Multifunctionality of PIWI proteins in control of germline stem cell fate

PIWI proteins interacting with specific type of small RNAs (piRNAs) repress transposable elements in animals. Besides, they have been shown to participate in various cellular processes: in the regulation of heterochromatin formation including telomere structures, in the control of translation and the cell cycle, and in DNA rearrangements. PIWI proteins were first identified by their roles in the self-renewal of germline stem cells. PIWI protein functions are not limited to gonadogenesis, but the role in determining the fate of stem cells is their specific feature conserved throughout the evolution of animals. Molecular mechanisms underlying these processes are far from being understood. This review focuses on the role of PIWI proteins in the control of maintenance and proliferation of germinal stem cells and its relation to the known function of PIWI in transposon repression.     

Induction of transposon silencing in the <Emphasis Type="Italic">Drosophila</Emphasis> germline

In this review we consider the role of the piRNA system in transposable element silencing in the Drosophila melanogaster germline. We focus on new data that demonstrate the mechanisms of initiation of piRNA biogenesis in ovarian germinal cells and the role of Piwi protein in this process, including our own results.     

The effect of space—frequency characteristics of the organ of vision on the human psychophysiological state and working capacity

During the long-term stay in closed environment of the orbital space station, it is extremely important that the light conditions and color scheme were favorable for the working capacity of a cosmonaut. The systems of lighting should ensure visual comfort for the crew members under stressful conditions and, in addition, they should appropriate to their health and recovery of functional reserves during the long-duration flight. To solve this task, the distribution of luminosity and chromaticity within a closed space should be taken into account. For better understanding the perception of visual information, we studied the color space-frequency characteristics of the organ of vision (SFC VO). A set of sensors was used to estimate psychophysiological parameters. After preadaptation of an operator, VO contrast sensitivity was measured by determining the thresholds of advent and disappearance of the test objects; this was accompanied by fixation of the time and adaptive brightness. Analysis of the experimental data made it clear that the color contrast sensitivity and directly related SFC of the organ of vision are valuable markers for interrelationships between processing of visual information and psychophysiological state of a human. Note that the color SFC VO not only illustrates deviations but also enables their quantification. Changes in psychophysiological state are accompanied by the appropriate changes in SFC VO, which should be taken into account in developing the neural information technologies used for health recovery and light-and-color control of environment.     

Mobile Genes and RNA Interference

Current views on the role of RNA interference in controlling the expression and transposition of mobile genes in the eukaryotic genome are considered in connection with a recollected work resulting in the discovery of retrotransposons.     

Individual optimization: Mechanisms shaping the optimal reaction norm

In general, optimal reaction norms in heterogeneous populations can be obtained only by iterative numerical procedures (McNamara, 1991; Kawecki and Stearns, 1993). We consider two particular, but biologically plausible and analytically tractable cases of individual optimization to gain insight into the mechanisms which shape the optimal reaction norm of fecundity in relation to an environmental variable or an individual trait. In the first case, we assume that the quality of the environment (e.g. food abundance) or the quality of the individual (e.g. body size) is fixed during its entire life; it may also be a heritable individual trait. In the second case, individual quality is assumed to change randomly such that the probability distribution of quality in the next year is the same for the parent and for her offspring. For these two cases, we obtain analytical expressions for the shape of the optimal reaction norm, which are heuristically interpretable in terms of underlying selective mechanisms. It is shown that better quality may reduce the optimal fecundity. This outcome is particularly likely if better quality increases a fecundity-independent factor of parental survival in a long-lived species with fixed quality. This revised version was published online in July 2006 with corrections to the Cover Date.