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Biomedical subjects

L M Field

Publications and source records attributed to L M Field.

At least 73 records · Page 4Linked to original sources
PubMed1996

Analysis of amplicons containing the esterase genes responsible for insecticide resistance in the peach-potato aphid Myzus persicae (Sulzer).

The amplification of genes encoding an insecticide-detoxifying esterase (E4) in the peach-potato aphid Myzus persicae is one of the few examples where this genetic phenomenon has been shown to be involved in the response of an intact higher organism to artificial selection. Here we report quantitative and qualitative studies of the repeat units (amplicons) containing the E4 genes in a highly resistant aphid clone. Initial studies to quantify esterase sequences showed a 5-11-fold increase in resistant aphids compared with susceptible aphids, suggesting the presence of 10-22 gene copies per diploid genome. A more incisive analysis by pulsed-field gel electrophoresis confirmed the presence of about 12 copies of the E4 gene and showed them to be on about 24 kb amplicons, arranged as a tandem array of direct repeats. This, together with previous results from crossing experiments and with recent in situ hybridization studies, confirms that the E4 gene amplification in this aphid clone is heterozygous at a single locus. However, these data show that the gene amplification alone cannot account for the approx. 60 times higher levels of E4 protein and its mRNA present in this aphid clone, and therefore resistance must involve changes in both esterase gene copy number and gene expression.

Animals↗
PubMed1996

Changes in the methylation of amplified esterase DNA during loss and reselection of insecticide resistance in peach-potato aphids, Myzus persicae.

Insecticide resistance in peach-potato aphids, Myzus persicae, results from the amplification of genes encoding an esterase that hydrolyses and sequesters insecticides. Resistance is normally stable, but highly resistant aphid clones sometimes lose resistance when insecticidal selection pressure is removed. This loss of resistance, termed reversion, arises from a loss of elevated esterase enzyme through transcriptional control, i.e. without loss of the amplified esterase DNA sequences. We have shown that loss of the elevated enzyme occurred simultaneously with loss of methylation at CCGG sites in the amplified DNA sequences. During reselection of resistance in these revertant clones, enzyme levels increased, but there was no corresponding return of methylation to DNA sequences. Thus, although DNA methylation is closely correlated with expression of the amplified esterase genes during reversion, it may not be a factor in the reverse process.

Animals↗
PubMed1996

Polymerase chain reaction-based identification of insecticide resistance genes and DNA methylation in the aphid Myzus persicae (Sulzer).

The ability of a peach-potato aphid (Myzus persicae) to resist insecticides can depend on both the presence of amplified esterase genes and on differences in their expression. Here we report a polymerase chain reaction-restriction enzyme (PCR-REN) technique which can detect the presence of amplified esterase genes and distinguish between the two possible types of amplified gene (E4 and FE4) and a homologous fragment from susceptible aphids. The technique is quick and sensitive enough to be used on a fraction of an aphid or an individual embryo. Furthermore, it can be combined with a pre-PCR digestion using a methylation-sensitive enzyme (Hpall) to determine whether or not the esterase genes contain 5-methylcytosine, the presence or absence of which is known to correlate with changes in gene expression.

Animals↗
PubMed1996

Dermabrasion in xeroderma pigmentosum.

BACKGROUND: Dermabrasion is one choice of treatment for patients with severe actinic damage. OBJECTIVE: To report the youngest xeroderma pigmentosum patient ot have received the benefits of this procedure. METHODS: The dermabrasion was performed under general anesthesia using an acrotorque hand engine. RESULTS: New tumor formation was reduced for several months after the treatment. CONCLUSION: Dermabrasion can be considered as another therapeutic choice for young xeroderma pigmentosum patients with severe actinic damage.

Anesthesia, General↗
PubMed1996

Hairline reconstruction utilizing modified winged V-plastic hair-bearing flaps and focal anastomotic line excisions.

BACKGROUND: A large, recurrent basal cell carcinoma involving the left forehead and suprajacent hair-bearing scalp was excised, following which an esthetically acceptable reconstruction of the scalp and hairline margin was accomplished. OBJECTIVE: A method of utilizing two hair-bearing flaps to cover a large defect at the hair-bearing scalp margin will be photographically demonstrated, and the maneuvers to precisely reconstruct the scalp's anastomotic margin with the forehead will be shown and discussed. METHODS: Dual hair-bearing "winged" V-plastic flaps were evolved anteriorly, the two flaps joined, an M-plasty (Webster) was then incorporated to spare hair-bearing scalp posteriorly, and the entire conjoined scalp flap then advanced anteriorly to the forehead. The precise curvatures of the anastomotic line were reestablished by exact excisions of forehead skin underlying the hair-bearing scalp flaps, or amputations of overlying hair-bearing scalp in excess of forehead needs. RESULTS: An esthetically pleasing and reasonably exact reconstruction of the hair-bearing scalp and forehead anastomotic line was accomplished. CONCLUSION: A precise reconstruction of the forehead/scalp margin can be accomplished utilizing a combination of techniques, including hair-bearing "winged" V-plastic flaps, an M-plasty, and the serial removal of segments of both glabrous and nonglabrous skin to reestablish the frontal hairline margin.

Aged↗
PubMed1995

Sideburn hairline reconstruction by flap techniques. A Review.

BACKGROUND: A variety of flap techniques are utilized to accomplish aesthetic reconstruction of the sideburn hairline. OBJECTIVE: This communication is intended to review such techniques, and to discuss their applicability to this location. METHOD: Selected cases from the author will be presented using both a discussion and a photographic format. RESULTS: Reconstitution of a cosmetically acceptable sideburn hairline will be apparent in all cases. CONCLUSION: Proper selection from a variety of flap techniques allows reconstruction of aesthetically pleasing hairlines in the sideburn area.

Ear, External↗