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PubMed1990

Relationship between the regulation of membrane enzyme activities by gangliosides and a possible ganglioside segregation in membrane microdomains.

Laser and neutron scattering experiments showed that in mixed micelles of ganglioside GM2 and GT1b, a membrane mimicking system, the segregation of gangliosides may occur spontaneously. Photolabeling experiments using nitrophenylazide containing ganglioside GM1 proved that gangliosides added to cells in culture enter the cell and bind to its membrane as components of microdomains, which specifically interact with a protein of about 30 kDa. This suggests that ganglioside segregation may be a natural phenomenon. Gangliosides when added to granule cells in culture led to increase in protein phosphorylation, the effect exerted being related to the amount of ganglioside molecules inserted stably into the cell lipid layer and an increase of 0.7% of the cell original ganglioside content promoted an increase of 57% in the incorporation of 32P into cell membrane proteins. From the above results a possible relationship between ganglioside segregation and involvement of ganglioside in enzyme activity control is suggested.

Animals↗
PubMed1990

[The effect of oligomycin and cycloheximide on the ultrastructure of the segregation apparatus and on protein synthesis in the erythrocytes of the common frog].

The incubation of frog erythrocytes in the Ringer solution with novocaine (4.6 x 10(-3) M) during 24 hours at 10 degrees C provoked vacuole formation (segregation zones). Changes of the novocaine solution for a fresh Ringer solution and the following 48 hour incubation was accompanied by a decrease in the number of vacuoles both electron-translucent and containing membranous material. Simultaneously, the number of vacuoles with amorphous material only and with amorphous and membranous substances was seen to increase. Under the action of cycloheximide (1.10(-2) M) or oligomycin (2.5 x 10(-6) M) on erythrocytes with preformed vacuoles for 48 hours the total number of vacuoles and their dimensions decreased, with numerous amorphous inclusions appearing. Vacuoles with amorphous and membranous material increased in size. Similar ultrastructural changes in the segregation zones under the influence of both the inhibitors were observed showing the appearance of thick threads and a decreased share of electron-translucent vacuoles. A specific effect of cycloheximide, compared to that of oligomycin, involved the expansion of smooth endoplasmic reticulum cisternae. Under the influence of novocaine, 3H-leucin incorporation in proteins of frog erythrocytes was intensified. However, this incorporation was considerably inhibited by cycloheximide. Erythrocytes with segregation zones were more inhibitor susceptible than erythrocytes without vacuoles. The inhibitory effect was stronger early after their administration to the incubation medium, compared to the later periods.

Animals↗
PubMed1989

Meiotic segregation of normal and deletion chromosomes in Saccharomyces cerevisiae.

We explored the behavior of meiotic chromosomes in Saccharomyces cerevisiae by examining the effects of chromosomal rearrangements on recombination and disjunction. Chromosome III derivatives in which the entire left arm or the entire right arm was deleted (telocentric) segregated with fidelity from a normal chromosome III. Recombination between either of these two deletion chromosomes and the intact chromosome also appeared normal. In a strain containing a right arm telocentric, a left arm telocentric and one normal chromosome both telocentrics disjoined from the normal chromosome. Homology on one arm was sufficient for proper recombination and segregation of these chromosomes. In strains containing two normal chromosomes and one telocentric chromosome the two normal chromosomes preferentially disjoined. In a few cases however, the two normal chromosomes cosegregated. Recombination between the two normal chromosomes or between one normal chromosome and the deletion chromosome increased the probability that they would disjoin, although cosegregation of recombinants was observed. A chromosome III derivative which contained a large centromeric deletion and an insertion of the centromere from chromosome V into a nonhomologous position segregated with fidelity from a normal chromosome III. These studies demonstrate that it is not pairing of the centromeres, but pairing and recombination along the arms of the homologs that directs meiotic chromosome disjunction.

Chromosome Deletion↗
PubMed1986

[Segregation function of the cell and its molecular mechanisms].

Current literature on the cell segregation function is reviewed. The modern data on the role of coated pits, coated vesicles and endosomes in receptor-mediated and fluid endocytosis are regarded. Mechanisms of segregation both of inorganic and organic substances in lysosomes are considered. A special attention is paid to the selective accumulation in lysosomes of substances penetrating through plasma membrane. Some modern considerations concerning the role of the ATP-dependent proton pump in maintaining low intralysosomal pH and accumulation of weak bases in lysosomes by means of protonation are given. A great attention is paid to the effect of accumulated foreign substances in lysosomes on lysosomal apparatus functions and some metabolic disorders as consequences of it. The importance of the cell segregation functions and of lysosomotropic compounds for cytopharmacology and cytopathology is emphasized.

Animals↗
PubMed1985

[ATPase activity of the novocaine segregation zones isolated from the erythrocytes of the common frog].

Novocaine segregation zones in frog's erythrocytes, isolated by differential centrifugation, were shown to be ATPase active. The enzyme displays half of its maximum activity at 0.18 Mm ATP concentration to be inhibited by high concentrations of ATP. ATPase is activated by both Mg2+ and Ca2+ (in a lesser degree), with the maximum activity being at pH 7.5. A 5 minutes heating without the substrate results in decreasing the enzyme activity at 30 degrees, and in the total inhibition at 50 degrees C. Along with ATP, the enzyme can hydrolyse GTP and, in a lesser degree, ADP and sodium pyrophosphate. The ATPase activity is not effected with oligomycin (0.5-1.5 mkg/ml) or ouabaine (0.1 mM). Oligomycin in concentration 5 micrograms/ml induced non-specific inhibition of ATPase. Uncouplers, like 2,4-dinitrophenol and carbonyl cyanid p-trifluorometoxyphenylhydrazone, stimulate the enzyme activity. The lack in the ATP-ase sensitivity to oligomycin (specific inhibitor of mitochondrial F1-ATPase) and ouabaine (specific inhibitor of Na+, K+-ATPase) may suggest that the ATPase activity of novocaine segregation zones in frog's erythrocytes is not associated with a random contamination with mitochondria or cytoplasmic membranes. The ATPase under study has much in common with the lysosomal +H-ATPase. The results obtained support a hypothesis that +H-ATPase may function as a course of protones for maintaining acidic medium in segregation zones and promote accumulation of weak bases by means of their protonation.

Adenosine Triphosphatases↗
PubMed1986

DNA "fingerprints" and segregation analysis of multiple markers in human pedigrees.

Tandem-repetitive DNA hybridization probes based on a putative human recombination signal detect multiple polymorphic minisatellite fragments in human DNA. The genetic complexity of the resulting individual-specific DNA "fingerprints" was investigated by studying a large sibship affected by neurofibromatosis and a more extensive pedigree segregating for two different hemoglobinopathies. The segregation of up to 41 different heterozygous DNA fragments from each parent could be analyzed in a single sibship, using two different repeat probes. Most of these variable DNA fragments could not be paired as alleles, to an extent which suggests that the DNA fingerprints are together derived from approximately 60 heterozygous loci (approximately 120 variable fragments), only a proportion of which can be scored in a given individual. Two or three of the DNA fragments detected by one probe showed tight linkage and may be derived from long minisatellite(s) that are cleaved to produce more than one polymorphic DNA fragment. Excluding allelic and linked DNA fragments, almost all remaining scorable fragments segregated independently, allowing up to 34 unlinked loci to be examined simultaneously. These loci are scattered over most or all of the human autosomes. Minisatellite probes are therefore suitable for rapid marker generation and can be applied to linkage analysis in human pedigrees.

Alleles↗
PubMed1988

Intracellular insulin-receptor dissociation and segregation in a rat fibroblast cell line transfected with a human insulin receptor gene.

The cellular processing of insulin and insulin receptors was studied using a rat fibroblast cell line that had been transfected with a normal human insulin receptor gene, expressing approximately 500 times the normal number of native fibroblast insulin receptors. These cells bind and internalize insulin normally. Biochemical assays based on the selective precipitation by polyethylene glycol of intact insulin-receptor complexes but not of free intracellular insulin were developed to study the time course of intracellular insulin-receptor dissociation. Fibroblasts were incubated with radiolabeled insulin at 4 degrees C, and internalization of insulin-receptor complexes was initiated by warming the cells to 37 degrees C. Within 2 min, 90% of the internalized radioactivity was composed of intact insulin-receptor complexes. The total number of complexes reached a maximum by 5 min and decreased rapidly thereafter with a t 1/2 of approximately 10 min. There was a distinct delay in the appearance, rate of rise, and peak of intracellular free and degraded insulin. The dissociation of insulin from internalized insulin-receptor complexes was markedly inhibited by monensin and chloroquine. Furthermore, chloroquine markedly increased the number of cross-linkable intracellular insulin-receptor complexes, as analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis autoradiography. These findings suggest that acidification of intracellular vesicles is responsible for insulin-receptor dissociation. Physical segregation of dissociated intracellular insulin from its receptor was monitored, based on the ability of dissociated insulin to rebind to receptor upon neutralization of acidic intracellular vesicles with monensin. The results are consistent with the view that segregation of insulin and receptor occurs 5-10 min after initiation of dissociation. These studies demonstrate the intracellular itinerary of insulin-receptor complexes, including internalization, dissociation of insulin from the internalized receptor within an acidified compartment, segregation of insulin from the receptor, and subsequent ligand degradation.

Animals↗
PubMed1987

[Genetic analysis of polyauxotrophy and early mitotic progeny of Saccharomyces cerevisiae zygotes. II. Spore-forming segregants in the mitotic and meiotic progeny of polyauxotrophic clones].

This article continues the investigation of polyauxotrophic (PA) clones formed in early mitotic progeny of zygotes. Cloning and segregation analysis of PA progeny suggest an unusual state of diploid genome in these strains, which is expressed as elimination of the dominance effect of the wild allele and as suppression or conversion of either of two loci of mating type. In PA progeny, except for recombinant haploids, sporulating diploids and unstable clones were detected. The tetrad analysis of the diploids points to homozygotization for individual markers. Over-replication of diploid set of chromosomes, prior to meiosis, and replacement of the haploid nucleus (the product of meiosis) for the diploid nucleus may explain the appearance of sporulating segregants in the diploid meiotic progeny. Unstable segregants may be considered as heterokaryons with complex interaction of nuclei.

Alleles↗
PubMed1988

Cellular interrelationships during laminar segregation in the dorsal lateral geniculate nucleus.

In order to gain insight into the mechanisms involved in the formation of groupings of functionally similar cells in the developing nervous system, we have studied the formation of cell layers in the developing dorsal lateral geniculate nucleus (dLGN). To examine the possibility that a higher affinity or adhesion between cells in individual layers may play a role in laminar segregation, we studied cellular interrelationships in the dLGN of tree shrews before (P0), during (P4 and P7), and just after (P15) laminar segregation has taken place. We compared our observations at these stages of development with similar observations in the adult. In none of the cases do we see evidence of gap junctions either between adjacent neurons or between neurons and processes in the surrounding neuropil. However, we frequently observe the presence of puncta adherentes between adjacent neurons at all stages of development. These profiles are also present between neurons and cellular processes in the neuropil. We also see subsurface cisternae in all of our cases, although these are more pronounced before and during interlaminar space formation. As with the puncta adherentes, these are found both between adjacent neurons as well as between neurons and other elements in the neuropil. We also see some evidence of what appear to be cytoplasmic bridges between adjacent neurons; these are quite rare but appear to be present only before and during laminar segregation. Finally, we frequently see cytoplasmic processes interdigitated between otherwise immediately adjacent cells. These processes also are often found oriented along other portions of the neuronal plasmalemma. Whether these processes are portions of neuronal growth cones or glial processes is impossible to determine at this time. Because of the potential role glial processes may play in the formation and maintenance of laminar cell groupings during layer formation, we have also made a preliminary survey of whether glial cells can be distinguished ultrastructurally at the stages we have studied.

Animals↗
PubMed1986

[Chromosome segregation in mice heterozygous for Robertsonian translocations. I. The effect of mutation in chromosome 17 on the disjunction of homologs in females].

The effects of mutations on chromosome 17 upon the segregation of the metacentric and acrocentric homologues in the progeny of female mice heterozygous for Robertsonian translocations Rb(8.17) 1Iem and Rb(16.17) 7Bnr were studied. Genetic analysis indicated that the ratio of Rb to non-Rb (normal karyotype) progeny from mothers heterozygous for mutations tf, qk, t12 were not significantly different from 1:1 expected. Introduction of mutations T, Ki, Fu, t6 into the female genotype caused strong distortion of segregation and an increase in the proportion of progeny with normal karyotype (65-70%). From the data on embryonic mortality and cytogenetic observations, it is concluded that distortion of equal transmission arises before MII of meiosis. Consequently, preferential distribution of the metacentric chromosome into the polar body during the first meiotic division is relevant to the segregation distortion observed.

Animals↗
PubMed1987

A genetic epidemiologic investigation of breast cancer in families with bilateral breast cancer. I. Segregation analysis.

A complex segregation analysis was conducted of breast cancer in 200 families with bilateral breast cancer. Results for two analyses are presented. The first analysis considered only premenopausal cases of breast cancer as affected. The results indicate that mendelian transmission of a single locus is not sufficient to explain the distribution of premenopausal breast cancer seen. A mixed model, i.e., a major locus plus other transmission (genetic and/or cultural), is necessary to explain the distribution. The second analysis added postmenopausal cases of breast cancer to the premenopausal ones, thus considering all breast cancer cases to be affected with the same disorder. The all-cases analysis is unable to reject a mixed model with no generation differences in heritability when tested against the general model, which allows for generation differences (i.e., the likelihoods for the two models were not significantly different). Approaches to studying etiologic heterogeneity in segregation analysis and results of other segregation analyses of breast cancer are presented.

Breast Neoplasms↗
PubMed1985

The cultural context of gender segregation in children's peer groups.

Recent American research has explored developmental trends in gender segregation of children's peer groups. It is important to differentiate, however, systematic trends in children from systematic changes in their environments. Observational data are presented from 152 rural Kenyan children ages 18 months to 9 years. There is no gender segregation in peer groups until around age 6, at which time changes in settings, parental expectations, and customary duties result in an increase in the proportion of same-sex peers. Even within this pattern, however, there is some evidence that children do not interact more with same-sex peers, given their greater presence. A contrast is drawn with the adult pattern of gender segregation and emphasis is given to the importance of culture and development as interactive systems.

Child↗
PubMed1977

On the components of segregation distortion in Drosophila melanogaster.

The segregation distorter (SD) complex is a naturally occurring meiotic drive system with the property that males heterozygous for an SD-bearing chromosome 2 and an SD(+)-bearing homolog transmit the SD-bearing chromosome almost exclusively. This distorted segregation is the consequence of an induced dysfunction of those sperm that receive the SD(+) homolog. From previous studies, two loci have been implicated in this phenomenon: the Sd locus which is required to produce distortion, and the Responder (Rsp) locus that is the site at which Sd acts. There are two allelic alternatives of Rsp-sensitive (Rsp(sens)) and insensitive (Rsp(ins)); a chromosome carrying Rsp(ins) is not distorted by SD. In the present study, the function and location of each of these elements was examined by a genetic and cytological characterization of X-ray-induced mutations at each locus. The results indicate the following: (1) the Rsp locus is located in the proximal heterochromatin of 2R; (2) a deletion for the Rsp locus renders a chromosome insensitive to distortion; (3) the Sd locus is located to the left of pr (2-54.5), in the region from 37D2-D7 to 38A6-B2 of the salivary chromosome map; (4) an SD chromosome deleted for Sd loses its ability to distort; (5) there is another important component of the SD system, E(SD), in or near the proximal heterochromatin of 2L, that behaves as a strong enhancer of distortion. The results of these studies allow a reinterpretation of results from earlier analyses of the SD system and serve to limit the possible mechanisms to account for segregation distortion.

Alleles↗
PubMed1976

The segregation of C-band polymorphisms on chromosomes 1, 9, and 16.

Eleven normal families with at least four children were studied cytogenetically using the C-band technique to identify polymorphisms in the constitutive heterochromatin of chromosomes 1, 9 and 16. Thirteen individuals showed one or more variants in such chromosomes. The analysis of the segregation ratios in the 35 offspring of these 13 individuals showed that these marker chromosomes generally segregated according to the expected 50:50. However, one of these variants, chromosome no. 9 with an increased heterochromatin block in the secondary constriction, has an apparently preferential segregation, when the findings from this study are combined with those of other authors.

Chromosomes, Human, 1-3↗
PubMed1981

Lipid segregation from human erythrocyte tethers.

Fluid shear force may deform point-attached erythrocytes to become droplike shaped and anchored by a single long or 2-4 short tethers. By addition of glutaraldehyde to the medium the cells were fixed such as to stabilize this deformation for ensuing SEM, freeze-fracture, fine structural, and ultrahistochemical studies. Freeze-fracture specimens revealed identical numbers and distribution patterns of membrane particles in both the membrane of tethers and of the droplike portions of red cells. Segregated vesicles most often were located adjacent to the attachment site of the tether. All of the vesicles were devoid of membrane particles. Irrespective of their length, the tethers were about 0.1 micrometer in diameter. Cross-sections of the tether membrane and the plasmalemma of the major part of the cell appeared identical. Ultrahistochemical studies revealed the same intensity of iron binding capacity and affinity to ferritin labelled anti AHP at either area of the deformed erythrocyte membrane. Segregating vesicles were also stained by colloidal iron and by fer-anti AHP. By means of the DAB-reaction no haemoglobin was demonstrated within the vesicles. All of these findings corroborate the notion, that lipid molecules were segregated from the membrane whose curvature increased considerably during the formation of the tether.

ABO Blood-Group System↗
PubMed1983

Cell-free processing and segregation of insulin precursors.

The biosynthesis, segregation, and processing of preproinsulin (116 amino acids) was investigated to determine the mechanism(s) by which it is translocated across the endoplasmic reticulum membrane. Islet mRNA was translated in the wheat germ cell-free system, and at various times during preproinsulin synthesis, puromycin was added, followed by addition of microsomal membranes. Neither processing of preproinsulin nor translocation of proinsulin into microsomal membranes occurred in the presence of puromycin. Synchronization of preproinsulin translation by addition of 7-methylguanosine 5'-phosphate enabled the timing of preproinsulin synthesis and proinsulin (91 amino acids) segregation into microsomal membranes to be determined. Membrane binding occurs when about 60 amino acids have been polymerized, i.e. prior to the completion of the polypeptide chain. The binding of signal recognition particle to the nascent signal is demonstrated to be an absolute requirement for translocation and processing of preproinsulin. The results indicate that segregation and processing of preproinsulin are co-translational events; no evidence for a post-translational mechanism was found. Furthermore, this work, together with similar studies, suggests that presecretory polypeptides must be synthesized as part of a precursor with a minimum size of 60-80 amino acids in order to effect membrane binding and translocation of the polypeptide chain within the intracisternal space of the endoplasmic reticulum.

Animals↗
PubMed1984

Detection of genetic heterogeneity among pedigrees through complex segregation analysis: an application to hypercholesterolemia.

Several methods for investigating genetic heterogeneity for extreme levels of a quantitative trait with hypothesized multiple genetic etiologies require a priori stratification of families and/or identification of distinct phenotypes among affected individuals. We present a statistical approach for detecting genetic heterogeneity that does not rely on either a priori stratification or discrete disease phenotypes. Complex segregation analysis was applied to total serum cholesterol measurements in 709 relatives of 98 healthy index cases selected from 3,666 school children surveyed for lipid levels in Rochester, Minnesota. Thirty-three of the index cases and 109 relatives had hypercholesterolemia (cholesterol levels greater than the 95th percentile for their age and sex). Through application of the mixed genetic model and then estimation of conditional probabilities for having the mutant allele at the major locus, genetic heterogeneity for hypercholesterolemia was indicated. In three of 70 pedigrees with one or more hypercholesterolemics, there is strong evidence for segregation at a major locus. In the remaining pedigrees, only polygene variation and/or environmental variation are associated with cholesterol variability. Grandparents in the three pedigrees that were segregating at the major locus had the highest rates of death due to coronary heart disease. This study establishes that the mixed model has the potential to identify pedigrees with different genetic etiologies for variability in quantitative traits.

Adult↗
PubMed1982

Microstructure change and segregation distribution in dental 32 Ni-23 Cu-25 Mn casting alloy. (Part 1) Effect of air-vent system.

In low-melting 32 Ni-23 Cu-25 Mn alloy, the structure change and the segregation distribution were investigated in optical microscopy. The use of air-vent system to casting specimen had a notable effect to morphology and grain-size distribution, but the segregation showed the same tendency as the air-cooled specimen without air-vent system, except Cu segregated in B-grain less than in C-grain.

Copper↗