Regulation of Ki-ras expression in Reuber H35 cells

Temporal and spatial expression of glutamic acid decarboxylases in human fetal brain

The expression of two isoforms of glutamic acid decarboxylase, GAD67 and GAD65, was analyzed in central nervous system (CNS) tissues obtained from normal second trimester human fetuses after elective termination of pregnancy. After RT-PCR amplification of sequences contained in total RNA extracts, Southern blotting indicated that GAD67 and GAD65 mRNAs can be detected in frontal pole tissue as early as the 12th week of gestation (12 GW). GAD67 message is strongly expressed during early second trimester and decreases slightly thereafter but remains abundant. In contrast, GAD65 message decreases rapidly and becomes undetectable by the 19 GW. However, GAD67 and GAD65 are similar in their spatial expression in the CNS at 22 GW. GAD67 and GAD65 messages are highly expressed in the cerebellum but expressed in low levels, if at all, in the spinal cord during this gestational period. These results suggest that GAD67 may have a greater role in neuron differentiation than GAD65 during human brain development.

Cloning and developmental expression of human 66 kd neurofilament protein

The complete human 66 kd neurofilament cDNA was isolated and its sequence was determined. Both the DNA and the predicted amino acid sequences showed a high degree of homology to the rat NF-66. This was substantiated by cross hybridization between the human NF-66 probe and rat NF-66 mRNA. Single gene copy was suggested from Southern blot analysis. RNase protection assay indicated that NF-66 was expressed in human fetal brain as early as the 16th gestational week. On the other hand, NF-L message was not detected until the 20th gestational week. NF-M message was not detectable up to the 24th gestational week.

Insulin induction of c-Ki-ras in rat liver and in cultured normal rat hepatocytes

1. Insulin administration in neonatal rats causes a dramatic accumulation of the major c-Ki-ras transcript. 2. The level of c-Ki-ras transcript is greatly reduced in alloxan-induced diabetic rats. 3. Injection of insulin in alloxan-induced diabetic rats is able to restore almost completely the level of c-Ki-ras transcript found in insulin-induced normal rats. 4. Results from nuclear run-off experiments reveal that the inductive effect of insulin is at the level of transcription of the c-Ki-ras gene. 5. As in whole animals, insulin is also able to induce the expression of c-Ki-ras in cultured normal hepatocytes. 6. This inductive effect of insulin is markedly reduced in hepatocytes which have been previously treated with the tumour promoter, 12-O-tetradecanoylphorbol-13 acetate for 24 hr, a result suggesting that at least part of the effect of insulin is mediated via protein kinase C.

Transcription induction of c-Ki-ras with the tumour promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) in normal and transformed liver cells

Results from nuclear run-off assays show that exposure of hepatocytes and Reuber H35B hepatoma cells to the tumour promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA), leads to enhanced transcription of c-Ki-ras gene. This increase in transcription in turn results in an accumulation of the functionally active c-Ki-ras message. The half life of c-Ki-ras message in both normal and transformed livers cells is not altered by TPA and is determined to be 3.5 hr. The induction of c-Ki-ras message is accompanied by an increase in the level of c-Ki-ras protein.

Expression of c-Ki-ras in developing rat liver

1. Two major c-Ki-ras transcripts are present in rat liver throughout development. 2. Both transcripts are functional, i.e. translatable into ras protein. 3. They exhibit low levels in early foetuses and increase gradually towards term. 4. Peak levels of transcripts are detected on the fourth day of postnatal life. 5. Results from nuclear run-off assays demonstrate that the rise in level of transcripts is a result of increase in rate of transcription with the highest rate detected on the fourth day of postnatal life. 6. Western blot analysis reveals that the accumulation of c-Ki-ras protein clearly follows the pattern of changes in transcription of c-Ki-ras gene.