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D A Stephenson

Publications and source records attributed to D A Stephenson.

43 records · Page 3Linked to original sources
PubMed1986

Investigation of the potential for mitotic recombination in the mouse.

A variation of the mouse spot test is described that is designed to distinguish between spots of altered coat colour that arise by reciprocal mitotic recombination and those caused by somatic mutation or non-disjunction. Mouse fetuses that were heterozygous for two, linked coat colour genes were irradiated (1.5 Gy X-rays) in utero at 10.25-10.50 days post coitum (p.c.) or left untreated. Subsequently, the coats were classified for the presence of spots of altered colour. The irradiated embryos were heterozygous for the linked genes pink-eyed dilution (p) and albino (c) and were produced by both the repulsion and coupling crosses. Half of the reciprocal recombination events between the centromere and the proximal marker (p), in heterozygotes with p and c in repulsion, should produce twin spots. No such twin spots would be expected from a similar event in the coupling heterozygotes. The coats of 238 irradiated and 208 untreated repulsion heterozygotes plus 107 irradiated and 314 untreated coupling heterozygotes were classified for spots. One irradiated, repulsion heterozygote had a diffuse twin spot that was only recognisable by microscopic examination of the hairs. We conclude that if the treatment described induces mitotic recombination in the mouse, it does so with low efficiency.

Animals↗
PubMed1986

Effects of X-rays on the induction of somatic mutations and growth in the retinal pigmented epithelium during development of the mouse eye.

The coat and eye colour mutant beige (bg) leads to the production of distinctive retinal melanocytes with abnormally large pigment granules. Heterozygotes for bg were given 2 Gy acute X-irradiation at various times between day 11.5 of fetal life and 3 days after birth, at which age whole mounts were prepared of the retinal pigmented epithelium (RPE). These were scanned for the presence of mutant retinal melanocytes with large granules, either as single cells or as clones. The earlier the fetal irradiation, the greater was the effect on RPE area at 3 days post-partum (p.p.), which fell to about half normal with the 11.5-day fetal exposures. However, the ultimate size of the retinal melanocytes seemed little affected by the irradiation, although their normal size increased approximately 3-fold between 12.5 days post-coitum (p.c.) and 3 days p.p. Mean numbers of mutant melanocytes per eye were markedly higher than in +/bg controls at all irradiation ages other than 3 days p.p.; when allowance was made for final sizes of irradiated RPE's mutation frequencies fell steadily from 30.0 x 10(-5) at 11.5 days p.c. to 1.0 x 10(-5) at 3 days p.p., with 0.8 x 10(-5) in +/bg and 0.1 x 10(-5) in +/+ controls. The doubling dose of 0.18 Gy at 16.5 days p.c. was similar to that found at 17.5 days p.c. in a previous somatic mutation experiment in which follicular melanocytes were scanned for mutations at different (d and ln) loci.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1985

Gene expression at the pink-eyed dilution (p) locus in the mouse is confirmed to be pigment cell autonomous using recombinant embryonic skin grafts.

Sash (Wsh), a viable and fully fertile allele of the dominant spotting (W) locus (Lyon & Glenister, 1982) has been used in a modified test system to investigate the site of gene expression at the pink-eyed dilution (p) locus. Reciprocal recombinant epidermal@dermal skin grafts were constructed from 13-day embryonic skin of p and Wsh homozygotes. Thus in the reciprocal experiments pink-eyed dilution melanocytes were exposed to any environmental influence from the wild-type allele of the p locus in either the epidermis (when WshWsh) or the dermis (when WshWsh). The hair pigmentation of the grafts recovered after three weeks beneath the testicular tunica of adult male mice was always typical of the p phenotype showing that p is melanocyte autonomous. This result was supported by experiments using a modification of Mayer's (1965) neural crest grafting technique and the construction of 14-day recombinant skin grafts. Sash (WshWsh) epidermis can support melanocyte differentiation and pigment production but lacks functional melanocytes. The advantages of Wsh in experimental systems for testing the site of pigment gene expression have been demonstrated. Control experiments confirmed the dermal influence of agouti (A) over non-agouti (a) epidermis but non-agouti dermis did not overrule agouti pink-eyed dilution (AA pp) epidermis suggesting an epistatic effect of p in the melanocyte.

Animals↗
PubMed1982

An in vivo method for the detection of somatic mutations at the cellular level in mice.

This new method for detection of somatic mutations is based on the fact that recessive mutations at the dilute (d) and leaden (ln) loci change the shape of pigment-cells in the hair follicles from their normal highly dendritic appearance (nucleofugal) to a rounded-up almost non-dendritic form (nucleopetal). Gene action is autonomous and individual mutant melanocytes can be recognised in whole mounts of dorsal skin made after the post-natal onset of melanogenesis. Foetal heterozygotes for d and ln were treated with X-rays (0-200 rad) or procarbazine (0-300 mg/kg body mass by maternal i.p. injection) 17 days after detection of a vaginal plug; whole mounts of dorsal skin (fixed 3 days after birth) were microscopically scanned for mutant melanocytes in the hair follicles.About half a million follicular melanocytes were present in the 2 mounts made per mouse. Mutant cells were mainly in the form of small intrafollicular clones; the few mount containing large interfollicular clones were excluded from the analysis. For both treatments, dose-response relationships showed good fits to both a quadratic and a power-law curve. Equations for the latter were: For X-rays, y = 3.2 x 10(-5) + 3.12 x 10(-9) D2.07; for procarbazine, y = 3.6 x 10(-5) + 0.4 x 10(-10) D2.60. However, neither of these differed significantly from a square-law relationship. The estimated mutation rate at the 100 rad X-ray level of 4.7 x 10(-7)/rad/locus was in good agreement with that obtained by Russell and Major's (1957) pioneer studies of somatic mutation in mice, by looking for mutant patches in the coat ("spot test"). Possible ways in which the present method might be improved and extended are discussed.

Animals↗
PubMedDate not supplied

Golden: a novel coat color mutant in the wild mouse Mus caroli.

We identified a spontaneous pigmentation mutant in the wild mouse species Mus caroli. Mutant mice exhibit a golden coat color on the agouti background, easily distinguishable from the darker wild type. The golden phenotype segregates as an autosomal recessive, showing no linkage to the sex-linked enzyme marker glucose-6-phosphate dehydrogenase. Obligate heterozygotes are phenotypically indistinguishable from the wild type. At birth, homozygotes have poorly pigmented eyes, which darken with age to become indistinguishable from the wild type. Pigmentation of the ears, tail, and footpads is reduced in intensity. Preliminary studies indicate that the phenotype may be due to an alteration in the shape and pigmentation of the eumelanosomes. The viability and fertility of both heterozygotes and homozygotes, as measured by litter size, sex ratio, or frequency of survival to weaning, appear to be normal for M. caroli. Spectrophotometric analysis of hair samples from the mouse variant at the putative golden locus (gdn) suggests that this mutant is not homologous to at least six independent pigment mutants previously identified in M. musculus.

Alleles↗