David Spencer Smith

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Dnmt3a and Dnmt3b are de novo DNA methyltransferases that also act as transcriptional repressors independent of methyltransferase activity. To elucidate the underlying mechanism of transcriptional repression, Dnmt3a was purified from mouse lymphosarcoma cells (P1798) by extensive fractionation on five different chromatographic matrices followed by glycerol(More)
The distribution of esterase activity in the last abdominal ganglion, the connectives and the cereal nerves of the cockroach Periplaneta americana has been investigated cytochemically. Activity of an unspecific eserine-insensitive esterase (or esterases) has been found in glial elements in these regions of the nerve cord. In addition, sites of(More)
The structure of peripheral nerves, and the organization of the myoneural junctions in flight muscle fibers of a beetle is described. The uniaxonal presynaptic nerve branches display the "tunicated" structure reported in the case of other insect nerves and the relationship between the axon and the lemnoblast folds is discussed. The synapsing nerve terminal(More)
An electron microscopic investigation of the Malpighian tubules of a leaf hopper, Macrosteles fascifrons, shows that these organs comprise three quite distinct cell types, and the structure of these and of the mid- and hindgut epithelial cells is described. In particular, a comparison is made between the organization of the basal and apical surfaces of(More)
The determination of cortisol levels in saliva offers a number of significant advantages as compared with plasma or serum measurements, and radioimmunoassay is the technique of choice because of the greater sensitivity required. To date, the assay of salivary cortisol has been limited to only a few centres employing 'in-house' reagents. We describe some(More)
PURPOSE Previous studies in our laboratory have shown the progressive methylation and suppression of the gene encoding protein tyrosine phosphatase, PTPRO, in the livers of rats fed a methyl-deficient diet that induces hepatocarcinogenesis. Subsequently, we observed the methylation of PTPRO in primary human lung tumors and also showed its potential tumor(More)
Fluorescence polarization immunoassay (FPIA) is a homogeneous (without separation) competitive immunoassay method based on the increase in fluorescence polarization (FP) of fluorescent-labeled small antigens when bound by specific antibody. The minimum detectable quantity of FPIAs with fluorescein label (about 0.1 ng analyte) is comparable with(More)
The organization of the luminescent organ of an adult firefly has been studied with the electron microscope, and particular attention has been given to the disposition of nerve terminals within the organ. The cytological structure of the cells of the tracheal system, the peripheral and terminal axons, the photocytes and the cells of the dorsal(More)
As is typically the case in insects, the cellular layer underlying the cuticle of the body surface in Carausius morosus (Br.) comprises both epidermal cells and enocytes (Wigglesworth, 1953). In this insect a cicadan rhythm of color change occurs, reported to be associated with the movement of pigment granules within the epidermal cells (Schleip, 1911 ;(More)