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Biomedical subjects

J L Olsen

Publications and source records attributed to J L Olsen.

At least 19 recordsLinked to original sources
PubMed2004

Geographically specific heteroplasmy of mitochondrial DNA in the seaweed, Fucus serratus (Heterokontophyta: Phaeophyceae, Fucales).

The presence of more than one type of mitochondrial DNA within the same organism (mtDNA heteroplasmy) has been reported in vertebrates, invertebrates, basidiomycetes and some angiosperms, but never in marine (macro)algae. We examined sequence differences in a 135-base pair (bp) region of the nad11 gene in mitochondria of the intertidal rockweed, Fucus serratus, using single-strand conformation polymorphism (SSCP). Each of 70 and 22 individuals from Blushøj (Denmark) and Oskarshamn (Sweden), respectively, displayed haplotypes 2, 3, and 4 (= mtDNA heteroplasmy), whereas only haplotype 2 was found in each of 24 individuals from locations in Spain, France, Ireland, Iceland and Norway. As Blushøj and Oskarshamn were among the last areas to emerge from ice cover during the Last Glacial Maximum (18000-20000 years BP), the geographically specific heteroplasmy may represent a founder effect and therefore, a valuable marker for understanding the role of post-Ice Age recolonization. Geographically specific heteroplasmy also has important implications in phylogeographical studies based on mtDNA sequences.

Base Sequence↗
PubMed2003

Post-ice age recolonization and differentiation of Fucus serratus L. (Phaeophyceae; Fucaceae) populations in Northern Europe.

The seaweed Fucus serratus is hypothesized to have evolved in the North Atlantic and present populations are thought to reflect recolonization from a southern refugium since the last glacial maximum 18 000-20 000 years bp. We examined genetic structure across several spatial scales by analysing seven microsatellite loci in populations collected from 21 localities throughout the species' range. Spatial auto-correlation analysis of seven microsatellite loci revealed no evidence for spatial clustering of alleles on a scale of 100 m despite limited gamete dispersal in F. serratus of approximately 2 m from parental individuals. Pairwise theta analysis suggested that the minimal panmictic unit for F. serratus was between 0.5 and 2 km. Isolation by distance was significant along some contiguous coastlines. Population differentiation was strong within the Skagerrak-Kattegat-Baltic Seas (SKB) (global theta= 0.17) despite a short history of approximately 7500 years. A neighbour-joining tree based on Reynold's distances computed from the microsatellite data revealed a central assemblage of populations on the Brittany Peninsula surrounded by four well-supported clusters consisting of the SKB, the North Sea (Ireland, Helgoland), and two populations from the northern Spanish coast. Samples from Iceland and Nova Scotia were most closely aligned with northwest Sweden and Brittany, respectively. When sample sizes were standardized (N = 41), allelic diversity was twofold higher for Brittany populations than for populations to the north and threefold higher than southern populations. The Brittany region may be a refugium or a recolonized area, whereas the Spanish populations most likely reflect present-day edge populations that have undergone repeated bottlenecks as a consequence of thermally induced cycles of recolonization and extinction.

Alleles↗
PubMed2002

Hybridization of the marine seaweeds, Fucus serratus and Fucus evanescens (Heterokontophyta: Phaeophyceae) in a 100-year-old zone of secondary contact.

Historically, the intertidal seaweeds Fucus serratus (Fs) and Fucus evanescens (Fe) were sympatric only along the western coast of Norway. In the mid-1890s, Fe (monoecious) was accidentally introduced into the Oslofjord. Putative hybridization with the endemic Fs (dioecious) was observed in Oslofjord by 1977 and in the Kattegat and western Baltic Seas by 1998. At Blushøj, Denmark (Kattegat Sea) putative Fs x Fe hybrids were present only when densities of Fe and Fs exceeded 14 and 2 m(-2), respectively. All of the 58 putative hybrids that were collected in 1999 were dioecious and intermediate in morphology. Essentially all (57 out of 58) were reproductively mature, but the oogonia possessed fewer and more variably sized eggs than either parent. Examination of each parental species and putative hybrids with nuclear, mitochondrial and chloroplast molecular markers confirmed the occurrence of hybridization. Furthermore, all of the hybrids possessed Fe-type chloroplasts and mitochondria, indicating that only the Fe egg x Fs sperm pairing was successful in the field. The reciprocal cross of Fs egg x Fe sperm was absent in the field and significantly less successful in laboratory crossings. Asymmetrical hybridization has also been reported for several species of plants and animals.

Crosses, Genetic↗
PubMed2002

The contribution of haploids, diploids and clones to fine-scale population structure in the seaweed Cladophoropsis membranacea (Chlorophyta).

Local populations of Cladophoropsis membranacea exist as mats of coalesced thalli composed of free-living haploid and diploid plants including clonally reproduced plants of either phase. None of the phases are morphologically distinguishable. We used eight microsatellite loci to explore clonality and fine-scale patch structure in C. membranacea at six sites on the Canary Islands. Mats were always composites of many individuals; not single, large clones. Haploids outnumbered diploids at all sites (from 2:1 to 10:1). In both haploid and diploid plants, genetic diversity was high and there was no significant difference in allele frequencies. Significant heterozygote deficiencies were found in the diploid plants at five out of six sites and linkage disequilibrium was associated with the haploid phase at all sites. Short dispersal distances of gametes/spores and small effective population sizes associated with clonality probably contribute to inbreeding. Spatial autocorrelation analysis revealed that most clones were found within a radius of approximately 60 cm and rarely further than 5 m. Dominance of the haploid phase may reflect seasonal shifts in the relative frequencies of haploids and diploids, but may alternatively reflect superiority of locally adapted and competitively dominant, haploid clones; a strategy that is theoretically favoured in disturbed environments. Although sexual reproduction may be infrequent in C. membranacea, it is sufficient to maintain both life history phases and supports theoretical modelling studies that show that haploid-diploid life histories are an evolutionarily stable strategy.

Chlorophyta↗
PubMed2002

Population structure of plaice (Pleuronectes platessa L.) in northern Europe: microsatellites revealed large-scale spatial and temporal homogeneity.

Philopatry to spawning grounds combined with well-known migratory patterns in the flatfish Pleuronectes platessa (plaice) has led to the hypothesis that regional populations may reflect relatively discrete, genetic stocks. Using six microsatellite loci we genotyped 240 adult individuals collected from locations in Norway, the Faeroe plateau, the Irish Sea, the Femer Baelt, Denmark, and the southern North Sea, and 240 0-class juveniles collected from five nursery-ground locations in Iceland, northwest Scotland, two sites in the Wadden Sea, and the Bay of Vilaine in Southern Brittany. The mean number of alleles/locus ranged from 5.3 to 20.4, with a mean of 13.9. Expected heterozygosity was uniformly high across all locations (multilocus H(exp)= 0.744 +/- 0.02). Pairwise comparisons of theta; among all 11 locations revealed significant differentiation between Iceland and all other locations (theta = 0.0290*** to 0.0456***), which is consistent with the deep-water barrier to dispersal in plaice. In contrast, no significant differentiation was found among any of the remaining continental-shelf sampling locations. This suggests that regional stocks are themselves composed of several genetic stocks under a model of panmixia which persists even to the spawning grounds. The presence of significant heterozygote deficiencies at all locations (not due to null alleles) suggests a temporal Wahlund effect yet the absence of significant population differentiation among continental shelf localities makes this explanation alone, difficult to reconcile. Sampling of eggs at the spawning grounds will be required to resolve this issue. Causes of the mismatch between genetic and geographical stocks is discussed in the context of high gene flow.

Alleles↗
PubMed2002

Polymerase chain reaction-single strand conformation polymorphism analyses of nuclear and chloroplast DNA provide evidence for recombination, multiple introductions and nascent speciation in the Caulerpa taxifolia complex.

Independent lines of evidence support an Australian origin for the Mediterranean populations of the tropical alga Caulerpa taxifolia. To complement previous biogeographical studies based on nuclear rDNA internal transcribed spacer (ITS), a new chloroplast marker was developed--the cp 16S rDNA intron-2. Sequence variability for both nuclear and chloroplast markers were assessed in 110 individuals using single strand conformation polymorphism. Comparison of intrapopulation genetic diversity between invasive Mediterranean and 'native' Australian populations revealed the occurrence of two divergent and widespread clades. The first clade grouped nontropical invasive populations with inshore-mainland populations from Australia, while the second clustered all offshore-island populations studied so far. Despite our finding of nine distinct nuclear and five distinct chloroplast profiles, a single nucleocytoplasmic combination was characteristic of the invasive populations and sexual reproduction was found to be very rare. C. taxifolia is clearly a complex of genetically and ecologically differentiated sibling species or subspecies.

Australia↗
PubMed2001

Phylogenetic analyses of Caulerpa taxifolia (Chlorophyta) and of its associated bacterial microflora provide clues to the origin of the Mediterranean introduction.

The accidental introduction of Caulerpa taxifolia into the Mediterranean is no longer under dispute. What has eluded researchers until now, is definitive evidence for the original, biogeographical source population. Here we present two independent lines of evidence that support an Australian origin for the Mediterranean populations of C. taxifolia. First, we reanalysed algal rDNA-internal transcribed spacer (rDNA-ITS) sequences, combining previously published sequences from different studies with 22 new sequences. The ITS sequence comparison showed that the Australian sample is the sister group of the Mediterranean-aquarium clade. Second, cloned bacterial 16S rDNA gene sequences were analysed from the associated microflora of C. taxifolia collected from Australia, Tahiti, the Philippines and the Mediterranean. Five bacterial lineages were identified, of which three were dominant. Alpha Proteobacteria were the most abundant and were found in all samples. In contrast, members of the beta Proteobacterial line and Cytophaga-Flexibacter-Bacteroides line (CFB) were mainly associated with Mediterranean and Australian samples. Frequency distributions of the five bacterial lineages were significantly different among biogeographical locations. Phylogenetic analyses of the 54 bacterial sequences derived from the four C. taxifolia individuals resulted in a well-resolved tree with high bootstrap support. The topologies of the beta Proteobacteria and CFB mirror the geographical sources of their algal hosts. Bacterial-algal associations provide an identification tool that may have wide application for the detection of marine invasions.

Base Sequence↗
PubMed2000

A microsatellite-based estimation of clonal diversity and population subdivision in Zostera marina, a marine flowering plant.

We examined the genetic population structure in eelgrass (Zostera marina L.), the dominant seagrass species of the northern hemisphere, over spatial scales from 12 km to 10 000 km using the polymorphism of DNA microsatellites. Twelve populations were genotyped for six loci representing a total of 67 alleles. Populations sampled included the North Sea (four), the Baltic Sea (three), the western Atlantic (two), the eastern Atlantic (one), the Mediterranean Sea (one) and the eastern Pacific (one). Microsatellites revealed substantial genetic variation in a plant group with low allozyme diversity. Average expected heterozygosities per population (monoclonal populations excluded) ranged from 0.32 to 0.61 (mean = 0. 48) and allele numbers varied between 3.3 and 6.7 (mean = 4.7). Using the expected frequency of multilocus genotypes within populations, we distinguished ramets from genetic individuals (i.e. equivalent to clones). Differences in clonal diversity among populations varied widely and ranged from maximal diversity (i.e. all ramets with different genotype) to near or total monoclonality (two populations). All multiple sampled ramets were excluded from further analysis of genetic differentiation within and between populations. All but one population were in Hardy-Weinberg equilibrium, indicating that Zostera marina is predominantly outcrossing. From a regression of the pairwise population differentiation with distance, we obtained an effective population size Ne of 2440-5000. The overall genetic differentiation among eelgrass populations, assessed as rho (a standardized estimate of Slatkin's RST) was 0.384 (95% CI 0.34-0.44, P < 0.001). Genetic differentiation was weak among three North Sea populations situated 12-42 km distant from one another, suggesting that tidal currents result in an efficient exchange of propagules. In the Baltic and in Nova Scotia, a small but statistically significant fraction of the genetic variance was distributed between populations (rho = 0.029-0. 053) at scales of 15-35 km. Pairwise genetic differentiation between European populations were correlated with distance between populations up to a distance of 4500 km (linear differentiation-by-distance model, R2 = 0.67). In contrast, both Nova Scotian populations were genetically much closer to North Sea and Baltic populations than expected from their geographical distance (pairwise rho = 0.03-0.08, P < 0.01). A biogeographical cluster of Canadian with Baltic/North Sea populations was also supported using a neighbour-joining tree based on Cavalli-Sforza's chord distance. Relatedness between populations may be very different from predictions based on geographical vicinity.

Gene Frequency↗
PubMed1999

Microsatellite loci in eelgrass Zostera marina reveal marked polymorphism within and among populations.

Using an enriched genomic library, we developed seven (CT)n/(GA)n microsatellite loci for eelgrass Zostera marina L. Enrichment is described and highly recommended for genomes in which microsatellites are rare, such as in many plants. A test for polymorphism was performed on individuals from three geographically separated populations (N = 15/population) and revealed considerable genetic variation. The number of alleles per locus varied between five and 11 and the observed heterozygosities for single loci ranged from 0.16 to 0.81 within populations. Mean allele lengths were markedly different among populations, indicating that the identified loci will be useful in studying population structure in Z. marina. As the frequency of the most abundant multilocus genotype within populations was always < 1%, these loci have sufficient resolving power to address clone size in predominantly vegetatively reproducing populations.

Genetic Variation↗
PubMed1995

Evolution of nuclear rDNA ITS sequences in the Cladophora albida/sericea clade (Chlorophyta).

Ribosomal DNA ITS sequences were compared among 13 different species and biogeographic isolates from the monophyletic "albida/sericea clade" in the green algal genus Cladophora. Six distinct ITS sequence types were found, characterized by multiple insertions and deletions and high levels of nucleotide substitution. Conserved domains within the ITS regions indicate the presence of ITS secondary structure. Low transition/transversion ratios among the six types and nearly symmetrical tree-length frequency distributions indicate some saturation, and low phylogenetic signal. Although branching order among five of the six ITS sequence types could not be resolved, estimates of ITS sequence divergence as compared with 18S divergence in a subset of the taxa suggests that the origin of the different ITS types is probably in the mid-Miocene (12 Ma ago) but that biogeographic isolates within a single ITS type (including both Pacific and Atlantic representatives) have probably dispersed on a time scale of thousands rather than millions of years.

Base Sequence↗
PubMed1994

The Cladophora complex (Chlorophyta): new views based on 18S rRNA gene sequences.

Evolutionary relationships among species traditionally ascribed to the Siphonocladales/Cladophorales have remained unclear due to a lack of phylogenetically informative characters and extensive morphological plasticity resulting in morphological convergence. This study explores some of the diversity within the generic complex Cladophora and its siphonocladalaen allies. Twelve species of Cladophora representing 6 of the 11 morphological sections recognized by van den Hoek were analyzed along with 8 siphonocladalaen species using 18S rRNA gene sequences. The final alignment consisted of 1460 positions containing 92 phylogenetically informative substitutions. Weighting schemes (EOR weighting, combinatorial weighting) were applied in maximum parsimony analysis to correct for substitution bias. Stem characters were weighted 0.66 relative to single-stranded characters to correct for secondary structural constraints. Both weighting approaches resulted in greater phylogenetic resolution. Results confirm that there is no basis for the independent recognition of the Cladophorales and Siphonocladales. The Siphonocladales is polyphyletic, and Cladophora is paraphyletic. All analyses support two principal lineages, of which one contains predominantly tropical members including almost all siphonocladalean taxa, while the other lineage consists of mostly warm- to cold-temperate species of Cladophora.

Base Sequence↗
PubMed1993

Evidence for independent acquisition of group I introns in green algae.

We report the occurrence of a group I intron, 452 nucleotides in length, in the nuclear small-subunit ribosomal gene of the benthic seaweed Urospora penicilliformis, a member of the green algal class Ulvophyceae. Group I introns have been reported in fungi, myxomycetes, the ciliate genus Tetrahymena, and recently in five unicellular chlorophycean algae. The sequence of the conserved core of the U. penicilliformis group I intron was aligned with that of 15 other introns of this type, and the evolutionary relationships among these introns were examined. Comparison of the "intron" tree with phylogenetic hypotheses of the intron-harboring organisms shows that nuclear group I introns in green algae have arisen several times and are not lineage specific.

Animals↗
PubMed1984

The effects of high fat feeding during one cycle of reproduction consisting of pregnancy, lactation and recovery on body composition and fat pad cellularity in the rat.

The changes in adipose depot weight, cell size, cell number and body composition during pregnancy, lactation and recovery were studied in Osborne-Mendel rats fed standard or high fat diets. Rats were killed on day 21 of pregnancy, after 21 days of lactation, and after 21 or 22 days of a postlactational recovery period. Nonpregnant control groups were killed at the beginning and at the conclusion of the experimental period. The high fat-fed, mated group was always fatter than similarly treated animals fed standard diets throughout pregnancy and lactation. However, by the end of the recovery period, carcass composition of the animals fed high fat or standard diets and the nonpregnant groups were not statistically different. The weight of the parametrial, retroperitoneal and subscapular depots was higher in the high fat-fed animals at the end of the recovery period, and in the latter two pads, this increase was statistically significant. Thus, despite the extensive lipid mobilization that occurs during lactation, the high fat-fed animals appear to be predisposed to postpartum obesity.

Adipose Tissue↗
PubMed1981

A review of parenteral sustained-release naltrexone systems.

The ideal naltrexone sustained-release delivery system should be easy to inject or implant, not cause adverse tissue reaction, release the drug at a relatively constant rate for at least 30 days, and biodegrade within a short time afterwards. Mechanisms which can be used for sustaining drug release include reducing solubility and surface area, coating, encapsulation and microencapsulation, complexation, binding and hydrophilic gelation. Drug release from such systems is controlled by diffusion through a barrier/film, diffusion from a monolithic device, erosion of the surface, hydrolysis, ion exchange, biodegradation, or a combination of these. Injectable systems would seem to be ultimately preferred because of the ease of administration and handling, while the implantable devices may find first use in man since they are easily removable, should that be necessary. Maintaining particulate-free products and sterilization methods are two problems with all parenteral dosage forms. Production must be particularly well controlled and validated.

Biodegradation, Environmental↗
PubMed1981

Solid solutions as long-acting naltrexone delivery systems.

Solid solutions and solid dispersions have been used both to increase and to decrease solubility. Solid solutions may extend the release of naltrexone depending upon composition and production methods. Several combinations of naltrexone and cholesterol esters were prepared and evaluated. These combinations did prolong release of the drug in some cases, but none acceptably long enough. Preparation of these solutions and dispersions involved compression and heat as well as solvent mixing. Drug release from particles is dependent upon surface area, composition, and method of preparation. Suspendable, injectable particles can be produced which will give acceptable release rates. The preparation and evaluation are complex and will require much more research effort.

Analgesics↗