Yu. F. Ivlev

Three-Dimensional Reconstruction of the Chromatin Structure in the Somatic Nucleus of the Infusorian Bursaria truncatella

Reconstruction of the three-dimensional chromatin structure in the cell nucleus is of great interest both in terms of determination of the organization of the higher chromatin levels and with regard to the recent data that the structural mechanisms of distribution of genetic material in the nucleus may be involved in the regulation of the function of large groups of genes. In situ hybridization studies provided convincing data in favor of the hypothesis on the existence of “chromosomal territories” in the nucleus of eukaryotic cells, according to which each chromosome occupies a separate fixed part of the nucleus and does not penetrate to the territory of other chromosomes. It was shown for several genes that their expression is correlated with their spatial distribution within the “chromosomal territory” [1–4].

Concentration and size distribution of plant fiber in the digestive tract of muroid rodents

The weight parameters that characterize the size and the degree of fullness of fermentation chambers (forestomach and cecum), namely, the weight of the walls and the content of these organs, and the concentration and size distribution of fibers in the chyme have been investigated in five muroid rodent species (Arvicola terrestris, Microtus oeconomus, Microtus arvalis sp., Clethrionomys glareolus, and Sylvaemus flavicollis). No distinct regularities were observed in the above-mentioned parameters of the forestomach. These parameters of the cecum were generally found to be in good agreement with the conventional concept of dietary specialization of the rodent species under investigation, but the results have provided a more precise assessment of the role of dietary fiber in the diet of free-living rodents under specific environmental conditions.

Three-Dimensional Structure of the Ciliate Didinium nasutum Nucleoli

The nucleolar organization in ciliate Didinium nasutum somatic interphase nuclei was studied using serial ultrathin sections and compared for various physiological states of the cell, namely, fed ciliates, starved ciliates, and dormant cysts. It has been shown that the interphase nucleoli are large structures with a complex architecture: the fibrillar component forms an intricate network in the macronucleus space, while the granular component is located inside this network. The structures looking as individual nucleoli in single sections are actually parts of branched nucleolar networks. The intricate nucleolar networks do not disintegrate after a 30-h starvation; however, the granular component becomes denser and develops numerous cavities filled with fine fibrils of a nonribonucleoprotein nature. In fed D. nasutum, the fibrillar structures on the periphery of nucleoli contain numerous pores (virtually absent in starved cell nucleoli), which can potentially serve for transporting newly synthesized rRNP. Branched nucleolar networks are undetectable in cysts. Their nucleoli are individual structures consisting mainly of the fibrogranular component.

The use of olfaction by the Russian desman (Desmana moschata L.) during underwater swimming

280 In this communication, previously unknown elee ments of the behavior of the Russian desman that allow us to suggest that this animal uses underwater olfaction with the help of the bubblebased system of collection and delivery of smell to the nasal cavity are described, and the functional limitations of this system in semiaquatic mammals are preliminarily analyzed. The Russian desman is generally a carnivorous mammal [1] conducting a semiaquatic mode of life. During search for mobile prey and its seizure under water, especially in the dark time of the day, vision can be ineffective. For these tasks, desman should have other flexible efficiently functioning sensory mechaa nisms. One of such mechanisms may be olfaction. At least two representatives of insectivores—water shrew (Sorex palustris) and starrnosed mole (Condylura cristata)—are capable of using olfaction during orienn tation and hunting under water [2, 3]. Animals periodd ically squeeze air out of the nostrils and touch the examined objects with the forming bubbles. Odorant molecules of substances that determine the smell of these objects diffuse into air bubbles. Inhaling bubbles back into the nose, the animals can obtain the respecc tive olfactory information. We recorded similar elee ments of behavior in a desman in the process of video recording during the study of the kinematics of this animals swimming under water. For video recording, we used one desman (male) taken from the nursery of the Chernogolovka Research Experimental Station of the Institute of Ecology and Evolution of the Russian Academy of Sciences where studies on breeding of these rare anii mals in captivity are being performed. The animal was in a good state, its body mass during several weeks before the experiment remained relatively stable (approximately 520 g); however, the age of this animal excluded its use in reproduction. After the experiment, the desman was returned to the nursery where it lived for more than half year. Video recording of desmans swimming was perr formed in a glass tank whose dimensions were 135 × 60 × 35 cm. The tank was in a laboratory room in which air temperature was 20–25°C, water temperature in the tank being considerably lower (about 10°C) to prevent overheating of the animal. The animal freely swam or rested on a dry platform in one of the sections. In this section, a mirror was mounted with dimensions of 110 × 28 cm and located at an angle of 45° …

Relative Position of Nucleolar Chromatin and Nucleolar Components in Ciliate Didinium nasutum Somatic Nuclei

According to our computer modeling data obtained earlier, nucleoli in interphase ciliates Didinium nasutum are complex netlike structures, in which the trabeculumor lamella-shaped fibrillar component is located on the periphery, and the granular component in the central part of the nucleolus. Chromatin bodies connected with nucleoli act as the nucleolar organizers in D. nasutum. In the present work, the arrangement of all chromatin bodies, which could correspond to nucleolar organizers by morphological criteria, is studied by means of a 3D-reconstruction. It is shown that all of these chromatin bodies are localized outside the nucleoli, on the fibrillar component’s periphery. Even those chromatin bodies which appeared to be completely surrounded by the fibrillar nucleolar component on single ultrathin sections are actually settled down in nucleolus cavities open to the nucleoplasm. This proves that the RNA processing in D. nasutum nucleoli is directed toward the center of nucleoli, where the granular component is located. The analysis of the nucleolar chromatin distribution made it possible to conclude that different parts of the complex interfase netlike nucleoli of D. nasutum have approximately the same activity.

A decrease in heat insulation of the black-clawed brush-furred rat (Lophuromys melanonyx, Petter) during adaptation to high altitudes.

The results of the body-surface infrared thermography of rodents of the genus Lophuromys suggest that heat insulation of the black-clawed brush-furred rat L. melanonyx, a large specialized species of the AfroAlpine zone, is worse than that of the related smaller species, the golden-footed (L. chrysopus) and shorttailed (L. brevicaudus) brush-furred rats, that inhabit tropical forest and Erica shrub, respectively. A decrease in heat insulation of the alpine species may facilitate the use of solar radiation for supporting heat balance of these diurnal animals.

Viscoelastic features of adhesive setae of the tokay gecko (Gekko gecko L.)

Deformations of particular setae of adhesive toe pad of the tokay gecko were investigated by atomic-force microscopy. The effective elastic modulus of the investigated setae varying within 0.34–19 GPa, a pronounced hysteresis was observed during reversible bending of setae. The hysteresis-related energy losses may be as high as 98% of the total bending work. The pronounced viscous features of the setae contradict the hypothesis of dynamic self-cleaning of the gecko adhesive cover, according to which the setae are considered as absolutely elastic cantilever beams.

The Insulating Properties of the Pelage of the North-American Porcupine (Erethizon dorsatum): The Influence of Quill-Like Structures on Heat Transfer

Multifunctionality is characteristic of the hairy pelage of mammals, the key function of which is insulation. As a rule, mammalian fur can effectively insulate the body at a certain density of thin hair in it and sufficient thickness of the pelage in general [1]. The fulfillment of other functions (in particular, mechanical protection) may be related to changes in the pelage, as a result of which its structure becomes markedly different from the structure that may be regarded optimal from the standpoint of insulation. Apparently, more or less significant redistribution of roles between the insulating and defensive functions of the pelage took place in parallel more than once in the course of evolution of mammals. In particular, quill-like modifications of hair differing in the degree of modification occur in different taxa [2]. In extreme cases, the pelage turns into a strongly differentiated multilayer defensive formation consisting of a great number of various quills of a complex structure. Nevertheless, the functional aspects of these transformations have not been studied thus far. For example, it is unknown to which extent the presence of quills may affect the insulating properties of the pelage. Filling up this gap was the goal of this study, in which we performed quantitative estimation of the effect of the presence of quills on the insulating properties of the pelage using the North American porcupine ( Erethizon dorsatum L . ) as an example.