bluuebunny/crossref_metadata_2025_split huggingface dataset:
Induction of constitutive melanogenesis in amelanotic mouse melanoma cells by transfection of the human melanocortin-1 receptor gene
Authors: Tapia Johanna Chluba-de , Bagutt Claudia , Cotti Renato , Eberle Alex N. 
Published: April 2021

ABSTRACT
The human melanocortin-1 (MC1) receptor was stably expressed in the amelanotic mouse melanoma cell clone B16-G4F which does not express its own (mouse) MC1 receptor and hence is unresponsive to α melanocyte stimulating hormone (αMSH). From several stable transfectant cell lines expressing the human MC1 receptor in relatively high numbers, three melanin producing clones (G4F-12, 14, and 15) and one amelanotic clone (G4F-7) were further analyzed in competition binding experiments and in cAMP and melanin assays. The dissociation constants (KD) for [Nle4, D-Phe7]-αMSH in all four clones ranged from 0.187 to 0.705 nmol/l, thus corresponding to the KD observed with the different human melanoma cell lines so far studied. Intracellular cAMP content was 3-to 5-fold higher than that of control cells, and αMSH induced an additional 1.5-to 1.7-fold increase. G4F-15 cells secreted melanin into the medium whereas the other clones did not secrete melanin. The extent of melanin secretion was similar to that of fully αMSH-stimulated B16-F1 mouse melanoma cells but the onset of secretion was delayed. αMSH induced an additional dose-related increase (up to 1.3-fold) in melanin production which could be suppressed by the addition of specific αMSH antibodies without altering the constitutive part of melanogenesis. Human and mouse agouti proteins, which inhibit basal and αMSH-induced melanogenesis in B16-F1 cells, both reduced αMSH-induced melanin production in G4F-15 cells but did not affect the constitutive melanogenesis. These results indicate that human MC1 receptor expressed in mouse B16-G4F cells induces constitutive activation of the signalling pathway controlling melanogenesis, most likely by tightly coupling to Gsα, in a similar manner to that reported for constitutively active receptor mutants in other systems.
Identification of two distinctly localized mitochondrial creatine kinase isoenzymes in spermatozoa
Authors: Kaldis Philipp , Stolz Martin , Wyss Markus , Zanolla Else , Rothen-Rutishauser Barbara , Vorherr Thomas , Wallimann Theo 
Published: April 2021

ABSTRACT
The creatine kinase (CK) isoenzyme system is essential for motility in rooster and sea urchin sperm. In the present study, biochemical characterization as well as immunofluorescence and confocal laser microscopy with highly specific antibodies against various chicken CK isoenzymes revealed that cytosolic brain-type CK isoenzyme (B-CK) is the only CK isoenzyme in rooster seminal plasma, while three isoenzymes, cytosolic B-CK, sarcomeric mitochondrial CK (Mib-CK), and a variant of ubiquitous Mi-CK (‘Mia-CK variant’), are found in rooster spermatozoa. These three isoenzymes are localized in different regions of the sperm cell. B-CK and Mib-CK were localized along the entire sperm tail and in the mitochondria-rich midpiece, respectively. The ‘Mia-CK variant’, on the other hand, was found predominantly at the head-midpiece boundary, in a non-uniform manner in the midpiece itself and, surprisingly, at the distal end of the sperm tail as well as at the acrosome. Several lines of evidence show that the ‘Mia-CK variant’ shares some characteristics with purified Mia-CK from chicken brain, but also displays distinctive features. This is the first evidence for two different Mi-CK isoenzymes occurring in one cell and, additionally, for the coexpression of Mib-CK and cytosolic brain-type B-CK in the same cell. The relevance of these findings for sperm physiology and energetics is discussed.
The internalization of a short acyl chain analogue of ganglioside GM1 in polarized neurons
Authors: Sofer Anat , Schwarzmann Güenter , Futerman Anthony H. 
Published: April 2021

ABSTRACT
In order to study the endocytosis of membrane lipids during the development of neuronal polarity, we examined the internalization of a short acyl chain fluorescent derivative of ganglioside GM1, N-(6-(4-nitrobenz-2-oxa-1,3-diazole-7-yl)-aminohexanoyl)-GM1 (C6-NBD-GM1), in hippocampal neurons cultured at low density. C6-NBD-GM1 was internalized by temperatureand energy-dependent mechanisms, and after short times of incubation, accumulated in endosomes in the axon, cell body and dendrites of neurons maintained for up to 4-5 days in culture. C6-NBD-GM1 was subsequently transported in a retrograde direction to a pool of recycling endosomes in the cell body, with little transport to lysosomes, as indicated by the lack of degradation of C6-NBD-GM1 even after long times, and the re-appearance of intact C6-NBD-GM1at the cell surface after recycling; similarly, little degradation of C6-NBD-GM1 was detected in N18TG-2 neuroblastoma cells. In hippocampal neurons maintained for longer than 6 days in culture, there was little internalization of C6-NBD-GM1 along the length of axons, but the amount of endocytosis from dendrites was similar to that observed in younger neurons. These results demonstrate that gangliosides turnover rapidly in dendritic membranes at all stages of neuronal development, whereas ganglioside turnover in axons is much less rapid, at least in mature, polarized neurons.
The basolateral sorting signal of the polymeric immunoglobulin receptor contains two functional domains
Authors: Reich Vanda , Mostov Keith , Aroeti Benjamin 
Published: April 2021

ABSTRACT
Basolateral sorting of the polymeric immunoglobulin receptor (pIgR) expressed in Madin-Darby canine kidney (MDCK) cells is mediated by a 17-residue sorting signal that resides in the cytoplasmic domain. We have recently analyzed the sequence requirements of the signal by alanine scanning mutagenesis. We found that basolateral sorting is mediated primarily by three amino acids: H656, R657 and V660. Individual mutations of each of these residues to Ala caused a substantial decrease in basolateral sorting and a corresponding increase in targeting to the apical surface. Structural analysis of 17-residue peptides corresponding to the signal revealed that V660 is in a β-turn (probably type I) secondary structure, and its mutation to Ala destabilized the turn. H656 and R657 were not part of the turn and substitution of Arg657 to Ala had no effect on the turn stability. These results suggested that the signal is comprised of two structurally distinct domains: a critical V660 in the context of the β-turn and an additional two residues (H656 and R657) that are not in the turn and probably are unimportant for its stability. Here we provide evidence suggesting that the two domains are distinguishable not only by their structure but also by their function. Basolateral targeting of pIgR mutants bearing Ala mutations at either 656 or 657 was not affected by treatment with brefeldin A (BFA), while basolateral targeting of pIgR containing an Ala substitution at position 660 was markedly and uniquely stimulated by BFA. Compared to single Ala substitutions, simultaneous mutations of H656 and R657 to Ala caused an additional minor effect on basolateral and apical sorting, whereas double mutations of V660 and either H656 or R657 resulted in a maximal decrease in basolateral targeting and corresponding increase in apical targeting. These results suggest the existence of two domains in the signal. When both domains are destroyed, basolateral targeting is maximally inhibited. The results also imply that V660 mediates basolateral sorting by a different mechanism from H656 and R657. We suggest that V660 and perhaps more generally the β-turn may interact with BFA-sensitive adaptor complexes.
Focal cellular origin and regulation of interstitial collagenase (matrix metalloproteinase-1) are related to menstrual breakdown in the human endometrium
Authors: Kokorine I. , Marbaix E. , Henriet P. , Okada Y. , Donnez J. , Eeckhout Y. , Courtoy P. J. 
Published: April 2021

ABSTRACT
Recent studies suggest that interstitial collagenase (MMP-1) is an essential enzyme in the early events leading to menstruation. This study analyses its cellular origin, regulation and relation to extracellular matrix breakdown in the human endometrium, both in cultured and non-cultured samples. The source of MMP-1 was identified by in situ hybridization and by immunohistochemistry on serial sections. This was compared with the immunolocalization of other MMPs, steroid receptors, macrophages, and laminin. In non-cultured endometrium, MMP-1 was only expressed during the perimenstrual period. It was either restricted to superficial foci of stromal cells or extended towards the entire functional layer. MMP-1 expression remarkably correlated with matrix breakdown, as assessed by silver staining, and was prominent at the periphery of shedding fragments and along some arterioles. In cultured non-menstrual explants, MMP-1 expression was induced within two days after deprivation of sex steroids. Both in cultured and non-cultured samples, progesterone receptors were not detectable in epithelial cells at foci of MMP-1 expression. The same stromal cells could synthesize MMP-1, MMP-2 (gelatinase A) and MMP-3 (stromelysin-1), as well as laminin, and did not correspond to macrophages. In conclusion, MMP-1 is focally expressed in stromal cells of the functional layer of the endometrium, when and where steroid receptors disappear, and especially where tissue breakdown is prominent. These observations point to an essential role for MMP-1 in the early stages of menstruation.
Alterations in neural intermediate filament organization: Functional implications and the induction of pathological changes related to motor neuron disease
Authors: Straube-West Karen , Loomis Patricia A. , Opal Puneet , Goldman Robert D. 
Published: April 2021

ABSTRACT
The properties regulating the supramolecular organization of neural intermediate filament (NIF) networks have been investigated in cultured dorsal root ganglion (DRG) neurons. The studies described take advantage of the ability of endogenous NIF to incorporate purified biotinylated neurofilament triplet (NFT) proteins, NF-L, NF-M and NF-H. When injected at concentrations of 0.8-1.0 mg/ml injection buffer, each of these proteins is incorporated without perturbing the endogenous NIF network. However, at progressively higher concentrations, NF-H induces the aggregation and accumulation of NIF in the cell body. Subsequent to the induction of these aggregates, numerous alterations in the cytoarchitecture of neurons can be detected. The latter occur in a temporal sequence which appears to begin with the fragmentation of the Golgi complex. At later times, accumulation of mitochondria within the proximal region of neurites, peripheralization of the nucleus, and a significant decrease in neurite caliber become obvious. After longer time periods, the NIF aggre gates are seen to react with an antibody which reveals abnormally phosphorylated NF-H. These observations demonstrate that an imbalance in the normal stoichiometric relationships among the NFT proteins rapidly alters the supramolecular organization of the NIF network. These changes most likely reflect the normal functions of neurofilaments in cell shape and the organization and cytoplasmic distribution of membranous organelles. Interestingly, virtually all of these changes closely resemble those which have been reported in motor neuron diseases such as amyotrophic lateral sclerosis (ALS). These findings suggest that cultured neurons can be used as models for more precisely defining the relationships between the formation of N?F aggregates and the sequence of cytopathological events which typify neurodegenerative diseases.
An apoptotic endonuclease activated either by decreasing pH or by increasing calcium
Authors: Collins Mary K. L. , Furlong Isla J. , Malde Prupti , Ascaso Rosalia , Oliver Javier , Rivas Abelardo Lopez 
Published: April 2021

ABSTRACT
DNA fragmentation in isolated nuclei from the murine IL3-dependent bone marrow cell line BAF3 could be stimulated either by decreasing pH below 6.5 or by adding μM calcium at neutral pH. An endonuclease which could also be stim-ulated either by a decrease in pH, to 6.5, or by the presence of μM calcium at neutral pH, was purified 104-fold from nuclei of BAF3 cells. Digestion of DNA with the purified enzyme resulted in 5′-terminal hydroxyl and 3′-terminal phosphate ends. These characteristics are distinct from those described for other mammalian endonucleases. The possible role of this enzyme in genome digestion during apoptosis is discussed.
A method of maintaining parenchymal cells from adult rat liver in vitro
Authors: Alwen J. , Gallhai-Atchard Jennifer J. 
Published: April 2021

ABSTRACT
A method for preparing suspensions of adult rat hepatocytes suitable for maintenance in vitro is described. Cultures were established from the cell suspensions by the squash technique. Cells were examined by light and electron microscopy; histochemically for glycogen, bile, lipid and glucose-6-phosphatase; and by autoradiography for DNA, RNA and protein synthesis. Hepatocytes could be maintained in vitro for at least 3 days and began to aggregate after 1 day. Uridine and leucine were incorporated, but not thymidine. Cultures consisted mainly of hepatocytes, though reticulo-endothelial cells were sometimes present.
Helical filaments in the glial cells of the locust (Schistocerca gregaria)
Authors: Osborne M. P. 
Published: April 2021

ABSTRACT
Organelles consisting of a spirally wound filament are present in the cytoplasm of glial cells in Schistocerca gregaria. The diameter of the helix is 32·5 ran with an average pitch length of 23·0 ran. The filament is comprised of only a single strand about 6·0 nm in diameter which appears to be made up of a chain of globular subunits. In order to distinguish between these helical structures and organelles made up of more than one strand, i.e. microtubules and microfilaments, it is suggested that they be termed ‘microhelices’.
The structural features of microtubules, microfilaments and microhelices are compared, and the possible functions of microhelices are discussed in the light of what is known about the physiological properties of microtubules.
It is pointed out that the microhelix is structurally very similar to the internal ribonucleo-protein component of the influenza virus, and that the possibility cannot be discounted that the microhelix might be a viral particle.
Acceleration of nuclear growth and advanced initiation of mitosis in u.v.-irradiated plasmodia of Physarum polycephalum
Authors: Telatnyk Maureen M. , Guttes E. 
Published: April 2021

ABSTRACT
In the multinucleated plasmodia of Physarum polycephalum the intermitotic period lasts from 2·5–5 days on diluted (1:8) growth medium and 3 − 7 days on non-nutrient balanced salt solution. When such plasmodia were irradiated with u.v. light approx. 15 − 20 h after mitosis, the next mitosis was considerably advanced and the intermitotic period lasted only between 36 − 48 h. During this time, numerous nuclei became pyknotic and disappeared, while the others became larger than in unirradiated controls. It is proposed that the abbreviation of the inter-mitotic period preceding the first post-irradiation mitosis was caused by incorporation into the surviving nuclei of a substance(s) which was released from the degenerating nuclei.
Fine-structural studies on spontaneous and induced fusion of higher plant protoplasts
Authors: Withers Lyndsey A. , Cocking E. C. 
Published: April 2021

ABSTRACT
During the treatment of some plant tissues with cell-wall-degrading enzymes adjacent cells within the tissue fuse forming large multinucleate protoplasts. These have been termed spon-taneous fusion bodies. The symplastic nature of plant tissues suggests that the retention of plasmodesmatal connexions might facilitate such spontaneous fusion. An electron-microscopic investigation of spontaneous fusion in tobacco-leaf and oat-root tissues has confirmed this suggestion. Enzymic degradation of the walls removes constrictions on the plasmodesmata, permitting their expansion, and as a result mixing of the cytoplasms of the fusing protoplasts can then occur.
The fine structure of plasmodesmata and their relationship to the endoplasmic reticulum can be more easily studied in plasmodesmata which are undergoing expansion. It has been observed that the tubule which passes through the plasmodesma is in continuity with the endoplasmic reticulum membranes at either end. Models for plasmodesmatal structure are discussed in the light of this observation.
The induced fusion of freely isolated protoplasts by sodium salts has been previously studied using the light microscope. Since it is difficult to follow the detailed mechanisms involved in the process, electron-microscopic methods have been employed in the present investigation. It appears that sodium nitrate first induces protoplast adhesion. This occasionally involves protrusions from the plasmalemma, not unlike microvilli. Following adhesion membrane fusion occurs, initially in localized regions, and then more generally. Eventually vacuolar fusion occurs facilitating complete cytoplasmic mixing.
These findings are compared with events occurring during animal cell fusion and are discussed in relationship to a recent theoretical model for membrane fusion.
The fine structure of the embryogenic callus of Ranunculus sceleratus l
Authors: Thomas E. , Konar R. N. , Street H. E. 
Published: April 2021

ABSTRACT
Sections of callus of Ranunculus sceleratus reveal its organization into cellular aggregates, the superficial cells of which are highly cytoplasmic and the inner cells of which are larger, have less-dense cytoplasm and are more highly vacuolated. Expansion and ultimate death of some of the internal cells leads to cell separation and break up of the aggregates.
Many of the superficial cells are involved in the initiation of embryoids in the callus and they correspond in structure with the embryogenic cells of the seedling stem epidermis. The embryoids are retarded in their development in presence of 2,4-dichlorophenoxyacetic acid (2,4-D) and embryoid development becomes more rapid and more prolific when cultures are transferred to a medium without 2,4-D.
The similarity between the embryogenic cells of the callus cultures and those of the seedling stem epidermis extends to cell size, nuclear size, degree of vacuolation, abundance of ribosomes and mitochondria, presence of amyloplasts and prominence of spherosomes. The various forms of spherosome are described and their possible function discussed. Amyloplasts differentiating into chloroplasts are observed in the more advanced embryoids.
There is evidence that embryoids can arise from single cells but it is uncertain whether all are of single-cell origin. The embryogenic cells are in protoplasmic continuity with surrounding cells when they embark upon embryogenesis.
Some of the superficial cells, also clearly undergoing active division, are of rather different structure; characteristically their nuclei show a high degree of chromatin condensation and their cytoplasm contains bundles of fibrous material. It is suggested that these cells do not function directly in embryogenesis.
The internal cells of the aggregates have a low density of ribosomes and very few ER profiles or normal mitochondria. Extremely elongated mitochondrial structures following the outline of the nucleus are observed in these cells.
An unidentified structure is frequently observed in cells in which cytoplasmic disorganization appears to be occurring.
Raphide crystal cell development in leaves ofPsychotria punctata(rubiaceae)
Authors: Horner H. T. , Whitmoyer R. E. 
Published: April 2021

ABSTRACTThe distribution and development of raphide cry8tal cells in nodulated leaves of Psychotria punctata were studied by light and electron microscopy. Crystal cells in the leaf are oriented in various ways depending on whether they occur in the spongy or palisade parenchyma. Crystals are never found within the bacterial nodules and are not concentrated around them. Developing leaf crystal cells become larger than surrounding cells and have larger nuclei and nucleoli. Raphides develop within membrane chambers in the large central vacuole in association with membrane complexes, vesicles and tubules, the latter measuring 10–13 nm in diameter. Certain cytoplasmic organelles, the plasmalemma, and a cytoplasmic vacuolar channel complex also appear to be associated with crystal development. These results are compared with other recent investigations dealing with calcium oxalate crystals in higher plants.
Variable amounts of dna related to the size of chloroplasts: IV. three-dimensional arrangement of dna in fully differentiated chloroplasts of Beta vulgaris L
Authors: Kowallik K. V. , Herrmann R. G. 
Published: April 2021

ABSTRACT
Glutaraldehyde-fixed strips of fully differentiated leaves of Beta vulgaris L. were treated with proteases. With this method it is possible to display DNA-regions in chloroplasts selectively and to reconstruct them from serial sections.
As in young plastids, the DNA in mature plastids is also distributed within several regions which are separated rather clearly by thylakoids. The number of such regions depends upon the size of the organelle and thus upon its developmental state. The shape of the regions is, in contrast to less-differentiated plastids, mostly elongated. The individual regions seem to contain unequal quantities of DNA-fibrils.
A comparison of our ultrastructural results and biochemical data (DNA-amounts per plastid depending on the size of the organelle; kinetic complexity of chloroplast-DNA of Beta) as well as a comparison of the chloroplast with similar prokaryotic systems (as in bacteria, blue-green algae, and mitochondria) leads to the suggestion that each DNA-containing region can be regarded as a single nucleoid. In addition, each nucleoid already contains several (on average, 4–8) genetic units. Thus the chloroplast of Beta seems genetically polyvalent in at least 2 respects: (i) it is of polyenergidic organization, and (ii) the individual nucleoids can be polyploid to varying degrees.
Further experiments on the role of the nucleolus in the expression of structural genes
Authors: Deák I. , Sidebottom E. , Harris H. 
Published: April 2021

ABSTRACT
When a chick erythrocyte nucleus is introduced into the cytoplasm of a mouse cell it under-goes reactivation and eventually determines the synthesis of chick-specific proteins in the cytoplasm of the heterokaryon. It has previously been shown that there is a close temporal correlation between the onset of synthesis of the chick-specific proteins and the appearance of nucleoli in the erythrocyte nuclei. We now show that the synthesis of chick-specific proteins in the heterokaryon decays if the nucleolus in the reactivated erythrocyte nucleus is irradiated with an ultraviolet microbeam. The synthesis of chick-specific proteins does not, however, decay if only one of two nucleoli in the erythrocyte nucleus or if extranucleolar areas of the nucleus are irradiated. These observations confirm that some function located at or near the nucleolus is essential for the full expression of structural genes.