Differential Condensation Of Chromosomes Research Articles

Karyotype Analysis and 4C Nuclear DNA Estimation in Different Cultivars of <i>Clitoria ternatea</i> L.

The present article has reported a detailed karyotype analysis and 4C nuclear DNA estimation in different cultivars and populations of Clitoria ternatea L. of Fabaceae. This plant, widely distributed in tropical regions in India, is a climber and is an economically important medicinal plant. The karyotype study has revealed a constancy in the diploid somatic chromosome number (2n=16) in all these cultivars and populations. However, the nature and number of nucleolar chromosomes varied. The centromeric chromosomes were either metacentric or sub-metacentric in all these cultivars. The total chromosome length and volume differed among these cultivars and populations having the same somatic chromosome number. The differential condensation of chromosomes and the association of variable amounts of proteins in chromosome composition might have been responsible for such differences. In situ cytophotometric studies revealed an intermediate genome size in this species. This is the first report on the detailed karyotype and genome size of cultivars of Clitoria ternatea L.

A Novel Thyroid Hormone Mediated Regulation of HSV-1 Gene Expression and Replication is Specific to Neuronal Cells and Associated with Disruption of Chromatin Condensation.

Previously we showed that thyroid hormone (T3) regulated the Herpes Simplex Virus Type -1 (HSV-1) gene expression and replication through its nuclear receptor TR via histone modification and chromatin remodeling in a neuroblastoma cell line neuro-2a cells (N2a). This observation suggested that T3 regulation may be neuron-specific and have implication in HSV-1 latency and reactivation. In this study, our in vitro latency/reactivation model demonstrated that removal of T3 can de-repress the HSV-1 replication and favor reactivation. Transfection studies and infection assays indicated that HSV-1 thymidine kinase (TK), a key viral gene during reactivation, was repressed by TR/T3 in cells with neuronal origin but not in non-neuronal cells. Additional studies showed that RCC1 (Regulator of Chromosome Condensation 1) was sequestered but efficiently detected upon viral infection in N2a cells. Western blot analyses indicated that addition of T3 repressed the RCC1 expression upon infection. It is likely that diminution of RCC1 upon infection in neuronal cells under the influence of TR/T3 may lead to repression of viral replication/gene expression thus promote latency. Together these results demonstrated that TR/T3 mediated regulation is specific to neuronal cells and differential chromosome condensation may play a critical role in this process.

Prematurely condensed chromosomes of the Indian muntjac: a model system for the analysis of chromosome condensation and banding.

Premature chromosome condensation, PCC, was induced in interphase cells of the Indian muntjac (Muntiacus muntjak), by fusion with mitotic Lu106 (human) or muntjac cells, using inactivated Sendai virus. The G1 and G2 chromosomes appeared as single-respectively double-structured threads of variable length. Calculations of relative chromosome lengths at variable degrees of condensation indicated that the chromosome arm is the basic unit for chromosome condensation. Application of a G-banding procedure on PCC chromosomes demonstrated a clear differentiation of dark and light bands. Comparative analysis of banding patterns in metaphase, prophase and PCC chromosomes demonstrated a positive relationship between the number of G-bands and chromosome length. Based on the banding pattern at metaphase, a model system for the interpretation of differential chromosome condensation and band expression in prophase and PCC chromosomes is suggested. Condensation and banding indices were defined and exemplified for chromosome 1. By comparing PCC and metaphase chromosomes, it was found that proximal regions were proportionally less extended than intercalary regions and that terminal regions were about equally extended. There were proportionally fewer dark G-bands in more extended compared to less extended regions. Exceptions from both these trends and their significance are pointed out.

Highly Unstable Male Meiosis in Two Aberrant Plants Isolated from the Mutant Population of Nigella damascena L. (love-in-a-mist)

Two aberrant (plant type I and II) plants possessing meiotic instability in the microsporocytes were identified from the mutant population of Nigella damascena L. (commonly known as love-in-a-mist; family: Ranunculaceae). Plant type I (screened from 10 kR M1 generation) was a weak plant with small sized flowers and shrunken anthers devoid of any pollen grains at anthesis. The plant dried up at blooming stage. Male meiotic study revealed the occurrence of condensed and compact chromatin masses of variable sizes and numbers (12 to 13 mostly and 3 to 5 rarely) and occasional formation of bivalent and univalent like configurations in the meiocytes. Plant type II (isolated at M2 from the M1 progeny of 0.25% EMS treatment) was a small flower mutant (SF2), the morphological nature and chromosomal behaviour of which have been compared to control and SF1 (small flower mutant arising in different M2 line). SF1 showed similar morphological behaviour as SF2 but demonstrated normal meiosis like control. SF2 manifested hypoploid (2n 12) chromosome numbers at MI and AI and prevalence of unstable meiosis in the form of asynaptic and desynaptic chromosome behaviour, differential condensation of chromosomes, persistent nucleolar body and occasional multivalent formation in first and mid-flowering phases. SF2 showed more diploid PMCs at late flowering phase. SF2 was also found to be associated with defects in female gametophytic tissues. Possible mode of gene action in the plant types has been predicted.

Karyotype and C‐Banding Patterns of Mitotic Chromosomes in Diploid Bromegrass (Bromus riparius Rehm)

Previous cytogenetic studies of the genus Bromus L. were limited to chromosome counts and construction of karyotypes on the basis of Feulgen staining. Since the chromosomes of Bromus are similar in morphology, these karyotypes are of limited use for chromosome identification and genome analysis. The objectives of this study were to develop and evaluate a Giemsa C‐banding procedure to use in identification of individual bromegrass chromosomes and to develop a karyotype for diploid Bromus riparius Rehm. (2n = 14; PI 440215). All chromosomes had one or more C‐bands which were located mainly at telomeric regions. A group (I) of four pairs of chromosomes had telomeric bands on only one arm and could be differentiated. In this group, one pair had an interstitial C‐band along with a telomeric band, one pair had a nucleolus organizer region (NOR) at a subtelomeric location on the short arm, and the other two pair could be distinguished by centromere location. The other group (II) of three pairs of chromosomes had telomeric bands on both arms. The unequivocal identification of specific chromosomes of Group II was not possible in all cells because of their similarity and differential condensation of chromosomes. Chromosomes of both groups were either metacentric or submetacentric. The total length of individual chromosomes ranged from 5.58 to 6.87 μm and the arm ratios ranged from 1.02 to 1.5. The homologous chromosomes were paired and assigned numbers I to VII in decreasing length. A karyotype was constructed by means of the C‐bands, mean chromosome lengths, and arm ratios. The C‐banding procedure used in this study could be used to developed karyotypes for the other species of the genus Bromus and these C‐banded karyotypes could be used to compare genomes within the genus.

COMPARATIVE ANALYSIS OF KARYOTYPES AND NUCLEOLAR ORGANIZER REGIONS IN DIFFERENT POPULATIONS OF MYTILUS TROSSULUS, MYTILUS EDULIS AND MYTILUS GALLOPROVINCIALIS

The cylotaxonomical characteristics of Mytilus tros-sulus, M. edulis and M. galloprovincialis were studied using karyometric analysis and silver staining. The karyotype of M. trossulus, reported here for the first time, consists of six metacentric and eight submetacentric-subtelocentric chromosome pairs. The occurrence of five metacentric chromosome pairs in M. galloprovincialis differentiates this taxon from M. trossulus and M. edulis which both have six meta-centrics. The number of submetacentric to subtelo-centric chromosome pairs was variable between populations and between taxa. We suggest that this variability has arisen from differential chromosome condensation rather than from structural change. Intercomparison of chromosome relative length showed strong similarity among the three taxa. Chromosomal nucleolar organizer regions (NORs) were identically located on two submetacentric-subtelocentric chromosome pairs in all three taxa. However, M. trossulus showed a characteristic difference in the occurrence of NORs on one metacentric pair, which was absent in M. galloprovincialis and M. edulis. Variability in the number of NORs per cell was observed in all populations studied. We conclude that the three taxa of Mytilus studied here cannot be differentiated by asingle karyological character, but that a combination of karyological characters is virtually diagnostic

Dynamic changes in the morphology of barley chromosomes during the mitotic metaphase stage.

Dynamic changes in the morphology of barley chromosomes during the mitotic metaphase stage were observed and attributed to the differential condensation of the chromosome arms. The mitotic stage of the 250 metaphase spreads was classified into five sub-stages from early metaphase to late metaphase. At each sub-stage, the relative length (RL) and the arm ratio (AR) of the chromosomes were examined and the ranking of the chromosomes for the two parameters was also determined for the respective chromosomal spreads. As a result, the RL and AR values of some of the chromosomes as well as their ranking for the two parameters were found to vary with the progression of the metaphase stage. The dynamic changes in the RL and AR values were closely related to the differences in the condensation rate of the chromosome arm. Factors involved in the differential chromosome condensation are discussed.

Karyomorphological observations in Cymbopogon Sprengel.

The details of chromosome morphology in 16 plant types belonging to 11 different species and chemocytotypes of Cymbopogon are presented for the sake of karyological assessment and chromosome identification. In general, the karyotypes are nearly symmetrical with median to submedian centromeres. The range of total chromatin length (haploid complement) varies from 17.46μm to 28.7μm in diploids (2n=20), 38.9μm to 42.7μm in 2n=40 types and 81.75μm in 2n=60 type; and the individual chromosome length between 1.2μm to 5.65μm. The occurrence of polyploid series within C. flexuosus as reported by earlier authors seems to be an illusion due to ambiguity in identification. The assessment of karyological data reveal that repatterning of the karyotype, tandom variation and allopatric polyploidisation might have played an important role in speciation in the genus.The organisation of chromatin and centromere seem to be in transitory stage of specialisation consummated through differential chromosome condensation and centromere localisation. Such an endowment is likely to generate instant chromosomal instability due to reduced kinetochore activity to some extent. so commonly encountered in the various species of this genus.

High resolution analysis and differential condensation in RBA-banded human chromosomes.

Human prophase, premetaphase, and mid-metaphase chromosomes are prepared and analyzed using the thymidine cell synchronization technique and R-banding patterns (RBA). Haploid sets with 700-1000 bands can be demonstrated. Sequences of chromosomes of different degrees of condensation are helpful for a better understanding and classification of regions of extended chromosomes. A considerable variation in the condensation of parts of homologous chromosomes is reflected in the variability of the arm ratio. This differential condensation of chromosomes is entirely effected by variation of the degree of condensation in AT rich interbands and can be attributed to the degree of labeling by BrdU.

Cytogenetics of 16 Chromosome Plants in Pearl Millet

Plants with two extra chromosomes were obtained in the progeny of a triploid plant. The extra chromosomes were deficient for short segments in one of their arms. Meiotic studies in PMC's of these plants showed that these extra chromosomes were not pairing with any of the other chromosomes of the complement but were only pairing among themselves. In cells with the extra chromosomes there was a significant variation in PMC' chiasma frequency. Meiotic abnormalities like differential condensation of chromosomes, persistent nucleoli and cytomixis were observed. The effect of these extra chromosomes on the behaviour of the other chromosomes was compared with the effect of B's when present in numbers of five or more on the A-chromosomes.

Cytology of inbreds and f 1 hybrids of pearl millet

The meiotic behaviour of chromosomes was studied in four inbred lines and their F 1 hybrids of P. typhoides. The inbred lines showed a decrease in mean chiasma frequency when compared with the population plants, but differed from one another in their mean chiasma frequencies. Together with the decrease in mean chiasma frequency the inbreds showed variation in mean chiasma frequencies. The inbred lines showed a number of meiotic abnormalities such as extra chromosomes, extra fragments, desynapsis, persistent nucleoli and differential condensation of chromosomes. The F 1 hybrids of these inbreds exhibited heterosis for chiasma frequency. All the F 1's had mean chiasma frequencies higher than the means of the respective participating parents. The F 1's, however, differed in the degree of heterosis exhibited. In the F 1 hybrids, the variation in mean chiasma frequency, both between plants and between PMC's within plants, was significantly lower than that of the inbred lines. The effect of environment was studied in the inbred lines and their F 1 hybrids. The mean chiasma frequencies of the inbred lines were significantly lower, and the variation in mean chiasma frequencies was greater, in the stress season. The mean chiasma frequencies of F 1's did not show any significant differences between the two seasons. The F 1's exhibited less variation in mean chiasma frequency than the inbred lines, showing that F 1's were developmentally more stable. The F 1's did not show any meiotic abnormalities in either season.

COLCHICINE-INDUCED SUPERCONTRACTION OF CHROMOSOMES AND HETEROCHROMATIC SEGMENTS IN VICIA FABA

The question whether the degree of chromosome condensation of heterochromatic region differs from that of euchromatic region in the process of colchicine-induced supercontraction was studied using Vicia faba root-tips. The results obtained did not indicate the differential chromosome condensation between heterochromatin and euchromatin.

The Karyotype of <i>Petunia hybrida</i> and the Differential Chromosome Condensation

1. The karyotype of Petunia hybrida was re-investigated and was determined as follows. K(2n)=14=2csAsm1(n) +2Am2+2Bst+2Cm1+2Csm2+2Dsm1+2Dm2.2. The present study has revealed the differential chromosome condensation to take place from late prophase to metaphase in somatic mitosis. And the differential chromosome condensation probably has its relationship to heterochromatin.