Changes In Template Activity Of Chromatin Research Articles

Muscle and nonmuscle cell RNA polymerase activities in early myocardial hypertrophy

RNA polymerase was solubilized from separated rat cardiac muscle and nonmuscle cells during the development of myocardial hypertrophy 1 or 3 days after sham operation or aortic constriction. Six fractions of enzymes designated IA, IB, IIA, IIB, IIIA, and IIIB were identified by DEAE-Sephadex chromatography in each cell population. Fractions designated IA and IB, IIA and IIB, and IIIA and IIIB were similar to RNA polymerase I, II, and III, respectively, found in other eukaryotes. Muscle cell enzyme activity from sham-operated and aortic-constricted rats did not significantly differ 1 day after intervention. By 3 days there was a significant increase in the activity of each enzyme fraction in muscle cells from aortic-constricted rats. There was a slight increase in IIA activity in nonmuscle cells from aortic-constricted rats at 1 day. By 3 days after aortic constriction RNA polymerase IIA, IIB, and IIIB activities increased in nonmuscle cells, but no change was noted in nonmuscle RNA polymerase IA, IB, and IIIA. Changes in RNA polymerase activities in cardiac muscle and nonmuscle cells occur during the development of myocardial hypertrophy but do not appear to correlate with reported changes in RNA synthesis. chromatin-template activity, however, did increase in cardiac muscle cells at both 1 and 3 days after aortic constriction. A similar increase was not seen in nonmuscle cell chromatin-template activity until 3 days. These data suggest that the initial increase in RNA synthesis during the development of myocardial hypertrophy is related to changes in chromatin-template activity in muscle cells. The activities of the RNA polymerase increase after a short delay and vary in their response.

Changes in chromatin template activity for in vitro transcription during the development of the rat mammary gland.

The template activities of chromatin isolated from virgin, pregnant, lactating, and regressed rat mammary glands were compared by using exogenously added bacterial and mammalian RNA polymerases. Template activity increased during the stage of pregnancy, then decreased during the stage from early lactation to regression. It showed the highest level at early lactation when intracellular levels of rRNA and mRNA are known to be at their maximums. These results suggest that transcriptional activity in the mammary gland is regulated, at least in part, by a modulation of chromatin template activity.

Progesterone-regulated changes in transcriptional events in rabbit uterus

The role of steroid receptors in the early events of progesterone action was elucidated by examining the temporal relationship between the nuclear accumulation of progestin receptor and changes in activities of RNA polymerases I and II, as well as that of chromatin template in rabbit uterus. Following a 5-day estrogen pretreatment, the animals received an intravenous injection of progesterone (10 mg), after which they were killed at timed intervals. Nuclear progestin receptor level, as measured by an exchange assay, reached the peak value 30 min after hormone administration (11 600 to 46 600 sites/nucleus) and declined to the control levels by 4 h. Changes in the activities of RNA polymerases I and II did not follow identical time courses: polymerase I rose at 30 min and remained elevated for 2 h and then declined to about 75% of the pretreatment activity, whereas RNA polymerase II activity increased more rapidly (at 15 min), and was followed by a sharp decrease to about 50% of the initial value. Thereafter, the latter enzyme activity rose slowly and reached the pretreatment level within 12 h of progesterone administration. Early changes in chromatin template activity were similar to those in RNA polymerase I with a second rise by 8–10 h. The early inhibition of transcriptional events by progesterone may result from antiestrogenic properties of this steroid. Accumulation of nuclear progestin receptor occurs at a similar time to early changes in the transcriptional events suggesting a regulatory role for the hormone receptor complexes.

Template activity of chromatin during stimulation of cellular proliferation in human diploid fibroblasts.

1. Contact-inhibited confluent monolayers of WI-38 human diploid fibroblasts can be stimulated to divide by replacing the medium with fresh medium containing 30% foetal calf serum. 2. Of the cells 40-75% are stimulated to divide with a peak DNA synthesis between 15 and 21h and a peak mitotic index between 28 and 30h after stimulation. 3. In the first 12h before the initiation of DNA synthesis there is a biphasic increase in the incorporation of [(3)H]uridine into RNA of whole cells. 4. This is paralleled by a similar biphasic stimulation of chromatin template activity measured in vitro in a system in which purified cell chromatin is incubated with an exogenous RNA polymerase isolated from Escherichia coli. 5. The changes in chromatin template activity are believed to represent activation of the genome, with more sites available for RNA synthesis, and to account almost entirely for the changes in RNA synthesis occurring in the whole cell.