Circulation time and dynamics of 3H-thymidine incorporation into DNA at various stages of chick embryo development

The most adequate method for carrying out radioautographic investigation on proliferation in the chorioallantoic tissues and in the chick embryo proper is dropping 3H-thymidine on the membrane under the shell in the area where the chorioallantois grows under. Using the application method, the radioautographic analysis of proliferation could be performed by the saturation method.     

Endocytosis of EGF-receptor complexes at various cell cycle stages

Parameters of EGF-receptor complex endocytosis have been studied in the early and late G1 phase and in mitosis. As a model, mouse mammary epithelial cells HC11 were used, whose growth depends on EGF presence in the medium. The Scatchard analysis has demonstrated that the surface receptors are represented by two receptor populations: 4800 high affinity (KD = 10(-11) M) receptors, and 73,000 low affinity (KD = 4.10(-9) M) receptors. Incubation of cells with the growth factor (5 ng/ml) resulted in a decrease in 125I-EGF binding, with its level being low until entering the S-phase. Under these conditions, receptors disposed on the plasma membrane presented a homogeneous population (KD = 8.10(-11) M, 14,000 receptors per cell). No reliable difference was revealed between the EGF-receptor complexes, internalized in early and late G1 phases, in respect to the internalization rate, level of recycling, degradation, and dynamics of compartmentalization. However, endocytosis of EGF-receptor complexes was found to be completely blocked in mitosis at the stage of internalization.     

Inorganic polyphosphate functions at various stages of cell evolution

An important property of all chemical components of the living cells is their polyfunctionality.However, the complex of their functions may significantly change in the process of evolution. This can be well illustrated by the example of polyphosphates. In procaryotes, polyphosphates are involved in many biochemical and physiological processes and their metabolic regulation. Their metabolism is first closely connected with adenyl metabolism and bioenergetics. In the lower eucaryotes, the cells of which are evidently of endosymbiotic origin, polyphosphate metabolism of various organelles is considerably different and closely connected with the specificity of their function. In these organisms, polyphosphates are involved in metabolic and probably in genetic regulation of phosphate and adenyl metabolism. However, they first play the role of an osmotically inert reserve of inorganic phosphorus. In the higher animals having the hormonal and nervous systems of cell metabolism regulation, the function of polyphosphates as a metabolic regulator disappears. However, they apparently still function as regulators of gene expression and some transport processes.     

Carbohydrates in Digitalis purpurea at various stages of development

The concentrations of carbohydrates in Digitalis purpurea have been determined at various stages of development. An increase of the carbohydrate content was observed during growth. Glucose was the major carbohydrate component in the leaves and stem, whereas fructose predominated in the inflorescence. The growing tips and other actively growing parts of the plant contained relatively high concentrations of two new compounds.     

DNA synthesis in the brain and liver of rats in various stages of postnatal development]

The intensity of incorporation of 3H- and 14C-thymidine in the brain and liver DNA in rats of different ages was investigated. It was proved that both the replicative and oxyurea-resistant DNA synthesis might proceed in the rat brain cells. The intensity of these processes changes sharply during postnatal development.     

Larval habitat duration and size at metamorphosis in frogs

The relationship between size at metamorphosis and adult size was studied in 12 closely-related species of frog from Malawi (Central Africa). These species of frogs breed in water of different durations, and occupy different habitats as adults. We could demonstrate no correlation between size at metamorphosis and size of adults when frogs were divided into groups on the basis of occupying similar habitats as adults, but when frogs were divided into groups on the basis of similar duration of larval habitat we demonstrated a strong correlation between size at metamorphosis and adult size. Thus we suggest that duration of the larval habitat is a major determinant of size at metamorphosis, with species which breed in the more temporary habitats metamorphosing at smaller size than species which breed in more permanent habitats, but which are of similar size as adults. Such manipulation of the life cycle appears to be adaptive since it results in individuals becoming independent of water earlier when the likelyhood of early loss of larval habitat is high.     

Molecular markers of various stages of nonsmall cell lung cancer development

Studies performed in the recent decade in the Laboratory of the Regulation of Cell and Virus Oncogenes associated structural and functional defects of several oncogenes and tumor suppressor genes with various stages of non-small-cell lung cancer. High risk of lung cancer was established for carriers of rare alleles of the Hras1 minisatellite, the hypermethylated p16INK4A promoter, and microsatellite defects in chromosome regions 3p12, 3p14.2, 3p22-24, 3p21, 3p25, 9p21, and 17p13. Analysis of the Hras1 minisatellite and microsatellites located in two minimal deletion overlap regions of 1p36 was shown to allow a more reliable prognosis in lung cancer. The results testified again that panels of molecular markers are useful for individual risk assessment, early and differential diagnosis, and prognosis in cancer.     

Glucose uptake by chicken embryo hearts at various stages of development

d-glucose, but not l-glucose, was found to readily enter the cells of 5- to 6-day chick embryo heart. This suggests the operation of a specific transport system for glucose. The rate of glucose uptake was found to decrease as development proceeds from 5 to 15 days of development, but no further decrease was found between 15 and 20 days. Uptake of glucose is a saturable process, from 5–6 days of embryonic life on. The large decrease in glucose uptake between 5 and 10 days of development is found to be associated with a fourfold increase in the apparent K_m of the uptake process. From 10 days of development onward, the apparent K_m remains about 40 mM. The rate of 2-deoxyglucose uptake also decreased from 5 to 15 days of embryonic life with no further decrease from 15 to 20 days. Glucose competitively inhibits the uptake of 2-deoxyglucose with a K_i close to the K_m for glucose uptake. The uptake of 2-deoxyglucose is stimulated by physiological levels of insulin as early as 5–6 days, although the extent to which insulin enhances uptake is not quite as great as at 15 days of development.