Light-dependent N-end rule-mediated disruption of protein function in Saccharomyces cerevisiae and Drosophila melanogaster

Here we describe the development and characterization of the photo-N-degron, a peptide tag that can be used in optogenetic studies of protein function in vivo. The photo-N-degron can be expressed as a genetic fusion to the amino termini of other proteins, where it undergoes a blue light-dependent conformational change that exposes a signal for the class of ubiquitin ligases, the N-recognins, which mediate the N-end rule mechanism of proteasomal degradation. We demonstrate that the photo-N-degron can be used to direct light-mediated degradation of proteins in Saccharomyces cerevisiae and Drosophila melanogaster with fine temporal control. In addition, we compare the effectiveness of the photo-N-degron with that of two other light-dependent degrons that have been developed in their abilities to mediate the loss of function of Cactus, a component of the dorsal-ventral patterning system in the Drosophila embryo. We find that like the photo-N-degron, the blue light-inducible degradation (B-LID) domain, a light-activated degron that must be placed at the carboxy terminus of targeted proteins, is also effective in eliciting light-dependent loss of Cactus function, as determined by embryonic dorsal-ventral patterning phenotypes. In contrast, another previously described photosensitive degron (psd), which also must be located at the carboxy terminus of associated proteins, has little effect on Cactus-dependent phenotypes in response to illumination of developing embryos. These and other observations indicate that care must be taken in the selection and application of light-dependent and other inducible degrons for use in studies of protein function in vivo, but importantly demonstrate that N- and C-terminal fusions to the photo-N-degron and the B-LID domain, respectively, support light-dependent degradation in vivo.

Much of what we know about biological processes has come from the analysis of mutants whose loss-of-function phenotypes provide insight into their normal functions. However, for genes that are required for viability and which have multiple functions in the life of a cell or organism one can only observe mutant phenotypes produced up to the time of death. Normal functions performed in wild-type individuals later than the time of death of mutants cannot be observed. In one approach to overcoming this limitation, a class of peptide degradation signals (degrons) have been developed, which when fused to proteins-of-interest, can target those proteins for degradation in response to various stimuli (temperature, chemical agents, co-expressed proteins, or light). Here we describe a new inducible degron (the photo-N-degron or PND), which when fused to the N-terminus of a protein, can induce N-end rule-mediated degradation in response to blue-light illumination and have validated its use in both yeast and Drosophila embryos. Moreover, using the Drosophila embryonic patterning protein Cactus, we show that like the PND, the previously-described B-LID domain, but not the previously-described photosensitive degron (psd), can produce detectable light-inducible phenotypes in Drosophila embryos that are consistent with the role of Cactus in dorsal-ventral patterning.

Isolation of secreted proteins from Drosophila ovaries and embryos through in vivo BirA-mediated biotinylation

The extraordinarily strong non-covalent interaction between biotin and avidin (kD = 10-14-10-16) has permitted this interaction to be used in a wide variety of experimental contexts. The Biotin Acceptor Peptide (BAP), a 15 amino acid motif that can be biotinylated by the E. coli BirA protein, has been fused to proteins-of-interest, making them substrates for in vivo biotinylation. Here we report on the construction and characterization of a modified BirA bearing signals for secretion and endoplasmic reticulum (ER) retention, for use in experimental contexts requiring biotinylation of secreted proteins. When expressed in the Drosophila female germline or ovarian follicle cells under Gal4-mediated transcriptional control, the modified BirA protein could be detected and shown to be enzymatically active in ovaries and progeny embryos. Surprisingly, however, it was not efficiently retained in the ER, and instead appeared to be secreted. To determine whether this secreted protein, now designated secBirA, could biotinylate secreted proteins, we generated BAP-tagged versions of two secreted Drosophila proteins, Torsolike (Tsl) and Gastrulation Defective (GD), which are normally expressed maternally and participate in embryonic pattern formation. Both Tsl-BAP and GD-BAP were shown to exhibit normal patterning activity. Co-expression of Tsl-BAP together with secBirA in ovarian follicle cells resulted in its biotinylation, which permitted its isolation from both ovaries and progeny embryos using Avidin-coupled affinity matrix. In contrast, co-expression with secBirA in the female germline did not result in detectable biotinylation of GD-BAP, possibly because the C-terminal location of the BAP tag made it inaccessible to BirA in vivo. Our results indicate that secBirA directs biotinylation of proteins bound for secretion in vivo, providing access to powerful experimental approaches for secreted proteins-of-interest. However, efficient biotinylation of target proteins may vary depending upon the location of the BAP tag or other structural features of the protein.

Reconstitution of Torso signaling in cultured cells suggests a role for both Trunk and Torso-like in receptor activation

Formation of the Drosophila embryonic termini is controlled by the localized activation of the receptor tyrosine kinase Torso. Both Torso and Torso's presumed ligand, Trunk, are expressed uniformly in the early embryo. Polar activation of Torso requires Torso-like, which is expressed by follicle cells adjacent to the ends of the developing oocyte. We find that Torso expressed at high levels in cultured Drosophila cells is activated by individual application of Trunk, Torso-like or another known Torso ligand, Prothoracicotropic Hormone. In addition to assays of downstream signaling activity, Torso dimerization was detected using bimolecular fluorescence complementation. Trunk and Torso-like were active when co-transfected with Torso and when presented to Torso-expressing cells in conditioned medium. Trunk and Torso-like were also taken up from conditioned medium specifically by cells expressing Torso. At low levels of Torso, similar to those present in the embryo, Trunk and Torso-like alone were ineffective but acted synergistically to stimulate Torso signaling. Our results suggest that Torso interacts with both Trunk and Torso-like, which cooperate to mediate dimerization and activation of Torso at the ends of the Drosophila embryo.

Maternal control of the Drosophila dorsal-ventral body axis

The pathway that generates the dorsal-ventral (DV) axis of the Drosophila embryo has been the subject of intense investigation over the previous three decades. The initial asymmetric signal originates during oogenesis by the movement of the oocyte nucleus to an anterior corner of the oocyte, which establishes DV polarity within the follicle through signaling between Gurken, the Drosophila Transforming Growth Factor (TGF)-α homologue secreted from the oocyte, and the Drosophila Epidermal Growth Factor Receptor (EGFR) that is expressed by the follicular epithelium cells that envelop the oocyte. Follicle cells that are not exposed to Gurken follow a ventral fate and express Pipe, a sulfotransferase that enzymatically modifies components of the inner vitelline membrane layer of the eggshell, thereby transferring DV spatial information from the follicle to the egg. These ventrally sulfated eggshell proteins comprise a localized cue that directs the ventrally restricted formation of the active Spätzle ligand within the perivitelline space between the eggshell and the embryonic membrane. Spätzle activates Toll, a transmembrane receptor in the embryonic membrane. Transmission of the Toll signal into the embryo leads to the formation of a ventral-to-dorsal gradient of the transcription factor Dorsal within the nuclei of the syncytial blastoderm stage embryo. Dorsal controls the spatially specific expression of a large constellation of zygotic target genes, the Dorsal gene regulatory network, along the embryonic DV circumference. This article reviews classic studies and integrates them with the details of more recent work that has advanced our understanding of the complex pathway that establishes Drosophila embryo DV polarity. For further resources related to this article, please visit the WIREs website.

CONFLICT OF INTEREST

The authors have declared no conflicts of interest for this article.

The CREATE Strategy for Intensive Analysis of Primary Literature Can Be Used Effectively by Newly Trained Faculty to Produce Multiple Gains in Diverse Students

The CREATE (Consider Read, Elucidate the hypotheses, Analyze and interpret the data, and Think of the next Experiment) strategy aims to demystify scientific research and scientists while building critical thinking, reading/analytical skills, and improved science attitudes through intensive analysis of primary literature. CREATE was developed and piloted at the City College of New York (CCNY), a 4-yr, minority-serving institution, with both upper-level biology majors and first-year students interested in science, technology, engineering, and mathematics. To test the extent to which CREATE strategies are broadly applicable to students at private, public, research-intensive, and/or primarily undergraduate colleges/universities, we trained a cohort of faculty from the New York/New Jersey/Pennsylvania area in CREATE pedagogies, then followed a subset, the CREATE implementers (CIs), as they taught all or part of an existing course on their home campuses using CREATE approaches. Evaluation of the workshops, the CIs, and their students was carried out both by the principal investigators and by an outside evaluator working independently. Our data indicate that: intensive workshops change aspects of faculty attitudes about teaching/learning; workshop-trained faculty can effectively design and teach CREATE courses; and students taught by such faculty on multiple campuses make significant cognitive and affective gains that parallel the changes documented previously at CCNY.

Localized serine protease activity and the establishment of Drosophila embryonic dorsoventral polarity

Drosophila embryo dorsoventral polarity is established by a maternally encoded signal transduction pathway in which three sequentially acting serine proteases, Gastrulation Defective, Snake and Easter, generate the ligand that activates the Toll receptor on the ventral side of the embryo. The spatial regulation of this pathway depends upon ventrally restricted expression of the Pipe sulfotransferase in the ovarian follicle during egg formation. Several recent observations have advanced our understanding of the mechanism regulating the spatially restricted activation of Toll. First, several protein components of the vitelline membrane layer of the eggshell have been determined to be targets of Pipe-mediated sulfation. Second, the processing of Easter by Snake has been identified as the first Pipe-dependent, ventrally-restricted processing event in the pathway. Finally, Gastrulation Defective has been shown to undergo Pipe-dependent, ventral localization within the perivitelline space and to facilitate Snake-mediated processing of Easter. Together, these observations suggest that Gastrulation Defective, localized on the interior ventral surface of the eggshell in association with Pipe-sulfated eggshell proteins, recruits and mediates an interaction between Snake and Easter. This event leads to ventrally-restricted processing and activation of Easter and consequently, localized formation of the Toll ligand, and Toll activation.

A ventrally localized protease in the Drosophila egg controls embryo dorsoventral polarity

Drosophila embryo dorsoventral (DV) polarity is defined by serine protease activity in the perivitelline space (PVS) between the embryonic membrane and the inner layer of the eggshell. Gastrulation Defective (GD) cleaves and activates Snake (Snk). Activated Snk cleaves and activates Easter (Ea), exclusively on the ventral side of the embryo. Activated Ea then processes Spätzle (Spz) into the activating ligand for Toll, a transmembrane receptor that is distributed throughout the embryonic plasma membrane. Ventral activation of Toll depends upon the activity of the Pipe sulfotransferase in the ventral region of the follicular epithelium that surrounds the developing oocyte. Pipe transfers sulfate residues to several protein components of the inner vitelline membrane layer of the eggshell. Here we show that GD protein becomes localized in the ventral PVS in a Pipe-dependent process. Moreover, ventrally concentrated GD acts to promote the cleavage of Ea by Snk through an extracatalytic mechanism that is distinct from GD's proteolytic activation of Snk. Together, these observations illuminate the mechanism through which spatially restricted sulfotransferase activity in the developing egg chamber leads to localization of serine protease activity and ultimately to spatially specific activation of the Toll receptor in the Drosophila embryo.

The microRNA pathway regulates the temporal pattern of Notch signaling in Drosophila follicle cells

Multicellular development requires the correct spatial and temporal regulation of cell division and differentiation. These processes are frequently coordinated by the activities of various signaling pathways such as Notch signaling. From a screen for modifiers of Notch signaling in Drosophila we have identified the RNA helicase Belle, a recently described component of the RNA interference pathway, as an important regulator of the timing of Notch activity in follicle cells. We found that loss of Belle delays activation of Notch signaling, which results in delayed follicle cell differentiation and defects in the cell cycle. Because mutations in well-characterized microRNA components phenocopied the Notch defects observed in belle mutants, Belle might be functioning in the microRNA pathway in follicle cells. The effect of loss of microRNAs on Notch signaling occurs upstream of Notch cleavage, as expression of the constitutively active intracellular domain of Notch in microRNA-defective cells restored proper activation of Notch. Furthermore, we present evidence that the Notch ligand Delta is an important target of microRNA regulation in follicle cells and regulates the timing of Notch activation through cis inhibition of Notch. Here we have uncovered a complex regulatory process in which the microRNA pathway promotes Notch activation by repressing Delta-mediated inhibition of Notch in follicle cells.

The C.R.E.A.T.E. approach to primary literature shifts undergraduates' self-assessed ability to read and analyze journal articles, attitudes about science, and epistemological beliefs

The C.R.E.A.T.E. (Consider, Read, Elucidate hypotheses, Analyze and interpret data, Think of the next Experiment) method uses intensive analysis of primary literature in the undergraduate classroom to demystify and humanize science. We have reported previously that the method improves students' critical thinking and content integration abilities, while at the same time enhancing their self-reported understanding of "who does science, and why." We report here the results of an assessment that addressed C.R.E.A.T.E. students' attitudes about the nature of science, beliefs about learning, and confidence in their ability to read, analyze, and explain research articles. Using a Likert-style survey administered pre- and postcourse, we found significant changes in students' confidence in their ability to read and analyze primary literature, self-assessed understanding of the nature of science, and epistemological beliefs (e.g., their sense of whether knowledge is certain and scientific talent innate). Thus, within a single semester, the inexpensive C.R.E.A.T.E. method can shift not just students' analytical abilities and understanding of scientists as people, but can also positively affect students' confidence with analysis of primary literature, their insight into the processes of science, and their beliefs about learning.

No requirement for localized Nudel protein expression in Drosophila embryonic axis determination

Drosophila embryonic dorsal-ventral polarity is defined by a maternally encoded signal transduction pathway. Gastrulation Defective, Snake, and Easter comprise a serine protease cascade that operates in the perivitelline space to generate active ligand for the Toll receptor, which resides in the embryonic membrane. Toll is activated only on the ventral side of the embryo. Spatial regulation of this pathway is initiated by the ventrally restricted expression of the sulfotransferase Pipe in the follicular epithelium that surrounds the developing oocyte. Pipe is thought to modify a target molecule that is secreted and localized within the ventral region of the egg and future embryo, where it influences the activity of the pathway such that active Toll ligand is produced only ventrally. A potential substrate for Pipe is encoded by nudel, which is expressed throughout the follicle cell layer and encodes a large, multi-functional secreted protein that contains a serine protease domain as well as other structural features characteristic of extracellular matrix proteins. A previous mosaic analysis suggested that the protease domain of Nudel is not a target for Pipe activity as its expression is not required in pipe-expressing cells, but failed to rule out such a role for other functional domains of the protein. To investigate this possibility, we carried out a mosaic analysis of additional nudel alleles, including some that affect the entire protein. Our analysis demonstrated that proteolytically processed segments of Nudel are secreted into the perivitelline space and stably localized, as would be expected for the target of Pipe, However, we found no requirement for nudel to be expressed in ventral, pipe-expressing follicle cells, thereby eliminating Nudel as an essential substrate of Pipe sulfotransferase activity.

Pipe-dependent ventral processing of Easter by Snake is the defining step in Drosophila embryo DV axis formation

The establishment of Drosophila embryonic dorsal-ventral (DV) polarity relies on serine proteolytic activity in the perivitelline space between the embryonic membrane and the eggshell. Gastrulation Defective cleaves and activates Snake, which processes and activates Easter, which cleaves Spätzle to form the activating ligand for the Toll receptor. Ventral restriction of ligand formation depends on the Pipe sulfotransferase, which is expressed in ventral cells of the follicular epithelium surrounding the developing oocyte. Pipe modifies components of the developing eggshell to produce a ventral cue embedded in the vitelline membrane. This ventral cue is believed to promote one or more of the proteolysis steps in the perivitelline space. By examining the processing of transgenic, tagged versions of the perivitelline proteins during DV patterning, we find that the proteolysis of Easter by Snake is the first Pipe-dependent step and therefore the key ventrally restricted event in the protease cascade. We also find that Snake and Easter associate together in a complex in both wild-type and pipe mutant-derived embryos. This observation suggests a mechanism in which the sulfated target of Pipe promotes a productive interaction between Snake and Easter, perhaps by facilitating conformational changes in a complex containing the two proteins.

Distinct functional specificities are associated with protein isoforms encoded by the Drosophila dorsal-ventral patterning gene pipe

Spatially regulated transcription of the pipe gene in ventral cells of the Drosophila ovary follicle cell epithelium is a key event that specifies progeny embryo dorsal-ventral (DV) polarity. pipe encodes ten putative protein isoforms, all of which exhibit similarity to vertebrate glycosaminoglycan-modifying enzymes. Expression of one of the isoforms, Pipe-ST2, in follicle cells has previously been shown to be essential for DV patterning. pipe is also expressed in the embryonic salivary gland and its expression there is required for normal viability. Here, we show that in addition to Pipe-ST2, seven of the other Pipe isoforms are expressed in the ovary, whereas all Pipe isoforms are abundantly expressed in the embryo. Of the ten isoforms, only Pipe-ST2 can restore ventral and lateral pattern elements to the progeny of otherwise pipe-null mutant females. By contrast, three Pipe isoforms, but not Pipe-ST2, support the production of a novel pipe-dependent epitope present in the embryonic salivary gland. These data indicate that differences in functional specificity, and presumably enzymatic specificity, are associated with several of the Pipe isoforms. In addition, we show that uniform expression of the Pipe-ST2 isoform in the follicle cell layer of females otherwise lacking pipe expression leads to the formation of embryos with a DV axis that is appropriately oriented with respect to the intrinsic polarity of the eggshell. This suggests the existence of a second mechanism that polarizes the Drosophila embryo, in addition to the ventrally restricted transcription of the pipe gene.

Sulfation of eggshell components by Pipe defines dorsal-ventral polarity in the Drosophila embryo

Drosophila embryonic dorsal-ventral (DV) polarity is controlled by a group of sequentially acting serine proteases located in the fluid-filled perivitelline space between the embryonic membrane and the eggshell, which generate the ligand for the Toll receptor on the ventral side of the embryo. Spatial control of the protease cascade relies on the Pipe sulfotransferase, a fly homolog of vertebrate glycosaminoglycan-modifying enzymes, which is expressed in ventral cells of the follicular epithelium surrounding the developing oocyte. Here we show that the vitelline membrane-like (VML) protein undergoes Pipe-dependent sulfation and, consistent with a role in conveying positional information from the egg chamber to the embryo, becomes incorporated into the eggshell at a position corresponding to the location of the follicle cells from which it was secreted. Although VML influences embryonic DV pattern in a sensitized genetic background, VML is not essential for DV axis formation, suggesting that there is redundancy in the composition of the Pipe enzymatic target. Correspondingly, we find that additional structural components of the vitelline membrane undergo Pipe-dependent sulfation. In identifying the elusive targets of Pipe, this work points to the vitelline membrane as the source of signals that generate the Drosophila DV axis.

Learning our L.I.M.I.T.S.: less is more in teaching science

The rapid and accelerating pace of change in physiology and cell biology, along with the easy access to huge amounts of content, have altered the playing field for science students, yet most students are still mainly taught from textbooks. Of necessity, textbooks are usually broad in scope, cover topics much more superficially than do journal articles, and present the scientific process as a linear string of successful experiments, largely ignoring the reality of rejected hypotheses, unanticipated discoveries, or surprising findings that may shift paradigms. We suggest that a more narrow focus on scientific thinking, using a new method for reading a series of journal articles that track the evolution of a single project over a period of years, can more realistically convey the excitement and challenges of research science and perhaps stimulate some students to consider research careers for themselves. Our approach, termed "CREATE" (for Consider, Read, Elucidate hypotheses, Analyze data, and Think of the next Experiment), has proven successful at both demystifying the scientific literature and humanizing science/scientists in undergraduate biology courses (8), and we suggest that it could be profitably expanded to physiology courses.

Selective use of the primary literature transforms the classroom into a virtual laboratory

CREATE (consider, read, elucidate hypotheses, analyze and interpret the data, and think of the next experiment) is a new method for teaching science and the nature of science through primary literature. CREATE uses a unique combination of novel pedagogical tools to guide undergraduates through analysis of journal articles, highlighting the evolution of scientific ideas by focusing on a module of four articles from the same laboratory. Students become fluent in the universal language of data analysis as they decipher the figures, interpret the findings, and propose and defend further experiments to test their own hypotheses about the system under study. At the end of the course students gain insight into the individual experiences of article authors by reading authors' responses to an e-mail questionnaire generated by CREATE students. Assessment data indicate that CREATE students gain in ability to read and critically analyze scientific data, as well as in their understanding of, and interest in, research and researchers. The CREATE approach demystifies the process of reading a scientific article and at the same time humanizes scientists. The positive response of students to this method suggests that it could make a significant contribution to retaining undergraduates as science majors.

Synthesis of the sulfate donor PAPS in either the Drosophila germline or somatic follicle cells can support embryonic dorsal-ventral axis formation

The establishment of dorsal-ventral (DV) polarity in the Drosophila embryo depends upon a localized signal that is generated in the perivitelline space of the egg through the action of a serine proteolytic cascade. Spatial regulation of this pathway is determined by the expression of the pipe gene in a subpopulation of ventral follicle cells in the developing egg chamber. The Pipe protein exhibits homology to vertebrate glycosaminoglycan sulfotransferases. In a previous study, we demonstrated that embryonic DV polarity depends upon the sulfotransferase activity of Pipe. Surprisingly, however, our results also indicated that formation of the embryonic DV axis does not require the synthesis of the high-energy sulfate donor, 3'-phosphoadenosine 5'-phosphosulfate (PAPS) in the follicle cells in which Pipe is presumed to function. Here, we resolve this apparent paradox by demonstrating that dorsalized embryos are only produced by egg chambers in which both germline and follicle cells lack PAPS synthetase activity. Thus, PAPS produced either in the germline or in the follicular epithelium can support the requirement for Pipe sulfotransferase activity in embryonic DV patterning. This finding indicates the existence of a conduit for the movement of PAPS between the germline and the follicle cells, which highlights a previously unappreciated mechanism of soma/germline cooperation affecting pattern formation.

Cyclosporine-induced coronary endothelial dysfunction: is tetrahydrobiopterin the solution?

BACKGROUND

Coronary endothelial dysfunction after heart transplantation is predictive of cardiac allograft vasculopathy. Immunosuppressive drugs, particularly cyclosporine may contribute to this dysfunction by a direct effect. Tetrahydrobiopterin (BH(4)) is a potent antioxidant and an essential cofactor of nitric oxide biosynthesis. The purpose of this study was to investigate whether BH(4) could reverse the endothelial dysfunction induced by cyclosporine.

METHODS

A previously described in vitro model of drug incubation in Krebs-bicarbonate solution (4 degrees C, 48 hours) of porcine epicardial coronary arteries was used. Coronary endothelial function studies were performed in organ chamber experiments after incubation with cyclosporine (10(-4) mol/L) in the presence or absence of 6-methyltetrahydropterin (MH(4) [0.1 mol/L], a BH(4) analog) to assess its effect on the cyclosporine-induced endothelial dysfunction.

RESULTS

The average doses of PGF2(alpha) required to attain 50% of the maximal contraction to KCl was significantly lower (P < .001) in the cyclosporine group (8.6 +/- 1.94 x 10(-6) mol/L) compared to the control group (24.8 +/- 5.2 x 10(-6) mol/L). Exposure to cyclosporine induced a significant decrease in endothelium-dependent relaxations to serotonin (5HT) (% E(max) [5HT]: 77% +/- 4%; P < .05). Addition of MH(4) significantly reversed this impaired response (% E(max) [5HT]: 62% +/- 4%; P < .05). No alterations of relaxation were observed with bradykinin in both groups. Endothelium-independent relaxations to sodium nitroprussiate were fully preserved.

CONCLUSIONS

These results suggest a significant protective role of BH(4) on coronary endothelial function following exposure to cyclosporine, which could reduce the incidence of endothelial dysfunction and cardiac allograft vasculopathy following cardiac transplantation.

Influence of diabetes and bilateral internal thoracic artery grafts on long-term outcome for multivessel coronary artery bypass grafting☆

OBJECTIVE

Diabetes mellitus is a major independent risk factor for morbidity and mortality after coronary artery bypass grafting (CABG). The aim of this study was to assess the effect of bilateral (B) internal thoracic artery grafting (ITA) in diabetic patients with multivessel CABG.

METHODS

Between 1985 and 1995, 4382 patients underwent primary isolated multivessel CABG with ITA grafting and concomitant saphenous vein grafting (SVG). Outcome of diabetic and nondiabetic patients undergoing single (S) ITA+SVG (n=419 and 2079) and BITA+SVG (n=214 and 1594) grafting was obtained at a mean follow-up of 11+/-3 years.

RESULTS

Diabetic patients were older, included more women, and had more obesity, hypertension and peripheral vascular disease than nondiabetic patients. Deep sternal wound infection rate was 1.9% for diabetic patients vs 1.2% for nondiabetic patients (P=0.2) and 30-day mortality was 1.7 vs 1.8% (P=0.9). Cox regression analysis with interaction term and propensity scoring showed that BITA grafting decreased the risk of death (Hazard Ratio=0.72 [0.57-0.91, 95%CI]) and coronary reoperation (HR=0.38 [0.19-0.77]) in both diabetic and nondiabetic patients, with no significant interaction noted. BITA grafting decreased the risk of myocardial infarction at long-term follow-up in nondiabetic patients (HR=0.72 [0.60-0.86]) but not in diabetic patients. Ten-year freedom rate from myocardial infarction in diabetic patients was 80 and 76% for SITA and BITA grafting patients, respectively. However, survival following myocardial infarction was better for patients who underwent BITA grafting, in both diabetic and nondiabetic subgroups.

CONCLUSIONS

BITA+SVG grafting in diabetic patients improves survival and decrease coronary reoperation compared with SITA+SVG at long-term follow-up. Survival following myocardial infarction is improved with BITA grafting.

Single versus bilateral internal thoracic artery grafts with concomitant saphenous vein grafts for multivessel coronary artery bypass grafting: effects on mortality and event-free survival

BACKGROUND

The issue of superiority of single internal thoracic artery grafting versus bilateral internal thoracic artery grafting remains unresolved. The aim of this study was to compare the long-term outcome of single and bilateral internal thoracic artery grafting with concomitant saphenous vein grafting for multivessel coronary artery bypass grafting.

METHODS

Between March 1985 and April 1995, 6650 patients underwent primary isolated coronary artery bypass grafting with internal thoracic artery grafts, including 4382 patients with multivessel bypass grafting requiring at least 3 grafts. Outcomes of patients undergoing single internal thoracic artery plus saphenous vein grafting (n = 2547) and bilateral internal thoracic artery plus saphenous vein grafting (n = 1835) were obtained at a mean follow-up of 11 +/- 3 years.

RESULTS

Patients with bilateral internal thoracic artery grafting were younger, were mostly male, and had less diabetes, hypertension, unstable angina, and recent myocardial infarction than patients undergoing single internal thoracic artery grafting. Thirty-day mortality was 2.3% for the group undergoing single internal thoracic artery grafting versus 1.2% for those undergoing bilateral internal thoracic artery grafting (P =.007). Survival probability at 10 years was 88% for the single-graft group compared with 93% for the bilateral-graft group (P <.001). Multivariate analysis with propensity scoring showed that bilateral internal thoracic artery grafting decreased the risk of death (hazard ratio, 0.74; 95% confidence interval, 0.60-0.90), myocardial infarction (hazard ratio, 0.79; 95% confidence interval, 0.67-0.93), and coronary reoperation (hazard ratio, 0.41; 95% confidence interval, 0.21-0.80) throughout the follow-up period. Other significant predictors of death were diabetes, prior myocardial infarction, need for intra-aortic balloon pump, chronic heart failure, and peripheral vascular disease.

CONCLUSION

Patients undergoing bilateral internal thoracic plus saphenous vein grafting appear to have a significantly better long-term clinical outcome than patients undergoing single internal thoracic artery plus saphenous vein grafting for multivessel coronary artery bypass grafting.

A prospective randomized study of diluted versus non-diluted cardioplegia (minicardioplegia) in primary coronary artery bypass surgery

AIM

Sanguineous (blood) cardioplegia has been established as the prime option for myocardial protection but the choice of dilution (4:1 blood to crystalloid ratio) versus use of blood from the cardiopulmonary bypass alone (minicardioplegia) remains controversial. The purpose of this prospective randomized clinical trial was to compare the clinical outcome and enzymatic endpoints (troponin I, CK-MB isoenzyme release) in patients undergoing primary CABG surgery.

METHODS

From June 1999 to October 2000, 59 patients were randomized preoperatively to undergo coronary artery bypass grafting surgery using cardiopulmonary bypass and either diluted (4:1 blood to crystalloid ratio; n=25) or undiluted sanguineous cardioplegia (minicardioplegia; n=4) at the Montreal Heart Institute. Clinical data and biochemical markers of ischemia were recorded. Tepid cardioplegia and moderate hypothermic cardiopulmonary bypass were used in 92% of patients.

RESULTS

There were no significant differences in preoperative variables between the 2 groups. There were no statistically significant differences in low output syndrome, stroke rate, arrhythmia or hospital length of stay between both groups. There was no statistically significant difference between minicardioplegia and diluted groups in the release of troponin T 24 hours postoperatively (0.36+/-0.31 versus 0.23+/-0.22, respectively). There was a slightly higher release of troponin T in the minicardioplegia group 48 hours after surgery (0.38+/-0.35 versus 0.20+/-0.16) (p=0.03) and of CK-MB 24 hours postoperatively (22.9+/-18.6 versus 10.2+/-5.3) (p<0.01).

CONCLUSION

Clinical outcomes are similar in patients undergoing primary CABG surgery with tepid cardioplegia and moderate hypothermic bypass with diluted or minicardioplegia. Minicardioplegia may be the optimal method of myocardial protection because of low cost, ease of use and lack of hemodilutive effect.

Drosophila dMyc is required for ovary cell growth and endoreplication

Although the Myc oncogene has long been known to play a role in many human cancers, the mechanisms that mediate its effects in both normal cells and cancer cells are not fully understood. We have initiated a genetic analysis of the Drosophila homolog of the Myc oncoprotein (dMyc),which is encoded by the dm locus. We carried out mosaic analysis to elucidate the functions of dMyc in the germline and somatic cells of the ovary during oogenesis, a process that involves cell proliferation, differentiation and growth. Germline and somatic follicle cells mutant for dm exhibit a profound decrease in their ability to grow and to carry out endoreplication,a modified cell cycle in which DNA replication occurs in the absence of cell division. In contrast to its dramatic effects on growth and endoreplication,dMyc is dispensable for the mitotic division cycles of both germline and somatic components of the ovary. Surprisingly, despite their impaired ability to endoreplicate, dm mutant follicle cells appeared to carry out chorion gene amplification normally. Furthermore, in germline cysts in which the dm mutant cells comprised only a subset of the 16-cell cluster,we observed strictly cell-autonomous growth defects. However, in cases in which the entire germline cyst or the whole follicular epithelium was mutant for dm, the growth of the entire follicle, including the wild-type cells, was delayed. This observation indicates the existence of a signaling mechanism that acts to coordinate the growth rates of the germline and somatic components of the follicle. In summary, dMyc plays an essential role in promoting the rapid growth that must occur in both the germline and the surrounding follicle cells for oogenesis to proceed.

The Drosophila embryonic patterning determinant torsolike is a component of the eggshell

The development of the head and tail regions of the Drosophila embryo is dependent upon the localized polar activation of Torso (Tor), a receptor tyrosine kinase that is uniformly distributed in the membrane of the developing embryo. Trunk (Trk), the proposed ligand for Tor, is secreted as an inactive precursor into the perivitelline fluid that lies between the embryonic membrane and the vitelline membrane (VM), the inner layer of the eggshell. The spatial regulation of Trk processing is thought to be mediated by the secreted product of the torsolike (tsl) gene, which is expressed during oogenesis by a specialized population of follicle cells present at the two ends of the oocyte. We show here that Tsl protein is specifically localized to the polar regions of the VM in laid eggs. We further demonstrate that although Tsl can associate with nonpolar regions of the VM, the activity of polar-localized Tsl is enhanced, suggesting the existence of another spatially restricted factor acting in this pathway. The incorporation of Tsl into the VM provides a mechanism for the transfer of spatial information from the follicle cells to the developing embryo. To our knowledge, Tsl represents the first example of an embryonic patterning determinant that is a component of the eggshell.

The torso ligand, unmasked?

When a transmembrane receptor protein tyrosine kinase (RTK) is expressed throughout the plasma membrane, yet only a specific handful of them must be activated, what's a ligand to do? During the development of the anterior and posterior termini of the Drosophila embryo, uniformly secreted ligand precursors are activated by proteolysis near the location of the receptors that must be activated. Stein and Stevens discuss the recent publication by Casali and Casanova that describes the mechanism of activation of the Drosophila RTK called Torso. In addition, Casali and Casanova may have identified a physiologically relevant ligand for Torso called Trunk. Proteolytic cleavage of the Trunk precursor can activate Torso-dependent signaling, but the existence of cleaved Trunk has not yet been demonstrated in vivo for Drosophila. Stein and Stevens discuss the ramifications of such a highly regulated process of ligand activation, and also prefer alternative scenarios for Torso activation.

Investigating the function of follicular subpopulations during Drosophila oogenesis through hormone-dependent enhancer-targeted cell ablation

Although it is known that the establishment of polarity during Drosophila oogenesis is initiated by signalling from the oocyte to the overlying follicle cells, much less is understood about the role of specific follicular subpopulations. One powerful approach for addressing this question, toxigenic cell ablation of specific subpopulations, has not previously been applicable to studying follicular subpopulations because many of the genes and Gal4 enhancer trap insertions that are expressed in the ovary are also expressed at earlier times in development. To overcome this problem, we have utilized a fusion protein between Gal4 and the human estrogen receptor to achieve hormone-dependent, tissue-specific gene expression of UAS-linked transgenes in flies. We used this system to study the role of the polar subpopulations of follicle cells during oogenesis by expressing within them a modified form of diphtheria toxin that causes cell death. Our results confirmed previous functions ascribed to these cells, and also demonstrated a previously undescribed role for the border cells in facilitating the migration of the anterior Fasciclin III-expressing polar pair cells to the edge of the oocyte.

Chromosomal and extrachromosomal instability of the cyclin D2 gene is induced by Myc overexpression

We examined the expression of cyclins D1, D2, D3, and E in mouse B-lymphocytic tumors. Cyclin D2 mRNA was consistently elevated in plasmacytomas, which characteristically contain Myc-activating chromosome translocations and constitutive c-Myc mRNA and protein expression. We examined the nature of cyclin D2 overexpression in plasmacytomas and other tumors. Human and mouse tumor cell lines that exhibited c-Myc dysregulation displayed instability of the cyclin D2 gene, detected by Southern blot, fluorescent in situ hybridization (FISH), and in extrachromosomal preparations (Hirt extracts). Cyclin D2 instability was not seen in cells with low levels of c-Myc protein. To unequivocally demonstrate a role of c-Myc in the instability of the cyclin D2 gene, a Myc-estrogen receptor chimera was activated in two mouse cell lines. After 3 to 4 days of Myc-ER activation, instability at the cyclin D2 locus was seen in the form of extrachromosomal elements, determined by FISH of metaphase and interphase nuclei and of purified extrachromosomal elements. At the same time points, Northern and Western blot analyses detected increased cyclin D2 mRNA and protein levels. These data suggest that Myc-induced genomic instability may contribute to neoplasia by increasing the levels of a cell cycle-regulating protein, cyclin D2, via intrachromosomal amplification of its gene or generation of extrachromosomal copies.

Establishment of dorsal-ventral and terminal pattern in the Drosophila embryo

Dorsal-ventral and terminal pattern formation in the Drosophila embryo is mediated via inductive signals originating during oogenesis from the somatic follicle cells that ensheath the developing oocyte. This somatically expressed spatial information controls dorsal-ventral development by defining the polarity of a signal transduction pathway that results in the graded nuclear concentration of the dorsal gene product, a transcription factor.

Localized requirement for torso-like expression in follicle cells for development of terminal anlagen of the Drosophila embryo

The torso (tor) gene, one of six identified maternal genes essential for the development of the anterior and posterior terminal structures in the Drosophila embryo, is likely to function as a transmembrane receptor tyrosine kinase. Although tor protein is uniformly distributed in the membrane of the egg cell and syncytial embryo, genetic and molecular data suggest that tor is locally activated at the ends of the embryo by a ligand present in the perivitelline space. Local activation of tor could be achieved if the ligand were expressed by a subpopulation of the follicle cells that surround the developing oocyte. Here we describe torso-like (tsl), the sixth member of the terminal gene class, and show that it is unique among these genes in that its expression is required in the somatic follicle cells rather than in the germ line. Moreover, mosaic analysis demonstrates that tsl expression is necessary only in subpopulations of follicle cells located at the poles of the oocyte. Thus, the spatially regulated expression of tsl in the follicle cell layer may generate a localized signal that is transduced by tor, ultimately resulting in the formation of the terminal structures of the embryo.

Target influences on transmitter choice by sympathetic neurons developing in the anterior chamber of the eye

In contrast to the majority of sympathetic neurons which are noradrenergic, the sympathetic neurons which innervate sweat glands are cholinergic. Previous studies have demonstrated that during development the sweat gland innervation initially contains catecholamines which are lost as cholinergic function appears. The neurotransmitter phenotype of sweat gland neurons further differs from the majority in that they contain vasoactive intestinal peptide (VIP) rather than neuropeptide Y (NPY). In the experiments described here, we addressed the question of whether sympathetic targets influence the neurotransmitter-related properties of the neurons which innervate them; in particular, do sweat glands play a role in reducing the expression of noradrenergic properties and inducing the expression of cholinergic properties and VIP in sympathetic neurons? This was accomplished by cotransplanting to the anterior chamber of the eye of host rats the superior cervical ganglia (SCG) which contains neurons that normally innervate targets other than the sweat glands and differentiate noradrenergically and footpad tissue from neonatal rats. Sweat glands developed in the transplanted footpad tissue and became innervated by the cotransplanted SCG neurons. The transplanted neurons and sweat gland innervation initially exhibited catecholamine histofluorescence which declined with further development in the anterior chamber. After 4 weeks, choline acetyltransferase (ChAT) and VIP immunoreactivities were evident. These observations suggest that as in the neurons which innervate the glands in situ, noradrenergic properties were suppressed and cholinergic function was induced in the neurons which innervated the glands in oculo. To distinguish a specific influence of the sweat glands on transmitter choice, SCG were also cotransplanted with the pineal gland, a normal target of the ganglion. Neurons cotransplanted with the pineal gland continued to exhibit catecholamine histofluorescence and contained NPY immunoreactivity. At least some neurons in SCG/pineal cotransplants, however, developed ChAT immunoreactivity. The target-appropriate expression of catecholamines and peptides in these experiments is consistent with the hypothesis that some transmitter properties are influenced by target tissues. The indiscriminant expression of ChAT, however, suggests that at least in oculo, additional factors can influence transmitter choice.

The Drosophila gene torso encodes a putative receptor tyrosine kinase

The maternal gene torso, required for determination of anterior and posterior terminal structures in the Drosophila embryo, was cloned using P-element tagging. Genetic evidence suggests that the action of the gene product is spatially restricted to the terminal regions; the torso messenger RNA, however, is evenly distributed. Structural similarities of the predicted torso protein with growth-factor receptor tyrosine kinases suggest that the spatial restriction of torso activity results from a localized activation of the torso protein at the anterior and posterior egg pole.

Developmental interactions between sweat glands and the sympathetic neurons which innervate them: effects of delayed innervation on neurotransmitter plasticity and gland maturation

The neurotransmitter properties of the sympathetic innervation of sweat glands in rat footpads have previously been shown to undergo a striking change during development. When axons first reach the developing glands, they contain catecholamine histofluorescence and immunoreactivity for catecholamine synthetic enzymes. As the glands and their innervation mature, catecholamines disappear and cholinergic and peptidergic properties appear. Final maturation of the sweat glands, assayed by secretory competence, is correlated temporally with the development of cholinergic function in the innervation. To determine if the neurotransmitter phenotype of sympathetic neurons developing in vivo is plastic, if sympathetic targets can play a role in determining neurotransmitter properties of the neurons which innervate them, and if gland maturation is dependent upon its innervation, the normal developmental interaction between sweat glands and their innervation was disrupted. This was accomplished by a single injection of 6-hydroxy-dopamine (6-OHDA) on Postnatal Day 2. Following this treatment, the arrival of noradrenergic sympathetic axons at the developing glands was delayed 7 to 10 days. Like the gland innervation of normal rats, the axons which innervated the sweat glands of 6-OHDA-treated animals acquired cholinergic function and their expression of endogenous catecholamines declined. The change in neurotransmitter properties, however, occurred later in development than in untreated animals and was not always complete. Even in adult animals, some fibers continued to express endogenous catecholamines and many nerve terminals contained a small proportion of small granular vesicles after permanganate fixation. The gland innervation in the 6-OHDA-treated animals also differed from that of normal rats in that immunoreactivity for VIP was not expressed in the majority of glands. It seems likely that following treatment with 6-OHDA sweat glands were innervated both by neurons that would normally have done so and by neurons that would normally have innervated other, noradrenergic targets in the footpads, such as blood vessels. Contact with sweat glands, therefore, appears to suppress noradrenergic function and induce cholinergic function not only in the neurons which normally innervate the glands but also in neurons which ordinarily innervate other targets. Effects of delayed innervation were also observed on target development. The appearance of sensitivity to cholinergic agonists by the sweat glands was coupled with the onset of cholinergic transmission.(ABSTRACT TRUNCATED AT 400 WORDS)

Development and properties of the secretory response in rat sweat glands: relationship to the induction of cholinergic function in sweat gland innervation

Previous studies suggest that the sympathetic innervation of the sweat glands in the rat is initially noradrenergic and during development undergoes a transition in neurotransmitter phenotype to become cholinergic. To characterize this system and its development further, we have examined the adrenergic and cholinergic components of the secretory response in adult and immature rats and have studied the onset of sweating in the plantar sweat glands of developing rats. Stimulation of the sciatic nerve in adult rats elicited a secretory response which was completely blocked by the cholinergic antagonist, atropine, and was unaffected by adrenergic antagonists, indicating that nerve-evoked secretion was cholinergic. In adult rats, the sweat glands were quite sensitive to cholinergic agonists. In addition to acetylcholine, the mature sweat gland innervation contains vasoactive intestinal peptide (VIP). In some rats, the injection of VIP alone elicited a secretory response which was blocked by atropine, suggesting that the response to VIP was mediated cholinergically. In contrast to cholinergic agonists, the glands responded relatively infrequently and with reduced volumes of sweat to the alpha- and beta-adrenergic agonists 6-fluoronorepinephrine and isoproterenol. However, when VIP, which is a potent vasodilator, was simultaneously injected with adrenergic agonists, glands in many of the injected footpads exhibited a secretory response. The response to adrenergic agonists in combination with VIP was reduced by atropine and by phentolamine plus propranolol, but was blocked completely only by a combination of the three antagonists, indicating that both adrenergic and cholinergic mechanisms were involved. In immature rats, sweating evoked by nerve stimulation first appeared at 14 days of age in 25% of the rats tested. Both the percentage of rats sweating and the number of active glands increased rapidly. At 16 days, 50% of the rats tested exhibited some active glands, and by 21 days all rats tested exhibited a secretory response. In 16-day-old rats, nerve-evoked sweating was almost completely inhibited by local injection of 1 microM atropine, but was unaffected by phentolamine and propranolol in concentrations up to 10 microM. Similarly, the glands were sensitive to 10 microM muscarine, but they exhibited no secretory response to the alpha-adrenergic agonists, clonidine and 6-fluoronorepinephrine, nor to the beta-adrenergic agonist, isoproterenol, at concentrations up to 50 microM. The simultaneous injection of VIP with adrenergic agonists did not reveal an adrenergically mediated secretory response in 16-day-old animals.(ABSTRACT TRUNCATED AT 400 WORDS)