Search PubMed⌕ Search

Biomedical subjects

O A Ryder

Publications and source records attributed to O A Ryder.

At least 55 records · Page 3Linked to original sources
PubMed1990

Phylogeny and evolution of antlered deer determined from mitochondrial DNA sequences.

Mitochondrial DNA sequences of both ribosomal RNA genes and three adjacent transfer RNA genes were obtained for the three extant subfamilies of antlered deer (Cervinae, Muntiacinae, and Odocoileinae) as well as for their antlerless sister group Hydropotinae (family Cervidae). Phylogenetic analysis of these sequences (each nearly 2.7 kilobase pairs in length) supports a cervine/muntiacine clade to the exclusion of odocoileines. These results are statistically significant, stable, and congruent with some independent data. Our mitochondrial DNA sequences, when coupled with other information, indicate that the earliest fossil antlered deer are not closely related to living muntiacines or any other contemporary subfamily. From this information, we hypothesize an Old World, Late Miocene origin of Odocoileinae.

Animals↗
PubMed1988

Identification of the gene coding for the Endo B murine cytokeratin and its methylated, stable inactive state in mouse nonepithelial cells.

The Endo B type-I keratin intermediate filament protein is first expressed at the 4- to 8-cell stage of mouse development. In the adult, its expression is restricted to a variety of simple epithelial cell types. To investigate the mechanisms responsible for the restricted expression of Endo B, the gene coding for Endo B has been identified from among the five different Endo B genes found in the mouse genome by Southern hybridization analysis and cloning all or part of four of the genes. Nuclear run-on experiments demonstrate that Endo B expression is regulated at the level of transcription. The 5' end of the active gene, designated Endo beta 1, was found to be highly methylated and in a relatively nuclease-resistant chromatin conformation in fibroblasts and myoblasts that do not express Endo B, but undermethylated and relatively sensitive to nuclease digestion in endodermal cells or F9 embryonal carcinoma cells. The inactive state of the Endo B beta 1 gene in fibroblast appears to be very stable, because somatic cell hybrids formed by the fusion of HeLa cells, which express the homologous human protein, keratin 18, and mouse fibroblasts, continue to express keratin 18 but do not activate Endo B expression. Similarly, the fusion of mouse endodermal cells and fibroblasts results in hybrids that do not extinguish Endo B expression. These results suggest that Endo B transcription is limited by two different mechanisms. In somatic cells such as fibroblasts or myoblasts, expression may be restricted by methylation and a stable, nonpermissive transcriptional state. However, in embryonal carcinoma cells, the Endo B beta 1 gene is undermethylated and in a relatively nuclease-sensitive conformation, but it is restricted by an additional, negative regulatory mechanism.

Animals↗
PubMed1986

Mitochondrial DNA evolution in the genus Equus.

Employing mitochondrial DNA (mtDNA) restriction-endonuclease maps as the basis of comparison, we have investigated the evolutionary affinities of the seven species generally recognized as the genus Equus. Individual species' cleavage maps contained an average of 60 cleavage sites for 16 enzymes, of which 29 were invariant for all species. Based on an average divergence rate of 2%/Myr, the variation between species supports a divergence of extant lineages from a common ancestor approximately 3.9 Myr before the present. Comparisons of cleavage maps between Equus przewalskii (Mongolian wild horse) and E. caballus (domestic horse) yielded estimates of nucleotide sequence divergence ranging from 0.27% to 0.41%. This range was due to intraspecific variation, which was noted only for E. caballus. For pairwise comparisons within this family, estimates of sequence divergence ranged from 0% (E. hemionus onager vs. E. h. kulan) to 7.8% (E. przewalskii vs. E. h. onager). Trees constructed according to the parsimony principle, on the basis of 31 phylogenetically informative restriction sites, indicate that the three extant zebra species represent a monophyletic group with E. grevyi and E. burchelli antiquorum diverging most recently. The phylogenetic relationships of E. africanus and E. hemionus remain enigmatic on the basis of the mtDNA analysis, although a recent divergence is unsupported.

Animals↗
PubMed1985

Immunological systematics of the extinct quagga (Equidae).

It has been debated whether the extinct quagga was a distinct fourth species of African zebra or whether it was merely the southern variant of the Plains zebra (Equus burchelli). Using a radioimmunoassay (RIA) technique, we have shown that proteins remaining in quagga skins from museums are much more similar to serum proteins of the Plains zebra than to those of the other two extant zebras.

Animals↗
PubMed1983

Molecular cytogenetics of the equidae. II. purification and cytological localization of a (G + C)-rich satellite DNA from Equus hemionus onager and cross-species hybridization to E. asinus chromosomes.

A (G + C)-rich satellite DNA component (p = 1.716 g/ml) has been fractionated from the total DNA of the Iranian subspecies of the Asiatic wild ass, Equus hemionus onager, by successive dactinomycin-CsCl and netropsin sulfate-CsCl isopycnic gradients. Complementary 3H-RNA (cRNA) transcribed from the satellite DNA hybridized predominantly to the centromeric and telomeric constitutive heterochromatic regions of onager chromosomes. These studies have suggested that satellite DNA's with similar sequences are present in the centromeric, as well as telomeric, heterochromatic regions of some onager chromosomes. The centromeric region of the fusion metacentric t(23;24) of the onager is deficient in sequences homologous to the onager 1.716 g/ml satellite DNA, indicating a loss of satellite DNA during fusion or an amplification of the satellite DNA in the centromeric regions of the acrocentric chromosomes 23 and 24 subsequent to fission. Sequences complementary to onager 1.716 g/ml satellite DNA show extensive hybridization to the constitutive heterochromatin of the feral donkey (E. asinus) karyotype, consistent with a view of conservation and amplification of similar or identical sequences in the two species.

Animals↗
PubMed1982

Characterization of a cloned repetitive DNA sequence concentrated on the human X chromosome.

A tandemly repeated DNA sequence organized predominantly, if not entirely, in a specific manner on the human X chromosome has been cloned in pBR322 and characterized. The sequence was detected as a 2-kilobase band in ethidium bromide-stained agarose gels of BamHI-digested total human nuclear DNA. Although in situ hybridization of the cloned sequence to human metaphase chromosomes showed a single major site of hybridization at the centromere region of the X chromosome and minor sites of hybridization at several autosomal centromeres, Southern blot analysis of restricted total human DNA indicated that the cloned probe is related to other repeated DNAs, particularly the human alphoid DNAs. Restriction enzyme analysis of the cloned fragment revealed an internal repeat structure based upon multiples of 170 base pairs, confirming this relatedness. All available data, however, suggest that the 2-kilobase spacing of BamHI sites within the repeat may be specific to the X chromosome.

Cells, Cultured↗
PubMed1981

Satellite DNA relationships in man and the primates.

We have investigated the genomes of a series of primates to identify the presence of sequences related to human satellite DNAs I, II and III by restriction enzyme digestion and hybridisation with probes of these satellite DNAs. Where we have found such related sequences we have examined the extent to which they have diverged by measuring the stability of the hybrids. DNA satellite III is the oldest sequence being common to species which have diverged some 24 million years ago. In contrast DNA satellites I and II are of much more recent origin. Our results permit us to draw conclusions about the way these sequences have evolved, and how the evolution of repeated DNA sequences may be related to the evolution of the primate lineage.

Animals↗
PubMed1979

Molecular cytogenetics of the Equidae. I. Purification and cytological localization of a (G + C)-rich satellite DNA from Equus przewalskii.

A (G + C)-rich density satellite DNA (rho = 1.713 gm/cc) has been purified from splenic DNA of Przewalski's horse, Equus przewalskii, by successive equilibrium density gradient centrifugations. The purified satellite, which may comprise as much as 29% of the total DNA, renatures rapidly; however, analyses of native, single-stranded, and reassociated molecules by analytical ultracentrifugation and melting properties suggest that some sequence heterogeniety exists in the 1.713 gm/cc satellite. Complementary RNA (cRNA) transcribed from satellite DNA has been utilized for in situ hybridization studies with E. przewalskii metaphase chromosomes previously identified by quinacrine-banding. These studies establish that sequences complementary to the 1.713 g/cc satellite are greatly enriched in the centromeres of some, but not all, chromosomes. The differential distribution of satellite DNA sequences over heterochromatic regions allows discrimination of three classes of heterochromatin and serves to define three types of pericentromeric regions in the karyotype of this endangered equine species. Additionally, apparent polymorphism in concentrations of satellite DNA sequences between homologs in the same karyotype is noted.

Animals↗
PubMed1979

Hemoglobin polymorphism in Equus przewalskii and E. caballus analyzed by isoelectric focusing.

1. Through the use of isoelectric focusing and peptide analysis, the hemoglobins of Przewalski's horse. Equus przewalskii and the domestic horse, E. caballus have been compared. 2. Przewalski's horses have two separate alpha-globin chain polymorphisms similar to domestic horses. Each hemoglobin phenotype could be accurately determined by isoelectric focusing. 3. Confirmation of the electrofocusing hemoglobin determinations was made by comparison to amino acid composition analyses of purified tryptic peptides and by analysis of the rare hemoglobins phenotypes observed in a family of Norwegian trotting horses. 4. Hemoglobin genotypes of fifteen Przewalski's horses were determined and inheritance of hemoglobin haplotypes has been observed.

Amino Acids↗
PubMed1978

Common and species-specific esterases of Equidae--IV. Horse of przewalski, onager and Zebra hartmannae.

1. Among several species of Equidae only E. przewalskii possesses a serum esterase identical with that of E. caballus. 2. The esterases of Hemionidae differ slightly from that of domestic horse by electrophoretic migration and by antigenic structure. 3. Zebras (grevyi, burchelli) appear devoid of this component but Z. hartmannae possesses an esterase of high enzymatic activity, differing notably from that of horse by electrophoretic and antigenic properties.

Animals↗
PubMed1978

Detection of proviral DNA in horse cells infected with equine infectious anemia virus.

Equine infectious anemia virus (EIAV) recently has been shown to possess a high-molecular-weight RNA genome and a virion reverse transcriptase. We completed the demonstration that EIAV is a retrovirus by showing the presence of proviral DNA in equine cells infected in vitro, but not in normal horse DNA. These studies were performed by using a highly representative cDNA probe synthesized by the virion polymerase. It was found that this cDNA reassociated extensively, and with high thermal stability, with either viral RNA or DNA extracted from infected cells, but showed no detectable reassociation with DNA from uninfected horse cells. Similarly, sequences related to EIAV were neither found in the DNA of four other Equus species, nor in a variety of other mammals including sheep, cows, pigs- dogs, cats, and humans; nor did EIAV cDNA hybridize with a variety of other retrovirus RNAs. These experiments were performed under conditions of very low stringency to enable detection of distantly related sequences, with a sufficient ratio of DAN to cDNA to allow detection of less than one viral copy per haploid genome. We conclude that EIAV is not an endogenous virus of the horse or of the other species tested.

Animals↗
PubMed1978

Chromosomal polymorphism in Equus hemionus.

The first cytogenetic studies of the Turkmenian kulan, Equus hemionus kulan, are reported, and a polymorphism in diploid chromosome number is described. Chromosome fusion is apparently involved in the alterations of the karyotype of E. hemionus kulan (2n = 55, 54) when compared to the karyotype of the onager, E. hemionus onager (2n = 56). Additionally, the rearrangement involved has been identified in animals unrelated through captive breeding; inheritance of the fusion chromosomes has also been observed.

Animals↗
PubMed1976

Electron microscopy of membrane-associated folded chromosomes of Escherichia coli.

Membrane-associated folded chromosomes were purified from log-phase cultures of Escherichia coli 15 TAU-bar and prepared for electron microscopy by aqueous spreading techniques. A spectrum of structures was observed, ranging from condensed structures with no DNA fibers visible, to extended structures with DNA fibers. In the extended structures, loops of DNA radiated from residual envelope, the loops sometimes appeared supercoiled, and both their number and apparent contour length approximated previous estimates from physical and biochemical data. It is proposed that the structures with free DNA arose from the condensed structures.

Chromosomes, Bacterial↗
PubMed1975

Properties of membrane-associated folded chromosomes of E. coli related to initiation and termination of DNA replication.

Analysis of folded chromosomes prepared from amino acid-starved E. coli cells of from a dnaC initiation mutant indicates that a unique structure is associated with completion or near completion of rounds of chromosome replication in E. coli. Chromosomes remain associated with portions of the bacterial cell envelope throughout the DNA replication cycle, but become more rapidly sedimenting as replication proceeds in the absence of reinitiation. Before reinitiation of chromosome replication occurs after restoring required amino acids to amino acid-starved cells or after lowering the temperature in a thermosensitive dnaC mutant, sedimentation velocities of the membrane-associated folded chromosomes decrease substantially. The decrease in sedimentation velocity does not depend on renewed DNA synthesis, but does require the activity of at least the dnaC gene product.

Amino Acids↗
PubMed1974

Isolation of membrane-associated folded chromosomes from Escherichia coli: effect of protein synthesis inhibition.

The sedimentation properties of membrane-associated folded chromosomes prepared from Escherichia coli TAU-bar at 0 to 4 C were studied. Utilizing a modification of the procedure of Stonington and Pettijohn (1971), quantitative yields of membrane-associated folded chromosomes may be obtained. Folded chromosomes remained associated with the cell envelope during their replication and after completion of residual synthesis in the absence of required amino acids, as demonstrated by sedimentation velocities and the presence of high levels of cosedimenting protein. Membrane-associated folded chromosomes isolated from amino acid-starved cells sedimented more rapidly than membrane-associated folded chromosomes isolated from exponentially growing cells.

Amino Acids↗
PubMedDate not supplied

DNA sequences from the quagga, an extinct member of the horse family.

To determine whether DNA survives and can be recovered from the remains of extinct creatures, we have examined dried muscle from a museum specimen of the quagga, a zebra-like species (Equus quagga) that became extinct in 1883 (ref. 1). We report that DNA was extracted from this tissue in amounts approaching 1% of that expected from fresh muscle, and that the DNA was of relatively low molecular weight. Among the many clones obtained from the quagga DNA, two containing pieces of mitochondrial DNA (mtDNA) were sequenced. These sequences, comprising 229 nucleotide pairs, differ by 12 base substitutions from the corresponding sequences of mtDNA from a mountain zebra, an extant member of the genus Equus. The number, nature and locations of the substitutions imply that there has been little or no postmortem modification of the quagga DNA sequences, and that the two species had a common ancestor 3-4 Myr ago, consistent with fossil evidence concerning the age of the genus Equus.

Animals↗
PubMedDate not supplied

Centric fusion polymorphisms in waterbuck (Kobus ellipsiprymnus).

Twenty-six captive individuals of the ellipsiprymnus subspecies group of Kobus ellipsiprymnus were found to have chromosomal complements of 2n = 50-52 (FN = 61-62), and 26 of the defassa subspecies group, including three specimens from Lake Nakuru National Park, Kenya, had complements of 2n = 53-54 (FN = 62). G-banded karyotypes that were numbered according to the standard karyotype of Bos taurus revealed that variation in diploid number was the result of polymorphism for two independent centric (Robertsonian) fusions. The ellipsiprymnus group was polymorphic for a 7;11 centric fusion. Both elements of chromosome pairs 7 and 11 were fused in fusion homozygotes (2n = 50); in fusion heterozygotes (2n = 51), only one element of each pair was fused. The 7;11 fusion was lacking in specimens with 2n = 52. The defassa group was polymorphic for a 6;18 centric fusion; individuals were either heterozygous for the fusion (2n = 53) or lacking it (2n = 54). There were no defassa group individuals that were homozygous for the 6;18 fusion (2n = 52), but this may be a sampling artifact. The 6;18 fusion was fixed in the ellipsiprymnus group, whereas the 7;11 fusion was absent in the defassa group. In G- and C-banded karyotypes, all autosomal arms and the X chromosomes of the two subspecies groups appeared to be completely homologous. However, the Y chromosome was acrocentric in the ellipsiprymnus group and submetacentric in the defassa group, possibly the result of a pericentric inversion. Fixed chromosomal differences between the two subspecies groups reflect a period of supposed geographic isolation during which time they diverged genetically and phenotypically, and the centric fusion polymorphisms raise the possibility of reduced fertility in hybrids. These data, in conjunction with phenotypic and mitochondrial DNA data, suggest to us that populations of the ellipsiprymnus and defassa groups should be managed separately.

Animals↗