bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ascidian eggs release glycosidase activity which aids in the block against polyspermy
Authors: Lambert Charles C. 
Published: April 2021

ABSTRACT
To ensure normal development, most animals have evolved a number of mechanisms to block polyspermy including prevention of binding to surface coats as well as sperm-egg fusion. Ascidian sperm bind to vitelline coat (VC) glycosides. In the genus Ascidia, N-acetylglu-cosamine (GlcNAc) is the ligand to which sperm bind. The number of sperm bound to the VC is biphasic following fertilization; sperm binding increases through the first minute or so, then abruptly declines. At fertilization, the eggs of Ascidia callosa, A. ceratodes, A. méntula, A. nigra and Phallusia mammillata release N- acetylglucosaminidase into the sea water (SW). This has been shown to inactivate VC GlcNAc groups, blocking the binding of supernumerary sperm and polyspermy in A. nigra. This block to polyspermy is inactivated by GlcNAc (2mm) or 150mm-Na+ (choline substituted) SW. These treatments are not additive and therefore probably affect the same process. In A. callosa, fertilization in low Na+ SW causes a 60 % decline in enzyme release and a similar increase in the number of sperm remaining on the VC at 4 min as well as a great increase in polyspermy. Thus the principal block to polyspermy in ascidian eggs involves the release of N-acetylglucosa-minidase which appears to be Na+ dependent. Enzyme activity is found in the supernatant SW by 15 s after fertilization, suggesting that it is stored very near the egg surface. Histochemical staining of whole eggs and embryos shows loss of surface-associated enzyme activity following fertilization. Like other lysosomal enzymes this N-acetylglucosaniinidase is mannosylated and has an acidic pH optimum.
Non-genic inheritance of cellular handedness
Authors: Nelsen E. Marlo , Frankel Joseph , Jenkins Leslie M. 
Published: April 2021

ABSTRACT
Ciliates exhibit an asymmetry in arrangement of surface structures around the cell which could be termed handedness. If the usual order of placement of structures defines a ‘right-handed’ (RH) cell, then a cell with this order reversed would be ‘left-handed’ (LH). Such LH forms appear to be produced in Tetrahymena thermophila through aberrant reorganization of homopolar doublets back to the singlet condition. Four clones of LH forms were selected and subjected to genetic analysis to test whether this drastic phenotypic alteration resulted from a nuclear genetic change. The results of this analysis indicate that the change in handedness is not due to a genetic change in either the micronucleus or macronucleus. The LH form can, under certain circumstances, revert to the RH form, but typically it propagates itself across both vegetative and sexual generations with similar fidelity.
While this analysis does not formally rule out certain possibilities of nuclear genic control involving regulatory elements transmitted through the cytoplasm, when the circumstances of origin and propagation of the LH condition are taken into account direct cortical perpetuation seems far more likely. Here we outline a conceptual framework centred on the idea of longitudinally propagated positional information; the positive evidence supporting this idea as well as further application of the idea itself are presented in the accompanying paper.
Re-expression of 117 antigen, a cell surface glycoprotein of aggregating cells, during terminal differentiation of Dictyostelium discoideum prespore cells
Authors: Browne Lois H. , Sadeghi Homa , Blumberg Daphne , Williams Keith L. , Klein Claudette 
Published: April 2021

ABSTRACT
117 antigen is a glycoprotein expressed on the surface of D. discoideum cells at aggregation. It then disappears and is later re-expressed on the surface of a subpopulation of cells at culmination, the terminal differentiation stage (Sadeghi et al. 1987). A cDNA clone was used to show that the appearance of cell surface 117 antigen accurately reflects the expression of the 117 gene as measured by mRNA levels. It was also shown that during multicellular development there is a reciprocal relationship between the levels of 117 mRNA and the mRNA which codes for prespore surface glycoprotein, PsA. Dual parameter flow cytometry was used to demonstrate that the 117 antigen is found on the surface of maturing prespore cells after the PsA glycoprotein disappears, but that it is not found on mature spores. Using three monoclonal antibodies which identify respectively 117 antigen, PsA, and MUD3 antigen (a spore coat glycoprotein - probably Sp96), two new stages of final spore maturation were defined. These results indicate that there is a recapitulation of at least one aggregative cell surface glycoprotein in the prespore subpopulation of cells as they rise up the stalk during final spore development. This raises the possibility that culmination, which involves complex three dimensional morphogenetic movements not unlike those observed during animal embryogenesis, involves components of the two-dimensional pattern seen during aggregation.
XIHbox 8: a novel Xenopus homeo protein restricted to a narrow band of endoderm
Authors: Wright Christopher V. E. , Schnegelsberg Patrick , Robertis Eddy M. De 
Published: April 2021

ABSTRACT
We report the isolation of a new homeobox gene from Xenopus laevis genomic DNA. The homeodomain sequence is highly diverged from the prototype Antennapedia sequence, and contains a unique histidine residue in the helix that binds to DNA. The homeo-domain is followed by a 65 amino acid carboxy-terminal domain, the longest found to date in any vertebrate homeobox gene. We have raised specific antibodies against an X1Hbox 8-β-gal fusion protein to determine the spatial and temporal expression of this gene. The nuclear protein first appears in a narrow band of the endoderm at stage 33 and develops into expression within the epithelial cells of the pancreatic anlagen and duodenum. Expression within the pan-creatic epithelium persists into the adult frog. This unprecedented restriction to an anteroposterior band of the endoderm suggests that vertebrate homeobox genes might be involved in specifying positional information not only in the neuroectoderm and mesoderm, but also in the endoderm. Our data suggest that X1Hbox 8 may therefore represent the first member of a new class of position-dependent transcription factors affecting endodermal differentiation.
IGF I induces differentiation in a transformed human keratinocyte line
Authors: Kamalati T. , Howard M. , Brooks R. F. 
Published: April 2021

ABSTRACT
A comparison of normal epithelial cells with their transformed counterparts could lead to the definition of parameters related to growth and differentiation which are altered by viral transformation and which may be relevant to malignant changes in vivo. Using the SV40-transformed human keratinocyte line, SVK14, which exhibits characteristics of simple, nonkeratinizing epithelia, we have shown that IGF I stimulation of these cells results in extensive multilayering, increased cell size, accumulation of involucrin, modulation of keratin 18 and expression of keratins 14 and 10, whilst T-antigen expression is maintained in the multilayered cells. Since T-antigen expression is correlated directly with impairment of stratification and differentiation, it is interesting that treatment of SVK14 with a single growth factor, IGF I, results in molecular events characteristic of differentiating normal keratinocytes.
Cross-species recognition of tectal cues by retinal fibers in vitro
Authors: Godement Pierre , Bonhoeffer Friedrich 
Published: April 2021

ABSTRACT
The retinae of vertebrates project in a topographic manner to several visual centers of the brain. The formation of these projections could depend on the existence of position-specific properties of retinal and target cells. In this study, we have tested the in vitro growth of mouse retinal fibers on membranes derived from various regions of the embryonic superior colliculus, a main target of the retina in this species. Fibers had the choice of elongating on membranes taken from either the anterior or the posterior half of the superior colliculus. Fibers from temporal areas of the retina prefer to elongate on anterior collicular membranes, while fibers from nasal areas do not show a preference. These phenomena are observed with membranes from embryonic (E15–E18) or young postnatal mice. In interspecies cultures where mouse retinal fibers had to grow on chick tectal membranes, or vice versa, the same preference for anterior tectal or collicular membranes in growth of temporal retinal fibers is observed, suggesting some similarities in the cues used in both species.
Cutaneous nerves of the embryonic chick wing do not develop in regions denuded of ectoderm
Authors: Martin Paul , Khan Akbar , Lewis Julian 
Published: April 2021

ABSTRACT
Peripheral nerves travel to their targets along precise routes, and it is likely that different cues provide guidance at different stages of the journey. In a develop­ing chick limb, the cutaneous nerve fibres follow at first deep mixed nerve trunks, in company with motor axons; they branch from these trunks at predictable points and approach the skin; they then ramify profusely to form a plexus at a precisely defined depth beneath the ecto­derm, at exactly the same level as the blood vascular plexus. To analyse the role of signals from the target patch of skin in regulating cutaneous nerve develop­ment, we have ablated patches of dorsal wing ectoderm using short-wave ultraviolet irradiation at E4 (embry­onic day 4), approximately one day before nerves grow into the limb bud. The irradiated patches remain denuded of ectoderm for more than a week, by which time the cutaneous nerve plexus on the contralateral control side is well developed and can be revealed by whole-mount silver staining. Where the ectoderm has been ablated, no cutaneous nerve plexus forms, and the nerve branches that normally would have diverged from the neighbouring mixed nerve trunk to innervate the missing patch of skin are absent - ab initio, apparently. The routes of the mixed nerve trunks are not affected. Partial ablation of the territory of a cutaneous nerve branch often leads to loss of the whole nerve branch; the intact skin territory thus left vacant is invaded by ramifications from the remaining cutaneous branches, as expected if the normal extent of a cutaneous nerve’s territory is regulated by competition. Where there is an ectodermal lesion, cutaneous innervation stops precisely at its boundary, even though the vascular plexus extends for some distance beyond this margin, beneath the denuded surface. The data suggest that the embryonic skin is required firstly to trigger divergence of cutaneous nerve branches from the mixed nerve trunks, and secondly, once the nerve fibres have reached the skin, to supply a trophic cue (probably NGF) encouraging growth of a plexus; at the same time, the embryonic skin generates a signal inhibiting nerves from approaching closer than about 70 μm to the surface.
Transcriptional regulation of a Xenopus embryonic epidermal keratin gene
Authors: Jonas Erzsebet A. , Snape Alison M. , Sargent Thomas D. 
Published: April 2021

ABSTRACT
XK81A1 is a type I epidermal keratin gene expressed in early developmental stages of Xenopus (Jonas et al. 1985). Fusion of the keratin promoter (-5900 to +26) to a human β globin gene led to fully epidermis-specific accumulation of human globin mRNA and protein when this DNA was injected into fertilized eggs. Further localization of regulatory sequences was accomplished by injecting marked, 5’-deleted keratin gene DNA into fertilized eggs and evaluating tissue specificity of expression. All 5’ flanking DNA upstream from -487 could be removed without interfering with keratin gene expression or regulation. These results suggest that the primary mode of regulation of epidermis-specific keratin gene expression is at the level of transcription, and that sequence elements in the 5’ flanking region of the keratin gene, between -487 and +26, are responsible for this regulation.
Fibronectin gene expression during limb cartilage differentiation
Authors: Kulyk William M. , Upholt William B. , Kosher Robert A. 
Published: April 2021

ABSTRACT
A critical event in limb cartilage differentiation is a transient cellular condensation process in which pre-chondrogenic mesenchymal cells become closely juxtaposed and interact with one another prior to initiating cartilage matrix deposition. Fibronectin (FN) has been suggested to be involved in regulating the onset of condensation and chondrogenesis by actively promoting prechondrogenic aggregate formation during the process. We have performed a systematic quantitative study of the expression of the FN gene during the progression of chondrogenesis in vitro and in vivo. In high-density micromass cultures of limb mesenchymal cells, FN mRNA levels increase about 5-fold coincident with the crucial condensation process, and remain relatively high during the initial deposition of cartilage matrix by the cells. Thereafter, FN mRNA levels progressively decline to relatively low levels as the cultures form a virtually uniform mass of cartilage. The changes in FN mRNA levels in vitro are paralleled closely by changes in the relative rate of FN synthesis as determined by pulselabeling and immunoprecipitation analysis. The relative rate of FN synthesis increases 4- to 5-fold at condensation and the onset of chondrogenesis, after which it progressively declines to low levels as cartilage matrix accumulates. High levels of FN gene expression also occur at the onset of chondrogenesis in vivo. In the proximal central core regions of the limb bud in which condensation and cartilage matrix deposition are being initiated, FN mRNA levels and the relative rates of FN synthesis become progressively about 4-fold higher than in the distal subridge region, which consists of undifferentiated mesenchymal cells that have not yet initiated condensation. The striking increase in FN gene expression that occurs during condensation and the onset of chondrogenesis is consistent with the suggestion that this molecule may play a role in the crucial cell-cell or cell-matrix interactions involved in regulating the onset of cartilage differentiation.
Mammalian neuronal differentiation: early expression of a neuronal phenotype from mouse neural crest cells in a chemically defined culture medium
Authors: Boisseau Sylvie , Simonneau Michel 
Published: April 2021

Summary
We show that mouse neural crest cells cultured in a serum-deprived chemically defined medium on appropriate culture substrata can be induced to express a neuronal phenotype. The uncommitted neural crest cells express a mesenchymal intermediate filament protein such as vimentin, but not the usual neuronal markers such as receptor sites for tetanus toxin or neurofilaments. In the chemically defined medium, receptor sites for tetanus toxin or neurofilaments can be characterized after a few hours in culture. Furthermore, these cells acquire tetrodotoxin-sensitive voltage-dependent Na+ channels and can generate action potentials. Such an in vitro system should allow us to analyze and manipulate early stages of neuronal differentiation in a mammalian embryo, at a level so far restricted to lower vertebrate embryos.
Melanogenesis of avian neural crest cells in vitro is influenced by external cues in the periorbital mesenchyme
Authors: Campbell Steven 
Published: April 2021

ABSTRACT
Avian melanoblast differentiation was studied by explantation of the neural tube and periorbital mesenchyme. Outgrowths from the mesenchymal expiants consisted of a mixed population of melanocytes, melano-blasts and fibroblasts, whilst typical neural crest populations migrated from the neural tube expiants. Cells that differentiated within expiants of mesenchyme, produced elongate black eumelanosomes of normal ultrastructure which were identical to those found in the ocular connective tissues. However, melanoblasts that differentiated within outgrowths of mesenchyme or neural tube produced round brown melanosomes of highly abnormal ultrastructure. Some of these melanosomes contained a few disorganised melanosomal filaments whilst others had granular melanin with complete absence of filaments. This abnormality of phenotype was invariant over a range of culture conditions that modified cell behaviour, the timing of differentiation and the abundance of the pigmented cells. These experiments suggest that local factors in the mesenchyme are essential for the induction of melanogenesis in the presumptive connective tissue melanocyte.
The appearance of neural and glial cell markers during early development of the nervous system in the amphibian embryo
Authors: Messenger N. J. , Warner Anne E. 
Published: April 2021

ABSTRACT
Cell-type-specific antibodies have been used to follow the appearance of neurones and glia in the developing nervous system of the amphibian embryo. Differentiated neurones were recognized with antibodies against neurofilament protein while glial cells were identified with antibodies against glial fibrillary acidic protein (GFAP). The appearance of neurones containing the neurotransmitters 5-hydroxytryptamine and dopamine has been charted also.
In Xenopus, neurofilament protein in developing neurones was observed occasionally at NF stage 21 and was present reliably in the neural tube and in caudal regions of the brain at stage 23. Antibodies to the low molecular weight fragment of the neurofilament triplet recognized early neurones most reliably. Radial glial cells, identified with GFAP antibody, were identified from stage 23 onwards in the neural tube and caudal regions of the brain. In the developing spinal cord, GFAP staining was apparent throughout the cytoplasm of each radial glial cell. In the brain, the peripheral region only of each glial cell contained GFAP. By stage 36, immunohistochemically recognizable neurones and glia were present throughout the nervous system.
In the axolotl, by stage 36 the pattern of neural and glial staining was identical to that observed in Xenopus. GFAP staining of glial cells was obvious at stage 23, although neuronal staining was clearly absent. This implies that glial cells differentiate before neurones.
5-HT-containing cell bodies were first observed in caudal regions of the developing brain on either side of the midline at stage 26. An extensive network of 5-HT neurones appeared gradually, with a substantial subset crossing to the opposite side of the brain through the developing optic chiasma. 5,7-dihydroxytryptamine prevented the appearance of 5-HT. Depletion of 5-HT had little effect on development or swimming behaviour. Dopamine-containing neurones in the brain first differentiated at stage 35-36 and gradually increased in number up to stage 45-47, the latest stage examined. The functional role of 5-HT- or dopamine-containing neurones remains to be elucidated.
We conclude that cell-type-specific antibodies can be used to identify neurones and glial cells at early times during neural development and may be useful tools in circumstances where functional identification is difficult.
Regeneration and pattern formation in planarians: III. Evidence that neoblasts are totipotent stem cells and the source of blastema cells
Authors: Baguñà Jaume , Saló Emili , Auladell Carme 
Published: April 2021

ABSTRACT
In most regenerating systems, blastema cells arise by dedifferentiation of functional tissue cells. In planarians, though, it is still debatable whether dedifferentiated cells or a population of undifferentiated cells, the neoblasts, are the main source of blastema cells. Moreover, it is unclear whether in the intact organisms neoblasts are quiescent cells ‘reserved’ for regeneration or if they serve as functional stem cells of all differentiated cell types. Both uncertainties partly stem from the failure to distinguish by conventional labelling methods neoblasts from differentiated cells.
Here we describe a new approach to these problems based on testing the regenerative and stem cell capabilities of purified neoblasts and differentiated cells when introduced, separately, into irradiated hosts. Introduc tion of neoblasts led to resumed mitotic activity, blastema formation, and extended or complete survival of the host; differentiated cells, in contrast, never did so.
Therefore, planarian neoblasts can be qualified as totipotent stem cells and the main source of blastema cells, while dedifferentiation does not seem to operate either in intact or regenerating organisms. In addition, these results strengthen the idea that different types of regeneration and blastema formation, linked to the tissular complexity of the organisms, are present in the animal kingdom.
Changes in cell surface glycoproteins during Dictyostelium development analysed using monoclonal antibodies
Authors: Crandall Ian E. , Newell Peter C. 
Published: April 2021

ABSTRACT
We have produced a series of monoclonal antibodies that recognize carbohydrate epitopes on cell surface glycoproteins of developing amoebae of Dictyostelium discoideum. The antibodies were found to have differential specificity for amoebae at different stages of development and were classified into types A to E on the basis of their temporal pattern of reactivity with the developing amoeba! cell surface. Evidence from Western Blots and digestion of the glycoproteins with alkaline phosphatase were consistent with previous reports that the cell surface glycoproteins are extensively processed during development, leading at 16 h of development to the exposure of a highly antigenic core recognized by antibodies in group E. The nature of this core structure is indicated by the finding that antibodies in group E were found also to bind with high avidity to the plant glycoprotein horse radish peroxidase.
Antisera to basal lamina and glial endfeet disturb the normal extension of axons on retina and pigment epithelium basal laminae
Authors: Halfter Willi 
Published: April 2021

ABSTRACT
In order to determine the role of the extracellular matrix in regulating the directed growth of embryonic neurites, antisera to retina (a-RBL I and II), to pigment epithelium (a-PBL) and to glomerular (a-GBL) basal lamina were probed for an effect on the ordered extension of neurites. In the assays, retina explants from chick and quail were cultured on basal lamina from embryonic chick retina and pigment epithelium either in the presence of anti-basal lamina antisera or in the presence of the corresponding preimmune sera. In the presence of all anti-basal lamina antisera, normal extension of axons was greatly inhibited both on retina and on pigment epithelium basal lamina. The antisera affected the growth pattern and the morphology of the individual axons in two ways: in the presence of a-RBL I the short axons were less directed, developed more and longer side branches, and the lamellipodia of the growth cones were reduced in size compared to axons from control cultures. In the presence of a-RBL II and a-GBL, axons grew slowly out from the explants as very thick bundles, strikingly different from axons in control cultures. The antiserum to pigment epithelium basal lamina induced both strong fasciculation and disorganization of the linear fiber extension, being intermediate between the two types of effects observed after antiserum addition. The results suggest that adhesive matrix molecules in basal laminae have important functions in elongation, fasciculation and in the morphology of growing axons.