It has been demonstrated that embryonic stem cells form adhesive contacts with external blastomeres of mouse morula, while there is no such contact with blastocysts. The development of morula in the blastocysts is delayed inside a dense layer of such cells; however, in some cases, external blastomeres of the morula begin to differentiate into trophoblastic cells. The introduction of an excessive number of embryonic stem cells (15-20) into a 4-8-cell embryo results in abnormal development. When heterotypic embryonic mink stem cells are co-cultivated, they show only very weak adhesion with mouse blastomeres and are displaced as a result of compactization. When blastocysts are formed after the injection of heterotypic embryonic stem cells, such cells remain in the perivitelline space. In some cases, heterotypic embryonic stem cells continue to be determined in the trophoblastic direction and produce trophoblastic vesicles autonomously. The role of cell interaction in the determination of cells during early mammalian development is discussed.

Micronuclei of preimplantation embryos of the hypertensive rat strain with inherited spontaneously induced arterial hypertension (ISIAH) are studied. Also studied are the formation of micronuclei and other morphological changes in these embryos after freezing, cryoconservation, and consequent transplantation to Wistar recipient rats. Analysis of semithin sections demonstrates that the above procedures lead to the formation of micronuclei in most embryos, while the shape of nuclei changes in only some embryos. There is a tendency towards perinuclear location of organelles and inclusions and to the partial disappearance of polarity in the majority of blastomeres. We believe that the increase in the number of micronuclei can be associated with a certain selection of embryos during cryoconservation and transplantation.

Cloning of vertebrates, in particular, amphibians and mammals, is discussed. In the last decade, significant progress was made cloning mammals, while cloning of adult amphibians remained problematical. Low-traumatic methods of enucleation of recipient oocytes and transplantation of donor nuclei were worked out. In 1997, an adult sheep was cloned in Great Britain, thus demonstrating the possibility of cloning adult mammals. However, methods of cloning mammals need improvement because of the high lethality of reconstructed embryos (nuclear transplants). The use of in vitro cultured low-differentiated stem cells to obtain donor nuclei seems promising. Works on human cloning are not expedient in the near future because of technical and ethical aspects.

Cloning efficiency of erythroid progenitor cells in gel diffusion chambers from patients irradiated as a result of the Chernobyl accident was studied. Stimulation of erythroid progenitor cells, activation of enzymatic activity in peripheral blood cells and an increase of 2,3-D Ph G were detected. These data supplement the notion about the development of adaptative processes in the erythron system as a response to effects of radiation.

The statement about dominating role of stem cell failure (exhaustion) in acute radiation bone marrow syndrome outcome needs to be changed. Cytokine-producing cells lacking reactivity that prevent usage of stem cell compartment reserves can play important role in immunohemopoiesis radiation damage.

The peripheral blood from 30 patients presenting with preleukosis states was studied. Both quantitative and qualitative indices of blood and bone marrow were determined. It has been ascertained that the following signs should be taken in consideration where the diagnosis is "preleukosis": anemia presenting with qualitative changes in erythron, neutrophylopenia presenting with a shift to the left, thrombocytopenia, nuclear anomalies of neutrophylocytes and lymphocytes (pelgeroides, fragmentation, pyknosis, Rider's nuclei).

Many microorganisms are capable of prolonged persistence in the marrow. In this study, carried out by the method of negative selection based on the treatment of mouse marrow cells with specific antimicrobial sera and complement, Mycoplasma arthritidis and L-forms of group B streptococci were found to be capable of persisting in the marrow in close association with the late category of clonogenic precursor cells, CFU-7, as well as, to a lesser extent, with late erythroid precursors, CFUe. Early colony-forming cells, CFUs-12 and PFUe, as well as granulocyto-macrophagal precursors, CFUgm, did not practically express antigens to the given infective agents on their surface.

Electrolytic destruction of the median raphe nuclei or locus ceruleus (I = 1.5-2.0 V, 20 sec with a change of polarity) in the period of winter solstice weakens the manifestation of free flowing rhythms of the active-search component of behavior. Lithium hydroxybutyrate (10 mg/kg i.m. for one week) only after evening administration compensates the effects of lysis of the serotonin- or norepinephrine-containing stem cells on the behavioral rhythm. Whatever the phase of administration, the drug acts as a social time-assigner for body temperature rhythms under the indicated conditions.

The stem cell compartment of hemopoietic clonogenic cells (CFU-S) of mouse embryos in a closed system was studied, when the hemopoietic tissue was devoid of supply of the hemopoietic cells and grafted into adult recipients with diverse regulatory influences. The content of hemopoietic clonogenic cells (CFU-S-7, CFU-S-11, and CFU-S-el) was determined in the transplants of the 14-day embryonic liver placed under the renal capsule of preirradiated syngeneic adult recipients. Relatively younger clonogenic cells (CFU-S-11) were practically absent from the transplant in the end of cultivation, while the more advanced stages (CFU-S-7) became more abundant. CFU-S-el were preserved in the transplant for 24 h, and they were absent by the fourth day of cultivation. Disappearance of the clonogenic cells, which are referred to according to some properties as pre-CFU-S (CFU-S-el) from the stem compartment, a decreased content of another category of the clonogenic cells (CFU-S-11), and an increased content of the more advanced cells (CFU-S-7) suggest that in a closed system, maturation of the hemopoietic cells is accompanied by the exit of CFU-S to differentiation and is not compensated by their reproduction from the cells of earlier stages or self-reproduction.

The effect of Ebola virus antigen on the growth of hemopoietic precursors was studied. Incubation of mononuclear cells with the viral antigen led to a dose-dependent decrease of erythroid colony formation but did not alter the growth of the granulocyto-macrophagal precursors. Hence, Ebola virus antigen is capable of directly affecting the hemopoietic activity of precursors in man by inhibiting the growth of erythroid colonies.