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Biomedical subjects

A Ben-Zvi

Publications and source records attributed to A Ben-Zvi.

17 recordsLinked to original sources
PubMed1992

A stable Escherichia coli-Mycobacterium smegmatis plasmid shuttle vector containing the mycobacteriophage D29 origin.

A plasmid shuttle vector for Escherichia coli and mycobacteria was constructed from an E. coli plasmid containing the ColE1 origin, a 2.6-kb PstI fragment from bacteriophage D29 that grows in numerous mycobacterial species, and the kanamycin resistance gene either of Tn903 or of Tn5. The resultant plasmid is 7.63 kb and can be introduced via transformation into Mycobacterium smegmatis with high efficiency. In M. smegmatis the plasmid is stable and apparently present in multiple copies. Bioluminescence (luxA and luxB of Vibrio harveyi and fischeri) has been expressed in M. smegmatis from the aminoglycoside transferase promoter of Tn5. The D29 fragment should carry an origin of replication and some associated genes that act on it since various mutations destroy the ability of this fragment to replicate in M. smegmatis. The fragment was localized on the D29 genome map.

DNA Transposable Elements↗
PubMed1991

Citrate synthase from Mycobacterium smegmatis. Cloning, sequence determination and expression in Escherichia coli.

A Mycobacterium smegmatis PstI library was constructed by cloning these fragments downstream from the lac promoter of the expression vector pHG171. Three identically sized clones were isolated by complementation of an Escherichia coli strain (chi 2338) deficient in citrate synthase. One insert (pBL265) was used in hybridization experiments with DNA from E. coli and M. smegmatis and it was demonstrated that the clones were indeed from M. smegmatis. The transcription of the M. smegmatis citrate synthase gene in E. coli relied upon the lac promoter. In translation experiments performed in vitro pBL265 gave rise to a novel protein of about 42 kDa. This band was not seen in 'opposite-orientation' subclones. Various subclones in which the 5'-end was shortened nevertheless complement E. coli chi 2338 and produce the 42 kDa protein. This demonstrates that the M. smegmatis citrate synthase gene uses its own ribosome-binding site in E. coli. The relevant 1.8 kb of the 2.8 kb insert was sequenced. A consensus E. coli ribosome-binding site was found centred precisely 10 bp upstream of the methionine codon. Other interesting features revealed by the sequence are discussed. Citrate synthase activity was assayed in vitro and the mycobacterial enzyme was found to be similar to those of the Gram-positive bacteria.

Amino Acid Sequence↗
PubMed1989

Use of an autologous reaction in vitro to assess contributions of T and B lymphocytes to immune hyperreactivity of atopics.

The in-vitro proliferation reaction of peripheral blood lymphocytes (measured by [3H]thymidine incorporation) to autologous pokeweed mitogen (PWM)-induced lymphoblasts (PWM-lymphoblast-stimulated autologous mixed leucocyte reaction, PWM.AMLR) was used as a measure of immune hyperreactivity for comparison of atopic with non-atopic individuals. Accordingly, 10/24 non-atopics responded in the PWM.AMLR, and 19/19 atopics reacting to inhaled allergens responded. Autologous stimulation was associated with release of mitogenic factors from the PWM-activated stimulating cells (2/15 non-atopics, 9/15 atopics). For non-atopics, stimulation delivered by staphylococcus A (SAC)-activated cells was similar to that delivered by PWM-induced cells, while in atopics, the SAC.AMLR was never more than 50% of the PWM.AMLR, indicating a possible T cell component. Separation by panning of the stimulation cells into lymphocyte subsets supported the notion that stimulation involved a cooperation between B and T4+ T cells. It is proposed that a positive PWM.AMLR is dependent upon an initial B cell activation followed by the PWM stimulus dependent upon a previous T cell activation, where atopics have more lymphocytes in an activated state than healthy non-atopics. Such a baseline priming may contribute to an innate sensitivity of atopics to environmental allergens.

Adolescent↗
PubMed1987

Actin filament localization in developing and pathologic human corneas.

Actin is associated with motility, cell morphology, and cell-substrate adhesion. The molecular probe NBD phallacidin, which reacts with filamentous actin, was used to study the distribution of actin filaments in the corneal and conjunctival epithelium, stroma, and endothelium. Frozen sections of human fetal eyes from 8 weeks to 40 weeks of gestation were reacted with NBD phallacidin. Pathologic tissues included keratoplasty specimens from patients with hereditary posterior polymorphous corneal dystrophy (PPMD) and surgically excised tissues removed for treatment of epithelial down-growth. Normal human cornea was used as a control. Immunofluorescent staining disclosed actin filament distribution in corneal epithelium as early as 9-10 weeks of gestation. Staining increased with maturation until term. Adult human corneal epithelium showed more pronounced staining of the surface layers. Stromal staining was more extensive in earlier stages of gestation and decreased in later stages of gestation, after 20-21 weeks. In pathologic corneas with posterior polymorphous dystrophy, there was localization of actin, as well as keratin, in the abnormal epithelial-like layers lining the posterior cornea. In epithelial downgrowth, actin and keratin were demonstrated in multilayered squamous epithelium on the anterior iris surface. Actin appears to be involved in migration of corneal epithelial and endothelial cells.

Actin Cytoskeleton↗
PubMed1987

Suprabasal expression of a 64-kilodalton keratin (no. 3) in developing human corneal epithelium.

We have previously shown that a basic 64-kilodalton (no. 3 in the catalog of Moll et al.) and an acidic 55-kilodalton (no. 12) keratin are characteristic of suprabasal cell layers in cultured rabbit corneal epithelial colonies, and therefore may be regarded as markers for an advanced stage of corneal epithelial differentiation. Moreover, using an AE5 mouse monoclonal antibody, we showed that the 64-kilodalton keratin marker is expressed suprabasally in limbal epithelium but uniformly (basal layer included) in central corneal epithelium, suggesting that corneal basal cells are in a more differentiated state than limbal basal cells. In conjunction with previous data implicating the centripetal migration of corneal epithelial cells, our data support a model of corneal epithelial maturation in which corneal epithelial stem cells are located in the limbus, the transitional zone between the cornea and conjunctiva. In the present study, we analyzed the expression of the 64-kilodalton keratin in developing human corneal epithelium by immunohistochemical staining. At 8 weeks of gestation, the presumptive corneal epithelium is composed of a single layer of cuboidal cells with an overlying periderm; neither of these cell layers is AE5 positive. At 12-13 weeks of gestation, some superficial cells of the three- to four-layered epithelium become AE5 positive, providing the earliest sign of overt corneal epithelial differentiation. At 36 weeks, although the epithelium is morphologically mature (four to six layers), AE5 produces a suprabasal staining pattern, this being in contrast to the adult epithelium which exhibits uniform staining.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1986

Immunohistochemical characterization of extracellular matrix in the developing human cornea.

Collagen, fibronectin and laminin are important components of the extracellular matrix of the human cornea. We used the immunofluorescence technique with polyclonal antibodies directed against these proteins and to bullous pemphigoid antigen (BPA), in order to study their distribution in human corneas from 8 weeks of gestation to term and in adult corneas. Immunoreactivity was observed with antibodies to type I collagen in the limbus and the corneal stroma at 8 weeks of gestation. At 11 weeks of gestation it was found in epithelial basement membrane (EBM) and Descemet's membrane (DM) and continued thus throughout fetal and adult life. Type II collagen was not detected in fetal or adult cornea. Type III collagen was detected during 8-20th weeks of gestation in the EBM, DM and stroma. After 27th weeks of gestation, type III collagen could no longer be detected in the central cornea. Type IV collagen was detected in the EBM as early as 8 weeks of gestation and remained positive throughout fetal and adult life. Descemet's membrane was negative for type IV collagen at 8 weeks of gestation and became positive thereafter. Immunostaining for fibronectin in DM was negative at 8 weeks of gestation, followed by patchy staining of corneal stroma and EBM up to the age of 37 weeks of gestation. Staining in the EBM was negative or variable up to 70 years of age, and then became positive again in a 77 year old individual. Staining for LN was positive in the EBM after 8 weeks of gestation. Staining was negative in DM at that age, but became positive after 9 weeks of gestation. Staining for BPA was negative at 8-9 weeks of gestation, then gradually became positive.

Antibodies↗
PubMed1978

Disseminated Herpes simplex virus infection in ataxia-telangiectasia.

The clinical and pathological features are described in a child with ataxia-telangiectasia, complicated by fatal disseminated herpes simplex virus infection. Herpes simplex virus was isolated from the patient's blood, and the histopathological findings in the skin, liver and adrenals were consistent with herpes simplex virus infection. The patient had a combined immune deficiency state, as a part of the ataxia-telangiectasia syndrome. She had imparied cellular immune response to herpes simplex virus and developed no antibodies against the virus. To our knowledge, this is the first fatal case of disseminated herpes simplex virus infection in ataxiatelangiectasia.

Ataxia Telangiectasia↗
PubMed1976

Familial iminoglycinuria with normal intestinal absorption of glycine and imino acids in association with profound mental retardation, a possible "cerebral phenotype".

Spasticity and severe psychomotor retardation in a 2-year-old girl, apparently in expression of chronic progressive encephalopathy, was found in association with prolinuria, hydroxyprolinuria and hyperglycinuria. The pattern and levels of these amino acids in plasma proved to be normal, however, as was their intestinal absorption as well as their concentration in cerebrospinal fluid. The proband appears to be homozygous for iminoglycinuria with an apparent inborn defect of the renal tubular transport system specific to these amino acids. An isolated hyperglycinuria, however, was traced in several obligate heterozygotes in this family. The possibility of a more direct causative link between this anomaly and her clinical manifestations is discussed. Where instances of iminoglycinuria occur in association with cerebral pathology of this type, an analogous impairment of a correspondingly specific cerebral amino acid transport system is postulated.

Amino Acid Metabolism, Inborn Errors↗