The relationship between the frequency of participation of acrocentric chromosomes in formation of satellite associations and the duration of human lymphocyte cultivation with phytohemmaglutinin]

All acrocentrics were shown to take part in the formation of satellite association at the 52nd, 72nd and 90th hr of human lymphocytes culturing, in the first mitosis with equal frequency but having different associative capacity in further mitoses. It seems likely that a single nucleolus in the lymphocytes at initial stage of activation, the high frequency of satellite associations, and a random participation of acrocentrics in the associations in first mitosis are due to that all acrocentrics form association in small lymphocytes which are sensitive to PHA.     

Comparison of two means of identifying satellite associations in man]

Two methods of identifying satellite associations were compared in ten normal donors. Conventional Giemsa stain proved to identify by 31% less of 3-chromosomal associations, by 50% less of 4- and 5-, and by 66.6% less of 6-chromosomal associations than in staining with ammoniacal silver, whereas the number of 2-chromosomal associations was by 10% greater, this conditioning the prevalence of small associations. Silver staining used to expose intersatellite associations revealed acrocentric chromosomes mutually oriented, placed close to one another, but without any intersatellite connection. In Giemsa-stained preparations these are considered to be associating, which increases the number of multiple groups. Both errors of the conventional Giemsa method cannot be corrected. Identification of associations according to intersatellite connections is free of these errors after silver staining.     

Satellite association patterns in postpartum women and in newborn infants

Different features of the satellite associations between the acrocentric chromosomes of 100 postpartum mothers, between 14 and 43 years of age, and 100 neonates (51 males and 49 females) from Puriscal, Costa Rica, were compared (400 cells were examined, 2 from each individual). Several types of satellite associations showed higher frequencies in the mothers than in the neonates. The associations most frequently found in the two groups were those of two chromosomes, followed by those of three chromosomes. The D/G ratio was 1.43 in the children and 1.40 in the mothers. The number of associations per cell in the mothers was almost twice that of the children. The mean number of acrocentric chromosomes per association was 2.2 in the children and 2.35 in the mothers. No significant difference was found between observed and expected values of D and G chromosomes in the two groups. Thus, the probable factors responsible for the increase of satellite associations in the mothers similarly influenced the two types of acrocentric chromosomes.     

BUdR-Giemsa labeling and satellite association in human leukocytes

Summary Satellite associations were analysed in differentially stained human leukocyte chromosomes, obtained from four patients with Down's syndrome and four normal probands. A particular type of close association between two acrocentrics, showing a non-random arrangement of sister chromatids in a concordant dark-to-dark and light-to-light alignment, was found to be more common in patients with Down's syndrome compared with the normal controls. Apart from this particular type of association, sister chromatids are randomly arranged in satellite associations between two acrocentrics in both groups of probands. Considerable differences in the mean frequencies of satellite associations between first and second metaphases of the same individual were found in some probands of both groups of individuals. Since a high degree of inter-individual variability in the proliferative response of human leukocytes in culture is well established, the use of BUdR-Giemsa labeling for comparative analysis of satellite association frequencies is suggested.     

The study of X-rays and TCDD effects on satellite associations may suggest a simple model for application in environmental mutagenesis

Summary Satellite associations were used as parameters to test nucleolar organizer activity. Assuming that toxic and/or mutagenic agents may affect the ribosomal genes, satellite associations in human lymphocytes were analysed following exposure to X-rays and compared with the satellite association pattern of subjects exposed to TCDD. A significant decrease in the satellite association frequency in D group chromosomes was found both in irradiated lymphocytes and in subjects exposed to Dioxin. The findings seem to be in accordance with the hypothesis based on random damage of functional nucleolar organizing regions.     

Support for random alignment of mitotic chromatids in associating nucleolus organizers

Summary Peripheral blood cultures of five healthy chromosomally normal adults were used to study the lateral orientation of mitotic chromatids in satellite associations. Chromosomes were prepared after bromodeoxyuridine substitution for two S phases and the fluorescence-plus-Giemsa (FPG) technique. Conventionally stained preparations were used to assess the polymorphisms of the acrocentrics in each individual. Satellite association pairs in which the acrocentrics were involved in a close, relatively straight end-to-end configuration were analyzed in cells with differentially stained sister chromatids. The number of concordant (light-light) and discordant (light-dark) chromatid alignments in associations varied from individual to individual. Chi square analysis revealed that four of the five subjects and the combined cell population from all subjects showed no deviation from the expected frequency of random alignment. The one subject with preferential nonrandom alignment had the widest range of polymorphisms and very long stalks involved in the majority of the associations, compared with the rest. We have obtained no evidence that as a general rule satellite associations are nonrandom with preferential orientation of dark-to-dark and light-to-light chromatids, although this may be the case in some individuals with very active NORs.     

Mating strategy shifts in male green treefrogs (Hyla cinerea): An experimental study

Four field experiments were designed to study calling and satellite mating strategies in the green treefrog, Hyla cinerea. (1) The calling male was removed from 19 satellite associations and 11 of the 19 satellite males began calling. (2) After the calling male was removed from 10 satellite associations, a speaker broadcast synthetic mating calls. All of the satellite males oriented to the speaker. (3) Synthetic mating calls were played back to 14 calling males. Eleven males stopped calling and oriented to the speaker during at least one trial. (4) Sequences of synthetic mating calls and synthetic encounter calls were broadcast to 12 calling males. Nine males became satellites when the speaker emitted mating calls; none did so when encounter calls were presented.     

Generation of different fates from multipotent muscle stem cells

Although neuronal and mesenchymal stem cells exhibit multipotentiality, this property has not previously been demonstrated for muscle stem cells. We now show that muscle satellite cells of adult mice are able to differentiate into osteoblasts, adipocytes and myotubes. Undifferentiated muscle progenitor cells derived from a single satellite cell co-expressed multiple determination genes including those for MyoD and Runx2, which are specific for myogenic and osteogenic differentiation, respectively. Determination genes not relevant to the induced differentiation pathway were specifically downregulated in these cells. Similar multipotent progenitor cells were isolated from adult human muscle. Based on these observations, we propose a 'stock options' model for the generation of different fates from multipotent stem cells.     

Possible origin of a small bisatellited additional chromosome

Summary The possible derivation of a small supernumerary marker chromosome was investigated by means of different staining techniques and the frequency of satellite associations. It could be demonstrated that the marker chromosome participates at satellite association more than randomly. The marker chromosome is supposed to derive from 2 of chromosomes 13, 14, 21, or 22.Who died accidentally in 1978     

Differences between cystic fibrosis and normal cells in the degree of satellite association

Summary The degree of satellite association was found to be significantly higher in phytohemagglutinin (PHA)-stimulated lymphocytes from cystic fibrosis (CF) patients than from those of control individuals. PHA-stimulated lymphocytes from obligatory heterozygotes for the CF mutant allele showed an intermediate degree of satellite association. The degree of satellite association was estimated by the frequency of cells exhibiting associations, by the number of associations per cell, and by the number of chromosomes in an association. The differences in the degree of satellite association were dependent on the concentration of colchicine used for cell arrest. These findings may assist in developing a diagnostic method for the early identification of heterozygotes for the CF allele and for prenatal detection of CF homozygous fetuses.This paper is based on a portion of a dissertation to be submitted by Y. Ravia in partial fulfilment of the Ph. D. requirements in the Graduate School of Tel Aviv University     

Stochasticity,Bistability and the Wisdom of Crowds: A Model for Associative Learning in Genetic Regulatory Networks

It is generally believed that associative memory in the brain depends on multistable synaptic dynamics, which enable the synapses to maintain their value for extended periods of time. However, multistable dynamics are not restricted to synapses. In particular, the dynamics of some genetic regulatory networks are multistable, raising the possibility that even single cells, in the absence of a nervous system, are capable of learning associations. Here we study a standard genetic regulatory network model with bistable elements and stochastic dynamics. We demonstrate that such a genetic regulatory network model is capable of learning multiple, general, overlapping associations. The capacity of the network, defined as the number of associations that can be simultaneously stored and retrieved, is proportional to the square root of the number of bistable elements in the genetic regulatory network. Moreover, we compute the capacity of a clonal population of cells, such as in a colony of bacteria or a tissue, to store associations. We show that even if the cells do not interact, the capacity of the population to store associations substantially exceeds that of a single cell and is proportional to the number of bistable elements. Thus, we show that even single cells are endowed with the computational power to learn associations, a power that is substantially enhanced when these cells form a population.     

Colour learning when foraging for nectar and pollen: bees learn two colours at once

Bees are model organisms for the study of learning and memory, yet nearly all such research to date has used a single reward, nectar. Many bees collect both nectar (carbohydrates) and pollen (protein) on a single foraging bout, sometimes from different plant species. We tested whether individual bumblebees could learn colour associations with nectar and pollen rewards simultaneously in a foraging scenario where one floral type offered only nectar and the other only pollen. We found that bees readily learned multiple reward–colour associations, and when presented with novel floral targets generalized to colours similar to those trained for each reward type. These results expand the ecological significance of work on bee learning and raise new questions regarding the cognitive ecology of pollination.     

Alignment of BrdU-substituted chromatids in satellite association in human metaphase cells

We have studied the orientation of BrdU-substituted chromatids in satellite associations in cells double-stained to reveal both the Ag/As nucleolar organizer regions and, simultaneously, sister chromatid differentiation. In those satellite associations with all four chromatids joined by Ag stain, and with the axes in a virtually straight line, we have observed an excess of concordant configurations. Where an association was considered single, dark chromatids were involved in significantly more associations than light chromatids. Within this group, the observed excess of concordant associations was not greatly different from the numbers observed in the straight, double-chromatid group of configurations. Whether the increased involvement of dark chromatids in satellite associations provides a complete explanation for the observed excess of concordant associations, or whether certain individuals show a specific tendency to form concordant associations, must await further data.     

Satellite associations and the identification of the Y chromosome in man

In a sample of cells from a leucocyte culture of an XY/XO mosaic the number of satellite associations between two acrocentric chromosomes (groups 13–15 and 21–22) was determined. Three different types of associations were distinguished. A comparison of the numerical frequencies of the different types in XO and XY cells suggests that the Y chromosome does not take part in the associations and is therefore unsatellited.     

Characteristics of the cis- and trans-positions of chromatids of human acrocentric chromosomes in extreme old age

Cis- and trans-positions of chromatid associations of human acrocentric chromosomes were examined at extreme old age. Lymphocyte cultures were prepared by the usual method, from peripheral blood of 9 subjects aged 80-90 years (analysis of 179 metaphases) and 7 subjects aged 20-48 years (analysis of 124 metaphases). The functional difference between stalks of the sister chromatids was found. In the subjects at the age 80-90 years satellite stalks of chromatids-1 (in all DNA strands thymidine was substituted by 5-BrdU) of the D chromosome in cis-position are included into associations with lower frequency, as compared with the satellite stalks of chromatids-2 (thymidine+ is only substituted by 5-BrdU in a half DNA strands of the chromosome). This apparently reflects variability of regulation of functional activity of satellite stalks of sister chromatids.     

Association mapping of stigma and spikelet characteristics in rice (Oryza sativa L.)

Stigma and spikelet characteristics play an essential role in hybrid seed production. A mini-core of 90 accessions developed from USDA rice core collection was phenotyped in field grown for nine traits of stigma and spikelet and genotyped with 109 DNA markers, 108 SSRs plus an indel. Three major clusters were built upon Rogers’ genetic distance, indicative of indicas, and temperate and tropical japonicas. A mixed linear model combining PC-matrix and K-matrix was adapted for mapping marker-trait associations. Resulting associations were adjusted using false discovery rate technique. We identified 34 marker-trait associations involving 22 SSR markers for eight traits. Four markers were associated with single stigma exsertion (SStgE), six with dual exsertion (DStgE) and five with total exsertion. RM5_Chr1 played major role indicative of high regression with not only DStgE but also SStgE. Four markers were associated with spikelet length, three with width and seven with L/W ratio. Numerous markers were co-associated with multiple traits that were phenotypically correlated, i.e. RM12521_Chr2 associated with all three correlated spikelet traits. The co-association should improve breeding efficiency because single marker could be used to assist breeding for multiple traits. Indica entry 1032 (cultivar 50638) and japonica entry 671 (cultivar Linia 84 Icar) with 80.65 and 75.17% of TStgE, respectively are recommended to breeder for improving stigma exsertion.     

Molecular analysis of a polymorphic domain of alpha satellite from the human X chromosome.

Alpha satellite DNA, a diverse family of tandemly repeated DNA sequences located at the centromeric region of each human chromosome, is organized in a highly chromosome-specific manner and is characterized by a high frequency of restriction-fragment-length polymorphism. To examine events underlying the formation and spread of these polymorphisms within a tandem array, we have cloned and sequenced a representative copy of a polymorphic array from the X chromosome and compared this polymorphic copy with the predominant higher-order repeat form of X-linked alpha satellite. Sequence data indicate that the polymorphism arose by a single base mutation that created a new restriction site (for HindIII) in the sequence of the predominant repeat unit. This variant repeat unit, marked by the new HindIII site, was subsequently amplified in copy number to create a polymorphic domain consisting of approximately 500 copies of the variant repeat unit within the X-linked array of alpha satellite. We propose that a series of intrachromosomal recombination events between misaligned tandem arrays, involving multiple rounds of either unequal crossing-over or sequence conversion, facilitated the spread and fixation of this variant HindIII repeat unit.     

Infertility associated with two accessory bisatellited chromosomes

Summary Two extra bisatellited chromosome identified as inv dup (15) (pterq11.2::q11.2pter) were found in an oligoasthenospermic male. Analysis of Ag-staining in the proband and in one fertile brother with a normal karyotype revealed that nucleolar organizer region (NOR) activity was significantly increased in the patient. The frequency of satellite associations was also significantly higher in the index case, but no correlation was found between NOR activity and acrocentric associations. These results suggest that extra NOR activity and the elevated frequency of satellite associations could predispose to gametogenic impairment.