Search PubMed⌕ Search

Biomedical subjects

P Stanley

Publications and source records attributed to P Stanley.

At least 55 records · Page 3Linked to original sources
PubMed1998

1,2-Benzisothiazol-3-one 1,1-dioxide inhibitors of human mast cell tryptase.

A library of compounds were prepared by reacting 2-(bromomethyl)-1, 2-benzisothiazol-3(2H)-one 1,1-dioxide (5) with commercially available carboxylic acids in the presence of potassium carbonate or a tertiary amine base. From this library, (1,1-dioxido-3-oxo-1, 2-benzisothiazol-2(3H)-yl)methyl N-[(phenylmethoxy)carbonyl]-beta-alanate (7b) emerged as a potent inhibitor of human mast cell tryptase (IC50 = 0.85 microM). Extension of the side chain of 7b by two carbons gave (1, 1-dioxido-3-oxo-1,2-benzisothiazol-2(3H)-yl)methyl 5-[[(phenylmethoxy)carbonyl]amino]pentanoate (7d) which was an 8-fold more potent inhibitor (IC50 = 0.1 microM). Further modification of this series produced benzoic acid derivative (1, 1-dioxido-3-oxo-1,2-benzisothiazol-2(3H)-yl)methyl 4-[[(phenylmethoxy)carbonyl]amino]benzoate (7n) which is the most potent inhibitor identified in this series (IC50 = 0.064 microM). These compounds exhibit time-dependent inhibition consistent with mechanism-based inhibition. For 7b, the initial enzyme velocity is not a saturable function of the inhibitor concentration and the initial Ki could not be determined (Ki > 10 microM). The steady-state rate constant, Ki, was determined to be 396 nM. On the other hand, compounds 7d and 7n are time-dependent inhibitors with a saturable initial complex. From these studies, an initial rate constant, Ki, for 7d and 7n was found to be 345 and 465 nM, respectively. The steady-state inhibition constants, Ki, for 7d and 7n were calculated to be 60 and 52 nM, respectively. Compound 7n is a 13-fold more potent inhibitor than 7b, and these kinetic studies indicate that the increase in inhibitory activity is due to an increase in initial affinity toward the enzyme and not an increase in chemical reactivity. These inhibitors generally show high selectivity for tryptase, being 40-fold weaker inhibitors of elastase, being 100-fold weaker against trypsin, and showing no inhibition against thrombin. These compounds are not inhibitors of thrombin, plasmin t-PA, urokinase, and factor Xa (IC50 > 33 microM). In the delayed-type hypersensitivity (DTH) mouse model, a model of skin inflammation, a 5% solution of 7d reduced edema by 69% compared to control animals.

Animals↗
PubMed1998

The I domain of integrin leukocyte function-associated antigen-1 is involved in a conformational change leading to high affinity binding to ligand intercellular adhesion molecule 1 (ICAM-1).

On T cells the leukocyte integrin leukocyte function-associated antigen-1 (LFA-1) (CD11a/CD18) can be induced to bind its ligand intercellular adhesion molecule 1 (ICAM-1) (CD54) either by increasing the affinity of the receptor with Mg2+ and EGTA or by receptor clustering following activation with phorbol ester. The existence of these two adhesion-inducing pathways implies that alternative mechanisms might exist by which LFA-1 engages ICAM-1. The LFA-1 alpha subunit I domain contains a major binding site for ICAM-1. In this study we show that soluble LFA-1 I domain blocks ICAM-1 binding of the high affinity Mg2+-induced form of LFA-1 but not the phorbol ester-induced form. Under conditions of Mg2+-activation, the soluble I domain also prevents expression of an activation dependent epitope on LFA-1, implying that it inhibits a conformational change necessary for conversion to the high affinity form of this integrin. In addition, the binding of Mg2+-activated LFA-1 to ICAM-1 is blocked by peptides covering the alpha4-beta3 loop, the beta3-alpha5 loop, and the alpha5 helix of the I domain, whereas none of the peptides tested blocks phorbol ester-mediated adhesion. The blocking peptides localize to the same face of the crystal structure of the LFA-1 I domain and define an area that, during activation, may be involved in association of the I domain with another region of LFA-1, potentially the beta-propeller domain. This is the first evidence linking a structural domain of an integrin, in this case the I domain, with a particular activation mechanism.

Amino Acid Sequence↗
PubMed1998

Mammalian cytidine 5'-monophosphate N-acetylneuraminic acid synthetase: a nuclear protein with evolutionarily conserved structural motifs.

Sialic acids of cell surface glycoproteins and glycolipids play a pivotal role in the structure and function of animal tissues. The pattern of cell surface sialylation is species- and tissue-specific, is highly regulated during embryonic development, and changes with stages of differentiation. A prerequisite for the synthesis of sialylated glycoconjugates is the activated sugar-nucleotide cytidine 5'-monophosphate N-acetylneuraminic acid (CMP-Neu5Ac), which provides a substrate for Golgi sialyltransferases. Although a mammalian enzymatic activity responsible for the synthesis of CMP-Neu5Ac has been described and the enzyme has been purified to near homogeneity, sequence information is restricted to bacterial CMP-Neu5Ac synthetases. In this paper, we describe the molecular characterization, functional expression, and subcellular localization of murine CMP-Neu5Ac synthetase. Cloning was achieved by complementation of the Chinese hamster ovary lec32 mutation that causes a deficiency in CMP-Neu5Ac synthetase activity. A murine cDNA encoding a protein of 432 amino acids rescued the lec32 mutation and also caused polysialic acid to be expressed in the capsule of the CMP-Neu5Ac synthetase negative Escherichia coli mutant EV5. Three potential nuclear localization signals were found in the murine synthetase, and immunofluorescence studies confirmed predominantly nuclear localization of an N-terminally Flag-tagged molecule. Four stretches of amino acids that occur in the N-terminal region are highly conserved in bacterial CMP-Neu5Ac synthetases, providing evidence for an ancestral relationship between the sialylation pathways of bacterial and animal cells.

Amino Acid Sequence↗
PubMed1998

Progression of hepatic neoplasms is severely retarded in mice lacking the bisecting N-acetylglucosamine on N-glycans: evidence for a glycoprotein factor that facilitates hepatic tumor progression.

The glycosyltransferase termed GlcNAc-TIII is dedicated to the transfer of a single N-acetylglucosamine (GlcNAc) residue (the bisecting GlcNAc), to a subset of N-glycans in glycoproteins. The addition of this GlcNAc is differentially regulated during development and is induced in certain cancers, particularly in hepatic tumorigenesis. To investigate a functional role for the bisecting GlcNAc in the development of liver cancer, the Mgat3 gene that codes for GlcNAc-TIII, was inactivated by targeted gene disruption, and the susceptibility of Mgat3-/- mice to tumor induction was tested. After a single injection with diethylnitrosamine and subsequent treatment with phenobarbitol for 6 months, Mgat3+/+ and Mgat3+/- mice had grossly enlarged livers that contained numerous tumors. By stark contrast, Mgat3-/- mice had livers of normal size, and only 50% of mice had one to four small tumors. However, histological examination showed that Mgat3-/- livers had significant numbers of basophilic foci, and by 10-12 months after diethylnitrosamine injection, tumors had developed in Mgat3-/- mice. Therefore, initiation occurred in Mgat3-/- mice but progression was severely retarded. Assays for Mgat3 gene expression in tumor tissue gave an unexpected result. In contrast to the situation in the rat, hepatic tumor formation in the mouse was not accompanied by a dramatic increase of GlcNAc-TIII activity nor of glycoproteins with a bisecting GlcNAc, nor of Mgat3 gene expression in tumor tissue from wild-type mice. The data suggest that a glycoprotein factor with the bisecting GlcNAc facilitates tumor progression in liver. In the absence of the bisecting GlcNAc in Mgat3-/- mice, the factor is reduced in activity, and tumor progression is severely retarded.

Acetylglucosamine↗
PubMed1998

Gain-of-function Chinese hamster ovary mutants LEC18 and LEC14 each express a novel N-acetylglucosaminyltransferase activity.

LEC18 and LEC14 cells are gain-of-function glycosylation mutants isolated from Chinese hamster ovary cells for resistance to pea lectin. Structural studies have shown that LEC18 cells synthesize complex N-glycans with a GlcNAc residue linked at the O-6 position of the core GlcNAc (Raju, T. S., Ray, M. K., and Stanley, P. (1995) J. Biol. Chem. 270, 30294-30302), whereas LEC14 cells synthesize complex N-glycans with a GlcNAc residue linked at the O-2 position of the core beta-linked Man residue (Raju, T. S., and Stanley, P. (1996) J. Biol. Chem. 271, 7484-7493). Both modifications are novel and have not been reported in glycoproteins from any other source. We now show that, in both LEC18 and LEC14 cells, GlcNAc transfer is mediated by a distinct N-acetylglucosaminyltransferase (GlcNAc-T) activity. The LEC18 activity, termed GlcNAc-TVIII, transfers GlcNAc to GlcNAcbeta1-O-pNP and to a GlcNAc-terminating, biantennary, complex N-glycan, with or without a core fucose. By contrast, the LEC14 transferase, termed GlcNAc-TVII, does not have significant activity with simple acceptors, and transfers GlcNAc preferentially to a GlcNAc-terminating biantennary glycopeptide that contains a core fucose residue. The acceptor specificities and other biochemical properties of GlcNAc-TVII and GlcNAc-TVIII differ from previously characterized GlcNAc-transferases including GlcNAc-TIII, indicating that they represent new members of the mammalian GlcNAc-T group of transferases.

Acetylglucosamine↗
PubMed1998

The I domain of integrin LFA-1 interacts with ICAM-1 domain 1 at residue Glu-34 but not Gln-73.

Using a solid phase assay, we show that isolated LFA-1 I domain binds ICAM-1 in a Mg2+-dependent manner and is blocked by anti-I domain monoclonal antibodies. This activity mirrors that of the intact receptor (Dransfield, I., Cabañas, C., Craig, A., and Hogg, N. (1992) J. Cell Biol. 116, 219-226) and suggests that the I domain controls divalent cation-dependent receptor function. In ICAM-1, domain 1 residues Glu-34 and Gln-73 have been identified as critical for binding of LFA-1 as an intact receptor (Staunton, D. E., Dustin, M. L., Erickson, H. P., and Springer, T. A. (1990) Cell 61, 243-254). For the first time, we show that isolated I domain binds to domain 1 of ICAM-1 and that this interaction is inhibited partially by mutation of Glu-34 but not by Gln-73. The anti-ICAM-1 monoclonal antibody RR1/1, which maps to Gln-73 (Staunton, D. E., Dustin, M. L., Erickson, H. P., and Springer, T. A. (1990) Cell 61, 243-254), enhances I domain binding, suggesting potential allosteric control or coordinate binding by this region. Finally, I domain binding inhibited by Glu-34 ICAM-1 mutation correlates with divalent cation dependence, indicating that this residue might be in direct contact with the metal ion-dependent adhesion site. Thus, we describe the interaction between the LFA-1 I domain and ICAM-1, an event that controls the function of the intact receptor but includes only part of the complete ligand binding site.

Animals↗
PubMed1998

Hepatobiliary rhabdomyosarcoma in children: diagnostic radiology.

Rhabdomyosarcoma (RMS) occurs infrequently in the liver and biliary tree. Although the radiological diagnosis may be simple when the tumour involves the extrahepatic bile ducts, no specific imaging features are known for hepatic RMS. We present four cases and discuss the role of diagnostic radiology in the management of this tumour.

Biliary Tract Neoplasms↗
PubMed1998

Structuring ward rounds for learning: can opportunities be created?

This paper explores the ways in which ward rounds can be conducted to maximize educational opportunities, as part of a project to improve the effectiveness of on-the-job training (OJT) for hospital doctors. Ninety ward rounds taken by 24 trainers in the Anglia region were observed. Each observation produced a note of the ward round's structure and routines and of the contributions made to it by trainers and trainees. Teaching was a feature of all ward rounds and different types of rounds were valued for different reasons. A range of ward round structures was observed and, within each, a range of routines for conducting the round. Ward round structures fell into four categories, with almost three-quarters of trainers making no use of either pre- or post-round meetings. Where such meetings took place, however, opportunities for OJT were created and, in some cases, optimized through routines to encourage trainee contributions. Discussion time away from patients structured into ward rounds enabled trainers and trainees to take advantage of many opportunities to learn from service. Although unplanned and unsystematic opportunities for OJT do arise, far more reliable are those created through systematic planning and preparation. Trainers have choices to make about how they conduct ward rounds and by choosing to make use of pre- and/or post-ward round sessions, valuable opportunities for OJT can be created.

Education, Medical, Undergraduate↗
PubMed1998

Acylation of Escherichia coli hemolysin: a unique protein lipidation mechanism underlying toxin function.

The pore-forming hemolysin (HlyA) of Escherichia coli represents a unique class of bacterial toxins that require a posttranslational modification for activity. The inactive protoxin pro-HlyA is activated intracellularly by amide linkage of fatty acids to two internal lysine residues 126 amino acids apart, directed by the cosynthesized HlyC protein with acyl carrier protein as the fatty acid donor. This action distinguishes HlyC from all bacterial acyltransferases such as the lipid A, lux-specific, and nodulation acyltransferases, and from eukaryotic transferases such as N-myristoyl transferases, prenyltransferases, and thioester palmitoyltransferases. Most lipids directly attached to proteins may be classed as N-terminal amide-linked and internal ester-linked acyl groups and C-terminal ether-linked isoprenoid groups. The acylation of HlyA and related toxins does not equate to these but does appear related to a small number of eukaryotic proteins that include inflammatory cytokines and mitogenic and cholinergic receptors. While the location and structure of lipid moieties on proteins vary, there are common effects on membrane affinity and/or protein-protein interactions. Despite being acylated at two residues, HlyA does not possess a "double-anchor" motif and does not have an electrostatic switch, although its dependence on calcium binding for activity suggests that the calcium-myristoyl switch may have relevance. The acyl chains on HlyA may provide anchorage points onto the surface of the host cell lipid bilayer. These could then enhance protein-protein interactions either between HlyA and components of a host signal transduction pathway to influence cytokine production or between HlyA monomers to bring about oligomerization during pore formation.

Acyl Carrier Protein↗
PubMed1998

Familial occurrence of an arteriovenous fistula with a giant perimedullary pseudoaneurysm of the thoracic spinal cord in 2 young siblings.

Two siblings, a sister at age 3 years and a brother (15 years later) at 4 years of age, both presented with similar clinical pictures consisting of back pain, progressive gait difficulty, lower extremity weakness and hyperreflexia. Imaging studies in both cases showed the presence of a perimedullary mass with expansion of the bony spinal canal at T10-T12. Angiography demonstrated almost identical vascular lesions that in each case was being fed by a single left-sided T8 fistulous vessel that expanded into a giant perimedullary venous pseudoaneurysm. Each malformation was successfully obliterated using endovascular techniques, balloon occlusion of the feeding vessel in the first case and coil embolization of the pseudoaneurysm in the second. Following treatment the neurologic deficits resolved in both patients. These young siblings represent the first known case of familial occurrence of very similar giant perimedullary venous pseudoaneurysms of the thoracic spinal cord.

Adolescent↗
PubMed1998

Survival and prognostic factors following radiation therapy and chemotherapy for ependymomas in children: a report of the Children's Cancer Group.

OBJECT: Ependymomas in children continue to generate controversy regarding their histological diagnosis and grading. optimal management, and possible prognostic factors. To increase our knowledge of these tumors the authors addressed these issues in a cohort of children with prospectively staged ependymomas treated with radiotherapy and chemotherapy. METHODS: Children between the ages of 2 and 17.3 years harboring an intracranial ependymoma confirmed by a central review of the tumor's pathological characteristics were treated according to Children's Cancer Group Protocol 921 from 1986 to 1992. Treatment following surgery and postoperative tumor staging (including brain computerized tomography or magnetic resonance [MR] imaging, spinal MR imaging or myelography, and cerebrospinal fluid cytological investigation) included craniospinal irradiation with a local boost to the primary tumor and patient randomization to receive adjuvant chemotherapy with either 1) CCNU, vincristine, and prednisone, or 2) the eight-drugs-in-1-day regimen. Centralized review of the tumor pathological characteristics revealed 20 ependymomas and 12 anaplastic ependymomas in the 32 children included in the study. Diagnoses made at the individual institutions included anaplastic (malignant) ependymoma (15 patients), ependymoma (four patients), ependymoblastoma (nine patients), ependymoastrocytoma (one patient), and primitive neuroectodermal tumor (three patients), which were discordant with the centralized review diagnosis in 22 of 32 cases. Only three of the 32 patients had metastatic disease (two with M and one with M3 stages). At surgery, 47% of tumors were estimated to be totally resected. Among the 14 of 17 patients who suffered a relapse and were evaluated for site of relapse, 10 (71%) had an isolated local relapse, three (21%) had concurrent local and metastatic relapse, and only one (7%) had an isolated metastatic relapse. Kaplan-Meier estimates of 5-year progression-free survival (PFS) and overall survival rates were 50 +/- 10% and 64 +/- 9%, respectively. CONCLUSIONS: Predictors of PFS duration included an estimate of the extent of resection made at surgery (total compared with less than total, p = 0.0001) and the amount of residual tumor on postoperative imaging as verified by centralized radiological review (< or = 1.5 cm2 compared with > 1.5 cm2, p < 0.0001). No other factors, including centrally reviewed tumor histopathological type, location, metastasis and tumor (M and T) stages, patient age, race, gender, or chemotherapy treatment regimen significantly correlated with PFS duration. The pattern of predominantly local relapse and the important influence of residual tumor or the extent of resection on PFS duration confirms a prevailing impression that local disease control is the major factor in the prediction of outcome of ependymoma. Survival rates were comparable with those reported by other investigators who have treated patients with similar doses of radiation and no chemotherapy.

Adolescent↗
PubMed1997

Complex N-glycans in Mgat1 null preimplantation embryos arise from maternal Mgat1 RNA.

Mice with a null mutation in the Mgat1 gene lack N-acetyl-glucosaminyltransferase I (GlcNAc-TI; EC 2.4.1.101), and die at mid-gestation. This result suggested that development of Mgat1-/- blastocysts and their implantation could occur in the absence of complex and hybrid N-glycans. However, inner cell mass of all blastocysts from several Mgat1 +/- heterozygous crosses bind the lectin E-PHA, indicating that Mgat1 null mutant blastocysts are able to synthesize complex N-glycans (Campbell et al., (1995) Glycobiology, 5, 535-543). In order to directly test this hypothesis, Mgat1-/- blastocysts were positively identified by polymerase chain reaction (PCR) of genomic DNA. Reverse transcriptase PCR (RT-PCR) of RNA isolated from the same blastocysts, and restriction analysis of the PCR products, revealed that Mgat1 null blastocysts contained Mgat1 RNA derived from the wild-type Mgat1 gene. Consistent with this, all 3.5 day blastocysts from five heterozygous crosses bound the lectin L-PHA, a lectin previously shown not to bind to E8.5 or E9.5 Mgat1-/- embryos that lack complex N-glycans (Ioffe and Stanley (1994) Proc. Natl. Acad. Sci., USA, 91, 728-732). Blastocysts of 4.5 days postcoitum (dpc) obtained by culturing 3.5 dpc blastocysts also bound L-PHA. However, mutant embryos that did not bind L-PHA were present among progeny from E5.5 onward. Therefore, the effects of the Mgat1 null mutation are not operative until sometime between implantation and E5.5, due to the continued presence of maternally derived Mgat1 mRNA in preimplantation embryos.

Animals↗
PubMed1997

BMS-190394, a selectin inhibitor, prevents rat cutaneous inflammatory reactions.

Selectin binding is the first step in extravasation of leukocytes through the endothelium. Infiltration of leukocytes is a hallmark of an inflammatory response. Blockade of selectin-dependent adhesion, therefore, represents a specific mechanism-based anti-inflammatory strategy. We have used the natural product sulfatide, one of the selectin ligands, as a template to design a novel selectin antagonist. BMS-190394, a structural analog of sulfatide, is an inhibitor of cell binding to P-, E- and L-selectin-Ig fusion proteins. BMS-190394 also inhibits binding mediated by native P-selectin expressed on the surface of activated platelets. Pharmacokinetic analysis of BMS-190394 showed that the compound remained in circulation with a T1/2 of 7 hr, long enough to inhibit the development of an acute inflammatory response. The in vitro activity and pharmacokinetic profile of this selectin-blocking compound led to the determination of its in vivo anti-inflammatory activity. BMS-190394 was a potent inhibitor of the dermal immune complex-induced reverse passive Arthus reaction in rats when delivered by the i.v. or i.p. route. The ED50 of the compound in the reverse passive Arthus reaction compares favorably to that for dexamethasone. BMS-190394 was also an effective inhibitor of the delayed-type hypersensitivity reaction in the rat. Compared with previous reports of the use of antibodies and complex oligosaccharides to inhibit the activity of the selectins, this low-molecular-weight inhibitor of the selectins presents a novel class of anti-inflammatory agents.

Animals↗
PubMed1996

A comparison of the fine saccharide-binding specificity of Dioclea grandiflora lectin and concanavalin A.

The lectin from the seeds of Dioclea grandiflora (DGL) is a Man/Glc-specific tetrameric protein with physical and saccharide-binding properties reported to be similar to that of the jack bean lectin concanavalin A (ConA). Unlike other plant lectins, both DGL and ConA bind with high affinity to the core trimannoside moiety, 3,6-di-O-(alpha-D-mannopyranosyl)-alpha-D-mannopyranoside, which is present in all asparagine-linked carbohydrates. In the present study, hemagglutination inhibition techniques have been used to investigate binding of DGL and ConA to a series of mono- and dideoxy analogs of methyl 3,6-di-O-(alpha-D-mannopyranosyl)-alpha-D-mannopyranoside and to a series of asparagine-linked oligomannose and complex oligosaccharides and glycopeptides. The results indicate that both DGL and ConA recognize epitopes on all three residues of the trimannoside: the 3-, 4-, and 6-hydroxyl groups of the alpha(1-6)Man residue, the 3-hydroxyl group of the alpha(1-3)Man residue, and the 2- and 4-hydroxyl groups of the central Man residue of the core trimannoside. However, unlike ConA, DGL does not bind to biantennary complex carbohydrates. This was confirmed by showing that biantennary complex glycopeptides do not bind to a DGL-Sepharose affinity column. Unlike ConA, DGL does not show enhanced affinity for a large N-linked oligomannose carbohydrate (Man9 glycopeptide) relative to the trimannoside. Thus, DGL and ConA share similar epitope recognition of the core trimannoside moiety. However, they exhibit differences in their fine specificities for larger N-linked oligomannose and complex carbohydrates.

Carbohydrate Conformation↗
PubMed1996

A point mutation causes mistargeting of Golgi GlcNAc-TV in the Lec4A Chinese hamster ovary glycosylation mutant.

The Lec4A and Lec4 Chinese hamster ovary glycosylation mutants lack N-linked glycans with GlcNAcbeta(1,6)Manalpha(1,6) branches that are initiated by the transferase termed GlcNAc-TV. Detergent extracts of Lec4 cells have no detectable GlcNAc-TV activity, but Lec4A extracts have activity equivalent to that of parental Chinese hamster ovary cells. This discrepancy occurs because Lec4A GlcNAc-TV activity co-localizes with membranes of the endoplasmic reticulum (ER) instead of with Golgi membranes (Chaney, W., Sundaram, S., Friedman, N., and Stanley, P. (1989) J. Cell. Biol. 109, 2089-2096). cDNAs from the coding region of the GlcNAc-TV gene have now been isolated from each mutant line. Lec4 GlcNAc-TV cDNA was found to possess two insertions, the first of which shifts the open reading frame and codes for a truncated transferase missing 585 amino acids from the catalytic domain. By contrast, Lec4A GlcNAc-TV cDNA possesses a single point mutation from T to G, which results in a change from Leu to Arg at position 188. When transfected into Lec4 cells, both cDNAs gave the appropriate phenotype; Lec4 cDNA was unable to restore GlcNAc-TV activity, whereas Lec4A cDNA converted Lec4 cells to the Lec4A phenotype, with an active GlcNAc-TV mislocalized to ER membranes. Moreover, Lec4A cDNA cured of its mutation restored a functional, Golgi-localized GlcNAc-TV to Lec4 cells. The results demonstrate that a single change in the 740 amino acids of GlcNAc-TV serves to functionally inactivate the transferase in an intact cell by causing it to localize to the ER instead of the Golgi compartment. The mislocalized transferase retains full enzyme activity, showing that it is well folded and stable and suggesting that the L188R mutation either prevents association with exit complexes from the ER or causes retrograde transport from a Golgi compartment.

Amino Acid Sequence↗
PubMed1996

Essential role for complex N-glycans in forming an organized layer of bronchial epithelium.

Mice lacking the complex subset of N-glycans due to inactivation of the Mgat1 gene die at mid-gestation, making it difficult to identify specific biological functions for this class of cell surface carbohydrates. To circumvent this embryonic lethality and to uncover tissue-specific functions for complex N-glycans, WW6 embryonic stem cells with inactivated Mgat1 alleles were tracked in chimeric embryos. The Mgat1 gene encodes N-acetylglucosaminyltransferase I (Glc-NAc-TI; EC 2.4.1.101), the transferase that initiates the synthesis of complex N-glycans. WW6 cells carry an inert beta-globin transgene that allows their identification in chimeras by DNA-DNA in situ hybridization. Independent Mgat1-/- and Mgat1+/- mutant WW6 isolates contributed like parent WW6 cells to the tissues of embryonic day (E) 10.5 to E16.5 chimeras. However, a cell type-specific difference was observed in lung. Homozygous null Mgat1-/- WW6 cells did not contribute to the epithelial layer in more than 99% bronchi. This deficiency was corrected by transfection of a Mgat1 transgene. Interestingly, heterozygous Mgat1+/- WW6 cells were also deficient in populating the layer of bronchial epithelium. Furthermore, examination of lung bud in E9.5 Mgat1-/- mutant embryos showed complete absence of an organized epithelial cell layer in the bronchus. Thus, complex N-glycans are required to form a morphologically recognizable bronchial epithelium, revealing an in vivo, cell type-specific function for this class of N-glycans.

Animals↗
PubMed1996

Comparison of preoperative selective spinal angiography and somatosensory-evoked potential monitoring with temporary occlusion of segmental vessels during anterior spinal surgery.

STUDY DESIGN: The results of preoperative selective spinal angiography were compared with intraoperative occlusion of segmental arteries and somatosensory-evoked potential monitoring during anterior spinal surgery. OBJECTIVES: To determine if temporary occlusion of major radicular vessels supplying the spinal cord would result in intraoperative somatosensory-evoked potential changes. SUMMARY OF BACKGROUND DATA: Temporary occlusion of segmental spinal arteries with concomitant somato-sensory-evoked potential monitoring has been used during anterior spinal surgery to avoid intraoperative vascular paraplegias caused by permanent ligations of vessels critical to the blood supply of the spinal cord. METHODS: Preoperative selective spinal angiography was performed in 16 patients to identify important radicular arteries supplying the spinal cord. At the time of anterior spinal surgery, temporary occlusion of segmental vessels was accomplished with somatosensory-evoked potential monitoring. RESULTS: Thirty-two radicular arteries were identified by arteriography in 16 patients. Temporary occlusion of nine segmental arteries in the surgical field supplying these radicular vessels resulted in no somatosensory-evoked potential changes. CONCLUSIONS: The lack of somatosensory-evoked potential changes after temporary occlusion of segmental arteries from which radicular arteries supply the spinal cord demonstrates sufficient perimedullary collateral circulation in that area of the spinal cord.

Adolescent↗