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Biomedical subjects

J A Buchanan

Publications and source records attributed to J A Buchanan.

46 records · Page 3Linked to original sources
PubMed1987

Ten families with fragile X syndrome: linkage relationships with four DNA probes from distal Xq.

We present clinical, cytogenetic, and linkage data of four DNA probes from the terminal long arm of the X chromosome in ten new families with fragile X syndrome. A prior/posterior method of multipoint linkage analysis is employed to combine these results with published data to refine the linkage map of terminal Xq. Ten possible probe/disease orderings were tested. The order with the greatest posterior probability (0.78) of the five loci is 52a-F9-fragile X gene-DX13-St14, although the order with reversal of the positions of 52a and F9 has a posterior probability 0.15. The mean estimates of the distances between the probes and the fragile X gene are 38 cM and 33 cM for the proximal probes 52a and F9, and 8 cM and 12 cM for the distal probes DX13 and St14. Although the current method of choice in the prenatal diagnosis and carrier detection of the fragile X syndrome remains detailed cytogenetic analysis, consideration is given to the potential role of these DNA probes, both singly and in pairs.

Chromosome Banding↗
PubMed1987

Cyclic AMP induces changes in distribution and transport of organelles within growth cones of Aplysia bag cell neurons.

This report examines cAMP-induced regulation of directed organelle transport in bag cell neuron growth cones using video-enhanced differential interference contrast (DIC) microscopy (Allen et al., 1981; Inoue, 1981) and digital image analysis techniques. Under control conditions, organelle transport is evident in the central cytoplasmic regions of bag cell neuron growth cones, but not in lamellae. Motility of lamellae takes the form of slow (less than 0.01 micron/sec) extension of margins and ruffling motions that propagate as waves (velocity, approximately 0.07 micron/sec) in a retrograde direction. Application of forskolin and a phosphodiesterase (PDE) inhibitor at concentrations known to induce changes in bag cell protein phosphorylation resulted in (1) rapid extension of directed organelle transport into lamellae, and (2) inhibition of the retrograde ruffling waves. These changes effected transformation of lamellae into neurite endings packed with microtubules and organelles, a large proportion of which appeared to be neurosecretory granules. The effects were reversible, dose-dependent, potentiated by a variety of PDE inhibitors, and mimicked by 6-N-butyl-8-benzyl-thio-cAMP (BT-cAMP). Though forskolin may normally promote depolarization and Ca entry, these changes in growth cone structure are not secondary to influx of external Ca, as they persist in Ca-free/EGTA solutions; furthermore, they do not resemble the effects of depolarization induced by perfusion with elevated K solutions. The cAMP-induced changes in growth cone morphology that we report here suggest a possible role for protein phosphorylation in promoting growth cone differentiation and structural changes accompanying secretion.

Animals↗
PubMed1987

Genetic markers for assessment of retinoblastoma predisposition.

Here we provide a conceptual framework for the application of current approaches in the analysis of retinoblastoma to the clinical setting. The aim of genetic medicine is to minimize the burden of inherited disease through appropriate diagnosis and management of patients and to maximize information, so that families can make reasonable decisions about reproduction. Recent genetic, cytogenetic and molecular genetic approaches have improved our understanding of the biological events leading to the occurrence of retinoblastoma and, in addition, have provided tools for the enhanced assessment of risk for some individuals. The knowledge, however, is incomplete and the tools imperfect, as indicated by our continued provision of risk probabilities that are neither one nor zero. We therefore hope to emphasize both the scope and the limitations of these techniques so that their application can be effectively considered.

Child↗
PubMed1986

An experimental study of timing and topography of early tooth development in the mouse embryo with an analysis of the role of innervation.

The putative involvement of the innervation in determining the sites of dental development was investigated by intra-ocular homografting and organ culture methods. Mandibular arches were dissected from 9 and 10-day-old (E9-E10) mouse embryos and grafted to the anterior eye chambers of homologous adult mice for 12-14 days. There was no significant difference in the incidence of tooth formation between grafts in which the trigeminal ganglion was included (n = 82, 68 per cent) or excluded (n = 72, 65 per cent). A parallel in vitro study in which E9 and E10 mouse embryo mandibular arches were cultured in the absence of trigeminal innervation showed that definitive tooth germs were formed during the 7-9 day culture period. It is concluded that innervation plays no part in determination of tooth development. In further experiments with E9 and E10 material, the complete mandibular arch, the hemimandibular arch and the ventral midline region of the mandibular arch (including the median epithelial isthmus) were each grafted for a period of 21 days. Alizarin-red whole-mount staining of recovered grafts revealed that bone had been deposited and mineralized in the majority of grafts of all types. Incisor and molar teeth with near normal crown shapes developed in grafts of complete mandibular arches. Hemimandibular arches gave rise almost exclusively to molars. Grafts of the E10 ventral midline region gave rise exclusively to incisors, but the same graft performed at E9 did not produce teeth. It is concluded that incisor primordia are localized in or near the median epithelial isthmus (and are thus destroyed or damaged when the mandibular arch is hemisected) and that incisors are not determined until E10. At E9 the odontogenic neural crest has yet to complete its ventrad migration into proximity with presumptive incisor epithelium. By this time, however, odontogenic crest and presumptive molar epithelium have already reached juxtaposition and molar primordia are fully competent. In grafts of the frontonasal and maxillary processes made at E10, prior to merging of their respective mesenchymes, frontonasal processes gave rise exclusively to incisors, whereas maxillary processes gave rise exclusively to molars.

Animals↗
PubMed1985

Transport competence of plasma membrane vesicles from cultured human fibroblasts.

We obtained plasma membranes from cultured human skin fibroblasts. The preparation was enriched 10-fold with about 40 percent yield. There was minimal contamination with other cell membranes. Various observations indicated vesicular conformation of a portion of the plasma membranes, notably by electron microscopy and from the effect of osmotic pressure on the distribution of solutes between mass and medium at equilibrium. Other studies indicated that these fibroblast plasma membrane vesicles retained mediated transport processes for a variety of substrates. The evidence included: stereospecific and temperature-dependent uptake of glucose; dependence of L-alanine uptake on sodium ion and an inward-directed transmembrane Na+ gradient; stimulation of L-alanine uptake, with overshoot, by enhancement of the interior-negative transmembrane potential; concentration dependent uptake of methotrexate with apparent competitive inhibition by folinic acid; stimulation of L-lysine uptake by trans-L-arginine. These findings indicate that human fibroblast plasma membrane vesicles could be used to study membrane transport processes and, perhaps, expression of mutant genes that cause inborn errors of transport.

Amino Acids↗
PubMed1984

An alternative approach to analyzing occupational mortality data.

It is widely recognized that analyzing occupational mortality by calculating standardized mortality ratios based on death rates from the general population is subject to a number of limitations. An alternative approach described in this report takes advantage of the fact that comparisons of mortality by subgroups and assessments of trends in mortality are often of equal or greater interest than overall assessments and that such comparisons do not require an external control. A computer program is available for performing the needed calculations for several diseases. This program provides tests for differences and trends among subcategories defined by variables such as length of employment, job category, or exposure measurements and also provides control for age, calendar year, and several other potentially confounding variables.

Adult↗