Biomedical subjects

Travis C Glenn

Publications and source records attributed to Travis C Glenn.

15 recordsLinked to original sources

PubMed2006

Genetics of cattails in radioactively contaminated areas around Chornobyl.

Research on populations from radioactively contaminated areas around Chornobyl has produced ambiguous results for the presence of radiation effects. More studies are needed to provide information on whether radiation exposure at Chornobyl significantly affected genetic diversity in natural populations of various taxa. Eleven and nine variable microsatellite loci were used to test for differences in genetic diversity between reference and Chornobyl populations of two cattail species (Typha angustifolia and Typha latifolia, respectively) from Ukraine. Our purpose was to determine whether radiation had a significant impact on genetic diversities of the Chornobyl Typha populations, or if their genetic composition might be better explained by species demography and/or changes in population dynamics, mainly in sexual and asexual reproduction. Populations closest to the reactor had increased genetic diversities and high number of genets, which likely were due to factors other than radiation including increased gene flow among Chornobyl populations, enhanced sexual reproduction within populations, and/or origin of the genets from seed bank. Both Typha species also demonstrated small but significant effects associated with latitude, geographical regions, and watersheds. Typha's demography in Ukraine possibly varies with these three factors, and the small difference between Chornobyl and reference populations of T. latifolia detected after partitioning the total genetic variance between them is probably due primarily to these factors. However, the positive correlations of several genetic characteristics with radionuclide concentrations suggest that radiation may have also affected genetics of Chornobyl Typha populations but much less than was expected considering massive contamination of the Chornobyl area.

Alleles↗

PubMed2006

Coselection for microbial resistance to metals and antibiotics in freshwater microcosms.

Bacterial resistances to diverse metals and antibiotics are often genetically linked, suggesting that exposure to toxic metals may select for strains resistant to antibiotics and vice versa. To test the hypothesis that resistances to metals and antibiotics are coselected for in environmental microbial assemblages, we investigated the frequency of diverse resistances in freshwater microcosms amended with Cd, Ni, ampicillin or tetracycline. We found that all four toxicants significantly increased the frequency of bacterioplankton resistance to multiple, chemically unrelated metals and antibiotics. An ampicillin-resistant strain of the opportunistic human pathogen Ralstonia mannitolilytica was enriched in microcosms amended with Cd. Frequencies of antibiotic resistance were elevated in microcosms with metal concentrations representative of industry and mining-impacted environments (0.01-1 mM). Metal but not antibiotic amendments decreased microbial diversity, and a weeklong exposure to high concentrations of ampicillin (0.01-10 mg l-1) and tetracycline (0.03-30 mg l-1) decreased microbial abundance only slightly, implying a large reservoir of antibiotic resistance in the studied environment. Our results provide first experimental evidence that the exposure of freshwater environments to individual metals and antibiotics selects for multiresistant microorganisms, including opportunistic human pathogens.

Ampicillin↗

PubMed2005

Elevated microbial tolerance to metals and antibiotics in metal-contaminated industrial environments.

To test the hypothesis that industrial metal contaminants select for microorganisms tolerant to unrelated agents, such as antibiotics, we analyzed metal and antibiotic tolerance patterns in microbial communities in the intake and discharge of ash settling basins (ASBs) of three coal-fired power plants. High-throughput flow-cytometric analyses using cell viability probes were employed to determine tolerances of entire bacterioplankton communities, avoiding bias toward culturable versus nonculturable bacteria. We found that bacterioplankton collected in ASB discharges were significantly more tolerant to metal and antibiotic exposures than bacterioplankton collected in ASB intakes. Optical properties of microorganisms collected in ASB discharges indicated no defensive physiological adaptations such as formation of resting stages or excessive production of exopolymers. Thus, it is likely that the elevated frequency of metal and antibiotic tolerances in bacterioplankton in ASB discharges were caused by shifts in microbial community composition, resulting from the selective pressure imposed by elevated metal concentrations or organic toxicants present in ASBs.

Anti-Bacterial Agents↗

PubMed2005

Evolutionary origin of the feather epidermis.

The formation of scales and feathers in reptiles and birds has fascinated biologists for decades. How might the developmental processes involved in the evolution of the amniote ectoderm be interpreted to shed light on the evolution of integumental appendages? An Evo-Devo approach to this question is proving essential to understand the observation that there is homology between the transient embryonic layers covering the scale epidermis of alligators and birds and the epidermal cell populations of embryonic feather filaments. Whereas the embryonic layers of scutate scales are sloughed off at hatching, that their homologues persist in feathers demonstrates that the predecessors of birds took advantage of the ability of their ectoderm to generate embryonic layers by recruiting them to make the epidermis of the embryonic feather filament. Furthermore, observations on mutant chickens with altered scale and feather development (Abbott and Asmundson [1957] J. Hered. 18:63-70; Abbott [1965] Poult. Sci. 44:1347; Abbott [1967] Methods in developmental biology. New York: Thomas Y. Crowell) suggest that the ectodermal placodes of feathers, which direct the formation of unique dermal condensations and subsequently appendage outgrowth, provided the mechanism by which the developmental processes generating the embryonic layers diverged during evolution to support the morphogenesis of the epidermis of the primitive feather filament with its barb ridges.

Alligators and Crocodiles↗

PubMed2005

Isolating microsatellite DNA loci.

A series of techniques are presented to construct genomic DNA libraries highly enriched for microsatellite DNA loci. The individual techniques used here derive from several published protocols but have been optimized and tested in our research laboratories as well as in classroom settings at the University of South Carolina and University of Georgia, with students achieving nearly 100% success. Reducing the number of manipulations involved has been a key to success, decreasing both the failure rate and the time necessary to isolate loci of interest. In our lab during the past 3 years alone, these protocols have been successfully used to isolate microsatellite DNA loci from at least 55 species representing three kingdoms. These protocols have made it possible to reduce the time to identify candidate loci for primer development from most eukaryotic species to as little as 1 week.

Animals↗

PubMed2005

Developing antibodies to synthetic peptides based on comparative DNA sequencing of multigene families.

Using antisera to analyze the expression of specific gene products is a common procedure. However, in multigene families, such as the beta-keratins of the avian integument where strong homology exists among the scale (ScbetaK), claw (ClbetaK), feather (FbetaK), and feather-like (FlbetaK) subfamilies, determining the cellular and tissue expression patterns of the subfamilies is difficult because polyclonal antisera produced from any one protein recognize all family members. Traditionally, researchers produced and screened multiple monoclonal antisera produced from the proteins of interest until an antiserum with sufficient specificity could be obtained. Unfortunately, this approach requires a lot of effort, and once obtained, such antisera may have limited applications. Here, we present procedures by which comparative DNA sequences of members from the beta-keratin multigene family were translated and aligned to identify amino acid domains that were conserved within the FbetaK subfamily, but which were divergent from the other subfamilies. A synthetic 23-mer peptide with the conserved amino acid sequence was generated and used to produce a polyclonal antiserum that recognizes only the FbetaK subfamily of proteins. Western blot analysis and confocal microscopy with this antiserum are now providing valuable new insights concerning the developmental and evolutionary relationships between the scale, claw, and feather proteins found in birds. This represents a powerful new approach combining techniques from molecular evolution and developmental biology to study the expression and evolution of specific members of multigene families.

Amino Acid Sequence↗

PubMed2005

Population genetics of the diamondback terrapin (Malaclemys terrapin).

We examined the population genetic structure of the diamondback terrapins (Malaclemys terrapin), within and among estuaries. Based on mark-recapture studies, these estuarine turtles have high site fidelity that is likely to make them vulnerable to local extinctions. We tested if observed site fidelity of adults would be reflected in intraestuarine population genetic structure of six highly polymorphic microsatellite loci (five tetranucleotide and one dinucleotide). No evidence was found for population structuring within the Charleston estuary nor among three different estuaries in South Carolina. We then examined four other terrapin populations from North Carolina to New York, as well as from the Florida Keys and from Texas. With increasing geographical distance, genetic differentiation increased from South Carolina through New York, but overall values were low. The dinucleotide locus contributed significantly more to the genetic differentiation of some population comparisons than any of the other loci. Interestingly, terrapins from South Carolina to New York were much more genetically similar to those from Texas (rho = 0.154) than to those from Florida (rho = 0.357). We attribute this pattern to extensive translocations of terrapins during the early 20th century to replenish diminished populations and to provide turtle farms with stocks. Terrapins collected in Texas were especially sought for shipment to the northeastern US because of their larger size. Our study indicates no population structure within or among adjacent estuaries. Thus, the mark-recapture information from adult and subadult feeding locations is a poor predictor of population genetic structure. Additionally, it appears that past human activities may have drastically altered the genetics of current populations. Finally, our data suggest that translocation of eggs or head starting of terrapins within estuaries or among adjacent estuaries is acceptable from a genetic standpoint.

Animals↗

PubMed2003

Origin of archosaurian integumentary appendages: the bristles of the wild turkey beard express feather-type beta keratins.

The discovery that structurally unique "filamentous integumentary appendages" are associated with several different non-avian dinosaurs continues to stimulate the development of models to explain the evolutionary origin of feathers. Taking the phylogenetic relationships of the non-avian dinosaurs into consideration, some models propose that the "filamentous integumentary appendages" represent intermediate stages in the sequential evolution of feathers. Here we present observations on a unique integumentary structure, the bristle of the wild turkey beard, and suggest that this non-feather appendage provides another explanation for some of the "filamentous integumentary appendages." Unlike feathers, beard bristles grow continuously from finger-like outgrows of the integument lacking follicles. We find that these beard bristles, which show simple branching, are hollow, distally, and express the feather-type beta keratins. The significance of these observations to explanations for the evolution of archosaurian integumentary appendages is discussed.

Animals↗

PubMed2003

Origin of feathers: Feather beta (beta) keratins are expressed in discrete epidermal cell populations of embryonic scutate scales.

The feathers of birds develop from embryonic epidermal lineages that differentiate during outgrowth of the feather germ. Independent cell populations also form an embryonic epidermis on scutate scales, which consists of peridermal layers, a subperiderm, and an alpha stratum. Using an antiserum (anti-FbetaK) developed to react specifically with the beta (beta) keratins of feathers, we find that the feather-type beta keratins are expressed in the subperiderm cells of embryonic scutate scales, as well as the barb ridge lineages of the feather. However, unlike the subperiderm of scales, which is lost at hatching, the cells of barb ridges, in conjunction with adjacent cell populations, give rise to the structural elements of the feather. The observation that an embryonic epidermis, consisting of peridermal and subperidermal layers, also characterizes alligator scales (Thompson, 2001. J Anat 198:265-282) suggests that the epidermal populations of the scales and feathers of avian embryos are homologous with those forming the embryonic epidermis of alligators. While the embryonic epidermal populations of archosaurian scales are discarded at hatching, those of the feather germ differentiate into the periderm, sheath, barb ridges, axial plates, barbules, and marginal plates of the embryonic feather filament. We propose that the development of the embryonic feather filament provides a model for the evolution of the first protofeather. Furthermore, we hypothesize that invagination of the epidermal lineages of the feather filament, namely the barb ridges, initiated the formation of the follicle, which then allowed continuous renewal of the feather epidermal lineages, and the evolution of diverse feather forms.

Amino Acid Sequence↗

PubMed2003

Developing transgenic Arabidopsis plants to be metal-specific bioindicators.

Deoxyribonucleic acid (DNA) microarrays provide a means to assess genome-wide expression patterns after exposure of an organism to different xenobiotics. Potential uses for this technology include identification of unknown toxicants, assessment of toxicity of new compounds, and characterization of the cellular mechanisms of toxicant action. Here we describe another use of DNA microarrays in toxicant-specific gene discovery. Combining results from two DNA microarray experiments, we have identified genes from the model plant Arabidopsis thaliana that are induced in response to one but not other heavy metals. The promoters of these genes should be useful in developing metal-specific transgenic biomonitors. To test this idea, we have fused the promoter of one of the newly identified Ni-inducible genes (AHB1) to the beta-glucuronidase (GUS) reporter gene. Arabidopsis plants containing the AHBI::GUS transgene show reporter gene activity when they are grown on media containing Ni but not when grown on media containing Cd, Cu, Zn, or without added metals. Thus, this approach has resulted in the creation of a transgenic strain of Arabidopsis that can report on the presence and concentration of Ni in plant growth media. Such transgenic models can serve as cheap and efficient biomonitors of bioavailable heavy metal contamination in soils and sediments.

Biological Availability↗

PubMed2002

Microsatellite DNA analyses support an east-west phylogeographic split of American alligator populations.

We examined the population genetic structure of American alligators (Alligator mississippiensis) sampled from 12 localities across the southeastern United States. The primary goal of this study was to determine the extent of population differentiation among alligators from four Florida lakes using eight microsatellite loci and compare the results to additional sites located at varying distances from them. Analyses of population structure revealed little differentiation (F(ST)=0.039; Rho=0.012) among the four Florida lakes, Apopka, Griffin, Orange and Woodruff, which are all located in the St. John&'s River watershed in north-central Florida. Further, there was little differentiation among these samples and samples collected from the Everglades National Park (F(ST)=0.044; Rho=0.009) and south Georgia (F(ST)=0.045; Rho=0.032). Therefore, these six samples were pooled together as a "FL/sGA group." Similarly, samples collected in the western extent of the range, Anahuac National Wildlife Refuge in Texas and Salvador Wildlife Management Area, Marsh Island Wildlife Refuge and Rockefeller Wildlife Refuge in Louisiana, also lacked population structure (F(ST)=0.024; R(ST)=0.040). These four populations were pooled into the "TX/LA group." Comparisons of these two groups with samples taken from the Santee Coastal Reserve in South Carolina and Mobile, Alabama yielded three to four times more differentiation among groups (F(ST)=0.131; Rho=0.187). These and other analyses support the hypothesis of an east-west phylogeographic split in American alligator populations and are consistent with studies of many freshwater fish and aquatic and terrestrial turtles distributed throughout this same geographic region.

Alligators and Crocodiles↗

PubMed2002

Low mitochondrial DNA variation among American alligators and a novel non-coding region in crocodilians.

We analyzed 1317-1823 base pairs (bp) of mitochondrial DNA sequence beginning in the 5' end of cytochrome b (cyt b) and ending in the central domain of the control region for 25 American alligators (Alligator mississippiensis) and compared these to a homologous sequence from a Chinese alligator (A. sinensis). Both species share a non-coding spacer between cyt b and tRNA(Thr). Chinese alligator cyt b differs from that of the American alligator by 17.5% at the nucleotide level and 13.8% for inferred amino acids, which is consistent with their presumed ancient divergence. Only two cyt b haplotypes were detected among the 25 American alligators (693-1199 bp surveyed), with one haplotype shared among 24 individuals. One alligator from Mississippi differed from all other alligators by a single silent substitution. The control region contained only slightly more variation among the 25 American alligators, with two variable positions (624 bp surveyed), yielding three haplotypes with 22, two, and one individuals in each of these groups. Previous genetic studies examining allozymes and the proportion of variable microsatellite DNA loci also found low levels of genetic diversity in American alligators. However, in contrast with allozymes, microsatellites, and morphology, the mtDNA data shows no evidence of differentiation among populations from the extremes of the species range. These results suggest that American alligators underwent a severe population bottleneck in the late Pleistocene, resulting in nearly homogenous mtDNA among all American alligators today.

Alligators and Crocodiles↗

PubMed2002

Studies on the molecular evolution of the Crocodylia: footprints in the sands of time.

A reasonably large number of studies focusing on the molecular evolution of crocodilians have been completed during the past 100 years. Proteins were initially studied before DNA was known to carry the genetic information of cells and organisms, and were subsequently studied to infer changes at the DNA level. More recently, studies on the DNA itself have been completed. We have had the pleasure of taking part in or facilitating many studies conducted over the past 50 years, especially several of the earliest studies done using newly developed molecular techniques. We provide a review of the molecular genetic studies on crocodilians, summarizing the findings of these studies as well as the context in which they were undertaken. This review is a personal look at the history of molecular studies on the evolutionary biology of crocodilians. Our excuse for this focus is that our professors, our students and we have had the opportunity to be among the first to apply many new techniques to studies of crocodilians since 1950, when one of us (HCD) was a graduate student of Roland Coulson and Tom Hernandez. Although we will review much of the material in this subject area, we do not claim that it is complete. Instead, we focus our presentation on work in which we have participated or with which we are particularly familiar. We especially focus on materials relevant to the research presented at the 2(nd) International Crocodilian DNA Workshop, 7-9 November, 2001, at the San Diego Zoo. Thus, the following review also stands as a tribute to our mentors, students, and colleagues.

Alligators and Crocodiles↗

PubMed2002

Frequency distributions of 137Cs in fish and mammal populations.

We collected fish and mammals in several radioactively contaminated locations in the Chornobyl Exclusion Zone and analyzed them for 137Cs content. Frequency distributions were built for populations of channel catfish, yellow-necked mice and bank voles. We combined our data with similar data from several other studies to demonstrate the relationship between the standard deviations and means of 137Cs of fish and mammal populations. The frequency distributions of 137Cs in populations of fish and mammals are not normal, as indicated by the strong relationship between standard deviation and mean. Distributions for mammals are more skewed than those for fish. Fish and mammals probably use their environments in fundamentally different ways. The highest concentrations and thus greatest risks are therefore confined to relatively few individuals in each population.

Animals↗

PubMed2002

Detection by microsatellite analysis of early embryonic mortality in an alligator population in Florida.

In the 1980s, alligators (Alligator mississippiensis) of Lake Apopka (Florida, USA) underwent a population decline associated with decreased egg viability, effects that have been associated with endocrine-disrupting, persistent organochlorine pesticides. It is currently unknown whether the decreased egg viability is due to fertilization failure or early embryonic death. Therefore, we conducted a preliminary study to evaluate the use of microsatellite DNA loci to determine the fertilization status of nonviable eggs. Using microsatellite analysis, we compared genotypes from blasto-disks and embryos with the genotypes from females trapped at the nest. Four of five nonviable egg samples tested yielded evidence of fertilization. No evidence of unfertilized eggs was obtained, but amplifiable DNA could not be obtained from one entirely nonviable clutch. Thus, we demonstrate that early embryonic mortality in alligators can be detected by microsatellite analysis, but also suggest substantial effort is needed to improve the recovery of DNA and amplification of alligator microsatellite loci.

Alleles↗