Nuclear and cytoplasmic RNase-activity in regenerating mouse liver

Nuclear and cytoplasmic RNase activities at pH 5.0 and 7.6 were analyzed in regenerating mouse liver at 6, 12, 24, 48, and 72 h after partial hepatectomy. Two different nucleus-isolation methods were used, one in a EDTA-spermidine medium free from divalent cations, and one in a sucrose medium containing these ions. During regeneration, the cytoplasmic alkaline RNase activity in the sucrose medium was unchanged, but in the spermidine medium showed an increase toward the end of the period. Also the cytoplasmic acid RNase activity was unchanged in sucrose medium, whereas in the spermidine it slightly increased during regeneration. The nuclear alkaline RNase activity showed a notable peak 6 h after the operation and later decreased. Also the nuclear acid RNase activity displayed a similar marked peak 6 h after operation, then decreased, but remained high throughout the period. The nuclear RNase activities were about 1% of the corresponding cytoplasmic RNase activities. The absolute activities varied greatly according to the nucleus-isolation methods. In the controls, the absolute activity of nuclear alkaline RNase was slightly above (1.2 times) that of the corresponding acid activity after the spermidine method. After the sucrose method the nuclear alkaline activity was 2.7 times that of the acid activity. The absoluted activity of cytoplasmic alkaline RNase was slightly above (1.2 times) the acid activity after the spermidine method but after the sucrose method it was only 0.25 times that of the acid activity. In sham-operated animals, cytoplasmic acid and alkaline RNase activities generally were fairly similar to the normal value, but corresponding nuclear activities showed marked variations indicating an influence by anesthesia.     

AN AUTORADIOGRAPHIC STUDY OF THE 3H-URIDINE AND 3H-THYMIDINE INCORPORATION IN THE REGENERATING MOUSE LIVER

An autoradiographic study was made of the ³H-uridine incorporation into RNA and DNA in nucleus and cytoplasm of parenchymal cells in the regenerating liver of the mouse after a pulse time of 2 hr. After a decreased uptake of precursor into the parenchymal nucleus during the first 6 hr compared with the normal value, incorporation increased and was maximal at 36 hr; normal values were restored at 72 hr. The cytoplasmic labelling, after an initial small decrease, reached a maximum at 12 hr; this changed to normal 48 hr after hepatectomy. RNase-digestion of the liver sections left a small incorporation in both nucleus and cytoplasm: presumably DNA. This incorporation is maximal at 12 hr over the nucleus and at 24 hr over the cytoplasm. After a 2 hr pulse of ³H-thymidine, there was a marked uptake of the precursor into DNA about 24 hr after hepatectomy. This was maximal at 48 hr and reached normal values at 72 hr. A small amount of incorporation of ³H-thymidine into DNA was seen immediately after the operation, and this population of weakly labelled nuclei was still rather large 72 hr later.