Biomedical subjects

I Nanda

Publications and source records attributed to I Nanda.

68 records · Page 4Linked to original sources

PubMed1992

Early stages of sex chromosome differentiation in fish as analysed by simple repetitive DNA sequences.

Animal sex chromosome evolution has started on different occasions with a homologous pair of autosomes leading to morphologically differentiated gonosomes. In contrast to other vertebrate classes, among fishes cytologically demonstrable sex chromosomes are rare. In reptiles, certain motifs of simple tandemly repeated DNA sequences like (gata)n/(gaca)m are associated with the constitutive heterochromatin of sex chromosomes. In this study a panel of simple repetitive sequence probes was hybridized to restriction enzyme digested genomic DNA of poeciliid fishes. Apparent male heterogamety previously established by genetic experiments in Poecilia reticulata (guppy) was correlated with male-specific hybridization using the (GACA)4 probe. The (GATA)4 oligonucleotide identifies certain male guppies by a Y chromosomal polymorphism in the outbred population. In contrast none of the genetically defined heterogametic situations in Xiphophorus could be verified consistently using the collection of simple repetitive sequence probes. Only individuals from particular populations produced sex-specific patterns of hybridization with (GATA)4. Additional poeciliid species (P. sphenops, P. velifera) harbour different sex-specifically organized simple repeat motifs. The observed sex-specific hybridization patterns were substantiated by banding analyses of the karyotypes and by in situ hybridization using the (GACA)4 probe.

Animals↗

PubMed1991

On the stability of dispensable constituents of the eukaryotic genome: stability of coding sequences versus truly hypervariable sequences in a clonal vertebrate, the amazon molly, Poecilia formosa.

In clonal unisexual vertebrates, the genes specifying the males become dispensable. To study the fate of such genes the gynogenetic all-female fish Poecilia formosa was treated with androgens. Phenotypic males were obtained that exhibited the complete set of male characteristics of closely related gonochoristic species, including body proportions, pigmentation, the extremely complex insemination apparatus of poeciliid fish, sexual behavior, and spermatogenesis. The apparent stability of such genic structures, including those involved in androgen regulation, is contrasted by high instability of noncoding sequences. Frequent mutations, their clonal transmission, and at least two truly hypervariable loci leading to individual differences between these otherwise clonal organisms were detected by DNA fingerprinting. These observations substantiate the concept that also in "ameiotic" vertebrates certain compartments of the genome are more prone to mutational alterations than others.

Journal Article↗

PubMed1990

Heterogeneities in the distribution of (GACA)n simple repeats in the karyotypes of primates and mouse.

Tandemly organized simple repetitive sequences are widespread in all eukaryotes. The organization of the simple tetrameric (GACA)n sequences at chromosomal loci has been investigated using in situ hybridization with chemically pure oligonucleotide probes. Both biotin- and digoxigenin-attached (GACA)4 probes reveal specific hybridization signals over the short arms of all acrocentric autosomes in man. In the other examined primates the NOR-bearing autosomes could be detected by in situ hybridization with (GACA)4, and a major concentration of the GACA simple repeats could be observed on the Y chromosome in the gibbon and mouse: the hybridization site in the gibbon Y chromosome coincides particularly with the silver-stainable NOR. In the past, accumulations of (GACA)n sequences were demonstrated mainly on vertebrate sex chromosomes. Therefore, the organization of GACA simple sequences is discussed in the context of their evolutionary potential accumulation and the possible linkage with the primate rDNA loci.

Animals↗

PubMed1990

Organization of DYZ2 repetitive DNA on the human Y chromosome.

The location of the human Y-specific repetitive DNA sequence DYZ2 with HaeIII cleavage sites spaced at 2.1 kb was reexamined. Previous reports had mapped the 2000 DYZ2 copies to the very distal end of the heterochromatic Yq12 band. In the present study, a cloned DYZ2 fragment (pHY2.1) was used for Southern and slot blot analyses of male DNA as well as for nonradioactive in situ hybridization to chromosomes. DNA and metaphase preparations from 79 individuals with polymorphic or aberrant Y chromosomes were examined. DYZ2 repeats are not confined to the distal tip of Yq12, but extend through the entire heterochromatin of Yq12. In the naturally occurring length polymorphisms of Yq, the amount of DYZ2 sequence varies in proportion to the measured sizes of band Yq12. Explanations are presented for the fact that previous studies restricted the location of DYZ2 to the telomeric end of Yq12.

Blotting, Southern↗

PubMed1989

Digoxigenated oligonucleotide probes specific for simple repeats in DNA fingerprinting and hybridization in situ.

A fast, reproducible and non-hazardous technique for non-isotopic DNA fingerprinting is presented. The method is based on digoxigenated oligonucleotides, which are specific for simple repetitive DNA sequences. The use of digoxigenin/anti-digoxigenin detection avoids many drawbacks inherent in e.g. the biotin/streptavidin system which often causes a poor signal-to-background ratio. Synthesis and purification of digoxigenated oligonucleotides and their use in filter hybridization are described in detail. Hybridization patterns obtained with four different radioactively labeled oligonucleotides have been compared with those of the respective digoxigenated probes. When slightly less stringent hybridization conditions are applied for digoxigenated oligonucleotides than for those labeled with 32P, the signal intensities are satisfying but additional minor bands occur as a result of the reduced stringency. With one explainable exception, these bands increase the information content of the fingerprint. In addition, hybridization of the digoxigenated (CAC)5 probe has been performed in situ with human metaphase chromosomes. The hybridization patterns in many mitoses resemble R-bands.

DNA↗

PubMed1988

Simple GATCA repeats characterize the X chromosomal heterochromatin of Microtus agrestis, European field vole (Rodentia, Cricetidae).

The sex chromosomes of Microtus agrestis are extremely large due to the accumulation of constitutive heterochromatin. We have identified two prominent satellite bands of 2.0 and 2.8 kb in length after HaeIII and HinfI restriction enzyme digestion of genomic DNA, respectively. These satellites are located on the heterochromatic long arm of the X chromosome as shown using Microtus x mouse somatic cell hybrids. By in-gel hybridization with oligonucleotide probes, the organization of the two satellites was studied: among the many copies of the simple tandem tetranucleotide repeat GATA are interspersed rare single GACA tetramers. One of the satellites also harbours related GGAT simple tandem repeats. In situ hybridizations with plasmid-carried or oligonucleotide GATCA probes show clustered silver grains on the long and short arm of the X chromosome. Interspersion of differently organized (GATA)n elements is also demonstrable in the autosomal complement and on the Y chromosome. These results are discussed in the context of the evolution of vertebrate sex chromosomes in relation to heterochromatin and simple repetitive DNA sequences.

Animals↗

PubMed1988

DNase I nick translation in situ on meiotic chromosomes of the mouse, Mus musculus.

DNase-I-sensitive sites have been located on the meiotic chromosomes of the mouse, Mus musculus, by the in situ DNase I nick-translation method. We find that: (1) of all the cell types studied, pachytene nuclei are the most sensitive to DNase I; (2) in diplotene the nicks occur preferentially in the vicinity of chiasmata; (3) the sex chromosomes are also sensitive to the enzyme despite their transcriptional quiescence; and (4) in the sex bivalent the nicks are primarily observed in the putative region of recombination. We conclude that, in addition to discriminating between the transcriptionally active and inactive states of chromatin, DNase I identifies recombination-specific chromatin changes in meiotic prophase.

Animals↗

PubMed1987

Mammalian sex chromosomes. II. Pairing and alignment of the X and Y chromosomes of the pygmy mouse, Mus dunni.

In the pygmy mouse, Mus dunni, the entire Y chromosome and the short arm of the X and distal region of its long arm are constitutively heterochromatic. Different banding studies on somatic chromosomes revealed the GC nature of the distally located heterochromatin of the long arms of both the X and Y chromosomes. The short arm of the X and the rest of the Y are AT-rich. During meiosis, the long arms of the X and Y paired extensively, sometimes more than half of the Y pairing with the X. This observation is in disagreement with that of Pathak and Hsu (1976) who reported end-to-end pairing between the long arm of the X and the short arm of the Y. The orientation observed by us is favourable to a successful meiotic recombination but whether this takes place remains to be demonstrated.

Animals↗

PubMed1986

Mammalian sex chromosomes. I. Cytological changes in the chiasmatic sex chromosomes of the male musk shrew, Suncus murinus.

The X and Y chromosomes of the musk shrew are the two largest in the complement and they regularly form a single chiasma during meiosis. This chiasma is located in the short arms of the X and Y, both of which show partial C-banding at meiosis. The in vitro incorporation of 5-bromodeoxyuridine/tritiated thymidine during late S reveals that the non-C-band region of the Y finishes replication later than the C-band positive heterochromatin. During meiosis, the sex bivalent opens out early in pachytene to reveal a single chiasma which persists until late metaphase-I. In surface-spread, silver-stained meiocytes, the sex bivalent morphology changes from a phase of extensive pairing to one which includes a visible chiasma through a brief diffuse stage. Observations on C-banded meiocytes show a shift in the sex pair from a C-band positive to a negative state as compared to their corresponding somatic pattern. Comparable changes are also observed in the sex bivalents of other mammals which undergo a chiasmatic exchange. This suggests that in addition to pairing homology, an alteration in the chromatin configuration may be necessary for crossing over to occur between the sex chromosomes.

Animals↗

PubMed1983

A simple method of staining the synaptonemal complex with Coomassie brilliant blue for light microscopy.

A simple technique for staining synaptonemal complexes with Coomassie brilliant blue for light microscopy has been described. The testis cells were exposed to prolonged hypotonic treatment and dropped on Formvar-coated slides. Following fixation with paraformaldehyde the slides were stained with Coomassie brilliant blue for 15 min to 1 h at room temperature and rinsed in distilled water. For its simplicity and rapidity this technique may serve as an effective alternative to silver staining for light microscopic observation of synaptonemal complexes.

Animals↗

PubMed1982

Identification and patterns of synapsis of the autosomally translocated Y-chromosome of the Indian mongoose, Herpestes auropunctatus (Hodgson).

The multiple sex chromosome system, X1X2Y male/X1X1X2X2 female, in the small Indian mongoose, Herpestes auropunctatus, results from a translocation of a part of Y chromosome to an autosome. It is not possible to distinguish the autosome which harbours the Y chromosome element in the somatic complement. By employing the surface-spreading technique to prophase I meiocytes we have identified the region to which the Y chromosome has been translocated as the short arm of chromosome 9 which is a subtelocentric chromosome. This Y chromosome component lacks heterochromatin and no sex vesicle is organised during meiotic prophase. This suggests to us that Y heterochromatin in mammals may be required for the production of a sex vesicle.

Animals↗

PubMed1981

Cytological similarity between the heterochromatin of the large x and y chromosomes of the soft-furred field rat, Millardia meltada (family: muridae).

Patterns of DNA replication, fluorescence, and meiotic pairing have been studied in the composite X and Y chromosomes of a rodent, the soft-furred field rat, Millardia meltada. The heterochromatin of both the chromosomes replicated during late S and fluoresces brightly with Netropsin-Olivomycin. The fluorescence with Actinomycin D-Hoechst is dull, suggesting that the heterochromatin of both the X and the Y is relatively GC-rich. When surface-spread testis cells are analyzed after silver staining considerable portions of the X and Y exhibit synapsis. On the basis of this study it appears that the heterochromatin of the X chromosome of M. meltada is substantially similar to that of the Y chromosome.

Animals↗

PubMedDate not supplied

Chromosomal organization of simple repeated DNA sequences used for DNA fingerprinting.

Stretches of short, simple DNA sequences are widespread in all eukaryote genomes studied so far. Simple sequences are thought to undergo frequent expansion and deletion due to intrinsic genomic mechanisms. Some of the simple sequences were used successfully to detect hypervariable loci in various genomes. Hybridization experiments using synthetic probes not only revealed the informative simple repeats suitable for DNA fingerprinting in a particular species, but also reflected the wide range of distribution of the simple sequences among eukaryotes. The organization of these simple repetitive sequences at the chromosomal loci was investigated using in situ hybridization with chemically synthesized, pure oligonucleotide probes. Both biotin- and digoxigenin-attached probes detected specific chromosomal sites that are enriched in the respective simple-repeat blocks. Depending on the organism and probe used, accumulation of simple DNA sequences at individual or multiple sites on the chromosomes of different vertebrates could be demonstrated. The simple repetitive DNA sequences are located in different chromosomal regions (e.g., heterochromatin on the sex chromosomes, nucleolus organizer regions, and R-band sites), which are constrained considerably during evolution.

Amphibians↗

PubMedDate not supplied

An extraordinarily low diploid chromosome number in the reptile Gonatodes taniae (Squamata, Gekkonidae).

Mitotic and meiotic chromosomes of the gekkonid lizard Gonatodes tanieae from Venezuela were analyzed with conventional staining, differential banding techniques, and in situ hybridization using a synthetic telomeric DNA probe. The karyotype of this species is distinguished by the extraordinarily reduced diploid chromosome number of 2n = 16, which is the lowest value known for reptiles. In contrast to most other reptilian species, G. taniae has exclusively bi-armed (meta- and submetacentric) macrochromosomes and no microchromosomes. Examination of the mitotic chromosomes with AT and GC base pair-specific fluorochromes shows the absence of multiple banding patterns in euchromatic regions. The n = 8 diakinetic bivalents of male meiosis present terminal, subterminal, interstitial, and pericentromeric chiasmata. Comparison of the karyotypes of G. taniae and G. vittatus (also collected in Venezuela), and with those of three other Gonatodes species, indicates that the exceptional diploid number of 2n = 16 is the result of repeated centric fusions. In addition to the telomeres, all pericentromeric regions of the G. taniae chromosomes contain considerable amounts of the (TTAGGG)n telomeric sequence. These are probably not only relics of the centric fusions, but also a major component of the highly repetitive DNA in the C band-positive heterochromatin.

Animals↗