An in silico investigation into the causes of telomere length heterogeneity and its implications for the Hayflick limit

In telomerase-negative cell populations the mean telomere length (TL) decreases with increasing population doubling number (PD). A critically small TL is believed to stop cell proliferation at a cell-, age- and species-specific PD thus defining the Hayflick limit. However, positively skewed TL distributions are broad compared to differences between initial and final mean TL and strongly overlap at middle and late PD, which is inconsistent with a limiting role of TL. We used computer-assisted modelling to define what set of premises may account for the above. Our model incorporates the following concepts. DNA end replication problem: telomeres loose 1 shortening unit (SU) upon each cell division. Free radical-caused TL decrease: telomeres experience random events resulting in the loss of a random SU number within a remaining TL. Stochasticity of gene expression and cell differentiation: cells experience random events inducing mitoses or committing cells to proliferation arrest, the latter option requiring a specified number of mitoses to be passed. Cells whose TL reaches 1SU cannot divide. The proliferation kinetics of such virtual cells conforms to the transition probability model of cell cycle. When no committing events occur and at realistic SU estimates of the initial TL, maximal PD values far exceed the Hayflick limit observed in normal cells and are consistent with the crisis stage entered by transformed cells that have surpassed the Hayflick limit. At intermediate PD, symmetrical TL distributions are yielded. Upon introduction of committing events making the ratio of the rates of proliferating and committing events (P/C) range from 1.10 to 1.25, TL distributions at intermediate PD become positively skewed, and virtual cell clones show bimodal size distributions. At P/C as high as 1.25 the majority of virtual cells at maximal PD contain telomeres with TL>1SU. A 10% increase in P/C within the 1.10-1.25 range produces a two-fold increase in the maximal PD, which can reach values of up to 25 observed in rodent and some human cells. Increasing the number of committed mitoses from 0 to 10 can increases PD to about 50 observed in human fibroblasts. Introduction of the random TL breakage makes the shapes of TL distributions quite dissimilar from those observed in real cells. CONCLUSIONS: Telomere length decrease is a correlate of cell proliferation that cannot alone account for the Hayflick limit, which primarily depends on parameters of cell population kinetics. Free radical damage influences the Hayflick limit not through TL but rather by affecting the ratio of the rates of events that commit cells to mitoses or to proliferation arrest.     

Mycocinogeny in smut yeast-like fungi of the genus <Emphasis Type="Italic">Pseudozyma</Emphasis>

The fungistatic agent secreted by Pseudozyma prolifica VKM Y-2835 shows activity against some representatives of the Ustilaginales under acidic conditions. This mycocin, with a molecular mass of no less than 15 kDa, is thermolabile and sensitive to proteolytic cleavage.     

Two-dimensional modeling of a transverse collisionless shock wave

Transverse collisionless shock waves in a plasma in which the initial β value is equal to zero for electrons and is small but nonzero for ions are studied in the two-dimensional approximation with allowance for anomalous resistivity. A hybrid model is applied such that the ions are treated in the kinetic approximation and the electrons are described in the hydrodynamic approximation. A collisionless shock wave is generated using a piston with a small two-dimensional perturbation. The ion distribution downstream of the shock front and the effect of electron and ion heating are analyzed. It is shown that, for Alfvén-Mach numbers M _A>2, ion heating is attributed primarily to the ions that have experienced a reflection from the shock front and whose velocities downstream of the front are very high. This conclusion agrees with the results of one-dimensional calculations. Solving the problem as formulated shows that two-dimensional effects are insignificant in the range of low Alfvén-Mach numbers (M _A≤5): the direction of the magnetic field is always close to its initial direction, the ions acquire low velocities along the magnetic field, and the quantitative parameters of the plasma downstream of the shock front are close to those obtained from the one-dimensional model. In the range of higher Alfvén-Mach numbers, two-dimensional effects are more pronounced and the ion distribution function is less anisotropic.     

Biotinylated DNA probe for detection of streptotricin acetylation genes

The biotin-labelled DNA probe for identification of functioning and silent genes for streptotricin acetylation has been constructed. The probe is homologous to sat1 gene of the movable genetic element Tn1825. The simplified modification of the hybridization technique using the biotin-labelled DNA probe is described.     

Effect of Soil-Dwelling Fungi on the Seedlings of Sorghum in the Presence of Polycyclic Aromatic Hydrocarbons

Russian Journal of Plant Physiology - Morphometric, physiological, and biochemical characteristics were determined in the seedlings of Sorghum bicolor (L.) Moench treated with natural metabolites...     

Macromolecular synthesis during embryogenesis of Habrotrocha rosa Donner I. Replication of DNA

DNA synthesis was inhibited during embryogenesis of Habrotrocha rosa with mitomycin C and hydroxyurea. Inhibition of DNA replication in early stages of embryogenesis, at the beginning of organogenesis, just after cavitation of the stomodeum, resulted in a complete inhibition of further development. After this stage of embryogenesis development was insensitive to inhibition of DNA replication.     

Comments on the Paper of B.P. Vjuschkov “Locality of Permian Terrestrial Vertebrates in the Vicinities of the Town of Vyazniki”

The paper of B.P. Vjuschkov considering Late Permian vertebrates from the Vyazniki locality, prepared more than half a century ago and remained unpublished until the present time, was the first preliminary generalization of the geological and paleontological data on this burial. The material of this study collected by Vjuschkov during excavations in 1955–1957 revealed a unique composition of the local tetrapod assemblage compared to previously known contemporaneous analogues. Further studies of the Vyazniki fauna performed during the last decades provided a better understanding of its composition and age, showing that it is of paramount importance as a record of the terminal episode in the history of the Paleozoic precrisis biota.     

Mycocinotyping of Cyberlindnera Species

Microbiology - According to their sensitivity to Wickerhamomyces anomalus mycocins, Cyberlindnera spp. may be subdivided into two groups, one comprising heterothallic species with hat-shaped...     

Vyazniki biotic assemblage of the terminal Permian

A new unique and diverse biotic assemblage of the terminal Permian has recently been discovered in the town of Vyazniki (Central Russia). The Vyazniki terrestrial community is transitional between Permian and Triassic ones and represents the last, so far unknown stage of the global ecological crisis of the continental biota at the Permian-Triassic boundary. The successive development of land biotic crisis in the Late Permian, which was followed by mass extinction at the Permian-Triassic boundary, and long, successive postcrisis development and specialization of new Triassic groups as well as rearrangement and diversification of the biotic assemblage composition and community structure suggest predominance of intrinsic, biotic causes of this crisis, realized in destabilization, alteration, and new stabilization of continental communities and ecosystems.