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Biomedical subjects

R Golub

Publications and source records attributed to R Golub.

At least 19 recordsLinked to original sources
PubMed2001

Laparoscopic repositioning of a ventriculo-peritoneal catheter tip for a sterile abdominal cerebrospinal fluid (CSF) pseudocyst.

Abdominal cerebrospinal fluid (CSF) pseudocyst is an uncommon but well-described complication that is reported to occur in <1% of ventriculo-peritoneal (VP) shunts. Management options for pseudocysts include various types of shunt revisions, which recently have been conducted laparoscopically. We report the case of an 11-year-old girl in whom a sterile abdominal CSF pseudocyst was successfully fenestrated and the VP catheter repositioned using laparoscopy. This technique in the setting of a noninfected pseudocyst has proven to be safe, with results comparable to the conventional open technique. However, the long-term success rate is still unknown.

Abdomen↗
PubMed2001

VH gene replacement in thymocytes.

The quasi-monoclonal (QM) mouse has a functionally rearranged H chain gene inserted into its natural position in the IgH locus. In this position, the H chain gene is subject to many of the same activities as normally arranged H chain genes, including somatic hypermutation, V(H) gene replacement, and class switch recombination. Here, we have used this mouse strain to determine some of the rules that govern the V(D)J recombination activity of the IgH locus in thymus. We focused on the requirements for V(H) gene replacement. In normal mice, thymic DJ(H) rearrangements are common, but VDJ(H) rearrangements are not. We found intermediate products of V(H) replacement in double-positive CD4(+)CD8(+) cells of the QM thymus, demonstrating that the inserted V(H) gene was accessible and ruling out the possibility that a V(H) gene per se cannot be rearranged in the thymus. We found transcripts from the knocked-in H chain gene of QM, but no mu H chain protein was detectable in thymocytes. Cloning and sequencing of these transcripts revealed that some had been generated by V(H) gene replacement. Corresponding signal joints could also be identified. These results suggest that neither a B cell-specific signal nor an Ig protein are necessary to activate V(H)-to-VDJ(H) joining in thymocytes. Possible mechanisms remaining to account for overcoming the barrier to V(H) joining in thymocytes include the insertion of a transcriptionally active gene segment and/or the inactivation of a silencer.

Animals↗
PubMed2001

Valpha gene replacement in a TCRalpha knock-in mouse.

Using a TCRalpha chain knock-in mouse, we demonstrate that V-gene replacement can operate in the T cell receptor alpha locus. Functional TCRalpha chain transcripts generated by Valpha-gene replacement at the site of the Valpha-embedded heptamer were identified in splenic T cells. This finding shows that Valpha-gene replacement can likely be used to shape the peripheral T cell repertoire. The conservation of the embedded heptamer in most Valpha segments adds support to the notion that V-gene replacement is a mechanism maintained to diversify the immune system and that argues that it is common to B and T cells.

Animals↗
PubMed2000

Evolution of the recombination signal sequences in the Ig heavy-chain variable region locus of mammals.

The Ig and T cell receptor (TCR) loci have an exceptionally dynamic evolutionary history, but the mechanisms responsible remain a subject of speculation. Ig and TCR genes are unique in vertebrates in that they are assembled from V, D, and J segments by site-specific recombination in developing lymphocytes. Here we examine the extent to which the V(D)J recombination in germline cells may have been responsible for remodeling Ig and TCR loci in mammals by asking whether gene segments have evolved as a unit, or whether, instead, recombination signal sequences (RSSs) and coding sequences have different phylogenies. Four distinct types of RSS have been defined in the human Ig heavy-chain variable region (Vh) locus, namely H1, H2, H3, and H5, and no other RSS type has been detected in other mammalian species. There is a well-supported discrepancy between the evolutionary history of the RSSs as compared with the Vh coding sequences: the RSS type H2 of one Vh gene segment has clearly become replaced by a RSS type H3 during mammalian evolution, between 115 and 65 million years ago. Two general models might explain the RSS swap: the first involves an unequal crossing over, and the second implicates germline activation of V(D)J recombination. The Vh-H2/RSS-H3 recombination product has likely been selected during the evolution of mammals because it provides better V(D)J recombination efficiency.

Base Sequence↗
PubMed2000

Magnetic trapping of neutrons

Accurate measurement of the lifetime of the neutron (which is unstable to beta decay) is important for understanding the weak nuclear force and the creation of matter during the Big Bang. Previous measurements of the neutron lifetime have mainly been limited by certain systematic errors; however, these could in principle be avoided by performing measurements on neutrons stored in a magnetic trap. Neutral-particle and charged-particle traps are widely used for studying both composite and elementary particles, because they allow long interaction times and isolation of particles from perturbing environments. Here we report the magnetic trapping of neutrons. The trapping region is filled with superfluid 4He, which is used to load neutrons into the trap and as a scintillator to detect their decay. Neutrons in the trap have a lifetime of 750(+330)(-200) seconds, mainly limited by their beta decay rather than trap losses. Our experiment verifies theoretical predictions regarding the loading process and magnetic trapping of neutrons. Further refinement of this method should lead to improved precision in the neutron lifetime measurement.

Journal Article↗
PubMed2000

Specific antibody production by V(H)-gene replacement.

V(H)-gene replacement is a recombination event in which a pre-existing immunoglobulin heavy chain gene can be altered by the replacement of the rearranged V(H) gene segment with another V(H) gene segment. Although this event has been demonstrated in various model systems, its role in generating antibody diversity is still unsettled. We have used a genetically modified mouse strain, QM, with a quasi monoclonal primary B cell repertoire specific for NP to determine whether V(H) gene replacement can generate a new antigen specificity. Hybridomas generated from QM splenocytes after immunization with different antigens, gave rise to antibodies with specificity to the immunizing antigen or with new specificities. We found V(H)-gene replacement was used to change the original heavy chain gene rearrangement specific for NP into a heavy chain gene encoding the new antigen specificity. V(H)-gene replacement intermediates were detected both before and after the immunization, suggesting that the event was selective rather than instructive. These results demonstrate that V(H)-gene replacement can generate a new antibody heavy chain gene with a different functional and selectable antigen specificity.

Animals↗
PubMed2000

Evolutionarily conserved and divergent expression of members of the FGF receptor family among vertebrate embryos, as revealed by FGFR expression patterns in Xenopus.

Fibroblast growth factors (FGFs) mediate many cell-cell signaling events during early development. While the actions of FGFs have been well-studied, the roles played by specific members of the FGF receptor (FGFR) family are poorly understood. To characterize the roles played by individual FGFRs we compared the regulation and expression of the three Xenopus FGFRs described to date (XFGFR-1, XFGFR-2, and XFGFR-4). First, we describe the expression of Xenopus FGFR-4; XFGFR-4 is present as a maternal mRNA and is found in the embryo through at least the tadpole stage. XFGFR-4 and XFGFR-1 mRNAs are present at comparable levels, arguing that both mediate FGF signaling during early development. Second, the expression of XFGFR-4 in animal caps differs from the expression of XFGFR-1 and XFGFR-2, suggesting that the FGFRs are independently regulated in ectoderm. Third, using whole-mount in situ hybridization, we show that XFGFR-1, XFGFR-2, and XFGFR-4 are expressed in dramatically different patterns, arguing that specific FGF signaling events are mediated by different members of the FGFR family. Among these, FGF signaling during the induction of neural crest cells is likely to be mediated by XFGFR-4. Comparison of our results with previously reported FGFR expression patterns reveals that FGFR-1 expression is highly conserved among vertebrate embryos, and FGFR-2 expression shows many features that are conserved and some that are divergent. In contrast, the expression pattern of FGFR-4 is highly divergent among vertebrate embryos.

Animals↗
PubMed2000

Bilateral eventration of the diaphragm with perforated gastric volvulus in an adolescent.

Bilateral congenital eventration of the diaphragm almost uniformly presents in infancy with respiratory compromise and is associated with a high mortality rate. Delayed presentation of diaphragmatic eventration in older children and adults may be associated with acute gastric volvulus. Thus, any patient with abdominal pain, vomiting, or nonspecific gastrointestinal symptoms in association with abnormal diaphragmatic findings on chest x-ray should undergo further diagnostic workup with upper gastrointestinal series or computed tomography (CT) scan. Treatment of gastric volvulus requires immediate surgical repair to prevent subsequent necrosis and perforation. The authors describe a case report of bilateral congenital diaphragmatic eventration complicated by a perforated gastric volvulus in a 13-year-old boy. Emergent reduction of the volvulus, closure of the perforated stomach, plication of the diaphragm, and placement of gastrostomy was performed successfully.

Adolescent↗
PubMed2000

Same-session endoscopic retrograde cholangiopancreatography and cholecystectomy.

The objective was to determine the efficacy and safety of same-session endoscopic retrograde cholangiopancreatography (ERCP) and cholecystectomy. Twenty-two patients who had ERCP and cholecystectomy performed in the same session under one general anesthetic were compared with 77 patients who had ERCP followed by surgery in the ensuing days. In the 93 patients who underwent attempted laparoscopic cholecystectomy, there was no difference in conversion to open rates between the same-session group and the delayed group. The length of stay after ERCP was longer in the delayed group. Same-session ERCP and cholecystectomy is safe and efficacious, and its routine use should be considered.

Anesthesia, General↗
PubMed1999

The role of components of recombination signal sequences in immunoglobulin gene segment usage: a V81x model.

It has long been appreciated that some immunoglobulin (and T-cell receptor) gene segments are used much more frequently than others. The VHsegment V81x is a particularly striking case of overusage. Its usage varies with the stage of B-cell development and with the strain of mice, but it is always high in B cell progenitors. We have found that the coding sequence and the recombination signal sequences (RSS) are identical in five mouse strains, including CAST/Ei, a strain derived from the species Mus castaneus. Thus, the strain differences cannot be attributed to sequences within V81x itself. V81x RSS mediated recombination at rates significantly higher than another VHRSS. Although the V81x nonamer differs at one base pair from the consensus sequence, an RSS with this nonamer and a consensus heptamer recombines as well as the consensus RSS. When the V81x spacer is replaced by that of VA1, the frequency of recombination decreases by approximately 5-fold; thus, the contribution of variation in natural spacers to variability in VHusage in vivo is likely to be more than has been previously appreciated. Furthermore, the contribution of the heptamer and nonamer to differential VHusage in our assay is correlated inversely with their conservation throughout the VHlocus.

Animals↗
PubMed1998

Structure, diversity, and repertoire of VH families in the Mexican axolotl.

The Mexican axolotl V(H) segments associated with the Igh C mu and C nu isotypes were isolated from anchored PCR libraries prepared from spleen cell cDNA. The eight new V(H) segments found bring the number of V(H) families in the axolotl to 11. Each V(H) had the canonical structural features of vertebrate V(H) segments, including residues important for the correct folding of the Ig domain. The distribution of ser AGC/T (AGY) and TCN codons in axolotl V(H) genes was biased toward AGY in complementarity-determining region-1 (CDR1) and TCN in framework region-1 (FR1); there were no ser residues in the FR2 region. Thus, the axolotl CDR1 region is enriched in DNA sequences forming potential hypermutation hot spots and is flanked by DNA sequences more resistant to point mutation. There was no significant bias toward AGY in CDR2. Southern blotting using family-specific V(H) probes showed restriction fragments from 1 (V(H)9) to 11-19 (V(H)2), and the total number of V(H) genes was 44 to 70, depending on the restriction endonuclease used. The V(H) segments were not randomly used by the H mu and H nu chains; V(H)1, V(H)6, and V(H)11 were underutilized; and the majority of the V(H) segments belonged to the V(H)7, V(H)8, and V(H)9 families. Most of the nine J(H) segments seemed to be randomly used, except J(H)6 and J(H)9, which were found only once in 79 clones.

Ambystoma mexicanum↗
PubMed1998

V(H) gene replacement occurs in the spleen and bone marrow of non-autoimmune quasi-monoclonal mice.

Genes encoding the heavy chain portion of immunoglobulin molecules arise from the combinatorial association of V, D and J gene segments, which occurs during discrete stages of B lineage development in the bone marrow. Recently, V(H) replacement, a form of receptor editing, has been described, in which the variable region of an existing VDJ(H) rearrangement is replaced by another V(H) gene segment in a recombination event believed to involve an embedded heptamer within the coding region of the V(H). Studies of transgenic mice with "knocked-in" VDJ(H) genes encoding anti-DNA specificity have demonstrated that receptor editing of the heavy chain is one mechanism by which autoreactive B cell receptors can be modified. Another mouse, the "quasi-monoclonal", which encodes a "knocked-in" VDJ(H) for the hapten NP also contains B lineage cells that undergo V(H) replacement. This suggests that V(H) replacement may play a role in the normal diversification of the antibody repertoire. Using a ligation-mediated PCR assay, we have identified V(QM) double-stranded DNA breaks indicative of V(H) replacement intermediates from bone marrow and splenic B lineage cells of quasi-monoclonal mice in the absence of immunization. V(QM) to J558 recombination deletion products consistent with V(H) replacement were also detected in both the bone marrow and spleen of non-immunized quasi-monoclonal mice. Moreover, RAG-1 transcripts were detected in the spleen. These data suggest that V(H) replacement can be part of the mechanism(s) used by B lineage cells to generate diversity throughout B lineage development, including later stages occurring in secondary lymphoid tissues.

Animals↗
PubMed1998

Laparoscopic versus open appendectomy: a metaanalysis.

BACKGROUND: There have been numerous retrospective and uncontrolled series of laparoscopic appendectomy (LA), as well as 16 prospective randomized studies published to date. Although most of these have concluded that the laparoscopic technique is as least as good as open appendectomy (OA), there has been considerable controversy as to whether LA is superior. To help clarify this issue, we performed a metaanalysis of the randomized prospective studies. STUDY DESIGN: A metaanalysis of all formally randomized prospective trials of LA versus OA in adults. RESULTS: A total of 1,682 patients were analyzed. When compared with OA, LA results in significantly less postoperative pain, earlier resumption of solid foods, a shorter hospital stay, and a faster return to normal activities. The wound infection rate in the LA patients is less than one half the rate in patients undergoing OA. LA, however, requires longer operating times and the incidence of intraabdominal abscess is higher, but this failed to reach statistical significance. There were no differences in complications or hospital charges. CONCLUSIONS: LA offers considerable advantages over OA, primarily because of its ability to reduce the incidence of wound infections and shorten recovery times. Its widespread acceptance should be considered. The trend toward increased intraabdominal abscess formation is worrisome, however, and demands further investigation.

Abdominal Abscess↗
PubMed1998

The prediction of common bile duct stones using a neural network.

BACKGROUND: The role of preoperative ERCP and endoscopic sphincterotomy (ES) in the diagnosis and treatment of suspected common bile duct stones (CBDS) in the laparoscopic age is controversial. The preoperative diagnosis of CBDS by ERCP and the removal of CBDS by ES are advantageous because of technical difficulties in performing laparoscopic exploration of the common bile duct. Approximately 50% of preoperative ERCP examinations are normal, however. The noninvasive diagnosis of CBDS has assumed new importance, but it has proved to be an elusive goal. Neural networks are a form of artificial computer intelligence that have been used successfully to interpret ECGs and to diagnose myocardial infarcts. The purpose of this study was to determine whether a neural network could be trained to predict CBDS accurately in patients at high risk of having duct stones. STUDY DESIGN: We trained a back-propagation neural network to predict the presence of CBDS. Retrospective data from patients who had a cholecystectomy and either a preoperative ERCP or intraoperative cholangiogram were used to build the network, and it was tested using unseen data. RESULTS: One hundred forty patients were used to train the network, and 16 patients were used to test it. The trained network was able to predict CBDS in 100% of the patients in both the training and test sets. CONCLUSIONS: Screening of high-risk patients for CBDS by neural network analysis is highly accurate. This promising new, noninvasive, and inexpensive technique can potentially decrease the need for preoperative ERCP by 50%, but additional prospective evaluation is indicated.

Adult↗
PubMed1998

Appendiceal ultrasonography performed by nonradiologists: does it help in the diagnostic process?

We performed a retrospective study to compare the sensitivity, specificity, predictive value, and diagnostic accuracy of appendiceal ultrasonography performed by unsupervised technicians during the nighttime hours with studies performed during the day by supervised technicians. Fifty-nine percent of the 163 sonographic examinations were done during the day, and 41% were performed at night. The sensitivity during the day (61%) was significantly higher than at night (26%), as was the positive predictive value (93% day, 71% night). We conclude that ultrasonography is an operator-dependent study. Its sensitivity is so diminished when not performed by an experienced radiologist or technician that a negative examination is not reliable.

Adolescent↗
PubMed1997

Structure and diversity of the heavy chain VDJ junctions in the developing Mexican axolotl.

The immune capacity of young and adult axolotls (Ambystoma mexicanum) was evaluated by examining the combinatorial and junctional diversity of the VH chain. A large number of VDJ rearrangements isolated from 2.5-, 3.5-, 10-, and 24-month-old animals were sequenced. Six JH segments were identified with the canonical structure of all known vertebrate JHs, including the conserved Trp103-Gly104-X-Gly106 motif. Four core DH-like sequences were used by most (80%) of the VDJ junctions. These G-rich sequences had structures reminiscent of the TCRB DB sequences, and were equally used in their three reading frames. About 25% of the Igh, VDJ junctions from 3.5-month-old axolotls were out of frame, but most rearrangements were in frame at 10 and 24 months, suggesting that there is active selection of the productively rearranged Igh chains in the developing animals. There was no significant difference between the size of CDR3 in young (3.5 months) and subadult (10 months) axolotls (mean: 8.5 amino acids). However, the CDR3 loop was 1 amino acid longer in 2-year-old adult animals (mean: 9.5 residues). Several pairs of identical VDJ/CDR3 sequences were shared between 3.5-month-old individually analyzed axolotls, or between groups of axolotl of different ages. These identical rearrangements might be provided by the selection of some B-cell clones important for species survival, although the probability that different 3.5-month-old axolotl larvae would produce identical junctions seems very low, considering their limited number of B cells (less than 10(5)). The high frequency of tyrosine residues and the paucity of charged residues in the axolotl CDR3 loops may explain the polyreactivity of natural antibodies, and also clarify why it is so difficult to raise specific antibodies against soluble antigens.

Ambystoma↗
PubMed1997

Economic analyses of phase III cooperative cancer group clinical trials: are they feasible?

Both economic and clinical evaluations of new pharmaceutical agents are important to physicians who practice in the current health care environment. While cooperative cancer groups carry out large-scale phase III clinical evaluations of these agents, few cooperative group studies incorporate economic analyses because of concerns over overburdening of data management, investigators, and statistical center personnel. In this study, we describe the results and operational considerations of one of the first completed economic analyses of a phase III cooperative group trial of the Eastern Cooperative Oncology Group (ECOG). We developed an economic model estimating economic benefits of yeast-derived granulocyte-macrophage colony-stimulating factor (GM-CSF) as adjunct therapy for adult patients (56-70 years) with acute myelogenous leukemia. Clinical data were based on prospectively collected information from a recently reported double-blind phase III multi-institutional study carried out by ECOG. Retrospective economic data were obtained from financial information systems at our hospital, one of the study sites. The cost-minimization analyses were based on the perspective of a third-party payer. Indirect costs related to loss of earnings by patients and caregivers as well as quality-of-life adjustments were not incorporated into the model. Clinical trial results indicated that patients treated with GM-CSF had shorter times to recovery of absolute neutrophil count of 500 cells/mm3 and 1000 cells/mm3 and fewer serious infections than patients who received placebo following induction chemotherapy, while no significant differences were noted in red blood cell and platelet transfusion dependency, toxicities, and duration of hospitalization. The economic model estimated that the group treated with GM-CSF was estimated to have lower costs of care, associated with lower frequencies of serious infections and lower overall infection-related costs. Sensitivity analyses indicated that these results held true over a wide range of estimates of costs and infection rates. Prospective economic analyses of phase III cooperative cancer group clinical trials have not been completed to date. Strategies that are not likely to overburden data managers and statistical center personnel are possible to devise. However, these studies require careful planning and coordination between clinical trialists, economists, and health services researchers.

Adult↗