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Biomedical subjects

C Green

Publications and source records attributed to C Green.

At least 289 records · Page 16Linked to original sources
PubMed1980

Targeted deletions of sequences from closed circular DNA.

Closed circular DNA interacts with complementary sequences of single-stranded DNA to form displacement loop (D loop) structures in vitro. The site of D-loop formation can be directed by using single-stranded DNA derived from a selected restriction fragment. Circular DNA containing a D loop can then be linearized by cleavage with endonuclease S1. This cleavage appears to remove a limited number of nucleotides from each strand of the circular DNA substrate. Incubation with polynucleotide ligase followed by propagation in vivo leads to circular DNA molecules that bear small, single deletions in the region of the single-stranded DNA sequence chosen for the formation of the D loops. We have utilized these manipulations of DNA to construct tetracycline-sensitive deletion mutants of plasmid pBR322. The level of mutagenesis obtained by the procedure is sufficiently high that selective growth and screening procedures are not necessary for the isolation or identification of mutants. The frequency, variety, and small size of the deletions obtained within the selected target regions present considerable advantage for genetic and biochemical analysis. The method is quite general in rationale and should be immediately applicable to phage and viruses having infectious circular DNA genomes or recombinant DNA species propagated in circular plasmid vectors.

Chromosome Deletion↗
PubMed1980

Issues concerning parents after the death of their newborn.

Thirty-five families were interviewed by members of the intensive care nursery staff 2-4 months after the death of their newborn. Of the families interviewed, 74% wanted to review the events leading to their child's death and ask questions about information they already knew. Most families who were interested in the autopsy findings used the results to find out "how normal everything else was." Topics frequently discussed by parents involved feelings of guilt and problems that arose after the infant's death (isolation by friends, somatic complaints, marital and sexual problems, memories of prior losses, problems with siblings and disposal of baby's things). One-third of the families were felt to need continuing emotional support due to their inability to assume previously accepted responsibilities. For many families, the physician may be the only individual who can tolerate listening to their distress.

Adaptation, Psychological↗
PubMed1979

A murine teratocarcinoma stem cell line carries suppressed oncogenic virus genomes.

Murine teratocarcinoma stem cells are nonpermissive for productive infection by a variety of DNA (polyoma and SV40 virus) and RNA (murine leukemia and sarcoma virus) tumor viruses whereas differentiated murine cells derived from the stem cells are permissive for productive (or abortive in the case of SV40) infection by these same viruses. The block to productive infection by these oncogenic viruses is at a postpenetration step in the replication cycle of these viruses but the precise level of the block has not been established for any of these viruses. In this report we describe teratocarcinoma-derived stem and differentiated cell lines which should be especially useful in determining the level of the block to replication of ecotropic murine leukemia virus in murine teratocarcinoma stem cells. The stem cell line, OTT6050AF1 BrdU, which is completely nonpermissive to productive infection by Moloney murine leukemia virus and consists of 97% pluripotent stem cells, contains DNA copies of an RNA tumor virus which is indistinguishable from the N-tropic murine leukemia virus of AKR mice. The stem cells are negative for expression of viral reverse transcriptase, p30 and gp69/71 and no virus is found by XC plaque assay or other biological tests. Differentiated cells established from the same teratocarcinoma tumor are 100% positive for viral gp69/71, p30, and produce large amounts of reverse transcriptase activity and N-tropic virus as detected by biological assay. The virus isolated from the differentiated cells is closely related, if not identical to AKR N-tropic virus by nucleic acid hybridization studies and is thus not an endogenous virus of the 129 strain of mice. The teratocarcinoma tumor from which the cell lines were established had been carried in 129 mice and perhaps at some time in the mouse passage history the tumors were infected (nonproductively) with the N-tropic virus. Regardless of the origin of this viral DNA, the OTT6050A derived stem and differentiated cell lines should be extremely useful in defining in stem cells the step at which ecotropic murine leukemia virus replication is blocked.

Animals↗
PubMed1979

Isoenzymes of beta-hexosaminidase from normal rat colon and colonic carcinoma.

N-Acetyl-beta-D-hexosaminidase isolated from normal rat colon was compared to that obtained from a transplantable rat colonic carcinoma. Levels of total hexosaminidase from purified epithelial cells of normal colon were similar to those from purified malignant cells from the transplantable tumor. Cultured malignant cells had significantly higher levels of activity than did freshly purified tumor cells. Isoelectric focusing of hexosaminidase from normal rat colon indicated approximately equal amounts of A (pI 5.0 ) and B (pI 8.1) isoenzyme activity. The B isoenzyme (normal cell) was more stable to heat inactivation than was the A isoenzyme and had significantly higher activity at low pH's. In contrast, the B isoenzyme from the tumor was relatively unstable to heat and low pH.

Animals↗
PubMed1979

Do parents utilize physician follow-up after death of their newborn?

Numerous authors have advocated appropriate physician-patient counseling following a perinatal death. We examined, in a prospective manner, how many families utilized physician follow-up when such follow-up was offered. Seventy-six percent of the 108 families who experienced a neonatal death chose to have physician follow-up in the weeks after the death. A family's utilization of subsequent physician contact was not related to the distance they lived from the medical center, the duration of survival of the infant, or the racial background of the mother. Parents utilized follow-up visits whether or not an autopsy was performed or an interpreter was needed. Certain features distinguished the parents who did not utilize the physician follow-up service: parents were less likely to utilize the service if they were not married, the mother was a teenager, the head of the household was unemployed, or there was no phone at home.

Adolescent↗
PubMed1979

Combination chemotherapy in vitro. IV. Response of human colon carcinoma cells to combinations using cis-diamminedichloroplatinum.

Combination effects of cis-dichlorodiammine platinum (II) (DDP) paired with 12 other antineoplastic agents were investigated on a human carcinoembryonic antigen producing colon carcinoma cell line in vitro. DDP was effective in increasing the killing efficiency of many different drugs. Supraadditive effects were noted with hydroxyurea, bleomycin, cis-acid, BCNU, adriamycin and mitomycin C, and a marked synergistic effect was noted with ara-C. DDP displayed simple additive effects wit 5-fluorouracil (5-FU), Ftorafur and methotrexate, and subadditive effects in simultaneous combination with vincristine. In view of its powerful cytotoxic effects on this particular cell line and of the supraadditive effects of its combinations with nitrosoureas and mitomycin C, DDP appears as a potentially useful antineoplastic agent for combination therapeutic regimens for human colon carcinoma.

Antineoplastic Agents↗
PubMed1978

Follow-up families who experience a perinatal death.

We conducted a retrospective study by telephone interview (10 to 22 months later) of 26 families who had experienced a perinatal death. Six of 26 mothers had a prolonged grief reaction (12 to 20 months). Those mothers with a surviving twin or subsequent pregnancy less than five months following the death were at higher risk for a prolonged grieving period than were those without subsequent pregnancy or one more than six months later. Half of the families obtained information about the cause of death and risk of recurrence only during hospitalization; subsequent contact, weeks to months later, provided additional information for the other half. Twenty-two of 26 mothers met predetermined criteria for having an adequate understanding of cause of death and risk of recurrence; four of 26 knew neither. Sixty percent of the mothers who had adequate understanding and who had no prolonged grief response felt totally dissatisfied or only partially satisfied with the information they received and the way they received it. Follow-up contact by phone or in person increased understanding significantly; mothers who had had in-person follow-up were more likely to be satisfied with the information they received.

Attitude to Death↗
PubMed1977

Transmembrane migration ('flip-flop') of cholesterol in erythrocyte membranes.

After exchange with [14C]cholesterol-labelled plasma lipoproteins for 0.5-4h, erythrocytes were extracted with bile-salt solutions. The extracted cholesterol (mainly from the outside of the erythrocyte membrane) had the same specific radioactivity as the residual sterol. Thus cholesterol equilibrates rapidly (half-time less than 1 h) between the two sides of the membrane.

Animals↗
PubMed1977

The dispersion of cholesterol with phospholipids and glycolipids.

Of the polar lipids studied (phospholipids and glycolipids), only phosphatidylcholine and sphingomyelin can disperse in water with up to 2 mol cholesterol/mol polar lipid. However, mixtures of phosphatidylethanolamine with small amounts of phosphatidylcholine and mixed lipids from mitochondria and myelin will also form sterol-rich dispersions. Steroids in which the 3beta-OH group is replaced by an oxo function do not form such steroid-rich dispersions. Electron microscopy and optical rotatory dispersion (ORD) show that sterols disperse with cerebrosides and gangliosides to form cylindrical structures with the regions around C atoms 3 and 7 of the sterol in less polar environments than those they occupy in phospholipid liposomes. It is proposed that choline-containing phospholipids facilitate entry of sterol molecules into the outer leaflet of cell surface membranes but that the phospholipid composition itself will not give rise to an asymmetric distribution of sterol in membranes with a high cholesterol content.

Cerebrosides↗
PubMed1977

Antigen-binding lymphocytes in guinea pigs. I.B cell expansion to the monovalent antigen L-tyrosine-p-azophenyl trimethylammonium (tyr(TMA)) in the absence of antibody production.

The monofunctional antigen L-tyrosine-p-azophenyltrimethylammonium chloride, tyr(TMA), and the polyfunctional antigen, TMA-human gamma-globulin (TMA-HGG), were used to investigate the antigen structural requirements necessary for clonal proliferation of B cells. This clonal expansion was characterized with respect to receptor immunoglobulin class and affinity maturation. Antigen-binding analysis revealed that inoculation of tyr(TMA), although only of m.w. 344, triggers clonal expansion of B lymphocytes 9-fold in the absence of any apparent antibody production. There does not appear to be any maturation with respect to antibody class since greater than 90% of the tyr(TMA)-specific B cells bear the micron receptor in the nonimmune and immune state. However, the average avidity of the B cells for this antigen increases with time after immunization. In contrast, immunization with TMA-HGG results in an 18-fold increase in B lymphocytes with significant amounts of anti-TMA antibody production. With time after immunization, both maturation of average avidity and class of Ig receptor (micron leads to gamma shift) occur. These findings indicate that the functionally T cell-specific antigen tyr(TMA) can trigger clonal B cell expansion and affinity maturation at the receptor level in the absence of detectable antibody production.

Animals↗
PubMed1977

Cellular response to treatment with 4-(3-(2-chloroethyl)-3-nitrosoureido)-cis-cyclohexanecarboxylic acid, a water-soluble nitrosourea derivative.

The lethal effects of 4-(3-(2-chloroethyl)-3-nitrosoureido)-cis-cyclohexanecarboxylic acid (cis-acid), a water-soluble nitrosourea derivative, were investigated on a human lymphoma cell line. The survival of asynchronous cells exposed to increasing concentrations of the drug was characterized by a threshold exponential curve (Do = 20 microgram/ml; Dq = 20 microgram/ml, 1 hour) similar to that of other nitrosourea derivatives. cis-Acid exerted its main killing effect on cells in early S and in late G2 phase. Cells in mid S and early G1 phase were tenfold more resistant. Changes in survival response as a function of cell cycle stage were reflected primarily by changes in the extent of the shoulder region of the survival curve. In contrast to other nitrosoureas, the lethal effectiveness of cis-acid in solution was stable and the drug could sterilize large numbers of cells in short periods of time. Another important major difference observed for cis-acid with respect to classic nitrosourea derivatives was the capacity of treated cells to recover from sublethal and potentially lethal damage. Our studies have shown that cis-acid is as effective in killing cultured human lymphoma cells as other nitrosoureas, but possibly with a mechanism different from that of these compounds. The major shortcoming noted for cis-acid, namely the capacity of treated cells to recover from drug-induced damage, is offset by the relatively long stability of its killing effect. This, and the fact that cis-acid can be administered in an aqueous solution, make this agent an appealing compound for clinical trials.

Antineoplastic Agents↗