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J D Murray

Publications and source records attributed to J D Murray.

At least 181 records · Page 10Linked to original sources
PubMed1981

On pattern formation mechanisms for lepidopteran wing patterns and mammalian coat markings.

The patterns on wings of Lepidoptera can be generated with a few pattern elements, but no mechanism has been suggested for producing them. I consider two of the basic patterns, namely, central symmetry and dependent patterns. A biochemically plausible model mechanism is proposed for generating major aspects of these patterns, based on a diffusing morphogen that activates a gene or colour-specific enzyme in a threshold manner to generate a stable heterogeneous spatial pattern. The model is applied to the determination stream hypothesis of Kühn & von Engelhardt (Wilhelm Roux Arch. Entw Mech. Org. 130, 660 (1933)), and results from the model compared with their microcautery experiments on the pupal wing of Ephestia kühniella. In the case of dependent patterns, results are compared with patterns on specific Papilionidae. For the same mechanism and a fixed set of parameters I demonstrate the important roles of geometry and scale on the spatial patterns obtained. The results and evidence presented here suggest the existence of diffusion fields of the order of several millimetres, which are very much larger than most embryonic fields. The existence of zones of polarizing activity is also indicated. Colour patterns on animals are considered to be genetically determined, but the mechanism is not known. I have previously suggested that a single mechanism that can exhibit an infinite variety of patterns is a candidate for that mechanism, and proposed that a reaction-diffusion system that can be diffusively driven unstable could be responsible for the laying down of the spacing patterns that generates the pre-pattern for animal coat markings. For illustrative purposes I consider, a practical reaction mechanism, which exhibits substrate inhibition, and show that the geometry and scale of the domain (part of the epidermis) play a crucial role in the structural patterns that result. Patterns are obtained for a selection of geometries, and general features are related to the coat colour distribution in the spotted Felidae, giraffe, zebra and other animals. The patterns depend on the initial conditions, but for a given geometry and scale are qualitatively similar, a positive feature of the model and a necessary model attribute in view of the pattern individuality on animals of the same species.

Animals↗
PubMed1981

Inheritance and expression of two peptidases in the wallaroo, Macropus robustus (Gould).

The formal genetics of two peptidase loci in M. robustus are presented. Both loci are autosomal but do not appear to be located on the same chromosome pair. Alleles at both loci are codominantly expressed in neonates, pouch young and adults. The application of autosomal loci segregating for three or more alleles in studies of embryonic gene expression is discussed.

Alleles↗
PubMed1981

Flow cytometric analysis of DNA content of mouse liver cells following in vivo infection by human adenovirus type 5.

Human adenovirus type 5 caused acute hepatocellular damage when injected intravenously into C57B1/6 mice. Early protein (P) and late virus protein (V) antigen staining by immunofluorescence was located principally, if not exclusively, in hepatocytes. Autoradiography following incorporation of tritiated thymidine into Ad5-infected liver cells in vivo indicated that DNA synthesis was initiated in hepatocytes. Flow cytometry showed that cells with a 4n DNA content prior to infection were highly susceptible to infection, with 75% being lost from the liver cell population by 5 days post-infection. This observation was correlated with the observed pathology during the course of the infection.

Adenoviridae Infections↗
PubMed1981

Alterations to controls of cellular DNA synthesis by adenovirus infection.

Human adenovirus type 5 and temperature-sensitive mutants ts36, ts37, and ts125 induced cellular DNA synthesis in quiescent rodent cells at both permissive and nonpermissive temperatures. Cellular DNA synthesis induced by adenovirus type 5 or by serum required protein synthesis for both initiation and continuation, whereas viral DNA synthesis was not dependent upon continued protein synthesis once it was initiated. Both cellular and viral DNA replication was induced in adenovirus type 5-infected cells in the presence of dibutyryl cyclic AMP at concentrations which inhibited induction by serum which suggested that some of the controls of DNA synthesis in serum-treated and virus-infected cells are different. After adenovirus infection of quiescent cells, there was a decrease in the number of cells with G1 DNA content and an increase in cells with G2 diploid and greater DNA contents. Thus, adenovirus type 5 induces a complete round of cellular DNA replication, but in some cells, it induces a second round without completion of a normal mitosis. These results suggest that adenovirus type 5 is able to alter cell growth cycle controls in a way which may be related to its ability to transform cells.

Adenoviruses, Human↗
PubMed1980

Karyotypes, constitutive heterochromatin and taxonomy of ringtail opossums of the genus Pseudocheirus (Marsupialia: Petauridae).

Karyotypes are presented for three forms of the common ringtail oppossum, Pseudocheirus peregrinus. These are tentatively regarded as the subspecies P.p. cookii, P.p. pulcher, and P.p. rubidus. In addition, we report for the first time the karyotype of the rock ringtail oppossum, P. dahli. The three forms of P. peregrinus each have a diploid number of 2n=20. C-banding studies indicate that the addition of large blocks of constitutive heterochromatin has played a major role in the evolution of all chromosomes in the karyotype. The X chromosome of P.p. pulcher is metacentic and approximately twice the relative size of the acrocentric X chromosomes of the other two forms of peregrinus. All three forms had two or three pairs of autosomes with secondary constrictions, a rare occurrence within the superfamily Phalangeroidea. P. (Pseudochirops) dahli has a diploid number of 2n=16; a reduction in chromosome number may have occurred by Robertsonian fusions. Four of the eight chromosome pairs lack large blocks of C-band material and the secondary constrictions are located on the sex chromosomes.

Animals↗
PubMed1979

Studies on metatherian sex chromosomes. IX. Sex chromosomes of the greater glider (Marsupialia: Petauridae).

The greater glider, currently but incorrectly known as Schoinobates volans, is widely distributed in forested regions in eastern Australia. All animals studied from six different localities had 20 autosomes but there were four chromosomally distinct populations. At Royal National Park, N.S.W., all female greater gliders studied had 22 chromosomes including two large submetacentric X chromosomes with subterminal secondary constrictions in their longer arms. This form of X chromosome occurred also at Bondo State Forest, Myall Lakes and Coff's Harbour, N.S.W., and at Eidsvold, Qld. At Coomooboolaroo, Qld, the X chromosome was also a large submetacentric but a secondary constriction occurred in the shorter arm. Two chromosomally distinct types apparently occur in Royal National Park, one with XY males as in all other populations, and one with XY1Y2 males. Y or Y1, but not Y2, chromosomes were eliminated from the bone marrow in all populations but were present in spermatogonia, primary spermatocytes and cultured fibroblasts. Animals from Bondo State Forest had three or more acrocentric or metacentric supernumerary chromosomes.

Animals↗
PubMed1977

Effect of the rate of oxygen consumption on muscle respiration.

An important role of myoglobin in red muscle is to facilitate the diffusion of oxygen for metabolism. We consider a model for muscle respiration in which the oxygen consumption is of a Michaelis-Menten form. The resulting mathematical model is solved in two different ways with two different boundary conditions. The first uses the singular perturbation method of Murray (1974), while the second, which gives another justication of the simpler procedure, is a direct numerical computation of the full problem. The oxygen tension and saturation are often small. For realistic values of the Michaelis-MENTEN CONSTANT the oxygen tension, the saturation and the radius of the region in which the oxygen tension is negligibly small can be calculated using the constant consumption model of Murray (1974), with corrected boundary conditions (those for a Stefan problem), which in certain circumstances mardedly affect the solution.

Diffusion↗
PubMed1977

The effect of carbon monoxide on haem-facilitated oxygen diffusion.

The aim of this paper is to quantify the effect of small quantities of carbon monoxide on the facilitated diffusion of oxygen by haemoglobin in the steady state. It is the first phase in the study of a mathematical model for carbon monoxide poisoning. Here we extend the Wyman model for facilitated diffusion to the case in which there are two ligands. The equations are solved using an asymptotic technique developed by Murray. We obtain accurate analytic approximations for the biologically important quantities of the problem for various percentages of carbon monoxide. These are the concentrations of free oxygen, haemoglobin, oxyhaemoglobin and carboxyhaemoglobin, and hence the saturation of the protein and the facilitated oxygen flux. The major effect of very small quantities of carbon monoxide on the oxygen flux is shown.

Carbon Monoxide↗
PubMed1977

Nonrandom sex-chromosome association and constitutive heterochromatin in the brush-tailed possum, Trichosurus vulpecula (Marsupialia: Phalangeridae).

Nonrandom associations between the short arms of the sex chromosomes of six Trichosurus vulpecula were studied in 455 cells from the spleen and bone marrow. The association occurs in both sexes and was found to be independent of age. There was, however, a significant difference in the degree of association between the two tissues studied. Regions of constitutive heterochromatin were found to be located in the short arms of the X and Y chromosomes by using a C-banding technique. Nucleolar organizers were detected in the middle of the long arm of the X chromosome and in the short arm of the Y chromosome by N-banding. These results indicate that the nonrandom association of the sex chromosomes may reflect an association between heterochromatin regions during interphase of the cell cycle.

Animals↗