Biomedical subjects
Publications and source records attributed to F C Leung.
DNA Simdex Version 2.1 is a third-generation Windows computer program that uses sophisticated image-analysis techniques to automatically locate bands on electrophoresis gel images and calculate similarity indexes. Here we give a functional description of the program.
In response to the deluge of genome data, we are developing Visual Genome Explorer, an interactive graphical interface to genome data. Given is a description of the prototype program, which introduces the concept of visual comparative genomics for complete bacterial genomes.
The effect of GTP concentration of forskolin-stimulated adenylyl cyclase activity was examined in synaptosomal membranes from 15-day-old rats that were hypothyroid owing to administration of propylthiouracil and a low-iodine diet to the mothers during pregnancy and suckling. In membranes from the forebrain hypothyroidism abolished the overall stimulatory effect of GTP, which was seen in the euthyroid case. In membranes from the hindbrain hypothyroidism had the opposite effect in that there was an enhancement of an overall stimulatory effect of GTP. It is suggested that these findings reflect changes during early development of the brain in the expression of various G-proteins and/or the expression of different isoforms of adenylyl cyclase.
The abundances of G protein alpha-subunits (Gi1 alpha, Gi2 alpha, G0 alpha and Gq/ll alpha) were measured in synaptosomal membranes isolated from forebrain and hindbrain regions of euthyroid and hypothyroid neonatal rats at 10, 15, 20 and 25 days post-partum. The findings show that hypothyroidism causes a distinct perturbation of the normal developmental profile of these signalling components. It is suggested that these changes may contribute to some of the neurological deficits arising from hypothyroidism in early development.
DNA SIMDEX is a DOS-based computer program designed to assist in the visual scoring of DNA fingerprint assays. DNA SIMDEX uses the migration distances of the individual DNA bands to generate lists of probable matching and nonmatching bands and automatically calculates a probable similarity index between DNA fingerprints based on these initial predictions. After comparisons are edited by the user, the final similarity index, along with accompanying data, can be saved on a floppy disk or hard drive for easy storage and retrieval or can be printed directly on a laser or line printer. The program has been developed to function with or without an image-analysis system, thus making it an inexpensive alternative for small laboratories.
Treatment of rats for 3 days with T3 halved the abundance of the alpha-subunits of Gi1 and Gi2 in synaptosomal membranes isolated from the cerebral cortex. It is suggested that these changes could contribute to behavioural abnormalities in hyperthyroidism. Similar T3 treatment did not alter abundance of Gi1 alpha or Gi2 alpha in the medulla oblongata nor did it alter abundance of G(o) alpha-subunits in three tested brain regions.
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The objective of this study is to examine and characterize epidermal growth factor receptor (EGF-R) binding in inhaled plutonium-induced canine lung-tumor tissue and to compare it with that in normal canine lung tissue. Crude membrane preparations from normal and lung-tumor tissue from beagle dogs were examined in a radioreceptor assay, using 125I-labeled epidermal growth factor (EGF) as a ligand. Specific EGF receptor binding was determined in the presence of excess unlabeled EGF. We have examined EGF receptor binding in eight lung-tumor samples obtained from six dogs. Epidermal growth factor receptor binding was significantly greater in lung-tumor samples (31.38%) compared with that in normal lung tissue (3.76%). Scatchard plot analysis from the displacement assay revealed that there was no statistical difference in the binding affinity but significantly higher concentration of EGF-R sites in the lung-tumor tissue (619 fmol/mg) than in normal lung tissue (53 fmol/mg). The increase in EGF-R number in plutonium-induced dog lung tumors does not seem to correlate with increase in the initial lung burden exposure to plutonium. Our results demonstrate that there is a significant increase in EGF-R binding in inhaled plutonium-induced dog lung tumors.
An improved and simplified radioimmunoassay for measuring pineal, serum, and in vitro cultured medium melatonin is described. Using 2-[125I]iodomelatonin as radiolabeled ligand and a polyclonal rabbit antimelatonin antiserum, melatonin concentrations were determined in all three types of samples by a 2-day direct equilibrium double-antibody assay method without prior extraction. Serial dilutions of pineal homogenates, serum, and cultured medium all gave parallel displacement curves. Cross-reactivity of the antisera with other indoles was negligible. Intraassay coefficients of variation (n = 3) were 5.09, 3.32, and 5.05% at 7.81, 62.5, and 500 pg/tube, respectively, and the interassay coefficients of variation (n = 20) were 12.18% at 62.5 pg/tube. A characteristic diurnal rhythm of melatonin was observed using this direct assay for measuring daytime and nighttime chicken pineal and serum samples. An in vitro incubation of chicken pineal glands with a lighting cycle of 12-hr light:12-hr dark showed that the diurnal rhythm of melatonin secretion into the cultured medium was maintained. The direct assay method described in this report for measuring chicken melatonin using 2-[125I]iodomelatonin as radiolabeled ligand coupled with the in vitro cultured chicken pineal gland clearly offers great potential for studying the chicken pineal circadian oscillator and its underlying mechanism.
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An increased incidence and severity of a brownish coloration of hair has been observed around the nose and on the ears of female rats that were chronically exposed to 60-Hz electric fields. Microscopic examination of the colored areas revealed a red-brown globular deposit on hair shafts in affected areas without signs of physical injury.
Three transcriptional regulatory regions including a human cytomegalovirus immediate-early region (CMVIE) promoter, the simian virus-40 early region (SV40E) promoter, and Moloney murine leukemia virus (MoMLV) long terminal repeat (LTR) were ligated to the bovine growth hormone (bGH)-coding gene. Using a bGH transient expression system, the CMVIE and SV40E gene transcriptional regulatory regions were found to be approximately two-fold more efficient than the MoMLV LTR in directing expression of bGH in mouse L cells.
Growth hormone (GH)-containing cells in the hypophyseal pars distalis of the chick embryo were identified immunohistochemically using anti-chicken GH sera. GH cells are first demonstrable in Rathke's Pouch as early as Day 4.5 of incubation. By Day 9.5, when the two lobes (rostral and caudal) of the pars distalis are easily recognized, GH cells are confined exclusively to the caudal lobe. Although the number of GH cells increases gradually during embryonic development, there is a statistically significant difference between Days 10.5 and 12.5 in both the cellular density and the percentage of somatotrophs. GH cells, which contain coarse granules evenly distributed throughout the cytoplasm, varied in diameter from 9.3 micron on Day 4.5 to 11.8 micron on Day 20.5, while the nuclear diameter of these cells increased from 2.8 micron on Day 4.5 to 4.9 micron on Day 20.5. There was a statistically significant difference in the nuclear/cytoplasmic ratio between Days 4.5 and 13.5 and between Days 13.5 and 20.5 of incubation. Aspects of the regulation of growth hormone synthesis and secretion in the chick embryo are discussed.
Hepatic growth hormone (GH) receptor binding was compared in normal and sex-linked dwarfs (SLD) from both Hubbard and Cornell strain chickens. At 6, 8, and 20 weeks of age, hepatic GH receptor binding in the Hubbard SLD chickens was significantly lower than that of normal fast-growing birds. At 20 weeks of age, only 2 of 22 SLD chickens in the Hubbard broiler strain showed positive binding at a high enough level to allow for Scatchard analysis. The affinity constants and binding capacities of these two SLD chickens were numerically (but not significantly) lower than those of the normal fast-growing birds. We further examined hepatic GH receptor binding in two closely related White Leghorn strains of chickens that have been maintained as closed breeding populations for many years. We observed no detectable hepatic GH binding in the Cornell SLD chickens (N = 20), as compared to the normal-growing control strain (K strain). In both SLD strains, pretreatment with 4 M MgCl2 did not enhance GH binding, suggesting that there was no endogenous GH binding to the receptor. Based on these data, we suggest that the lack, or greatly reduced number, of GH receptors may be a major contributing factor to the dwarfism observed in these strains.
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Purified chicken GH (cGH) and a synthetic human GH-releasing hormone (hpGRF) were tested for the ability to improve growth performance in chickens. Purified cGH was given to 4-week-old cockerels at 5, 10, and 50 micrograms/day for 14 days via daily iv injection. Body weights of chickens receiving 5 and 10 micrograms/day cGH were significantly increased at 6 days by 13.5% and 11.2%, respectively, relative to control values. At 14 days, body weights averaged 8.1% and 7.7% greater than controls, but these values were not statistically significant. There was a slight stimulation of body weight gain in chickens receiving 50 micrograms/day cGH. In general, cGH produces a transient stimulation of body weight gain in chickens. hpGRF was also given to 4-week-old cockerels for 14 days via daily iv injection at 0.1, 1.0, and 10.0 micrograms/day. hpGRF at 0.1 microgram/bird daily increased body weight on day 14 (9.1% over the control value). The stimulating effects of hpGRF on body weight are also transient. The effects of cGH on serum somatomedin-C (SM-C) were examined. Serum SM-C concentrations were significantly elevated 24 and 36 h after injection of cGH. In conclusion, purified cGH and hpGRF appear to have some growth-promoting activity. The stimulatory effect of hpGRF on weight gain may be mediated via GH, and the stimulatory effect of cGH could be mediated through SM-C.
Mouse fibroblast cell lines which secrete bovine (b) GH have been generated. This was accomplished by cotransforming mouse L cells (thymidine kinase-negative [TK-] and adenine phosphoribosyl transferase-negative [APRT-]) with DNA molecules encoding the Rous sarcoma virus-long-terminal repeat and bGH genes along with the herpes viral TK gene and the hamster APRT gene. One stable cell line, Pd lambda-pbGH 4-13, was found to secrete approximately 75 micrograms bGH per 24 h/5.0 X 10(6) cells. Media from this cell line were collected for purification of recombinant bGH (rbGH). Purification involved (NH4)2SO4 fractionation, ion-exchange chromatography, and gel filtration on Sephacryl S-200. The rbGH was characterized by bioassay, RIA, radioreceptor assay, and sodium dodecyl sulfate gel electrophoresis. Results of these analyses were compared with those obtained with a highly purified pituitary bGH. In the rat tibia bioassay, rbGH was found to be as potent as pituitary bGH. Results from the RIA, radioreceptor assay, and sodium dodecyl sulfate gel electrophoresis and Western blot analysis also suggested that the rbGH was similar to that of pituitary origin. Amino acid composition, partial (amino-terminal) sequence, and tryptic peptide maps were also found to be similar between the rbGH and pituitary bGH preparations. The amino terminus of the rbGH showed similar heterogeneity to that of the bGH of pituitary origin. We conclude that rbGH which was synthesized, processed, and secreted from transformed mouse fibroblasts possessed almost exactly the same physiochemical properties as pituitary bGH.