt Ulrich , Muggleton-Harris Audrey 
Published: April 2021

Abstract
The nucleocytoplasmic ratio of fertilized mouse eggs was manipulated by removing or injecting cytoplasm by micropipette, and bisection of denuded eggs to obtain both pronuclei in one half of the eggs cytoplasm. The experimental eggs were capable of cleavage to the morula stage and, in some instances, developed to the blastocyst stage similar to unmanipulated eggs. The removal of large quantities of cyto-plasm by micropipette and injecting them into a recipient egg did not provide sufficient numbers of viable eggs, whereas transfer of smaller quantities (about a quarter of the cytoplasm) was less deleterious, at least for recipient eggs. However, the alteration of the nucleocytoplasmic ratio by this method was not of the correct magnitude for the purpose of this experiment. Therefore, bisection was the preferred method whereby the nucleocytoplasmic ratio was doubled. This resulted in both pronuclei residing in one half of the egg’s cytoplasm. Half eggs with one pronucleus (haploid) but retaining a nucleocytoplasmic ratio similar to unmanipulated control eggs served as additional controls for the bisection experiments. Protein synthesis was analysed by two-dimensional gel electrophoresis, showing that the 2-cell- and 4-cell-stage bisected embryos with double and normal nucleocytoplasmic ratio expressed equivalent protein synthesis patterns as control embryos of the same stage. Likewise, the stage-specific surface antigen SSEA-1 did not appear before the 6- to 8-cell stage. Also in cytoplasm transfer experiments, there was no indication that altering the nucleocytoplasmic ratio in either direction changed the timing of stage-specific gene expression. These results support the idea that stage-specific gene activity during early mouse cleavage might proceed in parallel to DNA replication cycles and is independent of the nucleocytoplasmic ratio.
Intercalation and the cellular origin of supernumerary limbs inXenopus
Authors: Muneoka Ken , Murad Eden H. B. 
Published: April 2021

AbstractThe hypothesis that a specialized polarizing zone controls the pattern of the anterior-posterior axis during limb development in Xenopus has been tested by analysing the cellular contribution to supernumerary limbs. Supernumerary limbs were generated by grafting hindlimb buds contralaterally between X. borealis and X. laevis to appose anterior and posterior limb tissues. Cells derived from these two species of Xenopus are readily identified by staining with quinacrine. The analysis of cellular contribution showed that supernumerary limbs consist of approximately half anterior-derived (57 %) and half posterior-derived (43 %) cells. These data are not consistent with the polarizing zone theory but are consistent with the hypothesis that both supernumerary limbs and normally developing limbs arise from intercalary interactions between limb bud cells with different positional values.
Pathfinding by dorsal column axons in the spinal cord of the frog tadpole
Authors: Holder Nigel , Clarke J. D. W. , Tonge David 
Published: April 2021

AbstractSensor fibres from dorsal root ganglia (DRG) enter the spinal cord and run within a clearly defined ipsilateral pathway, the dorsal column, which lies in the dorsal funiculus. We have examined the characteristics of this pathway as a defined substrate for dorsal column axons in Rana temporaria tadpoles by rotating the thoracic spinal cord through 180° from dorsal to ventral. Using HRP as a neuronal tracer we establish that many dorsal column axons from the hindlimb locate the ipsilateral or contralateral dorsal column pathway in the rotated cord. Other axons locate and grow caudally down the contralateral dorsal column returning to the lumbar region. Axons of the dorsal column never take an inappropriate pathway except at the transection sites where they negotiate abnormal routes to reach the contralateral or ipsilateral dorsal columns in normally positioned or rotated cord. The results demonstrate that the dorsal columns act as highly specific pathways for axons from DRG neurones but the axons’ interactions with the pathway do not control the craniocaudal or left-right options for growth.
The parasitophorous vacuole membrane surrounding Plasmodium and Toxoplasma: An unusual compartment in infected cells
Authors: Lingelbach Klaus , Joiner Keith A. 
Published: April 2021

ABSTRACT
Plasmodium and Toxoplasma belong to a group of unicellular parasites which actively penetrate their respective mammalian host cells. During the process of invasion, they initiate the formation of a membrane, the so-called parasitophorous vacuolar membrane, which surrounds the intracellular parasite and which differs substantially from endosomal membranes or the membrane of phagolysosomes. The biogenesis and the maintenance of the vacuolar membrane are closely related to the peculiar cellular organization of these parasites and are unique phenomena in cell biology. Here we compare biological similarities and differences between the two parasites, with respect to: (i) the formation, (ii) the maintenance, and (iii) the biological role of the vacuolar membrane. We conclude that most differences between the organisms primarily reflect the different biosynthetic capacities of the host cells they invade.
The expression of an Ets1 transcription factor lacking its activation domain decreases uPA proteolytic activity and cell motility, and impairs normal tubulogenesis and cancerous scattering in mammary epithelial cells
Authors: Delannoy-Courdent A. , Mattot V. , Fafeur V. , Fauquette W. , Pollet I. , Calmels T. , Vercamer C. , Boilly B. , Vandenbunder B. , Desbiens X. 
Published: April 2021

ABSTRACT
Cell migration and invasion play a crucial role during normal and pathological development. The expression of several members of the Ets family of transcription factors has been shown to correlate with the occurrence of these processes. In the present study, we investigated the effect of the expression of Ets1-DB, the DNA-binding domain of c-Ets1, on the functional properties of NMuMG and MMT epithelial cell lines, from normal and cancerous mouse mammary tissues, respectively. We found that stable expression of this Ets1-DB mutant inhibited, in both cell types, the gene expression and activity of urokinase typeplasminogen activator (uPA), a potential target of c-Ets1. uPA is a key serine proteinase in the proteolytic cascade leading to the degradation of the extracellular matrix. In two-dimensional cultures, expression of the Ets1-DB mutant resulted in a decrease in cell migration and invasion in both cell lines. In three-dimensional collagen gels, NMuMG cells underwent tubular morphogenesis, while MMT cells developed as scattered structures. The Ets1-DB mutant impaired the capacity of NMuMG cells to form tubules and reduced the ability of MMT cells to invade these gels. Similar inhibition of cell migration, invasion and morphogenesis were observed in non-infected NMuMG and MMT cell lines treated with aprotinin, a serine proteinase inhibitor, suggesting that the inhibition of the plasmin cascade mediates in part the biological effects induced by the Ets1-DB mutant. These results demonstrate that Ets family members are involved in the control of uPA activity, cell motility and invasion during normal tubular morphogenesis and cancerous scattering in mammary epithelial cells.
Spinalin, a new glycine- and histidine-rich protein in spines of Hydra nematocysts
Authors: Koch Alexander W. , Holstein Thomas W. , Mala Carola , Kurz Eva , Engel Jürgen , David Charles N. 
Published: April 2021

ABSTRACT
Here we present the cloning, expression and immunocytochemical localization of a novel 24 kDa protein, designated spinalin, which is present in the spines and operculum of Hydra nematocysts. Spinalin cDNA clones were identified by in situ hybridization to differentiating nematocytes. Sequencing of a full-length clone revealed the presence of an N-terminal signal peptide, suggesting that the mature protein is sorted via the endoplasmic reticulum to the post-Golgi vacuole in which the nematocyst is formed. The N-terminal region of spinalin (154 residues) is very rich in glycines (48 residues) and histidines (33 residues). A central region of 35 residues contains 19 glycines, occurring mainly as pairs. For both regions a polyglycine-like structure is likely and this may be stabilized by hydrogen bond-mediated chain association. Similar sequences found in loricrins, cytokeratins and avian keratins are postulated to participate in formation of supramolecular structures. Spinalin is terminated by a basic region (6 lysines out of 15 residues) and an acidic region (9 glutamates and 9 aspartates out of 32 residues). Western blot analysis with a polyclonal antibody generated against a recombinant 19 kDa fragment of spinalin showed that spinalin is localized in nematocysts. Following dissociation of the nematocyst’s capsule wall with DTT, spinalin was found in the insoluble fraction containing spines and the operculum. Immunocytochemical analysis of developing nematocysts revealed that spinalin first appears in the matrix but then is transferred through the capsule wall at the end of morphogenesis to form spines on the external surface of the inverted tubule and the operculum.