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U Arnason

Publications and source records attributed to U Arnason.

At least 55 records · Page 3Linked to original sources
PubMed1994

The complete mitochondrial DNA sequence of the horse, Equus caballus: extensive heteroplasmy of the control region.

The sequence of the mitochondrial (mt) DNA of the horse (Equus caballus) was determined. The length of the sequence presented is 16,660 bp. This figure, however, is not absolute due to pronounced heteroplasmy caused by variable numbers of the motif GTGCACCT in the control region of different molecules. Boundaries of the 13 peptide-coding genes were determined by the presence of start and stop codons, and by analogy with other eutherian mtDNAs. Three genes (COIII, NADH3 and NADH4) were not terminated by a stop codon. Comparison among the peptide-coding genes of the horse and eight other mammals suggests that the boundaries of some mt genes should be redefined. The number of repeats in the control region was determined by sequencing 77 different clones (20 direct plus 57 PCR clones). The number of repeats ranged from 2 to 29. There was a pronounced overrepresentation of clones with many repeats (22-27). Very few clones had a repeat number that was close to the mean number of repeats.

Animals↗
PubMed1994

Relationship of baleen whales established by cytochrome b gene sequence comparison.

A recent revision of whale phylogeny suggested that the sperm whale was more closely related to rorquals than to other toothed whales. This made the suborder Odontoceti (toothed whales) paraphyletic, and implied that the latest common ancestor of rorquals and sperm whales may have lived only 10-13 million years ago. This is at variance with palaeontological evidence for the greater antiquity for both mysticetes (baleen whales) and sperm whales, so the Mysticeti, as well as the Odontoceti, must also be paraphyletic if the dates implied in ref. 1 were correct. Here we present a more comprehensive phylogenetic analysis that demonstrates the monophyly of mysticetes and identifies no particular affinity between the sperm whales and rorquals.

Animals↗
PubMed1994

Comparative chromosome painting discloses homologous segments in distantly related mammals.

Comparative chromosome painting, termed ZOO-FISH, using DNA libraries from flow sorted human chromosomes 1, 16, 17 and X, and mouse chromosome 11 discloses the presence of syntenic groups in distantly related mammalian orders ranging from primates (Homo sapiens), rodents (Mus musculus), even-toed ungulates (Muntiacus muntjak vaginalis and Muntiacus reevesi) and whales (Balaenoptera physalus). These mammalian orders have evolved separately for 55-80 million years (Myr). We conclude that ZOO-FISH can be used to generate comparative chromosome maps of a large number of mammalian species.

Animals↗
PubMed1993

Comparison between the complete mtDNA sequences of the blue and the fin whale, two species that can hybridize in nature.

The sequence of the mitochondrial DNA (mtDNA) molecule of the blue whale (Balaenoptera musculus) was determined. The molecule is 16,402 bp long and its organization conforms with that of other eutherian mammals. The molecule was compared with the mtDNA of the congeneric fin whale (B. physalus). It was recently documented that the two species can hybridize and that male offspring are infertile whereas female offspring may be fertile. The present comparison made it possible to determine the degree of mtDNA difference that occurs between two species that are not completely separated by hybridization incompatibility. The difference between the complete mtDNA sequences was 7.4%. Lengths of peptide coding genes were the same in both species. Except for a small portion of the control region, disruption in alignment was usually limited to insertion/deletion of a single nucleotide. Nucleotide differences between peptide coding genes ranged from 7.1 to 10.5%, and difference at the inferred amino acid level was 0.0-7.9%. In the rRNA genes the mean transition difference was 3.8%. This figure is similar in degree to the difference (3.4%) between the 12S rRNA gene of humans and the chimpanzee. The mtDNA differences between the two whale species, involving both peptide coding and rRNA genes, suggest an evolutionary separation of > or = 5 million years. Although hybridization between more distantly related mammalian species may not be excluded, it is probable that the blue and fin whales are nearly as different in their mtDNA sequences as hybridizing mammal species may be.

Adenosine Triphosphatases↗
PubMed1993

The nucleotide sequence of the mitochondrial DNA molecule of the grey seal, Halichoerus grypus, and a comparison with mitochondrial sequences of other true seals.

The sequence of the mtDNA of the grey seal, Halichoerus grypus, was determined. The length of the molecule was 16,797 base pairs. The organization of the molecule conformed with that of other eutherian mammals but the control region was unusually long due to the presence of two types of repeated motifs. The grey seal and the previously reported harbor seal, Phoca vitulina, belong to different but closely related genera of family Phocidae, true (or earless) seals. In order to determine the degree of differences that may occur between mtDNAs of closely related mammalian genera, the 2 rRNA genes, the 13 peptide coding genes, and the 22 tRNA genes of the 2 species were compared. Total nucleotide difference in the peptide coding genes was 2.0-6.1%. The range of conservative difference was 0.0-1.5%. In the inferred peptide sequences the amino acid difference was 0.0-4.5%, and the difference with respect to chemical properties of amino acids was 0.0-3.0%. A gene that showed a limited degree of difference in one mode of comparison did not necessarily show a corresponding limited difference in another mode. The ratio for differences in codon positions 1, 2, and 3 was approximately 2.7:1:16. The corresponding ratio for conservative differences was approximately 1.8:1.1:1. The evolutionary separation of the two species was calculated to have taken place 2-2.5 million years ago. This dating gives the figure approximately 8 x 10(-9) as the mean rate of substitution per site and year in the entire mtDNA molecule. Comparison with the cytochrome b gene of the Hawaiian monk seal and the Weddell seal suggested that the lineage of these two species and that of the grey and harbor seals separated approximately 8 million years ago.

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PubMed1993

Sequence organization and evolution, in all extant whalebone whales, of a DNA satellite with terminal chromosome localization.

A heavy (GC rich) DNA satellite with terminal chromosomal localization is characteristic for all mysticete (whalebone whale) genomes. Sequences of 58 repeats of the satellite were compared in all ten extant mysticete species. In three families comprising eight species, the typical repeat length was 422 (421) bp. In two species, the northern right whale and the bowhead, of family Balaenidae (right whales) the repeats were much longer, typically ca. 900 and ca. 1200 bp. In all species the repeats were composed of a unique portion of constant length (212/211 bp), and a subrepeat portion, the length of which was variable. The evolutionary rigidity of the unique portion of the repeat is contrasted by the pronounced length variability of the subrepeat portion. The subrepeat portion consists essentially of 6 bp motifs, such that length differences are usually in multiples of 6 bp. The motif TTAGGG constituted 35%-50% of the subrepeats. Comparison between the unique portion of the 58 sequenced repeats revealed that the repeats divided into two primary groups, one comprising the two balaenids, the other including the eight remaining species. The mean difference between the two groups averaged 8.4%. In this sequence comparison the repeats of the pygmy right whale constituted a group that was separated from repeats of the other species. In all other cases repeats were intermingled to some extent between species. Comparison of individual repeats suggests that the unique portion evolves in concert, at a slow rate. A neighbor-joining comparison between the consensuses of all species suggests that the unique portion of the repeats evolves at a somewhat different rate in different lineages.

Animals↗
PubMed1993

Molecular studies on two variant repeat types of the common cetacean DNA satellite of the sperm whale, and the relationship between Physeteridae (sperm whales) and Ziphiidae (beaked whales).

In the sperm whale (Physeter macrocephalus) two different repeat types (A and B) of the common cetacean DNA satellite were identified. The evolution of each group of repeats appears to be independent from that of the other. The sequence similarity between the two groups is less than the similarity between group A and repeats of the satellite in related whale species. The systematic relationship within and between the families Physeteridae (sperm whales) and Ziphiidae (beaked whales) was addressed by both sequence analysis of the satellite and comparisons with the families Delphinidae and Phocoenidae. The mysticete blue whale (Balaenoptera musculus) was used as an outgroup in the comparisons. The molecular phylogeny, when maximum-parsimony analysis and the neighbor-joining method were used, grouped together species of each family. At the family level the ziphiids grouped closet to the families Phocoenidae and Delphinidae. The similarities between the common cetacean satellite of the blue whale and the sperm whale were greater than those between the blue whale and the other odontocetes included, suggesting that the evolution of the satellite is slower in the sperm whale than in the other odontocetes.

Animals↗
PubMed1993

Cetacean mitochondrial DNA control region: sequences of all extant baleen whales and two sperm whale species.

The sequence of the mitochondrial control region was determined in all 10 extant species commonly assigned to the suborder Mysticeti (baleen or whalebone whales) and to two odontocete (toothed whale) species (the sperm and the pygmy sperm whale). In the mysticetes, both the length and the sequence of the control region were very similar, with differences occurring primarily in the first approximately 160 bp of the 5' end of the L-strand of the region. There were marked differences between the mysticete and sperm whale sequences and also between the two sperm whales. The control region, less its variable portion, was used in a comparison including the 10 mysticete sequences plus the same region of an Antarctic minke whale specimen and the two sperm whales. The difference between the minke whales from the North Atlantic and the Antarctic was greater than that between any acknowledged species belonging to the same genus (Balaenoptera). The difference was similar to that between the families Balaenopteridae (rorquals) and Eschrichtiidae (gray whales). The findings suggest that the Antarctic minke whale should have a full species status, B. bonaerensis. Parsimony analysis separated the bowhead and the right whale (family Balaenidae) from all remaining mysticetes, including the pygmy right whale. The pygmy right whale is usually included in family Balaenidae. The analysis revealed a close relationship between the gray whale (family Eschrichtiidae) sequence and those of the rorquals (family Balaenopteridae). The gray whale was included in a clade together with the sei, Bryde's, fin, blue, and humpback whales. This clade was separated from the two minke whale types, which branched together.

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PubMed1992

The complete mitochondrial DNA sequence of the harbor seal, Phoca vitulina.

The nucleotide sequence of the mitochondrial DNA (mtDNA) of the harbor seal, Phoca vitulina, was determined. The total length of the molecule was 16,826 bp. The organization of the coding regions of the molecule conforms with that of other mammals, but the control region is unusually long. A considerable portion of the control region is made up of short repeats with the motif GTACAC particularly frequent. The two rRNA genes and the 13 peptide-coding genes of the harbor seal, fin whale, cow, human, mouse, and rat were compared and the relationships between the different species assessed. At ordinal level the 12S rRNA gene and 7 out of the 13 peptide-coding genes yielded a congruent topological tree of the mtDNA relationship between the seal, cow, whale, human, and the rodents. In this tree the whale and the cow join first, and this clade is most closely related to the seal.

Amino Acid Sequence↗
PubMed1992

Evolution of the common cetacean highly repetitive DNA component and the systematic position of Orcaella brevirostris.

The common cetacean highly repetitive DNA component was analyzed with respect to its evolution and value for establishing phylogenetic relationships. The repeat length of the component, which is tandemly organized, is approximately 1750 bp in all cetaceans except the delphinids, in which the repeat length is approximately 1580 bp. The evolution of the component was studied after sequencing the component in different odontocetes representing the Delphinidae (delphinids), Monodontidae (narwhals), and Ziphiidae (beaked whales). The evolution of this component is very slow, and comparisons showed that sequence divergence among species corresponds closely to their generally accepted phylogenetic relationships and that the component evolves in a concerted manner. The phylogenetic information obtained in this study identified the Irrawaddy dolphin (Orcaella brevirostris) as a delphinid and did not support a close relationship of this species with the Monodontidae.

Animals↗
PubMed1992

Mysticete (baleen whale) relationships based upon the sequence of the common cetacean DNA satellite.

The genomes of all extant cetaceans are characterized by the presence of the so-called common cetacean DNA satellite. In the mysticetes (whalebone whales) the repeat length of the satellite is 1,760 bp. In the odontocetes (toothed whales), other than the family Delphinidae, the repeat length is usually approximately 1,740 bp. The Delphinidae are characterized by a repeat length of approximately 1,580 bp. It has been shown in odontocetes that the satellite evolves in concert and that differences between species, with respect to the sequence of the satellite, correspond reasonably well to their evolutionary distances. In the present study the sequence of the satellite was determined in three repeats in each of seven mysticete species, and a consensus for each species established. Parsimony and neighbor-joining analyses based upon sequences of all repeats showed that the primary evolutionary distinction among the mysticetes is between the Balaenidae sensu stricto (i.e., the bowhead whale and the right whale) and all remaining species, including the pygmy right whale, a species that usually has been included in the Balaenidae. The comparisons also showed that the humpback whale and the gray whale were approximately equidistant from the blue whale and the fin whale (genus Balaenoptera). Concerted evolution of the satellite was also demonstrated among the mysticetes, but it appeared to evolve more slowly in the mysticetes than in the odontocetes.

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PubMed1991

The long leader sequence of the mouse ornithine decarboxylase mRNA, previously suspected to be a cloning artifact, is probably a product of recombination with MuLV-like retrovirus.

Sequence analysis of the first 549 nucleotides (nt) of the non-translated 5' end of the cloned mouse ornithine decarboxylase (ODC; L-ornithine carboxy-lyase, EC 4.1.1.17)-encoding sequence shows that this sequence is closely related to nt 1946-1395 of Moloney murine leukemia virus (MuLV). The viral sequence, however, is oriented anti-sense relative to the ODC sequence. This orientation makes it unlikely to be a cloning artifact mediated by reverse transcriptase, but rather a recombination between genomic DNA and a MuLV-like provirus. In the cell line, from which the cDNA clone originated, Katz and Kahana [EMBO J. 8 (1989) 1163-1167] have shown that an intragenic deletion and amplification of the ODC gene had taken place. We believe that an additional recombination also has occurred in this cell line. The cDNA clone studied was obtained after selecting for high ODC expression. It is conceivable that the retroviral sequence contains an intragenic enhancer which is also functional in the anti-sense orientation. The inserted sequence contains two repeats which share homology with known enhancer elements. The reported recombination event shows that caution is needed when selective pressure is applied for the isolation and characterization of genes.

Animals↗
PubMed1991

The complete nucleotide sequence of the mitochondrial DNA of the fin whale, Balaenoptera physalus.

The composition of the mitochondrial DNA (mtDNA) of the fin whale, Balaenoptera physalus, was determined. The length of the molecule is 16,398 bp, and its organization conforms with that of other mammals. The general similarity between the mtDNA of the fin whale and the cow is greater than the similarity between the fin whale and other species (human, mouse, rat) in which the composition of the entire molecule has been described. The D-loop region of the mtDNA of the fin whale is 81% identical to the D-loop of dolphin DNA, and the central portion of the D-loop is similar to the bovine D-loop. The accumulation of transversions and gaps in the 12S and 16S rRNA genes was assessed by comparing the fin whale, cow, and human. The sequence difference between human and the whale and human and the cow was at the same level, indicating that the rate of evolution of the mtDNA rRNA genes is about the same in artiodactyls and cetaceans. In the 12S rRNA gene an accumulation rate of 0.05% per million years places the separation of cetaceans and artiodactyls at about 55 million years ago. The corresponding figure for human and either the whale or the cow is about 80 million years. In the 16S rRNA gene a 0.08% accumulation rate of transversions and gaps per million years yields concurring figures. A comparison between the cytochrome b gene of the fin whale and cytochrome b sequences in the literature, including dolphin (Stenella) sequences, identified the cetaceans as monophyletic and the artiodactyls as their closest relatives. The comparison between the cytochrome b sequences of the fin whale and Stenella showed that differences in codon positions one or two were frequently associated with a change in another codon position.

Amino Acid Sequence↗
PubMed1991

Molecular identification of hybrids between the two largest whale species, the blue whale (Balaenoptera musculus) and the fin whale (B. physalus).

Three anomalous balaenopterid whales, one pregnant female and two sterile males, were investigated by applying molecular approaches in order to establish their identity. The analysis showed that the whales were species hybrids between the blue and the fin whales. The female and one of the males had a blue whale mother and a fin whale father. The other male had a fin whale mother and a blue whale father. The difference between the mitochondrial cytochrome b gene of the two species suggests that they separated greater than or equal to 3.5 million years ago. The sequences of the mitochondrial control region of the blue and the fin whales differ by 7%. The difference in the mtDNA control region between three blue whale mtDNA haplotypes was less than or equal to 1%, about one tenth of the difference between the two species.

Animals↗
PubMed1990

Localization of cloned, repetitive DNA sequences in deer species and its implications for maintenance of gene territory.

The deer family shows the largest variation in chromosome number known in mammals (2n = 6 to 2n = 70). The drastic rearrangement of the chromosomes allows to test the prediction, based on the chromosome field theory, according to which DNA sequences tend to occupy specific territories within the eukaryotic chromosome. Nuclear DNAs were isolated from eight Deer and two Bovidae species. These DNAs were cleaved with the restriction enzymes Eco RI and Alu I. Following Eco RI digestion highly repetitive sequences formed two bands which were common to all deer species. These bands had about 1520 and 2240 base pairs and were particularly clear in Capreolus capreolus (2n = 70, roe deer). The 1520 band DNA was cloned in plasmid pUC9, nick translated, and hybridized with the DNAs of all ten species. The Capreolus DNA showed a high homology with the DNAs of all the species including the Indian muntjac (Muntiacus muntjak, 2n = 7, male) and the Chinese muntjac (Muntiacus reevesi, 2n = 46). 3H hybridization was carried out in situ with metaphase chromosomes of Cervus elaphus (2n = 68, red deer), M. muntjak, and M. reevesi. In C. elaphus all the chromosomes are heavily labeled except the regions of the arms near the centromere. In the muntjacs all chromosomes and most regions appear to be labeled. These results were checked with a different technique that involved the use of two antibodies and biotin labeling of the DNA. The hybridization picture was essentially the same as obtained with 3H. These results disclose that the 1520 bp DNA piece maintains its main territory independently of the drastic changes in chromosome number.

Animals↗
PubMed1989

Composition and chromosomal localization of cetacean highly repetitive DNA with special reference to the blue whale, Balaenoptera musculus.

Three highly repetitive DNA components--the common cetacean component, the heavy (GC-rich) satellite and the light (AT-rich) satellite--were were studied in the blue whale. Consensus sequences of the common component and the heavy satellite were determined on the basis of three repeats of the common component and eight repeats of the heavy satellite. The tandemly organized common cetacean component, which comprises a large portion of all cetacean--both odontocete (toothed whale) and mysticete (whalebone whale)--genomes has a repeat length of 1,760 bp and the three clones analysed showed a high degree of conformity. The repeat contains a 72 bp sequence with dyad symmetry and striking intrastrand complementarity. The rest of the repeat comprises a unique sequence. The repeat unit of the heavy satellite of the blue whale is 422 bp. Also this component is tandemly organized. About half the length of the repeat constitutes a unique sequence and the other half is made up of subrepeats with TTAGGG as a frequent motif. The light satellite has not been sequenced and its basic repeat unit has not yet been identified. The chromosomal localization of the three components was determined by in situ hybridization using 3H-labelled cloned fragments as probes. The common cetacean component was located in most interstitial and terminal C-bands. The heavy satellite occurred primarily in terminal C-bands. When the two components hybridized to the same terminal C-bands, the localization of the heavy satellite was distal to that of the common cetacean component. Neither component shared localization with the light satellite which is located in centromeric C-bands in just a few chromosome pairs.

Animals↗
PubMed1987

Novel cytogenetic expression of gene amplification in actinomycin D-resistant somatic cell hybrids: transfer of resistance by centric chromatin bodies.

SEWATC13 mouse cells, resistant to 0.1 microgram/ml of actinomycin D (AMD), were fused to AMD-sensitive cells of the Chinese hamster ovary cell line (CHO). Twenty-two hybrid clones were isolated and put into serial culture in the selective medium. Unexpectedly, identifiable mouse chromosomes were found only in one of the hybrids. All the others had only hamster chromosomes and, in addition, numerous chromatin bodies (CBs), mostly small and irregularly shaped, but also larger, more chromosome-like ones. The CBs were distinctly C-band positive and a mouse satellite probe hybridized strongly to them. The AMD resistance of the murine parental cells had previously been attributed to gene amplification in two large homogeneously staining regions (HSR-AMD1 and 2). They were not observed in the hybrid cells but had supposedly reappeared in the guise of the CBs. It was established by Southern DNA blot analysis that amplified DNA sequences, localized to the HSR-AMD1 and 2 of the SEWA parent were present in multiple copies in the hybrids. It was also established by in situ hybridization that they were located in the CBs. Unlike double minutes (DMs) the CBs were all centric.

Animals↗