Biomedical subjects

D K Chiu

Publications and source records attributed to D K Chiu.

6 recordsLinked to original sources

PubMed1992

A survey of multiple sequence comparison methods.

Multiple sequence comparison refers to the search for similarity in three or more sequences. This article presents a survey of the exhaustive (optimal) and heuristic (possibly sub-optimal) methods developed for the comparison of multiple macromolecular sequences. Emphasis is given to the different approaches of the heuristic methods. Four distance measures derived from information engineering and genetic studies are introduced for the comparison between two alignments of sequences. The use of entropy, which plays a central role in information theory as measures of information, choice and uncertainty, is proposed as a simple measure for the evaluation of the optimality of an alignment in the absence of any a priori knowledge about the structures of the sequences being compared. This article also gives two examples of comparison between alternative alignments of the same set of 5SRNAs as obtained by several different heuristic methods.

Algorithms↗

PubMed1991

Covering events in eigenimages of biomolecules.

Multivariate statistical analysis of a large set of micrographs of biological macromolecules involves the computation of eigenimages representing principal features, on the basis of which similar views of the complexes can be grouped. It is not generally clear what these eigenimages represent physically and which ones should be used in the classification process. In this paper, hierarchical maximum entropy discretisation and event covering are used to (1) detect statistically significant relationships in the eigenimages, (2) select the most relevant eigenimages for classifying biomolecular projections, and (3) build a prototype of the biomolecular complex under study.

Algorithms↗

PubMed1991

Inferring consensus structure from nucleic acid sequences.

This paper presents an unsupervised inference method for determining the higher-order structure from sequence data. The method is general, but in this paper it is applied to nucleic acid sequences in determining the secondary (2-D) and tertiary (3-D) structure of the macromolecule. The method evaluates position - position interdependence of the sequence using an information measure known as expected mutual information. The expected mutual information is calculated for each pair of positions and the chi-square test is used to screen statistically significant position pairs. In the calculation of expected mutual information, an unbiased probability estimator is used to overcome the problem associated with zero observation in conserved sites. A selection criterion based on known structural constraints of the strongest interdependent position pairs is applied yielding position pairs most indicative of secondary and tertiary interactions. The method has been tested using tRNA and 5S rRNA sequences with very good results.

Algorithms↗

PubMed1987

The expression of oncogenes in human developing liver and hepatomas.

Oncogene expression was examined in the human fetal liver and human hepatomas. Erb (B), erb (A+B), Ha-ras, myc, fos and fms oncogene expression elevated in certain stages of fetal liver development and in hepatoma as compared to the normal adult human liver. In contrast, rel, src, mos, sis, myb, Ki-ras and bas oncogenes showed no apparent change of their mRNA levels during fetal liver development and in hepatoma. Further study of erb B oncogene expression in human cirrhotic liver and hepatoma demonstrated a strong correlation between erb B expression and alteration of its gene structure.

Adult↗

PubMed1984

Oophorectomy leads to a selective decrease in 1,25-dihydroxycholecalciferol receptors in rat jejunal villous cells.

The distribution of 1,25-dihydroxycholecalciferol [1,25-(OH)2D3] receptors in isolated rat jejunal cells was investigated in normal and oophorectomized female rats and also in vitamin D-deficient animals. Oophorectomy caused a selective reduction in 1,25-(OH)2D3 receptor numbers in villous cells, the reduction being similar (37%) in both normal and vitamin D-deficient animals. The data suggest that this effect of oophorectomy reflects a direct effect of oestrogens in the intestinal synthesis of 1,25-(OH)2D3 receptors, independent of the renal synthesis of 1,25-(OH)2D3. It is proposed that this phenomenon may, in part, explain the reduction in calcium absorption which occurs after oophorectomy or the menopause.

Animals↗

PubMed1984

Mechanism of the regulation of the 1 alpha,25-dihydroxyvitamin D3 receptor in the rat jejunum by glucocorticoids.

The distribution of 1 alpha,25-dihydroxyvitamin D3 (1,25-(OH)2D3) receptors in isolated jejunal villous and crypt cells was investigated in normal and adrenalectomized male rats, and also in animals treated with the synthetic glucocorticoid, dexamethasone, and/or the glucocorticoid antagonist, 11-deoxy-cortisol. Adrenalectomy caused an increase in 1,25-(OH)2D3 receptors whilst dexamethasone treatment led to a reduction in receptor number. 11-Deoxy-cortisol was able to reverse the 'down-regulation' effect caused by glucocorticoids. In all cases, the changes in receptor numbers were more pronounced in crypt cells. The data suggest that, in the small intestine, glucocorticoids may control the synthesis of 1,25-(OH)2D3 receptors via the mediation of a glucocorticoid receptor, and that the adrenal hormones mainly express their effect in crypt cells. It is proposed that this phenomenon may, in part, explain the reduction in calcium absorption which occurs in man after chronic glucocorticoid treatment.

17-Hydroxycorticosteroids↗