bluuebunny/crossref_metadata_2025_split huggingface dataset:
Autosomal spindle fibres influence subsequent sex-chromosome movements in crane-fly spermatocytes
Authors: Sillers Peggy J. , Forer Arthur 
Published: April 2021

ABSTRACT
In meiosis-I in crane-fly spermatocytes 3 autosomal half-bivalents move to each pole in anaphase while the 2 sex-chromosomal univalents remain at the equator. The sex chromosomes move to opposite poles only after the autosomes reach the poles; the sex chromosomes start to move polewards about 25 min after the autosomal half-bivalents have begun to move.
We irradiated portions of single autosomal spindle fibres with an ultraviolet microbeam and found that these irradiations altered the subsequent sex-chromosome movements. Two effects were observed. In one, one of the sex chromosomes did not move at all; the sex chromosome that remained at the equator would normally have moved to the pole associated with the irradiated autosomal spindle fibre. In the second, both sex chromosomes moved to the same pole, always that of the non-irradiated side. These effects occurred whether or not autosomal anaphase movement was blocked by the irradiation. There was no wavelength dependence for altering sex-chromosome movements.
Sex-chromosome movements were altered only when at least one sex-chromosomal spindle fibre was adjacent to the irradiated autosomal spindle fibre; when neither sex chromosome had a spindle fibre adjacent to the irradiated autosomal spindle fibre the sex chromosomes always moved normally. Irradiation of sex-chromosomal spindle fibres during sex-chromosomal anaphase showed short blockages of movement (usually 5–8 min), and then complete recovery. Direct irradiations of sex-chromosomal spindle fibres (without irradiating autosomal spindle fibres) when the autosomes were in anaphase but the sex chromosomes were in metaphase never caused abnormal sex-chromosome movements. These results eliminate the possibility that when we irradiated autosomal spindle fibres that were adjacent to sex-chromosomal spindle fibres the sex-chromosomal spindle fibres were irradiated inadvertently and were unable to recover from the damage.
We suggest that the irradiations of autosomal spindle fibres alter a control system involved in ‘turning on’ the sex-chromosomal spindle fibre motors, rather than directly altering the motors. We suggest that interactions between spindle fibres are somehow involved in this control system.
Influence of molecular charge upon the endocytosis and intracellular fate of peroxidase activity in cultured arterial endothelium
Authors: Davies Peter F. , Rennke Helmut G , Cotran Ramzi S. 
Published: April 2021

ABSTRACT
The molecular charge of the macromolecule, horseradish peroxidase (HRPase, 40000 mol. wt), was modified to yield highly anionic (pl &lt; 3·68) and cationic (pl = 9·5–10·5) derivatives. The effects upon the interactions between HRPase and arterial endothelium were then studied in vitro. The net rate of uptake of HRPase into endocytic vesicles and vacuoles of confluent endothelium was influenced by its molecular charge, there being less internalization of the anionic HRPase than of the native (pl = 7·9–8·2) and cationic derivatives. The molecular diameter was not significantly different between the cationic (Ae= 28·8 Å), anionic (Ae= 31·2 Å) and native (Ae= 29·6 Å) HRPase. The rate of uptake of [U-14C]sucrose, a tracer of bulk fluid endocytosis, was unaffected by the presence of the differently charged HRPase, indicating that the volume of vesicles formed per cell per hour remained constant. The intracellular fate of HRPase of different charge was investigated biochemically and morphologically. The rate of loss of internalized HRPase activity in the endothelial cells approximated first-order kinetics. The rate of disappearance of intracellular HRPase activity was much greater for cationic (t 1/2 = 8 h) and native (t 1/2 = 18 h) than for anionic HRPase (t 1/2 = 80-100 h). By electron microscopy, all 3 forms of HRPase were restricted to intracellular membrane-bounded vesicles and vacuoles consistent with a vesicle-lysosomal pathway. Studies with purified lysosomal cathepsin D indicated that the differences in the intracellular half-lives of HRPase may be attributable in small part to decreased and increased rates of lysosomal proteolysis of anionic and cationic HRPase, respectively, in comparison with native HRPase. Pre-labelling of endothelial secondary lysosomes by inhibitors of phagosome-lysosome fusion (dextran sulphate, polyglutamate) lengthened the intracellular half-life of native HRPase, while introduction of cationic ferritin to cells pulsed with anionic HRPase greatly decreased its half-life. Thus an influence of molecular charge upon endosome-lysosome fusion cannot be excluded. The studies indicate that the net charge carried by exogenous HRPase influences both its internalization in endocytic vesicles and its subsequent intracellular fate, which in turn may be modified by the introduction of other differently charged macromolecules. These results are discussed in relation to macromolecular transport by vascular endothelium in vivo.
Synthesis of an enzyme determined by an erythrocyte nucleus in a hybrid cell
Authors: Harris H. , Cook P. R. 
Published: April 2021

ABSTRACT
When a chick erythrocyte nucleus is introduced into the cytoplasm of a mutant mouse cell lacking the enzyme inosinic acid pyrophosphorylase, synthesis of the enzyme is induced. However, this synthesis does not begin until the erythrocyte nucleus develops a nucleolus. The kinetics of synthesis of the enzyme are essentially similar to those previously described for the synthesis of surface antigens specified by the chick nucleus. The results of both sets of experiments indicate that the nucleolus plays a critical role in the transfer of information from the genes to the cytoplasm of the cell.
Microtubules and filaments in the filopodia of the secondary mesenchyme cells of Arbacia Punctulata and Echinarachnius Parma
Authors: Tilney L. G. , Gibbins J. R. 
Published: April 2021

ABSTRACT
In an attempt to understand the mechanism of contraction of the filopodia of the secondary mesenchyme cells and thus secondary invagination of the archenteron, the fine structure of these processes was examined. Whereas microtubules are commonly encountered in the cell body and at the base of the filopodia, very few (one or two) are present near the tip of the filopodia. Instead the slender processes are filled with 50-Å filaments. Colchicine and hydrostatic pressure were applied to the embryos to elucidate the action of these different fibrous elements. Both agents cause cessation of archenteron movement and the disassembly of the microtubules. Hydrostatic pressure causes the disappearance of the filaments as well. Because of the small numbers of microtubules in the slender filopodia and the fact that in no other system is there any evidence for contraction of these elements, it was concluded that they do not function in the contraction process, but are probably involved in the formation of these cell extensions: hence the effect of colchicine on archenteron movement. The 50-Å filaments, on the other hand, are likely candidates for the contraction process.
The distribution of dna within the nucleoli of the amphibian oocyte as demonstrated by tritiated actinomycin d radioautography
Authors: Ebstein Bonnie S. 
Published: April 2021

ABSTRACT
The distribution of DNA within the nucleoli of the newt oocyte has been studied using tritiated actinomycin D (3H-AD) radioautography. In the course of the study further evidence was found for the specificity of this technique. In many of the cytological preparations the specificity of binding was enhanced by extraction with ethanol after exposure to 3H-AD. The actinomycin D-DNA complex is somewhat unstable in cytological preparations. Incubation in buffers causes some dissociation of the complex; divalent cations accentuate the effect. The technique of 3H-AD radioautography was again shown to be more sensitive than Feulgen staining by the detection of 3H-AD binding in the Feulgen-negative forms of the nucleoli of the amphibian oocyte. The binding of 3H-AD to all of the nucleolar forms confirms the presence of DNA in these organelles. Results from this study and from others using [3H]uridine in the same system provide evidence that the nucleolar DNA is a detached loop-chromomere complex.
Formation and loss of dna in intestinal epithelium
Authors: Appleton T. C. , Pelc S. R. , Tarbit M. H. 
Published: April 2021

ABSTRACT
The hypothesis that all nuclei containing labelled DNA in the jejunum of adult mice divide before migrating into the villi and that the amount of labelled DNA is constant during the passage of cells through the villi was tested experimentally. Mice were killed 40 min, 12, 18, 24, 30 and 36 h after a single intraperitoneal injection of [3H]thymidine. Grain counts in stripping film autoradiographs showed (i) considerably higher grain counts in the villi 24 h after injection than expected from those in the crypts at 40 min, and (ii) a loss of 32 % of the grain count during passage of the cells through the villi. Consideration of various factors which might influence the grain counts show that the findings have to be accepted as correct. It is suggested that a considerable proportion of the nuclei labelled in the crypts migrate into the villi without subsequent division and that labelled DNA is lost during passage through the villi. The hypothesis of formation of metabolic DNA during differentiation and loss during function provides an explanation of the findings.
Cytogenetic and nuclear studies on A9 and B82 cells fused together by sendai virus: The early phase
Authors: Engel E. , Mcgee B. J. , Harris H. 
Published: April 2021

ABSTRACT
A 9 and B82 enzyme-deficient mutants of the L line of mouse cells were hybridized artificially in vitro. After exposure of the cells to the fusing agent (inactivated Sendai virus), cultures were grown in a selective medium with aminopterin, which allows the survival only of heterokaryons which contain both A and B nuclei. The chromosome make-up of the fused cells was then studied for an initial 3-month period under various conditions. Polykaryons with 2 or more nuclei were at first observed but, as the cultures progressed, only mononucleate cells (synkaryons) persisted. Most cells in mitosis showed the chromosomal set of one A and one B cell, with an average mode and chromosome make-up very similar to, but not exactly, the sum of the average s chromosome number of one A and one B nucleus (2s cells). As a rule, the synkaryons contained three ‘dot-like’ chromosomes, two of which were probably derived from the A cell and one from the B cell.
In the course of the 3-month study the relative frequency of the 2S cells and their average modal number varied little. However, an increasing number of 2s cells with abnormally shaped chromosomes, in particular new ring chromosomes, was noted. Some of the cells had a mode intermediate between the 2s number and the s number (hypo-2S cells). They were thought to represent new segregants, but they were scarce, and their frequency did not increase when established fused cells were removed from the selective medium and then grown for up to 3 weeks.
Nuclear polymorphism was present in all cultures and certain cytological observations gave the impression that fractions of the genomes of fused cells could be rejected through nuclear fragmentation.
Synkaryons resulting from cell fusion induced by Sendai virus showed a remarkably stable chromosomal constitution for the first 3 months of culture, and were endowed with striking reproductive fitness.
The role of the nucleolus in the transfer of RNA from nucleus to cytoplasm
Authors: Sidebottom E. , Harris H. 
Published: April 2021

ABSTRACT
The role of the nucleolus in the transfer of RNA from nucleus to cytoplasm was examined by means of experiments in which inactivation of the whole nucleus, or of the nucleolus, was achieved by a microbeam of ultraviolet light. In heterokaryons in which a chick erythrocyte nucleus had been reactivated, no detectable amount of RNA was transferred from the reactivated nucleus to the cytoplasm of the cell until this nucleus had developed a nucleolus. In HeLa cells, inactivation of the nucleolus alone inhibited the transfer to the cytoplasm, not only of the RNA synthesized at the nucleolar site, but also of the RNA made elsewhere in.the nucleus. It thus appears that the nucleolus governs the transport not only of its own RNA, but also of the RNA which is made on other parts of the chromosomes.
Linear synthesis of sucrase and phosphatases during the cell cycle of Schizosaccharomyces Pombe
Authors: Mitchison J. M. , Creanor J. , Williams D. A. 
Published: April 2021

ABSTRACT
The synthesis of sucrase, acid phosphatase and alkaline phosphatase has been followed in synchronous cultures of the fission yeast Schizosaccharomyces pombe prepared by gradient sedimentation. These three enzymes follow a linear pattern of synthesis through the cell cycle, with a doubling in rate at a ‘critical point’ about one-fifth of the way through the cycle.
Sucrasecan be rapidly derepressed by lowering the glucose concentration in the medium. This has been used to measure the sucrase ‘potential’ or capacity to synthesize sucrase on derepression. The potential exists at all times in the cycle, and follows a stepwise pattern with a sharp rise at the critical point.
These results suggest that the functional genome doubles at the critical point. Since, however, the period of DNA synthesis is nearly one-third of a cycle before this point, there must be an appreciable delay between chemical replication and functional replication of the genome. In this respect S. pombe, a eukaryotic cell, differs markedly from bacteria.
Other physiological events take place near the critical point, and a tentative model is suggested of what may be happening at the chromosomal level.
Experiments with cycloheximide indicate that there is a delay between the synthesis and the appearance of the active enzyme in the case of sucrase and alkaline phosphatase.
Mitosis in Aspergillus Nidulans
Authors: Robinow C. F. , Caten C. E. 
Published: April 2021

ABSTRACT
Mitosis in growing hyphae of haploid and diploid Aspergillus nidulans has been studied with the light microscope in Helly-fixed preparations. At the periphery of the nucleus a sharply defined granule is invariably found which has strong affinity for acid fuchsin. Mitosis begins with the duplication of this granule and the development inside the nucleus of a gradually lengthening fibre between the daughter granules. This fibre is also visible in dividing nuclei of living hyphae examined by phase-contrast microscopy, when it appears as a grey bar traversing the non-nucleolar region. Division of the chromatin has been studied in preparations stained with aceto orcein, directly or after hydrolysis. It proceeds through four phases, beginning with the condensation of distinct chromosomes from the chromatin network of the resting nuclei. Later the chromosomes become arranged in two parallel rows of chromatinic masses in which individual chromosomes can no longer be distinguished. Division is completed by migration of the chromatin to the ends of each row, giving the appearance of a transverse break in the double bar. The chromatin accumulating at the ends of the double bar condenses to form the two daughter nuclei. The number of chromatinic elements appears to be the same in both haploid and diploid nuclei, although the individual elements are larger in the latter.
Successive staining of the same dividing nucleus, first for the fibre (acid fuchsin) and then for the chromosomes (HCl-aceto orcein or HCl-Giemsa) has established that the fibre lies among the chromosomes, and that its elongation is closely related to the anaphase-telophase movements of the chromosomes. This suggests that the fibre is the equivalent of a mitotic spindle. That the fibre is connected with the chromosomes is further suggested by the observa-tion that, in stained preparations, the fibre is considerably thicker in dividing diploid than in haploid nuclei.
Electron microscopy of dividing nuclei has revealed that mitosis is carried out within the intact nuclear envelope. The mitotic spindle is composed of a bundle of fibrils which traverses the nucleus between two plaques of dense material associated with the envelope.
In order to explain the configurations seen during the division of the chromatin it is proposed that the chromosomes become attached to the central spindle at various points along its length. With the elongation of the spindle the sister chromatids separate and pass, asynchronously, to opposite ends of the spindle along two preferred lines, thereby producing the characteristic double bar figure. The absence of a metaphase plate is thus accounted for by the scattered points of attachment of the chromosomes to the spindle and by their asynchronous division.
A study of granule formation in the bat parafollicular cell
Authors: Nunez E. A. , Gould R. P. , Holt S. J. 
Published: April 2021

ABSTRACT
The fine structure of the bat thyroid parafollicular cell has been examined at monthly intervals throughout the hibernating period. During November and December parafollicular cells appear either partly or totally degranulated and intact dense secretory granules are relatively sparse. The degranulated cells exhibit an inconspicuous Golgi complex and relatively few lysosome-type bodies. Few degranulated parafollicular cells are present in thyroid glands from bats collected in January. When found they are characterized by the presence of whorls of cytoplasmic agTanular membranes which enclose a central mass of cellular debris. January bat thyroids are characterized by the presence of three different types of parafollicular cell. One type contains no secretory granules. The cytoplasmic matrix of this type is rich in granular endoplasmic reticulum and free ribosomes and its small Golgi complex consists of several slightly dilated saccules. In close proximity to the Golgi complex are numerous small to medium-sized vesicles which often appear to merge with Golgi elements. Such vesicles are considered to represent the vehicle by which secretory product is transferred from the endoplasmic reticulum to the Golgi complex. The second type of parafollicular cell differs from the first in containing large numbers of intact dense secretory granules. It is also characterized by an extensive Golgi complex which appears to be forming new secretory granules, and by a less extensive granular endoplasmic reticulum. The third type of parafollicular cell shows a structure intermediate between the first two. The cytoplasm of all three types of January parafollicular cells contains many structures belonging to the lysosomal-vacuolar system, including autophagic vacuoles, vacuolated dense bodies and multivesicular bodies. By February and March only parafollicular cells of type 2 are observed. They contain few lysosome-like structures. It is concluded that during mid-hibernation (January), parafollicular cells undergo a series of intracellular changes during which new dense secretory granules are produced. Accompanying granule formation is an augmentation of lysosome-like structures which probably serve as a means of digesting debris from previous secretory cycles.
Fine-structural changes in rat liver microsomes treated with phospholipase c
Authors: Higgins Joan A. 
Published: April 2021

ABSTRACT
Phospholipase C hydrolyses 50% of the phospholipids of rat liver microsomes. Our previous observations suggest that the hydrolysis is of the outer leaflet of the membrane bilayer. In the present investigation the products of hydrolysis and the effect of phospholipase C treatment on the morphology of total, rough and smooth microsomes were investigated. The only product of phospholipase C treatment of microsomes was diglyceride. After hydrolysis of half the phospholipid, the microsomes retained their vesicular structure; however, the average diameter of total and smooth microsomes was reduced by approximately half, and that of rough microsomes by a third. Profiles were observed that suggested that small vesicles may form by pinching off from large vesicles. About 10–15% of the phospholipase-treated microsomes had associated with them an amorphous droplet yielding a ‘signet-ring’-like structure. The rest of the vesicle membrane retained a bilayer structure. About 10–15% of the treated vesicles adhered in groups of two or three. In these groups the shared membrane was trilaminar. Freeze-fracture replicas of phospholipase C-treated microsomes exhibited a similar morphology to untreated microsomes having both concave and convex surfaces, the former exhibiting a greater density of intramembranous particles. These observations suggest that microsomal vesicles remain closed after treatment with phospholipase C and that the bilayer structure is retained. However, there are morphological changes that are possibly related to maintaining the stability of the membranes in which the outer leaflet consists essentially of diglyceride.
Mechanisms of displacement of sperm basic nuclear proteins in mammals. an in vitro simulation of post-fertilization results
Authors: Rodman Toby C. , Pruslin Fred H. , Allfrey Vincent G. 
Published: April 2021

ABSTRACT
A standardized cytological preparation of mature mouse sperm has been devised to serve as an in vitro system for probing the intra-ooplasmic molecular events of transformation of the fertilizing sperm. Two parameters of the early phase of transformation in vivo are defined at the resolution of the light microscope : deletion of sperm-unique nuclear proteins, detectable by immunofluorescence, and retention of homogeneity of the residual DNA complex, with intact chromatin boundaries detectable by ethidium bromide staining. These studies show that both parameters are conserved when in vitro sperm preparations are treated with NaCl under reducing conditions. The deletion of 2 different classes of the unique basic proteins of mouse sperm nuclei is specified by the NaCl concentration : 0·7 M-NaCl displaces the non-protamine class but not the protamines, while 1 M-NaCl displaces both. On the other hand, the effects of treatment with trypsin at various concentrations and intervals are less consistent with the in vivo parameters, indicating fragmentation and displacement, not only of the sperm-unique basic proteins, but also of structural proteins believed to maintain the fundamental cohesive organization of the DNA matrix. These observations suggest that mechanisms other than proteolysis, e.g. localized changes in ionic concentrations, may participate in the post-fertilization displacement of the sperm-unique nuclear proteins in vivo. This study also supports the validity of the in vitro simulation as a model with which to probe the progression of transformation of the sperm nucleus to the zygote pronucleus.
Regional mapping of the gene coding for enolase-2 on human chromosome 12
Authors: Law Martha Liao , Kao Fa-Ten 
Published: April 2021

ABSTRACT
Enolase-2 (ENO2), previously termed 14-3-2 protein, is an isozyme of enolase that is enriched in neuronal tissue. The gene coding for ENO2 was previously assigned to human chromosome 12. The present study presents data for a regional mapping of gene ENO2 using cell hybrids containing various deletions of human chromosome 12. These deletions were produced by treatment with chromosome-breaking agents. Cytogenetic analysis has allowed assignment of ENO2 to the short arm of chromosome 12, in the region of pter-pizos. This assignment is consistent with the segregation pattern of the 93 hybrid clones analysed. The segregation pattern has also established the linear order of 6 genes on chromosome 12: pter — TPI — GAPD — LDHB — ENO2— centromere — SHMT — PEPB — qter. Estimation of the relative distances between the 6 genes on chromosome 12 has been made by a statistical mapping analysis of the segregation data of the hybrid clones. A set of deletion hybrids containing various combinations of these 6 markers has been established for a rapid regional mapping of genes in one of these regions on chromosome 12.