Geomorphic processes of a dammed palaeo-lake in the middle Yarlung Tsangpo River, Tibet.

The failure of a natural dam is an extreme geological event. Palaeo-lake sediments were discovered in the broad Xigazê valley and Dazhuka-Yueju gorge in the middle reach of the Yarlung Tsangpo River in Tibet. However, the sedimentary processes, dam failure, and peak flood of the Xigazê dammed palaeo-lake are poorly understood. Hence, we conducted a field survey of eight lacustrine sedimentary terraces in the area. We divided the sedimentary processes of the palaeo-lake into five stages and deposit types: pre-palaeo-lake sediments (fluvial or aeolian deposits); early stage sediments of the palaeo-lake (coarse sand); main stage palaeo-lake sediments (clayey silt and sand), sediments following the discharge of the palaeo-lake (sand and gravel-cobbles); and cover deposits (aeolian sediments and colluvium). Additionally, the water level along the palaeo-lake was almost constant (3811 m a.s.l.). The dam was likely located at the eastern end of the Dazhuka-Yueju gorge. Based on the water level, dam location and 30-m ASTER GDEM2 data, the capacity of the palaeo-lake was estimated as 22.55 km3. To separate the water volume and sediment volume, the sediment surface elevation along the palaeo-lake was simulated based on the elevations of the six lacustrine sedimentary terraces. The volume of the sediment was ~11.56 km3, which was calculated from the dam location, sediment surface elevation, and the ASTER GDEM2 data. Finally, subtraction of the sediment volume from the capacity of the palaeo-lake gave a backwater volume of 10.99 km3. The peak flood possibly exceeded 3.4 × 105 m3/s as a moraine dam joined the discharge during the dam failure. However, the dammed event probably had a limited effect on the landforms at downstream because of the presence of another dammed palaeo-lake in the broad Zetang valley; moreover, the bedrock upstream of the dam was protected from erosion.

[Inhibitory effect of siRNA targeting ADAM17 on the proliferation of prostate cancer PC-3 cells].

OBJECTIVE: To study the effect of siRNA targeting ADAM17 (ADAM17-siRNA) on the proliferation of prostate cancer PC-3 cells. METHODS: After transfecting PC-3 cells with ADAM17-siRNA 1 and ADAM17-siRNA 2, we detected the expressions of ADAM17 mRNA and protein by RT- PCR and Western blotting, respectively. We measured the changes in the proliferation and DNA synthesis of PC-3 cells by MTT and bromodeoxyuridine (BrdU) incorporation assay, examined the cell cycle profile by flow cytometry, and determined the expressions of the genes associated with PC-3 cell proliferation by Western blotting. RESULTS: Both ADAM17-siRNA 1 and 2 effectively reduced the expressions of ADAM17 mRNA and protein in the PC-3 cells. Knockdown of ADAM17 with the two siRNAs significantly inhibited cell proliferation as compared with the control group (0.43 +/- 0.57 and 0.44 +/- 0.64 vs 0.80 +/- 0.51, P < 0.05) and down-regulated DNA synthesis (0.48 +/- 0.43 and 0.54 +/- 0.59 vs 0.79 +/- 0.72, P < 0.05). The cell cycle profile showed that the cell population of the G1 phase was markedly higher in both the ADAM17-siRNA groups than in the control ([61.83 +/- 2.41]% and [59.78 +/- 1.92]% vs [41.38 +/- 1.53]%, P < 0.05), but that of the S phase remarkably lower in the former two than in the latter ([23.64 +/- 2.56]% and [25.24 +/- 1.86]% vs [33.51 +/- 1.47]%, P < 0.05), with a concomitant decrease in the expression of the cell cycle protein cyclin D1 and increase in the cyclin-dependent kinase inhibitor p21. CONCLUSION: ADAM17-siRNA can effectively inhibit the proliferation of PC-3 cells by up-regulating cyclin D1 and down-regulating p21 protein, and ADAM17 has a potential value in the gene therapy of prostate cancer.