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Biomedical subjects

G Ballard

Publications and source records attributed to G Ballard.

7 recordsLinked to original sources
PubMed2005

Microevolution and mega-icebergs in the Antarctic.

Microevolution is regarded as changes in the frequencies of genes in populations over time. Ancient DNA technology now provides an opportunity to demonstrate evolution over a geological time frame and to possibly identify the causal factors in any such evolutionary event. Using nine nuclear microsatellite DNA loci, we genotyped an ancient population of Adélie penguins (Pygoscelis adeliae) aged approximately 6,000 years B.P. Subfossil bones from this population were excavated by using an accurate stratigraphic method that allowed the identification of individuals even within the same layer. We compared the allele frequencies in the ancient population with those recorded from the modern population at the same site in Antarctica. We report significant changes in the frequencies of alleles between these two time points, hence demonstrating microevolutionary change. This study demonstrates a nuclear gene-frequency change over such a geological time frame. We discuss the possible causes of such a change, including the role of mutation, genetic drift, and the effects of gene mixing among different penguin populations. The latter is likely to be precipitated by mega-icebergs that act to promote migration among penguin colonies that typically show strong natal return.

Animal Migration↗
PubMed2001

Protein tyrosine phosphatase-dependent proteolysis of focal adhesion complexes in endothelial cell apoptosis.

Adenosine and/or homocysteine causes endothelial cell apoptosis, a mechanism requiring protein tyrosine phosphatase (PTPase) activity. We investigated the role of focal adhesion contact disruption in adenosine-homocysteine endothelial cell apoptosis. Analysis of focal adhesion kinase (FAK), paxillin, and vinculin demonstrated disruption of focal adhesion complexes after 4 h of treatment with adenosine-homocysteine followed by caspase-induced proteolysis of FAK, paxillin, and p130(CAS). No significant changes were noted in tyrosine phosphorylation of FAK or paxillin. Pretreatment with the caspase inhibitor Z-Val-Ala-Asp-fluoromethylketone prevented adenosine-homocysteine-induced DNA fragmentation and FAK, paxillin, and p130(CAS) proteolysis. Asp-Glu-Val-Asp-ase activity was detectable in endothelial cells after 4 h of treatment with adenosine-homocysteine. The PTPase inhibitor sodium orthovanadate did not prevent endothelial cell retraction or FAK, paxillin, or vinculin redistribution. Sodium orthovanadate did block adenosine-homocysteine-induced FAK, paxillin, and p130(CAS) proteolysis and Asp-Glu-Val-Asp-ase activity. Thus disruption of focal adhesion contacts and caspase-induced degradation of focal adhesion contact proteins occurs in adenosine-homocysteine endothelial cell apoptosis. Focal adhesion contact disruption induced by adenosine-homocysteine is independent of PTPase or caspase activation. These studies demonstrate that disruption of focal adhesion contacts is an early, but not an irrevocable, event in endothelial cell apoptosis.

Adenosine↗
PubMed1993

Use of rRNA fluorescence in situ hybridization for measuring the activity of single cells in young and established biofilms.

We describe the in situ use of rRNA-targeted fluorescent hybridization probes in combination with digital microscopy to quantify the cellular content of ribosomes in relationship to the growth rate of single cells of a specific population of sulfate-reducing bacteria in multispecies anaerobic biofilms. Using this technique, we inferred that this population was growing with an average generation time of 35 h in a young biofilm, whereas the doubling time in an established biofilm was significantly longer. Conventional chemical determinations of the RNA, DNA, and protein contents of this culture at different growth rates were also carried out, and the resulting data were compared with the rRNA fluorescence in situ hybridization data.

Base Sequence↗
PubMed1992

Temporal lectin histochemical characterization of porcine small intestine.

A variety of biotinylated lectins was applied to formalin-fixed intestinal sections from isolator-reared pigs ranging in age from newborn through 12 weeks. Lectin binding to brush borders of villus enterocytes, crypt enterocytes, and dome epithelium, and lectin reactivity within goblet cells and Brunner's glands was semiquantified by microscopy and was used to estimate temporal changes in complex carbohydrates of enteric epithelium. Although variability in binding scores often was observed among pigs of the same age, several general patterns of lectin binding were detected. Dolichos biflorus and Ulex europaeus lectins had increasing binding to brush border membranes as pigs aged. The Dolichos biflorus, however, had decreased binding at the 12-week time point. Neuraminidase-treated Arachis hypogaea and Triticum vulgaris were associated with high mean binding scores at all time points. Canavalia ensiformis bound, with high mean score at all time points, to villus but not to crypt enterocytes. Arachis hypogaea was associated with variable but often high binding scores, regardless of pig age. Succinylated wheat germ agglutinin bound more to crypt than to villus enterocytes. Goblet cells were generally less reactive than were corresponding villi and crypts. Dome epithelium reactivity varied with the lectin used, whereas Brunner's glands reacted with all lectins tested. We conclude that age and regional variations in lectin binding may reflect differences in intestinal function and differentiation. Because complex carbohydrates may act as cell surface receptors for a variety of enteric pathogens, our results indicate that these differences may be partially responsible for age and anatomic differences in susceptibility or resistance to enteric disease.

Aging↗
PubMed1991

Characterization of subendometrial myometrial contractions throughout the menstrual cycle in normal fertile women.

The objective was to study the characteristics of ultrasonographically detected subendometrial myometrial contractions. The contractions were evaluated by 328 ultrasound scans throughout the menstrual cycle. Reproducibility of these findings were studied in consecutive cycles. Eighteen healthy ovulatory volunteers with proven fertility were evaluated for at least one complete menstrual cycle in the follicular, periovulatory, and luteal phases. Multiple cycles were studied in 10 volunteers. The results showed that the contractions increase in frequency, amplitude, and percentage toward the fundus throughout the follicular and periovulatory phases. The pattern is essentially reversed in the luteal phase. There is reproducibility of these patterns from cycle to cycle. We conclude that there is a definite identifiable pattern of subendometrial myometrial contractility that varies with the phases of the normal menstrual cycle and recurs in a similar fashion from cycle to cycle.

Adult↗
PubMed1990

Contractions of the inner third of the myometrium.

Forty-six consecutive endovaginal ultrasound examinations were screened for the presence of myometrial contractions. The study group contained pregnant women up to 10 weeks' menstrual age, nonpregnant, and postmenopausal women. Rhythmic myometrial contractions of the inner myometrial third not previously reported were seen in 35 studies in pregnant, nonpregnant, and postmenopausal women. The contractions involved the inner third of the myometrium in all but two cases. In these two cases, all three muscular layers were involved. The majority of women showed retrograde contractions, with the contraction wave moving from the cervix to the fundus. In menstruating women and one case of abortion, the contractions were antegrade. It is our speculation that these retrograde contractions of the inner myometrial third may be important in sperm transport and for the conservation of early pregnancies within the uterine cavity.

Adult↗