George Miloshev

Application of the single cell gel electrophoresis on yeast cells.

In the present paper, we have applied the single cell gel electrophoresis (SCGE) assay on yeast cells treating Saccharomyces cerevisiae cells with hydrogen peroxide and methyl methanesulfonate (MMS), two DNA damaging agents. In order to overcome the problem with the yeast cell wall that prevented DNA to be extended by the electric field, we disintegrated the cell wall after embedding the cells in agarose. A characteristic picture of comets with residual nuclei and tails was observed and the length of the comet tails was dependent on the concentration of the damaging agents. Yeast cells developed comets at concentrations at least 10 times lower than the concentrations at which comets begin to appear in mammalian cells after treatment with the two genotoxic agents. The higher sensitivity of the yeast comet assay and the fact that S. cerevisiae is one of the most thoroughly studied and easy to work with eukaryotic model system suggest that the proposed method could be an useful tool for investigation of the DNA damaging activity of potential genotoxins.

The nuclear actin-related protein Act3p/Arp4 influences yeast cell shape and bulk chromatin organization

ACT3/ARP4 is an essential gene, coding for the actin‐related protein Act3p/Arp4 of Saccharomyces cerevisiae located within the nucleus. Act3p/Arp4 is a stoichiometric component of the NuA4, INO80, and SWR1 chromatin modulating complexes, and recruits these complexes onto chromatin for their proper chromatin functions. Mutated Act3p/Arp4 leads to impairment of the functions of these complexes and affects transcription of specific genes. Our results revealed significant disorder in the cell size and shape of act3/arp4 mutant cells, when grown at permissive temperature. act3/arp4 mutants have also demonstrated an increase in their nuclear diameters, thus suggesting that Act3p/Arp4 is a key regulator in the maintenance of cellular shape and nuclear organization. Furthermore, the use of Chromatin Yeast Comet Assay (ChYCA) for assessment of single‐cell bulk chromatin organization in act3/arp4 mutant cells allowed us to detect an elevated sensitivity toward nuclease action, denoting differences in higher‐order chromatin structure of the mutants. J. Cell. Biochem. 104: 59–67, 2008.

Serotypes, antimicrobial susceptibility, and beta-lactam resistance mechanisms of clinical Haemophilus influenzae isolates from Bulgaria in a pre-vaccination period

Abstract Objective: To determine the serotypes, antimicrobial susceptibility, and beta-lactam resistance mechanisms of Haemophilus influenzae strains isolated from invasive and respiratory tract infections (RTIs) prior to the introduction of Haemophilus influenzae type b (Hib) vaccination in Bulgaria. Methods: A total of 259 isolates were serotyped by polymerase chain reaction. Susceptibility to antibiotics and beta-lactamase production were determined, and DNA sequencing of the ftsI gene was performed for ampicillin non-susceptible strains. Results: The invasive H. influenzae infections in children were mainly due to serotype b (94.5% in meningitis and 88.9% in other invasive cases). Non-typeable strains (97.4%) were the most frequently found H. influenzae strains in RTIs both in children and adults. Non-susceptibility to ampicillin occurred in 22% of all strains. Ceftriaxone and levofloxacin were the most active agents tested. Ampicillin resistance occurred in 34.4% of invasive strains, and beta-lactamase production was the only mechanism found. Among respiratory tract isolates, ampicillin non-susceptible strains (18%) were classified into the following groups: beta-lactamase-positive, ampicillin-resistant (BLPAR) strains (7.2%); beta-lactamase-negative, ampicillin-non-susceptible (BLNAR) strains (8.2%); and beta- lactamase-positive, amoxicillin–clavulanate-resistant (BLPACR) strains (2.6%). Among 21 BLNAR and BLPACR strains there were 9 different patterns of multiple-amino acid substitutions in penicillin-binding protein 3. Of these, most isolates (81.0%) belonged to group II, defined by the Asn526Lys substitution. Conclusions: Beta-lactamase production was more common among invasive strains than in respiratory isolates. BLNAR and BLPACR H. influenzae were found only among respiratory tract isolates.

The linker histone in Saccharomyces cerevisiae interacts with actin-related protein 4 and both regulate chromatin structure and cellular morphology.

Chromatin structure promotes important epigenetic mechanisms that regulate cellular fate by organizing, preserving and controlling the way by which the genetic information works. Our understanding of chromatin and its functions is sparse and not yet well defined. The uncertainty comes from the complexity of chromatin and is induced by the existence of a large number of nuclear proteins that influence it. The intricate interaction among all these structural and functional nuclear proteins has been under extensive study in the recent years. Here, we show that Saccharomyces cerevisiae linker histone physically interacts with Arp4p (actin-related protein 4) which is a key subunit of three chromatin modifying complexes - INO80, SWR1 and NuA4. A single - point mutation in the actin - fold domain of Arp4p together with the knock-out of the gene for the linker histone in S. cerevisiae severely abrogates cellular and nuclear morphology and leads to complete disorganizing of the higher levels of chromatin organization.

Saccharomyces cerevisiae Linker Histone—Hho1p Maintains Chromatin Loop Organization during Ageing

Intricate, dynamic, and absolutely unavoidable ageing affects cells and organisms through their entire lifetime. Driven by diverse mechanisms all leading to compromised cellular functions and finally to death, this process is a challenge for researchers. The molecular mechanisms, the general rules that it follows, and the complex interplay at a molecular and cellular level are yet little understood. Here, we present our results showing a connection between the linker histones, the higher-order chromatin structures, and the process of chronological lifespan of yeast cells. By deleting the gene for the linker histone in Saccharomyces cerevisiae we have created a model for studying the role of chromatin structures mainly at its most elusive and so far barely understood higher-order levels of compaction in the processes of yeast chronological lifespan. The mutant cells demonstrated controversial features showing slower growth than the wild type combined with better survival during the whole process. The analysis of the global chromatin organization during different time points demonstrated certain loss of the upper levels of chromatin compaction in the cells without linker histone. The results underlay the importance of this histone for the maintenance of the chromatin loop structures during ageing.

Comparison Between Alkaline and Neutral Variants of Yeast Comet Assay

ABSTRACT Comet assay gain its popularity because it is a fast and relatively easy-to-perform method for assessing damages in DNA. The two persisting variants of the method: alkaline and neutral, lead to some doubts which one would be suitable for a certain purpose. Here we present a comparison between the two versions of the developed by us Yeast Comet Assay (YCA). Since DNA damages can be quite diverse, i.e. single- or double- stranded cuts, oxidative damages, photodimers, etc., we warn that the method of YCA has to be applied with attention and a certain level of understanding concerning the exact damage that is attempted to be assessed.

Methanol extracts from the resurrection plant Haberlea rhodopensis ameliorate cellular vitality in chronologically ageing Saccharomyces cerevisiae cells.

Bioactive substances that are found in many natural plant extracts are very important for the cosmetics, pharmaceutical industry and biotechnology. Especially interesting for these industries are the substances that possess cell revitalizing and anti-ageing properties. The endemic plant Haberlea rhodopensis is known for its ability to withstand drought and to revitalize when returned to optimal conditions after a long time in desiccation. It is a mere fact that this plant not only can completely resurrect from a dried state but is also able to bring back the natural biochemical compositions of its cells. As a result H. rhodopensis offers a wide field for investigation of the exact mechanisms of the revitalization process as well as broadens the search for unique bioactive chemical substances in its cells. Here, by using the yeast Saccharomyces cerevisiae as a model we have demonstrated that methanol extracts from the plant H. rhodopensis hold specific properties to revitalize and ameliorate cellular growth as well as to balance intracellular metabolic states. Our results add valuable knowledge on the effects of natural compounds on ageing and reinforce the idea of using yeast as a model organism in the development of rapid tests for studying the efficacy of different bioactive substances.

Histone H1.0—a potential molecular marker with prognostic value for patients with malignant gliomas

BackgroundHistones are proteins closely associated with the DNA molecules and serve as a structural scaffold for the organization of chromatin. They play an important role in the regulation of gene expression by changing the level of DNA compaction.The special subtype of the linker histone family—H1 zero (H1.0) is generally expressed in non-dividing, terminally differentiated cells.The aim of our study is to investigate the correlation between the quantities of histone H1.0 in human gliomas, the histopathological grade and the overall survival.Material and methodTwenty-nine (N = 29) patients with intraaxial lesions underwent a microsurgical tumor resection. Tumor samples were snap-frozen in liquid nitrogen immediately after resection.Following a specific protocol, linker histones were extracted from the tumor specimens and the quantities of histone H1.0 were assessed. All patients were followed up prospectively.ResultsOf the 29 patients in our study (M:F = 17:12), five had a grade II astrocytoma, seven had a grade III, and 17 had a grade IV, according to the World Health Organization (WHO) classification.At the end of the study, three patients were still alive.The mean quantities of H1.0 were: 23.3 for grade II tumors, 13.9 for grade III and 11.3 for grade IV tumors.The statistical analysis demonstrated that the histological grade, age and Karnofsky performance status (KPS) remain among the most reliable predictive factors for the survival of patients with gliomas.Grade III–IV gliomas had significantly less histone H1.0 than grade II gliomas. Conformably, in a multivariate Cox regression analysis, H1.0 made a small but significant contribution (p < 0.05) to survival rates.ConclusionOur study confirmed that histone H1.0 is a potential biological marker with prognostic value for the survival of patients with gliomas. The quantities of histone H1.0 are correlated to the histopathological grade of the tumor. The more aggressive and malignant gliomas tend to have lower quantities of histone H1.0.

Presence of a H1o-type histone in an invertebrate: the bivalve mollusc Anodonta cygnea

Some terminally differentiated tissues of the bivalve mollusc Anodonta cygnea contain a histone subfraction with electrophoretic and immunological characteristics similar to those of the mammalian histone H1o.

Application of comet assay for the assessment of DNA damage caused by chemical genotoxins in the dairy yeast Kluyveromyces lactis

Kluyveromyces lactis, also known as dairy yeast, has numerous applications in scientific research and practice. It has been approved as a GRAS (Generally Recognized As Safe) organism, a probiotic, a biotechnological producer of important enzymes at industrial scale and a bioremediator of waste water from the dairy industry. Despite these important practical applications the sensitivity of this organism to genotoxic substances has not yet been assessed. In order to evaluate the response of K. lactis cells to genotoxic agents we have applied several compounds with well-known cyto- and genotoxic activity. The method of comet assay (CA) widely used for the assessment of DNA damages is presented here with new special modifications appropriate for K. lactis cells. The comparison of the response of K. lactis to genotoxins with that of Saccharomyces cerevisiae showed that both yeasts, although considered close relatives, exhibit species-specific sensitivity toward the genotoxins examined.