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Biomedical subjects

M Dempster

Publications and source records attributed to M Dempster.

26 records · Page 2Linked to original sources
PubMed1987

Linkage relationships between X-linked retinitis pigmentosa and nine short-arm markers: exclusion of the disease locus from Xp21 and localization to between DXS7 and DXS14.

Linkage data between X-linked retinitis pigmentosa (XLRP) and nine X-chromosomal markers are reported. To test the assignment of XLRP to the Xp21 region (as considered at Human Gene Mapping 8), an analysis of XLRP and six markers flanking this region was undertaken. The XLRP locus was found to be excluded from the chromosome distal to ornithine transcarbamylase (OTC) (P = 6.5 X 10(-5]. Further data were accumulated with three more probes proximal to DXS7 (L1.28), the closest linked probe. Multipoint analysis of these data suggests a posterior probability of .94 that XLRP is proximal to DXS7 (L1.28), which has been mapped to the region Xp11.3.

Chromosome Mapping↗
PubMed1986

Genetic linkage between X-linked retinitis pigmentosa and DNA probe DXS7 (L1.28): further linkage data, heterogeneity testing, and risk estimation.

Further linkage data relating X-linked retinitis pigmentosa and DNA probe DXS7 (L1.28) is presented in this paper. The current mean estimate of the recombination fraction (theta) including this and all published data, is 0.09, with confidence limits 0.04 to 0.17 (maximum Lod score of 14.01 at a theta of 0.08). There is no evidence for heterogeneity of recombination fraction between the 13 families for which data are available. However, it is argued that heterogeneity should be assumed to exist for the purposes of risk estimation. Mean estimates and variances of risk are calculated for hypothetical families each with different linkage data. In families in which no recombination has been observed, the mean and variance of risk are sufficiently small for the clinical use of this probe to be acceptable to many.

DNA↗
PubMed1986

A genetic linkage study of choroideremia.

One hundred and twenty-two members of 15 choroideremia families have been used in a genetic linkage study of choroideremia (TCD) using four DNA probes situated on the X chromosome. Linkage was analysed using DNA probes DXS14 (p58-1), DXYS1 (pDP 34), DXS178 (p212) and DXS177 (lambda 2.7). Statistically significant linkage was demonstrated with DXYS1 (theta = 0.00, lod 4.95), in agreement with the findings of Nussbaum et al. (1985). Evidence consistent with loose linkage to TCD was also found with DXS14 (theta = 0.31, lod 0.23), DXS178 (theta = 0.18, lod 1.41) and DXS177 (theta = 0.27, lod 0.20). The results suggest that TCD is located in the region Xq13-q21. Probe DXYS1 is likely to prove useful in the prenatal diagnosis of this condition.

Choroid↗
PubMed1983

The regulation of yolk protein gene expression in Drosophila melanogaster.

The three genes, located in the X chromosome, which code for the three yolk polypeptides (YPs) of Drosophila melanogaster are expressed in the fat bodies and ovarian follicle cells of adult females. Both juvenile hormone and ecdysone are involved in regulating their expression. The yolk protein genes (YP genes), normally not transcribed in males, become expressed when males are injected with or fed 20-hydroxyecdysone. Superimposed on this hormonal regime is a sex determination mechanism which ensures that normally YP gene expression is female-specific. There are a series of autosomal genes in D. melanogaster which ensure that individual cells follow a male or female developmental pathway. When they are mutant, flies with two X chromosomes, which would normally be female, can become intersexual in phenotype or transformed into sterile males and flies with one X and one Y chromosome can become intersexual. It has been found that the YPs are part of the set of female characteristics controlled by these sex genes. The YP genes are expressed in female and intersexual flies, regardless of the X chromosome constitution, but not in males or pseudomales. Transcript levels of yolk proteins have been measured in female and intersexual flies by hybridization to cloned YP DNA sequences. It is suggested that transcription of the YP genes is under the cell-autonomous control of the sex genes and that the sex genes do not exert their effect by modulating the levels of steroid hormones in adults.

Age Factors↗
PubMed1983

Expression of the yolk-protein genes in the mutant doublesex dominant (dsxD) of Drosophila melanogaster.

Adult flies mutant for doublesex dominant (dsxD) are intermediate in phenotype between males and females. The dsxD mutation acts in the heterozygous state to transform only flies with two X chromosomes into intersexes, XY flies are unaffected by the mutation. Yolk-protein synthesis, which normally occurs in the ovaries and fat bodies of females, but not in males unless stimulated with 20-hydroxy-ecdysone, is reduced. The dsxD fat body synthesizes less yolk proteins throughout adult life, and the gonads rarely make yolk proteins. Using cloned yolk-protein genes as probes for measuring transcript levels we have shown that expression of these genes in dsxD is regulated both transcriptionally and post-transcriptionally. We suggest that the dsxD locus regulates the expression of the yolk-protein genes from within the fat body cells and does not operate by modulating ecdysteroid titres in the adults.

Animals↗
PubMed1983

20-hydroxyecdysone stimulates tissue-specific yolk-protein gene transcription in both male and female Drosophila.

The yolk polypeptides of Drosophila are normally synthesized in the fat body and ovarian follicle cells of adult females. In response to 20-hydroxyecdysone males synthesize yolk polypeptides. The actual level of yolk polypeptides synthesized in males is not always a direct reflection of the YP-transcripts present. Initially YP-transcripts are efficiently translated into polypeptides whereas later they are not and the YP-transcripts can have a half-life of less than 8 h in males. We suggest that the expression of the genes coding for the yolk polypeptides in males may be regulated at transcriptional and translational levels. Treatment of females with 20-hydroxyecdysone leads to a transient increase in YP-transcript accumulation, but the response is difficult to assess in whole flies due to the high variability in transcript levels during normal development. Analysing the response to 20-hydroxyecdysone at the level of specific tissues shows that transcript accumulation is dramatically increased in body walls (fat-body cells, epidermis and oenocytes) of both males and females. Gut, Malpighian tubules, testis and ovaries are not affected. Treatment of females with 20-hydroxyecdysone followed by measuring YP-transcript accumulation over the next 24 h in ovaries and body walls separately, confirms that only body walls respond to the hormone. There is an increase in yolk-polypeptide synthesis during the period of increased YP-transcript accumulation in females. We conclude that the response of the YP-genes to 20-hydroxyecdysone is tissue-, but not sex-specific.

Animals↗
PubMed1981

Characterisation of a new tumorous-head mutant of Drosophila melanogaster.

A new homoeotic mutant, I127, showing abnormal growths in the head region including homoeotic transformation of eye to genitalia and antenna to leg, was isolated in a screen designed to find new alleles of the tumourous head (tuh-3), mutation. Similarities in the phenotype and genetics of the mutant, and complementation studies with tuh-I; tuh-3, suggest that I127 is indeed an allele of tuh-3. In combination with the first chromosome modifier tuh-1, the mutant is temperature-sensitive during the third larval instar, giving an increased penetrance of the tumorous head phenotype when reared at 25 degrees C as opposed to 18 degrees C. The isolation of further alleles at the tumorous-head locus are essential. The type of morphological defects which can result from mutations at this locus would enable us to establish if this is a complex locus, and if null mutations are lethal during development. The interactions of the tumorous-head gene with first chromosome modifiers and other homoeotic mutations will only be understood if we are able to induce a number of mutations at this locus, and as a consequence begin to elucidate the role of the wild-type gene product in normal development.

Alleles↗