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PubMed1988

Characterization of a spontaneously segregating Cf16-v1 lysogen of Xanthomonas campestris pv. citri.

Filamentous phage Cf16 undergoes a unique neolysogenic infectious cycle in Xanthomonas campestris pv. citri and generates stable lysogens. In contrast, we have isolated a distinctive unstable lysogen, designated LW. This new lysogen segregated spontaneously into three nonparental types, each with a unique combination of colony morphology, phage-producing capacity, and phage genome content. In a given population of LW lysogens the segregation frequency of these types varied randomly with drastic fluctuations from experiment to experiment. Heat and UV treatment failed to increase the segregation frequency with a magnitude matching the sporadic intrinsic fluctuations. The characteristics of an LW lysogen were transmitted through the phage it released. Designated as Cf16-v1, this phage, which produced clear instead of turbid plaques as its progenitor Cf16, was exceedingly unstable in the host cell. Only 4% of the infected cells, rather than 95% as in the case of Cf16, retained the phage genome and completed the neolysogenization process. The prophage integration site on the host chromosome, however, appeared to be the same for both phages.

Bacteriophages↗
PubMed1984

Polymorphism of erythrocyte galactose-1-phosphate uridyl-transferase in Italy: segregation analysis in 693 families.

In the course of a population study in Italy, blood samples collected from 802 unrelated newborns and both their parents (when possible) have been examined for galactose-1-phosphate uridyltransferase (GALT) polymorphism. Electrophoresis and quantitative assay of GALT activity were not always sufficient for an accurate identification of the different GALT genotypes; segregation analysis provided better criteria for classification. A parent-child correlation coefficient for GALT activity equal to 0.107-0.155 was found when only the transmission of the normal allele was concerned, but the correlation rose to 0.618-0.682 when the Duarte and Los Angeles alleles were segregating. This confirmed the existence of a low (Duarte) and high (Los Angeles) activity variant. The overall validity of our genotype classification is supported by the good agreement between observed and expected mating types and segregations. The following gene frequencies were found for the different alleles: N = 0.9192, G = 0.0036, D = 0.0372 and LA = 0.0400.

Adult↗
PubMedDate not supplied

Identifiability of segregation parameters using estimating equations.

To eliminate the need for distributional assumptions and to reduce the computational burden associated with the method of maximum likelihood, several researchers have proposed using estimating equations techniques for segregation analysis. One concern with the application of this technique has been that the first and second order moments may not carry sufficient information for identifying all of the parameters in segregation models. It is shown that in addition to the marginal means and covariances from nuclear family data, up to the third order product moments need to be used in estimating equations for identifying all of the segregation parameters in a major gene model. A polygenic component and potentially a common family environment parameter can also be identified using up to the fourth order moments. Two weighting functions are developed to improve statistical efficiency.

Environment↗
PubMed1998

Segregation analysis of plasminogen activator inhibitor-1 and fibrinogen levels in the NHLBI family heart study.

Elevated plasminogen activator inhibitor-1 (PAI-1) and fibrinogen concentrations are risk factors for coronary heart disease. We investigated environmental, familial, and genetic influences on PAI-1 antigen and fibrinogen concentrations in 2029 adults from 512 randomly ascertained families in 4 US communities. We used maximum-likelihood segregation analysis to fit several genetic and nongenetic modes of inheritance to the data to determine whether mendelian inheritance of a major gene could best explain the familial distributions of these 2 hemostatic factors. Age- and gender-adjusted familial correlations for PAI-1 antigen level averaged 0.16 in first-degree relatives (95% CI=0.11 to 0.21); the spouse correlation was positive but not statistically significant (r=0.10, 95% CI=-0.02 to 0.23). Complex segregation analysis indicated a major gene associated with higher PAI-1 concentrations in 65% of individuals from these families. Demographic, anthropometric, lifestyle, and metabolic characteristics together explained 37% to 47% of the variation in PAI-1 antigen levels, and the inferred major gene explained an additional 17% of the variance. Positive and statistically significant age- and gender-adjusted familial correlations in first-degree relatives indicated a possible heritable component influencing plasma fibrinogen concentration (r=0. 17, 95% CI=0.13 to 0.22); however, segregation analysis did not provide statistical evidence of a major gene controlling fibrinogen level. These family data suggest that there are modest familial and genetic effects on the concentration of PAI-1.

Adult↗
PubMed2002

Figure-ground segregation in a recurrent network architecture.

Here we propose a model of how the visual brain segregates textured scenes into figures and background. During texture segregation, locations where the properties of texture elements change abruptly are assigned to boundaries, whereas image regions that are relatively homogeneous are grouped together. Boundary detection and grouping of image regions require different connection schemes, which are accommodated in a single network architecture by implementing them in different layers. As a result, all units carry signals related to boundary detection as well as grouping of image regions, in accordance with cortical physiology. Boundaries yield an early enhancement of network responses, but at a later point, an entire figural region is grouped together, because units that respond to it are labeled with enhanced activity. The model predicts which image regions are preferentially perceived as figure or as background and reproduces the spatio-temporal profile of neuronal activity in the visual cortex during texture segregation in intact animals, as well as in animals with cortical lesions.

Feedback↗
PubMed1987

Perceptual segregation and retinal position.

This study is concerned with the dependence of perceptual segregation performance on the retinal position at which the performance is evaluated. Segregation performance consisted in detecting a target texture composed of line elements of constant length and orientation embedded in a background texture. The background texture was made up of the same line elements as the target texture but the background line elements were set at 90 deg to the target elements. Results showed that, at least for 40- and 50-ms presentation times, this task could be much more effectively completed outside the fovea centralis than within this area. These findings indicate that extrafoveal areas of the retina may make a significant and previously underestimated contribution to perceptual segregation.

Female↗
PubMed1996

Airway hyperresponsiveness to acetylcholine: segregation analysis and evidence for linkage to murine chromosome 6.

A genetic predisposition to nonspecific airway hyperresponsiveness (AHR) can be demonstrated in humans and in many animal models. The goal of the current study was to gain insight into the molecular mechanisms that determine AHR by mapping the genes that control this phenotype. We describe genetic studies in a mouse model of differential sensitivity to acetylcholine (ACh)-induced AHR. This model was used to ascertain the number, magnitude of effect, and chromosomal location of quantitative trait loci (QTL) providing susceptibility to ACh-induced AHR. Segregation analyses indicated that a major locus acting additively with a polygenic effect segregates with the airway pressure-time index (APTI) in the progeny of hyperresponsive A/J and hyporesponsive C3H/HeJ mice. Additionally, four loci segregate with respiratory system resistance (Rrs). Examination of the genome for markers linked to these phenotypes indicated that a QTL on chromosome 6 was common to both traits. QTL analysis in the [(C3H/HeJ x A/J)F1 x A/J] backcross generation revealed significant linkage for ACh-induced AHR within the interval spanning the chromosome 6 deoxyribonucleic acid (DNA) markers D6Mit16 and D6Mit13. A/J alleles in this interval were associated with significantly greater airway responsiveness than were C3H/HeJ alleles. Several important candidate genes map to this region, including the locus for the interleukin-5 (IL-5) receptor. This mapping information in the mouse may relate to human studies in which bronchial hyperresponsiveness links to the chromosomal region containing the gene for IL-5 (1).

Acetylcholine↗
PubMed1993

Segregation in precious-metal dental-casting alloys.

The aim of this study was to conduct a theoretical analysis of segregation in Au-Ag-Cu and Ag-Pd-Au-Cu dental-casting alloys, and to confirm and extend the results experimentally. Both theoretical and experimental data showed greater segregation in the Ag-Pd-Au-Cu alloy than in the Au-Ag-Cu alloy. There was very little segregation of gold, zinc, and platinum, while between the dendrites copper increased and silver and palladium decreased.

Copper↗
PubMedDate not supplied

Segregation of a major gene influencing ovulation in progeny of Lacaune meat sheep.

Inheritance of the ovulation rate (OR) in the Lacaune meat breed was studied through records from a small nucleus of 36 hyper-prolific ewes screened on farms on the basis of their natural litter size, and from progeny data of three selected Lacaune sires. These sires were chosen at the AI centre according to their breeding values estimated for the mean and the variability of their daughters' litter size. Non-carrier Lacaune dairy ewes were inseminated to produce 121 F1 daughters and 27 F1 sons. Twelve sons (four from each sire) were used in turn to inseminate non-carrier Lacaune dairy ewes providing 260 BC progeny ewes. F1 and BC progeny were brought from private farms and gathered after weaning on an experimental farm where ovulation rates were recorded in the first and second breeding seasons. With an average of 6.5 records each, the mean OR of hyper-prolific ewes was very high (5.34), and 38.4% of records showed a rate of 6 or more. F1 data showed high repeatability of OR (r = 0.54) within ewe, with significant variability among ewes. High OR (> or = 4) were observed in each family. A segregation analysis provided a significant likelihood ratio and classified the three founders as heterozygous. BC ewes also displayed high repeatability of OR (r = 0.47) and the mean OR varied considerably between families (from 1.24 to 1.78). Seven of the 12 BC families presented high-ovulating ewes (at least one record > or = 4) and segregation analysis yielded a highly significant likelihood ratio as compared to an empirical test distribution. The high variability of the mean ovulation rate shown by a small group of daughters of BC ewes inseminated by putative carrier F1 rams, and the very high ovulation rate observed for some of these ewe lambs, confirmed the segregation of a major gene with two co-dominant alleles borne by an autosome. The difference between homozygous non-carriers and heterozygous ewes was about one ovulation on the observed scale and 2.2 standard deviations on the underlying scale.

Animals↗
PubMed2003

Segregation and linkage analysis for longitudinal measurements of a quantitative trait.

We present a method for using slopes and intercepts from a linear regression of a quantitative trait as outcomes in segregation and linkage analyses. We apply the method to the analysis of longitudinal systolic blood pressure (SBP) data from the Framingham Heart Study. A first-stage linear model was fit to each subject's SBP measurements to estimate both their slope over time and an intercept, the latter scaled to represent the mean SBP at the average observed age (53.7 years). The subject-specific intercepts and slopes were then analyzed using segregation and linkage analysis. We describe a method for using the standard errors of the first-stage intercepts and slopes as weights in the genetic analyses. For the intercepts, we found significant evidence of a Mendelian gene in segregation analysis and suggestive linkage results (with LOD scores >or= 1.5) for specific markers on chromosomes 1, 3, 5, 9, 10, and 17. For the slopes, however, the data did not support a Mendelian model, and thus no formal linkage analyses were conducted.

Adult Children↗
PubMed2003

Segregation analysis comparing liability and quantitative trait models for hypertension using the Genetic Analysis Workshop 13 simulated data.

Discrete (qualitative) data segregation analysis may be performed assuming the liability model, which involves an underlying normally distributed quantitative phenotype. The appropriateness of the liability model for complex traits is unclear. The Genetic Analysis Workshop 13 simulated data provides measures on systolic blood pressure, a highly complex trait, which may be dichotomized into a discrete trait (hypertension). We perform segregation analysis under the liability model of hypertensive status as a qualitative trait and compare this with results using systolic blood pressure as a quantitative trait (without prior knowledge at that stage of the true underlying simulation model) using 1050 pedigrees ascertained from four replicates on the basis of at least one affected member. Both analyses identify models with major genes and polygenic components to explain the family aggregation of systolic blood pressure. Neither of the methods estimates the true parameters well (as the true model is considerably more complicated than those considered for the analysis), but both identified the most complicated model evaluated as the preferred model. Segregation analysis of complex diseases using relatively simple models is unlikely to provide accurate parameter estimates but is able to indicate major gene and/or polygenic components in familial aggregation of complex diseases.

Adult↗
PubMed2005

Tree measures and the number of segregating sites in time-structured population samples.

BACKGROUND: Time-structured genetic samples are a valuable source of information in population genetics because they provide several correlated observations of the underlying evolutionary processes. In this paper we study basic properties of the genetic variation in time-structured samples as reflected in the genealogies relating individuals and the number of segregating sites observed. Our emphasis is on "measurably evolving populations" i.e. populations from which it is possible to obtain time-structured samples that span a significant interval of evolutionary time. RESULTS: We use results from the coalescent process to derive properties of time-structured samples. In the first section we extend existing results to attain measures on coalescent trees relating time-structured samples. These include the expected time to a most recent common ancestor, the expected total branch length and the expected length of branches subtending only ancient individuals. The effect of different sampling schemes on the latter measure is studied. In the second section we study the special case where the full sample consists of a group of contemporary extant samples and a group of contemporary ancient samples. As regards this case, we present results and applications concerning the probability distribution of the number of segregating sites where a mutation is unique to the ancient individuals and the number of segregating sites where a mutation is shared between ancient and extant individuals. CONCLUSION: The methodology and results presented here is of use to the design and interpretation of ancient DNA experiments. Furthermore, the results may be useful in further development of statistical tests of e.g. population dynamics and selection, which include temporal information.

Animals↗
PubMed2005

The missense mutation in Abcg5 gene in spontaneously hypertensive rats (SHR) segregates with phytosterolemia but not hypertension.

BACKGROUND: Sitosterolemia is a recessively inherited disorder in humans that is associated with premature atherosclerotic disease. Mutations in ABCG5 or ABCG8, comprising the sitosterolemia locus, STSL, are now known to cause this disease. Three in-bred strains of rats, WKY, SHR and SHRSP, are known to be sitosterolemic, hypertensive and they carry a missense 'mutation' in a conserved residue of Abcg5, Gly583Cys. Since these rat strains are also know to carry mutations at other genetic loci and the extent of phytosterolemia is only moderate, it is important to verify that the mutations in Abcg5 are causative for phytosterolemia and whether they contribute to hypertension. METHODS: To investigate whether the missense change in Abcg5 is responsible for the sitosterolemia we performed a segregation analysis in 103 F2 rats from a SHR x SD cross. Additionally, we measured tail-cuff blood pressure and measured intestinal lipid transport to identify possible mechanisms whereby this mutation causes sitosterolemia. RESULTS: Segregation analysis showed that the inheritance of the Gly583Cys mutation Abcg5 segregated with elevated plant sterols and this pattern was recessive, proving that this genetic change is responsible for the sitosterolemia in these rat strains. Tail-cuff monitoring of blood pressure in conscious animals showed no significant differences between wild-type, heterozygous and homozygous mutant F2 rats, suggesting that this alteration may not be a significant determinant of hypertension in these rats on a chow diet. CONCLUSION: This study shows that the previously identified Gly583Cys change in Abcg5 in three hypertension-susceptible rats is responsible for the sitosterolemia, but may not be a major determinant of blood pressure in these rats.

ATP Binding Cassette Transporter, Subfamily G, Mem↗
PubMed1993

Variable distribution of mutant mitochondrial DNAs (tRNA(Leu[3243])) in tissues of symptomatic relatives with MELAS: the role of mitotic segregation.

We studied multiple different postmortem tissue samples from a woman and two of her daughters with the MELAS (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes) tRNA(Leu(UUR)) mutation at nucleotide 3243 in mitochondrial DNA (mtDNA). All tissues examined were heteroplasmic for the mutation. The mean proportion of mutant mtDNAs in the mother's tissues (0.30 +/- 0.10) was significantly lower than that of each of her daughters' (0.76 +/- 0.11, p < 0.03, and 0.72 +/- 0.13, p < 0.001); there was no difference in the fraction of mutant mtDNAs between the daughters (p < 0.71). This difference in the mean proportion of mtDNA mutants between family members correlates with their clinical profiles; the mother had the latest onset of disease and lived longest, while the two daughters had a strikingly similar clinical course. In individual patients, the mean proportion of mutant mtDNAs was not different in tissues deriving from ectodermal, mesodermal, and endodermal germ layers. Variance in the mutant:wild-type mtDNA ratio was normally distributed about the mean, both when all tissues were considered together and when different regions of the CNS were considered separately. Thus, the proportion of mtDNAs carrying the tRNA(Leu(3243)) mutation was not uniform in members of this pedigree and did not undergo rapid mitotic segregation along germ-layer divisions. These findings are consistent with the hypothesis that the overall proportion of mtDNAs carrying this mutation is primarily determined by segregation during oogenesis or early embryologic development and that random replicative (mitotic) segregation, subsequent to the establishment of primary germ layers, is responsible for the variation between tissues.

Adolescent↗
PubMed2003

Centrin deficiency in Chlamydomonas causes defects in basal body replication, segregation and maturation.

Centrin, a 20 kDa calcium-binding protein, is a constituent of contractile basal body-associated fibers in protists and of various centrosomal structures. A construct inducing centrin RNAi was used to study the effect of centrin deficiency in Chlamydomonas. Transformants contained variable amounts of residual centrin (down to 5% of wild-type) and lacked centrin fibers. They displayed a variable flagellar number phenotype with mostly nonflagellate cells, suggesting that centrin is required for basal body assembly. Furthermore, basal bodies often failed to dock to the plasma membrane and to assemble flagella, and displayed defects in the flagellar root system indicating that centrin deficiency interferes with basal body development. Multiple basal bodies caused the formation of additional microtubular asters, whereas the microtubular cytoskeleton was disordered in most cells without basal bodies. The number of multinucleated cells was increased, indicating that aberrant numbers of basal bodies interfered with the cytokinesis of Chlamydomonas. In contrast to wild-type cells, basal bodies in centrin-RNAi cells were separated from the spindle poles, suggesting a role of centrin in tethering basal bodies to the spindle. To test whether an association with the spindle poles is required for correct basal body segregation, we disrupted centrin fibers in wild-type cells by over-expressing a nonfunctional centrin-GFP. In these cells, basal bodies were disconnected from the spindle but segregation errors were not observed. We propose that basal body segregation in Chlamydomonas depends on an extranuclear array of microtubules independent of the mitotic spindle.

Animals↗
PubMed2005

Plastid segregation and cell division in the apicomplexan parasite Sarcocystis neurona.

Apicomplexan parasites harbor a secondary plastid that is essential to their survival. Several metabolic pathways confined to this organelle have emerged as promising parasite-specific drug targets. The maintenance of the organelle and its genome is an equally valuable target. We have studied the replication and segregation of this important organelle using the parasite Sarcocystis neurona as a cell biological model. This model system makes it possible to differentiate and dissect organellar growth, fission and segregation over time, because of the parasite's peculiar mode of cell division. S. neurona undergoes five cycles of chromosomal replication without nuclear division, thus yielding a cell with a 32N nucleus. This nucleus undergoes a sixth replication cycle concurrent with nuclear division and cell budding to give rise to 64 haploid daughter cells. Interestingly, intranuclear spindles persist throughout the cell cycle, thereby providing a potential mechanism to organize chromosomes and organelles in an organism that undergoes dramatic changes in ploidy. The development of the plastid mirrors that of the nucleus, a continuous organelle, which grows throughout the parasite's development and shows association with all centrosomes. Pharmacological ablation of the parasite's multiple spindles demonstrates their essential role in the organization and faithful segregation of the plastid. By using several molecular markers we have timed organelle fission to the last replication cycle and tied it to daughter cell budding. Finally, plastids were labeled by fluorescent protein expression using a newly developed S. neurona transfection system. With these transgenic parasites we have tested our model in living cells employing laser bleaching experiments.

Animals↗
PubMed1993

Topoisomerase II inhibition prevents anaphase chromatid segregation in mammalian cells independently of the generation of DNA strand breaks.

Yeast temperature-sensitive mutants of DNA topoisomerase II are incapable of chromosome condensation and anaphase chromatid segregation. In mammalian cells, topoisomerase II inhibitors such as etoposide (VP-16-123) have similar effects. Unfortunately, conclusions drawn from work with mammalian cells have been limited by the fact that the standard inhibitors of topoisomerase II also generate DNA strand breaks, which when produced by other agents (e.g. ionizing radiation) are known to affect progression into and through mitosis. Here we show that the anti-tumour agent ICRF-193, recently identified as a topoisomerase II inhibitor operating by a non-standard mechanism, generates neither covalent complexes between topoisomerase II and DNA, nor adjacent DNA strand breaks, in mitotic HeLa. However, the drug does prevent anaphase segregation in HeLa and PtK2 cells, with effects similar to those of etoposide. We therefore conclude that topoisomerase II function is required for anaphase chromosome segregation in mammalian cells, as it is in yeast.

Anaphase↗
PubMed2001

Segregation of nucleolar components coincides with caspase-3 activation in cisplatin-treated HeLa cells.

We studied morphological changes of the nucleoli in HeLa cells treated with cisplatin and compared them with induction of markers of programmed cell death and TUNEL staining. We used different light microscopic nucleolar staining methods allowing us to visualize not only nucleolar proteins but also nucleolar RNA. Our results show predominantly compact, centrally localized nucleoli in intact control HeLa cells. In cisplatin-treated HeLa cells, we found an early onset of nucleolar segregation of proteins detected by argyrophilic nucleolar organizer regions and anti-nucleolar monoclonal antibody as well as an increased immunoreactivity for activated caspase-3 after 6 hours. Staining with Toluidine Blue and Methyl-green Pyronine revealed segregated nucleoli 12 hours after the treatment with cisplatin. TUNEL positivity in cisplatin-treated HeLa cells was accompanied by the aggregation of the argyrophilic proteins in the central portion of nucleus, disappearance of nucleolar RNA and shrinkage of the nucleus after 24 hours. Monitoring of the biochemical changes by immunoblotting revealed that activation of distinct caspases and degradation of their downstream protein substrates is executed in two phases. During an early apoptotic stage beginning 4.5 hours post treatment an activation of caspase-9 and caspase-3 was observed. This was accompanied by proteolytic cleavage of poly(ADP-ribose) polymerase-1 (PARP-1). The caspase-9 activation seems to be mediated by recruitment by the activating factor Apaf-1 because the increased accumulation of Apaf-1 and cytochrome C in cytosol preceded the generation of mature caspase-9 form. A second phase of apoptosis occurring between 10 and 15 hours post treatment was characterized by degradation of other nucleolar and nuclear proteins such as nuclear lamins, topoisomerase I and B23. In conclusion, remarkable segregation of nucleolar argyrophilic proteins, nucleolar RNA and a simultaneous activation of the cascade of caspases markedly preceded the TUNEL positivity in cisplatin-treated HeLa cells thereby substantiating the hypothesis that the nucleolus is a preferred target for caspase-3-dependent proteolysis in cisplatin-treated HeLa cells.

Apoptosis↗