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I Nardi

Publications and source records attributed to I Nardi.

At least 37 records · Page 2Linked to original sources
PubMed1993

Identification of an amphibian oocyte nuclear protein as a candidate for a role in embryonic DNA replication.

Monoclonal antibody B24/3 recognizes a nuclear protein of 104 kD in germinal vesicles of newt oocytes. Immunohistostaining of oocytes at different stages of growth shows an accumulation of B24 protein throughout oogenesis. During development B24 protein is located inside embryonic cell nuclei from the onset of cleavage onwards. It gradually decreases from gastrulation and disappears at the tailbud stage. The NvB24 17.1 clone was isolated from an ovary expression library of the newt Notophthalmus viridescens and then sequenced: the open reading frame is capable of encoding a polypeptide of 744 amino acids. Northern blot experiments have shown that the 17.1 clone recognizes a single transcript of about 3 Kb in the ovary. In situ hybridization experiments showed that B24 mRNA transcription starts from previtellogenic oocytes, and is followed by the appearance and gradual accumulation of B24 protein in germinal vesicles of medium and large size oocytes. Keeping in mind the sequence similarity shown by the B24 protein to the mouse P1 protein as well as to the budding yeast Mcm3 and fission yeast cdc21 proteins, B24 protein can be speculated to play a role in the events of DNA replication during early amphibian embryogenesis. As B24 antigen is located in the sphere organelles both inserted on the lampbrush chromosomes and free in the oocyte nucleoplasm, an additional possible role of B24 protein could be related to assembling and/or storing snRNPs during oogenesis.

Amino Acid Sequence↗
PubMed1991

A centromeric satellite DNA in the European plethodontid salamanders (Amphibia, Urodela).

A highly repeated satellite DNA (Hy500) located in the centromeric heterochromatin of the European plethodontid salamander Speleomantes (formerly Hydromantes) was studied. The Hy500 family represents about 1% of the Speleomantes supramontis genome and has a major repeating unit of about 500 base pairs, which may have evolved from the progressive amplification of shorter sequences. This centromeric satellite is conserved in all the Speleomantes species, which nevertheless show distinct patterns of chromosomal distribution, which are of relevance as to their phylogenetic relationships.

Animals↗
PubMed1988

Extra-ribosomal spacer sequences in Triturus.

We show that, in Triturus vulgaris meridionalis, sequences homologous to the rDNA "non-transcribed" spacer (NTS) are clustered at chromosomal loci where they are not associated with 18 S or 28 S rDNA genes: these sequences are referred to as the extra-ribosomal spacer sequences. Genomic clones containing such extra-ribosomal spacer sequences have been isolated. As shown by restriction mapping, these clones appear to consist mostly of repetitive BamHI fragments that are, in turn, internally repetitious and highly homologous to each other. The structure of the clones was confirmed by nucleotide sequence analysis, which also demonstrates the high degree of conservation between the BamHI elements and the homologous NTS sequences. An intriguing 12 base-pair homology between the extra-ribosomal spacer sequences and a Xenopus NTS enhancer sequence is reported. The possibility that a repetitive octanucleotide motif found within the BamHI elements could act as a recombination hotspot by virtue of its similarity with the Escherichia coli chi sequence is discussed.

Animals↗
PubMed1986

Heterochromatic DNA in Triturus (Amphibia, Urodela). I. A satellite DNA component of the pericentric C-bands.

We have studied the structure, genome organization, chromosomal location, conservation across species and transcription on lampbrush chromosomes, of an AT-rich satellite DNA component of the newt, Triturus vulgaris meridionalis. The satellite (Sat G), originally isolated by gradient centrifugation, represents about 2% of the vulgaris genome and comprises a highly repetitive sequence family (HindIII family), whose monomers have been cloned. The repeat units are about 330 bp long, as measured on gels, and a cloned unit (pTvm1) is 310 bp long, as shown by sequencing. Abundant clusters of the HindIII family sequences are located within the pericentric heterochromatin (i.e. the C-bands placed at both sides of, and at a certain distance from, the centromeres) in most chromosomes. Both the sequence family and its overall pattern of chromosomal distribution are conserved within the genus Triturus, despite a few species-specific differences. The great majority of the HindIII family sequences are unexpressed on lampbrush chromosomes; they reside within pericentric, condensed segments of the chromosome axis ("loopless bars"). Only a few sequences are transcribed on some loops, suggesting that transcription promotion does not depend on the satellite sequences themselves.

Ambystoma↗
PubMed1985

Molecular organization of ribosomal RNA genes clustered at variable chromosomal sites in Triturus vulgaris meridionalis (Amphibia, Urodela).

The ribosomal RNA genes of Triturus vulgaris meridionalis (Amphibia, Urodela) show the peculiar feature of being clustered not only at the nucleolar organizer, present in the species at a definite chromosome location, but also at "additional ribosomal sites" which are highly variable in number and chromosomal distribution among individuals. The additional ribosomal sites are most often found at specific chromosome regions, such as telomeres, C-bands and centromeres, in virtually all the chromosomes. With increasing numbers of additional clusters, the genomic dosages of ribosomal RNA genes are found to increase over a tenfold range, though not linearly. At a molecular level, the ribosomal DNA repeats differ in size because of discrete variations in the length of the non-transcribed spacers. However, the resulting length heterogeneity of the gene family is rather limited within a single genome as well as within the species. Many of the ribosomal loci appear to be internally homogeneous with respect to the repeat length. Moreover, separate clusters from distant genomic regions can share the same size class of ribosomal repeats even in the same specimen. The nucleolar organizer is mostly endowed with "shorter" ribosomal repeating units, ranging in size from 13.7 X 10(3) to 15.2 X 10(3) base-pairs. The additional ribosomal sites are characterized by the occurrence of "longer" repeats, ranging in size from 16.2 X 10(3) to 19.7 X 10(3) base-pairs. The "shorter" class of ribosomal repeats is always detected in the amplified ribosomal DNA, suggesting that the nucleolar organizer locus is involved in the amplification process in most oocytes. "Longer" ribosomal repeats are also detectable in the amplified ribosomal DNA of a few females.

Animals↗
PubMed1982

Chromosomal localization of 18S + 28S and 5S Ribosomal RNA genes in evolutionarily diverse anuran amphibians.

The chromosomal locations of the 18S + 28S and 5S ribosomal RNA genes have been analyzed by in situ hybridization in ten anuran species of different taxonomic positions. The chosen species belong to both primitive and evolved families of the present day Anura. Each examined species has 18s + 28S rRNA genes clustered in one locus per haploid chromosome set: this locus is placed either in an intercalary position or proximal to the centromere, or close to the telomere. The 5S rRNA genes are arranged in clusters which vary in number from one to six per haploid set. The 5S rDNA sites are found in intercalary positions, at the telomeres, and at, or close to, the centromeres. Microchromosomes and small chromosomes in primitive karyotypes have been found to carry 5S rDNA sequences. The results are discussed in relation to ideas on the karyological evolution of Amphibia.

Animals↗
PubMed1980

Cytological evidence of transcription of highly repeated DNA sequences during the lampbrush stage in Triturus cristatus carnifex.

Highly repeated, or satellite, DNA fractions have been isolated from total Triturus cristatus carnifex DNA by renaturation kinetics, caesium salt centrifugation and restriction endonuclease digestion. We have shown by DNA/DNA in situ hybridisation and autoradiography that all of these probes bind to C-band positive regions on mitotic or lampbrush chromosomes of T.c. carnifex. Under conditions of DNA to RNA-transcript in situ hybridisation labelled satellite DNA binds to nascent RNA transcripts that are still associated with the DNA axes of many lampbrush loops. The majority of the loops that label heavily in these experiments are located on the long arms of chromosome I, a region previously shown to be rich in highly repeated DNA and to have many of the properties of heterochromatin. These satellite DNA probes also label many loops on a comparable chromosome region in T. marmoratus, a species closely related to T. cristatus. However, in DNA/RNA-transcript hybrids to other more distantly related species of Triturus, there are no chromosome regions that have the same concentration of labelled loop pairs as the long arms of T.c. carnifex and T. marmoratus, although some loop pairs do label. We have cloned two satellite sequences in pBR322, and have obtained the same results using these pure probes as we obtained using satellite probes isolated by other techniques. These results demonstrate unequivocally that satellite DNA is transcribed on lampbrush chromosomes during oogenesis in crested newts.

Animals↗
PubMed1978

Chromosome location of the ribosomal RNA genes in Triturus vulgaris meridionalis (Amphibia, Urodela).

The mitotic chromosomes of six specimens from Triturus vulgaris meridionalis have been examined by both in situ hybridization with 3H 18S + 28S rRNA and AS-SAT staining method. The results of these two sets of experiments can be summarized as follows: 1) in each specimen the NORs and the additional ribosomal sites, which react positively to in situ hybridization with 3H 18S + 28S rRNA, are also stained by silver; 2) other chromosomal regions, which do not hybridize in situ with 3H 18S + 28S rRNA, are on the other hand stained by the AS-SAT method. These latter AG-positive sites show a species-specific pattern of chromosomal distribution.

Animals↗
PubMed1978

Chromosome location of the ribosomal genes in Triturus vulgaris meridionalis (Amphibia Urodela). III. Inheritance of the chromosomal sites for 18S + 28S ribosomal RNA.

In Triturus vulgaris meridionalis, the 18S + 28S rDNA sequences have been shown to be located in a number of additional chromosomal sites besides the nucleolus organizing region. The additional ribosomal sites have been found to vary as to their number and chromosomal location in different individuals of the species.--The data presented in this study concern the chromosomal distribution of the ribosomal sequences as analyzed by in situ hybridization technique in two individuals as well as in their offspring. The evidence obtained by this analysis indicates quite clearly that all 18S + 28S rRNA sites present in each individual genome are inherited according to simple mendelian principles.

Animals↗
PubMed1977

Chromosome location of the ribosomal RNA genes in Triturus vulgaris meridionalis (Amphibia, Urodela). II. Intraspecific variability in number and position of the chromosome loci for 18S + 28S ribosomal RNA.

Ribosomal genes have been localized on mitotic and lampbrush chromosomes of 20 specimens of Triturus vulgaris meridionalis by in situ hybridization with 3H 18S + 28S rRNA. The results may be summarized as follows: 1) each individual shows positive in situ hybridization at the nucleolus organizing region (NOR) on chromosome XI; 2) in addition, many specimens exhibit a positive reaction in chromosomal sites other than the NOR (additional ribosomal sites); 3) the chromosomal distribution of the additional sites appears to be identical in different tissues from the same specimen and to follow a specific individual pattern; 4) the additional ribosomal sites are preferentially found at the telomeric, centromeric or C-band regions of the chromosomes involved.

Animals↗