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Biomedical subjects

C W Lo

Publications and source records attributed to C W Lo.

At least 73 records · Page 4Linked to original sources
PubMed1987

Tracking of mouse cell lineage using microinjected DNA sequences: analyses using genomic Southern blotting and tissue-section in situ hybridizations.

We examined the feasibility of applying DNA microinjection to label cells for lineage studies of mouse embryos. Tissues from three transgenic mice mosaic due to the insertion of an exogenously introduced mouse beta-major globin gene were analyzed by genomic Southern-blotting and in situ hybridization. These studies allowed the direct quantification and localization of lineage descendants derived from the marked or transformed founder cells. The results of these studies suggested an early segregation of cells in the somatic vs. germ-cell lineages. The in situ hybridization data further demonstrated that cells of the transformed lineages were usually finely dispersed, indicative of extensive cell-cell mixing during mouse development. However, a notable exception to this was the patchy distribution of cells in the kidney (corresponding to individual nephrons), the clustering of transformed cells in individual villi of the small intestine, and the segregation of positive and negative seminiferous tubules in the testis. These data suggest a clonal basis for the organization of development in organs like the kidney, intestine, and testis.

Animals↗
PubMed1986

High frequency DNA rearrangements associated with mouse centromeric satellite DNA.

A DNA transformed mouse cell line, generated by the microinjection of a pBR322 plasmid containing the herpes thymidine kinase (tk) gene, was observed to exhibit a high frequency of DNA rearrangement at the site of exogenous DNA integration. The instability in this cell line does not appear to be mediated by the tk inserts or the immediately adjacent mouse DNA, but instead may be a consequence of the larger host environment at the chromosomal site of tk insertion. Results obtained from restriction analysis, in situ chromosome hybridizations, and cesium chloride density-gradient fractionations indicate that the tk inserts are organized as a single cluster of direct and inverted repeats embedded within pericentromeric satellite DNA. To determine the molecular identity of the flanking host sequences, one of the mouse-tk junction fragments was cloned, and subsequent restriction and sequence analyses revealed that this DNA fragment consists almost entirely of classical mouse satellite DNA. On the basis of these observations, we suggest that the instability in this cell line may reflect the endogenous instability or fluidity of satellite DNA.

Animals↗
PubMed1986

Indian and Pakistani immigrants have the same capacity as Caucasians to produce vitamin D in response to ultraviolet irradiation.

To investigate whether the high prevalence of osteomalacia and rickets among Indian and Pakistani immigrants to Great Britain is due to impaired capacity to produce vitamin D3 in their skin, the serum vitamin D concentrations of six Asians in response to 1.5 times their minimal erythemal dose (MED) of whole-body ultraviolet radiation (UVR) was studied. The mean serum vitamin D concentrations rose from a baseline of 2 +/- 2 ng/ml before exposure to UVR to a peak of 38 +/- 12 ng/ml at 24 h, gradually declining back to baseline by day 9. This response was not significantly different from that seen in Caucasian controls. The UVR needed to produce an MED in Asians, with their darker skin, was greater (49-133 mJ/cm2) than that required in Caucasians (31-48 mJ/cm2). Asians may need longer exposure to sunlight than Caucasians do to give a similar response, but the capacity to produce vitamin D is no different in Asian than in Caucasian skin.

Adolescent↗
PubMed1986

Modulation of tk expression in mouse pericentromeric heterochromatin.

We have obtained a mouse transformant cell line containing two herpes viral thymidine kinase (tk) genes integrated in pericentromeric heterochromatin. Restriction analysis of tk- revertant and tk+ rerevertant derivatives suggest that one of the two tk genes is repressed in tk- cells, but is reactivated in tk+ rerevertants. The results of Northern analysis indicated that repression-activation is probably controlled at the transcriptional level. To examine the molecular basis for this repression, we cloned the tk gene from a tk- revertant cell line. Then, using the cloned tk gene as donor DNA to select for tk+ transformants, we found that it has a transfection efficiency indistinguishable from the viral tk gene. This indicates that repression is probably not mediated via any DNA sequence changes within the tk gene. The results of further studies by restriction analysis, azacytidine treatments, and secondary DNA transfection assays demonstrated that tk repression is associated with changes in DNA methylation. Surprisingly, derepression of the tk gene was accompanied by rearrangements in the flanking DNA. The latter result suggests that the flanking DNA may exert cis effects on tk gene expression. Additional studies with this system may provide insights into the molecular basis underlying position effects in heterochromatin.

Animals↗
PubMed1986

Localization of low abundance DNA sequences in tissue sections by in situ hybridization.

Specific DNA sequences were loaclized in the nuclei of paraffin-embedded mouse tissue sections with in situ hybridization using a biotinylated globin probe in conjunction with a streptavidin-alkaline phosphatase detection system. Globin inserts were clearly detected in the tissue sections of transgenic mice containing 1000, 120 or 5 copies of the exogenously introduced beta-globin genes. In addition, specific hybridization signal was also obtained for the endogenous complement of beta-globin genes in the tissue sections of normal mice. These results demonstrate that this hybridization procedure is very sensitive and should be useful for characterizing the distribution of low abundance DNA sequences in cells and tissue sections.

Animals↗
PubMed1985

Novel approach for restriction mapping repetitive DNA elements using DNA transformation.

We demonstrated that DNA transformation can be used to determine the linkage relationship between DNA restriction fragments in mouse genomic DNA. Using this experimental approach, we obtained linkage information which enabled us to construct a restriction map for the multiple thymidine kinase (tk) gene inserts present in a mouse L-cell line. This restriction map included cutting sites for seven restriction enzymes spanning a distance of over 10 kb. It revealed that the tk inserts in this cell line are arranged in a complex array consisting of direct and inverted repeats. In light of these results, we suggest that this approach will be particularly useful for restriction mapping DNA sequences that are repetitive as such DNA may be difficult to characterize by conventional methods alone.

Animals↗
PubMed1985

An anterior/posterior communication compartment border in engrailed wing discs: possible implications for Drosophila pattern formation.

Our previous studies have suggested that all the known lineage compartment borders in the wing imaginal disc of Drosophila are coincident with boundaries of reduced gap junctional communication (communication compartment borders). Since engrailed discs have a disrupted anterior/posterior (A/P) lineage border (G. Morata and P. A. Lawrence, 1975, Nature (London) 255, 614-617), it was of great interest to determine if their A/P communication restriction boundary is similarly disrupted. Examination of gap-junction-mediated exchange of small fluorescent molecules between cells in the engrailed wing disc revealed a boundary of restricted communication that appeared to be identical to the wild-type A/P communication restriction boundary. This result suggests that lineage compartments are not required for the formation of A/P communication restrictions. Furthermore, we suggest that perhaps communication compartments are the domains within which information is provided for specifying the formation of lineage compartments.

Animals↗
PubMed1985

Vitamin D absorption in healthy subjects and in patients with intestinal malabsorption syndromes.

We developed a test procedure for the clinical evaluation of the absorption of vitamin D. Serum vitamin D concentrations were evaluated in seven patients with intestinal fat malabsorption syndromes and in seven healthy, normal subjects, after being given a single oral dose of 50,000 IU (1.25 mg) vitamin D2. In the normal subjects, serum vitamin D concentrations rose from a baseline of less than 5 ng/ml to a peak of over 50 ng/ml by 12 h, gradually falling to baseline levels by 3 days. In five of the seven patients with intestinal fat malabsorption, oral administration of 50,000 IU vitamin D2 did not raise serum vitamin D concentrations above 10 ng/ml. Two patients with severe inflammatory bowel disease had a normal absorption pattern, however. These findings suggest that an oral vitamin D absorption test may be of value for determination of patients at risk for development of vitamin D deficiency. They also raise questions about the efficacy of oral vitamin D preparations in patients with intestinal fat malabsorption.

Adult↗
PubMed1985

Gap-junctional communication in a communication-defective and in a communication-competent teratocarcinoma cell line.

We examined the gap-junctional communication properties of a communication-defective cell line R5/3 and its communication-competent revertant H2T12. For these studies, we carried out microelectrode impalements to monitor ionic coupling and dye coupling. Our dye-injection experiments revealed that the H2T12 cells are much more efficient in dye coupling than the R5/3 cells. This latter observation is in agreement with the previous finding that the H2T12 cells are much better metabolically coupled than the R5/3 cells. With ionic coupling measurements, however, both cell lines exhibited similar levels of cell-cell coupling. The R5/3 cells demonstrated an ionic coupling coefficient of 0.19 +/- 0.011 (S.E.M.) and H2T12 a coupling coefficient of 0.25 +/- 0.009 (S.E.M.). These results in conjunction with observations from other studies indicate that the different experimental approaches for monitoring gap-junctional communication may have different levels of sensitivity for detecting as opposed to measuring the level of cell-cell coupling.

Cell Communication↗
PubMed1984

Gap-junctional communication compartments in the Drosophila wing imaginal disk.

Using intracellular injection of small fluorescent molecules, we examined the gap-junctional communication properties of cells in the wing imaginal disk of Drosophila. We observed extensive spread of the injected dye between cells in all parts of the wing disk epithelium, but we found that this spread is not uniform. Instead, the cell-to-cell movement of dye is partially restricted at several defined boundaries such that cells on one side of the boundary have a low level of communication with cells on the other side. These communication-restriction boundaries are delineated by bands of cells with a low level of communication, and they subdivide the disk epithelium into a number of "communication compartments." Interestingly, the boundaries of some of these communication compartments appear to be coincident with compartment borders identified in cell lineage studies. Given this striking coincidence, we suggest that gap-junctional communication may play a role in compartment formation, and in controlling the appropriate differentiation of cells within compartments.

Animals↗
PubMed1984

The tolerance and nutritional value of two microfungal foods in human subjects.

The tolerance of human subjects to two microfungal food products was studied in separate double-blind cross-over studies. As an addition to the subject's usual diets, cookies with and without 20 g of a product from Fusarium graminearium were fed to a group of 100 individuals daily. In a second study, cupcakes with and without 10 g of Paecilomyces variotii were given daily to 50 individuals. Mild rashes possibly related to one of the microfungal food products occurred in two individuals fed P variotii. Except for a decrease in serum cholesterol during the F graminearium study, no significant changes were noted in 17 serum constituents. During nutritive value studies, digestibility, biological value, and net protein utilization were calculated for the two microfungal proteins and for milk. The values for milk were 95, 85, and 80%, respectively. The values for F graminearium were 78, 84, and 65%, respectively. For P variotii corresponding figures were 81, 67, and 54%. On the basis of these results both microfungal foods may be deemed safe for human consumption at the levels tested.

Adolescent↗
PubMed1983

Cerebrospinal fluid [Met5]enkephalin level in schizophrenics during treatment with naloxone.

The effect of naloxone on CSF [Met5]enkephalin level and on the suppression of psychotic symptoms associated with schizophrenia was studied. Seven patients were treated with naloxone at a dose of 0.4 mg/day for seven days and six were treated with saline for the same period. Of the seven patients receiving naloxone, three showed signs of improvement. In the saline group, only one case of obvious improvement was observed. The mean CSF [Met5]enkephalin level before and after treatment in both the naloxone and saline group did not change significantly. However, there was a highly significant correlation (r = -0.73, P less than 0.01) between the increase of [Met5]enkephalin level and the decrease in psychotic symptoms.

Adult↗
PubMed1983

Met-enkephalin level in the cerebrospinal fluid of schizophrenic patients.

The level of met-enkephalin in the cerebrospinal fluid of 18 schizophrenic and 18 non-mental patients were determined by radioimmunoassay. The concentration of this peptide in the schizophrenic patients ranged from 12 to 39 ng/l with a mean of 22.2 ng/l. The mean and range of the non-mental patients were 28 ng/l and 16 to 41 ng/l, respectively. The difference between the mean enkephalin level of the two groups was statistically significant by the t-test. However, this difference must be interpreted with caution since the data obtained from the non-mental patients cannot be regarded as normal. No significant correlation was observed between the severity of schizophrenic symptoms and cerebrospinal fluid met-enkephalin level.

Enkephalin, Methionine↗
PubMed1983

Transformation by iontophoretic microinjection of DNA: multiple integrations without tandem insertions.

DNA transformations of mouse tissue culture cells and mouse embryos were carried out by iontophoretic microinjection of DNA. Iontophoresis involves the use of an externally applied electric current to expel DNA molecules from the injection micropipette into the impaled cell (microelectrophoresis). Restriction analysis of transformants obtained by using this procedure demonstrated that this method gave strikingly different results from those previously obtained by others with transformants generated by pressure injection. First, tandem insertions were never observed in any of our transformants. Second, despite the lack of tandem insertions, we have obtained transformants which have integrated many copies of the injected DNA sequences, probably via a comparably large number of independent integration events. And third, in one transformant, an injected BamHI restriction fragment was found to have been integrated in its entirety; this included the preservation of the terminal BamHI recognition sequence. Based on these observations, we discuss the potential usefulness of iontophoretic DNA microinjections in DNA transformation studies that are focused either on the analysis of the regulation of gene expression or on the targeting of DNA sequences into the eucaryotic cell genome.

Animals↗
PubMed1983

Chronic protracted diarrhea of infancy: a nutritional disease.

Diarrhea is an extremely common cause of morbidity in infancy. Occasionally, it becomes protracted, leading to a vicious cycle of malabsorption, malnutrition, and failure to thrive. A number of causes of chronic diarrhea in infancy are discussed, including postinfectious enteritis, celiac sprue, cow's milk allergy, and parasitic infection. Although many mechanisms may contribute to diarrhea, a similar pathophysiologic syndrome of mucosal atrophy, inflammation, and malabsorption results. Attention should be paid to recognition of malnutrition as well as etiologic diagnosis. Therapeutic efforts should concentrate on nutritional rehabilitation, through appropriate oral elemental formulas or total parenteral nutrition. However, encouragement of breast-feeding is probably a more effective way of preventing this difficult problem.

Animals↗