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M Lezzi

Publications and source records attributed to M Lezzi.

At least 37 records · Page 2Linked to original sources
PubMed1986

Low degree of ubiquitination of histone 2A in the dipteran Chironomus tentans.

A polyclonal antibody to ubiquitin has been prepared and shown to react with both ubiquitin and ubiquitinated histone 2A (uH2A). Applying this antibody in Western blotting experiments, we have observed that the salivary glands of Chironomus tentans contain an unusually low amount of uH2A (1% of histone 2A), while the amount of free ubiquitin is as abundant as in other animal cells, e.g. HeLa cells. The same low content of uH2A was also found in diploid epidermal cells of Chironomus origin suggesting that the low amount is not a characteristic of the polytene state of chromatin in salivary gland cells but rather a property of C. tentans as a species. The significance of the low degree of ubiquitination is discussed in relation to the information available on the organization of Chironomus chromatin into unusually large chromomeric entities.

Animals↗
PubMed1985

Two genes in Balbiani ring 2 with metabolically different 75S transcripts.

Balbiani ring 2 (BR2) in salivary glands of Chironomus pallidivittatus and C. tentans (two sibling species of the subgenus Camptochironomus) is a favoured model system for studies of gene organization and transcript formation. Here we show that BR2 is more complex than hitherto believed, containing two 75S RNA-producing genes, BR2a and BR2b, present in different 35-40 kb blocks of DNA. The transcripts hybridizing to two different repeat units originating in BR2 differ in size. Further support for the presence of two genes comes from RNA studies during experimentally induced BR2 regression. The amounts of BR2a RNA per cell remain more or less constant throughout the course of the experiment, whereas the BR2b RNA decreases considerably. Under normal conditions there is 5-6 times more BR2a RNA than BR2b RNA. This ratio increases 3-fold under experimental conditions. BR2a and BR2b, although partially homologous, contain repeat units with characteristic differences. BR2a contains a repeat unit that is much more similar to a BR1 repeat than it is to the BR2b repeat. The possibility is discussed that a Balbiani ring in general represents an integrated set of active genes rather than a singe gene.

Journal Article↗
PubMed1984

Bacterial meningitis in Johannesburg--1980-1982.

A 2-year retrospective study of aetiology, age distribution, seasonal variation and antimicrobial sensitivity patterns of bacteria isolated from patients with meningitis in five Johannesburg hospitals for White, Black, Coloured and Asian patients was performed. Neisseria meningitidis was isolated most frequently, followed by Streptococcus pneumoniae, Haemophilus influenzae, Escherichia coli and Streptococcus group B. In the Black population 73% of the meningococcal infections occurred in patients over 3 years of age, and the majority of these infections were caused by serogroup A organisms. Virtually all (93%) of the H. influenzae infections occurred in children of less than 3 years of age. Of the isolates tested, 16% of the meningococci, 4,5% of the H. influenzae and 47% of the pneumococci were resistant to sulphadiazine, ampicillin and penicillin respectively.

Adolescent↗
PubMed1984

Chromatin structure of a hyperactive secretory protein gene (in Balbiani ring 2) of Chironomus.

We examined the chromatin structure of a Balbiani ring (secretory protein gene) in the salivary glands of Chironomus larvae in its hyperactive state after stimulation with pilocarpine. For the inactive state of the gene an established tissue culture cell line, not expressing the gene, was used. Electron microscopy showed an RNA polymerase density of approximately 38/microns. Micrococcal nuclease digestion of purified nuclei followed by DNA transfer and hybridization revealed a smear with no recognizable discrete DNA fragments. Without pilocarpine stimulation a faint nucleosomal repeat was superimposed upon the smear, and in tissue culture cells a clear nucleosomal repeat was revealed. The restriction enzyme XbaI, which has a 6-bp recognition sequence, cut the gene in the hyperactive chromatin state, but not in its inactive conformation. The combined results are best explained by the absence of most of the nucleosomes in this hyperactive RNA polymerase II transcribed gene.

Animals↗
PubMed1983

The activity of Balbiani rings 1 and 2 in salivary glands of Chironomus tentans larvae under different modes of development and after pilocarpine treatment.

The activity of the Balbiani rings 1 and 2 (BR1 and BR2) in the salivary gland was followed during development of fourth instar larvae of Chironomus tentans under different modes of development, with or without a previous pilocarpine treatment. The activity was determined in parallel by two different methods, by incorporation of [3H]uridine into BR-RNA (75 S) and by morphometry of BR1 and of BR2. In glands of untreated larvae BR2 does not change dramatically except for a depression of activity during oligopause (resting phase). BR1 is completely inactive during this phase but exhibits a pronounced activity maximum in the middle of the prepupal period, in subitaneously developing (i.e., uninterrupted) as well as in postoligopause cultures. After pilocarpine treatment the activity of BR2 (rather than of BR1) is generally increased. The extent of this stimulation, however, is strongly development dependent. A most striking activity difference is observed in postoligopause between animals of stage 5 and of stage 6. The relationship between BR2 activity and degree of emptying of the salivary gland lumen was investigated. A model is proposed in which BR2 activity is conceived as being regulated by two parameters: by the degree of filling of the gland lumen and by the stage and mode of development of the larva.

Age Factors↗
PubMed1982

Isolation of DNA from single microsurgically excised bands of polytene chromosomes of Chironomus.

A method is described for excising by a glass knife single bands of isolated polytene chromosomes of the salivary glands of Chironomus tentans larvae. DNA strands were isolated from cut-out bands and their contour lengths were determined on electron micrographs. The mean contour length of DNA strands isolated from the double band I-8A was about twice that of the single band I-11B, namely 63 versus 34 micrometers. The described method may be applicable for molecular studies on single bands (e.g., by DNA cloning).

Animals↗
PubMed1982

Ultrastructural studies of Chironomus salivary gland cells in different states of Balbiani ring activity.

Chironomus tentans fourth instar larvae were awakened from oligopause (diapause) and treated with pilocarpine to stimulate Balbiani ring transcriptional activity. Salivary glands were fixed, sectioned and examined by conventional and stereo-electron microscopy. Balbiani ring RNP lateral fiber densities were measured in well-formed regions with clear Balbiani ring granules arranged along chromatin transcription axes. Despite an up to ten-fold range in Balbiani ring transcriptional activity [10, 12, 14], we observed no significant difference in lateral fiber densities. These data are discussed in terms of the variety of mechanisms for modulating overall transcriptional activity, including recruitment of parallel transcription units in the polytene chromosome. The lack of other major ultrastructural changes at the nuclear envelope and within the domains of tubular rough endoplasmic reticulum argue strongly against a major dismantling of subcellular structure during the induced oligopause.

Animals↗
PubMed1981

Heat shock phenomena in Chironomus tentans I. In vivo effects of heat, overheat, and quenching on salivary chromosome puffing.

Incubation of 4th instar larvae of Chironomus tentans at elevated temperatures leads in salivary and Malpighian chromosomes to the appearance of 4-5 new puffs. Previously present puffs, particularly Balbiani rings in salivary chromosomes, become drastically reduced. The reactions of region IV-5C and Balbiani ring 1 and 2 in salivary glands are quantitatively analyzed. Statistically significant heat shock effects are observed already after 5 min and reach a maximum between 30 and 60 min. The effective temperature range is small (between 33 to 40 degrees C) with an optimum at 37 degrees C. Above 40 degrees C, i.e., at overheat shock temperatures, heat shock reactions are suppressed. Larvae heat or overheat shocked for 1-7 h or 15-30 min, respectively, survive when returned to normal culturing temperatures. The recovery from heat shock of the puffing pattern occurs in two phases: a fast one (10-20 min) and a slow one (up to 5 h) sometimes separated by a period of backlash. Quenching of overheat shocked larvae does not result in a delayed heat shock reaction.

Animals↗
PubMed1979

A gravimetric system for lyophilized samples in the sub-microgram range.

A new quartz fiber balance is described which is evacuated and electrically shielded. This balance minimizes the problems of moisture uptake by the lyophilized sample, air convection inside the balance and static electricity. Besides it offers a wider useful weighing range and a higher handling comfort. It could be shown that in the regular (i.e. not evacuated) balance the moisture uptake varies considerably with the humidity of the air and with the kind of sample analyzed, and that it might be greater than previously reported.

Animals↗
PubMed1979

Elemental analysis of solid microscopic samples in the flameless atomic absorption cuvette.

Solid microscopic samples are precisely located by means of a newly developed applicator under microscopic control in the center of a flameless graphite tube cuvette. The parts of the applicator that reach into the cuvette are made of quartz which can be cleaned by heating. The values for the K and Na content of samples such applied are highly reproducible. No contamination could be detected. Solid samples yield higher signals than liquid samples. A method of calibration is described which uses lyophilized pieces of egg albumin containing known amounts of K and Na as standards.

Animals↗
PubMed1979

Change in nuclear potassium electrochemical activity and puffing of potassium-sensitive salivary chromosome regions during Chironomus development.

Changes in nuclear K+ electrochemical activity and total nuclear K+ content in salivary glands of Chironomus tentans were measured with ion-selective microelectrodes based on valinomycin and with flameless atomic absorption spectrometry, respectively. The K+ activity increased by a factor of 2.6 and the total K+, by a factor of 1.5 as oligopausing larvae developed into prepupae. The extent of decondensation (puffing) of K+-sensitive regions in the polytene chromosomes underwent a parallel increase during this developmental event. In vitro culture of glands from oligopausing larvae resulted in similar changes with respect to nuclear K+ activity and puffing.

Animals↗
PubMed1977

Mass isolation ofpolytene nuclei from Chironomus salivary glands.

In this paper we describe a method for the rapid mass isolation of polytene nuclei from Chironomus salivary glands. The procedure for the isolation of glands involves 5 principal steps; (a) freezing Chironomus larvae in liquid propane; (b) breaking open frozen animals in a pre-cooled mortar; (c) thawing the fragments in sucrose medium, free of divalent cations; (d) pressing the suspension of broken animals through a system of regularly spaced capillary constrictions of free organs; and (e) enrichment of glands by differential sedimentation and removal of contaminating material under a dissecting microscope. The nuclear isolation procedure is a large scale modification of a method previously described by Robert, using digitonin as a non-ionic detergent to solubilize cytoplasma and secretion without affecting the nuclear membrane. Nuclei obtained by this method show structural integrity and an unchanged chromosomal banding pattern. Their incorporation of UTP is within the same range as reported by other authors for nuclei by hand dissection.

Animals↗
PubMed1976

Correlated changes of Balbiani ring expansion and secretory protein synthesis in larval salivary glands of Chironomus tentans.

Salivary glands of various stages of the last larval instar of Chironomus tentans were quantitatively analyzed with respect to the expansion of their Balbiani rings (B1, B2, B3) by a fast green staining procedure as well as to the rate of synthesis of their secretory proteins (S1, S2, S3) by a scintillation counting procedure of electrophoretic fractions. The extent of expansion of B1, B2 and B3 correlates positively with the rate of synthesis of S3, S2 and S1, respectively. With B1 and S3 these parameters undergo a parallel and developmentally specific change being rather depressed in intermolt, and particularly in diapausing animals.

Animals↗