Heterochromatin Bands Research Articles

Physical mapping of 35S rRNA genes and genome size variation in polyploid series of Sisyrinchium micranthum and S. rosulatum (Iridaceae: Iridoideae)

Sisyrinchium micranthum and S. rosulatum are part of a species complex in which S. micranthum displays considerable morphological variation. S. rosulatum is a tetraploid species, whereas S. micranthum plants may present three different ploidy levels (2x, 4x, and 6x), so that polyploidy might have an important role in the diversification of this group. Notwithstanding, most cytogenetic studies on these species are based on chromosome counting. Aiming to understand how polyploidy may have impacted the genomes of these species, the DNA content of 184 specimens was estimated; fluorochrome banding with chromomycin A3 and fluorescent in situ hybridization using an 18S-5.8S-26S ribosomal DNA (rDNA) probe were also performed. The results showed a reduction in monoploid genome size (1Cx), as well as in the number of heterochromatin bands and rDNA sites per monoploid genome, from diploids to polyploids. Additionally, intraspecific and within-ploidy variations in genome size and number of rDNA sites were observed. The source of varying structure in genome organization of these plants may be the multiple independent formations of polyploids along with an ongoing diploidization process. However, the intraspecific and within-ploidy polymorphisms indicate genetic mechanisms other than genome duplication and diploidization to be important to the genome evolution of these taxa.

Variation of the centromeric heterochromatin region (CHR) in the Iranian house mouseMus musculusLinnaeus, 1758 (Rodentia: Muridae)

AbstractThe house mouse, Mus musculus, is known for its highly conserved morphology and chromosomal structure, but some chromosomal characters have been recognized as accurate taxonomic markers in this species, e.g. centromeric heterochromatin, which is useful to identify the taxonomic status of house mouse. In this study, comprehensive cytogenetic surveys have been carried out in five to eighteen specimens of house mouse from each locality of Iran using centromeric heterochromatin banding (C-banding). C-banding was performed on the karyotype, and the centromeric heterochromatin region size (CHRs) was calculated using karyotype analysis software. Results indicated that intra- and inter- population variation of C-band positive heterochromatin ranged from very large CHRs to small CHRs. Generally, chromosomes 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16 and 19 showed high variability in their CHRs whereas chromosomes 1, 2, 3, 13, 17, 18 and X had low variability in CHRs. Chromosome 4 had the largest CHRs in all ...

Using chromosomal data in the phylogenetic and molecular dating framework: karyotype evolution and diversification in Nierembergia (Solanaceae) influenced by historical changes in sea level.

Karyotype data within a phylogenetic framework and molecular dating were used to examine chromosome evolution in Nierembergia and to infer how geological or climatic processes have influenced in the diversification of this solanaceous genus native to South America and Mexico. Despite the numerous studies comparing karyotype features across species, including the use of molecular phylogenies, to date relatively few studies have used formal comparative methods to elucidate chromosomal evolution, especially to reconstruct the whole ancestral karyotypes. Here, we mapped on the Nierembergia phylogeny one complete set of chromosomal data obtained by conventional staining, AgNOR-, C- and fluorescent chromosome banding, and fluorescent insitu hybridisation. In addition, we used a Bayesian molecular relaxed clock to estimate divergence times between species. Nierembergia showed two major divergent clades: a mountainous species group with symmetrical karyotypes, large chromosomes, only one nucleolar organising region (NOR) and without centromeric heterochromatin, and a lowland species group with asymmetrical karyotypes, small chromosomes, two chromosomes pairs with NORs and centromeric heterochromatin bands. Molecular dating on the DNA phylogeny revealed that both groups diverged during Late Miocene, when Atlantic marine ingressions, called the 'Paranense Sea', probably forced the ancestors of these species to find refuge in unflooded areas for about 2Myr. This split agrees with an increased asymmetry and heterochromatin amount, and decrease in karyotype length and chromosome size. Thus, when the two Nierembergia ancestral lineages were isolated, major divergences occurred in chromosomal evolution, and then each lineage underwent speciation separately, with relatively minor changes in chromosomal characteristics.

Karyotype evolution in the genus Jacaranda Juss. (Jacarandeae, Bignoniaceae): chromosome numbers and heterochromatin.

Most taxa in the Bignoniaceae have 2n = 40, but the basal clade Jacarandeae has 2n = 36, suggesting that x = 18 is the ancestral basic number for the family. Variations in heterochromatin band patterns in genera that are numerically stable, such as Jacaranda, could facilitate our understanding of the chromosomal and karyotypic evolution of the family. We characterized heterochromatin distributions in six Jacaranda species using chromomycin A3 (CMA) and 4'6-diamidino-2-phenylindole (DAPI). All of them had 2n = 36, including first counts for Jacaranda bracteata Bureau & K. Schum., Jacaranda irwinii A.H. Gentry, Jacaranda jasminoides (Thunb.) Sandwith, and Jacaranda rugosa A.H. Gentry. Their karyotypes had four to eight terminal CMA+/DAPI- bands per monoploid set. In the section Monolobos, Jacaranda brasiliana (Lam.) Pers. had eight terminal bands and Jacaranda mimosifolia D. Don had four; in the section Dilobos, J. bracteata had six bands per monoploid set, with the other species having five. While three species in the section Dilobos had the same number of terminal bands, J. irwinii had two additional pericentromeric bands and a proximal heterozygotic band, and J. bracteata had two distended CMA bands. The consistent records of 2n = 36 in Jacaranda may represent a plesiomorphic condition for the Bignoniaceae; therefore, the family originated from an ancestor with x = 18. However, 2n = 36 may represent a derived condition, and the family could have had an ancestral basic number of x = 20 that is still conserved in most representatives of the family.

New chromosome characteristics of the monozoic tapeworm Caryophyllaeus laticeps (Cestoda, Caryophyllidea)

Summary The karyotype of a caryophyllidean tapeworm Caryophyllaeus laticeps (Pallas, 1781) from the freshwater bream Abramis brama (L.) caught in the Slovak part of the River Tisa, was described and originally inspected for amount of heterochromatin and its chromosome localization. The chromosome set comprised nine metacentric and one submetacentric (No. 3) pairs (2n = 20). The chromosomes were up to 12.0 ± 2.5 μm long and the mean total length of haploid genome (TLC) reached 80.6 μm that represents one of the highest yet recorded values among tapeworms. C-banding and staining with fl uorescent dyes DAPI and YOYO1 revealed a distinct banding pattern explicitly on chromosomes with centromeric bright heterochromatin bands present on all 10 chromosome pairs; no pair showed any interstitial heterochromatin. A complete course of spermatocyte meiosis and dynamics of nucleolus formation and degradation during meiotic division was described.

Analysis of the flanking sequences of the heterochromatic JNK region in Secale vavilovii chromosomes

The JNK motif is repeated 4 000 times in an additional heterochromatin band. Flanking sequences of a JNK region, which form extra heterochromatin in 2R rye (Secale vavilovii Grossh.) chromosomes, were studied using a genome walking technique. The results clearly indicate that there were blocks of JNK sequences adjacent to the R173 family of repeated sequences. Moreover, it appears that the R173 are sequences flanking in both directions, i.e., upstream and downstream. Downstream, the R173 is adjacent to the JNKs in an anti-parallel orientation, whereas upstream it is adjacent in a parallel orientation. In order to confirm the presence of the R173 sequence, fluorescence in situ hybridization was carried out. Using both JNK and R173 molecular probes, overlapping hybridization signals in the 2RL pair of chromosomes were observed, indicating an identical location of the two sequence elements.

A region of euchromatin coincides with an extensive tandem repeat on the mouse (Mus musculus) inactive X chromosome.

Euchromatic features are largely absent from the human inactive X chromosome (Xi), with the exception of several large tandem repeats that can be detected as euchromatin bands at metaphase. Despite residing megabases apart, these tandem repeats make frequent inactive X-specific interactions. The mouse homologue has been reported for at least one of the tandem repeats, but whether the mouse Xi is also characterized by distinct bands of euchromatin remains unknown. We examined the mouse Xi for the presence of euchromatin bands by examining the pattern of histone H3 dimethylated at lysine 4 and detected two major signals. The first band resides in the subtelomeric region of band XF5 and may correspond to the pseudoautosomal region. The second band localizes to XE3 and coincides with an extensive complex repeat composed of a large tandem and inverted repeat segment as well as several large short interspersed nuclear element (SINE)-rich tandem repeats. Fluorescence in situ hybridization reveals that sequences with homology to the repeat region are scattered along the length of the Y chromosome. Immunofluorescence analysis of histone H3 trimethylated at lysine 9 on metaphase chromosomes indicates that the repeat region corresponds to a band of constitutive heterochromatin on the male X and female active X chromosomes, whereas the euchromatin signal appears to be female specific. These data suggest that the band of euchromatin observed at XE3 is unique to the mouse Xi, comparable to the chromatin arrangement of several large tandem repeats located on the human X chromosome.

Poster #T23 AFFECTIVE PROSODY IN REMITTED AND NON-REMITTED SCHIZOPHRENIA PATIENTS COMPARED TO HEALTHY CONTROLS

The heterochromatin banding patterns as well as the physical locations of 45S and 5S rDNA of the mitotic metaphase chromosomes in Fagopyrum esculentum Moench were analyzed for the first time using orcein staining and double-color fluorescent in situ hybridization, respectively. These techniques led to the successful identification of the full set of F. esculentum trisomics from 25 trisomic lines. The results showed the abundant heterochromatin banding of 27 bands, which included 9 centromeric bands, 12 terminal bands, 5 intercalary bands, and 1 satellite band. These highly polymorphic bands exhibited significant differences in the heterochromatin banding among eight pairs of homologous chromosomes. The resulting rDNA physical map showed five pairs of 45S DNA loci located on IS, IIS, IIIS, IVS, and VIS, as well as two pairs of 5S rDNA loci located on IL and VS. The eight distinct pairs of homologous F. esculentum chromosomes can be differentiated based on the locations of the 45S and 5S rDNA as well as the karyotypic characteristics of the mitotic metaphase chromosomes. The full set of F. esculentum trisomics from the 25 trisomic lines include T10, T7, and T24 as T1Hch; T13 and T14 as T2Hch; T15, T16, and T23 as T3Hch; T4 and T18 as T4Hch; T3, T17, and T19 as T5Hch; T1, T6, and T20 as T6Hch; T5, T8, T21, T22, and T25 as T7Hch; and T9 and T11 as T8Hch.

Description of Karyotype of Kerodon acrobata, an endemic rodent in Brazilian Cerrado.

Kerodon acrobata is a caviidae rodent endemic from Brazilian Cerrado. It was described only in 1997 and the data about it is very scarce. The aim of this work was to characterize the karyotype of K. acrobata. Giemsa staining, nucleolar organizer region (NOR) banding, C-positive heterochromatin banding and DAPI fluorescence were used in N metaphases of a specimen collected in Asa Branca Farm, in Aurora do Tocantins municipality, Tocantins state, Brazil. K. acrobata showed the same diploid number, fundamental number and chromosome morphology as Kerodon rupestris. But its NOR location and heterochromatin distribution patterns indicated a unique cytogenetic profile when compared to its sister species, emphasizing the evolutionary uniqueness of this relatively new and unknown species. This record also extends the distribution of this species northward.

Banding patterns in plant chromosomes. III. Dactylis glomerata subsp. aschersoniana (Graebner) Thell. from Poland

The present paper presents part of the author's studies on the variability of the genus <em>Dactylis</em> from Poland. The karyotypes and Giemsa heterochromatin banding patterns of three population samples of <em>Dactylis glomerata</em> subsp. <em>aschersoniana</em> (Graebner) Thell. (2n = 14) from Poland were studied in detail.

Holocarboxylase synthetase acts as a biotin-independent transcriptional repressor interacting with HDAC1, HDAC2 and HDAC7

In human cells, HCS catalyzes the biotinylation of biotin-dependent carboxylases and mediates the transcriptional control of genes involved in biotin metabolism through the activation of a cGMP-dependent signal transduction pathway. HCS also targets to the cell nucleus in association with lamin-B suggesting additional gene regulatory functions. Studies from our laboratory in Drosophila melanogaster showed that nuclear HCS is associated with heterochromatin bands enriched with the transcriptionally repressive mark histone 3 trimethylated at lysine 9. Further, HCS was shown to be recruited to the core promoter of the transcriptionally inactive hsp70 gene suggesting that it may participate in the repression of gene expression, although the mechanism involved remained elusive. In this work, we expressed HCS as a fusion protein with the DNA-binding domain of GAL4 to evaluate its effect on the transcription of a luciferase reporter gene. We show that HCS possesses transcriptional repressor activity in HepG2 cells. The transcriptional function of HCS was shown by in vitro pull down and in vivo co-immunoprecipitation assays to depend on its interaction with the histone deacetylases HDAC1, HDAC2 and HDAC7. We show further that HCS interaction with HDACs and its function in transcriptional repression is not affected by mutations impairing its biotin-ligase activity. We propose that nuclear HCS mediates events of transcriptional repression through a biotin-independent mechanism that involves its interaction with chromatin-modifying protein complexes that include histone deacetylases.

Identification of the full set of Fagopyrum esculentum trisomics by heterochromatin banding analysis and rDNA physical mapping

The heterochromatin banding patterns as well as the physical locations of 45S and 5S rDNA of the mitotic metaphase chromosomes in Fagopyrum esculentum Moench were analyzed for the first time using orcein staining and double-color fluorescent in situ hybridization, respectively. These techniques led to the successful identification of the full set of F. esculentum trisomics from 25 trisomic lines. The results showed the abundant heterochromatin banding of 27 bands, which included 9 centromeric bands, 12 terminal bands, 5 intercalary bands, and 1 satellite band. These highly polymorphic bands exhibited significant differences in the heterochromatin banding among eight pairs of homologous chromosomes. The resulting rDNA physical map showed five pairs of 45S DNA loci located on IS, IIS, IIIS, IVS, and VIS, as well as two pairs of 5S rDNA loci located on IL and VS. The eight distinct pairs of homologous F. esculentum chromosomes can be differentiated based on the locations of the 45S and 5S rDNA as well as the karyotypic characteristics of the mitotic metaphase chromosomes. The full set of F. esculentum trisomics from the 25 trisomic lines include T10, T7, and T24 as T1Hch; T13 and T14 as T2Hch; T15, T16, and T23 as T3Hch; T4 and T18 as T4Hch; T3, T17, and T19 as T5Hch; T1, T6, and T20 as T6Hch; T5, T8, T21, T22, and T25 as T7Hch; and T9 and T11 as T8Hch.

Germ line-limited and somatic chromosomes of Acricotopus lucidus differ in distribution and timing of alterations of histone modifications in male gonial mitosis and meiosis

Special chromosomes limited to the germ line (=Ks) and exceptional genetic events such as elimination mitoses and a monopolar migration of the Ks in the last gonial mitosis are specific features of the complex chromosome cycle occurring in the chironomid Acricotopus lucidus. In the male, this unequal differential gonial mitosis results in a regular spermatocyte possessing all the Ks in addition to the somatic chromosomes (=Ss) and an aberrant spermatocyte containing only Ss. During evolution, the Ks have developed from the Ss and are composed of euchromatic S-homologous sections and heterochromatic segments. Less is known about the function and the transcriptional activity of the Ks. Specific post-translational histone modifications are known to be associated with transcriptionally active and inactive states of the chromatin. In an immunofluorescence study, the distribution of the following acetylated (ac), methylated (me) and phosphorylated (ph) amino acids in the histones H3 and H4 was analysed in Ks and Ss in male gonial mitoses and meiosis of A. lucidus, namely H3K18ac and H4K8ac, H3K4me3 and H3K9me3, H3S10ph, H3S28ph and H3T3ph. Ks and Ss clearly differ in the distribution of H3S28ph in gonial and meiotic metaphases. The H3S28ph mark covered the entire Ss, while the Ks showed this label only on their pericentromeric heterochromatin bands containing germ line-specific repetitive DNA sequences. A differential timing in the dephosphorylation of H3S10ph, H3S28ph and H3T3ph between Ks and Ss within the same cell was detected in the last gonial mitosis. The dephosphorylation occurred earlier in the Ks migrating first to the pole, than in the later equally segregating Ss. A programmed rapid histone deacetylation and dephosphorylation happened in the unseparated Ss of the aberrant spermatocyte at metaphase I in the connected primary spermatocyte, which correlated with the beginning of a permanent inactivation of these Ss in a metaphase-like condensed state. In meiosis, phosphorylated H3T3 could be detected only in metaphase II chromosomes at the inner centromeres of the attached sister chromatids. The H3T3ph labelling at this region was recently reported to be essential in mitosis for correct deposition of components of the chromosomal passenger complex and so for proper alignment, sister chromatid cohesion and segregation of chromosomes (Wang et al., Science 330:231-235, 2010; Curr Biol 21:1061-1069, 2011). Importantly, in spermatocytes, the euchromatic sections of the Ks were strongly acetylated at H3K18 and H4K8, and trimethylated at H3K4 during meiosis I and II, while the euchromatin of the meiotic Ss was hypoacetylated and hypomethylated at these sites. This result suggests a silencing of the Ss during spermatocyte meiosis. The high levels of active histone modifications detected in the euchromatic K sections support the idea that the Ks of A. lucidus are transcriptionally active in the germ line.

Ultrastructural identification of different subtypes of interstitial cells of Cajal in the chicken ileum

Ultrastructural characteristics of different subtypes of interstitial cells of Cajal (ICC) remain unclear in birds; however, birds have significant economical and scientific notability. Our aim was to describe and classify ICC in the chicken gut. The ileum of normal adult Three Yellow broiler chickens (n=10) were studied by transmission electron microscopy (TEM). The ICC were spindle- or stellate-shaped with ramified cell processes. They had numerous mitochondria, abundant intermediate filaments, fusiform nuclei (oval or indented), with a dense band of peripheral heterochromatin, and formed close contacts by true gap junctions with each other and with neighboring smooth muscle cells (SMC). The ICC were in close contact with enteric nerves, but true gap junctions were not found between them. A new subtype of ICC located in the lamina propria mucosae has been discovered. Some of the ICC showed typical features of SMC, including a basal lamina, caveolae, and dense bodies. Lacking intermediate filaments and caveolae distinguished them from the fibroblast-like cells showing well-developed secretory organelles, including coated vesicles and a patchy basal lamina. The ultrastructural features and distribution of ICC in chicken intestine is similar to mammals. They may play similar key regulatory roles in gastrointestinal motility. The new subtype of ICC discovered in the lamina propria mucosae may play a role in the regulation of secretion and absorption.

Trafficking and chromatin dynamics of holocarboxylase synthetase during development of Drosophila melanogaster

This work examines the cellular localization of holocarboxylase synthetase (HCS) and its association to chromatin during different stages of development of Drosophila melanogaster. While HCS is well known for its role in the attachment of biotin to biotin-dependent carboxylase, it also regulates the transcription of HCS and carboxylases genes by triggering a cGMP-dependent signal transduction cascade. Further, its presence in the nucleus of cells suggests additional regulatory roles, but the mechanism involved has remained elusive. In this study, we show in D. melanogaster that HCS migrates to the nucleus at the gastrulation stage. In polytene chromosomes, it is associated to heterochromatin bands where it co-localizes with histone 3 trimethylated at lysine 9 (H3K9met3) but not with the euchromatin mark histone 3 acetylated at lysine 9 (H3K9ac). Further, we demonstrate the association of HCS with the hsp70 promoter by immunofluorescence and chromatin immuno-precipitation (ChIP) of associated DNA sequences. We demonstrate the occupancy of HCS to the core promoter region of the transcriptionally inactive hsp70 gene. On heat-shock activation of the hsp70 promoter, HCS is displaced and the promoter region becomes enriched with the TFIIH subunits XPD and XPB and elongating RNA pol II, the latter also demonstrated using ChIP assays. We suggest that HCS may have a role in the repression of gene expression through a mechanism involving its trafficking to the nucleus and interaction with heterochromatic sites coincident with H3K9met3.

Cytogenetic characteristics of Microtus dogramacii (Mammalia: Rodentia) around Amasya, Turkey

The banding patterns of chromosomes of Microtus dogramacii, a recently described vole species endemic to Turkey, were studied. G-, C-, and Ag-NOR-banded patterns of this species are reported here for the first time. In this study, 2 karyotypical forms were determined. Each form had the same diploid chromosome numbers (2n = 48), but possessed different autosomal morphologies. For this reason, the samples collected from the research area were karyologically separated into 2 groups, cytotype-1 (NF = 50) and cytotype-2 (NF = 52). All chromosomes possessed centromeric/pericentromeric heterochromatin bands in both karyotypical forms. It was shown that the acrocentric chromosomes of pair 8 in cytotype-1 have been transformed into metacentric chromosomes in cytotype-2 through pericentric inversion. Variation in the number of active NORs was also observed, but the modal number of active NORs was 8. Due to the chromosomal variation found in M. dogramacii, the cytogenetic results presented in this study may represent a process of chromosomal speciation.

Molecular cytogenetic characterization of a new leaf rolling triticale

Leaf rolling occurs in some cereal genotypes in response to drought. We identified and made a phenotypic, cytological and physiological analysis of a leaf-rolling genotype (CMH83) of hexaploid triticale (X Triticosecale Wittmack) that exhibited reduced plant height, rolled and narrow leaves. Gliadin electrophoresis of seed protein showed that CMH83 was genetically stable. Sequential Giemsa-C-banding and genomic in situ hybridization showed that CMH83 contains 12 rye chromosomes; two pairs of these chromosomes have reduced telomeric heterochromatin bands. Tests of relative water content and water loss rate of leaves of CMH83 compared with those of wheat cultivars indicated that rapid water loss after drought stress in CMH83 is associated with the leaf rolling phenotypes. Leaf rolling in CMH83 was a dominant trait in our inheritance studies. Triticale line CMH83 could be used to study drought resistance mechanisms in triticale.

A description of karyotype of the giant liver fluke Fascioloides magna (Trematoda, Platyhelminthes) and a review of Fasciolidae cytogenetics

Abstract The study describes a karyotype of a common parasite of cervids, the giant liver fluke, Fascioloides magna (Trematoda, Platyhelminthes). The chromosome set of F. magna comprises 11 pairs of chromosomes, all classified as subtelocentric except for the submeta-metacentric pair No. 8 and the submetacentric pair No. 10 (2n = 22, n = 1sm + 1sm-m + 9st). The first longest pair is 4.65 μm long and the length decreases continuously to the 1.92 μm length of the last pair No. 11. No distinct secondary constriction has been observed in mitotic preparations. Fluorescent DAPI-staining reveals distinct heterochromatin bands on all 11 chromosome pairs in the centromeric regions; another DAPI-positive bands are localized at the end of the long arms of chromosomes No. 5 and the last less distinct signals appear interstitially on the long arms of the pair No. 6. Synchronous meiotic divisions of 8-spermatocyte groups have been observed during spermatogenesis, similarly with a development of spermatocytes in other trematodes. In the first two stages of heterotypic spermatocyte division, 11 bivalents (n = 11) are regularly observed, confirming the diploid number of 22 elements. Furthermore, the present analysis summarises and discusses available cytogenetic data on Fasciolidae flukes suitable for future studies on taxonomy or phylogenetic interrelationships within the family.

Possible ancient origin of heterochromatic JNK sequences in chromosomes 2R ofSecale vavilovii Grossh

Employing FISH analysis as well as BLAST and CUSTAL W (1.82) programs, we investigated types of DNA nucleotide sequences building an additional heterochromatic band in 2R chromosomes of 3 lines of Secale vavilovii Grossh. The probes used in FISH analysis were designed based on the reverse transcriptase sequence of Ty1-copia and Ty3-gypsy retrotransposons and the 5S rRNA gene sequence. No hybridization signals from the reverse transcriptase probes were observed in the chromosome region where the additional band occurs. On the other hand, signals were observed after hybridization with the 5S rDNA probe, clearly suggesting the presence of that type of sequences in the analyzed heterochromatin band. Using BLAST and CUSTAL W programs, we revealed high similarity of the JNK1 sequence to the 5S rRNA gene from Hordeum chilense (HCH1016, HCH1018, 88%) and to a fragment of the 5S rRNA sequence of H. marinum (HMAR003, 97%). In addition, the same fragment of JNK1 was shown to be very similar to the part of the Angela retrotransposon (92%) as well as to the SNAC 426K20-1 transposon (89%) belonging to CACTA family, both from Triticum monococcum, and to Zingeria biebersteiniana pericentromeric sequences (78%). The similarity of JNK1 to those sequences may be accidental or the JNK1 may represent an ancient mobile genetic element that caught the 5S rRNA sequence. During the evolution those sequences might have been accumulated in the particular region on the 2R chromosome. Our results suggest that the additional heterochromatin band in chromosomes 2R of S. vavilovii is a collection of defective genes and/or mobile genetic elements.

Chromosomal localization and evolution of satellite DNAs and heterochromatin in grasses (Poaceae), especially tribe Aveneae

The physical mapping of three abundant tandemly repeated DNA sequences, CON1, CON2, and COM2, and the distributional pattern of AT- and GC-rich regions in the chromosomes of 32 species of the grass family Poaceae have been established by means of fluorescence in situ hybridization and fluorochrome banding with chromomycin and DAPI. Additionally, locations of 5S, 35S rDNA, and the C-banding pattern were examined. All satellite DNAs (satDNA) tested are situated predominantly subtelomerically in the chromosomes, but occur also colocalized with 35S and 5S ribosomal DNAs (rDNA). Especially, CON2 is most often colocalized with the 5S rDNA, but is evolutionarily not derived from it. Subtelomeric heterochromatin bands are frequently, but not always correlated with satDNA bands. Moreover, the DAPI- or rarely chromomycin-positive stainability of heterochromatin is not caused by these satDNAs as revealed by their sequence organization, showing too few clusters of AT or GC base pairs as required for binding of the fluorochromes. The occurrence of satDNAs is not correlated with that of other components of the heterochromatin. Proportions of satDNAs and other sequences of the heterochromatin relative to the entire genome appear subjected to a much faster evolutionary change than the rather stable proportions of the rDNAs. Heteromorphism in banding patterns found in many species is related in most instances with breeding system and life form. The independent evolution and amplification of different satDNAs is discussed in relation to molecular phylogenetic data. The value and limitations of satDNA data in addressing systematic questions in grasses is exemplified for several grass subfamilies and tribes.