bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fluorescence microscopic studies of mitochondrial nucleoids during meiosis and sporulation in the yeast, Saccharomyces cerevisiae
Authors: Miyakawa Isamu , Aoi Hiroyuki , Sando Nobundo , Kuroiwa Tsuneyoshi 
Published: April 2021

ABSTRACT
Configurational changes of mitochondria and mitochondrial nucleoids (mt-nucleoids) during meiosis and sporulation in the yeast, Saccharomyces cerevisiae, were examined using the mitochondrial membrane-binding fluorescent dye, dimethyl aminostyrylmethylpyridiniumiodine (DASPMI) and the DNA-binding fluorescent dye, 4’,6-diamidino-2-phenylindole (DAPI).
In zygotes just after mating, mt-nucleoids were observed as many small discrete light spots in the cytoplasm. During meiosis in zygotes, mt-nucleoids at first coalesced with each other into a long string and then separated into spherical nucleoids in four spores. These changes paralleled those in mitochondria observed using DASPMI.
The use of spheroplasts allowed us to examine the behaviour of mt-nucleoids at higher resolution and to identify several distinct meiotic prophase stages of the cell nucleus during early sporulation. In diploid spheroplasts at the stationary phase, 50–7 0 of the mt-nucleoids were observed to be separated from each other and each spherical mitochondrion contained only one mt-nucleoid. At the later stage of premeiotic DNA synthesis, a single branched giant mitochondrion was formed as a result of complete mitochondrial fusion. All of the mt-nucleoids were arranged in an array on a giant mitochondrion and coalesced into a string-like network. Through meiosis I and II, strings of mt-nucleoids were observed close to the dividing nuclei. At late meiosis II, a ring of mt-nucleoids enclosing each daughter nucleus was formed. In ascospores, discrete small nucleoids were visible close to each spore nucleus with a ‘string-of-beads’ appearance. Many mt-nucleoids were excluded from the ascospores and remained in the residual cytoplasm of the ascus.
Pollen-stigma interactions inBrassica oleracea:II. the fate of stigma surface proteins following pollination and their role in the selfincompatibility response
Authors: Roberts Ian N. , Harrod Gillian , Dickinson Hugh G. 
Published: April 2021

ABSTRACTMature, self-incompatible stigmas exposed to cycloheximide for 2 h prior to pollination supported identical germination and growth of both cross and self pollen. Treatment of self-pollinated pistils with cycloheximide resulted in the germination of hitherto inactive pollen after some 2–4 h. Pollen germination and initial tube growth in an in vitro germination medium were not significantly affected by cycloheximide. A continuous synthesis of stigmatic proteins is therefore essential for the operation of the self-incompatibility (S.I.) system. However, light-microscope autoradiography of stigmas fed with L-[3H]leucine prior to pollination revealed no movement of stigmatic proteins into the pollen, independent of the compatibility of the pollen with respect to the stigma. Further, tunicamycin, when applied in the same way as cycloheximide, had no effect on the S.I. system. These results are discussed in terms of the proposed cycling of proteins in the papillar cell wall and the involvement of a stigmatic glycoprotein in the S.I. response.
The reproductive potential of normal mouse embryo fibroblasts during culture in vitro
Authors: Karatza Calliopi , Shall Sydney 
Published: April 2021

ABSTRACT
A direct estimate of the reproductive potential of mouse embryo fibroblasts through their entire lifespan has been made using the mini-clone technique, which permits the direct observation of the growth fraction in a bulk population by inspection of the growth behaviour of individual cells. We have measured the colony size on each island that contained one or two cells at the beginning and the fraction of islands which, starting from one or two cells failed to divide even once.
We observed that even in a young culture there are individual cells that can only reproduce two or three times. With each succeeding passage the distribution of colony sizes shifts to a greater proportion of small colonies. The median colony size decreases with each passage. Furthermore, the fraction of non-dividers directly observed increases smoothly with time; the fraction of non-dividers is quite small at the first passage but increases steadily to reach 0·6 at the last passage, after about 30 generations.
These smooth changes in the growth behaviour of this cell strain are accurately described by the mortalization theory of Shall and Stein, in which the single parameter γ, describes the change in reproductive potential over the entire lifespan. The parameter γ describes the rate at which the doubling time of the culture increases; it is the number of generations at which half of the newborn cells are themselves reproductively sterile. Our present data provide an estimate of y.for this cell strain equal to 21 ·2 generations, which compares well with a previous estimate of 20·3 generations.
An Ultrastructural Study Of Ovarian Development In The OTU
7 Mutant OF Drosophila Melanogaster
Authors: Bishop Donna L. , King Robert C. 
Published: April 2021

ABSTRACT
Females homozygous for the otu7 allele produce ovarian tumours, as well as egg chambers that reach a relatively late stage of development. Mutant ovarian nurse cells contain giant polytene chromosomes. These are transcriptionally active, and RNA is transported to the oocyte through ring canals, although at a reduced rate. Vitellogenic oocytes are endocytotically active. Protein (a yolk) spheres are formed, but glycogen (ft yolk) spheres were never seen in the ooplasm. Follicle cells migrate normally and secrete more vitelline membrane and chorion than is required to cover the slowly growing oocyte. Specialized follicle cells also secrete relatively normal dorsal appendages. The micropylar cone is secreted by another cluster of specialized follicle cells called border cells. These are out of phase with the oocyte, and the forming micropylar cone prevents the nurse cells from passing the remainder of their cytoplasm to the oocyte. The result is a morphologically abnormal chamber blocked at the p-12 stage. Sections through the micropylar cone of a p-12 chamber demonstrated that one of the border cells formed a projection containing a bundle of microtubules. Secretions of the border cells and oocyte were deposited against this tube, which later degenerates or is withdrawn. Normally this results in a canal, the micropyle, through which the sperm enters the egg. The slowed growth of the mutant oocyte presumably results from a defect in the transport of fluids or charged molecules to it, and the otu+ gene is therefore believed to play a vital role in this process.
In situ arrangement of nor-bearing chromosomes in the interphase nucleus of Aotus trivirgatus
Authors: Bourgeois C. A. , Costagliola D. , Laquerriere F. , Bard F. , Hemon D. , Bouteille M. 
Published: April 2021

ABSTRACT
The spatial organization of the two nucleolus-organizing region(NOR)-bearing chromosomes during interphase was studied in Aotus trivirgatus fibroblasts, using nucleoli as ultrastructural markers. Their distribution was examined by measuring the distances between them in 30 reconstructed nuclei, and comparing these experimental values with the theoretical ones obtained by simulation.
Results were as follows: (1) the nucleoli are arranged in a polarized manner inside the nucleus; (2) the nucleoli are tightly bound to the nuclear envelope at two opposites sites; (3) the distance between the two nucleoli is variable, and is shorter than it would be if the two nucleoli were distributed at random.
These findings indicate that the NOR-bearing chromosomes are fixed at the nuclear envelope in two opposite areas. They are also consistent with the hypothesis that each chromosome occupies a separate domain inside the nucleus. They can be interpreted according to the model in which chromosome arrangement within the interphase nucleus is based on the separation of the diploid complement into two independent haploid sets.
Microfilament organization and total actin content are decreased in hybrids derived from the fusion of HeLa cells with human fibroblasts
Authors: Gowing Linda R. , Tellam Ross L. , Banyard M. R. C. 
Published: April 2021

ABSTRACT
The organization of the microfilaments and the actin content of matched pairs of tumorigenic and non-tumorigenic HeLa/fibroblast hybrid cells was compared. Each pair consisted of a hybrid cell line with suppressed tumorigenicity and a segregant tumorigenic cell line derived from it. The tumorigenic HeLa parent cell line and a non-tumorigenic human fibroblast line were also included in the comparison. Microfilament organization of the cell lines was assessed by fluorescence microscopy using NBD-phallacidin, a probe that specifically binds to actin filaments. The re-expression of tumorigenicity is associated with a loss of microfilament organization. The actin content, as measured by the DNase I inhibition assay, was significantly lower in the tumorigenic hybrids and the HeLa parent than in the non-tumorigenic cells. The comparison was significant when the actin concentration was expressed either per cell or per protein. Despite this reduced level of total actin in tumorigenic cells, the ratio of monomeric to total actin remained constant in all cell lines tested.
Septum pattern in ts mutants of Schizosaccharomyces pombe defective in genes CDC3, CDC4, CDC8 and CDC12
Authors: Streiblová Eva , Hašek Jiří , Jelke Eckart 
Published: April 2021

ABSTRACT
Septum-defective mutants of Schizosaccharomyces pombe impaired in cdc genes 3, 4, 8 and 12 were compared by fluorescence microscopy, freeze-etching and ultrathin sectioning. This approach made it possible to recognize the internal organization of defective phenotypes under restrictive conditions. Of special interest in this study was the pattern of unusual septum malformations found to be regular features of the terminal phenotypes of the mutants. Their overall topology was visualized at the cellular level by primulin fluorescence. The subcellular location of septum defects was found to be identical in origin to the compartment where normal septum was assembled in the wild type. Delocalized septation involved both microfibrillar and matrix components, which participated in the final assembly of malformations. Unique contour views of delocalized septa were exposed by freeze-fracturing. Cytoplasmic microtubules and microfilaments were detected in ultrathin sections of the cytoplasm of mutant cells. The internal organization of malformationaccumulating phenotypes suggested a disruption of the directional mechanism that steers septum material to the periplasm at the cell equator.
An electron-microscopic study of the termination of the afferent fibres to the olfactory bulb from the cerebral hemisphere
Authors: Price J. L. , Powell T. P. S. 
Published: April 2021

ABSTRACT
An experimental investigation has been made of the site and mode of termination of the 3 groups of afferent fibres to the olfactory bulb which come from more caudal parts of the cerebral hemisphere. Lesions have been placed in the relevant parts of the brain of the rat and the resulting degeneration of axon terminals in the olfactory bulb studied with the electron microscope. All 3 groups of these extrinsic afferent fibres end in asymmetrical synapses upon the granule cells, and they have a differential termination upon its various processes. The possibility that these fibres also end upon other cells in the bulb (particularly the short-axon and penglomerular cells) cannot be excluded.
The centrifugal fibres end upon gemmules in the deep half of the external plexiform layer only; no degenerating terminals were found in relation to the glomeruh although degenerating centrifugal axons are present here. The fibres of the anterior commissure terminate upon spines and vancosities of the deep dendrites and upon somatic spines of the granule cells. After lesions of the anterior olfactory nucleus, degenerating terminals were found in the ipsilateral olfactory bulb, which could not be ascribed to the centrifugal fibres or to the fibres of the anterior commissure, as they ended upon the spines of peripheral processes in the granule cell layer, and upon gemmules in the superficial as well as in the deep half of the external plexiform layer. It is proposed that these terminals are those of the axon collaterals from the ipsilateral anterior olfactory nucleus. The axons which form symmetrical synapses, and many which form asymmetrical synapses, do not degenerate even after a lesion immediately behind the olfactory bulb, and are therefore intrinsic to the bulb. It is suggested that the axons which are associated with symmetrical synapses are those of the short-axon cells, and the asymmetrical synapses are formed by the axon collaterals of the mitral and tufted cells.
Electron-microscope observations on the structure of condensed chromatin: evidence for orderly arrays of unit threads on the surface of chicken erythrocyte nuclei
Authors: Everid A. C. , Small J. V. , Davies H. G. 
Published: April 2021

ABSTRACT
A unit thread has been identified by electron microscopy as the common structural element in the condensed chromatin of a variety of cell nuclei. From the previous studies of thin sections normal to the nuclear envelope it was concluded that the unit thread, of diameter about 17 nm but varying somewhat depending on fixation, packed with spacings of about 28 nm on the surface of the nucleus to form one or more layers. Thin sections tangential to the nuclear envelope, described in this paper, reveal directly the degree of order within the surface layer; there are small areas or patches in which the units are regularly arranged. Units are also orderly arranged around the pores in the nuclear envelope. Unit threads are less easily visible in electron micro graphs of mature erythrocytes than at earlier stages of development but the clarity with which they can be seen is increased by a brief treatment prior to fixation with sodium citrate.
The fine structure of meiotic chromosome pairing in natural and artificial Lilium polyploids
Authors: Moens P. B. 
Published: April 2021

ABSTRACT
In the autotetraploid Lilmm longiflonim (4n = 48), there are 12 sets of 4 homologous chromo somes. Within each set of 4 homologues, switches of pairing partners and crossovers occur at meiotic prophase. At the fine-structural level, the behaviour of the chromosomes is reflected in the switches between the axial cores of the homologous chromosomes. The normal synapto nemal complexes of the autotetraploid are compared with the complexes of the allotriploid L. tigrtnuvi, which have synaptonemal complexes with abnormal lateral elements. The possibility that the deformed lateral elements are the products of heteromorphisms between’ homologues’ is explored in the discussion. The observations on the chromosome cores are interpreted as support for the notion that the cores may be associated with the recombinationally active hereditary material during meiotic prophase.
The effect of insulin on the growth and metabolism of the human diploid cell, WI-38
Authors: Griffiths J.B. 
Published: April 2021

ABSTRACT
In a confluent culture of WI-38 cells the membrane area available for nutrient uptake is greatly reduced and the possibility exists that this reduction in uptake capacity of the cell is a contributory factor in contact inhibition. Insulin has been reported by many authors to facilitate glucose uptak and also to stimulate protein, DNA and RNA synthesis, glycolysis, pinocytosis and growth in cultured cells. The effect of insulin on WI-38 cells was determined, therefore, to find out whether it enabled the cell to escape from contact inhibition of growth.
The action of insulin was found to be dependent upon medium composition. Growth and protein synthesis were stimulated in Eagle’s minimal essential medium, but not when this medium was supplemented with glucose and glutamine. Apparently insulin is only effective when high-energy compounds become limiting. Whilst insulin did not induce any post-confluent division, the protein content of cells was increased by 30%, and this was correlated with an increased rate of protein synthesis. Despite this increased activity in protein metabolism, the utilization of amino acids was less in the presence of insulin indicating that a control mechanism for more economical utilization of amino acids for protein synthesis was activated by insulin. Insulin had no effect on RNA synthesis, and only a slight inhibitory effect on DNA synthesis. Evidence was produced suggesting that insulin blocked cell division and encouraged differentiation. Glucose uptake and incorporation into the cell was stimulated by insulin, and this was especially noticeable after the cell sheet became confluent. The turnover of labelled glucose and derivatives was also enhanced by insulin and this was accompanied by a much higher rate of lactic acid production.
It is concluded that insulin does not overcome contact inhibition and permit post-confluent division, but that it does enable the cell to take up and utilize nutrients more efficiently in confluent cultures with a resultant increase in metabolic activity and cell size.
Growth and macromolecular synthesis in the 3T6 mouse fibroblast: II. the role of serum
Authors: Bates C. J. , Levene C. I. 
Published: April 2021

ABSTRACT
Serum is necessary for growth of 3T6 mouse fibroblasts in log phase and for their maintenance in crowded cultures, at or near the stationary phase. Removal of the dialysable components of serum has only a small effect on growth and maintenance of these cells, and has no significant effect on macromolecular synthetic processes.
Fractionation of serum by ammonium sulphate precipitation did not reveal a specific association of growth-promoting activity with either of the major protein components: albumin or fetuin. The purest albumin-containing fraction, which was practically devoid of growth promoting activity, served as a control for the physical effects of protein in the absence of serum.
Omission of serum, or its replacement by albumin, caused the cells to die (i.e. disappear from the attached cell layer) at an approximately linear rate; the remainder increased in volume. Protein synthesis, including collagen synthesis, continued at a normal or enhanced rate in the remaining cells, but glucosamine incorporation was reduced.
Initiation and differentiation of microtubule patterns in the ciliate Nassula
Authors: Tucker J. B. 
Published: April 2021

ABSTRACT
The mechanisms specifying microtubule arrangement and controlling the dimensions and shaping of microtubular components during cytopharyngeal development have been investigated. Heat shocks interfere with, or prevent, the operation of some of the processes involved, while others continue in a fairly normal fashion. For certain microtubular components the patterns of microtubule packing and the shapes of the components are very largely specified by the arrangement of the sites where tubule growth is initiated. Here the development of cross connexions between tubules serves only to stablize pre-existing tubule arrangements. However, there are indications that other intertubular materials are involved in the rearrangement of certain tubules. At several points in development the shapes and positions of extant microtubular components influence the patterns of tubules and other components subsequently developing in contact with them.
Heat shocks inhibit initiation of the development of certain tubules but longitudinal growth of existing tubules continues. When the number of developing tubules is reduced they attain greater than normal lengths, indicating that the extent of longitudinal tubule growth is largely determined by the size of the tubule precursor pool.
Comparative freeze-fracture study of perialgal and digestive vacuoles in Paramecium bursaria
Authors: Meier Renate , Lefort-Tran Marcelle , Pouphile Monique , Reisser Werner , Wiessner Wolfgang 
Published: April 2021

ABSTRACT
In the endosymbiotic unit of Paramecium bursaria (Ciliata) and Chlorella sp. (Chlorophyceae) algae are enclosed individually in perialgal vacuoles, which do not show acid phosphatase activity and thus differ from digestive vacuoles. Both types of vacuoles have been studied by freeze-fracture.
Perialgal vacuoles are nearly spherical; their membrane always fits tightly to the algal surface. The vacuole size and shape do not vary much. During division of the algal cell into four autospores the vacuole diameter only doubles. After autospore formation the vacuole invaginates around the algal daughter cells and divides. Newly formed perialgal vacuoles remain in intimate contact and exhibit characteristic attachment zones before final separation. The two fracture faces of perialgal vacuole membranes are homogeneously covered with intramembranous particles (IMPs) but rarely show signs of vesicles pinching off or fusing with the membrane, except during vacuole division. The P-faces bear more IMPs (3164 ± 625 IMP/μ m2) than the E-faces (654 ± 208 IMP/μ m2). The range of IMP density on both faces is enormous, suggesting that the membrane is not static. Membrane changes are supposed to occur simultaneously with the enlargement of the vacuole and to be caused by fusion with cytoplasmic vesicles, as the fractured necks on vacuole membranes may indicate.
Digestive vacuoles in P. bursaria show significant variations in size, shape, membrane topography and IMP density, as well as signs of endocytic activity. Different vacuole populations are present in P. bursaria according to different feeding conditions: ciliates fed for a long time have small vacuoles with few IMPs (322 ±198 IMP/μ m2 on the E-faces, 1438 ± 458 IMP/μ m2on the P-faces), which are probably condensed digestive vacuoles, whereas organisms fed for a short time have larger vacuoles with highly particulate faces (680 ± 282 IMP/μ m2 on the E-faces, 2701 ± 503 IMP/μ m2 on the P-faces) and thus are supposed to be older vacuoles. The digestive vacuole membrane changes continuously.
Compared to digestive vacuoles perialgal vacuoles are characterized by small size combined with high IMP density on the two fracture faces. Their IMP densities resemble those of old digestive vacuole membranes. However, it would be premature to conclude that membranes of perialgal and old digestive vacuoles are identical. Membranes of old digestive vacuoles are mainly derived from lysosomal material, which presumably does not contribute to the formation of perialgal vacuole membranes as is indicated by the small vacuole diameter; fusion with lysosomes would considerably enlarge it. The conclusions from these results are discussed in relation to the formation of perialgal vacuoles during the establishment of a stable symbiotic unit after infection of alga-free P. bursaria with the Chlorella species exsymbiotic from green paramecia.