Vol 49, No 2 (2018)

A new insight into the mechanisms underlying implementation of genomic information in the individual development of eukaryotes through interactions of transposons with epigenetic factors dynamically changing during each cell division is described. These mechanisms of stepwise implementation of individual genetic information with characteristic stage- and tissue-specific features in the activities of certain mobile genetic element families are evolutionarily fixed at the species level. In addition, the individual differences caused by their “unscheduled” transpositions can significantly change the regulatory network of the genome altering the phenotype. These changes in individual development can bring about new traits leading to either a disease or better fitness and represent an important component of the variation for natural selection in evolution. A large part of the eukaryotic transposons is altered by mutations and used for formation of the regulatory gene network, changes in the protein-coding genes, and emergence of new nonprotein-coding genes. When inserted into new loci, mobile genetic elements form the basis for microRNA and the domain structures of long noncoding RNA, responding to various types of stress; this is reflected in the specific features of individual development and contributes to variation. The epigenetic factors, including noncoding RNA, DNA methylation, and histone modifications, are tightly associated with mobile genetic elements. The specific features in transposon location in individuals that have emerged owing to spontaneous mutations or those caused by stress impacts can considerably change the interactions in gene networks. This influences the likelihood of survival under changing environmental conditions and reflects a distinct interrelation between the mechanisms of individual development and evolution. There is a parallelism between the mechanisms underlying the rearrangements of genomes caused by transposons in evolution and in individual development. In particular, the responsiveness of transposons to external and internal (microenvironment) factors forms the background for evolutionary construction of transposon-mediated tissue-specific activation patterns of certain transposons during each cell division, which leads to maturation of a reproductive organism. This mechanism is based on tight stage- and tissuespecific interrelation between transposons, epigenetic factors, and protein-coding genes.

Primary roots of 98 species from different families of monocotyledonous and dicotyledonous plants and adventitious roots obtained from bulbs and rhizomes of 24 monocot species were studied. Root growth rate, root diameter, length of the meristem and elongation zones, number of meristematic cells in a file of cortical cells, and length of fully elongated cells were evaluated in each species after the onset of steady growth. The mitotic cycle duration and relative cell elongation rate were calculated. In all species, the meristem length was approximately equal to two root diameters. When comparing different species, the rate of root growth increased with a larger root diameter. This was due to an increase in the number of meristematic cells in a row and, to a lesser degree, to a greater length of fully elongated cells. The duration of the mitotic cycle and the relative cell elongation rate did not correlate with the root diameter. It is suggested that the meristem size depends on the level of nutrient inflow from upper tissues, and is thereby controlled during further growth.

There is still no consensus on the mechanisms regulating the formation and maintenance of morphological structures in the individual development of living organisms. The hypothesis that the mechanical forces are important for biological morphogenesis was put forward more than 100 years ago. In recent decades, studies indicating the regulatory role of mechanical stresses at different levels of organization of life have appeared. The signaling mechanisms that are responsible for the reception of mechanical influences and reprogramming of the properties of cells and tissues are studied. Since the mid-1970s, the principles of selfstressed structures or the tensegrity (tensional integrity) theory have been applied to understand the structure and functions of living structures in statics and dynamics. According to this standpoint, the cell can be represented as a self-stressed structure in which microtubules function as rigid rods and microfilaments serve as elastic threads. Such a system is anchored to extracellular matrix through cellular contacts, since it is adjusted to the external patterns of mechanical stresses. The notion of living systems as self-stressed structures provides a fresh look at the mechanotransduction, developing organism integrity, and biological morphogenesis. Although the application of the ideas of tensegrity to biological systems has not yet received broad support among biologists, the influence of these ideas on the formation of modern mechanobiology and understanding the crucial role of cytoskeletal structures in cellular processes should be mentioned.

Condition of sex glands and thyroid and steroid hormone levels in the blood are assessed in the young of the current year of rainbow trout cultivated in the high-mountain area of South Vietnam and subjected to injections of surfagon (synthetic analogue of gonadotropin-releasing hormone). In the conditions of the trout hatchery (Vietnam), gonads of the young of the current year are characterized by substantial anomalies, including an appearance (in addition to females and males) of hermaphrodite and sterile individuals. A single injection of surfagon 1 month after hatching leads to stabilization of the development of sex glands and decrease of the proportion of sterile individuals (from 41 to 22%). This study is the first attempt of the assessment of the effect of the injection of gonadotropin-releasing hormone analogue on the development of sex glands in the early ontogeny of fishes.

Populations of brown trout in the Mzymta River and its tributaries include anadromous (mainly female) and resident (mainly males) fish. Some resident males in the basin of the Mzymty River attain sexual maturity at the age 1+, and resident females mature at the age 2+ or 3+. The maximum age of resident fish is 4+ in the samples studied. Migrations of anadromous brown trout to the sea occur at the ages 1+, 2+, or 3+. Future spawners spend from 1 to 4 years at feeding grounds in the sea. Smolts of the population are characterized by performing not only spring but also autumn migrations to the sea. One smolt specimen has been detected upstream from the dam in the river where spawners of anadromous brown trout do not migrate; this means that the capability for sea migrations persists long in the population represented only by resident specimens of brown trout. The diversity of life cycles and ecological forms in populations of brown trout is not lower than in populations of brown trout in Northern and Western Europe. The comparison of the data obtained with published data makes it possible to come to the conclusion about the high plasticity of ontogenesis of Black Sea brown trout.