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A McDougall

Publications and source records attributed to A McDougall.

At least 19 recordsLinked to original sources
PubMed2006

Endoplasmic reticulum generates calcium signalling microdomains around the nucleus and spindle in syncytial Drosophila embryos.

Cell cycle calcium signals are generated by inositol trisphosphate-mediated release of calcium from internal stores [Ciapa, Pesando, Wilding and Whitaker (1994) Nature (London) 368, 875-878; Groigno and Whitaker (1998) Cell 92, 193-204]. The major internal calcium store is the ER (endoplasmic reticulum): the spatial organization of the ER during mitosis is important in defining a microdomain around the nucleus and mitotic spindle in early Drosophila embryos [Parry, McDougall and Whitaker (2005) J. Cell Biol. 171, 47-59]. Nuclear divisions in syncytial Drosophila embryos are accompanied by both cortical and nuclear localized calcium transients. Mitosis is prevented by the InsP(3) antagonists Xestospongin C and heparin. Nuclear-localized transients and cortical transients rely on extraembryonic calcium, suggesting that ER calcium levels are maintained by calcium influx.

Animals↗
PubMed2001

Simultaneous measurement of intracellular nitric oxide and free calcium levels in chordate eggs demonstrates that nitric oxide has no role at fertilization.

At fertilization in sea urchin, the free radical nitric oxide (NO) has recently been suggested to cause the intracellular Ca(2+) rise responsible for egg activation. The authors suggested that NO could be a universal activator of eggs and the present study was set up to test this hypothesis. Intracellular NO and Ca(2+) levels were monitored simultaneously in eggs of the mouse or the urochordate ascidian Ascidiella aspersa. Eggs were either fertilized or sperm extracts microinjected. Sperm-induced Ca(2+) rises were not associated with any global, or local, change in intracellular NO, although we were able to detect NO produced by the addition of a NO donor. Furthermore, the NO synthase inhibitor N(G)-nitro-L-arginine methyl ester had no effect on sperm-induced Ca(2+) release but did block completely ionomycin-induced NO synthase activation. Therefore, we suggest that the current data provide evidence that NO has no role in the fertilization of these two chordate eggs.

Animals↗
PubMed2000

Ca2+ oscillations and the cell cycle at fertilisation of mammalian and ascidian eggs.

At fertilisation of mammalian and ascidian eggs the sperm induces a series of Ca2+ oscillations. These Ca2+ oscillations are triggered by a sperm-borne Ca2+-releasing factor whose identity is still unresolved. In both mammals and ascidians Ca2+ oscillations in eggs are associated with the period leading up to exit from meiosis and entry into the first embryonic cell cycle. Thus, in mammals Ca2+ oscillations continue for several hours but are complete by within 30 min in the ascidian. In mammals and ascidians Ca2+ oscillations stop at around the time when pronuclei form in the 1-cell embryo. There is evidence to show that cell cycle factors are important in regulating the fertilisation Ca2+ signal. If the formation of pronuclei is blocked either in mammals (by spindle disruption) or in ascidians (by clamping maturation promoting factor levels high) then Ca2+ oscillations continue indefinitely. Here, we explore the nature of the sperm Ca2+-releasing factor and examine the relationship between cell cycle resumption and the control of Ca2+ oscillations at fertilisation.

Animals↗
PubMed2000

The initiation and propagation of the fertilization wave in sea urchin eggs.

Calcium waves sweep across most eggs of the deuterostome lineage at fertilization. The precise timing of the initiation and propagation of a fertilization calcium wave has been best studied in sea urchin embryos, since the rapid depolarization caused by sperm egg fusion can be detected as a calcium influx using confocal imaging of calcium indicator dyes. The time between sperm egg fusion and the first sign of the calcium increase that constitutes the calcium wave is comparable to the time it takes for the wave to sweep across the egg, once initiated. The latency and rise time of the calcium response is sensitive to inhibitors of the InsP3 signalling pathway, as reported previously. Using calcium green dextran and confocal microscopy, we confirm that the propagation time of the calcium wave is lengthened and that initiation of the calcium wave involves activation of calcium release at hot spots that may represent clusters of calcium release channels, as has been seen in other cell types.

Animals↗
PubMed2000

Repaglinide: prandial glucose regulation in clinical practice.

Prandial glucose regulation represents a new concept in the management of type 2 diabetes: targeting postprandial glycaemic excursions as a means of achieving long-term glycaemic control. Although control of the overall glycaemic load is the most important factor for the success of long-term management of type 2 diabetes, control of postprandial hyperglycaemia also has positive implications for preventing the development of diabetic complications. Repaglinide is the first prandial glucose regulator to become available in the clinical setting. It has a rapid and short-lived insulinotropic action and can therefore reduce postprandial glucose excursions without increasing the risk of hypoglycaemia. Short-term clinical studies showed that repaglinide is superior to glibenclamide in improving postprandial glycaemic control. Longer-term studies confirmed that improved PGR is accompanied by improved overall glycaemic control that is at least equivalent to that achieved by sulphonylurea treatment. Moreover, because repaglinide can be used with flexible meal patterns without compromising glucose control, it can improve quality of life as indicated by overall treatment satisfaction, well-being and health status. Repaglinide has few contraindications or drug interactions and can be used in a wide range of patients. Although careful titration of repaglinide dose is recommended for patients with mild to moderate renal impairment, no dosage adjustment is otherwise needed in the elderly. In addition to being an effective first-line hypoglycaemic agent, repaglinide is highly effective in combination therapy for patients with type 2 diabetes who require more intensive treatment. When glucose targets are not met using repaglinide monotherapy, the combination of repaglinide with metformin can further improve glycaemic control by enhancing insulin secretion and improving insulin sensitivity. Similarly, when required combination of repaglinide with troglitazone or NPH-insulin can produce better glycaemic control than monotherapy alone. Given that most patients with type 2 diabetes require a multitherapy approach to achieve and sustain adequate glycaemic control, repaglinide will be an important element in future intensive therapy regimens.

Carbamates↗
PubMed2000

Sperm-induced calcium oscillations at fertilisation in ascidians are controlled by cyclin B1-dependent kinase activity.

The generation of calcium oscillations at fertilisation and during mitosis appears to be controlled by the cell cycle machinery. For example, the calcium oscillations in oocytes and embryos occur during metaphase and terminate upon entry into interphase. Here we report the manipulation of sperm-triggered calcium oscillations by cyclin-dependent kinase (CDK) activity, the major component of maturation/M phase promoting factor (MPF). To control the CDK activity we microinjected mRNAs encoding full-length GFP-tagged cyclin B1 or a truncated and therefore stabilised form of cyclin B1 ((delta)90) into unfertilised oocytes. In the presence of full-length cyclin B1, the calcium oscillations terminate when cyclin B1 levels fall along with the concomitant fall in the associated CDK activity. In addition, when the CDK activity is elevated indefinitely with (delta)90 cyclin B1, the calcium oscillations also continue indefinitely. Finally, in oocytes that contain low mitogen-activated protein (MAP) kinase activity and elevated CDK activity, the sperm-triggered calcium oscillations are again prolonged. We conclude that the CDK activity of the ascidian oocyte can be regarded as a positive regulator of sperm-triggered calcium oscillations, a finding that may apply to other oocytes that display sperm-triggered calcium oscillations at fertilisation. Furthermore, these findings may have a bearing upon the mitotic calcium signals of early embryos.

Animals↗
PubMed2000

Cell cycle-dependent repetitive Ca(2+ )waves induced by a cytosolic sperm extract in mature ascidian eggs mimic those observed at fertilization.

Sperm-triggered Ca(2+) oscillations occur throughout the animal kingdom. The mechanism sperm use to trigger Ca(2+) oscillations at fertilization has not been resolved in any egg. The temporal, spatial and regulatory characteristics of the Ca(2+) oscillations during fertilization in ascidians offer a unique advantage over other systems for determining the mechanism of fertilization. For example, sperm trigger two phases of Ca(2+) oscillations that are all waves in ascidians. The first of these Ca(2+) waves begins at the point of sperm-egg fusion while a second phase of Ca(2+) waves originates at a vegetal protrusion termed the contraction pole. In addition, cyclin B1-dependent kinase activity provides a form of positive feedback, maintaining the second phase of Ca(2+) waves during meiosis and thereby ensuring meiotic exit. We therefore prepared cytosolic ascidian sperm extracts or MonoQ-fractionated ascidian sperm extracts from this urochordate to investigate if a Ca(2+)-releasing sperm-borne factor was responsible for egg activation. Spatially, ascidian sperm extract induced repetitive Ca(2+) waves that mimicked the spatial pattern displayed during fertilization: all the second-phase Ca(2+) waves originated at a vegetal protrusion termed the contraction pole (thus mimicking fertilisation). We also demonstrated that ascidian sperm extract-induced Ca(2+) oscillations were maintained when CDK activity was elevated and MAP kinase activity was low, as found previously for sperm-triggered Ca(2+) oscillations. As would be predicted, large doses of ascidian sperm extract injected into prophase-stage oocytes, lacking CDK activity, failed to induce any Ca(2+) release even though they responded to microinjection of the Ca(2+)-releasing second messenger inositol 1,4,5-trisphosphate. Finally, since the Ca(2+)-releasing activity from Mono-Q fractionated ascidian sperm extract eluted predominantly as one fraction, this may imply that one factor is responsible for the Ca(2+)-releasing activity. These data support a model of egg activation whereby the sperm introduces a Ca(2+)-releasing cytosolic factor into the egg. We demonstrated that ascidian sperm contain a protein factor(s) that is regulated by the egg CDK activity and can trigger all the Ca(2+ )waves observed at fertilization with a spatial pattern that mimics those initiated by sperm.

Animals↗
PubMed1998

Calcium waves and oscillations in eggs.

Eggs from several protostomes (molluscs, annelids, nemerteans, etc.) and two deuterostomes (mammals and ascidians) display repetitive calcium signals. Oscillations in the level of intracellular calcium concentration are occasionally triggered by maturing hormones (as in some molluscs) and mostly observed after fertilization which occurs at different stages of the meiotic cell cycle (oocytes are arrested in prophase, metaphase I or metaphase II). In most eggs examined so far, calcium oscillations last until the end of meiosis just before male and female pronuclei form. This ability depends on the sensitivity of InsP3 channels and on the permeability of the plasma membrane to extracellular calcium. In eggs that undergo cytoplasmic reorganization at fertilization (annelids, nemerteans, ascidians, etc.) the repetitive calcium signals are waves that originate from localized cortical sites that become calcium waves pacemakers. In ascidians we have identified the site of initiation of repetitive calcium waves as an accumulation of endoplasmic reticulum sandwiched between the plasma membrane and an accumulation of mitochondria. We compare and discuss the generation of calcium signals in the different eggs, their relationship with the cell cycle and the possible roles they play during development.

Journal Article↗
PubMed1998

Sperm-triggered calcium oscillations during meiosis in ascidian oocytes first pause, restart, then stop: correlations with cell cycle kinase activity.

We have investigated the relationship between the sperm-triggered Ca2+ oscillations and the activities of two cell cycle kinases (MPF activity and MAP kinase activity) at fertilisation of Ascidiella aspersa oocytes. Maturation Promoting Factor (MPF) activity is elevated in the metaphase I (MI)-arrested unfertilised oocyte (as measured by phosphorylation of exogenous histone H1) and falls 5 minutes after fertilisation to remain at low levels for 5 minutes. The first polar body (pb1) is extruded when the MPF activity is low. The MPF activity is elevated again 15 minutes after fertilisation and finally becomes inactivated 25 minutes after fertilisation when the pb2 is extruded. MAP kinase activity increases from an initially elevated level to reach maximal activity 10 minutes after fertilisation and subsequently falls to reach low levels 25 minutes after fertilisation. Sperm trigger a series of Ca2+ oscillations that pause for 5 minutes while only the MPF activity is low and are present when both MPF and MAP kinase activity are elevated. We next attempted to determine whether the second phase of calcium oscillations is required to reactivate the MPF activity that precedes extrusion of the second polar body. To do this, we triggered a monotonic Ca2+ signal. This leads to the inactivation of MPF followed by MPF reactivation. The MPF activity then remains elevated for an extended period of time. During this period, the chromatin remains condensed and a metaphase II (MII) spindle forms. Fertilisation of these MII oocytes triggers extrusion of pb2 in 7 minutes. Interestingly, the second phase of Ca2+ oscillations is completely absent when MII oocytes are fertilised. Thus, in both MI and MII oocytes, the sperm-triggered Ca2+ oscillations follow the MPF activity. Finally we discuss our finding that the Ca2+ release system remains sensitive during the metaphase-like state (including the period when the Ca2+ oscillations pause).

Animals↗
PubMed1997

Treatment of multiple sclerosis with the monoclonal anti-CD4 antibody cM-T412: results of a randomized, double-blind, placebo-controlled, MR-monitored phase II trial.

We report the results of a randomized, double-blind, placebo-controlled exploratory trial of the chimeric monoclonal anti-CD4 antibody cM-T412 in 71 patients suffering from active relapsing-remitting and secondary progressive multiple sclerosis. Infusion of the antibody produced frequent but usually minor side effects and resulted in a long-lasting reduction of circulating CD4-positive T cells. There was no significant effect on the primary measure of efficacy, the number of active lesions on monthly gadolinium-enhanced MRI over 9 months. Further statistical evaluation provided evidence that the degree of depletion of CD4-positive cells was important with regard to treatment efficacy; using CD4 counts as a covariate there was a statistically significant effect on the number of active lesions over 18 months (p = 0.04). There was a statistically significant reduction of 41% in the number of clinical relapses (a secondary efficacy parameter) after 9 months (p = 0.02), which was still present after 18 months, but this finding may be partly due to physician unblinding. Other secondary efficacy parameters (Expanded Disability Status Scale progression, number of courses of methylprednisolone) were not influenced by anti-CD4 treatment. We conclude that intravenous treatment with the monoclonal antibody cM-T412 in the dosage we used results in a substantial and sustained reduction of the number of circulating CD4-positive cells, but is not able to reduce MS activity as measured by monthly gadolinium-enhanced MRI, and is therefore unlikely to have a beneficial effect on the clinical disease course. We found preliminary evidence suggesting that more aggressive depletion of CD4-positive cells might lead to a more substantial reduction in MRI activity.

Adult↗
PubMed1995

Function and characteristics of repetitive calcium waves associated with meiosis.

BACKGROUND: Internal calcium waves and oscillations are now recognized as universal features of cellular activation, but their exact role remains uncertain. In mammalian and ascidian eggs, a large, sperm-triggered calcium activation wave crosses the egg at fertilization, followed by a series of periodic increases in intracellular calcium concentration ([Ca2+]i). We have previously shown that, in eggs of the ascidian Phallusia mammillata, these periodic, post-activation [Ca2+]i increases are in the form of waves, the origin of which relocalizes to a pacemaker region, and that they stop seconds before the completion of meiosis. RESULTS: We show here that the origin of the first one to four post-activation calcium waves in P. mammillata eggs transfers progressively from the site of sperm entry, usually in the animal hemisphere, towards an endoplasmic reticulum (ER)-rich contraction pole in the vegetal hemisphere, a process that takes about five minutes. Once the origin of these repetitive post-activation calcium waves has reached the contraction pole, all subsequent calcium waves originate from the domain of ER concentrated there, which acts as a pacemaker. The first few post-activation calcium waves are faster than the activation wave and, like the activation wave, they propagate homogeneously throughout the cytoplasm. Approximately five to ten minutes after fertilization, the post-activation calcium waves begin to propagate preferentially in the egg cortex. By manipulating intracellular calcium levels with caged inositol 1,4,5 trisphosphate (InsP3) and a competitive inhibitor of InsP3-induced calcium release, we show that the activation wave induced by the sperm is sufficient to induce extrusion of the first polar body, but that additional [Ca2+]i increases are necessary for completion of the second meiotic division. However, periodic calcium waves per se do not seem to be strictly necessary for the completion of meiosis, as a persistent and homogeneous increase in calcium, induced by the calcium ionophore ionomycin, is sufficient to cause second polar body formation and allow completion of meiosis on time. CONCLUSION: These results clearly show that, in the ascidian egg, post-activation calcium waves are required to complete meiosis. They also show that following a period of progressive relocalization of the wave origin, which lasts approximately five minutes, an ER-rich domain at the contraction pole finally becomes a pacemaker from which the calcium waves originate. Once their origin becomes stably localized, the calcium waves begin to propagate preferentially around the cortex of the egg rather than throughout the egg cytoplasm.

Animals↗
PubMed1995

Different calcium-dependent pathways control fertilisation-triggered glycoside release and the cortical contraction in ascidian eggs.

Fertilisation of ascidian eggs induces the rapid release of a cell surface N-acetylglycosaminidase that blocks sperm binding to vitelline coat sperm receptors resulting in a block to polyspermy. Fertilisation also triggers a large contraction of the egg (thus stimulating ooplasmic segregation) that is completed within 5 min of insemination. In eggs of the ascidian Phallusia mammillata, glycosidase release and cortical contractions are blocked by BAPTA-AM [bis-(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid, tetra(acetoxymethyl)-ester], a cell-permeant calcium chelator, indicating that both processes are probably dependent on a rise in intracellular calcium levels. Both glycosidase release and the cortical contraction are induced by treatment of the egg with the protein synthesis inhibitor emetine, while only the glycosidase release is induced by isoproterenol, carbachol or acetylcholine. Previous work with ryanodine demonstrated that ryanodine also caused glycosidase release but not the cortical contraction. Inversely, activation by ionomycin in calcium-free sea water causes cortical contractions but not glycosidase release. Thus the two processes can be activated independently. Dextran-coupled (10 kDa) calcium green-1 injected eggs show an increase in intracellular calcium 30-40 s before the cortical contraction is triggered by fertilisation or ionomycin-induced activation. This confirms previous findings that the cortical contraction is a consequence of the activation calcium wave triggered by the sperm. The extracellular calcium requirement for the glycosidase release suggests that calcium influx may be more important for this phase of egg activation. Thus activation of ascidian eggs appears to involve two independent pathways involving calcium.

Acetylcholine↗
PubMed1995

A five-year follow-up on the temporal stability of the Ego Impairment Index.

This study investigated the temporal stability of the Ego Impairment Index (EII) over a 5-year period. The EII is based on the Comprehensive System (Exner, 1993) and has shown promise as a measure of internal disturbance and psychopathology (Perry & Braff, 1994; Perry & Viglione, 1991; Perry, Viglione, & Braff, 1992). This study successfully recalled 17 subjects from an original sample of 46 who initially suffered from Major Depression, Melancholic-Type 5 years earlier and were treated with antidepressant medication. These subjects did not differ significantly from those Subjects who were not successfully recalled. The Rorschach and a variety of other measures were administered to the subjects. The results revealed impressive temporal consistency over 5 years: a rank-order, test-retest correlation of .68. The EII was also correlated with some of the measures of overall adaptation. These results are consistent with the notion that the EII is a stable trait-measure of psychopathology. Limitations because of the small subgroup of subjects, although not unusual in longitudinal research, are noted.

Journal Article↗
PubMed1995

Amphetamine on Rorschach measures in normal subjects.

Twenty-two normal undergraduate men were administered either d-amphetamine (0.2 mg/kg or 0.4 mg/kg) or placebo in a double-blind, counterbalanced design. The test sessions were exactly three weeks apart and included, among other measures, the Rorschach test. Rorschach anxiety and thought disorder variables were measured under drug and placebo conditions. The results suggest that amphetamine causes an increase in Rorschach anxiety indices but does not elevate Rorschach indices of thought disorder. The observed dissociation of anxiety and thought disorder on the Rorschach has implications for the role of the Rorschach in studying anxiety disorders and schizophrenic disorders.

Adult↗
PubMed1995

The sperm entry point defines the orientation of the calcium-induced contraction wave that directs the first phase of cytoplasmic reorganization in the ascidian egg.

Ascidians eggs are spawned with their cytoskeleton and organelles organized along a preexisting animal-vegetal axis. Fertilization triggers a spectacular microfilament-dependant cortical contraction that causes the relocalization of preexisting cytoplasmic domains and the creation of new domains in the lower part of the vegetal hemisphere. We have investigated the relationship between fertilization, the cortical contraction and the localization of cytoplasmic domains in eggs of the ascidian Phallusia mammillata. We have also examined the link between this first phase of ooplasmic segregation and the site of gastrulation. The cortical contraction was found to be initiated on the side of the egg where intracellular calcium is first released either by the entering sperm or by photolysis of caged InsP3. The cortical contraction carries the sperm nucleus towards the vegetal hemisphere along with a subcortical mitochondria-rich domain (the myoplasm). If the sperm enters close to the animal or vegetal poles the cortical contraction is symmetrical, travelling along the animal-vegetal axis. If the sperm enters closer to the equator, the contraction is asymmetrical and its direction does not coincide with the animal-vegetal axis. The direction of contraction defines an axis along which preexisting (such as the myoplasm) or newly created cytoplasmic domains are relocalized. Two microfilament-rich surface constrictions, the 'contraction pole' and the 'vegetal button' (which forms 20 minutes later), appear along that axis approximately opposite the site where the contraction is initiated. The contraction pole can be situated as much as 55 degrees from the vegetal pole, and its location predicts the site of gastrulation. It thus appears that in ascidian eggs, the organization of the egg before fertilization defines a 110 degrees cone centered around the vegetal pole in which the future site of gastrulation of the embryo will lie. The calcium wave and cortical contraction triggered by the entering sperm adjust the location of cytoplasmic domains along an axis within that permissive zone. We discuss the relation between that axis and the establishment of the dorsoventral axis in the ascidian embryo.

Animals↗
PubMed1994

Cytoplasmic domains in eggs.

One way of organizing the body plan of a developing embryo is to establish domains in the egg with distinct compositions in defined spatial relationships to one another: when the egg divides up, these domains segregate preferentially to certain regions of the embryo and influence their development. In this review we discuss the nature, formation and reorganization of distinguishable domains in various eggs.

Journal Article↗
PubMed1993

Redundant mechanisms of calcium-induced calcium release underlying calcium waves during fertilization of sea urchin eggs.

Propagating Ca2+ waves are a characteristic feature of Ca(2+)-linked signal transduction pathways. Intracellular Ca2+ waves are formed by regenerative stimulation of Ca2+ release from intracellular stores by Ca2+ itself. Mechanisms that rely on either inositol trisphosphate or ryanodine receptor channels have been proposed to account for Ca2+ waves in various cell types. Both channel types contributed to the Ca2+ wave during fertilization of sea urchin eggs. Alternative mechanisms of Ca2+ release imply redundancy but may also allow for modulation and diversity in the generation of Ca2+ waves.

Adenosine Diphosphate Ribose↗