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Biomedical subjects

M W Lambert

Publications and source records attributed to M W Lambert.

At least 37 records · Page 2Linked to original sources
PubMed1990

Electroporation of normal human DNA endonucleases into xeroderma pigmentosum cells corrects their DNA repair defect.

Cells from patients with the cancer-prone inherited disease, xeroderma pigmentosum (XP) are known to be defective in the endonuclease-mediated incision step in excision repair of a number of different types of DNA adducts, but the molecular events responsible have not been delineated. We have previously reported isolation of two DNA endonucleases, pI 4.6 and 7.6, from normal human chromatin which recognize adducts produced by psoralen plus long wavelength ultraviolet radiation (UVA). These endonucleases are both present in XP complementation group A (XPA) cells even though these cells are hypersensitive to this type of damage. We now report that introduction by electroporation of either normal endonuclease into XPA cells restored their markedly deficient DNA repair-related unscheduled DNA synthesis (UDS) to higher than normal levels following exposure to psoralen plus UVA. Introduction of XPA endonucleases into similarly treated XPA cells had little or no restorative effect on UDS. However, both normal and XPA endonucleases increased UDS in normal cells to higher than normal levels. These results indicate that XPA cells have endonucleases which can repair these adducts but which cannot function in intact cells unless a factor(s), which they lack is provided by normal cells.

DNA Repair↗
PubMed1989

How to write and take objective, multiple choice examinations. Quantitative analysis of the scientific data base.

Although there are numerous ways in which physicians evaluate one another and themselves, the multiple choice examination has become the key method for evaluating the scientific data base of both medical students and postgraduate physicians. Knowledge of the mechanisms at work in such examinations is thus important for both giving and taking these examinations. Analysis of these mechanisms is now provided.

Educational Measurement↗
PubMed1988

Two DNA endonuclease activities from normal human and xeroderma pigmentosum chromatin active on psoralen plus ultraviolet light treated DNA.

DNA endonuclease activities from the chromatin of normal human and xeroderma pigmentosum, complementation group A (XPA), lymphoblastoid cells were examined on DNA treated with 8-methoxypsoralen (8-MOP) or 4,5',8-trimethylpsoralen (TMP) plus long wavelength ultraviolet (UVA) light, which produce monoadducts and DNA interstrand cross-links, and angelicin plus UVA light, which produces mainly monoadducts. 9 chromatin-associated DNA endonuclease activities were isolated from normal and XPA cells and assayed for activity on PM2 bacteriophage DNA that had been treated with 8-MOP or TMP in the dark and then exposed to UVA light. Unbound psoralen was removed by dialysis and a second dose of UVA light was given. Cross-linking of DNA molecules was confirmed by alkaline gel electrophoresis. In both normal and XPA cells, two DNA endonuclease activities were found which were active on 8-MOP and TMP plus UVA light treated DNA. One of these endonuclease activities, pI 4.6, is also active on intercalated DNA and a second one, pI 7.6, is also active on UVC (254 nm) light irradiated DNA. The major activity against angelicin plus UVA light treated DNA in both normal and XPA cells was found in the fraction, pI 7.6. The levels of activity of both of these fractions on all 3 psoralen-damaged DNAs were similar between normal and XPA cells. These results indicate that in both normal and XPA cells there are at least two different DNA endonucleases which act on both 8-MOP and TMP plus UVA light treated DNA.

Cell Line↗
PubMed1988

Deficient DNA binding of an apurinic/apyrimidinic DNA endonuclease activity from xeroderma pigmentosum cells.

A chromatin-associated apurinic/apyrimidinic (AP) DNA endonuclease activity, pI 9.8, from both normal human and xeroderma pigmentosum, complementation group A (XPA), lymphoblastoid cells was examined for its ability to bind AP DNA using a filter binding assay. The endonuclease activity from normal cells produced significantly greater binding to AP DNA than to untreated DNA, but this increase in binding was not observed when the XPA endonuclease was incubated with AP DNA versus untreated DNA. These results indicate that the XPA AP endonuclease activity is deficient in its ability to bind to AP DNA.

Chromatin↗
PubMed1987

Positioning of nucleosomes reconstituted with xeroderma pigmentosum and normal histones.

Positioning of nucleosomes was examined in a reconstituted system using a plasmid DNA and histones from normal human and xeroderma pigmentosum, complementation group A (XPA), lymphoblastoid cells. The present studies indicate that the arrangement of nucleosomes, composed of normal human histones, in a region near the SV40 origin of replication on the plasmid DNA, is nonrandom. The alignment of nucleosomes in this region was not affected by the presence of histone H1. No difference in nucleosome positioning was observed when the nucleosomes were composed of histones from XPA cells.

DNA↗
PubMed1986

Enhancement of two apurinic/apyrimidinic endonuclease activities from normal but not xeroderma pigmentosum lymphoblastoid cells by nucleosome structure.

The influence of nucleosomes on the activity of two chromatin-associated apurinic/apyrimidinic (AP) DNA endonuclease activities, pIs 9.2 and 9.8, from normal and xeroderma pigmentosum, complementation group A (XPA), lymphoblastoid cells was examined. These AP endonuclease activities were studied on non-nucleosomal and nucleosomal plasmid pWT830/pBR322 DNA which had been reconstituted with core (H2A, H2B, H3, H4) or total (core plus H1) histones from normal or XPA cells. Both nucleosomal and non-nucleosomal DNA was rendered partially AP by alkylation with 12.5 mM methyl methanesulfonate, followed by heating it at 70 degrees C, to produce approximately three AP sites per DNA molecule. The activities of both normal lymphoblastoid AP endonuclease activities on nucleosomal AP DNA, reconstituted with core histones, was approximately 2.5 times greater than that on non-nucleosomal AP DNA. When histone H1 was added to the system, this increase was reduced. XPA AP endonuclease activities, on the other hand, did not show any increase in activity on nucleosomal AP DNA reconstituted with core histones. These differences between normal and XPA endonuclease activities on AP nucleosomal DNA were the same regardless of whether histones from normal or XPA cells were used in the reconstituted system.

Cells, Cultured↗
PubMed1986

Comparison of histones in normal and xeroderma pigmentosum lymphoblastoid cells.

Histones from normal human and xeroderma pigmentosum, complementation group A (XPA), lymphoblastoid cells were compared both quantitatively, qualitatively and for binding affinity for DNA. Electrophoretic examination of the histones showed that all five major histone species were present in both cell groups and that there were no quantitative differences between normal and XPA histones. Binding affinity to [3H] mammalian DNA of the histones was determined. No significant differences were observed in binding of either normal or XPA histones to DNA.

Animals↗
PubMed1986

Congenital melanocytosis with myelomeningocele and hydrocephalus.

We report an infant who had diffuse blue hyperpigmentation at birth, which rapidly progressed to gray, over the back, buttocks, and posterior aspect of the legs, and an associated congenital anomaly. The entire thickness of the dermis contained numerous very prominent melanocytic cells which, especially in the superficial dermis, were markedly dendritic, rather than merely fusiform. An epidermal melanocyte proliferation was also present. Histologically, the lesion thus differed markedly from a mongolian spot. We believe that diffuse hyperpigmentation in the neonate should call attention to the possibility of an associated neuroectodermal malformation.

Humans↗
PubMed1985

Colonization of nonmelanocytic cutaneous lesions by dendritic melanocytic cells: a simulant of acral-lentiginous (palmar-plantar-subungual-mucosal) melanoma.

Four cases of colonization of nonmelanocytic lesions by dendritic melanocytic cells are reported, one in a verruca vulgaris of the lip, one in a squamous cell carcinoma in situ of mucous membrane overlying a tonsil, one in a lesion of lichen simplex chronicus with a nevocellular nevus of the external ear, and one in a dermatofibrosarcoma protuberans (Bednar tumor). This is an important biological process of melanocytes that must not be confused with the acral-lentiginous (palmar-plantar-subungual-mucosal (P-S-M) melanoma. It is probably much more common than the paucity of published reports would indicate.

Adult↗
PubMed1985

Co-recessive inheritance: a model for DNA repair, genetic disease and carcinogenesis.

A genetic model for some cases of excision-deficient xeroderma pigmentosum (XP) is proposed in which the trait (i.e., XP) is expressed if and only if the individual is homozygous or hemizygous for defective alleles at more than one of a specific set of loci. The model might also apply in some cases of certain other diseases associated with defective DNA repair. The model accounts for several paradoxical aspects of XP, including the large number of complementation groups despite the biochemically limited DNA-repair defect, the co-existence of XP and Cockayne's syndrome in two different complementation groups of XP, siblings with markedly different degrees of severity of XP in one family and transmission of the disease in an X-linked manner in another, the existence of some individuals who appear to have the DNA-repair defect but not clinical XP, and the seeming paradox of a disease associated with a marked defect in a DNA-repair mechanism but not associated with an obvious increase in incidence of internal cancer. The model predicts that a large proportion of the general population is a carrier of one or more of these defective genes for DNA-repair mechanisms. Such genes may be important in the etiology of much of human cancer.

Chromosome Mapping↗
PubMed1985

Power analysis in dermatohistopathology.

Magnification of histologic and ultrastructural photoimages is frequently misrepresented in published reports. "Power," P, the usual mode of representation of magnification, is defined as the ratio of the distance between two points on the photoimage to that between the same two points on the original specimen, but is idiomatically denoted as xP rather than the mathematically correct xP2 in common usage. In this publication, the definitions of "power" and "area magnification," the relationship between "original magnification," "resolving power," and "empty magnification," sources of error that may be introduced during processing of papers for publication, and the relationship between magnification and perception are delineated. Practical suggestions, arising from this discussion, for expression of magnifications when publishing photoimages and for dealing with projected photoimages are provided.

Humans↗
PubMed1984

Criteria for diagnosis in dermatology and dermatopathology: a critical evaluation.

The logical processes of application of criteria to make diagnoses in dermatology and dermatopathology are examined. The limitations of use of a single criterion are delineated, and the advantages and limitations of multiple criteria are defined. It is important that all diagnostic criteria be applied with careful attention to the frequency of the designated entity in the study population and the sensitivities and specificities of the criteria used. The exclusive use of single, "favorite" criteria should be avoided, and multiple criteria should be applied, whenever possible.

Bayes Theorem↗
PubMed1983

Nuclear DNA endonuclease activities on partially apurinic/apyrimidinic DNA in normal human and xeroderma pigmentosum lymphoblastoid and mouse melanoma cells.

DNA endonuclease activities from nuclear proteins of normal human and xeroderma pigmentosum (XP), complementation group A, lymphoblastoid and Cloudman mouse melanoma cells were examined against partially apurinic/apyrimidinic (AP) DNA. Non-histone chromatin-associated and nucleoplasmic proteins, obtained from isolated nuclei, were subfractionated by isoelectric focusing and assayed for DNA endonuclease activity against linear, calf thymus DNA. All of the nine chromatin-associated and three of the nucleoplasmic fractions, which lacked DNA exonuclease activity, were tested for DNA endonuclease activity against both native and partially AP, circular, duplex, supercoiled PM2 DNA. In all three cell lines, four chromatin-associated, but none of the nucleoplasmic fractions, showed increased activity against DNA rendered AP by either heat/acid treatment or by alkylation with methyl methanesulfonate (MMS) followed by heat. One chromatin-associated activity, with pI 9.8, which was not active on native DNA, showed the greatest activity on AP DNA. AP activity was moderately decreased in XP cells and slightly decreased in mouse melanoma cells, as compared with normal cells, in the fraction at pI 9.8. Little or no increased activity was observed in any of the endonucleases from any of the cell lines on MMS alkylated DNA.

Animals↗
PubMed1983

Increased sensitivity of a xeroderma pigmentosum lymphoblastoid cell line to serum deprivation in vitro.

Two human lymphoblastoid cell lines, GM 1989, from a normal individual, and GM 2345, from a patient with xeroderma pigmentosum, complementation group A, were selected for comparative biochemical studies because they both grow rapidly and at virtually identical rates in sealed flasks in RPMI 1640 medium buffered to physiological pH with HEPES buffer, supplemented with 12% heat-inactivated fetal bovine serum. Although the two cell lines showed no difference in growth parameters assayed by standard methods, further studies showed that the GM 2345 cell line was markedly more sensitive to diminution of the serum concentration of the culture medium than was the normal cell line. These results indicate that lymphoblastoid cell lines, particularly those from individuals with certain genetic or metabolic diseases, may be growing under marginal or limiting circumstances, different from those of control cell lines, which are not detected by standard techniques used to monitor mammalian cell cultures.

Blood↗
PubMed1982

Nuclear deoxyribonuclease activities in human lymphoblastoid and mouse melanoma cells. A comparative study.

Deoxyribonuclease activities were examined in isoelectric focusing fractions of non-histone, chromatin-associated and nucleoplasmic proteins of isolated normal human lymphoblastoid and mouse melanoma cell nuclei using parallel procedures. A very similar series of eight DNA endonucleases, each active on calf thymus DNA and containing no exonuclease activity, were found in the chromatin proteins of both cell lines. Several differences were observed: an activity in human cells at pI 6.6 was absent from murine cells, and there was an increased activity in mouse cells at pI 4.4 and a decreased activity at pI 7.3, as compared with corresponding human cell activities. Assay of these fractions against supercoiled, circular phage PM2 DNA showed greater activity among the fractions with acidic pI valves and slightly lower activities in the murine cells than in the human cells. Analysis of the nucleoplasmic fractions showed a series of DNA endonuclease and exonuclease activities which were again very similar between the two cell lines, although greater endonuclease activity at pI 4.4 occurred in mouse than in human nucleoplasm. These results demonstrate an entire series of deoxyribonuclease activities in both chromatin and nucleoplasm which are nearly identical in two very different mammalian cell lines, suggesting that many of these enzymes are ubiquitous in mammalian cell nuclei.

Animals↗