Large Amount Of Heterochromatin Research Articles

Y chromosome-related genetic diseases

As a male-specific chromosome, the structure of Y chromosome is complex and lacks of recombination, with numerous repeating, amplifying and palindromic sequences. The research of Y chromosome is difficult and slow since there are few protein coding genes and a large amount of heterochromatin which has caused extreme difficulty for sequencing. In recent years, an increasing number of studies have been focused on the Y chromosome. With the completion of the sequencing of human Y chromosome, the rapid development of sequencing technology, and the composition of DNA sequences in human Y chromosomes and the determination of gene content. This paper has summarized the structural composition and genes function of human Y chromosome, as well as the related hereditary diseases, with an aim to provide reference for Y chromosome-related genetic research.

Structure and function of the male ventral organ in Onychiuroides granulosus (Collembola: Onychiuridae)

On the ventral tube of males of Onychiuroides granulosus (Stach, 1934) there is a male ventral organ, which consists of two groups of four setae that are thickened, slightly flattened and bent. All setae of the male ventral organ are inserted in a richly sculptured cuticle. At the base of each seta there are a few large cells (basal cells) that have large irregular nuclei that contain a large amount of heterochromatin. In the cytoplasm of the basal cells there are numerous mitochondria, ribosomes and a rich system of endoplasmic reticulum. The plasma membrane of the basal cells forms richly folded, deep invaginations, filled with a dense material, which also occurs in particular setae and on their surface. The present study indicates that the male ventral organ is secretory and does not confirm its previously suggested sensory function.

Chromosome caracterization of Melipona scutellaris (Hymenoptera, Apidae, Meliponini) based on repetitive DNAs

Repetitive DNAs constitute a significant part of the genomes and are used as cytogenetic markers for the understanding of chromosome evolution. Bees of the genus Melipona presents conserved chromosome number but high variability concerning heterochromatin distribution, dividing the genus into two groups: (i) species with low quantity of heterochromatin and (ii) species with high amount of heterochromatin. Here aiming the understanding of repetitive DNAs chromosomal organization in Melipona we mapped through fluorescence in situ hybridization (FISH) some repetitive DNAs in M. scutellaris. For this, FISH were performed with the amplification products of the 18S rDNA, U2 snDNA and DOP-PCR, as well as the product of the C0t fraction and different microsatellites. The mitotic chromosomes used in FISH were obtained by squashing the brain ganglia, and in this material, being performed also the C-band and CMA/DAPI. The distribution of the C0t fraction in other species of Melipona was verified with membrane hybridization. Chromosome number of n = 9 and 2n = 18 (male and female, respectively) was confirmed and a large amount of heterochromatin was observed along the chromosomes, except at the terminals that were characterized as euchromatic and only rich in different microsatellites. The heterochromatic regions were observed with richness in A + T and C + G. The FISH experiments showed signals from the 18S rDNA and U2 snDNA probes on distinct chromosomes. This demonstrates that these multigenic families followed different evolutionary paths in the chromosome evolution of the species. The DOP-PCR and C0t fraction showed signs of hybridization in the heterochromatic regions, and the C0t fraction of M. scutellaris was also observed in the genomes of M. rufiventris, M. rufiventris rufiventris and M. seminigra, evidencing the dispersion of similar repetitive elements in genomes of these three species. Thus, it was possible to characterize the karyotype of M. scutellaris with different cytogenetic markers. In addition, the results with membrane hybridization reinforce the hypothesis of the repetitive DNA sharing among nearby species, suggesting that there are different repetitive elements present in the genome of the genus Melipona.

Cytogenetic and phylogenetic studies of diploid and polyploid members of Tribe Anemoninae (Ranunculaceae)

The ancestry, phylogenetic differentiation and systematic classification of the worldwide-distributed genus Anemone have been debated for many years. In this paper 11 Anemone, three Pulsatilla species and Hepatica nobilis were subjected to detailed karyotype analysis with the aim of obtaining new cytogenetic data that will contribute to karyotype evolutionary studies of the tribe Anemoninae. The results are interpreted in a phylogenetic context, established from the intergenic nontranscribed spacer (NTS) of 5S rDNA and internal transcribed spacer (ITS) of 35S rDNA. One to three 35S and one to three 5S rDNA loci are present in diploid and polyploid taxa. The 35S rDNA loci are located terminally on the short arm of acrocentric chromosomes, while for 5S rDNA there is no preferential chromosomal position as it exhibits terminal, subterminal, interstitial or pericentromeric positions, and is located either on acrocentric or metacentric chromosomes. The karyotype of hexaploid A. baldensis (2n = 6x = 48) is presented for the first time, and A. sylvestris is proposed as one of its putative parental species. Chromosome fusion/translocation is proposed as the key mechanism involved in reduction of the basic chromosome number from 8 in the Anemone subgenus to 7 in the Anemonidium subgenus. The cytogenetic data obtained are mainly supported by ITS and NTS phylogeny. Diversification of the genus Anemone was accompanied by a large reduction of heterochromatin, from the Mediterranean anemones that have large amounts of heterochromatin to the New World anemones without any detectable heterochromatic blocks.

Cytogenetic characterization of Aloysia virgata Ruiz and Pavan (Verbenaceae)

Since previous cytogenetic reports of Aloysia have only described the meiotic behavior and chromosomal number of some species, the aim of this work was to provide detailed cytogenetic description of Aloysia virgata that would contribute to the understanding of the taxonomical organization of the Verbenaceae. Aloysia virgata had a karyotype with 2n = 36 metacentric chromosomes, all with similar size. The large amount of heterochromatin seen after Giemsa staining was confirmed by C-banding. Four nucleolar organizer regions (NORs) were detected with an rDNA 45S probe in two homologous pairs and two sites of 5S rDNA located on one chromosomal pair were detected by fluorescence in situ hybridization. The interphase nucleus was classified as semi-reticulate. Meiotic analysis showed a normal chromosomal behavior, with 18 bivalents in some parts of prophase I and in metaphase I. The number of chromosomes, NORs and 5S rDNA segments did not exclude a possible polyploid origin.

C-bands on chromosomes of 32 beetle species (Coleoptera: Elateridae, Cantharidae, Oedemeridae, Cerambycidae, Anthicidae, Chrysomelidae, Attelabidae and Curculionidae).

C-banding patterns of 32 beetle species from the families Elateridae, Cantharidae, Oedemeridae, Cerambycidae, Anthicidae, Chrysomelidae, Attelabidae and Curculionidae were studied using the C-banding technique. Mitotic and meiotic chromosomes were previously described for 14 species. From among 18 species that had never been cytogenetically studied, we determined the diploid and haploid chromosome numbers and the sex determination system for 12 beetles. The karyotype for 6 species is not described because of a lack of mitotic and meiotic metaphases. Results confirm that most of the beetle species possess a small amount of heterochromatin and C-positive segments are weakly visible in pachytene stages and weakly or imperceptible in mitotic and meiotic metaphases. In some species with a large amount of heterochromatin, C-bands were observed in the centromeric region in all autosomes and the X chromosome. The Y chromosome does not show C-bands with the exception of Oedemera viridis in which it possesses a small band of heterochromatin.

Karyotypic characterization of Prochilodus mariae, Semaprochilodus kneri and S. laticeps(Teleostei: Prochilodontidae) from Caicara del Orinoco, Venezuela

Fish of the family Prochilodontidae are considered one of the most important components of commercial and subsistence fishery in freshwater environments in South America. This family consists of 21 species and three genera. In the present study, the karyotypes of Prochilodus mariae, Semaprochilodus kneri, and S. laticeps from Caicara del Orinoco, Bolivar State, Venezuela were studied. The species P. mariae, S. kneri and S. laticeps exhibited 2n=54 chromosomes (40 metacentric and 14 submetacentric), a single chromosome pair with nucleolus organizer regions, and a large amount of heterochromatin found at centromeric and pericentromeric positions in almost all chromosomes. The P. mariae specimens studied displayed 0 to 3 supernumerary microchromosomes. The data obtained here confirm the conservative nature of the chromosome number and morphology of Prochilodontidae and reinforce the hypothesis that small structural chromosome rearrangements were the main cause of the karyotypic diversification seen in this group.

An uncommon condition for a sex chromosome system in Characidae fish. Distribution and differentiation of the ZZ/ZW system in Triportheus.

Triportheus is a neotropical freshwater Characidae fish that has a well-differentiated ZZ/ZW sex chromosome system. The W chromosome of this genus contains a large amount of heterochromatin and is smaller than the Z chromosome. This contrasts with other ZW fish systems where the W chromosome is larger in size due to increased heterochromatin. All species of Triportheus that have been studied cytologically (about 50% of the known species for this genus, from some of the major South American hydrographic basins) share this sex chromosome system, indicating a probable synapomorphic condition not present in other genera of the large Characidae family. However, while the Z chromosome appears to be largely conserved, the W chromosome shows a differential evolution with morphological differentiations not only among species, but also among populations from the same hydrographic basin, and with some species presenting a greater homology between the W and the Z chromosomes than others.

Exaggerated precocious centromere separation in cells of a human breast cancer line treated with a green tea extract.

In a breast cancer cell line, MDA-MB-468, established in our laboratory, an average of 3% of the mitotic cells exhibited a phenomenon known as centromere splaying, which is a characteristic feature of cells of patients with Roberts syndrome. However, centromere splaying in cells of Roberts syndrome patients is limited to i) the centromere region and ii) chromosomes with large amounts of heterochromatin. When the breast cancer cells were treated with an extract of green tea GTE-TP91, up to 45% of the metaphases were observed to exhibit this behavior; and the precocious centromere separation was highly exaggerated, affecting all chromosomes in such metaphases. Apparently, as the sister centromeres continued to pull apart, they carried the chromatids with them, except for the telomere regions, giving a ring-like configuration. Eventually, the sister chromatids became completely separated. Whether this bizarre phenomenon was induced by the polyphenols contained in this green tea extract GTE-TP91 is not known, but this phenomenon, upon further investigation, may throw some light on chromosomal proteins, centromere behavior, telomere behavior and related questions.

The chromosomes ofAzima tetracantha (Salvadoraceae)

Azima tetracantha has an asymmetrical karyotype with large chromosomes and a large amount of heterochromatin. The haploid number (n = 11) may represent the base number of the family. However, a possible secondary origin of this base number is also considered.

C-banding analysis of gamma-radiation-induced chromosomal interchanges in rye

Gamma-radiation-induced chromosomal interchanges in two inbred lines of rye were analyzed by using the C-banding technique. Neither the doses of radiation nor the time elapsed between radiation and cytological observation influenced the contribution of individual chromosomes to the observed interchanges. Dicentric are more frequent than monocentric interchanges. Neither the individual chromosome contribution to interchanges nor the chromosome combinations fit a random distribution. Chromosomes 6(5R), 4(4R) and 7(1R) of the inbred line Pool and 6(5R), 5(6R) and 4(4R) of line Riodeva, which are carriers of large amounts of heterochromatin, are much more frequently involved in interchanges than expected. Likewise, they are involved in the most frequent combinations observed (6-4, 6-7, 4-5, 4-7 and 6-3 (2R) in line Pool and 6-5, 6-4, 4-5 and 6-7 in line Riodeva). The role of C-heterochromatin in radiation-induced chromosomal interchanges is discussed.

Characterisation of a very complex constitutive heterochromatin in two Gerbillus species (Rodentia).

A large amount of heterochromatin is observed in two species of the genus Gerbillus, G. nigeriae and G. hesperinus. The C-band material represents about one-half of the total karyotype length in the former species, and about one-third in the latter. Several banding techniques and various 5-bromodeoxyuridine (BrdU) treatments were used to characterise these heterochromatic segments. After applying the R-banding technique, three different staining responses of the heterochromatin can be distinguished. In G. nigeriae, strongly stained segments (R-band positive) appear in most chromosomes and, in particular, constitute the short arms of all the larger chromosomes. Palely staining heterochromatic segments (R-band negative) are less abundant in G. nigeriae but predominate in G. hesperinus. In addition, in both species an intermediate staining of heterochromatin is observed near the centromere or in the heterochromatic short arms of some acrocentric and small submetacentric chromosomes. Very short BrdU treatment during the end of the last cell cycle results in asymmetrical staining of chromatids in heterochromatic segments after applying the acridine orange or FPG (fluorescence plus Giemsa) technique. The alternating location of strongly staining segments in one or the other chromatid simulates sister chromatid exchanges ("pseudo-SCE"). This pattern persists after longer BrdU treatment during different stages of the last cell cycle and is independent of the R-staining properties of the heterochromatin. The lateral asymmetric appearance of the large heterochromatic segments in Gerbillus is interpreted as reflecting an uneven distribution of adenine and thymidine between the two strands of DNA.

Regulation of ferritin mRNA: a possible gene-sparing phenomenon. Induction of ferritin synthesis by iron in liver as well as red cells combines high translational efficiency with increased utilization of preformed ferritin mRNA.

Control of ferritin synthesis by iron at the level of transcription is potentially hazardous to DNA because of the iron-catalyzed degradation of DNA. The induction of ferritin synthesis in reticulocytes of embryos (bullfrog tadpoles) occurs by two types of translational control i.e. increased availability of stored ferritin mRNA, in response to iron, coupled with a high translational efficiency. Since erythroid cell nuclei have large amounts of heterochromatin and may be relatively inactive genetically, the translational control of ferritin by iron observed in red cells was studied in other tissue by isolating poly (A+) RNA from tadpole liver and analyzing protein synthesis in vitro. Liver ferritin mRNA directed the synthesis of 7.0% of the protein in a wheat germ system, compared to 1.2% in vivo, suggesting that tadpole liver contained a large amount of stored ferritin mRNA. At levels of poly (A+) RNA which were saturating for total protein synthesis, ferritin synthesis was still linearly dependent upon RNA concentration, indicating a high efficiency of translation of ferritin mRNA. The results are analogous to those previously observed in red cells and confirm the storage of ferritin mRNA deduced from studies of the polysomal and nonpolysomal distribution of the mRNA in rat liver. The results indicate that the increased availability for translation of stored ferritin mRNA, in response to iron, and the high translational efficiency of ferritin mRNA are a general characteristic of ferritin synthesis rather than a specific feature of red cell maturation. This novel form of regulation of ferritin gene expression can be attributed to a need to protect DNA from degradation by iron and oxygen. The normal barrier between DNA and iron is apparently breached by the iron-oxygen complex of the drug bleomycin, an antitumor agent thought to act in vivo by iron-catalyzed cleavage of DNA.

746 A DE NOVO Y/A TRANSLOCATION WITH XO MOSAICISM IN A VIETNAMESE INFANT

A two-day old Vietnamese infant with ambiguous genitalia was referred to us for cytogenetic evaluation. He was the 2680 gram product of a full term pregnancy to a 20 year old mother. There was no family history of usage of drugs or birth control pills, or congenital anomalies. Physical findings were normal except that the genitourinary examination revealed a 3 cm long phallus with bifid scrotum, hypospadias, bilateral palpable gonads, normal kidneys, and midline ovoid structure consistent with an infantile uterus. There was no physical evidence of a vagina. Blood chromosome analysis by G-banding revealed two cell populations: 48 percent with 45,XO and 52 percent with 46,X,t(Y;Y) (p11;q12). The abnormal chromosome resembled a C-group chromosome in conventionally stained cells since the Y chromosome in Oriental populations normally has a large amount of heterochromatin. The heterochromatic segment involved in the translocation was confirmed by Q- and C-banding. The father's karyotype was normal, and the centromeric index of his Y chromosome was used to confirm our findings. The predominance of testicular tissue is due to the presence of complete euchromatic segments of the Y chromosome while the ambiguity of the genitalia may have resulted from the XO mosaicism.

Chromosomes and DNA of Mus. The behavior of constitutive heterochromatin in spermatogenesis of M. dunni.

Using C-banded preparations of Mus dunni it is possible to study the behavior of constitutive heterochromatin in early stages of meiotic prophase. The X and the Y chromosomes, both of which contain a large amount of heterochromatin, lie apart in leptotene but move toward each other during zygotene. They then form the sex vesicle at late zygotene. In autosomes zygotene pairing appears to start from the telomeric ends. The centromere of the Y chromosome associates end-to-end with the terminal end of the long arm of the X chromosome. The autosomal heterochromatic short arms show forked morphology in certain bivalents at pachytene, suggesting probable incomplete synapsis.

Location, structure and behaviour of C-heterochromatin during meiosis in Dichroplus silveiraguidoi (Acrididae-Orthoptera).

The constitutive heterochromatin of Dichroplus silveiraguidoi, a species which shows an exceptionally low chromosome number (2n=8), was studied at meiosis with a staining technique on normal and hypotonically treated specimens. The results showed: 1) an unusual behaviour of the heterochromatic blocks located in the so-called synaptic region of the sex bivalent (Neo Y-Neo X), which remains paired from early prophase through metaphase I; 2) in normal or in hypotonically treated cells a heterogeneous configuration of the C-heterochromatic blocks was observed. This configuration is characterized by the existence of small positive granules interconnected by euchromatic filaments and is enhanced by treatment with a low ionic strength solution; 3) A weakly positive stained (intermediate) material was demonstrated in the Neo X chromosome; 4) A large amount of heterochromatin is distributed in the form of granular material along the length of the autosomes and as telomeric and centromeric blocks in all chromosomes. The possible evolutionary mechanisms involved and the significance of the C-band heterochromatin demonstrated in this species are discussed.

Ultrastructure of the hypodermis during cuticle formation in the third molt of the nematode Nippostrongylus brasiliensis.

The fine structure of the hypodermis of Nippostrongylus brasiliensis, a parasitic nematode of the rat, was studied in free-living third-stage filariform (infective) larvae, and in parasitic forms undergoing the third molt. In filariform larvae the hypodermis displayed a comparatively poorly developed RER, and few Golgi complexes, mitochondria, and vesicles. Nuclei contained large amounts of heterochromatin and no nucleoli. After worms reached the lungs and the third molt began, the RER, Golgi complexes, mitochondria, multivesicular bodies, and coated vesicles greatly increased in amounts. Nuclei displayed less heterochromatin and contained prominent nucleoli. These morphological changes were associated with transition from the free-living to the parasitic mode in life. The results were correlated with the fact that the hypodermis in N. brasiliensis is actively synthesizing culticular collagen during the third molt.