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PubMedDate not supplied

Adenovirus-mediated gene transfer into selected liver segments using a vascular exclusion technique.

Adenovirus-mediated gene therapy is hampered by severe virus-related toxicity, especially to the liver. The aim of the present study was to test the ability of a vascular exclusion technique to achieve transgene expression within selected liver segments, thus minimizing both viral and transgene product toxicity to the liver. An E1-E3-deleted replication-deficient adenovirus expressing a green fluorescent protein (GFP) reporter gene was injected into the portal vein of BDIX rats, with simultaneous clamping of the portal vein tributaries to liver segments II, III, IV, V, and VIII. GFP expression and inflammatory infiltrate were measured in the different segments of the liver and compared with those of the livers of animals receiving the viral vector in the portal vein without clamping. The GFP expression was significantly higher in the selectively perfused segments of the liver as compared with the non-perfused segments (p < 0.0001) and with the livers of animals that received the vector in the portal vein without clamping (p < 0.0001). Accordingly, the inflammatory infiltrate was more intense in the selectively perfused liver segments as compared with all other groups (p < 0.0001). Fluorescence was absent in lungs and kidneys and minimal in spleen. The clinical usefulness of adenovirus-mediated gene transfer to the liver largely depends on the reduction of its liver toxicity. Clamping of selected portal vein branches during injection allows for delivery of genes of interest to targeted liver segments. Transgene expression confined to selected liver segments may be useful in the treatment of focal liver diseases, including metastases.

Adenoviridae↗
PubMed2000

ST-Segment recovery adds to the assessment of TIMI 2 and 3 flow in predicting infarct wall motion after thrombolytic therapy.

BACKGROUND: Early resolution of ST-segment elevation (ST-segment recovery) is associated with an improved outcome after infarction. Whether this relation is present in patients with Thrombolysis In Myocardial Infarction (TIMI) grade 2 or 3 flow (ie, patent) infarct-related arteries is not known. METHODS AND RESULTS: To examine the associations between time to achieve stable 50% ST-segment recovery assessed by continuous ECG monitoring, infarct artery flow, and infarct zone wall motion (at 48 hours), we studied 134 patients who underwent angiography at 99 (interquartile range 92 to 110) minutes after commencing streptokinase, initiated within 12 hours of onset of symptoms of myocardial infarction. Patients with TIMI 2 or 3 flow who failed to achieve early stable ST-segment recovery (50% ST-segment recovery sustained for > or 4 hours with <100 microV change in the peak lead) by 60 or 90 minutes had a higher fraction of chords in the infarct zone >2 SD below normal wall motion (TIMI 2: 55.5% vs 15.3%, P=0.006; and 56.5% vs 26.8%, P=0.01, respectively; and TIMI 3: 48.8% vs 28.3%, P=0.07; and 51.8% vs 29.9%, P=0.03, respectively). Time to stable ST-segment recovery was a multivariate predictor of infarct zone wall motion (P=0.04) independent of TIMI flow grade and the time from symptom onset to streptokinase therapy. CONCLUSIONS: In patients with TIMI 2 or 3 flow in infarct-related artery, early stable ST-segment recovery is associated with improved infarct zone wall motion at 48 hours. ST-segment recovery may provide additional information about the degree of myocyte reperfusion achieved in patients with a patent epicardial infarct-related artery after thrombolytic therapy.

Aged↗
PubMed1986

Quantitative analysis of segmental wall motion during maximal upright dynamic exercise: variability in normal adults.

Twenty-five healthy adults underwent subcostal-view, four-chamber two-dimensional echocardiographic examination while upright at rest and at the peak of maximal bicycle exercise. The purpose of the study was to determine whether the variability in regional left ventricular endocardial motion, previously demonstrated to be present at rest, persisted at peak exercise. The rest and exercise end-diastolic and end-systolic endocardial contours were visually identified, digitized, and divided into 32 radial segments after realignment by the computer. At rest there was similar percent segmental area reduction for the septum (segments 1 to 12) (54 +/- 4%, mean +/- 1 SD), apex (segments 13 to 20) (67 +/- 3%), and lateral wall (segments 21 to 32) (67 +/- 8%). At peak exercise the percent area reduction increased significantly: septum 84 +/- 5%, apex 88 +/- 2%, lateral wall 83 +/- 6% (p less than .001 compared with rest for all areas). However, there was considerable variability in percent area reduction between different radial segments in the same individual. At rest the difference between minimal and maximal percent area reduction within the same individual was 49 +/- 17 percentage units (range 21 to 83) and that at peak exercise was 32 +/- 17 percentage units (range 0 to 66). It is concluded that, because the range of standard deviation of normal endocardial motion and the degree of variability between radial segments in the same healthy individual are significant, qualitatively determined "hypokinesis," as commonly assessed clinically, may be a normal event. However, segmental akinesis or dyskinesis, which occurred rarely at rest and never at peak exercise, must be considered abnormal events.

Adolescent↗
PubMed1989

Recovery-phase patterns of ST segment depression in the heart rate domain. Identification of coronary artery disease by the rate-recovery loop.

Although the time course of ST segment depression after exercise has been related to the presence and severity of coronary artery disease, recovery-phase patterns of ST segment depression with reference to changing heart rate have not been quantified. We have found distinct recovery loop patterns of ST segment depression that distinguish subjects without coronary disease from patients with coronary artery disease when ST segment depression is examined in the heart rate domain. Continuous plots of ST segment depression and heart rate were constructed throughout treadmill exercise and recovery in 100 clinically normal subjects, in 124 patients with coronary artery disease proven by catheterization, and in 17 patients with no significant coronary disease at catheterization. Among clinically normal subjects, 95% (95 of 100) had normal (clockwise) rate-recovery loops, and 5% (five of 100) had abnormal (counterclockwise) rate-recovery loops. In these normal subjects, the resulting 95% specificity of a normal rate-recovery loop was similar to the 93% (93 of 100) specificity of standard end-exercise ST segment depression criteria. Among patients with coronary disease proven by angiography, 93% (115 of 124) had abnormal (counterclockwise) rate-recovery loops, and 7% (nine of 124) had normal rate-recovery loops. In contrast was the significantly lower 74% (92 of 124) sensitivity of standard ST segment criteria (p less than 0.001 vs. the rate-recovery loop). Specificity of a normal rate-recovery loop (71%, 12 of 17) and standard ST segment depression criteria (71%, 12 of 17) were similar in the patients with normal coronary arteries at angiography.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Compensatory vascular changes of remote coronary segments in response to lesion progression as observed by sequential angiography from a controlled clinical trial.

BACKGROUND: Local coronary artery enlargement to compensate for atherosclerotic plaques preserves the vessel lumen. The extent to which coronary segments remote from progressing lesions enlarge is unknown. This is clinically relevant since compensatory enlargement may be important in determining whether clinical complications result from progression of coronary artery disease (CAD). Additionally, compensatory change has implications for quantitative coronary angiographic (QCA) trials, since the effect of progression on diameter means may be mitigated by compensatory changes in remote coronary segments when QCA change is averaged over all lesions. METHODS AND RESULTS: Serial QCA data from 78 subjects in the Monitored Atherosclerosis Regression Study were used to demonstrate compensatory changes in coronary segments remote from progressing or regressing lesions. Coronary segments were first classified as progressing (regressing) if percent diameter stenosis (PS) increased or decreased by > 10 with a concurrent decrease or increase in minimum lumen diameter (MLD) of either > 0.32 mm or > 10% of the normal baseline reference diameter (DNORM). Segments not meeting these criteria were labeled stenosis stable. Stenosis-stable segments opposite progressing lesions showed increases in MLD (P = .0006), DNORM (P = .001), and average diameter (P = .001). On-trial apolipoprotein (apo) B, apo C-III, and blood pressure levels inversely correlated with these compensatory changes. CONCLUSIONS: Lesion progression in one coronary segment is associated with significant increases in segmental diameter of remote parts of the coronary tree. We hypothesize these increases to be vascular compensatory changes in response to progression of CAD. Vascular compensatory change is enhanced by LDL cholesterol and triglyceride-rich lipoprotein reduction and appears to be part of the treatment effect itself.

Adult↗
PubMed1975

Changes in myocardial blood flow and S-T segment elevation following coronary artery occlusion in dogs.

The relationship between regional blood flow and epicardial S-T segment elevation was studied in 26 open-chest anesthetized dogs with left anterior coronary artery ligations. Changes in myocardial blood flow, measured with 15 plus or minus 5mu (diameter) microspheres labeled with 141-Ce, 85-Sr, and 169-Yb, were correlated with summated S-T segment elevations 15 minutes, 1 hour, and 2 hours after coronary artery occlusion. In normal areas, myocardial blood flow was 113 plus or minus 5 ml/min 100 g- minus 1 and summated S-T segment elevation was 0.3 plus or minus 0.2 mv. Fifteen minutes after coronary artery occlusion in 26 dogs, S-T segment elevation was 5.7 plus or minus 0.7 mv over the center of the infarct and myocardial blood flow was 10 plus or minus 1 ml/min 100 g- minus 1; over the border zone, myocardial blood flow was 63 plus or minus 4 ml/min 100 g- minus 1 and S-T segment elevation was 3.1 plus or minus 0.1 mv. One third of the areas with a myocardial blood flow of 10 ml/min 100 g- minus 1 or less had no S-T segment elevation. In the center and border zones of the infarct in 9 dogs, myocardial blood flow increased from 11 plus or minus 2 and 67 plus or minus 8 ml/min 100 g- minus 1 15 minutes after occlusion to 20 plus or minus 4 and 84 plus or minus 12 ml/min 100 g- minus 1, respectively, 2 hours after coronary artery occlusion. These increases were not associated with a significant reduction in summated S-T segment elevation. The results do not suggest a simple quantitative relationship between epicardial S-T segment elevation and myocardial blood flow following acute coronary artery occlusion.

Animals↗
PubMed1976

Urea secretion by the straight segment of the proximal tubule.

Studies utilizing in vitro microperfusion were designed to examine whether urea is actively or passively transported across superficial and juxtamedullary straight segments of rabbit proximal tubules. With perfusate and bath solutions containing 1 mM urea and electrolytes similar to normal plasma, the efflux (lumen-to-bath) isotopic permeability (X 10(-5) cm s-1) of superficial segments was 1.37 +/- 0.16 and of juxtamedullary segments was 2.14 +/- 0.20. In the same tubules, the influx (bath-to-lumen) isotopic permeability was 3.70 +/- 0.35 in superficial segments and 4.75 +/- 0.37 in juxtamedullary segments. Despite net water movement in the opposite direction (0.5 nl mm-1 min-1), the influx rate was significantly higher than the efflux rate of urea in both groups. With a low perfusion rate (2 nl/min) and equivalent specific activities of [14C]urea in bath and perfusate, the collected-to-perfused ratio of [14C]urea, corrected for volume marker change, was 1.07 +/- 0.01 in superficial and 1.09 +/- 0.01 in juxtamedullary nephrons, thus indicating net secretion in both segments. In separate studies urea influx was inhibited by hypothermia (decrease from 37 degrees to 28 degrees C), by phloretin (0.1 mM in bath), by cyanide (1 mM), but not by probenecid (0.2 mM). In each case the inhibition was highly significant and reversible. These data suggest that urea is actively secreted by the straight segments of both the superficial and juxtamedullary proximal tubules. These segments may, therefore, contribute significantly to the high urea concentration found at the bend of Henle's loop by micropuncture.

Absorption↗
PubMed1984

Ammonia production by individual segments of the rat nephron.

Ammonia production was measured directly in 10 segments of the rat nephron to determine the relative importance of the segments as sites of renal ammonia production. Tubules were microdissected from normal rats and rats drinking 0.28 M NH4Cl or 0.28 M NaHCO3 for 3-8 d. The segments were incubated in vitro with and without 2 mM glutamine. Ammonia concentrations in the incubation fluid were measured by microfluorometry to determine ammonia production rates. All segments produced ammonia from glutamine. In normal rats, production with glutamine was highest (greater than 5 pmol/min per mm) in the proximal convoluted (S-1), proximal straight (S-3), and distal convoluted tubules, and lowest (less than or equal to 2) in cortical and medullary collecting ducts and thin descending limbs. Metabolic acidosis increased production by 60% in the S-1 segment of the proximal convoluted tubule and by 150% in the S-2 segment of the proximal straight tubule without significant effect in any other segment. Bicarbonate loading decreased production by S-1 but had no effect on S-2 or S-3. Thus, acid-base changes altered production only in specific segments of the proximal tubule. We infer that the bulk of ammonia production occurs in the proximal tubules and that production by collecting ducts can account for only a few percent of renal ammonia production and excretion in the rat.

Ammonia↗
PubMed1992

Germline variable region gene segment derivation of human monoclonal anti-Rh(D) antibodies. Evidence for affinity maturation by somatic hypermutation and repertoire shift.

To date, there has been no systematic study of the process of affinity maturation of human antibodies. We therefore sequenced the variable region genes (V genes) of 14 human monoclonal antibodies specific for the erythrocyte Rh(D) alloantigen and determined the germline gene segments of origin and extent of somatic hypermutation. These data were correlated with determinations of antibody affinity. The four IgM antibodies (low affinity) appear to be derived from two germline heavy chain variable region gene segments and one or two germline light chain variable region gene segments and were not extensively mutated. The 10 IgG antibodies (higher affinity) appear to be derived from somatic hypermutation of these V gene segments and by use of new V gene segments or V gene segment combinations (repertoire shift). Affinity generally increased with increasing somatic hypermutation; on average, there were 8.9 point mutations in the V gene segments of the four IgM antibodies (Ka = 1-4 x 10(7)/M-1) compared with 19 point mutations in the V gene segments of the 10 IgG antibodies. The four highest affinity antibodies (Ka = 0.9-3 x 10(9)/M-1) averaged 25.5 point mutations. The use of repertoire shift and somatic hypermutation in affinity maturation of human alloantibodies is similar to data obtained in inbred mice immunized with haptens.

Antibodies, Monoclonal↗
PubMed1987

The influence of R-wave amplitude on the degree of ST-segment depression in exercise electrocardiography in the individual patient.

Many factors have been found to influence the magnitude of ST-segment depression in the exercise electrocardiogram. We investigated whether R-wave amplitude is a significant factor. We studied the exercise electrocardiogram of 20 patients with angiographically documented coronary artery disease, including greater than or equal to 70% stenosis of the left anterior descending artery, who had an ischemic response to exercise but no previous anterior myocardial infarction. Precordial leads V1-6 were taken into account. When all 120 leads were measured, those with ST-segment depression greater than or equal to 2.0mm at peak exercise had a mean resting R-wave amplitude of 19.03 +/- 5.81mm; those with ST-segment depression 2.0-1.0mm, R 11.42 +/- 5.99mm; and those with ST-segment depression less than 1.0mm, R 5.9 +/- 5.21mm (p less than 0.001 between groups). When the R-wave amplitude was correlated with the ST-segment depression in each precordial lead, the correlation was 1.0. In leads V1-6, when 67 tracings with ST-segment depression greater than 0.5mm were measured, the correlation was 0.537 (p less than 0.001). In each precordial lead the t values of R-wave differences correlated very strongly (r less than 0.883) with the differences in ST-segment depression. We conclude that precordial R-wave amplitude significantly influences the magnitude of ST-segment depression.

Coronary Disease↗
PubMed1999

Influence of thrombolytic therapy on inferior acute myocardial infarction with concomitant anterior ST segment depression.

The purposes of this study were to analyze the prognostic significance of precordial ST segment depression and to determine whether thrombolytic therapy is effective for all patients with inferior acute myocardial infarction (AMI) or whether there is a different effectiveness for patients with concomitant anterior ST segment depression persisting for 24 hours or longer. Medical charts of 176 patients were studied. On the basis of ECG the patients were subclassified into three groups according to the presence, persistence, or absence of significant ST segment depression: Group 1: anterior ST segment depression persisting for less than 24 hours (45.4%); Group 2: anterior ST segment depression persisting for more than 24 hours (17.6%); Group 3: no anterior ST segment depression (37%). Age, Killip class, peak creatine kinase, hospital deaths, left ventricular ejection fraction, regional wall motion score, postinfarction angina, and ventricular/supraventricular arrhythmia of all patients were studied. Parameters of the three groups were compared: worse results were found in group 1 and the worst in group 2. This result is independent of thrombolytic therapy. Finally, the same parameters of thrombolyzed and nonthrombolyzed groups were compared: no statistically significant difference was observed. Among thrombolyzed patients the number of those with ST depression lasting more than 24 hours is lower than in nonthrombolyzed patients. It can be assumed that thrombolytic therapy in inferior AMI determines a shifting of patients from a worse prognosis group (ST segment depression persisting for more than 24 hours) to a better prognosis group (ST segment depression persisting for less than 24 hours).

Aged↗
PubMedDate not supplied

Metrical segmentation in Dutch: vowel quality or stress?

Previous experiments using a word-spotting task suggest that English listeners use metrically strong syllables to segment continuous speech into discrete words (Cutler & Norris, 1988). The present study is concerned with this metrical segmentation strategy in Dutch. Although Dutch and English share general metrical properties, they differ in ways that may affect segmentation. First, the acoustic cues for metrically strong syllables are less salient in Dutch than in English; hence a metrical segmentation strategy is less likely to be applied by Dutch listeners. Second, vowel quality depends less on metrical structure in Dutch than in English; hence segmentation in Dutch is presumably triggered by other acoustic cues, namely, those related to stress. Experiment 1 shows that stress strongly affects Dutch listeners' ability and speed in spotting Dutch monosyllabic words in disyllabic nonwords. Experiment 2, however, finds the same stress effect when only the target words are presented, without a subsequent syllable triggering segmentation. A third experiment shows a small effect of vowel quality on error scores, but not on latencies. These results suggest that Dutch listeners do not apply a metrical segmentation strategy. The discrepancy between the two languages suggests that segmentation strategies may depend on language-specific regularities in the phonology and in the lexicon.

Adolescent↗
PubMed1985

Location of the vibratory segment in tracheoesophageal speakers.

The Singer-Blom tracheoesophageal puncture procedure for surgical-prosthetic voice restoration has proved to be a viable option for alaryngeal speech rehabilitation. Following tracheoesophageal puncture, occlusion of the tracheostoma shunts pulmonary air through the Blom-Singer prosthesis into the cervical esophagus. The pulmonary air passing through the cervical esophagus and into the hypopharynx causes a portion of the upper alimentary tract to vibrate in a manner similar to that of the pharyngoesophageal segment during the production of esophageal speech. To study the location and shape of the vibratory segment in tracheoesophageal speakers, videofluoroscopy and simultaneous voice recording were performed with 16 patients. To analyze the vibratory segment(s), photographs were made of the videotaped image while it was stopped during the patients' production of the /a/ sound. The most frequent location of the vibratory segment was in the lower third of the neck, which corresponds to cervical vertebrae C5 through C7. Five of the subjects had two separate vibratory segments and two other subjects had long vibratory segments. The vibratory segment(s) in tracheoesophageal speakers was found to be similar to the vibratory segment(s) in esophageal speakers.

Aged↗
PubMed1998

Novel adaptation of a method to assess responsiveness of bronchial segments in vitro.

In vivo agonist delivery to the lungs is characterized by absorption through the mucosal layer followed by access to the smooth muscle. When agonists are applied to perfused bronchial segments, a difference in potency to agonists applied to the serosal (outside) or mucosal (inside) surface can be demonstrated. In order to elucidate this effect in canine bronchial segments, we adapted a method to assess responsiveness of agonists applied to the inside or outside surface of canine bronchial segments. A 2 cm "fluid-tight" length of bronchus was cannulated and mounted in a perfusion chamber. Auxotonic contraction of the bronchus displaced fluid inside the segment up a column and the change in height of fluid within the column (afterload) was measured as a change in hydrostatic pressure (volumetric). We assessed the optimal conditions for measuring bronchial responsiveness to acetylcholine. Neither stretching segments lengthways from 100 to 140% of resting length, nor altering the transmural pressure from 3 to 21 cmH2O had a significant effect on the potency of acetylcholine applied to the outside surface. Both acetylcholine (n=7) and methacholine (n=4) were approximately 10-fold more potent when applied to the outside surface than the inside surface of bronchial segments (p<0.0001). Furthermore, mechanical removal of the epithelium (n=6) led to a 67-fold increase in potency of acetylcholine applied to the inside surface compared with segments with epithelium. The advantages that this system has over previously reported methods include: 1) agonists can be injected at a low flow rate so as to minimize epithelial stress; 2) changes in luminal volume are measured under conditions of no flow; 3) after-load can be varied such that contraction is either practically isotonic or auxotonic; and 4) a "barrier effect" of the epithelium of canine bronchial segments can be demonstrated. This new adapted method will provide us with the means to assess the relationship between in vitro and in vivo responsiveness in human bronchi.

Acetylcholine↗
PubMed2004

Differential expression of E-cadherin, N-cadherin and beta-catenin in proximal and distal segments of the rat nephron.

BACKGROUND: The classical cadherins such as E- and N-cadherin are Ca2+-dependent cell adhesion molecules that play important roles in the development and maintenance of renal epithelial polarity. Recent studies have shown that a variety of cadherins are present in the kidney and are differentially expressed in various segments of the nephron. However, the interpretation of these findings has been complicated by the fact that the various studies focused on different panels of cadherins and utilized different species. Moreover, since only a few of the previous studies focused on the rat, information regarding the expression and localization of renal cadherins in this important species is lacking. In the present study, we have employed dual immunofluorescent labeling procedures that utilized specific antibodies against either E- or N-cadherin, along with antibodies that target markers for specific nephron segments, to characterize the patterns of cadherin expression in frozen sections of adult rat kidney. RESULTS: The results showed that N-cadherin is the predominant cadherin in the proximal tubule, but is essentially absent in other nephron segments. By contrast, E-cadherin is abundant in the distal tubule, collecting duct and most medullary segments, but is present only at very low levels in the proximal tubule. Additional results revealed different patterns of N-cadherin labeling along various segments of the proximal tubule. The S1 and S2 segments exhibit a fine threadlike pattern of labeling at the apical cell surface, whereas the S3 segment show intense labeling at the lateral cell-cell contacts. CONCLUSIONS: These results indicate that E- and N-cadherin are differentially expressed in the proximal and distal tubules of rat kidney and they raise the possibility that differences in cadherin expression and localization may contribute to the differences in the susceptibility of various nephron segments to renal pathology or nephrotoxic injury.

Animals↗
PubMed2004

Microsurgical approaches to the perimesencephalic cisterns and related segments of the posterior cerebral artery: comparison using a novel application of image guidance.

OBJECTIVE: To describe the exposure obtained through six approaches to the perimesencephalic cisterns with an emphasis on exposure of the posterior cerebral artery and its branches. METHODS: Dissections in 12 hemispheres exposed the crural, ambient, and quadrigeminal cisterns and related segments of the posterior cerebral artery. A Stealth Image Guidance workstation (Medtronic Surgical Navigation Technologies, Louisville, CO) was used to compare the approaches. RESULTS: The transsylvian approach exposed the interpeduncular and crural cisterns. The subtemporal approach exposed the interpeduncular and crural cisterns as well as the lower half of the ambient cistern. Temporal lobe retraction and the position of the vein of Labbé limited exposure of the quadrigeminal cistern. Occipital transtentorial and infratentorial supracerebellar approaches exposed the quadrigeminal and lower two-thirds of the ambient cistern. Transchoroidal approaches exposed the posterior third of the crural cistern, the upper two-thirds of the ambient cistern, and the proximal quadrigeminal cistern. Transchoroidal approaches exposed the posterior portion of the P2 segment (P2p) in 9 of 10 hemispheres and were the only approaches that exposed the lateral posterior choroidal arteries and the plexal segment of the anterior choroidal artery. Occipital transtentorial and infratentorial supracerebellar approaches provided access to the P3 segment in all cases and exposed the P2p segment in 4 of 10 hemispheres. The subtemporal approach provided access to the cisternal and crural segments of the anterior choroidal and medial posterior choroidal arteries and exposed the P2p segment in 3 of 10 hemispheres. CONCLUSION: Surgical approaches to lesions of the perimesencephalic cisterns must be tailored to the site of the pathological findings. The most challenging area to expose is the upper half of the ambient cistern, particularly the P2p segment of the posterior cerebral artery.

Choroid↗
PubMed2004

hunchback is required for suppression of abdominal identity, and for proper germband growth and segmentation in the intermediate germband insect Oncopeltus fasciatus.

Insects such as Drosophila melanogaster undergo a derived form of segmentation termed long germband segmentation. In long germband insects, all of the body regions are specified by the blastoderm stage. Thus, the entire body plan is proportionally represented on the blastoderm. This is in contrast to short and intermediate germband insects where only the most anterior body regions are specified by the blastoderm stage. Posterior segments are specified later in embryogenesis during a period of germband elongation. Although we know much about Drosophila segmentation, we still know very little about how the blastoderm of short and intermediate germband insects is allocated into only the anterior segments, and how the remaining posterior segments are produced. In order to gain insight into this type of embryogenesis, we have investigated the expression and function of the homolog of the Drosophila gap gene hunchback in an intermediate germ insect, the milkweed bug, Oncopeltus fasciatus. We find that Oncopeltus hunchback (Of'hb) is expressed in two phases, first in a gap-like domain in the blastoderm and later in the posterior growth zone during germband elongation. In order to determine the genetic function of Of'hb, we have developed a method of parental RNAi in the milkweed bug. Using this technique, we find that Oncopeltus hunchback has two roles in anterior-posterior axis specification. First, Of'hb is required to suppress abdominal identity in the gnathal and thoracic regions. Subsequently, it is then required for proper germband growth and segmentation. In milkweed bug embryos depleted for hunchback, these two effects result in animals in which a relatively normal head is followed by several segments with abdominal identity. This phenotype is reminiscent to that found in Drosophila hunchback mutants, but in Oncopeltus is generated through the combination of the two separate defects.

Abdomen↗
PubMed2004

Ftz modulates Runt-dependent activation and repression of segment-polarity gene transcription.

A crucial step in generating the segmented body plan in Drosophila is establishing stripes of expression of several key segment-polarity genes, one stripe for each parasegment, in the blastoderm stage embryo. It is well established that these patterns are generated in response to regulation by the transcription factors encoded by the pair-rule segmentation genes. However, the full set of positional cues that drive expression in either the odd- or even-numbered parasegments has not been defined for any of the segment-polarity genes. Among the complications for dissecting the pair-rule to segment-polarity transition are the regulatory interactions between the different pair-rule genes. We have used an ectopic expression system that allows for quantitative manipulation of expression levels to probe the role of the primary pair-rule transcription factor Runt in segment-polarity gene regulation. These experiments identify sloppy paired 1 (slp1) as a gene that is activated and repressed by Runt in a simple combinatorial parasegment-dependent manner. The combination of Runt and Odd-paired (Opa) is both necessary and sufficient for slp1 activation in all somatic blastoderm nuclei that do not express the Fushi tarazu (Ftz) transcription factor. By contrast, the specific combination of Runt + Ftz is sufficient for slp1 repression in all blastoderm nuclei. We furthermore find that Ftz modulates the Runt-dependent regulation of the segment-polarity genes wingless (wg) and engrailed (en). However, in the case of en the combination of Runt + Ftz gives activation. The contrasting responses of different downstream targets to Runt in the presence or absence of Ftz is thus central to the combinatorial logic of the pair-rule to segment-polarity transition. The unique and simple rules for slp1 regulation make this an attractive target for dissecting the molecular mechanisms of Runt-dependent regulation.

Animals↗