Patterns of association in the human metaphase complement: ring analysis and estimation of associativity of specific chromosome regions

Double in situ hybridization in combination with digital image analysis: a new approach to study interphase chromosome topography

Double in situ hybridization with mercurated and biotinylated chromosome specific DNA probes in combination with digital image analysis provides a new approach to compare the distribution of homologous and nonhomologous chromosome targets within individual interphase nuclei. Here we have used two DNA probes representing tandemly repeated sequences specific for the constitutive heterochromatin of the human chromosomes 1 and 15, respectively, and studied the relative arrangements of these chromosome targets in interphase nuclei of human lymphocytes, amniotic fluid cells, and fibroblasts, cultivated in vitro. We have developed a 2D-image analysis approach which allows the rapid evaluation of large numbers of interphase nuclei. Models to test for a random versus nonrandom distribution of chromosome segments are discussed taking into account the three-dimensional origin of the evaluated 2D-distribution. In all three human diploid cell types the measurements of target-target and target-center distances in the 2D-nuclear image revealed that the labeled segments of the two chromosomes 15 were distributed both significantly closer to each other and closer to the center of the nuclear image than the labeled chromosome 1 segments. This result can be explained by the association of nucleolus organizer regions on the short arm of chromosome 15 with nucleoli located more centrally in these nuclei and does not provide evidence for a homologous association per se. In contrast, evaluation of the interphase positioning of the two chromosome 1 segments fits the random expectation in amniotic fluid and fibroblast cells, while in experiments using lymphocytes a slight excess of larger distances between these homologous targets was occasionally observed. 2D-distances between the labeled chromosome 1 and 15 segments showed a large variability in their relative positioning. In conclusion our data do not support the idea of a strict and permanent association of these homologous and nonhomologous targets in the cell types studied so far.

The nuclear skeleton and the spatial arrangement of chromosomes in the interphase nucleus of vertebrate somatic cells

The topologic distribution of interphase chromosomes established by using various cytologic methods and data concerning the DNA-nuclear skeleton interactions in isolated nuclear fractions were reviewed and discussed. Comparison of these different data clearly showed that the position of chromosomes observed in situ is in agreement with the results obtained from isolated nuclear fractions, indicating that all DNA molecules are bound to the peripheral nuclear skeleton. Moreover, the in situ position of the rDNA near the nuclear envelope can be correlated with the existence of a nucleolar skeleton connected to the peripheral nuclear skeleton. Taking into account the discrepant results regarding the actual existence of an internal nuclear skeleton, we attempted to analyze how the various nuclear skeletal structures described in the literature can be involved in both the distribution of chromosomes and in their chromatin organization. As many questions are still unanswered, we considered the modes of investigation that seem to be the most promising.

The ordered arrangement of chromosomes in the Chinese hamster spermatocyte nucleus

The question of chromosome distribution in the mammalian nucleus is addressed, and data are provided in support of the ordered arrangement of chromosomes in the Chinese hamster spermatocyte. Testicular cells were dispersed and air-dried without prior fixation, then stained and karyotyped. The position of chromosome telomeres in 217 pachytene spermatocytes was determined in relation to four concentric rings which equally divided the nuclear area. The distribution of telomeres showed a progressive decline from the central to the peripheral rings. This was particularly pronounced for chromosomes 1-7, but was reversed for the XY chromosomes. The distribution of the total as well as of the individual chromosomes was significantly different from that expected on the basis of random distribution. The only exceptions to this were chromosomes 8-10, which exhibited random distribution. Thus, while chromosomes 1-7 had a central position, the XY pair had a peripheral localization. The mean ring position appeared to be related to chromosome length, except for the XY chromosomes, suggesting that chromosome length may determine chromosome position.

New data on the in-situ position of the inactive X chromosome in the interphase nucleus of human fibroblasts

The in situ spatial distribution of nucleolus-organizing-region (NOR) bearing chromosomes in relation to the inactive X chromosome was studied during interphase in human fibroblasts. The respective positions of these chromosomes were examined in 30 growing and 32 resting fibroblasts from reconstructed nuclei, using nucleoli and the Barr body as ultrastructural markers. Experimental values for the distance between the nucleoli and the Barr body were estimated by their coefficient of closeness and compared to the uniform distribution. The following results were obtained: the distribution patterns for the two populations of nuclei were similar, the distribution of the NOR-bearing chromosomes in relation to the inactive X chromosome varied and differed significantly from a uniform distribution, and in many cases the Barr body was observed to be in a juxta-nucleolar position. The internal distribution revealed by this study is compared with the data in the literature, especially with the conflicting data obtained by other methods used to determine the interphase arrangement of chromosomes. The relationship between interphase and metaphase arrangements such as can be deduced with these methods, is discussed in relation to the mechanisms of the formation of metaphase plates or chromatid translocations.

Contribution of reciprocal translocations to an understanding of chromosome displacement: inferences for studies of spatial order at metaphase

Chromosome displacement was analysed in three different translocations. Two alternative hypotheses were examined: (1) Displacement is determined by the spatial ordering of chromosomes on the metaphase plate. (2) Displacement is a function of the gross physical property of chromosome size and does not reflect ordering. Predicted numbers of displacements were calculated for each chromosome for each of the two hypotheses and these were compared with the observed numbers of displacements using a chi 2 analysis. In the analysis for two of the three translocations, the first hypothesis was rejected whilst the alternative hypothesis was supported by all three analyses. It is concluded that chromosome displacement is a function of chromosome size and does not reflect spatial ordering at metaphase. Furthermore, it is suggested that many studies of apparent ordering at metaphase may merely reflect chromosome displacement. The analysis of displacement rates in all other chromosomes of the complement was undertaken in one of the translocation carriers. This showed no alteration of relative displacement rates.

Proteins of de-membraned protamine-depleted mouse sperm. Homology with proteins of somatic cell nuclear envelope/matrix

Following treatment with Triton X/1 M NaCl/2-mercaptoethanol, mouse sperm heads are divested of protamines and other basic proteins; the residual structure is one in which the general morphological organization of the decondensed chromatin and the nuclear boundaries are conserved [1]. In this study, the protein complement of that residual structure has been characterized and subdivided into two sets: 1. Those that are sperm-unique, including constituents of the sperm head that may be intrinsically nuclear (or extra-nuclear, but exceedingly adherent to the nuclear envelope). 2. Those that display corresponding electrophoretic properties and immunologic cross-reactivity with proteins of similarly treated mouse somatic cell nuclei. Among the latter are proteins of molecular weight 52, 63 and 69 kD, two of which (63 and 69 kD) appear to be homologous to polypeptides of somatic nuclear envelope/pore complex lamina. Absence from sperm nuclei of the third of the characteristic predominant triplet of somatic nuclear lamina polypeptides of mammalian cells, here designated 67 kD, indicates cell-type variation in these structures. On the other hand, the identification of homologous polypeptides in the sperm and somatic complements suggests that those are specific instances of conservation and may represent the paternal contribution to the pool of polypeptides for assembly of the envelopes of the pronuclei of the one-cell embryo.

The central localization of the small and early replicating chromosomes in human diploid metaphase figures

Centromere-center distances are analyzed in 700 metaphase plates, which belong to four different samples. The descriptive analysis of the chromosome distribution shows that smaller, earlier replicating, genet-dense chromosomes are preferentially found near the metaphase plate center, surrounded by longer chromosomes which finish their replication rather late during S phase. This general pattern is highly constant in diploid metaphase samples and independent of sex, culture time, and number of individuals used in the sample. There is accumulating evidence that this overall distribution is not the result of technical artifacts. The metaphase plate data are complementary to the concept of an interphase nucleus structure in which late-replicating, genetically less active chromatin is accumulated at the periphery of the nucleus, while other, earlier replicating chromatin is connected with the intranuclear matrix. Although the currently available data should not be overinterpreted, an extension of the "bodyguard" hypothesis, which was suggested for C heterochromatin, provides a functional interpretation for these data: The peripherally localized, late-replicating genetic material protects the centrally localized euchromatin against mutagens, clastogens, and maybe also against viruses.

Telomere and centromere association tendencies in the human male metaphase complement

"Generalized distances" between centromeres and between telomeres were statistically analyzed (chi 2 tests) in 100 trypsin-banded metaphase figures derived from normal males. Analysis of association tendencies on the first column of obtained c-c, p-p, q-p, and p-q histograms showed significant heterochromatin attraction not only between nonacrocentrics and acrocentrics but also between two nonacrocentric chromosome pairs (1 and 16). However since not all c-heterochromatin-rich chromosomes were involved in associations (pair 5), and conversely, since chromosomes without an important centromeric heterochromatin block were involved in associations (pairs 8 and 11), it is probable that centromeric heterochromatin is not the only factor responsible for chromosome association. Moreover associations occur not only at the centromeres; in our circle analysis of the binding capacity of the telomeres or centromere of one chromosome pair with the telomeres or the centromeres of all other chromosome pairs, we also found preferential associations for T(4,13), T(9,15), T(11,15), T(13,19), T(15,19), T(17,18), T(17,22), and T(19,20). We therefore suggest that heterochromatin is not the only reason for chromosome association and that telomeres may also play an important part in this process.