DNA synthesis and content and the accumulation of total protein and hemoglobin during the differentiation of primary erythroid cells in chickens

Using cytophotometric and autoradiographic methods, it was shown that on days 2-3 of embryogenesis primary erythroid cells (PEC) divided actively. The distribution of erythroblasts (EB) according to their DNA content is not, however, typical of a proliferating population: it contains an unusually large number of 4c cells resulting from the cell cycle arrest at the G2 phase. It is established that reticulocytes (RC) do not divide and are arrested at G1 or G2 phases, since they do not incorporate 3H-thymidine after their formation is complete and their DNA contents are strictly confined to either 2c or 4c. All types of PEC include a large number of cells containing H2c DNA which is due either to the cell cycle arrest at the S phase, or to the formation of accessory nuclei. All PECs have much higher contents of hemoglobin and total protein than do adult hen erythrocytes (EC). Hemoglobin and total protein contents of H2c and accessory nuclei containing cells are much higher than those in 2c-cells. We have calculated that adult birds and embryos contain the same amount of hemoglobin per gram of weight, but the quantity of red blood cells in the former is ten times higher. A conclusion is drawn that proliferation and cytodifferentiation regulation mechanisms are directed, in primary erythropoiesis, to intense hemoglobinization of the cells, and, in adult erythropoiesis, to increasing their number. In both the cases homeostatic regulation of erythropoiesis works.(ABSTRACT TRUNCATED AT 250 WORDS)     

Characteristics of the pathways of erythroid cell differentiation in birds in anemia

A comparative study has been made of erythroid cell development pathways in the peripheral blood of pigeons during severe, moderate and weak forms of anaemia. Three modes of erythrocyte formation from bone marrow precursor are described: 1. A reserve erythropoiesis--the principal process during severe anaemia; the bone marrow precursors are basophylic erythroblasts which are reversibly blocked in phase G2 of the cell cycle; in results the rapid, increase of erythrocyte population above the normal level, although the cells have 25-30 per cent deficiency in haemoglobin content. 2) A mode of erythropoiesis, whose precursors are proliferating polychromatophylic erythroblasts; this is the principal mode of erythropoiesis at the moderate anaemia, leading to restoration of the normal quantity of erythrocytes with a normal haemoglobin content. 3) A mode of erythropoiesis with proliferating orthochromatic erythroblasts being precursors (which do not divide normally); this is the principal mode during the weak anaemia to result in a slow restoration of the number of erythrocytes with an excess in haemoglobin content. It is shown that regulation of the restoration processes during anaemia are characterized by a specific combination of cell proliferation and differentiation.     

DNA synthesis and content in the macrophage nuclei of normal mice, during carcinogenesis and during the administration of retinoids to the animals

It has been found that nearly 50% of the lymph node and spleen macrophages (MP) of the CBA line mice contain DNA at levels superior to the diploid value (H2c--H4c in mononuclear MP, and up to H16c among polynuclear ones, the latter comprising 2.5-9.0% of the whole MP population). No DNA synthesis and mitosis were detected by autoradiography, cytophotometry, and cytomorphological analysis. During carcinogenesis the proportion of MP with elevated DNA amounts ("activated MPs") decreases due to their migration to tumours. Also immature MPs (1.6%) appear in the population, which synthesize DNA, but do not divide. Injection of retinoids restores the percentage of MPs with elevated DNA amounts to the levels characteristic of the intact animals, the fraction of DNA-synthetizing cells increasing up to 2.8%. It is proposed that retinoids may accelerate the processes of MP maturation, activation and renewing. A mechanism of cooperative action of MPs and retinoids is discussed in addition to the role of DNA hyper-replication.     

Morphofunctional changes in the exocrine pancreatic cells in acute experimental pancreatitis in rats

Experimental pancreatitis was induced by cooling the splenetic part of rat pancreas with chlorethyl, and the cells of duodenal area of the pancreas were studied at different stages of pancreatitis using cytomorphometry, cytomorphology and autoradiography. Interlobular and interacinar oedemas were observed at the first hours after treatment. In 24 hours the intracellular oedema of exocrine pancreatic cells (EP) was detected. On day 14 after treatment typical acute edematous pancreatitis developed. The observed changes involve a pathological activation of EP of the duodenal area, a subsequent restoration of the structure of this area, and later a passage of pancreatitis into the chronic form. The usefulness of this model of pancreatitis for quantitative cytochemical studies of EP during pathogenesis and drug treatment is discussed.     

Changes in the content of nucleic acids and total protein in exocrine pancreatocytes and the composition of their population in experimental acute pancreatitis in rats]

Using cytophotometry, contents of DNA, RNA and total protein were measured in the rat's exocrine pancreatocytes (EP) in normal conditions and at different stages of pancreatitis induced by cooling the spleen part of the pancreas with chlorethyl. In the duodenal (not damaged) part of the pancreas some drastic changes in the EP ploidy distribution were shown to occur. They led to the formation of a qualitatively new population pattern with 4c and 2c + 2c cells prevailing (more than 60% of the total content), which are by 1.5-3 times more active in RNA and protein synthesis and accumulation than the normal cells. The population structure rearrangement in the EP and their functional activity rise took place at two stages. At the first one the intracellular defense mechanisms of the EP in response to acute necrobiotic processes in the pancreas tissue were activated, at the second one the supracellular mechanisms regulating synthetic processes leading to a rapid adaptation of viable EP to new conditions were switched on.     

In vitro culture of the hypothalamic supraoptic nucleus. I. General morphological characteristics

Kinetics and morphology of supraoptic nuclei (SON) organ culture of newborn rat hypothalamus have been described. Explants of SON were cultured for 7-90 days. Cell migration, growth of neuron sprouts, formation of nerve bundles and growth zone, and mitotic activity were followed. Neurosecretory cells (NSC) differing in size, shape and degree of activity, were identified in addition to other cell elements of SON. The neurosecret was shown to appear at the beginning of the second week of cultivation in large and middle size NSC. In small and old cultures of NSC no neurosecrete was discovered. It was established that NSC complete the terminal differentiation and maintain for a long time their viable and functional activity in vitro.     

A novel magnesium-dependent structural transition of chicken erythrocyte chromatin in situ

Lowering magnesium concentration below the value of 1 mM leads to a structural transition of chicken erythrocyte chromatin in situ, which results in a change in its fragmentation by pancreatic DNAase (DNAase I) from double-nucleosome to 100-basepairs mode. At 0.75 mM MgCl2, the pattern of chromatin fragmentation by DNAase I is similar to that generated by DNAase II, and it is further changed at lower concentrations of magnesium. This transition is, at least partly, reversible, and is, presumably, related to packing of the 25-30 nm chromatin fiber into higher-order structures.     

Two types of fragmentation of total chromatin by DNAase I--an artifact or reality?

The possibility of N+2N repeat (a nucleosomal-type repeat in which the even-numbered peaks dominate) being an artifact has been studied. The repeat results from digestion of chromatin of several rat cells by DNAase I. Endogenous nucleases are not shown to be involved in formation of the repeat. N+2N repeat is also formed during digestion of nuclei isolated from homogeneous lymphocyte populations indicating that the repeat is inherent of chromatin of distinct cells and is not the result of superimposition of different repeats arising from diverse tissue cells. We suppose the N+2N repeat to indicate the existence of the second type of total chromatin differing from the one giving rise to the dinucleosome repeat under the same conditions.