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K Brennan

Publications and source records attributed to K Brennan.

At least 19 recordsLinked to original sources
PubMed2001

Notch signaling targets the Wingless responsiveness of a Ubx visceral mesoderm enhancer in Drosophila.

BACKGROUND: Members of the Notch family of receptors mediate a process known as lateral inhibition that plays a prominent role in the suppression of cell fates during development. This function is triggered by a ligand, Delta, and is implemented by the release of the intracellular domain of Notch from the membrane and by its interaction with the protein Suppressor of Hairless [Su(H)] in the nucleus. There is evidence that Notch can also signal independently of Su(H). In particular, in Drosophila, there is evidence that a Su(H)-independent activity of Notch is associated with Wingless signaling. RESULTS: We report that Ubx(VM)B, a visceral mesoderm-specific enhancer of the Ubx gene of Drosophila, is sensitive to Notch signaling. In the absence of Notch, but not of Su(H), the enhancer becomes activated earlier and over a wider domain than in the wild type. Furthermore, the removal of Notch reduces the requirement for Disheveled-mediated Wingless signaling to activate this enhancer. This response to Notch is likely to be mediated by the dTcf binding sites in the Ubx(VM)B enhancer. CONCLUSIONS: Our results show that, in Drosophila, an activity of Notch that is likely to be independent of Su(H) inhibits Wingless signaling on Ubx(VM)B. A possible target of this activity is dTcf. As dTcf has been shown to be capable of repressing Wingless targets, our results suggest that this repressive activity may be regulated by Notch. Finally, we suggest that Wingless signaling is composed of two steps, a down-regulation of a Su(H)-independent Notch activity that modulates the activity of dTcf and a canonical Wingless signaling event that regulates the activity of Armadillo and its interaction with dTcf.

Animals↗
PubMed2001

Individual differences in sucrose consumption in the rat: motivational and neurochemical correlates of hedonia.

RATIONALE: Rats exhibit marked individual differences in consumption of freely available sucrose; however, the underlying mechanism(s) contributing to such interindividual differences remain unclear. OBJECTIVES: The current study examined whether: 1) motivational differences (as reflected by the degree of operant output to procure sucrose reward) underlie variability in sugar consumption, and 2) whether potential differences in dopaminergic and/or opioidergic systems contribute to such differences. METHODS: In the initial experiment, Sprague-Dawley rats were divided into those that spontaneously consumed High or Low amounts of sucrose, based on the consumption of freely available sugar (+/-2 SD from group median) over 7 consecutive test days. The potential differences in their motivation to seek and "earn" sucrose solution rewards were measured using the progressive ratio (PR) schedule of reinforcement. RESULTS: Performance of both groups on the PR schedule was sensitive to the concentration of sucrose (i.e. the higher the concentration, the greater the behavioral output). Furthermore, the High sucrose consumers earned a greater number of reinforcements (20% sucrose solution) than the Low group. Parenthetically, the degree of behavioral output by the High (but not the Low) group was comparable to that emitted for water under water-deprived condition. Treatment with the opioid antagonist, naloxone, attenuated PR performance for sucrose, whereas d-amphetamine (0.5 mg/kg) enhanced it. Furthermore, naloxone attenuated amphetamine-enhanced responding for sucrose reward, suggesting an interaction between the dopaminergic and opioidergic systems in the mediation of sucrose reward. CONCLUSIONS: These results support the contention that motivational differences may partially account for individual variability in sucrose consumption, and that dopaminergic and/or opioidergic agents differentially affect the "wanting" and/or "liking" of sucrose in the High and Low sucrose consumers.

Animals↗
PubMed2000

A novel duodenal iron-regulated transporter, IREG1, implicated in the basolateral transfer of iron to the circulation.

Iron absorption by the duodenal mucosa is initiated by uptake of ferrous Fe(II) iron across the brush border membrane and culminates in transfer of the metal across the basolateral membrane to the portal vein circulation by an unknown mechanism. We describe here the isolation and characterization of a novel cDNA (Ireg1) encoding a duodenal protein that is localized to the basolateral membrane of polarized epithelial cells. Ireg1 mRNA and protein expression are increased under conditions of increased iron absorption, and the 5' UTR of the Ireg1 mRNA contains a functional iron-responsive element (IRE). IREG1 stimulates iron efflux following expression in Xenopus oocytes. We conclude that IREG1 represents the long-sought duodenal iron export protein and is upregulated in the iron overload disease, hereditary hemochromatosis.

Amino Acid Sequence↗
PubMed2000

Structural requirements for notch signalling with delta and serrate during the development and patterning of the wing disc of Drosophila.

The delta and Serrate proteins interact with the extracellular domain of the Notch receptor and initiate signalling through the receptor. The two ligands are very similar in structure and have been shown to be interchangeable experimentally; however, loss of function analysis indicates that they have different functions during development and analysis of their signalling during wing development indicates that the Fringe protein can discriminate between the two ligands. This raises the possibility that the signalling of delta and Serrate through Notch requires different domains of the Notch protein. Here we have tested this possibility by examining the ability of delta and Serrate to interact and signal with Notch molecules in which different domains had been deleted. This analysis has shown that EGF-like repeats 11 and 12, the RAM-23 and cdc10/ankyrin repeats and the region C-terminal to the cdc10/ankyrin repeats of Notch are necessary for both delta and Serrate to signal via Notch. They also indicate, however, that delta and Serrate utilise EGF-like repeats 24-26 of Notch for signalling, but there are significant differences in the way they utilise these repeats.

Amino Acid Sequence↗
PubMed2000

Chronic effects of inhaled albuterol on beta-adrenoceptor system function in human respiratory cells.

The in vivo effects of beta-adrenergic receptor (betaAR) agonists given chronically by metered-dose inhaler (MDI) on the molecular components of the beta-adrenoceptor system expressed by human respiratory cells are poorly understood. This study examined the effects of inhaled albuterol (180 microg four times daily for 7 days) on betaAR function of airway epithelial cells (AECs) and alveolar macrophages (AMs) freshly isolated from 10 normal subjects. Responses were related to beta2AR genotype in codons 16 and 27, regions which affect chronic responses to beta2-agonists. In AEC, betaAR density and adenosine cyclic 3',5'-phosphate (cAMP) production in response to isoproterenol (ISO) were significantly lower in the albuterol versus placebo treatment arm (p < 0.01 for both). Moreover, in AEC, albuterol treatment increased betaAR-kinase (betaARK) protein immunoreactivity. In contrast, in AM, albuterol tended to decrease betaAR density and cAMP production but changes did not achieve statistical significance (p > 0.20 for both) and had no effect on betaARK immunoreactivity. Changes in betaAR density occurred in all subjects but tended to be greater in subjects with the glycine 16 genotype. In cultured cells exposed to equal concentrations of beta-agonist in vitro, the magnitude of betaAR down-regulation (p < 0.05) and cAMP densensitization (p < 0.05) was greater in AEC than AM. These results indicate that albuterol taken by inhalation in a therapeutically relevant dose for 1 week produces betaAR down-regulation, densensitizes the cAMP response of airway epithelial cells to a beta2-adrenergic agonist, and increases betaARK immunoreactivity. Greater densensitization of AEC than AM in response to chronic albuterol inhalation likely reflects cell type-specific responses.

Administration, Inhalation↗
PubMed1999

The abruptex mutations of notch disrupt the establishment of proneural clusters in Drosophila.

The receptor encoded by the Notch gene plays a central role in preventing cells from making decisions about their fates until appropriate signals are present. This function of Notch requires the product of the Suppressor of Hairless gene. Loss of either Notch or Suppressor of Hairless function results in cells making premature and incorrect cell fate decisions, whilst increases in Notch signalling prevent cells from making these decisions. Here we find that the proneural clusters are not established correctly in certain Abruptex mutations of Notch and this failure to establish proneural clusters correctly is not due to increased Notch signalling during lateral inhibition. In addition we show that the overexpression of certain dominant negative Notch molecules can disrupt the initiation of proneural cluster development in a manner similar to the Abruptex mutants.

Animals↗
PubMed1999

Wingless modulates the effects of dominant negative notch molecules in the developing wing of Drosophila.

The development and patterning of the wing in Drosophila relies on a sequence of cell interactions molecularly driven by a number of ligands and receptors. Genetic analysis indicates that a receptor encoded by the Notch gene and a signal encoded by the wingless gene play a number of interdependent roles in this process and display very strong functional interactions. At certain times and places, during wing development, the expression of wingless requires Notch activity and that of its ligands Delta and Serrate. This has led to the proposal that all the interactions between Notch and wingless can be understood in terms of this regulatory relationship. Here we have tested this proposal by analysing interactions between Delta- and Serrate-activated Notch signalling and Wingless signalling during wing development and patterning. We find that the cell death caused by expressing dominant negative Notch molecules during wing development cannot be rescued by coexpressing Nintra. This suggests that the dominant negative Notch molecules cannot only disrupt Delta and Serrate signalling but can also disrupt signalling through another pathway. One possibility is the Wingless signalling pathway as the cell death caused by expressing dominant negative Notch molecules can be rescued by activating Wingless signalling. Furthermore, we observe that the outcome of the interactions between Notch and Wingless signalling differs when we activate Wingless signalling by expressing either Wingless itself or an activated form of the Armadillo. For example, the effect of expressing the activated form of Armadillo with a dominant negative Notch on the patterning of sense organ precursors in the wing resembles the effects of expressing Wingless alone. This result suggests that signalling activated by Wingless leads to two effects, a reduction of Notch signalling and an activation of Armadillo.

Animals↗
PubMed1999

HFE downregulates iron uptake from transferrin and induces iron-regulatory protein activity in stably transfected cells.

Hereditary hemochromatosis (HH) is a common autosomal-recessive disorder of iron metabolism. More than 80% of HH patients are homozygous for a point mutation in a major histocompatibility complex (MHC) class I type protein (HFE), which results in a lack of HFE expression on the cell surface. A previously identified interaction of HFE and the transferrin receptor suggests a possible regulatory role of HFE in cellular iron absorption. Using an HeLa cell line stably transfected with HFE under the control of a tetracycline-sensitive promoter, we investigated the effect of HFE expression on cellular iron uptake. We demonstrate that the overproduction of HFE results in decreased iron uptake from diferric transferrin. Moreover, HFE expression activates the key regulators of intracellular iron homeostasis, the iron-regulatory proteins (IRPs), implying that HFE can affect the intracellular "labile iron pool." The increase in IRP activity is accompanied by the downregulation of the iron-storage protein, ferritin, and an upregulation of transferrin receptor levels. These findings are discussed in the context of the pathophysiology of HH and a possible role of iron-responsive element (IRE)-containing mRNAs.

Down-Regulation↗
PubMed1999

Repression by Notch is required before Wingless signalling during muscle progenitor cell development in Drosophila.

The larval muscles of Drosophila arise from the fusion of muscle founder cells, which give each individual muscle its identity, with myoblasts (reviewed in [1]). Muscle founder cells arise from the asymmetric division of muscle progenitor cells, each of which develops from a group of cells in the somatic mesoderm that express lethal of scute [2]. All the cells in a cluster can potentially form muscle progenitors, but owing to lateral inhibition, only one or two develop as such [2] [3] [4] [5]. Muscle progenitors, and the subsequent founder cells, then express transcription factors such as Krüppel, S59 and Even-skipped, which confer identity on the muscle [6] [7] [8]. Definition of some muscle progenitors, including three groups that express S59, depends on Wingless signalling [9]. Lateral inhibition requires Delta signalling through Notch and the transcription factor Suppressor of Hairless [3] [4] [5]. As the Wingless and lateral-inhibition signals are sequential [8], one might expect that muscle progenitors would fail to develop in the absence of Wingless signalling, regardless of the presence or absence of lateral-inhibition signalling. Here, we examine the development of the S59-expressing muscle progenitor cells in mutant backgrounds in which both Wingless signalling and lateral inhibition are disrupted. We show that progenitor cells failed to develop when both these processes were disrupted. Our analysis also reveals a repressive function of Notch, required before or concurrently with Wingless signalling, which is unrelated to its role in lateral inhibition.

Animals↗
PubMed1999

An activity of Notch regulates JNK signalling and affects dorsal closure in Drosophila.

BACKGROUND: The Drosophila Notch protein is a receptor that controls cell fate during embryonic development, particularly in lateral inhibition, a process that acts on groups of cells that share a particular developmental potential to restrict the number of cells that will adopt that cell fate. The process of lateral inhibition is implemented by the nuclear protein Suppressor of Hairless (Su(H)) and is triggered by the ligand Delta. Recent results have shown that the interaction between Delta and Notch triggers the cleavage of the intracellular domain of Notch which then translocates to the nucleus and binds to Su(H). RESULTS: We find that Notch plays a role in the patterning of the dorsal epidermis of the Drosophila embryo and that this function of Notch is independent of Su(H), requires Notch at the plasma membrane and targets the c-Jun N-terminal kinase (JNK) signalling pathway. Notch mutants show high levels of JNK activity and can rescue the effects of lowered JNK signalling resulting from mutations in the hemipterous and basket genes. Two regions of the intracellular domain of Notch are involved: the Cdc10/ankyrin repeats, which downregulate signalling through the JNK pathway, and a region carboxy-terminal to these repeats, which regulates this negative function. CONCLUSIONS: Our results reveal a novel signalling activity of Notch that does not require its cleavage and acts by modulating signalling through the JNK pathway. In the Drosophila embryo, this activity plays an important role in the morphogenetic movements that drive dorsal closure.

Animals↗
PubMed1999

Wnt signalling: pathway or network?

Members of the Wnt family of secreted glycoproteins participate in many signalling events during development. Recent findings suggest that Wnt signals can sometimes play a permissive role during cell-fate assignment. Wnt proteins have been shown to interact with a number of extracellular and cell-surface proteins, whereas many intracellular components of the Wnt-signalling pathway are also involved in other cellular functions. The consequences of Wnt signalling can be affected by members of the MAP kinase family. These observations suggest that the future understanding of Wnt signalling may require models that are based on a signalling network rather than a single linear pathway.

Animals↗
PubMed1999

Efficacy and compliance with noninvasive positive pressure ventilation in patients with chronic respiratory failure.

STUDY OBJECTIVES: Previous studies have shown the acute effects of noninvasive positive pressure ventilation (NPPV) in chronic respiratory failure; however, information on the chronic effects of NPPV is limited. We examined the acute and chronic effects of NPPV on gas exchange, functional status, and respiratory mechanics in patients with chronic respiratory failure related to restrictive ventilatory disorders or COPD. DESIGN: Descriptive analysis of prospectively collected clinical data. SETTING: Inpatient noninvasive respiratory care unit and outpatient clinic of university hospital. PATIENTS: Forty patients with chronic respiratory failure (20 with severe COPD and 20 with restrictive ventilatory disorders). INTERVENTIONS AND MEASUREMENTS: All patients were admitted to a noninvasive respiratory care unit for 20 +/- 3 days for inpatient evaluation consisting of medical treatment, rehabilitation, and NPPV evaluation and instruction. NPPV was titrated via a ventilatory support system (BiPAP; Respironics Inc; Monroeville, PA) or a portable volume ventilator (PLV 102; Lifecare, Inc; Boulder, CO) to achieve a > or = 20% increase in baseline minute ventilation while monitoring gas exchange, expired volume, and clinical evidence of a decrease in the patient's work of breathing. RESULTS: The patients' mean age (+/- SD) was 65 +/- 9.7 years, and there was a 3:1 female:male predominance. In the noninvasive respiratory care unit, 36 patients used NPPV for 7.31 +/- 0.26 h/night. Four patients (three with COPD, one with restrictive disorder) withdrew from the study during the 3-week inpatient stay because they could not tolerate NPPV. Six patients (5 with COPD, 1 with restrictive disorder) used a portable volume ventilator and 34 patients used BiPAP (15 with COPD, 19 with restrictive disorders). At discharge, compared with at admission, daytime PaO2/fraction of inspired oxygen (FIO2) increased (327 +/- 10 vs 283 +/- 13 mm Hg; p = 0.01), PaCO2 was reduced (52 +/- 2 vs 67 +/- 3 mm Hg; p = 0.0001), and functional score increased (4.76 +/- 1.16 vs 2.7 +/- 1.64 arbitrary units (AUs); p < 0.01). Six months after discharge, improvements in PaO2/FIO2 (317 +/- 10 vs 283 +/- 13; p = 0.05), PaCO2 (52 +/- 2 vs 67 +/- 3 mm Hg; p = 0.0001), and functional score (5.66 +/- 0.41 vs 2.7 +/- 0.3 AUs; p < 0.001) were maintained compared with admission values. FVC, FEV1, and maximum inspired and expired mouth pressures were unchanged before and after long-term NPPV. Ten patients (7 with COPD, 3 with restrictive disorders) discontinued NPPV at 6 months, and 3 progressed to tracheostomy. The remaining 26 patients continued to use NPPV at the 6-month follow-up. They claimed to use NPPV for 7.23 +/- 0.24 h/night, but logged metered use was 4.5 +/- 0.58 h/night. Problems that required adjustment in either the mask (36%) or ventilator source (36%) included mask leaks (43%), skin irritation (22%), rhinitis (13%), aerophagia (13%), and discomfort from mask headgear (7%). CONCLUSION: NPPV acutely and chronically improves gas exchange and functional status in patients with chronic respiratory failure, but a significant number of patients do not tolerate NPPV on a chronic basis. Comprehensive follow-up is required to correct problems with NPPV and ensure optimal patient compliance.

Activities of Daily Living↗
PubMed1999

Dose-response characteristics of nebulized albuterol in the treatment of acutely ill, hospitalized asthmatics.

We investigated the bronchodilator dose-response to nebulized albuterol and the dose of albuterol which produces maximal bronchodilation in the acutely ill, hospitalized asthmatic. Consecutively admitted patients from the emergency room in status asthmaticus who fulfilled the inclusion criteria (age <41 years old and <12 pack-years of smoking) were studied. Albuterol was administered by nebulizer (Puritan-Bennett Raindrop) in repeated 2.5-mg treatments up to a total dose of 10 mg and the bronchodilator response was measured by a computerized spirometer. Twenty-two patients were studied. Baseline spirometry showed a (mean +/- SE) forced expiratory volume in 1 sec (FEV1) of 1.26 +/- 0.14 L (42 +/- 4.0% predicted), which increased significantly (p < 0.05) during albuterol titration to a maximum FEV1 of 1.70 +/- 0.19 L (57 +/- 5% of predicted). After cumulative doses of 2.5, 5.0, 7.5, and 10.0 mg of nebulized albuterol, 27%, 45%, 72%, and 77% of patients, respectively, attained maximum bronchodilation. The remaining 23% of patients did not respond to doses up to 10 mg of albuterol. The maximum FEV1 response to albuterol did not correlate with the initial severity of airflow obstruction (r = 0.36, p > 0.05). Pulse rate and arterial oxygen saturation were not significantly affected by nebulized albuterol up to a total dose of 10 mg. No arrhythmias were noted. In summary, most hospitalized asthmatics (72%) required a cumulative dose of 7.5 mg of nebulized albuterol to achieve maximum bronchodilation and a large fraction (50%) required higher albuterol doses than the standard 2.5 mg. The bronchodilatory response to nebulized albuterol varied widely among patients in status asthmaticus and could not be predicted from the initial severity of airflow obstruction. Because side effects were minimal, it would be reasonable to use 7.5 mg of nebulized albuterol as initial therapy. Alternatively, dose-response titration with albuterol would be advantageous.

Acute Disease↗
PubMed1998

Breakdowns on the path of chronic illness: opportunities for learning.

An unusual case of calciphylaxis, presenting at the onset of end-stage renal disease and evolving into an extended and arduous hospital stay, is described. The medical approach to this case is addressed briefly, but the main focus of this paper is to describe, in the words of various participants, the events and interactions that occurred and to learn from this description how our management of such cases breaks down. When confronted by difficult circumstances, it is common for us to react emotionally in ways that are automatic and based on our own personal histories and behavior patterns. Such automatic reactions prevent us from seeing and understanding what we really need to know about a given situation and leave us vulnerable to discouragement and internal suffering when clinical events do not go well (A. Nierenberg, personal communication, April 1998). The result is often exasperation with patients and families, as well as emotionally laden interactions that do not forward problem solving. In retrospect, the appearance of such breakdowns is not only predictable in the course of chronic illness, but offers us the opportunity to observe our automatic reactions, to re-evaluate our approach, and to redesign our actions. We have written this review, not to find error or blame, but rather to emphasize that we are learning to view these breakdowns as signals first to step back from our automatic reactions and then to listen and communicate clearly as a means to navigating the best pathway through difficult and discouraging clinical challenges.

Calciphylaxis↗
PubMed1998

Cis-interactions between Delta and Notch modulate neurogenic signalling in Drosophila.

We find that ectopic expression of Delta or Serrate in neurons within developing bristle organs is capable of non-autonomously inducing the transformation of the pre-trichogen cell into a tormogen cell in a wide variety of developmental contexts. The frequencies at which Delta can induce these transformations are dependent on the level of ectopic Delta expression and the levels of endogenous Notch signalling pathway components. The pre-trichogen cell becomes more responsive to Delta- or Serrate-mediated transformation when the level of endogenous Delta is reduced and less responsive when the dosage of endogenous Delta is increased, supporting the hypothesis that Delta interferes autonomously with the ability of a cell to receive either signal. We also find that a dominant-negative form of Notch, ECN, is capable of autonomously interfering with the ability of a cell to generate the Delta signal. When the region of Notch that mediates trans-interactions between Delta and the Notch extracellular domain is removed from ECN, the ability of Delta to signal is restored. Our findings imply that cell-autonomous interactions between Delta and Notch can affect the ability of a cell to generate and to transduce a Delta-mediated signal. Finally, we present evidence that the Fringe protein can interfere with Delta- and Serrate-mediated signalling within developing bristle organs, in contrast to previous reports of the converse effects of Fringe on Delta signalling in the developing wing.

Animals↗
PubMed1997

An intrinsic dominant negative activity of serrate that is modulated during wing development in Drosophila.

The Serrate and Delta genes of Drosophila encode two transmembrane proteins that act as ligands for the Notch receptor. Both have been shown to promote Notch activity during wing development and the specification of cell fate during neurogenesis. This observation has led to the suggestion that Serrate and Delta are functionally equivalent ligands for Notch. In this study we compare the activities of these proteins during wing development. Our results show that Serrate can activate or inactivate Notch in a concentration-dependent manner. While the inactivation is likely to be mediated by a dominant negative effect over Notch, the activation is similar to that elicited by Delta and requires the product of the Suppressor of Hairless gene. These results indicate that regulation of the concentration of Serrate during development must be an important way of regulating its activity.

Animals↗
PubMed1997

Variations in the relative mRNA levels of actins and myosin heavy chains do not produce corresponding differences in their proteins in the adult human heart.

This paper examines the quantitative relationship between the expression of myosin heavy chain (MHC) and actin at both the levels of their mRNAs and their proteins. Explanted human left ventricle tissues were obtained from non-diseased (ND) individuals and from dilated cardiomyopathy (DCM) patients with terminally failing hearts who underwent heart transplantation. We found: (1) there are substantial differences in the stoichiometry of sarcomeric MHC and actin transcripts in hearts of DCM patients as well as in ND individuals; (2) there are substantial differences between levels of total sarcomeric actin transcripts from different individual patients; (3) by and large variations in transcript levels between samples from the same heart are much less than between samples from different hearts; and (4) the ratio of MHC to sarcomeric actin proteins expressed by different ND and DCM hearts remains essentially constant. We conclude that the human ventricle can accommodate a substantial imbalance between sarcomeric MHC and actin mRNA levels while maintaining a constant ratio of their corresponding proteins.

Actins↗