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Biomedical subjects

M Dunlop

Publications and source records attributed to M Dunlop.

16 recordsLinked to original sources
PubMed1992

Activation of phospholipase D by glyceraldehyde in isolated islet cells follows protein kinase C activation.

Our recent studies have demonstrated the presence in neonatal islet cells and intact adult islets of a phosphatidylcholine-directed phospholipase D (PLD) which is activated after phorbol ester stimulation. The present study describes PLD activation in the presence of a carbohydrate insulin secretagogue. At the highest concentration tested (20 mM) the triose, glyceraldehyde, induced formation of phosphatidic acid in cells prelabeled with [14C]arachidonic acid or [3H]myristic acid (164 +/- 7 and 210 +/- 9% of basal phosphatidic acid values, respectively). Experimental confirmation of a concentration-dependent specific activation of PLD was provided by the formation of a transphosphatidylation product, phosphatidylethanol, after stimulation with glyceraldehyde in the presence of added ethanol (1.5%). Additionally, there was an early (within 5 min) rise in [14C]arachidonate-labeled diacylglycerol (139 +/- 7% of basal) accompanied by an increase in intracellular diacylglycerol mass (51 +/- 2 pmol/mg protein) and an increase in membrane-associated protein kinase C activity (183 +/- 5% of basal) which preceded the activation of PLD, as indicated by the time course of glyceraldehyde-stimulated phosphatidylethanol formation in the presence of ethanol. Pretreatment of islet cells with 2 microM 12-O-tetradecanoylphorbol-13-acetate for 18 h, to down-regulate protein kinase C, was without effect on diacylglycerol and phosphatidic acid production after 5 min but inhibited completely the production of phosphatidylethanol at 30 min. The phosphohydrolase inhibitor propranolol (100 microM) potentiated the accumulation of phosphatidic acid and phosphatidylethanol incubation following incubation with glyceraldehyde. These findings demonstrate for the first time that a physiological nutrient activates a phospholipase directed against endogenous phosphatidylcholine in intact islet cells; furthermore, they indicate a role for PLD in a delayed formation of phosphatidic acid in the islet cell. The finding of an early rise in glyceraldehyde-stimulated diacylglycerol (which may be formed de novo or by the action of phospholipase C), suggests that PLD is recruited by the activation of protein kinase C by this nutrient.

Animals↗
PubMed1991

A candidate spermatogenesis gene on the mouse Y chromosome is homologous to ubiquitin-activating enzyme E1.

The human X-linked gene A1S9 complements a temperature-sensitive cell-cycle mutation in mouse L cells, and encodes the ubiquitin-activating enzyme E1. The gene has been reported to escape X-chromosome inactivation, but there is some conflicting evidence. We have isolated part of the mouse A1s9 gene, mapped it to the proximal portion of the X chromosome and shown that it undergoes normal X-inactivation. We also detected two copies of the gene on the short arm of the mouse Y chromosome (A1s9Y-1 and A1s9Y-2). The functional A1s9Y gene (A1s9Y-1) is expressed in testis and is lost in the deletion mutant Sxrb. Therefore A1s9Y-1 is a candidate for the spermatogenesis gene, Spy, which maps to this region. A1s9X is similar to the Zfx gene in undergoing X-inactivation, yet having homologous sequences on the short arm of the Y chromosome, which are expressed in the testis. These Y-linked genes may form part of a coregulated group of genes which function during spermatogenesis.

Amino Acid Sequence↗
PubMed1991

Modulation of phospholipase A2 activity by epidermal growth factor (EGF) in CHO cells transfected with human EGF receptor. Role of receptor cytoplasmic subdomain.

Activation of phospholipase A2 (PLA2) in response to external stimuli may play a pivotal role in signal-transduction pathways via the generation of important cellular intermediates, including prostaglandins. Epidermal growth factor (EGF) has been shown to modulate prostaglandin production, possibly via direct activation of PLA2 or indirectly via interaction with a PLA2-modifying protein such as lipocortin I. We have investigated these pathways with two CHO cell-lines, one (CHOwt) transfected with the full-length human EGF receptor and the second (CHO 11) with a deletion mutant, delta 990, that has lost the autophosphorylation sites and part of the internalization domain. CHOwt cells responded to EGF with a rapid rise in lysophosphatidylcholine and arachidonic acid release concomitant with an increase in prostaglandin production. However, in the non-internalizing CHO 11 cells no such activation of PLA2 was observed. This was not due to an intrinsic lack of PLA2 in these cells, as PLA2 activation was shown on melittin addition, nor was this difference due to a defect in intracellular pathways, as arachidonic acid was released from both cell types by Ca2+ and protein kinase C modulators. However, only in CHOwt cells were these responses potentiated by concomitant addition of EGF. Thus the cytoplasmic subdomain of the EGF receptor, containing the major sites of autophosphorylation and the internalization domain, seems to be involved in the activation of PLA2 by EGF. In addition, we have shown that phosphorylation of lipocortin I is unlikely to play a role in PLA2 activation. In CHOwt cells and a positive control cell line, A431, activation of PLA2 was complete by 10 min, at which time there was no evidence of lipocortin I phosphorylation.

Animals↗
PubMed1978

Lipogenesis in developing human adipose tissue.

De novo lipid synthesis can be demonstrated in human fetal subcutaneous tissue cells which are in the initial stages of liquid accumulation. Lipogenic capacity measured as ability to incorporate acetate into neutral lipid was shown to increase with gestational age. This lipogenic capacity was accompanied by an increased activity of acetyl co-enzyme A carboxylase. Insulin, which is known to activate this enzyme in mature adipose tissue, increased neutral lipid synthesis in fetal subcutaneous tissue. When tissue insulin levels were determined, insulin was found from 16 wk gestation. At this time triglyceride content of the tissue was also increasing. Thus de novo fatty acid synthesis is a means by which the developing adipose cell initiates lipid accumulation.

Acetates↗
PubMed1978

Identification of small cells in fetal and infant adipose tissue.

In developing adipose tissue, cells of size less than 25 micron may make a major contribution to adipose tissue cell populations. This study reports the separation, identification, and sizing of infant and foetal adipose tissue small cells. Subcutaneous adipose tissue was taken from the anterior abdominal wall of children aged 2 months and 22 months. Subcutaneous tissue was also obtained from a paraumbilical site in 4 fetuses of gestational age 16 weeks. Tissue samples were fixed in buffered osmium tetroxide solution containing collidine. Aliquots of cell preparations suspended in saline on microscope slides were viewed and separated using a dissecting microscope. A diameter distribution of particle size was obtained using at least 200 cells for each preparation. There was a substantial number of cells that were smaller than 20 micron. Their modal cell size was remarkably constant in fetuses and in 2-month-old and 22-month-old infants. Ultrastructural studies show that the tissue is composed of a relatively uniform population of cells within sparsely collagenous connective tissue. Although some of the cells show no intracytoplasmic aggregates of lipid material, others show variable amounts of lipid material which can occupy a very large part of the cell volume.

Adipose Tissue↗
PubMed1978

The growth and development of fat cells in infancy.

Studies on the development of adipose tissue in infancy would seem essential to test the hypothesis that adult fat stores relate to the numbers of fat cells developed during early childhood. Thirty infants aged from 1-28 months and 13 fetuses of approximately 11-16 weeks of gestation obtained at therapeutic abortion and two preterm infants of 28 weeks of gestation were studied. The cells of both fetal and infant adipose tissue were separated from connective tissue and fixed by treatment with osmium tetroxide in buffered collidine using a method modified from Hirsch and Gallian (J. Lipid Res.,9:100(1968) for estimation of cell size and number. In fetal and early infancy there are two populations of cells in adipose tissue. Small cells found in tissue before birth and the first months of postnatal life do not contain fat. The larger cells, which are fat containing, represent maturing fat cells. They are cells which include fat cells recognized by previous workers but up to 24.6% were found to be less than 25 micron in diameter. Small cells in the early stages of fat accumulation may make an important contribution to the cell population of fat mass. It is apparent that increasing fat accumulation in the first 6-12 months of life, as demonstrated by increased skinfold thickness measurements, is associated with increasing fat cell size and that this association bears a linear relationship.

Adipose Tissue↗
PubMed1976

Changes in the pituitary-testicular system with age.

In order to provide a comprehensive account of pituitary-testicular function in man, 466 subjects, ranging in age from 2 to 101 years, were studied to examine blood levels of the pituitary gonadotrophins (LH and FSH), the sex steroids testosterone and oestradiol, the binding capacity of the sex hormone binding globulin (SHBG), the free testosterone and oestradiol fractions, and the transfer constant for the peripheral conversion of testosterone to oestradiol. The results were compared with clinical indices of testicular size, sexual function and secondary sex hair distribution. Serum LH and FSH were low before puberty, increased in pubertal adolescents to levels somewhat above those of adults and subsequently increased progressively over the age of 40 years. Testosterone levels fell slowly after the age of 40, while there was a slight rise in plasma oestradiol with increasing age. FSH and testosterone showed small seasonal variations in young adult men, the lowest values being seen in winter. SHBG binding capacity was high in two prepubertal boys, fell in adult men, but increased in old age. Free testosterone and oestradiol levels fell in old age. The metabolic clearance rates (MCR) of testosterone and oestradiol also fell in old age, while the conversion of testosterone to oestradiol was increased. Many correlations were observed between various hormonal and clincial measurements. The evidence is consistent with a primary decrease in testicular function over the age of 40 years.

Adolescent↗
PubMed1975

Plasma lipid values and lipoprotein patterns during adolescence in boys.

Lipid studies were performed on fasting plasma samples in 214 healthy adolescent boys, 11-19 years of age. Ranges of normal values for plasma cholesterol and triglyceride concentrations, and normal lipoprotein patterns were established for this age group. The boys were grouped according to puberty rating. A significant increase in triglyceride values was obtained with adolescent maturity. Plasma cholesterol values did not change with age or puberty rating. One boy had hypercholesterolemia and a lipoprotein pattern consistent with Type II hyperlipoproteinemia (Fredrickson). Seventeen boys, all of whom had reached adolescent maturity, had elevated triglyceride values and a marked increase in pre-beta-lipoprotein. It appears from this study that increased concentrations of triglyceride and Type IV hyperlipoproteinemia of Fredrickson may be detected as boys reach maturity at adolescence.

Adolescent↗