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PubMed1992

Heterosynapsis and axial equalization of the sex chromosomes of the northern bobwhite quail.

The pairing behavior of the Z and W chromosomes in the female northern bobwhite quail (Colinus virginianus) was analyzed by electron microscopy of silver-stained synaptonemal complexes (SCs). After autosomal pairing was completed, synapsis of the sex chromosomes initiated at the short-arm end of the W chromosome and one end of the Z chromosome. Synapsis then progressed unidirectionally, producing a sex bivalent in which the entire length of the W axis was paired with an equivalent length of the Z axis. Progressive contraction and asymmetrical twisting of the Z axis ultimately resulted in a fully paired configuration with aligned axial ends. Further contraction of the Z axis reduced the extent of asymmetrical twisting such that only the nonaligned centromeric regions distinguished the SC of the ZW bivalent from SCs of similar-sized autosomes in late-pachytene nuclei. Quantitative analyses indicated that the length of the Z axis shortened significantly during the adjustment process, whereas no significant difference occurred in the length of the W axis. The nonalignment of the centromeric regions during transitional stages of ZW synapsis indicates that direct heterosynapsis of nonhomologous segments, followed by axial equalization of the length inequality, is responsible for the length adjustment during synapsis in the sex chromosomes of the bobwhite quail.

Animals↗

PubMed1990

Pachytene pairing and sperm counts in mice with single Robertsonian translocations and monobrachial compounds.

Data on testis weights, sperm counts, and synaptonemal complexes are presented for mice carrying the following Robertsonian translocations: Rb(6.15)lAld; Rb(4.6)2Bnr; Rb(4.15)4Rma; Rb(6.15)lAld/Rb(4.6))2Bnr, which is male-sterile; and Rb(6.15)lAld/Rb(4.15)4Rma, which is male-fertile. In RblAld/Rb2Bnr sperm were absent or sparse, whereas the sperm count in RblAld/Rb4Rma was just over 50% of the parental value. The translocated chromosomes appeared as fully paired bivalents in homozygotes, as trivalents in single heterozygotes, and as quadrivalents in compounds. About 20-40% of trivalents had unsynapsed ends. The proportion of quadrivalents with unsynapsed ends was about 85% in the male-sterile compound, compared with 75% in the male-fertile compound. The proportion of quadrivalents associated with XY was about 70% in both. Testis weights, but not sperm counts, were found to differ in two of three reciprocal crosses. It is concluded that, in addition to pairing failure and autosome/XY association, the effect of translocations on spermatogenesis is affected by other factors, including genetic background, inbreeding, and perhaps environmental factors. It remains to be elucidated whether pairing failure and XY association are primary or secondary effects.

Animals↗

PubMed2000

Meiosis and apoptosis in germ cells of X-autosome translocation carrier boars.

Meiotic features and fate of germ cells were studied using electron microscopy on surface spread spermatocytes and in situ tests for apoptosis on testicular tissues of normal boars and X-autosome translocation (X-AT) carrier boars. Histological sections of the translocation t(Xp+; 14q-) carrier boars showed accumulation of degenerating germ cells including binucleate and multinucleate cells, as well as pyknosis and nuclear fragmentation characteristic of apoptosis. Synaptonemal complex analysis of X-AT carrier boars revealed 19 bivalents including a large complex made up of the altered X (Xp+) and normal chromosome 14, and a smaller element representing the Y chromosome in synapsis with the derived chromosome 14 (14q-) in most (89.3%) of the germ cells. In situ tests for apoptotic DNA fragmentation revealed positive signals exclusively among early spermatocytes and degenerating germ cells. These findings and the absence of stages beyond pachytene suggest that the meiocytes are arrested at pachytene and eliminated through apoptotic process in spite of the complete synapsis displayed by the chromosomes involved in this translocation. Failure of meiotic progress in our X-AT carriers would appear to be the result of the disruption of gene sequence (or function) caused by the involvement of the X chromosome in this rearrangement, rather than the deleterious consequences of abnormal segregation anticipated in reciprocal translocation carriers. We hypothesize that this disruption could have affected the induction of stage-specific gene products in meiosis such as heat shock proteins and caused the excessive release of endonucleases normally produced by early prophase meiocytes, leading to their apoptosis in our X-autosome translocation carrier boars.

Animals↗

PubMed2006

Behaviour of human heterochromatic regions during the synapsis of homologous chromosomes.

BACKGROUND: Alterations of synapsis can disturb or arrest meiosis and result in infertility. Synaptic abnormalities are frequently observed in infertile patients but also in fertile men. METHODS: The subtelomere-specific multiplex fluorescence in-situ hybridization (stM-FISH) has been applied in combination with immunofluorescence to identify all synaptonemal complexes (SCs) and to analyse those presenting synaptic anomalies in fertile and infertile men. RESULTS: SCs with heterochromatin blocks other than centromere (noncentromeric heterochromatin) presented a higher frequency of gaps (SC discontinuities) and splits (unsynapsed SC regions) at pachytene, the incidences for 9qh, 1qh, 15p and 21p being the highest ones. Inter-individual variability in the incidence of synaptic anomalies in these regions has been observed. In addition, synaptic anomalies in other SC regions are more frequent in infertile cases than in controls. Clear association of the SC15 and SC21 to the XY pair has been seen. CONCLUSION: Noncentromeric heterochromatic regions are the last to synapse. The inter-individual variation observed in the incidence of gaps and splits in these regions may be explained by the heteromorphism of these regions in the general population. The presence of synaptic anomalies in other SC regions may indicate nuclei with a severely affected synapsis. Noncentromeric heterochromatic regions might play a role in the association of autosomal SC15 and SC21 with the XY pair.

Centromere↗

PubMed1989

Meiotic behavior of gonosomically variant females of Akodon azarae (Rodentia, Cricetidae).

The meiotic behavior of sex chromosomes has been investigated in variant females of Akodon azarae, both in pachytene oocytes and metaphase I. In somatic cells, these females have a heteromorphic sex pair, in which the minor chromosome has been previously interpreted as a major deletion of the long arm of the X chromosome (dX). After microspreading for synaptonemal complex analysis, pachytene oocytes show two axes of very different lengths (100:17.1), which correspond to the sex chromosomes X and dX. True synapsis is abnormally restricted (43.3%) between these sex chromosomes; on the other hand, self-synapsis of both the X and dX chromosomes is frequent (60%). Single, nonsynapsed axes or axial segments are thickened. Strong chromatin condensation occurs around nonsynapsed axes or axial segments, giving many of these sex pairs an appearance similar to an XY body ("sex vesicle"). The minor gonosome axis differs from that of the Y chromosome of male meiosis, as the former is shorter (relative to the X) and has a different synaptic behavior. In 17 metaphases I from XdX variant females, only heteromorphic, end-to-end joined sex pairs were observed. These variant females differ from the variant females of the wood lemming Myopus schisticolor in several respects, but a similar mechanism seems to be prevalent in other species of the genus Akodon. Self-synapsis of unequal gonosomes in oocytes is assumed as an escape from functional deterioration, following the hypothesis put forward by others.

Animals↗

PubMed2006

An azoospermic man with a double-strand DNA break-processing deficiency in the spermatocyte nuclei: case report.

BACKGROUND: The mechanisms of meiotic arrest in human spermatogenesis are poorly known. METHODS AND RESULTS: A testicular biopsy from an azoospermic male showed complete spermatogenesis arrest at the spermatocyte stage, asynapsis, lack of formation of the XY body, partial reversion to a mitotic-like division and cell degeneration both at the prophase and at the abnormal cell divisions. Synaptonemal complex analysis showed minor segments of synapsis and mainly single axes. Fluorescent immunolocalization of meiotic proteins showed normal SYCP3, scarcity of SYCP1, null MLH1 foci, about 10 patches of gamma-H2AX, abnormal presence of BRCA1 among autosomal axes, absence of RAD51 in early and advanced spermatocytes and permanence of gamma-H2AX labelling up to the abnormal spermatocyte divisions that are the most advanced stage reached. There are at least six dominions of evenly packed chromatin resembling that of the normal XY body, but no true XY body. CONCLUSIONS: The protein phenotype and the fine structure of the nuclei are compatible with a deficiency of the processing of double-strand DNA breaks in the zygotene-like spermatocytes, but the features of this defect do not agree with Spo11, Sycp1, Atm and Dmc1 null mutations, which give absence of XY body, synapsis disturbances and spermatocyte apoptosis in mice.

Adaptor Proteins, Signal Transducing↗

PubMed2003

High-resolution crossover maps for each bivalent of Zea mays using recombination nodules.

Recombination nodules (RNs) are closely correlated with crossing over, and, because they are observed by electron microscopy of synaptonemal complexes (SCs) in extended pachytene chromosomes, RNs provide the highest-resolution cytological marker currently available for defining the frequency and distribution of crossovers along the length of chromosomes. Using the maize inbred line KYS, we prepared an SC karyotype in which each SC was identified by relative length and arm ratio and related to the proper linkage group using inversion heterozygotes. We mapped 4267 RNs on 2080 identified SCs to produce high-resolution maps of RN frequency and distribution on each bivalent. RN frequencies are closely correlated with both chiasma frequencies and SC length. The total length of the RN recombination map is about twofold shorter than that of most maize linkage maps, but there is good correspondence between the relative lengths of the different maps when individual bivalents are considered. Each bivalent has a unique distribution of crossing over, but all bivalents share a high frequency of distal RNs and a severe reduction of RNs at and near kinetochores. The frequency of RNs at knobs is either similar to or higher than the average frequency of RNs along the SCs. These RN maps represent an independent measure of crossing over along maize bivalents.

Chromosome Mapping↗

PubMed2004

Meiosis-specific yeast Hop1 protein promotes synapsis of double-stranded DNA helices via the formation of guanine quartets.

In most eukaryotes, genetic exchange between paired homologs occurs in the context of a tripartite proteinaceous structure called the synaptonemal complex (SC). Genetic analyses have revealed that the genes encoding SC proteins are vital for meiotic chromosome pairing and recombination. However, the number, nature and/or the mechanism used by SC proteins to align chromosomes are yet to be clearly defined. Here, we show that Saccharomyces cerevisiae Hop1, a component of SC, was able to promote pairing of double-stranded DNA helices containing arrays of mismatched G/G sequences. Significantly, pairing was rapid and robust, independent of homology in the arms flanking the central G/G region, and required four contiguous guanine residues. Furthermore, data from truncated DNA double helices showed that 20 bp on either side of the 8 bp mismatched G/G region was essential for efficient synapsis. Methylation interference indicated that pairing between the two DNA double helices involves G quartets. These results suggest that Hop1 is likely to play a direct role in meiotic chromosome pairing and recombination by its ability to promote synapsis between double-stranded DNA helices containing arrays of G residues. To our knowledge, Hop1 is the first protein shown to promote synapsis of DNA double helices from yeast or any other organism.

Base Pair Mismatch↗

PubMed1995

Pachytene karyotype analysis of the nematode Meloidogyne spartinae in relation to the genus Meloidogyne.

Seven synaptonemal complexes (SC) were present in the pachytene nuclei of Meloidogyne spartinae. The SC was bipartite and consisted of two lateral elements, while lacking a striated central element. This pattern was similar in all Meloidogyne species studied thus far with the exception of M. microtyla. Each SC was attached by only one end to the nuclear envelope while the other end remained unattached and was free in the nucleoplasm. A bouquet formation at pachytene was absent. An average of eight recombination nodules were present on the SC during all stages of pachytene, although the length of SC increased approximately 77%, from an average of 78 to 138 microm from early to mid-late pachytene. In M. spartinae, there was no apparent relationship between SC length and amount of recombination at pachytene. In addition, nuclear volume increased >60% during pachytene while nucleolar volume decreased by approximately 35%. Two nucleolar organizer regions (NOR) were present during mid-pachytene, whereas other stages had only one NOR. This is the first time that two nucleoli have been identified at pachytene in any nematode. They were both the same chromosome yet in reverse order relative to the telomere attached to the nuclear envelope, suggesting that each telomere was competent to interact with the nuclear envelope.

Animals↗

PubMed1997

ATM and RPA in meiotic chromosome synapsis and recombination.

ATM is a member of the phosphatidylinositol 3-kinase (PIK)-like kinases, some of which are active in regulating DNA damage-induced mitotic cell-cycle checkpoints. ATM also plays a role in meiosis. Spermatogenesis in Atm-/- male mice is disrupted, with chromosome fragmentation leading to meiotic arrest; in human patients with ataxia-telangiectasia (A-T), gonadal atrophy is common. Immuno-localization studies indicate that ATM is associated with sites along the synaptonemal complex (SC), the specialized structure along which meiotic recombination occurs. Recombination, preceded by pairing of homologous chromosomes, is thought to require heteroduplex formation between homologous DNA, followed by strand exchange. These early meiotic steps (entailing the formation and processing of meiotic recombination intermediates with DNA-strand interruptions) require ssDNA-binding proteins such as replication protein A (RPA; refs 5-7). In somatic cells, DNA damage induces ATM-dependent phosphorylation of RPA. We demonstrate here that ATM and RPA co-localize along synapsed meiotic chromosomes and at sites where interactions between ectopic homologous chromosome regions appear to initiate. In Atm-/- meiotic prophase spermatocytes, immuno-localization shows that RPA is present along synapsing chromosomes and at sites of fragmentation of the SC. These results suggest that RPA and ATM co-localize at sites where interhomologous-DNA interactions occur during meiotic prophase and where breaks associated with meiotic recombination take place after synapsis, implying a possible functional interaction between these two proteins.

Animals↗

PubMed1996

Centromere and telomere movements during early meiotic prophase of mouse and man are associated with the onset of chromosome pairing.

The preconditions and early steps of meiotic chromosome pairing were studied by fluorescence in situ hybridization (FISH) with chromosome-specific DNA probes to mouse and human testis tissue sections. Premeiotic pairing of homologous chromosomes was not detected in spermatogonia of the two species. FISH with centromere- and telomere-specific DNA probes in combination with immunostaining (IS) of synaptonemal complex (SC) proteins to testis sections of prepuberal mice at days 4-12 post partum was performed to study sequentially the meiotic pairing process. Movements of centromeres and then telomeres to the nuclear envelope, and of telomeres along the nuclear envelope leading to the formation of a chromosomal bouquet were detected during mouse prophase. At the bouquet stage, pairing of a mouse chromosome-8-specific probe was observed. SC-IS and simultaneous telomere FISH revealed that axial element proteins appear as large aggregates in mouse meiocytes when telomeres are attached to the nuclear envelope. Axial element formation initiates during tight telomere clustering and transverse filament-IS indicated the initiation of synapsis during this stage. Comparison of telomere and centromere distribution patterns of mouse and human meiocytes revealed movements of centromeres and then telomeres to the nuclear envelope and subsequent bouquet formation as conserved motifs of the pairing process. Chromosome painting in human spermatogonia revealed compacted, largely mutually exclusive chromosome territories. The territories developed into long, thin threads at the onset of meiotic prophase. Based on these results a unified model of the pairing process is proposed.

Animals↗

PubMed1993

A balanced autosomal reciprocal translocation in an azoospermic bull.

This appears to be the first reported case of a bull with a balanced autosomal reciprocal translocation associated with azoospermia. The analysis includes somatic chromosome banding, conventional meiotic analysis, and electron microscopy of synaptonemal complexes (SCs). The karyotype of the bull was found to be 60,XY,rcp(8;13)(q11;q24). Electron microscopy of SCs in microspread pachytene spermatocytes revealed a high incidence of terminal asynapsis of the smallest arm of the quadrivalent. Most quadrivalents with such asynapsis and few with nonhomologous synapsis showed associations with the XY sex bivalent, leading to complete meiotic arrest at late pachynema. Except for one diakinetic cell, no diplotene and subsequent stages were encountered in air-dried meiotic preparations. The presence of degenerating primary spermatocytes in SC preparations, as well as in testicular sections, and the absence of spermatozoa in ejaculates confirm the chromosomally derived male sterility of the bull. X-chromosome reactivation, evidenced by the cytomorphological reversal of associated sex bivalents, appeared to be the initial step in the degeneration of spermatocytes. Consequently, the formation of a separate, fully developed XY body, which was previously demonstrated on the periphery of spermatocyte nuclei in fertile bulls, could not be attained in this case. Extensive end-to-end association of autosomal bivalents in meiotically arrested, as well as degenerating, spermatocytes was a consistent and unique observation of this study. Such associations may lead to enhanced reactivation of the X chromosome.

Animals↗

PubMed2000

Meiotic studies of a human male carrier of the common translocation, t(11;22), suggests postzygotic selection rather than preferential 3:1 MI segregation as the cause of liveborn offspring with an unbalanced translocation.

The t(11;22)(q23;q11) translocation is the only non-Robertsonian rearrangement for which there are a large number of unrelated families, apparently with the same breakpoints. These families most often have been ascertained through an abnormal child with the karyotype 47,XX or XY, +der(22) t(11;22)(q23;q11). To explain the high incidence of 3:1 segregants, rarely seen in offspring of carriers of other reciprocal translocations, a number of theoretical models have been suggested. We have used both electron microscope analysis of the synaptonemal complex (SC) and dual-color FISH to investigate the meiotic chromosome behavior in a male carrier of the translocation who has the karyotype 46,XY, t(11;22)(q23;q11). Chromosome synapsis, first-meiotic chiasma configuration, and segregation behavior of this translocation have been analyzed directly. Examination of SCs by electron microscopy showed pachytene-cross formation in 49/50 nuclei. Approximately 50% (26/50) revealed a classical fully synapsed quadrivalent. A proportion of these (10/26), however, showed some central asymmetry, suggesting heterologous synapsis. The remaining cells appeared to have incomplete synapsis. FISH analysis showed only quadrivalents in all 100 metaphase I nuclei. The chiasma frequency was increased within the interstitial segments, in comparison with the same region in normal bivalents. All types of segregation category were found in metaphase II nuclei. There was no indication of preferential 3:1 anaphase I segregation. We conclude that the +der(22) constitution in offspring of carriers of t(11;22)(q23;q11) is not likely to be due to meiotic 3:1 segregation being especially common. Rather, the +der(22) constitution is more likely to be the result of postzygotic selection against other unbalanced karyotypes.

Cell Nucleus↗

PubMed2003

Synaptic process in the rat (Rattus norvegicus): Influence of methodology on results.

Synaptonemal complex (SC) analysis is a widely used method for assessing the effects of genotoxic agents in germ cells. Although the evolution of the SCs and their related annexed structures, such as nucleoli, has been well established, sometimes it is difficult to assess whether the abnormal features observed correspond to genotoxic effects or to an artefact related to the method used to obtain the SC preparations. In this article, we describe a new method of obtaining SC preparations for electron microscopy, as well as the results of a study of the first meiotic prophase in oocytes and spermatocytes of the rat (Rattus norvegicus Sprague Dawley) in which we analysed how the methodology used can influence the results. Besides important sex-specific differences, mainly during desynapsis (diplotene), a relationship between several bivalents and nucleolar structures, that in some cases could disturb the synaptic process, was observed in oocytes. At the same time, the characteristic SC fragmentation in oocytes was verified, but this fragmentation, in addition to a sex-specific component, was influenced by the method itself. By reducing to a minimum the artefacts produced by the method, it is possible to optimise the analysis of SCs as a method of testing genotoxic effects in the germ line.

Animals↗

PubMed2002

Male mouse recombination maps for each autosome identified by chromosome painting.

Linkage maps constructed from genetic analysis of gene order and crossover frequency provide few clues to the basis of genomewide distribution of meiotic recombination, such as chromosome structure, that influences meiotic recombination. To bridge this gap, we have generated the first cytological recombination map that identifies individual autosomes in the male mouse. We prepared meiotic chromosome (synaptonemal complex [SC]) spreads from 110 mouse spermatocytes, identified each autosome by multicolor fluorescence in situ hybridization of chromosome-specific DNA libraries, and mapped >2,000 sites of recombination along individual autosomes, using immunolocalization of MLH1, a mismatch repair protein that marks crossover sites. We show that SC length is strongly correlated with crossover frequency and distribution. Although the length of most SCs corresponds to that predicted from their mitotic chromosome length rank, several SCs are longer or shorter than expected, with corresponding increases and decreases in MLH1 frequency. Although all bivalents share certain general recombination features, such as few crossovers near the centromeres and a high rate of distal recombination, individual bivalents have unique patterns of crossover distribution along their length. In addition to SC length, other, as-yet-unidentified, factors influence crossover distribution leading to hot regions on individual chromosomes, with recombination frequencies as much as six times higher than average, as well as cold spots with no recombination. By reprobing the SC spreads with genetically mapped BACs, we demonstrate a robust strategy for integrating genetic linkage and physical contig maps with mitotic and meiotic chromosome structure.

Adaptor Proteins, Signal Transducing↗

PubMed1996

[Cytogenetic patterns in synapsis of meiotic chromosomes in animals and plants].

Chromosome synapsis in meiosis is performed through the formation of a synaptonemal complex (SC). The SC aggregates homologues until the diplotene stage, when the function of physical binding is carried out by a chiasmata. SC formation is controlled by specific genes. Regularities of SC formation in animals and plants are being studied at the Laboratory of Cytogenetics, Vavilov Institute of General Genetics, the Russian Academy of Sciences. It was shown that, in Drosophila melanogaster, the presence or absence of SC in meiosis is determined by balance between autosomes and sex chromosomes. i.e., SC is formed according to regularities in sex determination. The dose of the 8C-11A segment of X chromosome plays a key role in this process. Eight mutations in synaptic genes that affect SC formation were studied in rye Secale cereale. SC variants occurring in heteromorphic sex chromosomes were analyzed in the Ellobius genera and in B-chromosomes of Apodemus peninsulae. It was shown that, in addition to homologous synapsis, non-homologous synapsis of aberrant chromosomes occurs in rye and mouse heterozygotes at chromosome rearrangements. Twice as many heterozygous chromosome rearrangements were revealed, when the SC was studied at pachytene instead of diakinesis and metaphase I. Simple methods of SC investigations extended the capabilities of cytogenetic analysis of meiosis and provided new perspectives for studying the action of meiotic gen.

Animals↗

PubMed1997

The yeast Red1 protein localizes to the cores of meiotic chromosomes.

Mutants in the meiosis-specific RED1 gene of S. cerevisiae fail to make any synaptonemal complex (SC) or any obvious precursors to the SC. Using antibodies that specifically recognize the Red1 protein, Red1 has been localized along meiotic pachytene chromosomes. Red1 also localizes to the unsynapsed axial elements present in a zip1 mutant, suggesting that Red1 is a component of the lateral elements of mature SCs. Anti-Red1 staining is confined to the cores of meiotic chromosomes and is not associated with the loops of chromatin that lie outside the SC. Analysis of the spo11 mutant demonstrates that Red1 localization does not depend upon meiotic recombination. The localization of Red1 has been compared with two other meiosis-specific components of chromosomes, Hop1 and Zip1; Zip1 serves as a marker for synapsed chromosomes. Double labeling of wild-type meiotic chromosomes with anti-Zip1 and anti-Red1 antibodies demonstrates that Red1 localizes to chromosomes both before and during pachytene. Double labeling with anti-Hop1 and anti-Red1 antibodies reveals that Hop1 protein localizes only in areas that also contain Red1, and studies of Hop1 localization in a red1 null mutant demonstrate that Hop1 localization depends on Red1 function. These observations are consistent with previous genetic studies suggesting that Red1 and Hop1 directly interact. There is little or no Hop1 protein on pachytene chromosomes or in synapsed chromosomal regions.

Cell Nucleolus↗

PubMed1996

Combined immunocytogenetic and molecular cytogenetic analysis of meiosis I human spermatocytes.

We have used a combination of immunocytogenetic and molecular cytogenetic technology on human spermatocytes to investigate (1) meiosis I chromosome pairing, and (2) organization of synaptonemal complex (SC)-associated chromatin with respect to whole chromosome paints, unique DNA sequences and repetitive DNA of heterochromatic blocks, centromeres and telomeres. It is evident that synapsis normally starts at the termini of homologues. In general, synapsis proceeds synchronously from termini towards the centre of bivalents without any indication of interstitial initiation. Some aberrant meiosis I spermatocytes showed asynchronous pairing, demonstrating not only large differences in the degree of SC formation between bivalents, but also chromosome alignment without synapsis as well as clear interstitial synaptic initiation. It may be the case that alignment normally takes place along the entire length of homologues before synapsis occurs and that the potential for synaptic initiation exists along the length of chromosomes. Telomeric sequences were seen tightly associated with the SCs, as might be expected considering their kinetic properties in relation to the nuclear membrane. Other repetitive DNA, i.e. centromeric alpha-satellites and classical satellites of the heterochromatic blocks 1qh and 9qh, were all found to form loops that are associated with SCs only at their bases. A unique DNA cosmid probe (21q22.3) was found to produce a hybridization pattern consisting of spots located outside SC. The fluorescence in situ hybridization (FISH) signals of these spread DNA sequences have a granular appearance, probably reflecting the pattern of coiling and chromatin condensation of the target DNAs.

Animals↗