Search PubMed⌕ Search

Biomedical subjects

J D Hall

Publications and source records attributed to J D Hall.

At least 55 records · Page 3Linked to original sources
PubMed1982

Repair of psoralen-induced crosslinks in cells multiply infected with SV40.

Experiments were conducted to study the relationship between the production of interstrand crosslinks by 4,5',8-trimethylpsoralen (psoralen) in simian virus 40 DNA and the ability of psoralen to inactivate the virus. Under conditions where only single viral particles enter a given host cell, approximately one crosslink was lethal to the virus and could not be repaired. In contrast, when multiple viral genomes infected a host cell, psoralen-induced crosslinks were repaired (multiplicity reactivation). A model is proposed for multiplicity reactivation which involves genetic recombination between damaged viral genomes.

Animals↗
PubMed1982

Scanning electron microscopy of post-ejaculatory spermiogenesis in the tick Ornithodoros moubata.

The final stages of spermiogenesis in ticks occur in the female genital tract. Scanning electron microscopy was used to follow the morphologic changes that occur in the sperm during this post-ejaculatory spermiogenesis in the African soft tick, Ornithodoros moubata, and to determine a time sequence for its occurrence in vivo. Characteristic features of the maturing and mature cell described include (1) differentiation and detachment of the operculum, (2) changes in cell shape corresponding to different developmental stages, (3) passive migration of the nucleus and acrosome from an anterior to a posterior position, and (4) eversion of that portion of the acrosomal canal containing the nucleus and acrosome. A possible fate for the remainder of the acrosomal canal is suggested by extrusion and detachment of spherical structures, the 'posterior bubbles', from the posterior end of the mature supermatozoon. A mechanism for cellular elongation resulting from contractions of the outer sheath is proposed.

Acrosome↗
PubMed1981

Transformation of ultraviolet-irradiated human fibroblasts by simian virus 40 is enhanced by cellular DNA repair functions.

Human fibroblasts irradiated with ultraviolet light were either tested for survival (colony formation) or infected with simian virus 40 and examined for transformation (foci formation). For normal cell cultures, the fractions of surviving colonies which were also transformed increased with increasing irradiation dose. In contrast, little increase in the transformation of ultraviolet-irradiated repair-deficient (xeroderma pigmentosum and xeroderma pigmentosum variant) cells was observed. Similar experiments with xeroderma pigmentosum variant cells treated with caffeine following irradiation indicated that, under these conditions, the deficient cells produced more transformants among the survivors of ultraviolet irradiation than did unirradiated cells. These results suggest (1) that DNA repair functions, not DNA damage per se, are required for enhanced viral transformation in normal cells; (2) that functions involved in excision repair and functions needed for replication of ultraviolet-damaged DNA appear necessary for this stimulation; and (3) that blocking DNA replication in ultraviolet-irradiated xeroderma pigmentosum variant cells by caffeine enhances viral transformation.

Adolescent↗
PubMed1981

Repair of psoralen-treated DNA by genetic recombination in human cells infected with herpes simplex virus.

Herpes simplex virus type 1 was treated with 4,5'-8-trimethylpsoralen (psoralen) plus near-ultraviolet light in order to produce lesions (monoadducts and DNA cross-links) in the viral DNA. Human fibroblasts were infected by damaged virus under conditions in which either a single virus particle or several particles entered a given cell, and the fraction of virus-producing cells was determined. This fraction was significantly greater for multiply infected cells than for singly infected cells, indicating that the psoralen lesions are repaired more efficiently in the present of homologous, damaged DNA (multiplicity reactivation). Evidence is presented that herpes simplex virus may code for functions which participate in its own repair, both during multiplicity reactivation and during repair which occurs in singly infected cells: (a) host cells deficient in repair of lesions induced by psoralen (xeroderma pigmentosum) or the DNA cross-linking agent mitomycin C (Fanconi's anemia) exhibited normal levels of multiplicity reactivation of psoralen-treated herpes virus; (b) while xeroderma pigmentosum cells have been previously shown to be deficient in repair of psoralen-treated adenovirus under conditions of single infection, herpes virus is repaired at near normal levels in these same cells. Recombination levels between genetically marked pairs of herpes viruses were found to increase after treatment of the parental viruses with psoralen, suggesting that psoralen damage stimulates genetic recombination. This stimulation provides convincing evidence for a repair pathway in which genetic recombination between damaged viral genomes can lead to the production of viable virus.

Cell Transformation, Viral↗
PubMed1980

Biological and biochemical properties of a human uveal melanocyte-derived cell line.

A human uveal melanocyte-derived cell line (U1I) is described. The cell line has a doubling time of 27.2 hr, a plating efficiency on plastic surfaces of 10%, and a cloning efficiency in soft agar of < 0.1%. U1I displays marked chromosomal aneuploidy and sensitivity to ultraviolet light. Biochemical studies indicate the presence of tyrosinase, which is stimulated by several compounds, including theophylline, progesterone, and nerve growth factor.

Adolescent↗
PubMed1979

Enhanced transformation of xeroderma pigmentosum variant cells by ultraviolet light-irradiated simian virus 40.

The role of DNA repair in transformation was investigated by infecting repair-deficient xeroderma pigmentosum (XP) variant cells, XP variant heterozygous cells, and normal human fibroblasts with simian virus 40 which had been irradiated by ultraviolet light. The transformation frequencies obtained were compared to those observed for unirradiated virus. While normal and heterozygous cells showed no differences between transformation frequencies using either irradiated or untreated virus, two XP variant cell lines were transformed 2- to 7-fold more readily with irradiated virus than with unirradiated virus. XP variant cells were also found to produce lower than normal quantities of virus following infection with either damages or undamaged virus, suggesting that increased viral production was not contributing to the increased transformation seen for these cells. Finally, the proportion of cells which repair ultraviolet light-irradiated simian virus 40 was found to be similar for wild-type and XP variant cells, suggesting that enhanced transformation in the mutant cells was not associated with a reduction in the numbers of cells which repair damaged virus. Several possible mechanisms to account for the increased transformation of XP variant cells by ultraviolet light-irradiated simian virus 40 are proposed.

Cell Line↗
PubMed1977

The characterization of SV40-transformed cell lines derived from mouse teratocarcinoma: growth properties and differentiated characteristics.

Mouse teratocarcinoma cells derived from embryoid bodies of 129SVsl mice were cultured in vitro to permit their differentiation. These cells were then infected with simiam virus 40 (SV40) and 31 cloned cell lines (SVTER) were derived from these cultures. All 31 SVTER cell lines contained the SV40 tumor (T) antigen and grew as permanent lines in culture. Mock-infected embryoid body cultures did not give rise to permanent cell lines. The morphology of each SVTER cell line was distinct and did not change during successive subclonings. The growth properties and tumorigenic potential of all 31 SVTER cell lines were investigated. None of these lines produced tumors in 129SVsl mice. Each cell line was tested for its ability to (1) grow in medium containing 1% serum, (2) plate on cell monolayer, and (3) form clones in methocel suspension. Only three of the SVTER cell lines were transformed with respect to all three of these criteria. Most of these cell lines were minimal transformants. The SVTER cell lines were tested for creatine phospholinase (CPK), an enzyme activity chracteristic of mouse brain and muscle tissue, and the protease, plasminogen activator (PA) which is found in embryoid bodies and several differentiated cell types. Some of the SVTER cell lines contained high levels of CPK, while others had high levels of PA and a third group of cells contained neither enzyme activity. No SVTER cell line was found with high levels of both these enzyme activities. This result suggests that mutually exclusive sets of genes are expressed in these cells as might be expected from the distinct tissue distribution of the two enzyme activities studied. These SVTER cell lines may be useful in reconstructing developmental pathways of differentiating teratomas in vitro.

Animals↗
PubMed1976

In vitro differentiation of teratomas and the distribution of creatine phosphokinase and plasminogen activator in teratocarcinoma-derived cells.

Mouse teratocarcinoma cells from embryoid bodies were cultured in vitro to permit their differentiation into a number of cell types. Two enzyme activities, creatine phosphokinase (CPK) and the protease plasminogen activator, were studied to follow the developmental sequence of events in these embryoid body-derived cell cultures. CPK activity increased with time in culture, indicating the appearance of new cell types with brain- or muscle-specific enzyme activities. Plasminogen activator was detectable in extracts of embryoid bodies. This protease activity first increased and then decreased to a low level as the embryoid bodies in culture developed into differentiated cell types. These cell cultures also showed a decreased potential for tumor formation in syngeneic mice as a function of time in culture. This decrease in tumorigenic potential was correlated with the appearance of differentiated cells in vitro. Simian virus 40 (SV40) was used to infect and transform cells derived from embryoid bodies in culture. This was done to permit the establishment of cloned teratocarcinoma-derived cell lines. Twenty-nine distinct cloned permanent cell lines (called SVTER) containing the SV40-specific tumor antigen were obtained. None of these cell lines was capable of producing tumors in syngeneic mice. An analysis of the levels of creatine phosphokinase and plasminogen activator in these SVTER cell lines indicated that : (a) some cell lines had high CPK activity and little or no plasminogen activator activity, (b) some cell lines contained high levels of plasminogen activator activity with little or no CPK activity, and (c) some cell lines contained neither of these enzyme activities. No example of a cell line with high levels of both enzyme activities was observed, indicating that these two enzymes may participate in mutually exclusive developmental pathways. The SVTER cell lines may therefore be useful in reconstructing these developmental pathways in vitro.

Animals↗
PubMed1975

Temperature-sensitive recA mutant of Escherichia coli K-12: deoxyribonucleic acid metabolism after ultraviolet irradiation.

A mutant of Escherichia coli K-12 temperature sensitive for genetic recombination was investigated and found to carry a mutation that could be cotransduced with cysC and hence could be in the recA gene. To determine whether recA+ can complement this mutation, matings were carried out at 35 and 40 C between Hfr donors that transfer recA+ or recA1 early and recipients carrying wild-type or mutant alleles. It was found that recA+ but not recA1 complements this mutation in zygotic temporary partial diploids. The mutant allele was accordingly designated recA44. A transductant carrying recA44 behaved normally at low temperatures but more like recA- strains at high temperatures with respect to recombinant colony formation in Hfr matings, cell survival, and deoxyribonucleic acid (DNA) synthesis after ultraviolet irradiation, cellular DNA breakdown, and prophage induction when lysogenic for lambda. Alkaline sucrose sedimentation studies of DNA from recA44 cells showed that short DNA molecules synthesized immediately after ultraviolet irradiation increased in molecular weight during subsequent incubation at 32 C but not at 45 C. Hence, recA+ is required for this molecular weight increase. Cells exposed to ultraviolet light synthesized DNA that remained of low molecular weight during a 40-min incubation at 32 C. This material increased in molecular weight in recArut not in recA44 cells during subsequent incubation at 45 C. Thus, the availability of recA+ during the first 40 min at 32 C after irradiation did not obviate the need for recA+ in the subsequent phases of this post-replication repair process.

Alleles↗
PubMed1972

The Ultrastructure of Chloroplasts in Mineral-deficient Maize Leaves.

The ultrastructure of mesophyll chloroplasts in full-nutrient and mineral-deficient maize (Zea mays) leaves was examined by electron microscopy after glutaraldehyde-osmium tetroxide fixation. Nitrogen, calcium, magnesium, phosphorus, potassium, and sulfur deficiencies were induced by growing the plants in nutrient culture. Distinctive chloroplast types were observed with each deficiency. Chloroplasts from nitrogen-deficient plants were reduced in size and had prominent osmiophilic globules and large grana stacks. Magnesium deficiency was characterized by the accumulation of osmiophilic globules and the progressive disruption of the chloroplast membranes. In calcium deficiency, the chloroplast envelope was often ruptured. Chloroplasts from potassium- or phosphorus-deficient plants possessed an extensive system of stroma lamellae. Sulfur deficiency resulted in a pronounced decrease of stroma lamellae, an increase in grana stacking, and the frequent occurrence of long projections extending from the body of the chloroplast. These morphological changes were correlated with functional alterations in the chloroplasts as measured by photosystem I and II activities. In chloroplasts of the nitrogen- and sulfur-deficient plants an increase in grana stacking was associated with an increase in photosystem II activity.

Journal Article↗
PubMed1972

Recombinant F' factors from Escherichia coli K-12 strains carrying recB or recC.

The frequency of genetic exchanges between F' factors and the bacterial chromosome was studied in recombination-deficient Escherichia coli mutants under conditions in which the recombinant F' factors were immediately transferred to new hosts. In a series of double matings, F101-1 thr(+)leu(-) episomes were first transferred into each of four intermediate F(-)thr(-)leu(+) strains carrying various rec alleles. After the original F' donors were killed with phage T6, the F101-1 episomes were then transferred from the intermediate cells to F(-)thr(-)leu(-)Str(R)recA(-) females. Recipients of nonrecombinant episomes formed Thr(+) (Str(R)) colonies, and recipients of recombinant episomes formed Leu(+)(Str(R)) colonies. A comparison of the numbers of Leu(+)(Str(R)) and Thr(+)(Str(R)) colonies shows that recB(-) males formed 18 to 21% and recC(-) formed 47 to 60% of the wild-type level of recombinant episomes that could be detected after transfer. No recombinant episomes were detected using a recA(-) intermediate strain. If the intermediate strains harboring the F101 episomes were purified, allowed to grow for 50 generations, and then mated with the recA(-) recipient, recombinant episomes were transferred at 8% of the wild-type level for recB(-) and 13% for recC(-). In contrast, only 0.4 and 0.6% of the normal number of recombinants were obtained from crosses between Hfr Cavalli donors and the same recB(-) and recC(-) strains. Recombinant episomes were detected with greater frequency among newly formed rec(+), recB(-), and recC(-) partial diploids than in those which were 50 generations old.

Alleles↗