Nuclei Of Parenchymal Cells Research Articles

Experimentally induced changes of extranucleolar ribonucleoprotein components of the interphase nucleus

The distribution of extranucleolar ribonucleoprotein (RNP) constituents of the rat liver parenchymal cell nuclei was investigated after starvation and refeeding, and after the action of cortisone, both methods being known to stimulate RNA synthesis. For visualization of nuclear RNP components, the EDTA staining method for preferential staining of RNA was employed as well as digestion of GMA embedded material with RNase. Perichromatin fibrils were found to be increased in both types of experiments. After cortisone administration a quantitative increase was visible as early as 15 minutes after the injection. One hour after refeeding or hormone treatment, they were particularly numerous. Perichromatin granules were counted and compared in the different experimental groups with normal controls. Their number was found to be relatively stable under the experimental conditions used. Interchromatin granules were not found to undergo changes. It is suggested that perichromatin fibrils might contain the morphological substrate for the rapidly labeled “chromosomal” or DNA-like RNA as found in biochemical studies.

Autoradiographic studies on nuclear DNA and RNA synthesis in the adenohypophysis of castrated rats.

ABSTRACT DNA and RNA synthesis was studied autoradiographically; 5 groups of cells were observed in the adenohypophysis of rats (gonadotrophs, thyrotrophs, acidophils, small and large chromophobes) 1, 2, 4 and 8 weeks following castration and the results compared with those obtained in control animals. The proliferation of cells in the anterior lobe of the hypophysis, determined by the incorporation of isotopically labelled 3H-thymidine into the nuclei of parenchymal cells, increases by 6 fold about two weeks after castration and returns to a normal level eight weeks after the operation. The number of silver grains/μm2 nuclear area =mean silver grain density (SGD) shows a doubling of the DNA-synthesis rate (= new formation/unit of time) two weeks following castration. This result agrees with a shortening of the DNA synthesis time – and very likely also of the G2 phase and the length of mitosis – to such an extent as to be characteristic for rapidly proliferating tissues. This effect on the mode of proliferation is reversible and normalized by the end of the experiment, i. e. eight weeks following castration. After the operation there is a more marked proliferation of the gonadotrophs than the chromophobic cells. RNA synthesis as measured by the incorporation of 3H=cytidine into the cell nucleus increases continuously in the nuclei of all cell groups throughout the whole period investigated. On the other hand, the average nuclear area diminishes. This dissociation of the extent of RNA synthesis and the nuclear size is discussed.

RADIOAUTOGRAPHIC STUDY ON THE INCORPORATION OF TRITIATED THYMIDINE BY MOUSE LIVER CELLS DURING RESTITUTION AFTER STARVATION

DNA synthesis has been studied on the liver cells of mice in the restitution period after starvation. Tritiated thymidine (3H-TdR) was subcutaneously injected twice a day for ten days during the restitution period, in order to examine the incorporation of 3H-TdR into hepatic nuclei and the persistence of 3H-labelled nuclei in the liver.After ten-day's labelling, about 40% of hepatic parenchymal cell nuclei was heavily labelled. More incidence of heavily labelled nuclei was observed at 1 week after the last injection of 3H-TdR. Thereafter, the percentage of heavily labelled nuclei remained nearly constant around 30%. If lightly labelled nuclei were taken into account, almost 80% of the parenchymal cell nuclei showed labelling of DNA. With exception at 1 week after the last dose of 3H-TdR, this total percentage of labelled nuclei remained unchanged about 60% for 6 weeks.The incorporation of 3H-TdR into littoral cells of the liver was also observed. Throughout the present experimental period from 35 to 40% of littoral cells had labelled nuclei.These results indiacte that DNA synthesis has occurred in the parenchymal and in the littoral cell nuclei during the restitution after starvation, and that the nuclei, which contain newly syntesized DNA, persist for a long period.

Nuclear ploidy in mammalian parenchymal liver cells.

ALTHOUGH it has generally been assumed that the nuclei of the parenchymal cells of mammalian liver have ploidies in the ratio of 2N : 4N : 8N : 16N … (ref. 1), contradictory reports have recently appeared. One described the existence in C3H mice of nuclei with ploidies of 3N, 6N and 12N, the first amounting to as much as 25–50 per cent of the nuclei during the first 2 weeks of life2. The other claimed that there is, in human liver, a continuum of nuclear DNA contents and volumes, and that individual classes of nuclei are not present3. The reasons for the discrepancies between these results and the generally accepted theory are not known, but one possibility is that the methods of preparation and measurement of the material may produce systematic errors. Both the studies were carried out on sections of fixed tissues with micro-spectrophotometric methods that were less than optimal. During the course of the investigation of the relationship of cell size to cell ploidy4, measurements of nuclear size and ploidy have been carried out with intact, single parenchymal cells. The results obtained again confirm the existence of clearly defined classes of parenchymal cell nuclei.

Oocytogenesis in rabbits. The role of neogenesis in the formation of the definitive ova and the stability of oocyte DNA measured with tritiated thymidine.

AbstractA series of six thymidine‐methyl‐H3 (thy‐H3) injections, one every 12 hours, was administered to 35 Dutch‐belted female rabbits (does) commencing on the day of their birth. Seventeen of the does were unilaterally ovariectomized as follows: five does at 4 and 12 weeks of age, five does at 4 and 20 weeks of age, five does at 12 and 20 weeks of age and two does at 4 and 40 weeks of age. Autoradiographs of ovarian tissue were prepared, up to 600 oocytes per ovary were randomly chosen and the silver grains associated with the oocyte nuclei recorded. The mean grain counts decreased significantly (P < 0.05) from 4 to 12 weeks, 13.5 vs. 10.1, and from 4 to 20 weeks, 14.7 vs. 11.4. However, the mean grain counts did not differ significantly (P > 0.1) between 12 and 20 weeks of age, 10.5 vs. 9.6. Although the mean grain count decreased between 4 to 40 weeks of age 21.5 vs. 14.6, the number of replications was too few to detect significant differences (P > 0.1). At 40 weeks of age 91% of the oocytes were still labeled. The reduction in grain counts from 4 to 12 weeks of age was attributed to the non‐random degeneration of the older, more highly labeled oocytes located deep in the cortical zone. The lack of significant differences between grain counts at 12 and 20 weeks of age suggests that (1) during this interval the desoxyribonucleic acid (DNA) is metabolically stable and (2) significant de novo oocyte formation did not occur. Nine rabbits were superovulated at 20 weeks of age and of the 217 ova recovered 82.5% were radioactive. This was similar to the 89.8% radioactive oocytes observed in the ovaries of the same animals.Artificial insemination of the remaining nine does at 35 and 60 weeks of age resulted in normal litters and superovulation and artificial insemination of this group at 52 weeks of age produced 73.8% radioactive ova.Five Dutch‐belted does injected at four weeks of age with thy‐H3 at the same rate and interval as the day‐old rabbits showed a slight incorporation of the isotope into both oocyte nuclei and cytoplasm suggesting that most of the incorporation was not related to any synthesis of new chromosomal DNA. A single thy‐H3 injection into three 20‐week‐old does did not result in appreciable uptake of the isotope by oocyte nuclei, although many nuclei of parenchymal cells in the ovary were highly labeled.The results conclusively support the view that most, if not all definitive ova are formed at birth and de novo oocytogenesis does not occur in the post‐pubertal rabbit.