Methylation and gene mutation in eukaryotic DNA

5-methylcytosine (m5C) as a rare base exists in eukaryotic genomes, which is a normal constitution in many eukaryotic DNA and the existence of m5C is a feature of eukaryotic DNA. Under regular physiological conditions, cytosine of eukaryotic DNA is usually methylated. Up to the present, many people consider that the m5C may be mutation hotspots by the deamination leading to gene mutation. Our study indicated that the spontaneous mutation caused by the transition of G.C --> A.T, in eukaryotic DNA, may result from the tautomer changing of base pairs and may also be cause by other factor actions, however it could not be caused by the deamination of m5C.

[Effect of sanchinoside Rg1 on experimental thrombosis and its mechanisms]

The effect of sanchinoside Rg1 on generation of thrombosis and its mechanism was studied. Rg1 was shown to markedly inhibit experimental thrombosis formation induced by extra corporeal shunt between the carotid artery and jugular vein. After Rg1 infusion, the activity of t-PA was found to be increased, so did the percentage of active-type t-PA, but the activity of PA-I decreased. Further data in our study indicate that incubation of endothelial cells with Rg1 for 24 h caused significant increase of NO production. This effect was found to be dose-dependent. These observations suggest that Rg1 is a potent anti-thrombosis substance and can enhance the function of fibrinolysis system and stimulate vascular endothelial cells to release NO.

[Effects of pollution with fluoride on bone dynamics of periosteum in iliac of domestic pigs]

Studies on bone dynamic parameters of iliac periosteum and endosteum in domestic pigs with fluorosis caused by coal-burning contamination were conducted. Bone dynamics of 12 pigs with experimental fluorosis and nine controls both labelled with double tetracycline was investigated. Results showed the distance between two labels on iliac periosteum of domestic pigs with fluorosis shortened and, rates of mineralization and bone matrix formation slowed. It suggested fluorosis played significantly inhibitory roles in bone formation on the periosteal membrane of pig iliac.

[The morphological changes in trabecular architecture of bone in severe primary hyperparathyroidism]

By histomorphometry bone biopsy specimens were evaluated from 10 patients with severe primary hyperparathyroidism (PHPT). The data suggest that the mean trabecular width and trabecular bone volume were slightly, but not significantly increased. As indices of bone remodeling activity, both trabecular osteoid surface and trabecular resorption surface were significantly increased indeed, indicating high bone turn-over occurred in PHPT. The dynamic study showed that much more trabecular bone surface was covered either with single or double tetracycline labels in PHPT than in control. The overproduction of osteoid in the patients leads to the accumulation of osteoid on the trabecular surface. Moreover, the mean osteoid width seemed to be thicker in PHPT than in control, suggesting the co-existence of osteomalacia, which might be a possible explanation for eucalcemia usually seen in the majority. Part of chinese PHPT patients.

[Trabecular connectivity in primary hyperparathyroidism]

By bone histomorphometry, 10 cases of primary hyperparathyroidism (PHPT) were used to study the trabecular connectivity, which in a few literatures was mentioned to be reserved somehow. Our data suggest that in comparison with the normal control (10 subjects) the nodes (N.Nd), the number of terminus (N.Tm), the total strut length (TSL), the length between the nodes (Nd.Nd), trabecular separation (Tb.Sp) and trabecular thickness (Tb.Th) were significantly increased while no significance was found in N.Nd/N.Tm, Tm.Tm and TBV. The correlation analyses indicate that there is no correlation between the variables in the normal controls. In contrast, however, TBV and Tb.Th showed negative correlations with N.Tm and Tm.Tm. Besides these, there were positive correlations between N.Nd/N.Tm and TBV or Tb.Th, and a negative correlation between N.Nd/N.Tm and Tb.Sp. The results suggest that to certain degree the trabecular connectivity in PHPT be destructed while the three dimensional architecture be reserved. Our data seem to be different from those reported previously. It may be due to the severity of PHPT in our patients.

A temperature-sensitive mutant of human p53

We discovered that the human 'hot-spot' p53 mutant 143Ala is temperature sensitive for the binding of two DNA elements and for mediating the transcription of a downstream luciferase reporter gene. At 32.5 degrees C, 143Ala possesses strong DNA binding ability. In addition, its transcriptional activities are stronger than those of wild-type p53. At 37.5 degrees C, however, both the mutant's DNA binding and transcriptional activation functions are greatly reduced or abolished. The activity differences correlate with the presence of two conformational states of p53, which are recognized by monoclonal antibodies: at 32.5 degrees C, 143Ala is recognized by PAb1620, which is specific for the wild-type conformation, whereas at 37.5 degrees C, 143Ala is almost undetectable by PAb1620-mediated immunoprecipitation. Although 143Ala's binding to p53 DNA recognition elements and its activation of reporter gene transcription at 32.5 degrees C is markedly higher than that of the wild-type p53, 143Ala inhibited proliferation less robustly than wild-type p53 and it did not increase inhibition of ras-induced focus formation. These results indicate a partial correlation between the events involved in transcriptional activation and events involved in the proliferation suppression of p53. 143Ala therefore will be of use in dissecting the relationship between the structure of p53 and its different cellular functions.